Download PowerPoint 프레젠테이션

02-03 물리화학
(Frontier of Physical Chmistry)
전승준
(고려대학교 화학과)
미국화학회에서 의 발표주제
03 Fall Symposium
•
•
•
•
•
•
•
•
Making and Breaking Chemical Bonds in Gas and
Condensed Phase
Physical Chemistry of Complex Fluids
Size-Selected Clusters on Surfaces
Slow Dynamics near the Glass Transition
Frontiers in Biophysical Methods
Combinatorial Biophysical Chemistry and Molecular
Evolution
The Conduction Band in Liquids and Disordered
Solids
Quantum Monte Carlo Methods
03 Spring Symposium
•
•
•
•
•
•
•
•
•
•
•
•
•
Spectroscopy and Dynamics in Liquids
Synthesis, Spectroscopy, Characterization, and Applications of
Nanoparticles
VUV Probes of Dynamics and Spectroscopy
Physical Chemistry of Biomolecular Motors
Present and Future Technologies in Chemical Instrumentation
Colloidal and Molecular Electro-Optics
Sequence-Dependent Curvature and Deformation in Nucleic
Acids and Protein-Nucleic Acid Complexes
Structure-Function Correlation for Biological Ion Channels
Iterative Methods in Quantum Mechanics and Applications to
Chemical Problems
New Electronic Structure Methods: From Molecules to Materials
Integrating Diverse Computational Approaches to Complex
Problem
Recent Developments and Applications of Time-Dependent
DFT and Related Ab Initio and Semiempirical Methods
Protein Flexibility Theory
03 Spring poster session
•
•
•
•
•
•
Theoretical Methods and Algorithms
Gas-Phase Dynamics and Structure
Condensed-Phase Dynamics and Structure
Surfaces and Interfaces
Materials and Polymers
Biophysical Chemistry
02 Fall Symposium
•
•
•
•
•
•
•
•
•
Ordered Molecular Assemblies of Nanoparticles
Chemical Studies Important in Astrobiology
Mesoscale Phenomena in Fluid Systems
Applications of Neutron Scattering in Structural Biology and
Biophysics
Frontiers in Atmospheric Chemistry
Nonlinear Dynamics in Polymeric Systems
Biologically Relevant Molecules in the Gas Phase
New developments in force fields for molecular modeling
Classical and quantum statistical mechanics studies of
solvation
02 Fall poster session
•
•
•
•
•
FRONTIERS OF ATMOSPHERIC CHEMISTRY
ORDERED MOLECULAR ASSEMBLIES OF
NANOPARTICLES
NEUTRON SCATTERING AND BIOPHYSICAL
CHEMISTRY
COMPUTATIONAL CHEMISTRY
GENERAL PHYSICAL CHEMISTRY
02 Spring Symposium
•
•
•
•
•
•
•
•
•
•
Frontiers in Chemical Dynamics
Dynamics and Friction at Submicron Confining Systems
Structural and Mechanistic Aspects of Amyloid Fibril Formation
Organic and Molecular Electronics
Forces in Biology
Modern Aspects of Structure Function Correlations of Biomolecules:
Phosphoryl and Nucleotidyl Transfer Reactions, Enzyme Action
Chemistry and the Environment in the 21st Century: Environmental
Chemistry at Interfaces
Biophysical Chemistry of Protein Binding Events
Molecular Modeling and Simulation of Reaction Mechanisms,
Kinetics and Catalysis
Recent Advances in Electron Correlation Methodology
02 Spring poster session
•
•
•
•
•
•
•
Frontiers in Chemical Dynamics.
Molecular Electronics, Surfaces and Interfaces
Biophysical Chemistry
Reaction Mechanisms and Kinetics
Environmental Chemistry
General Physical Chemistry
FRONTIERS OF ATMOSPHERIC CHEMISTRY
물리화학 실험연구
-Chemical structure and dynamics : Gas and Liquid state,
State selective, mode selective, bond selective
linear  nonlinear
Reaction control
-Spectroscopy : Conventional, Laser, Mass, NMR
Structure and dynamics
Imaging, Single molecular detection, Multi-dimentional
Attosecond time-resolved
-Complex system : surface, interface, biomolecules, mesoscope
Material science
Bio science
Nano science
SINGLE-BUBBLE MICROREACTORS
[Nature, 418, 394 (2002)].
