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uide
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Pharmaceutical Sciences
Overview:
This guide is intended for the pharmaceutical scientist wondering whether
calorimetry could directly benefit their research.
The adsorption or evolution of heat is a universal feature of chemical reactions pertinent to the pharmaceutical industry. The binding of a drug to a
macromolecular target, the interaction of an excipient with a drug, the degradation of a protein therapeutic upon storage, or the slow transformation of
a drug from a metastable to a stable polymorphic form all give rise to minute
changes in heat, the analysis of which provides fundamental insights into
the thermodynamics and kinetics controlling the reactions. These insights in
turn provide critical input for optimizing research strategies and processing
procedures. Calorimeters designed for the pharmaceutical industry rapidly
provide accurate and reliable information about potential drug candidates
and formulations, sometimes using just nanomoles of material. Calorimetric
techniques are direct: there is no requirement for spectroscopic probes, optical transparency, chemical modification or immobilization, and if the reaction is reversible (such as the unfolding of some proteins), the technique is
non-destructive. In addition, since the measurement of heat is independent
of the complexity of the sample, impurities are tolerated.
Three major types of calorimetry are used in the pharmaceutical industry:
isothermal, isothermal titration, and differential scanning. These approaches
allow the quantitative characterization of a large variety of small molecule
and macromolecular systems present either as solutions, membrane soluble
suspensions, insoluble suspensions or solids, making calorimetry an ideal
technique for studying:
• Drug stability and shelf life
• Solvent adsorption and
• Excipient compatibility
water permeation
• Amorphicity and crystallinity
• Surface oxidation
• Polymorphism
• Binding interactions
©2006 Calorimetry Sciences Corporation All rights reserved
Calorimetry Sciences Corporation
Table of Contents:
Theory and Experimental Design . . . . . . . . . . . . . . . . . . . . 5
What is a calorimeter? . . . . . . . . . . . . . . . . . . . . . . . . . 7
Isothermal Calorimetry . . . . . . . . . . . . . . . . . . . . . . . . 8
Isothermal Titration Calorimetry . . . . . . . . . . . . . . . . . . 10
Differential Scanning Calorimetry . . . . . . . . . . . . . . . . . . 13
Applications of Calorimetry to the Pharmaceutical Sciences . . . . 19
The drug design process . . . . . . . . . . . . . . . . . . . . . . . . 21
Pharmaceutical development . . . . . . . . . . . . . . . . . . . . . 23
Excipient compatibility . . . . . . . . . . . . . . . . . . . . . . . 23
Amorphous content . . . . . . . . . . . . . . . . . . . . . . . . 24
Shelf life predictions . . . . . . . . . . . . . . . . . . . . . . . . 24
Antibiotic assessment . . . . . . . . . . . . . . . . . . . . . . . . 25
Drug/membrane interactions . . . . . . . . . . . . . . . . . . . 25
Drug purity and polymorphism . . . . . . . . . . . . . . . . . . 26
Dissolution rates . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Energetics of solid drug surfaces . . . . . . . . . . . . . . . . . . 27
Drug adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Practical Issues to Consider when Choosing a Calorimeter . . . . . 29
Calorimeters for Pharmaceutical Research and Development . . . . 39
Calorimetry Sciences Corporation
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A calorimeter measures heat
generated or absorbed by reactions
Theory
theory
Theory
Theory
Theory and Experimental Design
What is a calorimeter and why is calorimetry such a
powerful pharmaceutical research and development
technique?
Calorimeters
Calorimetry Sciences Corporation
Practical Issues
Calorimetry can be used either as a screening technique to rapidly
determine whether or not a reaction occurs (for example, the undesirable
interaction of a drug with an excipient), or it can be used in comprehensive
studies to obtain a complete thermodynamic description of a reaction at
the molecular level, such as determining the number of protons exchanged
with the solvent when a protein and small
molecule drug bind. The power of calorimetry arises from the universal association of
heat with chemical reactions. Using one of a
small number of well-established experimental approaches, the thermodynamics associated with practically any pharmaceutical
process can be quickly assessed in a qualitative manner. This qualitative study can be followed directly by an in-depth
investigation, often using the same calorimeter, to provide a full quantitative
thermodynamic description of the reaction. The power and versatility of
calorimetry permits rapid, direct qualitative or quantitative thermodynamic information (depending on the researcher’s immediate needs) to be
obtained, without the need to establish new experimental protocols for each
system studied. Importantly, calorimetry can require as little material as a
spectrophotometric investigation.
Applications
A calorimeter designed for pharmaceutical research and development
accurately measures extremely small amounts of heat (nanocalories or
microcalories) generated or absorbed by reactions occurring in very dilute
solution, or in a small amount of suspension or solid sample.
Theory
Applications
Three major types of calorimetry are used in the pharmaceutical sciences: isothermal, isothermal titration,
and differential scanning
All three types of calorimetry can provide a thermodynamic description of
the reaction. Isothermal calorimetry is primarily used to study the stability
of small molecule drugs in the presence of excipients or moisture, isothermal titration calorimetry is principally used to study binding and catalytic
reactions, and differential scanning calorimetry is generally employed to
characterize the response of drugs (including biomacromolecules) and drug
formulations to thermal stress. As explained below, each type of calorimetry
answers rather different questions and subjects the sample to significantly
different experimental conditions. Depending on the questions being asked
and the nature of the sample, a comprehensive thermodynamic and functional study may require employing two or even all three techniques.
Calorimeters
Practical Issues
Isothermal Calorimetry
Isothermal calorimetry measures heat flow as a function of time. Isothermal calorimeters designed for pharmaceutical applications provide the most
reliable and sensitive test available for determining whether or not a reaction
is occurring.
All physical and chemical processes are accompanied by an exchange
of heat with the environment. If a small sample undergoing dissolution or
degradation is maintained under isothermal conditions in a sensitive calorimeter, a temperature gradient will be formed between the sample and its
surroundings, causing a minute change in heat flow (typically nanocalories/
second) which can be accurately measured by a sensitive isothermal calorimeter. For example, reactions occurring with rates as low as 0.5% conversion/year (e.g., slow hydrolysis or morphology changes in a small molecule
drug) can be characterized in a period of hours to several days, rather than
the weeks or months required by less sensitive methodologies. Since getting
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Calorimetry Sciences Corporation
Theory
a drug to market is a lengthy, multi-step, expensive process, any technique
that can expedite the process without compromising the quality of the analyses is an improvement over more traditional approaches such as HPLC.
