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A method of analysis of dynamic NMR spectra for A3B2 ? C3D2 spin systems is proposed. This method is based upon the assumption that the shape of the A–C part of the spectrum is the same as for the AB2 ? CD2 spin system and the shape of the B–D part is the same as for the A3B ? C3D system. By means of this simplification the iterative total line shape analysis of dynamic NMR spectra by the use of the least-squares method becomes feasible. The method proposed is applied to the determination of the thermodynamic parameters of activation for internal rotation in N,N-diethylbenzamide in CD3CN (ΔG = 62.6 kJ mol?1 ΔH≠ = 62 kJ mol?1, ΔS≠ = ?1 J/mol?1 K?1). The determination of natural line widths is discussed in detail and a method of estimation of the effect of systematic errors on the results is proposed. 相似文献
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van Wijngaarden J Shnitko I Batalov A Kolek P Fulara J Maier JP 《The journal of physical chemistry. A》2005,109(25):5553-5559
Electronic absorption spectra of C3Cl, C3Cl+, C3Cl-, C4Cl, and C4Cl+ have been recorded in 6 K neon matrices following mass selection. Ab initio calculations were performed (CCSD(T) and CASSCF) to identify the ground and accessible excited states of each molecule. The estimated excitation energies and transition moments aid the assignment. The absorptions observed for C3Cl are the 5(2)A' <-- X(2)A' and 3(2)A' <-- X(2)A' transitions of the bent isomer and the (2)A1 <-- X(2)B2 transition of the cyclic form in the UV (336.1 nm), visible (428.7 nm), and near-IR (1047 nm) regions, respectively. The band systems for bent C3Cl- (435.2 nm) and linear C3Cl+ (413.2 nm) are both in the visible region and correspond to 2(1)A' <-- X(1)A' and (1)pi <-- X(1)sigma+ type transitions. The C4Cl and C4Cl+ chains are linear, and the band origins of the 2(2)pi <-- X(2)pi and 2(3)pi <-- X(3)pi electronic transitions are at 427.0 and 405.7 nm. The spectral assignments are supported by analysis of the vibrational structure associated with each electronic transition. 相似文献
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Dr. Przemyslaw Dopieralski Dr. Jordi Ribas‐Arino Dr. Padmesh Anjukandi Dr. Martin Krupicka Prof. Dr. Dominik Marx 《Angewandte Chemie (International ed. in English)》2016,55(4):1304-1308
Understanding the impact of tensile forces on disulfide bond cleavage is not only crucial to the breaking of cross‐linkers in vulcanized materials such as strained rubber, but also to the regulation of protein activity by disulfide switches. By using ab initio simulations in the condensed phase, we investigated the response of disulfide cleavage by β‐elimination to mechanical stress. We reveal that the rate‐determining first step of the thermal reaction, which is the abstraction of the β‐proton, is insensitive to external forces. However, forces larger than about 1 nN were found to reshape the free‐energy landscape of the reaction so dramatically that a second channel is created, where the order of the reaction steps is reversed, turning β‐deprotonation into a barrier‐free follow‐up process to C?S cleavage. This transforms a slow and force‐independent process with second‐order kinetics into a unimolecular reaction that is greatly accelerated by mechanical forces. 相似文献
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Przemyslaw Mielczarek Piotr Suder Igor Kotsan Anna Bodzon-Kulakowska 《Journal of mass spectrometry : JMS》2023,58(4):e4916
Imaging mass spectrometry is a powerful technique for the molecular analysis of tissue sections. As in many analytical methods, sample preparation is one of the main and most important steps to obtain results of good quality. Usually, the matrix concentration and solvent composition in different studies are taken for granted without any further consideration. In our studies, we aimed to find how matrix concentration and a type of solvent influence the signal. Moreover, we also aimed to find the relationship between these parameters, how they influence the spectra, and how they influence obtained ion maps. In our experiments, we used SunCollect®, which is a commercially available wet-interface system for matrix deposition. We decided to choose two matrix concentrations (2,5-dihydroxybenzoic acid [DHB]: 15 and 25 mg/mL; 9-aminoacridine [9AA]: 7 and 5 mg/mL) and two different water solutions of solvents in two different percentages for the matrices (DHB: 50% and 70% of methanol [MeOH] and acetonitrile [ACN]; 9AA 70% and 50% of ethanol [EtOH] and MeOH). In the end, the influence of these parameters on obtained spectra and ion maps was assessed. 相似文献
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The standard picture of growth at a screw dislocation assumes that the movement of adatoms on a dislocation loop is the same as on an ideal plane. We have examined this proposition by investigating the movement of a single tungsten adatom on a W(110) plane intersected by a screw dislocation. Surprisingly enough, adatom movement was entirely different than on a normal (110) plane: the overall diffusivity was higher, and the mobility varied with the location of the adatom relative to the dislocation core. This study demonstrates that surface transport is strongly affected in the vicinity of dislocations. 相似文献
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Organic emitting compounds that are based on π‐conjugated skeletons have emerged as promising next‐generation materials for application in optoelectronic devices. In this Minireview, recent advances in the development of organic emitters that irradiate room‐temperature phosphorescence and/or thermally activated delayed fluorescence with extraordinary luminescence properties, such as aggregation‐induced emission, mechanochromic luminescence, and circularly polarized luminescence, are discussed. 相似文献