Kenneth S. Suslick (the University of Illinois, Urbana-Champaign)
Using sensitive fluorescence spectroscopy, chemists at the University
of Illinois, Urbana-Champaign, have made the first direct
measurements of energy dissipation and reaction rates inside an
isolated bubble in water driven to violent size oscillations by highintensity ultrasound. The results of postdoc Yuri T. Didenko and
chemistry professor Kenneth S. Suslick suggest that a cavitating
bubble could be thought of as a high-temperature, high-pressure
microreactor and have important implications for future work on
ultrasound-driven chemistry.
However, Didenko and Suslick conclude that the endothermic
reactions limit the temperatures that can be achieved inside a
cavitating bubble. The maximum temperature for single-bubble
cavitation is generally expected to be below 20,000 K--far less than
the 1 million K needed for the tabletop "bubble fusion" in a cavitating
deuteroacetone system that was reported in a controversial Science
paper earlier this year.
SONOCHEMISTRY A titanium rod vibrating at 20 kHz gives rise
to a cloud of cavitating bubbles that emit flashes of light and
house an array of chemical reactions.
STERIC, SOLVENT EFFECTS UNCOUPLED
[Science, 295, 2245 (2002)]
John I. Brauman (Stanford University)
At Stanford University, chemistry professor John I. Brauman and
coworkers have conducted studies that untangled the two
factors by measuring intrinsic steric barriers in the gas phase,
where solvation does not come into play. They conclude that
the rise in potential energy barriers caused by changes in
substituent size is about equally due to solvation effects as to
steric effects.
Brauman used Fourier transform/ion cyclotron resonance mass
spectrometry to measure steric effects. By following the gasphase reactions of chloride ions (37Cl–) with
methylchloroacetonitrile and with tert-butylchloroacetonitrile,
producing 35Cl–, they find that the steric effect of replacing the
methyl group with tert-butyl is 1.6 kcal/mol. That value is less
than that of the barrier for comparable reactions in solution-Cl– exchange with ethyl chloride and neopentyl chloride--which
is about 5 to 7 kcal/mol.
BUZZ OFF In the gas phase, the reaction
when R = tert-butyl is slower than when R =
methyl because of steric effects only. In
solution, bulky substituents hinder the
approach not only of the nucleophile but
also of solvent molecules.
SIMPLEST REACTION IS NOT SO SIMPLE
[Nature, 416, 67 (2002)]
Stuart C. Althorpe (the University of Durham, England)
Richard N. Zare (Stanford University)
In a new collaborative study by theoreticians and experimentalists,
both theory and experiment confirm that at certain collision
energies and a specific product rotational and vibrational state,
most of the HD product molecules are propelled (or "scattered")
forward after they form, in the same direction as the incoming H
atoms, and a lesser number of the HD product molecules are
backscattered.
The theoretical simulation predicts an approximately 25femtosecond time delay between formation of backscattered and
forward-scattered HD products in the reaction. The delay
demonstrates that there are two different reaction mechanisms
involved: a direct, billiard-ball type of collision resulting in
backscattering, and a "resonant" mechanism in which a transient
collision complex is formed and the product is then forward
scattered.
GOOD MATCH Excellent agreement
between experiment (dots) and theory
(solid curve) is shown in this plot of the
amount of HD produced in the hydrogenexchange reaction at a collision energy of
1.64 eV.
SCATTER In theoretical
simulation of the hydrogenexchange reaction, green
arrows in the first frame show
the direction of movement of H
and D2 before the reaction. The
reaction occurs within the red
circle, and the HD products are
shown in blue. One cloud is
formed earlier and is
backscattered (to the right), and
a second cloud forms about 25
femtoseconds later and is
forward scattered.
Dipeptide yields to laser control
[Science, 296, 2369 (2002)]
Timothy S. Zwier(Purdue University)
Chemists have used a laser to control the isomerization of a
relatively large molecule. Chemistry professor Timothy S. Zwier
and colleagues at Purdue University selectively excited the stretch
vibrational N–H modes in single conformations of N-acetyltryptophan methyl amide with infrared wavelengths. This propels
the molecule into alternate conformations.
This approach is similar to that of chemists who use lasers to
selectively break bonds. However, those processes are typically
attempted with small molecules, as it's believed that the input
energy would distribute itself throughout a larger molecule's many
bonds and merely heat it. Though Zwier and coworkers focus on
conformational changes rather than bond breaking, their result is
still surprising, they say. The molecules are collisionally cooled
immediately after isomerization in order to be detected; the group
speculates that this cooling, among other things, might help limit
energy redistribution.