Both kinetic and thermodynamic information about slow processes can
be derived from isothermal calorimetry without the need to make assumptions about the reaction mechanism. Sealing the samples in ampoules allows
solids, solutions, suspensions, gases or multi-phase systems to be studied
under controlled atmospheric conditions. Importantly, the effect of temperature on the kinetics of a process can be studied by simply re-equilibrating the
calorimeter at a new temperature and collecting data, without opening the
ampoules or adding fresh sample. In addition, because isothermal calorimeters are so sensitive, stability measurements can be conducted at realistic
storage temperatures rather than the elevated temperatures commonly used
to enhance degradation when other analysis techniques are used. Isothermal
calorimetry is often the most rapid and sensitive approach for characterizing
the stability, degradation and compatibility of pharmaceutical samples, and
is ideal for investigating:
Since getting a drug
• Excipient compatibility
• Drug stability
to market is a lengthy,
• Oxidation of drugs
multi-step, expensive
• Vapor sorption
process, any technique
• Drug dissolution
that can expedite the
• Drug amorphous/crystalline content
process without com• Drug polymorphism
promising the qual• Glass transition temperature
ity of the analyses
• pH stability
is an improvement
• Metals and metal chelator effects
over more traditional
• Drug-lipid interactions
• Drug-biopolymer interactions
approaches.
• Cell metabolism
• Stability of saturated and supersaturated drug formulations
Theory
An isothermal experiment can be set up in minutes and can require just
milligrams of material.
Calorimeters
Practical Issues
Applications
In a typical isothermal experiment, the calorimeter is equilibrated
at the desired temperature, then the sample in a sealed ampoule is
loaded in the sample chamber. The reference chamber is loaded with an
ampoule containing an inert material of similar mass and heat capacity.
The sample is maintained under isothermal conditions; as the sample
undergoes reaction, a temperature gradient is formed between the
sample and its surroundings and the resulting heat flow is measured as
a function of time. A typical isothermal calorimeter for pharmaceutical use (such as the Calorimetry Sciences’ 4500 Isothermal Nanocalorimeter) is capable of maintaining a baseline of ±1 nanocalorie/sec,
with a temperature stability of ± 0.0005 °C (at 25 °C). Because of their
sensitivity and stability, such isothermal calorimeters typically require
only milligrams of material and, even for samples undergoing very slow
reaction, allow a full thermodynamic investigation of the process to be
completed in a matter of hours.
Isothermal Titration Calorimetry (ITC)
Isothermal titration calorimetry is a universally applicable technique for
determining the thermodynamic processes controlling dynamic interactions
between molecules.
Isothermal titration calorimetry (ITC) allows the thermodynamics
controlling the interactions between two solute molecules, such as a drug
and its protein target, to be directly determined. When two molecules
interact noncovalently, they do so primarily through surface hydrophobic
patches, with binding specificity provided by the precise pairing of hydrogen
bond donors and acceptors, electrostatic interactions, dipole interactions,
etc. If two molecules interact, they must display greater affinity for each
other than they do for the solvent, as otherwise no binding would occur.
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Calorimetry Sciences Corporation
Theory
Applications
Typical incremental ITC data for the titration of 2’-CMP into RNase A. Integration
of the areas under each peak with respect to time, followed by normalization
per mole of added ligand, allows the enthalpy, the binding constant and the
stoichiometry to be calculated.
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Calorimeters
Calorimetry Sciences Corporation
Practical Issues
Isothermal titration calorimetry measures the heat changes associated with
these interactions. Depending on the calorimeter used, samples can be present either as a dilute solution, a suspension, or as a solid. In ITC, one component of a complex (such as DNA or an enzyme) is present in the calorimeter’s
sample cell, and the second component (for example, a drug or substrate) is
slowly added in an incremental, stepwise fashion. Analysis of the extremely
small thermal effects arising from the binding or catalysis reactions allows
a full thermodynamic characterization of the reaction and provides fundamental information about the molecular interactions driving the process.
Although there are many techniques for studying binding and catalytic
reactions, only calorimetry directly provides the enthalpy of the reaction. In
the case of a binding reaction, a single ITC experiment also provides the stoichiometry of the reactants and the association constant of the two interacting components. In the case of a catalytic reaction, ITC allows the Michaelis
constant, the turnover number and the rate of the reaction to be rapidly and
accurately determined. ITC is a highly versatile technique and is the method
of choice for characterizing a variety of dynamic interactions including:
Theory
• Biopolymer/drug binding
• Protein/protein interactions
• Drug/vesicle/liposome
interactions
• Drug/cell interactions
• Critical micelle concentration
• Non-aqueous adsorption
• pH effects
• Cell metabolism/drug
interactions
An ITC experiment is fully automated, takes between 20 - 90 minutes, and
Applications
requires no more material than a surface plasmon resonance or spectrophotometric experiment.
Calorimeters
Practical Issues
An isothermal titration calorimeter can quickly and sensitively
characterize dynamic reactions such as binding and catalysis. To
determine the affinity with which two molecules bind (for example, a
protein, polysaccharide or nucleic acid receptor to a drug candidate),
approximately 1 mL of a high nanomolar to low micromolar solution
of the receptor is loaded into the calorimetric sample cell, and the drug
solution is loaded into an injector syringe connected to the sample
cell. In a typical experiment, the drug is titrated incrementally into the
sample, and heat is generated and registered as a deflection peak by the
instrument. Integration of the area under each deflection peak allows
the amount of heat produced by each incremental addition of drug to
be calculated, until all the binding sites on the receptor are saturated
and no further binding is detected. A fully automated incremental ITC
experiment takes approximately an hour to run. Alternatively, the drug
can be slowly and continuously infused into the sample cell; a continuous titration experiment typically requires less than 20 minutes. Using
either approach and the Bindworks software supplied by Calorimetry
Sciences, a global fit of the data from a single experiment is often sufficient to allow the association constant (Ka), the binding enthalpy (∆H)
and the stoichiometry (n) of the reaction to be calculated.
Macromolecule/macromolecule interactions (with one macromolecule in the sample cell and the other in the syringe) can be studied in an
analogous manner. Importantly, for any titration experiment, conduct-
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Calorimetry Sciences Corporation
Theory
Applications
Practical Issues
ing the experiment twice, each time using a different buffer having the
same pH but different enthalpy of protonation, allows the number of
protons exchanged between the ligand and the binding site to be determined, thus providing information on the functional groups involved in
the binding reaction.
