Download PENTAL SODIUM (Thiopental sodium) and NORCURON

Interaction of anesthetics drugs: Pental Sodium and Norcuron
FT-IR Spectroscopic study, X-ray powder diffraction and molecular
calculations
SEVGI HAMAN BAYARIa*, SEMRA İDEb, TANER AYERDENc
a
Department of Physics,
Hacettepe University,
Faculty of Education, 06800Beytepe, Ankara,
TURKEY
b
Department of Physics Engineering,
Hacettepe University,
Faculty of Engineering, 06800 Beytepe, Ankara
TURKEY
c
Ankara Numune Hospital,
Department of Anesthesiology and Reanimation, Altındağ, Ankara
TURKEY
http://yunus.hacettepe.edu.tr/~bayari/
Abstract: The mechanism of interaction of a non-depolarizing neuromuscular blocking agent norcuron
(vecuronium bromide) and intravenous anesthetics thiopental sodium have been studied using FTIR
spectroscopy, X-ray powder diffraction and molecular mechanic-quantum chemical calculation methods. The
solid phase FTIR spectra of pental sodium, vecuronium bromide and their interacted compound have been
recorded in the regions 4000–400 cm-1. The spectra were interpreted following full structure optimization
calculation based on semi-empirical PM3 method and using scale factor yielding fairly good agreement
between observed and calculated frequencies. The infrared spectra were also predicted from the calculated
intensities. The changes observed in the some bands (wavenumber, shape) of interacted compound indicated
that there is an interaction between two molecules. On the other hand, molecular interaction has been also
obtained with bigger unit cell and different x-ray patterns. With the help of electric dipole calculations and
spectroscopic studies, new structure and interaction mechanism have been predicted.
Key-Words: pental sodium, vecuronium bromide, anesthetics drugs, FT-IR spectroscopy, X-ray diffraction,
molecular calculation
1 Introduction
Pental sodium (Thiopental sodium: 5-ethyldihydro5-(1-methylbuthly)-2-thioxao-4,6(1H,5H) pyrimi
dinedione monosodium salt) is administered
intravenously for the induction of general
anesthesia and for the production of complete
anesthesia of short duration and it is extremely
rapidly taken up by the brain (Fig.1a). Other uses
include the supplementation of regional anesthesia
.
H3C
or low potency agents such as nitrous oxide, the
control of convulsive states and as a hypnotic [1-3].
Vecuronium bromide (Fig.1b) is a non-depolarizing
neuromuscular blocking agent, chemically designed
as the amino steroid [1-(3α, 17β-diacetoxy-2β
piperidino-5α-androstan-16β-yl)-1 methyl piperi
dinium bromide].
H3C O
NH
S
H3C
N
Na
O
(a)
(b)
Fig.1. Chemical diagram of Pental Sodium (a) and Vecuronium bromide (b)
Br ions are located on the positions around
methyl connected N atom in the molecular structure
[4]. Vecuronium bromide blocks the transmission
process between the motor nerve-ending and
striated muscle by binding competitively with
acetylcholine to the nicotinic receptors located in
the motor end-plate region of striated muscle.
Neuromuscular blocking agents (NMBAs) interact
with many different drugs including general
anesthetics (vecuronium) is a no depolarizing
neuromuscular blocking agent possessing all of the
characteristic curariform pharmacological actions
of this class of drugs [5, 6].
The interaction of drugs is of interest from
theoretical and practical points of view because this
bonding plays an important role in the drug
carriers, adsorbents, etc. It is clear that, interactions
depend on the structures of the molecules and the
medium properties [7]. Thus their binding
characteristics are primary determinants of their
pharmacokinetic properties. Drug interactions with
anesthetics are likely to occur, but are not well
documented [8, 9]. To our knowledge, IR studies,
molecular calculations and their interaction of these
drugs have not been reported. In this work, the
interaction between pental sodium and vecuronium
bromide has been investigated by FT-IR, X-ray
diffraction and molecular calculation methods.
2 Material and methods
2.1 Sample preparation
0.9% isotonic sodium clorur solutions of pental
sodium and vecuronium bromide were mixed (1:1,
w/w). Then, process of mixing under constant
stirring was ended after two days. This was filtered
and powder sample dried under vacuum
2.2 Spectroscopic measurements
The FT-IR spectra of powder samples were
recorded using Mattson 1000 spectrometer with the
KBr technique, in the region 4000-400 cm-1 that
was calibrated by polystyrene. The powder X-ray
diffraction pattern of each samples (starting
compounds and interacted product) were recorded
using a Philips PW 1140 manual spectrogonimeter
employing CuK radiation. (=1.5418 Å) is over
the range 2, 2-40o.