First coherent extreme ultraviolet laser fits on a benchtop
[Science, 297, 376 (2002)]
Margaret M. Murnane (the University of Colorado and
the National Institute of Standards & Technology, Boulder)
A team of researchers at the National Institute of Standards &
Technology in Boulder, Colo.; Sofia University in Bulgaria;
and other institutions have created what they say is the first
spatially coherent laserlike beam in the extreme ultraviolet
(EUV) range.
And not only is the radiation produced in short bursts only
femtoseconds long, but the unit is also only 3 feet by 12 feet,
making it practical for the lab.
The group created holograms and diffraction patterns with the
light source, which should also be useful for high-spatialresolution nanoimaging and metrology.
EXTREME The first spatially coherent, tabletop extreme
ultraviolet beam produces striking diffraction patterns.
Attosecond laser methods
[Nature, 419, 803 (2002)]
Markus Drescher (the University of Bielefeld, Germany)
Ferenc Krausz (Vienna University of Technology, Austria)
Using newly developed attosecond laser methods, Markus Drescher
of the University of Bielefeld, Germany; Ferenc Krausz of Vienna
University of Technology; and coworkers probed inner-shell
electronic rearrangements in atoms in real time.
Krausz tells that these inner-shell processes could not be probed at
all in the time domain previously because neither the duration nor
the photon energy of femtosecond laser pulses was satisfactory.
LIGHT-HARVESTING ANTENNA MODEL
[J. Am. Chem. Soc., 125, 2372 (2003)]
Yoshiaki Kobuke(the Nara Institute of Science & Technology)
A supramolecular ring of
porphyrin dimers synthesized
in Japan mimics a circular
assembly of light-harvesting
bacteriochlorophyll molecules
in photosynthetic bacteria.
Professor of materials
science Yoshiaki Kobuke
prepared the porphyrin
macroring by self-assembly
of six phenylene-bridged
porphyrin dimers with a gable
structure
NMR method yields high-resolution spectra of disordered solids
[J. Am. Chem. Soc., 125, 4376 (2003)]
Lyndon Emsley (the Ecole Normale Supérieure, Lyon, France)
Alexander Pines (the University of California, Berkeley)
Nuclear magnetic resonance
(NMR) spectra of disordered,
noncrystalline solids such as
glasses, polymers, and
biological materials typically
have peaks that are broad,
relatively featureless, and of
limited use for materials
characterization. Now, using a
two-dimensional NMR
correlation approach, a team
has obtained high-resolution
NMR spectra of disordered
solids.
SPECTRAL WEIGHT LOSS Conventional 1-D 31P
spectrum (top) of a disordered solid amine has
broadened peaks. These peaks are narrowed
considerably in the correlation plot (bottom)
derived from a 2-D 31P spectrum of the same
material
New computational method leads to better NMR structures faster
[J. Am. Chem. Soc., 125, 1385 (2003)]
Thomas Szyperski and postdoc Seho Kim
(the State University of New York, Buffalo)
A new technique uses mathematical calculations to increase the speed
and precision of multidimensional nuclear magnetic resonance (NMR)
spectroscopy. G-matrix Fourier transform (GFT) NMR could help make
NMR more competitive with X-ray crystallography for biomolecular
structure determinations
NMR solution structures are obtained with multidimensional NMR, in
which measurement time increases exponentially with number of
dimensions. GFT NMR will potentially improve data collection speed by
orders of magnitude. In the JACS study, "the gain was a factor of 250,
while we increased the precision of the frequency measurements threeto fourfold," Szyperski notes. The technique uses linear equations (Gmatrices) and Fourier transforms to calculate and correlate resonance
frequencies from data obtained in large numbers of low-dimensional
NMR experiments.
Details of O2 dance in surface-diffusion mechanism
[Science, 299, 377 (2003)]
Flemming Besenbacher (University of Aarhus, Denmark)
University of Aarhus physics professor
Flemming Besenbacher and research
associates Renald Schaub and Erik
Wahlström and their coworkers have
followed individual diffusion events on a
TiO2 crystal surface using a rapid and
high-resolution scanning tunneling
microscopy (STM) method. In the
presence of gaseous oxygen, the group
finds, surface atoms undergo a type of
rearrangement that "heals" the defects
and creates new ones elsewhere--in
effect causing oxygen vacancies to
diffuse across the surface along specific
crystal directions
ON THE MOVE
Time-lapse STM
images (top and
center) show that
oxygen vacancies
(circled) are mobile.