ITC is also ideal for rapidly analyzing essentially any enzymatic reaction, using a wide range of physiological or synthetic substrates and
inhibitors, without the need for chromogenic derivatives or coupling
enzymes. To determine the rate of catalysis, the enzyme is typically
loaded into the calorimeter’s sample cell, and the substrate, dissolved
in the same buffer as the enzyme, is loaded into the injector syringe.
Appropriate concentrations of substrate and enzyme will vary depending on the exact reaction being studied, but generally picomolar to
nanomolar enzyme and micromolar substrate concentrations are appropriate. Approximately 20 µL of substrate is injected, and the rate of heat
production is monitored continuously until the substrate is depleted.
The data are plotted (rate vs. substrate concentration) and fit to yield
the catalytic rate constant (kcat) and the Michaelis constant (KM). The
experiment can be repeated by injecting a second aliquot of substrate: if
there is no product inhibition, the same curve will be obtained, whereas
if there is product inhibition, its severity can be determined over the
course of several injections. The efficiency of various exogenouslyadded inhibitors can be established by repeating the reaction in the
presence of a known concentration of the inhibitor. Pseudo-first-order
kinetics can also be studied using multiple small injections of substrate
rather then one large injection.
Differential Scanning Calorimetry (DSC)
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Calorimeters
Differential scanning calorimetry provides fundamental thermodynamic
insights into the physical and energetic properties of drugs, formulations and
biopharmaceuticals.
Partial Molar Heat Capacity (kJ K-1mol-1)
Theory
Applications
110
Tm
100
90
Area = $Hcal
80
70
60
50
40
30
20
10
$Cp
50
60
70
80
90
Temperature (°C)
Calorimeters
Practical Issues
A DSC experiment provides a complete thermodynamic description of a system
(in this example, a protein), including the midpoint of the thermal transition, the
enthalpy and the change in heat capacity.
DSC measures the change in energy in a sample as the temperature is
raised or lowered, and thus can determine absolute thermodynamic data
for thermally-induced transitions. Many small molecules undergo phase
transitions or degradation when heated, and many biopharmaceuticals
denature and unfold at elevated temperatures. Ultra-sensitive calorimeters
can quickly quantify the thermodynamic parameters (and hence stability)
of small molecule drugs and macromolecules in their native state, in contact
with excipients or stabilizers, following chemical alteration or mutation, or
undergoing hydration, dissolution or dehydration.
Under a given set of conditions, whether a molecule is folded or unfolded
(in the case of a biopharmaceutical), or is crystalline, amorphous, melted or
decomposed (in the case of a small molecule drug) depends on the relative
contributions of the enthalpic (∆H) and entropic (∆S) components of the
system (i.e., ∆G = ∆H – T∆S). Unfolding of a macromolecule occurs when
T∆S increases sufficiently (for example, by the absorption of heat) to overcome stabilizing enthalpic interactions such as hydrogen bonds, hydropho14
Calorimetry Sciences Corporation
Recrystallization
Tc
0
-2
Form II
Form I
-4
I
-6
II
HC
$Ho
$Ho
-8
-10
Applications
Heat Flow (mW)
Theory
2
-12
-14
-16
-18
130
Tm
140
150
I
Tm
160
170
Temperature (°C)
II
180
190
bic interactions and electrostatic interactions. Temperature-induced phase
changes of small molecules similarly reflect the strength of intermolecular
interactions: depending on the physical state of the sample, DSC can provide
the glass transition temperature, recrystallization temperature and enthalpy,
and the melting temperature and enthalpy of fusion, as well as detect
polymorphic states and quantify degradation and decomposition rates. In
a single experiment, DSC can directly measure and allow the calculation of
all the thermodynamic parameters characterizing a small molecule drug or
biological macromolecule, including:
Calorimetry Sciences Corporation
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Calorimeters
• ∆H, the calorimetric enthalpy due to thermal denaturation caused by the
breaking of hydrogen bonds, ionic interactions, and the disruption of
hydrophobic interactions.
Practical Issues
A DSC scan of a small molecule drug can reveal the enantiotropic conversion of a
drug between two forms. In this example, Form I melts at temperature TmI with a
characteristic enthalpy of fusion (∆H₀I), recrystallizes into Form II at temperature
Tc with a heat of crystallization ∆Hc . Form II melts at TmII with an enthalpy
corresponding to ∆H₀II.
Theory
Applications
DSC is therefore an equally powerful technique for determining the
phase behavior and stability of small molecule drugs and for understanding the thermodynamic parameters controlling the thermal and functional
characteristics of a macromolecular therapeutic. In addition, DSC can
also provide a global analysis of complex biological systems such as whole
cells (for example, determining thermally induced transitions in organelles
and in whole cells exposed to various drugs or antibiotics). DSC is thus an
extremely versatile and powerful approach to understanding:
• Small molecule phase changes
• Drug purity
• Drug polymorph content
• Polymorph stability
• Drug degradation and decomposition
• Drug-excipient compatibility
• Drug-hydrate formation
• Biopolymer conformation and stability
• Pharmacokinetics
• Stabilizing effects of ligand binding
• Organelle and whole cell stability
Calorimeters
Practical Issues
• Tm , the transition midpoint, where, in the case of small molecules, half
the molecules are in one physical state (e.g., crystalline) and half are in
another state (e.g., amorphous), or in the case of macromolecules, where
half of the molecules are folded and half unfolded.
• ∆Cp , the change in heat capacity, due to the disruption of crystalline
structure upon melting of a small molecule, or to the thermal unfolding
of a macromolecule.
• ∆S, the entropy, a measure of the molecular disorder.
• ∆G, the Gibbs free energy, a measure of the overall stability of the system.
A DSC experiment is fully automated and characterizes reactions faster
than most other physical techniques.
A DSC instrument contains one or several sample cells and a matched
reference cell. If a reaction occurs in a sample cell, the heat produced or
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Calorimetry Sciences Corporation
Small molecules:
DSC studies of small molecules can be conducted on neat solids (to study
melting, crystallization, dehydration or hydration, glass transitions and polymorphic transitions), degassed aqueous solutions (to study water-enhanced
instability and degradation), and solid mixtures, slurries and suspensions (to
study excipient compatibility or dissolution rates). A baseline is first collected, often using empty sealed pans or ampoules in the sample and reference cells. The sealed samples (micrograms to a few milligrams) are placed
in the calorimeter sample cells; depending on the instrument, the cells can
be maintained in a fixed humidity or oxygen environment during the thermal cycle. User-defined variables (starting and ending temperatures, heating
and cooling scan rate, number of scans, etc.) are input, then the instrument
software takes control and automatically performs the entire experiment.