2.3 Theoretical calculations
The molecular modeling studies were carried out
using molecular mechanics and quantum mechanics
methods as implemented in the HyperChem
Version 7.5 [10] and ALCHEMY 2000 programs
[11]. The lowest energy conformation obtained by
the MM+ molecular mechanics method was further
optimized at PM3 semi-empirical method. The
harmonic frequencies of molecules were also
computed. Infrared intensities were calculated for
free molecules and interacted sample and compared
to the experimental intensities. To calculate electric
dipoles of molecules, ALCHEMY 2000 program
was used.
3 Results and discussion
3.1 Molecular modeling and proposed
interaction mechanism
In order to find interaction site of pental sodium
and vecuronium bromide, firstly, the molecular
geometry were evaluated in a point of minimal
energy. After single point energy minimization
(41.344 kcal /mol for pental sodium and 25.362
kcal/mol for vecuronium), three dimensional most
probable structures and their electric dipoles were
obtained. Electric dipoles of pental sodium and
vecuronium bromide may give some point of view
for prediction about interacted sample. If Na+ ions
remove from the pental sodium, electric dipole
direction will change and will be through to the
position of NH-C-S group. In the vecuronium,
positive side of electric dipole indicates that the
positions of two carbon atoms of steroid skeleton as
molecular interaction points.
According to Bachmann’s ostron synthesis
[12], bromine and sodium ions are removing from
the structure and their atomic positions will be
connection point for remaining ionic parts of the
starting compounds. In this reaction, thiopental is
an ionic part of pental sodium without Na atom.
According to this chemical reaction and known
crystal and molecular structure of vecuronium
bromide [14], the positions of four bromine ions
around the nitrogen atom in the pyridine ring of
vecuronium will probably be filled with sulfur ions
of thiopental as seen in Fig. 2. Strong ionic
interaction between N and four S atoms cause to
very close positions of O=C-NH side in thiopental
and C atoms of steroid skeleton of vecuronium. So,
two possible hydrogen bonds can be constructed.
Because of the chelate structure in the connection
part, we can obtain more crystalline form of
interacted sample than those of vecuronium
bromide or pental sodium molecules. This
expectation was also supported by our experimental
observations. Geometric parameter values of
interacted groups of free molecules should be
changed in the proposed interacted structures.
O S¯
S¯
CH3
O
CH3
CH3
N
N+
CH3
O
H3C
CH
H
O
N
S¯
S¯
O
N
H3C
CH3
CH3
Fig.2.
Predicted structure of interacted sample
The distance between the O- of thiopental anion
and the carbon atom of vecuronium less than the
distance between the N- of thiopental anion and the
carbon atom of vecuronium. Thiopental sodium has
two possible donating entities (O and the N by its
lone pair of electrons). The electrostatic potential
surface of each molecules and interacted sample
were also calculated. It is acceptable that the
electrostatic surface area of two molecules can be
the mathematical sum of their individual total
surface areas. Strong electrostatic attraction at the
mentioned centers between the two molecules
when minimized together was found to result in an
actual total surface area of less than the
hypothetical sum. According to these theoretical
results, we may suggest that there is an interaction
between thiopental anion and vecuronium.
3.2 Infrared spectra
The infrared spectra of the free drugs and the
interacted sample are given in Fig. 3. IR spectrum
of interacted sample indicated that some vibrations
were changed with respect to the free molecules.
The FT-IR spectrum of pental sodium showed the
NH stretching band at 3223 cm-1 and the NH· · ·O
band of the intra-molecular hydrogen bonding at
3427 cm-1 [13]. The carbonyl group appears at
1694 cm-1 as a strong absorbance. The band
observed at 1613 cm-1 and the strong band at 1483
cm-1 are assigned to the (NH) and to the (C=N),
respectively. The IR spectrum of pental sodium
shows the other bands which assigned to the CH3,
CH2, C-S and ring vibrations.
Vecuronium molecule consists of acetoxy, steroid
skeleton, piperidino and piperidinium parts. The
assignments of the observed bands were made on
the basis of PM3 calculation. The carbonylstretching mode generally lies within the range
1755–1730 cm-1. In the present investigation, weak
peaks are observed in the infrared spectrum. it is
due to the interaction between this group and
steroid. We observed very strong bands at 3282,
1639,1604,1553 cm-1 and medium band at 1256
cm-1 in the IR spectrum of vecuronium. They are
absent in the IR spectrum of interacted sample.