The extent of the
diffusion is seen in
a difference image
(top minus middle,
shown at bottom).
Original vacancy
locations appear
bright. Final
locations appear
dark
SWITCHABLE SURFACE
[Science, 299, 371 (2003)]
Robert S. Langer (MIT)
The properties of a surface can be controlled by changing the conformation of
molecules in a self-assembled monolayer (SAM) on that surface.
The researchers give the molecules enough room to bend by forming a
monolayer with large globular end groups—similar to mushroom caps on thin
stalks. Once the SAM forms, the “caps” are lopped off, leaving a free carboxylate
end group. Applying an electrical potential to the underlying gold substrate
attracts the carboxylate to the surface, bending the SAM’s alkane chains and
exposing them to the surroundings.
물리화학 관련 타분야 연구
-Materials : so so
-Supramolecular chemistry : so so
-Nanotube :so so
-Nanoscience : up
-Molecular electronics : hot
-Bioscience : up
MATERIALS
[Science, 296, 1106 (2002)]
Seth R. Marder and Joseph W. Perry of the University of Arizona,
Christopher K. Ober of Cornell University, and coworkers
Sensitive two-photon dye promises to advance 3-D device fabrication
A two-photon dye that may permit device microfabrication to be carried
out in three dimensions and with greater efficiency, reliability, and
speed than previously possible was designed, synthesized, and
demonstrated by Seth R. Marder and Joseph W. Perry of the University
of Arizona, Christopher K. Ober of Cornell University, and coworkers.
Absorption of two photons by the dye leads to the production of acid,
which can be used to activate microfabrication reactions.
HOLLOWED OUT In positive-tone 3-D microfabrication,
achieved using a two-photon-absorbing dye, a laser
beam is used to "write" the blue-and-red microstructure
within a polymer film, and then the entire microstructure
is dissolved away. The blue volumes become open,
rectangular cavities with a sloped sidewall that are
connected by 12 buried channels (here shown as red
rods) lying 10 mm below the surface.
SUPRAMOLECULAR CHEMISTRY
[Nature, 418, 399 (2002)].
Steven C. Zimmerman and Kenneth S. Suslick at the
University of Illinois, Urbana-Champaign
Dendrimers built around template molecule offer shape selectivity
Dendrimers are large, roughly spherical macromolecules built from
smaller precursors through repeated branching reactions around a
single central molecule. The Illinois chemists construct their
dendrimers around a central porphyrin ring. The ring is held at the
center of the growing dendrimer by eight ester linkages that can
later be cleaved to produce a porphyrin-sized cavity at the center of
the dendrimer. The dendrimer is constructed so that its outer
surface is covered with alkene groups, which can be cross-linked to
one another using a Grubbs olefin metathesis catalyst. The result is
a large, stable, but soluble macromolecule that contains a single
binding site at its center
IN A BIND Dendrimer grown
around target porphyrin (blue),
when cross-linked, forms shapespecific cavity that selectively
binds new porphryins.
[Science, 295, 469 (2002)] [Science, 300, 1127 (2003)]
Omar M. Yaghi of the University of Michigan, Ann Arbor
Porous metal-organic frameworks offer
useful properties for gas storage
A new family of highly crystalline, porous
materials in which the size and chemical
functionality of the pores can be tailored
systematically shows promise for gasstorage applications. Yaghi and his
coworkers call the materials IRMOFs-which stands for isoreticular metal-organic
frameworks. They consist of cubical 3-D
networks of zinc-oxygen clusters connected
by molecular struts such as 1,4benzenedicarboxylate. By choosing
connectors based on longer molecules
such as terphenyl, the chemists have
shown that they can expand the pore size
in increments from 3.8 to 28.8 Å.
BIG EMPTINESS In one of the highly
porous metal-organic frameworks
synthesized by Yaghi's group, 91% of
the crystal volume is calculated to be
open space. The large orange spheres
are included to emphasize the size of
the cavities
NANOTUBES
[J. Am. Chem. Soc., 124, 760 (2002)].
Maurizio Prato and colleagues at the University of Trieste, in Italy;
the University of Notre Dame; and the University of ErlangenNürnberg, in Germany
Attaching large organic groups is
key to unclumping nanotubes
The group reports that a
method they've developed for
attaching organic groups to
nanotubes makes the tubes
soluble to the tune of 50 mg
per mL--much higher than
previously reported. In addition,
the researchers say, the tubes
remain in solution in water and
a number of organic solvents
indefinitely
FUNCTIONALIZED Carbon nanotubes
with organic appendages are highly
soluble
[Nature, 415, 599 (2002)].