The samples are heated at a constant rate (typically between 0.5 to 2 °C/min)
and the absorption or production of heat is monitored. Differences in heat
uptake or production by the sample and reference cells are measured and
compensated for by the instrument, thus maintaining both cells at the same temperature. The
instrument provides a constant readout of the
difference in heat absorption or release by the
two cells, which corresponds to differences in
the apparent heat capacities of the sample and
reference. An accurate sample mass measurement, and a steady baseline before and after
transitions, is necessary in order to allow quantitative estimates of energetic parameters such
as heat capacity and enthalpy of fusion.
Calorimetry Sciences Corporation
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Theory
absorbed relative to the reference cell provides a very sensitive test for
determining whether or not a process is occurring, often allowing characterization of a reaction in a period of an hour or two. The design of a
DSC experiment is dependent on whether a small molecule or biological macromolecule is being studied, as described below.
Theory
Biological macromolecules:
When DSC is used to determine the thermal stability of a biological
macromolecular sample such as a protein therapeutic, a buffer baseline is
first obtained to establish the linearity of the baseline. The sample is then
scanned: if the sample is a solution, it should be thoroughly degassed, dialyzed, buffered and of known concentraA few micrograms
tion (high nanomolar to low micromolar).
If the sample is a suspension or a solid,
of sample can provide
dialysis is not required. The sample is
a complete thermodyloaded into the sample cell, and the refernamic analysis.
ence cell is filled with an equal amount
of matching degassed dialysis buffer or
solvent. The cells are pressurized at constant pressure (to prevent bubble
formation during heating and allow determination of ∆Cp), thermally
equilibrated at the chosen starting temperature, then heated and cooled.
After cooling both cells to the starting temperature, the experiment can be
repeated to determine if the sample exhibits reversible thermal transitions.
Because of the extreme stability of buffer baselines obtained on Calorimetry
Sciences’ DSCs designed for biological macromolecules, subtraction of the
buffer baseline corrects the data for the partial molar heat capacity of the solvent, allowing the partial molar heat capacity of the biological sample to be
directly determined from the thermogram. The software package supplied
with the DSC performs this subtraction, and also calculates the calorimetric enthalpy and entropy changes of the sample. In addition, for
chemically defined (purified) samples, the data can be fit to twostate or multiple processes to determine the concentrations
of folded and unfolded macromolecule in the sample.
Thus, a single automated DSC run requiring as
little as a few micrograms of sample and limited
operator attendance can provide a complete
thermodynamic analysis of the thermal
stabilities of the sample components.
18
How calorimetry can be used to solve
research and development problems
19
Applications
applications
20
Applications
Theory
Applications of calorimetry to the
pharmaceutical sciences
Applications
Calorimetry Sciences has produced a number of detailed Pharmaceutical Sciences application notes which examine specific problems both in the
research and in the development phases of drug production. Additional
application notes of interest (especially for the drug design process) are
available in the Life Sciences series. Each application note outlines the basis
of the problem being addressed, discusses how calorimetry can be used
to study the problem, points out both the strengths and limitations of the
technique, provides practical examples (data, interpretation, discussion),
and concludes with a summary of how calorimetry can be used to provide a
comprehensive analysis of the problem. Please contact Calorimetry Sciences
for a current list and copies of these application notes, or visit our Web site
at: www.calorimetrysciences.com.
The Drug Design Process:
Practical Issues
The optimization of a lead compound into a viable drug candidate
involves maximizing its binding affinity towards the selected (usually conformationally flexible) target. In the absence of a thermodynamic understanding of the specific interactions between a drug and its target, the design
of a drug is often guided only by predictions of the entropic component of
the binding interaction. When only entropic contributions are considered
and enthalpic contributions are ignored during the design process, highly
hydrophobic and conformationally constrained drugs are often designed
Calorimeters
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Theory
Applications
Practical Issues
Calorimeters
which exhibit poor binding and specificity. In contrast, drugs with good
binding characteristics to their flexible targets pay a significant conformational entropy penalty upon binding, so optimization of their affinity
requires substantial favorable binding enthalpy. Enthalpic optimization is
less straightforward than entropic (generally hydrophobic) optimization,
since specific favorable interactions (hydrogen bonds, van der Waals interactions, electrostatic interactions, etc.) must be designed into the binding
interface.
Both ITC and DSC measure the enthalpy of a binding reaction and
provide a thermodynamic description of the binding of a drug candidate
to a target receptor. ITC is the most direct technique for dissecting the free
energy of binding into its entropic and enthalpic components. Coupling
this information with atomic-level structural data, the relationship between
thermodynamics, structure and function can be ascertained. Using this
comprehensive approach, new compounds with improved molecular interactions, increased specificity, heightened binding and enhanced efficacy can
be designed more rapidly. In addition, ITC is a completely general approach
for characterizing enzyme kinetics and catalytic inhibition. Since drugs are
increasingly designed to act as specific enzyme inhibitors, ITC can play a
major role in both the thermodynamic and functional characterization of
enzyme-specific inhibitor drugs (e.g., HIV protease inhibitors).
When a drug binds to a receptor, the temperature at which the drug/
receptor complex denatures will be higher compared to the temperature at
which the free receptor denatures. DSC thus provides a direct measure of
whether a receptor has bound a drug and how tightly, and so can complement studies of binding
equilibria obtained by
ITC. Indeed, DSC is the
preferable technique for
assessing drug binding
in several circumstances.
The first is if binding is
very tight (above 109 M-1).
Since DSC compares the
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Calorimeters
Calorimetry Sciences Corporation
Practical Issues
Excipient compatibility:
The formulation of an active pharmaceutical ingredient into a form that
can be easily administered (for example, a tablet) requires the addition of
stabilizers and binders (excipients). Traditionally, any degradation of the
drug in the presence of an excipient is followed by HPLC, however, isothermal calorimetry provides a significantly more rapid and direct approach.
To determine the compatibility of an excipient with a drug, the thermal
properties of a binary mixture of the drug and excipient are compared to the
properties of the excipient and the drug alone. All samples are maintained
at the same relative humidity. If the mixture produces heat at a rate different
from the two individual components, the compounds are reacting and that
excipient is therefore incompatible with that drug.
Excipient compatibility studies can also be conducted using DSC, especially if the effects of dynamic temperature changes on excipient/drug mixtures need to be rapidly assessed. Please see the CSC Pharmaceutical Sciences
application note entitled: ‘Characterization of drug-excipient compatibility’.
