排序方式: 共有36条查询结果,搜索用时 15 毫秒
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Williams JM Rowland B Jeffery MT Groenewold GS Appelhans AD Gresham GL Olson JE 《Langmuir : the ACS journal of surfaces and colloids》2005,21(6):2386-2390
At trace coverages on concrete surfaces, the nerve agent VX (O-ethyl S-2-diisopropylaminoethyl methyl phosphonothiolate) degrades by cleavage of the P-S and S-C bonds, as revealed by periodic secondary ion mass spectrometry (SIMS). The observed kinetics were (pseudo-) first-order, with a half-life of 2-3 h at room temperature. The rate increased with surface pH and temperature, with an apparent second-order constant of k(OH) = 0.64 M(-1) min(-1) at 25 degrees C and an activation energy of 50-60 kJ mol(-1). These values are consistent with a degradation mechanism of alkaline hydrolysis within the adventitious water film on the concrete surface. Degradation of bulk VX on concrete would proceed more slowly. 相似文献
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Anbalagan V Chien W Gresham GL Groenewold GS Van Stipdonk MJ 《Rapid communications in mass spectrometry : RCM》2004,18(24):3028-3034
Electrospray ionization was used to generate mono-positive gas-phase complexes of the general formula [UO2A(S)n]+ where A = OH, Cl, Br, I or ClO4, S = H2O, CH3OH or CH3CH2OH, and n = 1-3. The multiple-stage dissociation pathways of the complexes were then studied using ion-trap mass spectrometry. For H2O-coordinated cations, the dissociation reactions observed included the elimination of H2O ligands and the loss of HA (where A = Cl, Br or I). Only for the Br and ClO4 versions did collision-induced dissociation (CID) of the hydrated species generate the bare, uranyl-anion complexes. CID of the chloride and iodide versions led instead to the production of uranyl hydroxide and hydrated UO2+. Replacement of H2O ligands by alcohol increased the tendency to eliminate HA, consistent with the higher intrinsic acidity of the alcohols compared to water and potentially stronger UO2-O interactions within the alkoxide complexes compared to the hydroxide version. 相似文献
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Gabriela R. Stadler Dr. Takuya F. Segawa Matthias Bütikofer Dr. Venita Decker Dr. Sandra Loss Dr. Barbara Czarniecki Dr. Felix Torres Prof. Roland Riek 《Angewandte Chemie (International ed. in English)》2023,62(40):e202308692
Fragment-based drug design is a well-established strategy for rational drug design, with nuclear magnetic resonance (NMR) on high-field spectrometers as the method of reference for screening and hit validation. However, high-field NMR spectrometers are not only expensive, but require specialized maintenance, dedicated space, and depend on liquid helium cooling which became critical over the recurring global helium shortages. We propose an alternative to high-field NMR screening by applying the recently developed approach of fragment screening by photoinduced hyperpolarized NMR on a cryogen-free 80 MHz benchtop NMR spectrometer yielding signal enhancements of up to three orders in magnitude. It is demonstrated that it is possible to discover new hits and kick-off drug design using a benchtop NMR spectrometer at low micromolar concentrations of both protein and ligand. The approach presented performs at higher speed than state-of-the-art high-field NMR approaches while exhibiting a limit of detection in the nanomolar range. Photoinduced hyperpolarization is known to be inexpensive and simple to be implemented, which aligns greatly with the philosophy of benchtop NMR spectrometers. These findings open the way for the use of benchtop NMR in near-physiological conditions for drug design and further life science applications. 相似文献
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Site‐Specific Solid‐State NMR Studies of “Trigger Factor” in Complex with the Large Ribosomal Subunit 50S
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Dr. Emeline Barbet‐Massin Chih‐Ting Huang Dr. Venita Daebel Dr. Shang‐Te Danny Hsu Prof. Bernd Reif 《Angewandte Chemie (International ed. in English)》2015,54(14):4367-4369
Co‐translational protein folding is not yet well understood despite the availability of high‐resolution ribosome crystal structures. We present first solid‐state NMR data on non‐mobile regions of a prokaryotic ribosomal complex. Localized chemical shift perturbations and line broadening are observed for the backbone amide resonances corresponding to the regions in the trigger factor ribosome‐binding domain that are involved in direct contact with the ribosome or undergo conformational changes upon ribosome binding. This large asymmetric protein complex (1.4 MDa) becomes accessible for NMR investigations by the combined use of proton detection and high MAS frequencies (60 kHz). The presented results open new perspectives for the understanding of the mechanism of large molecular machineries. 相似文献
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Dr. Isaac J. Gresham Seamus G. Lilley Dr. Andrew R. J. Nelson Dr. Kaloian Koynov Prof. Chiara Neto 《Angewandte Chemie (International ed. in English)》2023,62(41):e202308008