Yoshio Bando at National Institute for Materials Science, Ibaraki, Japan
Latest nanodevice: Gallium-filled nanotube thermometer
Carbon nanotubes filled with liquid gallium can serve as tiny
thermometers for measuring temperature in microenvironments.
Professor Yoshio Bando and postdoctoral researcher Yihua Gao were
exploring new ways to make gallium nitride nanowires when they
found they had created something quite different: multiple-walled
carbon nanotubes filled with gallium. The researchers checked the
thermal expansion characteristics of gallium--which exists as a liquid
over a wider temperature range (30 to 2,403 °C) than most metals--by
heating the filled nanotubes in a transmission electron microscope
(TEM). They found that the volume of nanocolumns of gallium varies
linearly with temperature between 50 and 500 °C. The images show
how the height of gallium in a nanotube changes with temperature: At
left, the temperature is 58 °C; at right, 490 °C. (The scale bar at the
lower left equals 75 nm.) Bando and Gao think the nanothermometers
could have practical applications, such as estimating the thermal
effect of electron beams on a TEM sample.
Nanoscience
[Science, 295, 1702 (2002)
Northwestern's Chad A. Mirkin and the University of Chicago's
Milan Mrksich and coworker
Dip-pen nanolithography may lead to useful, miniaturized screening tools
By using the technique known as dippen nanolithography, chemists at
Northwestern University and the
University of Chicago have made
protein arrays with feature sizes
ranging from 100 to 350 nm. The
advance could lead to protein or
nucleic acid arrays--useful screening
tools--that are 1 million to 10 million
times denser than those currently
available.
NANOGRID Proteins can be adsorbed to a surface in a
variety of configurations, including dots and grid lines,
as shown in this topographic image of a lysozyme
nanoarray. The features' sizes were intentionally
varied, and there is no evidence of nonspecific protein
adsorption.
[Science, 296, 1836 (2002)].
Chad A. Mirkin at Northwestern University
Writing directly with DNA
Dip-pen nanolithography, in which an atomic force microscope
(AFM) tip is used to chemically "write" on a surface, can now be
used to directly pattern DNA on a variety of surfaces, including both
metals and oxides, according to researchers at Northwestern
University .The team, led by chemistry professor Chad A. Mirkin,
finds that by coating an AFM tip with a charged molecule, DNA will
coat the tip and can be efficiently transferred. In addition, the DNA
itself is modified with hexanethiol and sticks to the surface to form
stable nanostructures. The team can precisely control the feature
sizes generated with dip-pen nanolithography by varying the
humidity and the contact time between the surface and the tip,
Mirkin says. By attaching nanoparticles or other building blocks to
the DNA, the specific recognition properties of the DNA can be
used to direct the assembly of structures. In the future, dip-pen
nanolithography could be used to build ultra-high-density gene
chips, nanoscale circuits, photonic crystals, or catalysts.
[Science, 296, 1103 (2002)].
Hermann E. Gaub at the University of Munich
MOLECULAR MACHINE
Powered only by a burst of light, the
contraction of a single molecule has
enough muscle to bend the cantilever of
an atomic force microscope (AFM),
scientists in Germany report. This is the
first demonstration of an artificial, singlemolecule machine that converts light
energy to physical work.
Taking advantage of the azobenzene
polymer's well-known ability to switch
between its stretched-out trans and
contracted cis forms when exposed to
light, Hermann E. Gaub, professor of
biophysics at the University of Munich, and
colleagues show that a load attached to
the molecule can be moved as the
molecule shortens
FORCEFUL Exposing an
azobenzene polymer attached to a
cantilever to 420-nm light (left) puts
the polymer in its lengthened trans
state. Exposure to 365-nm light
causes the backbone to contract,
pulling on the cantilever (right).
[Nat. Mat., published online May 25]
Paul Alivisatos and his coworkers at the University of California, Berkeley,
and Lawrence Berkeley National Laboratory
Four-armed nanocrystals could find use in
solar cells or as polymer additives
A few years ago, A. Paul Alivisatos and his
coworkers noticed that some nanocrystals
would unexpectedly form branched
structures. Now, the researchers can
make those branched structures
controllably and reproducibly. Using the
material CdTe, they can make four-armed
structures known as tetrapods, which they
say could be used in solar cells or as
additives in polymers
BRANCHED The cubic and hexagonal
structures of the CdTe tetrapod share a
facet. The exploded view of the arm
shows the cubic (111) facet on the
crystal core and the hexagonal (0001¯)
facet at the end of the arm. Changing
the temperature switches which facet is
preferred. Cadmium = yellow; tellurium
= blue.