Applications
Pharmaceutical Development:
Theory
extent to which the drug/receptor complex is stabilized towards thermal
denaturation compared to the free receptor, DSC allows estimation of binding energies at all binding constants, including extremely tightly associated
complexes. The second circumstance is if the bound complex equilibrates
very slowly (hours to days) and so is not compatible with the ITC timeframe
(seconds to minutes). Finally, the solubilization of very hydrophobic drugs
may require the use of organic solvents which can give rise to such large
heats of dilution on ITC that the heat of binding is obscured, or the amount
of organic required for drug solubilization denatures the receptor. Since
DSC studies can be conducted in aqueous, organic or mixed solvent systems,
the presence of organics has no effect on the sensitivity or accuracy of the
measurement.
For detailed descriptions of ITC and DSC applications pertinent to drug
design, please see the Life Sciences application notes entitled: ‘Characterizing binding interactions by ITC’, ‘Characterizing enzyme kinetics by ITC’
and ‘Characterizing protein/ligand binding by DSC’.
Theory
Applications
Practical Issues
Calorimeters
Amorphous content:
Isothermal calorimetry can rapidly detect and quantify the amount of
amorphous material in a crystalline drug. Formulation and mechanical
processing can increase the amorphous content of a drug, leading to altered
physical properties and decreased stability of the product. Even low levels
(<1%) of amorphous content generated during processing can be quantified by comparing the heat produced by samples collected at various stages
of formulation. The samples, maintained at the same relative humidity by
means of a water adsorption cell, typically adsorb water over a period of
several hours in the calorimeter. Since adsorbed water acts as a plasticizer,
the glass transition temperature (the temperature at which an amorphous
compound crystallizes) is lowered, leading to an exothermic recrystallization
process that is proportional to the amount of amorphous compound present
in the sample.
The glass transition temperature can be most reliably determined using
DSC. Knowledge of this transition temperature is critical since the amorphous and crystalline forms of a compound can have significantly different
stabilities and bioavailabilities. Therefore, choosing storage temperatures
and formulation compositions which minimize amorphous/crystalline interconversions is important for maximizing the efficacy and extending the shelf
life of a drug. Please see the CSC Pharmaceutical Sciences application note
entitled: ‘Characterization of solid state drugs by calorimetry’.
Shelf life predictions:
Isothermal calorimetry is ideal for qualitatively and rapidly assessing the
oxidation or degradation of solid or solubilized drugs under various conditions (pH, water content, oxygen concentration, and the presence of metal
ions or antioxidants). For example, the thermal output of a drug solubilized
at different pH values provides chemical insights into the mechanisms
driving degradation: if a drug degrades endothermically at high pH and
exothermically at low pH, degradation is driven by entropic considerations
in basic conditions and by enthalpic events in acidic conditions. As a second
example, oxidation can be determined by first passing an inert gas over a
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Calorimeters
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Practical Issues
Drug/membrane interactions:
Critical micelle concentration (cmc) can be determined using ITC by
injecting a buffered concentrated solution of a detergent (above its cmc) into
Applications
Antibiotic assessment:
ITC is gaining prominence in characterizing the effect of compounds on
cell metabolism. If the titrant inhibits or kills the cells (for example, when an
antibiotic is added to a bacterial sample), the resulting decrease in heat output will be quantitatively registered by the calorimeter, providing an accurate
measure of the potency of the drug against its microbial target. Calorimetry
is also an effective approach for initial toxicity screening of drug candidates
against tissues. Regardless of the target, calorimetric measurements are done
directly on the sample and do not require time consuming steps to separate
the cells from the medium.
Theory
sample and measuring anerobic degradation, then switching the gas flow to oxygen
and measuring heat flow after
steady state conditions are
established; by measuring heat
flow at different temperatures,
the activation energy of the
compound can be determined.
It is generally advisable to conduct stability studies at the anticipated
storage temperature since multiple temperature-dependant reaction mechanisms are often involved in the aging process, so the overall reaction rate will
be dependent on the rate-determining step. However, isothermal calorimetry (and DSC) can be used to accelerate aging processes, so that the stability
of the drug at ambient temperature is estimated by measuring the degradative reaction rate at different elevated temperatures, then extrapolating to the
desired temperature. Please see the CSC Pharmaceutical Sciences application
note entitled: ‘Rapid and practical stability screening by microcalorimetry’.
Applications
either a dilute solution of the same detergent or into buffer. The micelles initially disassociate upon dilution, but as the titration proceeds, the detergent
concentration in the sample cell reaches the cmc and no further dissociation
occurs. A first-derivative plot of the heat recorded for each injection versus
detergent concentration shows a break point corresponding to the cmc.
Repeating the experiment in the presence of drugs designed to interact with
membranes alters the cmc and provides an assessment of the drug’s affinity
for membranes.
Drug purity and polymorphism:
DSC is the ideal technique for obtaining rapid, accurate, unambiguous
melting temperatures, for providing a measure of the purity of the sample
(impurities and crystal defects lower the melting temperature and broaden
the melting endotherm), and for allowing different polymorphs in a sample
to be distinguished. Polymorphs have the same chemical composition but
different crystalline structures, resulting in different melting temperatures,
solubilities, stabilities and bioavailabilities. Polymorph conversion is often
characterized by a ‘nucleation’ temperature at which the kinetics of conversion is significantly increased; the nucleation temperature can be decreased
and polymorph conversion accelerated by the presence of a small amount of
impurities. Characterization of polymorph conversion and knowledge of the
polymorphic composition of a drug formulation is increasingly required by
regulatory agencies. Please see the CSC Pharmaceutical Sciences application
note entitled: ‘Characterization of solid state drugs by calorimetry’.
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Drug absorption:
Scanning calorimetry can be used to monitor changes in the phase composition of liposomes as small or large molecules permeate the outer surface,
the bilayer, and finally the interior of the liposome. If drug dissolution or
penetration of the bilayer is slow, multiple temperature scans on the same
sample will show a gradual change in phase composition over time, providing
an indication of how effectively a drug formulation will be taken up by cells
prior to the initiation of in vivo testing. Slow temperature scanning results
in improved temperature resolution of overlapping peaks. If multi-modal
behavior is observed, this may indicate the formation of complexes in the
lipid bilayer which could be undesirable if they formed in cell membranes.