Slippery covalently-attached liquid surfaces (SCALS) with low contact angle hysteresis (CAH, <5°) and nanoscale thickness display impressive anti-adhesive properties, similar to lubricant-infused surfaces. Their efficacy is generally attributed to the liquid-like mobility of the constituent tethered chains. However, the precise physico-chemical properties that facilitate this mobility are unknown, hindering rational design. This work quantifies the chain length, grafting density, and microviscosity of a range of polydimethylsiloxane (PDMS) SCALS, elucidating the nanostructure responsible for their properties. Three prominent methods are used to produce SCALS, with characterization carried out via single-molecule force measurements, neutron reflectometry, and fluorescence correlation spectroscopy. CO2 snow-jet cleaning was also shown to reduce the CAH of SCALS via a modification of their grafting density. SCALS behavior can be predicted by reduced grafting density, Σ, with the lowest water CAH achieved at Σ≈2. This study provides the first direct examination of SCALS grafting density, chain length, and microviscosity and supports the hypothesis that SCALS properties stem from a balance of layer uniformity and mobility. 相似文献
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Leavitt CM Gresham GL Benson MT Gaumet JJ Peterman DR Klaehn JR Moser M Aubriet F Van Stipdonk MJ Groenewold GS 《Inorganic chemistry》2008,47(8):3056-3064
Diphenyldithiophosphinate (DTP) ligands modified with electron-withdrawing trifluoromethyl (TFM) substitutents are of high interest because they have demonstrated potential for exceptional separation of Am (3+) from lanthanide (3+) cations. Specifically, the bis( ortho-TFM) (L 1 (-)) and ( ortho-TFM)( meta-TFM) (L 2 (-)) derivatives have shown excellent separation selectivity, while the bis( meta-TFM) (L 3 (-)) and unmodified DTP (L u (-)) did not. Factors responsible for selective coordination have been investigated using density functional theory (DFT) calculations in concert with competitive dissociation reactions in the gas phase. To evaluate the role of (DTP + H) acidity, density functional calculations were used to predict p K a values of the free acids (HL n ), which followed the trend of HL 3 < HL 2 < HL 1 < HL u. The order of p K a for the TFM-modified (DTP+H) acids was opposite of what would be expected based on the e (-)-withdrawing effects of the TFM group, suggesting that secondary factors influence the p K a and nucleophilicity. The relative nucleophilicities of the DTP anions were evaluated by forming metal-mixed ligand complexes in a trapped ion mass spectrometer and then fragmenting them using competitive collision induced dissociation. On the basis of these experiments, the unmodified L u (-) anion was the strongest nucleophile. Comparing the TFM derivatives, the bis( ortho-TFM) derivative L 1 (-) was found to be the strongest nucleophile, while the bis( meta-TFM) L 3 (-) was the weakest, a trend consistent with the p K a calculations. DFT modeling of the Na (+) complexes suggested that the elevated cation affinity of the L 1 (-) and L 2 (-) anions was due to donation of electron density from fluorine atoms to the metal center, which was occurring in rotational conformers where the TFM moiety was proximate to the Na (+)-dithiophosphinate group. Competitive dissociation experiments were performed with the dithiophosphinate anions complexed with europium nitrate species; ionic dissociation of these complexes always generated the TFM-modified dithiophosphinate anions as the product ion, showing again that the unmodified L u (-) was the strongest nucleophile. The Eu(III) nitrate complexes also underwent redox elimination of radical ligands; the tendency of the ligands to undergo oxidation and be eliminated as neutral radicals followed the same trend as the nucleophilicities for Na (+), viz. L 3 (-) < L 2 (-) < L 1 (-) < L u (-). 相似文献
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Gary S. Groenewold Dr. Michael J. Van Stipdonk Prof. Wibe A. de Jong Dr. Jos Oomens Dr. Garold L. Gresham Dr. Michael E. McIlwain Dr. Da Gao Dr. Bertrand Siboulet Dr. Lucas Visscher Prof. Michael Kullman Nick Polfer Prof. 《Chemphyschem》2008,9(9):1278-1285
UO2+–solvent complexes having the general formula [UO2(ROH)]+ (R=H, CH3, C2H5, and n‐C3H7) are formed using electrospray ionization and stored in a Fourier transform ion cyclotron resonance mass spectrometer, where they are isolated by mass‐to‐charge ratio, and then photofragmented using a free‐electron laser scanning through the 10 μm region of the infrared spectrum. Asymmetric O=U=O stretching frequencies (ν3) are measured over a very small range [from ~953 cm?1 for H2O to ~944 cm?1 for n‐propanol (n‐PrOH)] for all four complexes, indicating that the nature of the alkyl group does not greatly affect the metal centre. The ν3 values generally decrease with increasing nucleophilicity of the solvent, except for the methanol (MeOH)‐containing complex, which has a measured ν3 value equal to that of the n‐PrOH‐containing complex. The ν3 frequency values for these U(V) complexes are about 20 cm?1 lower than those measured for isoelectronic U(VI) ion‐pair species containing analogous alkoxides. ν3 values for the U(V) complexes are comparable to those for the anionic [UO2(NO3)3]? complex, and 40–70 cm?1 lower than previously reported values for ligated uranyl(VI) dication complexes. The lower frequency is attributed to weakening of the O?U?O bonds by repulsion related to reduction of the U metal centre, which increases electron density in the antibonding π* orbitals of the uranyl moiety. Computational modelling of the ν3 frequencies using the B3LYP and PBE functionals is in good agreement with the IRMPD measurements, in that the calculated values fall in a very small range and are within a few cm?1 of measurements. The values generated using the LDA functional are slightly higher and substantially overestimate the trends. Subtleties in the trend in ν3 frequencies for the H2O–MeOH–EtOH–n‐PrOH series are not reproduced by the calculations, specifically for the MeOH complex, which has a lower than expected value. 相似文献