MOLECULAR ELECTRONICS
[Nature, 415, 617 (2002)]Charles M. Lieber at Harvard University
[Nano Lett., 2, 87 (2002)] Lars Samuelson of Lund University, Sweden
[Nano Lett., 2, 83 (2002)] Peidong Yang of UC Berkeley
NANOWIRES COME IN TWO TONES
Harvard University chemists prepared nanowires of gallium arsenide
and gallium phosphide containing up to 21 distinct segments--a
nanoscale bar code. The research group, which includes chemistry
professor Charles M. Lieber, graduate student Mark S. Gudiksen,
postdoctoral associate Lincoln J. Lauhon, and coworkers, also
prepared silicon nanowires and indium phosphide nanowires in
which some sections of the wires were doped with negative charge
carriers (n-doped) and other sections were doped with positive
charge carriers (p-doped)
At Lund University in Sweden, scientists grew indium
arsenide nanowires interspersed with segments of
indium phosphide. Electron microscopy analysis
shows that the interfaces between segments are
characterized by an atomic-scale abruptness, and
transport measurements reveal ideal electronic
properties at the interfaces.
Meanwhile, at the University of California, Berkeley,
Peidong Yang have synthesized nanowires consisting
of silicon and silicon-germanium.
All three research groups make use of synthesis
procedures in which nanoclusters of metal--for
example, gold--catalyze nanowire growth by serving
as nucleation points in a vapor-liquid-solid growth
process. The UC Berkeley team grows its two-tone
nanowires in a process that combines pulsed-laser
ablation and chemical vapor deposition (CVD).
Basically, Yang and coworkers use silicon-containing
gases to grow silicon nanowires in a CVD apparatus
and periodically add germanium to the gas mixture by
vaporizing a solid germanium target with a pulsed
laser. The germanium supply is switched on and off
with each laser pulse.
SANDWICH Microscopy
methods reveal abrupt
interfaces in an InAs/InP
(green and orange,
respectively) nanowire grown
at Lund University
[Nature, 417, 722 and 725 (2002)]
Hongkun Park at Harvard University and Jeffrey R. Long of the
University of California, Berkeley
Paul L. McEuen at Cornell University
Single molecules of metal complexes
govern nanoelectronic properties
Two research groups independently
report taking another key step toward
creating tomorrow’s molecular
electronic devices. The scientists
fabricated and tested transistors in
which one molecule of a transitionmetal organic complex bridges the
IN THE GAP Single-molecule electronic
nanometer-scale gap between the
devices are based upon the properties of a
devices’ electrodes and dictates their lone molecule trapped in a nanosized gap
between electrodes. A Harvard-Berkeley
electronic properties
team prepared devices based on a complex
with two vanadium atoms (top), while a
Cornell team studied cobalt-terpyridinyl
complexes (bottom)
[Appl. Phys. Lett., 81, 1851 (2002)]
Chang-Beom Eom of the University of Wisconsin, Madison
[Nat. Mater., 1, 35 (2002)]
Xiaoxing Xi at Pennsylvania State University
Groups led by Chang-Beom Eom of the University of Wisconsin,
Madison, and Xiaoxing Xi at Pennsylvania State University,
independently developed oriented thin films of magnesium
diboride that are potentially useful for making superconducting
devices. These would require less cooling than current niobiumbased superconductor circuits.
[Science, 300, 783 (2003)]. [Nano Lett., published online June 25]
Phaedon Avouris, Marcus Freitag, Richard Martel, and coworkers
at IBM's T. J. Watson Research Center, Yorktown Heights, N.Y
NANOSIZED LITE BRITE
A nanoscale light source based
on a single carbon nanotube has
been demonstrated by
researchers at IBM. The
electrically driven emitter, which
exploits unique semiconducting
properties of carbon nanotubes,
may enable development of
miniature photonic and
optoelectronic devices and other
applications that depend on fine
control of light.