Applications
Energetics of solid drug surfaces:
Direct heats of sorption and wetting can be made using water vapor, solvent vapors, or in the case of wetting, in non-solvent systems. Unlike other
methods, calorimetry does not rely upon a model to calculate approximate
surface energies.
Theory
Dissolution rates:
Isothermal calorimetry provides a quick method for determining if a tablet or other solid
formulation dissolves rapidly,
since dissolution is accompanied by significant evolution of
heat. Since this simple method
does not require any sample filtration or development of a spectroscopic or
HPLC protocol, it is a particularly useful tool in quality control, especially
in the preformulation stages of product development. Please see the CSC
Pharmaceutical Sciences application note entitled: ‘Characterization of solid
pharmaceutical systems from heats and rates of solution’.
Calorimeters
Practical Issues
Applications
Theory
Notes
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Calorimetry Sciences Corporation
What to consider
when choosing a calorimeter
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Practical Issues
practical
issues
30
Practical Issues
Theory
Practical issues to consider
when choosing a calorimeter
Several instruments of particular relevance to pharmaceutical scientists
are referred to below. Descriptions of these instruments are given on p. 39 of
this guide.
Calorimeters
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Practical Issues
Calorimetry Sciences Corporation
Applications
What technical expertise and support are available?
Calorimetry Sciences has been a leader in thermal instrumentation since
1978. The entire process of developing, designing, building, testing and
upgrading our hardware and software is done in-house, so our scientists and
engineers can competently and promptly answer any questions you have
regarding our instruments. In addition, our chemists and biophysicists are
available to help you optimize your experimental protocols, assist in analyzing data, inform you when new articles or techniques applicable to your
research are published or developed, and in general share our knowledge of
pharmaceutical calorimetry.
Although the intent of this guide is to
Potential customers
help researchers decide if calorimetry
could benefit their research, sometimes
are encouraged to send
the utility of an approach can only be
a sample for thermoestablished by trial. Potential customdynamic analysis.
ers are encouraged to send a sample for
thermodynamic analysis. We will discuss
our findings with you and make recommendations as to which instrument is
best suited to your requirements. Our goal is to ensure that you buy the best
calorimeter for your specific applications.
Calorimetry Sciences instruments are acknowledged to be exceptionally
durable, with many units continuing to produce research-quality data 15­ to
20 years after purchase. Calorimetry Sciences believes in constantly
upgrading and improving our
instrumentation: we do not believe
in programmed obsolescence!
Theory
Applications
Practical Issues
Calorimeters
How much sample is required?
The amount of sample required is determined by the type of experiment
being performed, the enthalpy of the reaction being studied, and the sensitivity of the instrument used. For isothermal measurements of low enthalpy
reactions (for example, typical excipient compatibility studies), fractions
of a gram to grams of material would be required by the 4400 Isothermal
Microcalorimeter (IMC), which can measure three samples simultaneously; similar reactions would require 20 times less material using the 4500
Isothermal Nanocalorimeter (INC). Reactions with larger enthalpies would
require substantially less sample for either calorimeter.
For ITC binding experiments, the amount of material is very dependent
on the binding constant of the reaction, with weak binding systems requiring substantially higher concentrations of material than tight binding systems, as explained in the CSC Life Science application note entitled: ‘Characterizing binding interactions by ITC’. The 5300 Nano-ITC would require
picomoles to nanomoles of macromolecule in the 1.0
mL sample cell. In the case of enzymatic reactions,
nanomolar to picomolar concentrations of enzyme are
often sufficient, depending on the enthalpy and rate
of the reaction. The 4200 ITC is less sensitive than the
5300 ITC and has a larger sample cell (1.3 mL), but has
a larger dynamic range, making it an ideal instrument
for studying weak binding reactions.
Ultra-sensitive DSC experiments on biomacromolecules are ideally performed using either the 6100
N-DSC II or, if variable pressure control is important,
the 6300 N-DSC III. Generally, micrograms of protein
or other macromolecule are sufficient to yield a DSC
thermogram of sufficient quality to allow a complete and accurate assessment of the enthalpy of unfolding, as well as the Tm. If sample size is less of
a constraint, the 4100 MC-DSC can simultaneously analyze three macromolecule or small molecule samples, although its sensitivity is less than the
6100/6300 DSCs.
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Are calorimeter cells difficult to fill?
Solid samples can be easily accommodated in instruments with removable
cells (4100 MC-DSC, 4200 ITC, 4400 IMC and 4500 INC). These instru-
Applications
Are pressure perturbation DSC experiments possible?
The Calorimetry Sciences model 6300 Nano-DSC III employs a high-precision piston driven by a computer-controlled linear actuator to control the
pressure in the cell. Constant pressure is applied during the DSC experiment to obtain constant pressure heat capacity data and to prevent bubble
formation or boiling. Importantly, pressure can be varied according to user
selectable functions allowing the pressure to be scanned, stepped, or altered
in a sinusoidal fashion. This allows exceptional control and flexibility in
designing experiments for studying the compressibility and thermal expansivity of samples.
Theory
How can protein aggregation and precipitation be minimized
during DSC scans?
The thermal denaturation of proteins exposes previously buried hydrophobic residues, often resulting in protein aggregation and precipitation. If
this process causes significant enthalpy changes that cannot be separated
from the unfolding process, the process cannot be thermodynamically
analyzed. Capillary cells minimize this problem by delaying the thermal
effects of aggregation and precipitation,
Capillary cells
often until unfolding of the protein is
complete. For example, 100 µM bovine
minimize biomacroserum albumin (in 0.1 M phosphate bufmolecule aggregation
fer, pH 7.2, scanned from 20 to 90 °C at
and precipitation.
1 °C/min) aggregated after a single scan
in a Calorimetry Sciences 6300 NanoDSC equipped with cylindrical cells, whereas under identical conditions
aggregation was not observed below 300 µM when capillary cells were used.
Calorimetry Sciences supplies its Nano-DSC instruments with capillary cells
unless cylindrical cells are specifically requested by the customer.
Theory
Applications
Practical Issues
Calorimeters
ments can also be used for solution samples: because of the relatively large
cell volumes, filling the cells without trapping air bubbles is not a problem
provided the solutions are degassed first.
Calorimetry Sciences has designed cells for the Nano series that greatly
diminish the possibility of a trapped air bubble in small solution volumes.
After degassing the sample, a scientist using a Calorimetry Sciences calorimeter for the first time can fill a cell in seconds and start a run in minutes,
confident that air bubbles will not affect the experiment. A degassing station
and vacuum pump is supplied with every 6300 N-DSC III calorimeter, and
is optional with the purchase of the 5300 Nano-ITC.
