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  • 1
    Publication Date: 2006-01-10
    Description: We present two quantum calculations of the infrared spectrum of protonated methane (CH5+) using full-dimensional, ab initio-based potential energy and dipole moment surfaces. The calculated spectra compare well with a low-resolution experimental spectrum except below 1000 cm(-1), where the experimental spectrum shows no absorption. The present calculations find substantial absorption features below 1000 cm(-1), in qualitative agreement with earlier classical calculations of the spectrum. The major spectral bands are analyzed in terms of the molecular motions. Of particular interest is an intense feature at 200 cm(-1), which is due to an isomerization mode that connects two equivalent minima. Very recent high-resolution jet-cooled spectra in the CH stretch region (2825 to 3050 cm(-1)) are also reported, and assignments of the band origins are made, based on the present quantum calculations.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Huang, Xinchuan -- McCoy, Anne B -- Bowman, Joel M -- Johnson, Lindsay M -- Savage, Chandra -- Dong, Feng -- Nesbitt, David J -- New York, N.Y. -- Science. 2006 Jan 6;311(5757):60-3.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemistry and Cherry L. Emerson Center for Scientific Computing, Emory University, Atlanta, GA 30322, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/16400143" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 2015-05-06
    Description: Knowledge of the structure and dynamics of RNA molecules is critical to understanding their many biological functions. Furthermore, synthetic RNAs have applications as therapeutics and molecular sensors. Both research and technological applications of RNA would be dramatically enhanced by methods that enable incorporation of modified or labelled nucleotides into specifically designated positions or regions of RNA. However, the synthesis of tens of milligrams of such RNAs using existing methods has been impossible. Here we develop a hybrid solid-liquid phase transcription method and automated robotic platform for the synthesis of RNAs with position-selective labelling. We demonstrate its use by successfully preparing various isotope- or fluorescently labelled versions of the 71-nucleotide aptamer domain of an adenine riboswitch for nuclear magnetic resonance spectroscopy or single-molecule Forster resonance energy transfer, respectively. Those RNAs include molecules that were selectively isotope-labelled in specific loops, linkers, a helix, several discrete positions, or a single internal position, as well as RNA molecules that were fluorescently labelled in and near kissing loops. These selectively labelled RNAs have the same fold as those transcribed using conventional methods, but they greatly simplify the interpretation of NMR spectra. The single-position isotope- and fluorescently labelled RNA samples reveal multiple conformational states of the adenine riboswitch. Lastly, we describe a robotic platform and the operation that automates this technology. Our selective labelling method may be useful for studying RNA structure and dynamics and for making RNA sensors for a variety of applications including cell-biological studies, substance detection, and disease diagnostics.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Liu, Yu -- Holmstrom, Erik -- Zhang, Jinwei -- Yu, Ping -- Wang, Jinbu -- Dyba, Marzena A -- Chen, De -- Ying, Jinfa -- Lockett, Stephen -- Nesbitt, David J -- Ferre-D'Amare, Adrian R -- Sousa, Rui -- Stagno, Jason R -- Wang, Yun-Xing -- HHSN261200800001E/PHS HHS/ -- R01 GM052522/GM/NIGMS NIH HHS/ -- T32 GM-065103/GM/NIGMS NIH HHS/ -- Intramural NIH HHS/ -- England -- Nature. 2015 Jun 18;522(7556):368-72. doi: 10.1038/nature14352. Epub 2015 May 4.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Protein-Nucleic Acid Interaction Section, Structural Biophysics Laboratory, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Frederick, Maryland 21702, USA. ; JILA, National Institute of Standards and Technology and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, USA. ; Biochemistry and Biophysics Center, National Heart, Lung and Blood Institute, Bethesda, Maryland 20892, USA. ; Structural Biophysics Laboratory, Basic Science Program, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, Maryland 21702, USA. ; Optical Microscopy and Analysis Laboratory, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, Maryland 21702, USA. ; Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA. ; Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25938715" target="_blank"〉PubMed〈/a〉
    Keywords: Adenine/analysis/chemistry/metabolism ; Aptamers, Nucleotide/analysis/chemistry/metabolism ; Automation/methods ; Base Sequence ; Biosensing Techniques ; DNA/genetics/metabolism ; *Fluorescence ; Fluorescence Resonance Energy Transfer ; In Vitro Techniques ; Isotope Labeling/*methods ; Magnetic Resonance Spectroscopy ; Molecular Sequence Data ; Nucleic Acid Conformation ; RNA/analysis/*chemical synthesis/*chemistry/genetics ; Riboswitch/genetics ; Robotics ; Templates, Genetic ; Transcription, Genetic
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 8009-8018 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The perturbed (v,b,K,n)=(1210),(1113)←(0000) band of ArHF is observed in a tunable laser/slit supersonic expansion spectrometer. The (1210) level correlates with j=2 rotation of the HF within the complex and therefore provides a test of high-order terms in a Legendre expansion of the intermolecular potential. Transitions to (1113) are observed due to intensity sharing with (1210), induced by a strong homogeneous (J-independent) perturbation that is analyzed quantitatively. The (1113) level has three quanta of Van der Waals stretch and thus probes the radial dependence of the potential close to the dissociation limit. The vibrational and rotational assignment is made possible by predictions based on the new H6(4,3,2) intermolecular potential of Hutson [J. Chem. Phys. 96, 6752 (1992)], which agree nearly quantitatively with experiment.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4418-4419 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The interconversion tunneling frequencies for (HCl)2 and (DCl)2 are obtained from near-infrared absorption spectra of the H(D)Cl stretching transitions, to spectroscopic precision for the mixed 35Cl–37Cl dimers. A phenomenological model of the interconversion process explains several experimental observations, and provides good estimates of the splittings expected for the 35Cl–35Cl and 37Cl–37Cl species.