MEET YOU HALFWAY By injecting positive
and negative charge carriers (holes and
electrons) simultaneously at opposite ends
of a carbon nanotube channel in a specially
configured field-effect transistor, IBM
researchers cause the particles to interact
near the center of the tube. The
recombination process produces polarized
infrared light.
SINGLE-NANOTUBE PHOTODETECTOR
By developing the means to control light and electrical current on ever
finer scales, scientists aim to produce tiny and sophisticated
optoelectronic devices. Working toward that end, a research team has
devised a procedure for measuring electrical current generated by
shining light on a single carbon nanotube.
Shining infrared light on the nanotube causes excitations that lead to
electron-hole pairs, the team reports. By applying voltages to the
device while irradiating it, the group was able to separate the charge
carriers and investigate the dependence of electrical current on the
frequency of the light and applied voltage. The measurements show
that the device can serve as a nanoscale photodetector.
SPARKLER Shining light on
a carbon nanotube that's
wired into a transistor
generates a measurable
current, making the device a
nanoscale photodetector
[Science, published online March 13]
James R. Heath of California Institute of Technology and
Pierre M. Petroff, at the UC, Santa Barbara
HIGHEST DENSITY NANOWIRE ARRAYS
Heath and his coworkers have
now devised a general
method for producing
ultrahigh-density arrays of
aligned nanowires and
nanowire circuits.
These arrays--some
containing hundreds of
aligned nanowires 2 to 3 mm
long--are dramatically denser
than previous arrays. The
highest density pattern they
report consists of 20 wires
that are 8 nm across and 8
nm apart.
IT'S A SNAP A method for making ultrahigh-density
nanowire arrays starts with a GaAs/AlGaAs
superlattice. The AlGaAs layers are selectively etched
so that they are recessed. Metal is deposited onto the
protruding GaAs edges, forming nanowires. When the
superlattice is used as a stamp, the nanowires are
imprinted onto an adhesive layer coating a silicon
wafer. The superlattice is then etched away.
Bioscience
[Science, 295, 1520 (2002)]
Dorothee Kern of Brandeis University and coworkers
NMR :ENZYME ACTIVITY- A MOVING EXPERIENCE
The rapid motions of an
enzyme's amino acid residues
when it's in its catalytic transition
state have been captured for the
first time. Dorothee Kern of
Brandeis University and coworkers used nuclear magnetic
resonance to detect backbone
motion in cyclophilin A and found
movement in one residue to be
strongly correlated with the
catalytic mechanism
MOTION PICTURE Motion of cyclophilin A's
arginine-55 residue (black) correlates strongly
with catalytic action: the cis-trans conversion of
the enzyme's substrate (light and dark green).
Other numbered residues (red) are among nine
whose motions are associated with substrate
binding and unbinding.
[Nature, 418, 207 (2002)]
Kurt Wüthrich of the Swiss Federal Institute of Technology,
Arthur L. Horwich of Yale University
HUGE PROTEIN ANALYZED BY NMR
Now researchers have
made nearly an order of
magnitude leap in the
mass range of proteins
amenable to NMR
analysis by analyzing
the GroEL-GroES
chaperone system, a
huge 900-kDa protein
complex. Chaperones
help proteins fold into
their native states
CHAPERONE In the
GroEL-GroES
complex (shown
here in surface and
cross-sectional
representations),
GroES (white) and
both halves of
GroEL (multicolored
and gold) are each
made up of seven
identical subunits
(highlighted in
multicolored
segment of GroEL).
[Science, 295, 1503 (2002)]
Chad A. Mirkin and coworkers at Northwestern
DNA nanoparticle sensor
Chad A. Mirkin and coworkers at
Northwestern developed a new type
of DNA detection technique that is
10 times more sensitive and 100,000
times more selective than previous
oligonucleotide detection methods.
Selective binding of DNA-derivatized
gold nanoparticles to target DNA
strands causes the nanoparticles to
line up between electrodes,
generating an electrical signal. The
technique could lead to a handheld
device for point-of-care
biodetection.
BRIDGED Complementary DNA
strands immobilize gold
nanoparticles between electrodes.
[Science, 297, 1536 (2002)]
Chad A. Mirkin and coworkers at Northwestern
SERS-nanoparticle DNA detection
Mirkin's group developed another
technique in which gold
nanoparticle probes labeled with
oligonucleotides and Raman-active
dyes are used for DNA and RNA
detection. The surface-enhanced
Raman scattering technique-which has femtomolar detection
limits and can detect multiple
pathogens simultaneously in one
solution--is a potential alternative
to molecular fluorescence-based
biodetection.