How easy is it to clean the cells?
The removable cells found in the 4100, 4200, 4300, 4400 and 4500 can be
aggressively cleaned and sonicated, then reassembled and reinserted into the
instrument in seconds.
The 5300 N-ITC III fixed-in-place conical-shaped cylindrical cell can be
very easily cleaned in minutes with acids, bases, organic solvents and water
as required (for example, after the analysis of liposomes or membrane proteins) by passing several liters of solvent through the cells using the supplied
vacuum pump and special cleaning tool.
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Calorimeters
Is it difficult to design a successful experimental protocol?
Calorimetry Sciences is committed to helping researchers maximize useful
data from their experiments. To that end, CSC has produced (and continues to expand) a series of application notes aimed at taking the guesswork
out of experiment design. The basic experimental approaches for ITC and
DSC experiments were presented at the beginning of this guide. Almost all
experimental protocols are variations of these approaches, and are described
and illustrated in detail in the application notes. In addition, Calorimetry
Sciences’ applications specialists are pleased to work with scientists to troubleshoot procedural problems or develop novel experimental approaches.
Practical Issues
What maintenance do the instruments require?
Fixed-in-place cells should be flushed with water between samples, and
cleaned with detergent or organics weekly or monthly (depending on the
hydrophobicity of the samples). Removable cells should be scrubbed with
detergent and water, or with more aggressive solvents if necessary. Water
baths should be drained and cleaned every six months to a year.
Otherwise, the instruments require no maintenance other than removal,
washing and reinstallation of the air filter a few times per year.
Applications
Is it easy to clean and refill the ITC syringe?
Removing the syringe from a Calorimetry Sciences ITC instrument is
extremely fast and easy. The syringe can be completely removed from the
burette assembly in seconds by loosening a thumb screw, allowing quick,
thorough cleaning of the syringe and easy refilling. Both a 100 µL and 250 µL
syringe are provided with each 4200 ITC and 5300 N-ITC instrument, and
are completely interchangeable in the burette assembly.
Theory
The 6100/6300 N-DSC instruments come with either fixed-in-place capillary or cylindrical cells which can be cleaned with a variety of solvents. Both
the continuous capillary cells and the cylindrical cells can be flushed with
liters of cleaning solution in a matter of minutes using the vacuum pump
supplied with the instrument.
Theory
Applications
Practical Issues
Calorimeters
Is the data acquisition and
analysis software straightforward and flexible?
The software included with
Calorimetry Sciences’ instruments was written in-house
by our software engineers in
consultation with our applications scientists and with
input from several leading
calorimetry experts. The goal
was to develop software that is
simple to use, yet sufficiently
sophisticated and versatile to
be able to handle essentially
any data set. Importantly, data
analysis is completely transparent: there are no ‘fudge factors’ built into the
analysis regimes, and the user has complete control over the manipulation of
the data.
The 4400 IMC and 4500 INC both collect heat rate data; the frequency of
data collection is set by the operator and depends on the rate of the reaction.
The 4300 RSC uses software specific for
Data analysis is
this instrument which also allows full user
control of acquisition parameters.
completely transparThe 5300 Nano-ITC instrument is supent: there are no ‘fudge
plied with three software modules. ITCfactors’ built into the
Run allows operating temperature, stirring
analysis regimes,
speed, injection volume, the number of
and the user has
injections and other control parameters
complete control over
to be easily specified. User selectable
the manipulation of
response time, automatic calibration functhe data.
tions and real-time monitoring of data are
also provided. The data analysis module,
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Calorimetry Sciences Corporation
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Calorimeters
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Applications
Calorimetry Sciences Corporation
Theory
BindWorks, is designed to easily fit data to the appropriate binding model.
This module produces a graphical representation of the fit in addition to the
parameters Ka, ∆H, ∆S and the stoichiometry (n). Preprogrammed fitting
models are included for three types of binding: independent binding sites, two sets of
multiple sites, and cooperative binding. In
Experiment Design
addition, customer-specific binding models
Wizard
can be easily input. Files are in ASCII
prevents precious
format and can be exported to other data
sample material from
analysis, graphical and spreadsheet probeing wasted.
grams (including Origin and Excel). Data
obtained with other manufacturer’s instruments can be analyzed with BindWorks.
Experiment Design Wizard is an important time-saving feature of BindWorks. This module allows experimental parameters (such as concentration)
and anticipated thermodynamic results to be input, and outputs a simulation
of the expected experimental thermogram. In addition to saving numerous hours re-running improperly designed experiments, this tool prevents
precious sample material from being wasted on runs that cannot produce
useable data due to improper concentration choices.
The 4200 ITC also uses BindWorks for data analysis, but data acquisition
is controlled by a custom data acquisition package.
The 6100/6300 N-DSC acquisition software, DSCRun, allows experimental
parameters such as scan rate, temperature range, number of scans, etc. to
be specified. All parameters are set and viewed from a single dialog screen,
and notes about the experiment can be attached to the data file. Automated
calibration functions and real-time monitoring of the collected data are also
provided.
The DSC data analysis software package, CpCalc, is designed to make
the analysis of raw DSC thermograms simple and straightforward. Blank
scans are easily selected and subtracted before converting data to molar
heat capacity, and calorimetric enthalpy change, entropy change, and partial
molar heat capacity of the sample are automatically calculated. Molar heat
Theory
Applications
Are training courses available?
Following purchase of a Calorimetry Sciences instrument, on-site installation and in-depth training in both instrument hardware and software are
available for a nominal fee. In addition, Calorimetry Sciences is initiating
a series of seminars and workshops dealing with experiment design, data
interpretation and novel applications of calorimetry. Please contact Calorimetry Sciences for details.
Calorimeters
Practical Issues
capacity data can be fit to two-state models to determine van’t Hoff enthalpy
change, melting temperature and change in heat capacity, and fitting may
also be done with two-state processes to help determine the accurate concentration of macromolecule in the sample. Thermograms can be deconvoluted and integrated to provide enthalpic information on the domains and
subunits of biological macromolecules. Data are in ASCII format and may
be exported into other software, including Origin, PeakFit, SigmaPlot or
Excel, at any stage of the analysis, and imported back into CpCalc if desired.
CpCalc is utilized by the 4100, 6100 and 6300 DSCs; the 4100, which can
operate in either the isothermal or temperature scan mode, utilizes separate
data acquisition software.