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: 294 transitions were measured by velocity modulation spectroscopy using a difference frequency laser system with a D2/O2 discharge and assigned to the ν3 (antisymmetric stretch) band of D3O+. A simultaneous analysis of this data with the ν2 band spectra reported by Sears, et al. [J. Chem. Phys. 83, 2676 (1985)] yielded a refined set of parameters for both the ground and the excited states of both bands. The ν3 bandcenters are 2629.6512(39) and 2624.2376(47) cm−1 for the s–s and a–a inversion components, respectively.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 722-731 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Direct absorption tunable difference frequency IR spectroscopy in a slit jet supersonic expansion has been used to observe complexes of Ne with HF for the first time. Spectra of both the weak HF stretch fundamental (1000)←(0000) and the 10–20 fold more intense bend and stretch combination band (111e,f0)←(0000) transitions are observed, and illustrate several interesting dynamical features. The large ratio of combination band to fundamental intensity is evidence for a highly isotropic potential with respect to HF rotation. The HF bend vibration is thus better thought of as nearly free internal rotor motion with a nearly good space fixed quantum number, jHF =1. Weak anisotropy in the potential permits the jHF=1 (Πebend) levels to relax intramolecularly to jHF =0 (Σ) levels, leading to predissociative line broadening in the sub-Doppler slit jet spectra. This observed dissociation of NeHF with 44 cm−1 of internal excitation provides a rigorous upper limit to the binding energy. The Πfbend levels, on the other hand, have no lower energy internal rotor states of the correct parity to relax into, and thus the (111f0) ←(0000) spectra exhibit linewidths limited by the apparatus resolution. The internal relaxation of the jHF=1 (Πebend) levels results from Coriolis mixing with the Σbend states (1200) by overall rotation of the NeHF complex, and thus the lifetimes depend dramatically on J. The J-dependent predissociation rates observed are in remarkably quantitative agreement with quantum scattering calculations on the CEPA ab initio surface of ONeil and co-workers.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 711-721 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have used ab initio methods to characterize the Ne–HF van der Waals complex. The interaction energy was determined using size consistent, correlated CEPA wave functions expanded in a Gaussian basis chosen to represent both intraatomic effects and the low order multipole moments and polarizabilities of Ne and HF. The calculated well depths are −65 cm−1 for linear Ne–HF and −39 cm−1 for linear Ne–FH, with an intervening saddle point at −27 cm−1. The induction contribution to the energy is significantly greater for Ne–HF than for Ne–FH, but dispersion remains the dominant attraction over the region of interest. Converged variational and close-coupling calculations using the ab initio potential surface reveal three bound levels of the Ne–HF stretch mode, and several metastable levels correlating asymptotically with rotationally excited HF( j=1). Though nearly degenerate, the lifetimes of the two metastable Π (body frame Λ=±1) bending levels differ markedly because of different rotational coupling strengths to the Σ (body frame Λ=0) bending state, which undergoes rapid rotational predissociation. From the calculated line positions, widths, and intensities we have synthesized far infrared and infrared spectra of Ne–HF and Ne–DF.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 6935-6946 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The absolute quantum yields (Φ) for OH production from 193 and 248 nm photolysis of HNO3 and H2O2 are measured at room temperature using flash kinetic spectroscopy in a flow tube. The OH radicals are produced by excimer laser photolysis and probed via direct absorption of high resolution, tunable IR laser light. The resulting quantum yields are found to be ΦHNO3193=0.47±0.06, ΦH2O2193=1.22±0.13, ΦHNO3248=0.75 ±0.10, and ΦH2O2248= 1.58±0.23. These results indicate quantum yields for both precursors at both wavelengths which are less than the maximum possible values of 1 for HNO3 and 2 for H2O2. The present measurements are discussed in light of contrasting results suggested from other work.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 42-48 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A novel, simple, and inexpensive calibration scheme for a continuous-wave difference frequency spectrometer is presented, based on the stabilization of an open transfer cavity by locking onto the output of a polarization stabilized HeNe laser. High frequency, acoustic fluctuations of the transfer cavity length are compensated with a piezoelectric transducer mounted mirror, while long term drift in cavity length is controlled by thermal feedback. A single mode Ar+ laser, used with a single mode ring dye laser in the difference frequency generation of 2–4 μm light, is then locked onto a suitable fringe of this stable cavity, achieving a very small long term drift and furthermore reducing the free running Ar+ linewidth to about 1 MHz. The dye laser scan provides tunability in the difference frequency mixing process, and is calibrated by marker fringes with the same stable cavity. Due to the absolute stability of the marker cavity, precise frequency determination of near infrared molecular transitions is achieved via interpolation between these marker fringes. It is shown theoretically that the residual error of this scheme due to the dispersion of air in the transfer cavity is quite small, and experimentally that a frequency precision on the order of 1 MHz per hour is routinely obtained with respect to molecular transitions.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1469-1471 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An apertureless near-field optical-imaging method is presented that achieves high spatial resolution as well as a ∼4000-fold increase in detection sensitivity, by exploiting the highly localized enhanced near-field interactions between the sample (e.g., Au nanospheres) and a sharp atomic force microscope tip under evanescent laser field illumination. This represents a general method for optical imaging at ≤2 nm spatial resolution, and is applicable to both resonant (i.e., scattering) as well as nonresonant (i.e., fluorescence, Raman, etc.) spectroscopic methods. © 1998 American Institute of Physics.
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