[Science, 300, 1434 (2003)]
Watt W. Webb at Cornell University
Studies show that nanoparticles have potential biological applications
Watt W. Webb and his coworkers
injected amphiphilic-coated
quantum dots made of CdSeZnS intravenously into mice.
Using multiphoton microscopy,
they obtained images of blood
vessels through skin and fat-tissues that are challenging for
imaging because they scatter
and absorb radiation. They could
easily measure blood flow and
detect heart rate directly through
the skin.
VASCULATURE
Quantum dots and
multiphoton
microscopy can be
combined to obtain
images such as these
of the surface of
adipose tissue
surrounding the ovary.
In the top image, the
blue is fluorescence
from the tissue itself,
and the yellow is
quantum dots in blood.
The bottom image
shows a projection of
capillary structure
through 250 µm of
adipose tissue. Scale =
20 µm.
The combination of quantum dots and multiphoton microscopy
(in which multiple lower energy photons are used to excite a
higher energy electron transition) lessens potential tissue damage
in two ways. First, the quantum dots require less excitation
intensity because they have a large excitation cross-section.
Second, the multiphoton microscopy limits any tissue damage to
the focal volume and avoids scattering and absorption problems.
IN A BARREL The chaperone protein GroEL forms an inclusion complex with a CdS
nanoparticle. In the presence of ATP, Mg2+, and K+, the protein changes conformation and
releases the nanoparticle, which can coagulate with other nanoparticles
[Proc. Natl. Acad. Sci. USA, published online July 23]
Charles L. Brooks III, at Scripps Research Institute
Modeling methods provide insights in ribosome dynamics of motion
A team of researchers led by Charles L. Brooks III has used a
theoretical method known as elastic-network normal-mode analysis
to shed light on what happens during ribosome motions and how
those motions are relevant for protein synthesis.
Brooks collaborated with
Joachim Frank, a
Howard Hughes Medical
Institute investigator at
the State University of
New York, Albany, who
studies the structure of
ribosomes using cryoEM.
DYNAMIC Structural rearrangements of the 70S ribosome
are obtained using computational methods. The 30S and
50S subunits are shown in yellow and blue, respectively.
The center structure shows the equilibrium conformation
of the ribosome. The left and right structures show the
ribosome following the rearrangements indicated by the
arrows. The red circle and arrow in the right structure
indicate the axis of rotation
[Science, 299, 2067 (2003)].
Karen N. Allen of Boston University School of Medicine, and
Debra Dunaway-Mariano of the University of New Mexico
X-ray study may have trapped transition state of enzymecatalyzed reaction
Crystallography has been used to probe the structures of enzymes bound
either to their substrate or product. But more transient species along the
reaction pathway--particularly the high-energy transition state, which sticks
around for only a few tenths of a picosecond--have proven intractable to
structural analysis. Consequently, enzymologists often resort to stopping the
reaction in midcatalysis by modifying or inhibiting the enzyme. Yet studying
the reactions of real substrates with active enzymes remains chemists'
ultimate goal.
The new phosphoglucomutase structure does just that. Determined by
associate professor Karen N. Allen and graduate student Sushmita D. Lahiri,
both of Boston University School of Medicine, and professor Debra
Dunaway-Mariano and graduate student Guofeng Zhang, both of the
University of New Mexico, Albuquerque, the structure catches this enzyme in
the act of transferring a phosphoryl group to glucose-6-phosphate, one of
its natural substrates. The pentacovalent phosphorus intermediate observed
shows that phosphoryl transfer goes by an SN2-like associative mechanism.
FREEZE-FRAME The trigonal bipy-ramidal oxyphosphorane observed in the
structure of phosphoglucomutase with glucose-6-phosphate is thought to be the
first-ever transition state directly observed by crystallography (phosphorus, purple;
oxygen, red; carbon, yellow)
Breakthrough of the year 2002
Science 298, 2296 (2002) Dec.20 issue
1. RNA 연구
2.Nutrinos 연구
3. Genome연구 : 쌀, 말라리아
4. Cosmic Twist
5. Attosecond move
6. A taste for temperature
7. Frozen image : cryoelectron
tomagraphy(cryo-ET)
8. Clear sky ahead : 천문대
Adaptive Optics(AO)
9. Retina receptors :
circadian clock - melanopsin
10. Evolutionary headlines :
고고학
HOT
-Complex system
-Dynamics
-New Method
-Variety