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Calorimetry Sciences Corporation
Calorimetry Sciences instruments for
calorimeters
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Calorimeters
pharmaceutical research and development
40
Calorimeters
Theory
Calorimetry Sciences Instruments for
Pharmaceutical Research and Development
CSC 6300 Nano DSC III
Calorimetry Sciences Corporation
41
Calorimeters
With the same sensitivity as the 6300,
the 6100 Nano DSC II (N-DSC II) is
ideal for measuring partial molar heat
capacities of biopolymers in dilute
solution when volumetric properties
are not a consideration. The N-DSC II
is a power compensation design using
a completely solid-state thermostat and
is equipped with the user’s choice of
Practical Issues
CSC 6100 Nano DSC II
Applications
The 6300 Nano DSC III (N-DSC III)
represents the latest development in
high precision biopolymer calorimetry.
Lower noise, greater baseline reproducibility, the choice of capillary or cylindrical cells and unparalleled sensitivity
in both the heating and cooling scans
establish this calorimeter as the ultimate instrument for making partial
molar heat capacity measurements on
very dilute solutions. Built-in computer
controlled cell pressurization allows
volumetric properties of biopolymers to
be determined. Since many biopolymers are expensive or difficult to obtain,
and others behave differently depending on their concentration, there is a
need for a scanning instrument that can make exquisite measurements with
very little sample. Using the N-DSC III, a full thermodynamic analysis of a
biopolymer can be obtained with as little as 2 µgrams of material.
Theory
either capillary or cylindrical cells. With an operating temperature of -10
to +130 °C (up to +160 °C in the HT version), scan rates up to 2 °C/min in
both the heating and cooling directions, and sensitivity at the 1µcalorie/°C
level, the N-DSC II can be used to study the thermal denaturation of most
biopolymers using just µgrams of sample.
The 5300 Nano ITC III (N-ITC III) is
designed specifically for studying biopolymer-ligand interactions. The N-ITC III
is the instrument of choice for those who
require the ultimate in sensitivity. State
of the art improvements in cell geometry,
temperature control, and ease-of-use
set the N-ITC III apart as superior for
almost all applications. The N-ITC III is
a power compensation design employing
a self-contained, solid-state thermostat,
and fixed-in-place 24K gold cells. Heat effects as small as 30 nanocalories
are detectable with 1 nanomole or less of biopolymer, with equilibrium
constants in the range of 102 to 108 M-1 easily determined in a single titration
experiment. One experiment can yield the complete set of thermodynamic
parameters (Keq , ∆H, ∆S, and n) for almost any reaction.
CSC 4500 Isothermal Nanocalorimeter
The 4500 Isothermal Nanocalorimeter (INC) is designed to measure very
slow or very small heat changes. Since
all chemical and physical processes are
accompanied by changes in heat, the
INC is a universal detector that can be
used to follow the progress of slow reactions at modest temperatures. The INC
can provide both kinetic and thermo-
Calorimeters
Practical Issues
Applications
CSC 5300 Nano ITC III
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Calorimetry Sciences Corporation
Theory
dynamic information about the stability/reactivity of liquid or solid samples
up to 3 mL in volume. The INC can detect changes in heat flow as small as
1 nanocalorie/sec (4 nanoJoules/sec) and heat effects as small as 0.1 calorie
(0.4 Joules). Typical applications for the INC include shelf life predictions,
excipient compatibility, drug polymorphism and cell metabolism.
CSC 4400 Isothermal Microcalorimeter
Calorimetry Sciences Corporation
43
Calorimeters
The 4300 Rapid Solution Calorimeter
(RSC) is designed to be used as either an
analytical tool for determining sample
purity or concentration, or as an instrument for studying the thermodynamics
of binding reactions in dilute solutions.
With a temperature resolution of 2 µ°C,
the RSC can measure heat changes as
small as 1 millicalorie (4 milliJoules).
Practical Issues
CSC 4300 Rapid Solution Calorimeter
Applications
The 4400 Isothermal Microcalorimeter (IMC) can detect changes in heat
flow as small as 25 nanocalories/sec (0.1
Watt) and heat effects as small as 10
cal (40 Joules). The IMC is available in
three temperature ranges: 0 to100 °C,
-40 to 80 °C, and 20 to 200 °C. The IMC,
which comes with three matched sample
cells and one reference cell, can provide
both kinetic and thermodynamic information for almost any process occurring
in a solid, liquid or gaseous sample.
When equipped with accessory flow adsorption, flow mixing, titration and
vapor adsorption cells, the IMC can be used to study solute dissolution,
solvent and/or solute adsorption at surfaces, binding equilibria, and heats of
mixing and/or dilution.
The RSC operates over the temperature range 0 to 100 °C, and is designed
to perform both batch addition and titration experiments. In addition, pH
data may be collected concurrently with the heat data. The RSC is used to
measure heats of reaction, equilibrium constants, solution heat capacity and
kinetics.
CSC 4200 Isothermal Titration Calorimeter
The 4200 Isothermal Titration Calorimeter (ITC) can detect heat effects as small
as 0.1millicalorie (0.4 milliJoule), allowing titrations to be done with nanomoles
of biopolymer. Equilibrium constants in
the range 102 to 108 M-1 are easily determined for almost any interaction over
the temperature range 0 to 100 °C. The
ITC, which can also be used as a model
4500 INC, is excellent for studying ligand
binding, pH effects and drug/metabolism
interactions in cells.
Calorimeters
CSC 4100 Multi-Cell Differential Scanning Calorimeter
The 4100 Multi-Cell Differential Scanning Calorimeter (MC-DSC) is equipped
with three sample cells matched to one
reference cell, and can analyze liquids,
solids, slurries and suspensions. The MCDSC is designed to study interactions
as a function of temperature change,
collecting Tm , ∆H, and ∆Cp data on the
three samples in a single experiment. The standard MC-DSC operates over
the temperature range -40 to 110 °C, while the high temperature version
scans up to 200 °C. Scan rates are useable selectable from 0 to 2 °C/minute.
Excellent for studying drug purity, polymorph stability, excipient compatibility and drug degradation.
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Calorimetry Sciences Corporation
Calorimeters
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Calorimeters
Practical Issues
Applications
Theory
Notes
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Calorimetry Sciences Corporation
Applications
Practical Issues
Calorimeters
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Calorimetry Sciences Corporation
Theory
Notes
890 West 410 North, Suite A
Lindon, Utah 84042
Phone: 801.763.1500 Fax: 801.763.1414
Web: www.calorimetrysciences.com
E-mail: [email protected]