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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