We observed new bands of the IR spectrum of
interacted sample. According to dipol moment and
electrostatic surfaces and X-ray results, the
tentative structure would be as follows: the carbon
atom of vecuronium attached to the N-H part of
thiopental; interaction between the oxygen atom of
thiopental and the carbon atom of vecuronium and
interaction between the S atom of thiopental and
piperidinium nitrogen of vecuronium. The broad
NH absorptions at 3265 and 3154 cm-1 show that
nitrogen bond to the adjacent carbon atoms. The
decreases in the vibration frequency of a particular
band have been used as evidence for a particular
site of a charge-transfer interaction [14].
We did not observed C=O stretching frequency of
pental sodium in the IR spectrum of interacted
sample. We observed medium band at 1736 cm-1
(belong to vecuronium). These wave number is
somewhat lower, since the carbonyl oxygen is
involved in intermolecular hydrogen bonding. The
strong bands at 1483 cm-1 [(NH)] and 1613 cm-1
[(C=N)] absent in the IR spectrum of interacted
sample. We observed new bands at 839 and 761
cm-1. The main contribution to these bands comes
from S-N and C-S vibration. The IR bands of the
C–O or the C–S in the complexed molecules are
shifted in frequency. This indicates a decrease in
the stretching force constant and favors
coordination to the sulphur atom. The absorption
frequencies assigned to the C–N stretches are
shifted to higher frequencies. These shifts are
expected if the oxygen or sulphur atoms are the
donor centers.
We also observed some changes at the frequencies
of acetoxy group of vecuronium. This can be
explained by intermolecular H bonding. (The all
observed frequencies from the IR spectra of the
pure drugs and interacted sample and the tentative
assignments of bands are avilable from S.Bayarı)
Fig. 3. The infrared spectra of a) vecuronium bromide b) pental sodium c) interacted sample
3.3 X-ray powder diffraction
In order to examine the accuracy of the FTIR
results, the powder X-ray Diffraction (XRD)
patterns were also obtained for these samples (Fig.
3) With the help of previous experimental results
related with the molecular and crystal structure of
vecuronium bromide, important and sharp peaks
were indicated for vecuronium bromide with Miller
indices [4]. It is not that the pattern of interacted
sample is not a summation pattern of two anesthetic
compounds. The some peaks corresponding to free
compounds are absent due to presence of molecular
interaction. The intensity peaks have been observed
in the low theta range respect to the patterns of
each compound. In low theta range (6-24 º), two
main diffraction humps have been observed for
pental sodium indicating crystallographic plane
groups which have six membered ring with S and
Na atoms. The effect of these two humps can be
seen in the pattern of the interacted sample. It
means that interaction will be along O=C-NH-S-Na
atomic side in the pental sodium.
Fig. 3. X-ray powder diffraction patterns of free drug molecules and interacted sample.
On the other hand, (015) and (064) peaks indicate
two important crystallographic plane, the effect of
these peaks can be seen in the interaction result.
First and third sharp peaks in the pattern of
interacted sample are indicating their importance.
Crystallographic projection along a axis was
investigated and obtained which atoms are locating
on these two planes. C6 and C7 atoms in the
vecuronium bromide [4] were common atoms. It is
clear that the other atoms were also locating on the
same planes. But interactive effect of these carbon
atoms were also obtained by another ways
mentioned before. More intensive (first) peak in the
top pattern shows more atoms located on the same
plane, so more heterocyclic structure than that of
the vecuronium bromide. The Bragg angle of this
peak has been deviated from 9.8 to 7.2º and this
result is an evidence for bigger unit cell expectation
supporting more heterocyclic structure. Finally,
these results are not sufficient to explain certain
structure of the interacted sample. But we may give
the most probable prediction as seen in Fig.2.
4 Conclusions
This article has reported the infrared spectra, X-ray
diffraction and molecular calculation results of free
and interacted (in vitro) drugs (pental sodium and
vecuronium bromide). The absence and occurs of
some bands in the IR spectrum of interacted sample
compare to free drugs spectra reveal that there may
be a conformational change due to their interaction
with the each other. In order to understand the
interaction mechanisms of drugs, it is crucial to
know its three-dimensional molecular structures. If
molecular structure of a molecule is not known,
theoretical calculations and modelling will be an
important support to experimental studies. From
calculated and spectroscopic results it could be
concluded that there is an interaction between
thiopental anion and vecuronium.
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