铵根离子在水溶液中的跳跃转动机理

铵根离子的动力学行为与生命体内的生物和化学过程密切相关.依据流体力学理论,由于铵根离子与水分子之间存在多个强氢键,其转动应较慢,但实验结果并非如此,其转动的微观机理尚不清晰.本文分子动力学模拟研究表明,水溶液中铵根离子主要以快速、大角度的跳跃方式进行转动,像水分子一样遵从扩展分子跳跃转动模型.通过微观转动模式的分解和两种转动弛豫时间的比较发现,相对其氢键骨架的扩散转动,跳跃转动对其转动速率贡献更大,并随浓度增大不断强化.与水分子氢键交换方式相比,铵根离子更倾向于在非氢键相连的水分子间发生交换.     

Studies of Molecular Motions of Ocotillol-Type Saponins in Solution by ~(13)C Nuclear Magnetic Relaxation

In this paper, the fully anisotropicoverall tumbling motions and side groups internal rotation of ocotillol-type saponins separated from the leaves of Panax Quidquefolium L. are investigated by ~(13)C nuclear magnetic relaxation. The fully anisotropic overall tumbling motion model with methyl conformation jumps internal rotation among three equivalent sites is presented, and the spectral density function of this model is derived. The rotation rates for overall tumbling motions to ocotillol-type saponins (OTS) are computed by Woessner's fully anisotropic overall tumbling motion model, and the internal rotation rate and barrier for side groups in OTS are calculated using free diffusion internal rotation model, restriction diffusion internal rotation model and conformation jumps internal rotation model, respectively.     

Phenyl group rotation in polystyrene and the nature of twofold anisotropic internal rotation

A review of the experimental evidence for phenyl group rotation in various polystyrenes and improvements in the interpretation of spin relaxation data for dilute solutions of randomly coiled polymers led to a new calculation of the correlation time for phenyl group rotation from nuclear magnetic resonance (NMR) data. Both ¹³C and ¹⁹F NMR data were reconsidered by using a model which includes motional modulation of the dipole–dipole interaction by overall rotatory diffusion, backbone rearrangements, and internal anisotropic rotation. The choice of a twofold potential to characterize local resistance to internal phenyl group rotation strongly influences the estimate of the rate of phenyl group rotation. The magnetic resonance data are found to be consistent with a correlation time for phenyl group rotation which is one to six times longer than the average correlation time for backbone rearrangement.     

Energy decomposition analysis of borane monoammoniate: origin of the rotational barrier to nonrigid rotation

Rotational barrier for borane monoammoniate was studied at the Hartree-Fock level using several Gaussian basis sets. Rotational barrier to nonrigid rotation was estimated to be 1.85 kcal/mol using the 6–31G^☆ basis set. Furthermore, energy decomposition of the barrier was performed. For the rigid rotation, the origin of the rotational barrier was dominantly due to the exchange repulsion term. On the contrary, for the nonrigid rotation, the electrostatic term was the most important contributor, and the exchange repulsion played rather minimal role. The nonrigid rotation is also explained as the two-step process of the rigid rotation and the geometry relaxation.     

Large Amplitude Torsions in Nitrotoluene Isomers Studied by Rotational Spectroscopy and Quantum Chemistry Calculations

Rotational spectra of ortho-nitrotoluene (2-NT) and para-nitrotoluene (4-NT) have been recorded at low and room temperatures using a supersonic jet Fourier Transform microwave (MW) spectrometer and a millimeter-wave frequency multiplier chain, respectively. Supported by quantum chemistry calculations, the spectral analysis of pure rotation lines in the vibrational ground state has allowed to characterise the rotational energy, the hyperfine structure due to the ¹⁴N nucleus and the internal rotation splittings arising from the methyl group. For 2-NT, an anisotropic internal rotation of coupled −CH₃ and −NO₂ torsional motions was identified by quantum chemistry calculations and discussed from the results of the MW analysis. The study of the internal rotation splittings in the spectra of three NT isomers allowed to characterise the internal rotation potentials of the methyl group and to compare them with other mono-substituted toluene derivatives in order to study the isomeric influence on the internal rotation barrier.     

Helix formation and formaldehyde crosslinking in gelatin solutions

Optical rotation measurements on 5% gelatin solutions containing 0, 2, and 5% formaldehyde (w/w gelatin) are carried out at a series of temperatures between 20°C and 50°C. The solutions without formaldehyde show a diminished growth in rotation with rising temperatures, but even at 50°C there is still a steady rise in rotation with time. The addition of formaldehyde diminishes the optical rotation growth, and at 40°C and above solutions with 5% formaldehyde show no change in rotation at all. The specific rotation and time figures are fitted to a series of third-degree polynomial equations. It is shown that the data do not conform to any pattern of simple reaction kinetics. The mechanism of the formaldehyde–gelatin interaction is discussed.     

碱金属团簇碰撞动力学研究

With in the framework of distance dependent tight-binding molecular dynamics (DDTBMD), the collision dynamics of sodium cluster Na n has been studied systematically. Some phenomena have been observed at different impact parameters b , such as fusion reaction, deep inelastic collision (DIC) and quasi-elasticcollision, which are similar to the nuclear heavy-ion collisions (HIC). For the system of Na6 (3D) + Na8, the reaction mechanism at b=9a0 is DIC, but when b is equal to 13a0, it corresponds to quasi-elastic collision. Further more the rotation processes during the collisions, are related to the collision energy and parameter. The larger collision energy is, the earlier relative rotation will occur, and the relaxation time becomes shorter and the relative rotation energy is much smaller. There exists maximal relative rotation energy which corresponding to b = 7a0. When b is smaller than 7a0, the rotation energy increases with b increasing, otherwise the energyd ecreases. And the maximal relative rotation energy is corresponding to DIC process. The maximal rotation energy can reach on etenth of total energy, which is much less than that in HIC.     

Microenvironment control of methyl rotation induced by proton transfer

Methyl rotation induced by proton transfer was found for cis-N-methylacetamide (NMA). More interestingly, it was found that the microenvironment could control the methyl rotation. The atom-centered density matrix propagation (ADMP) method, a recently developed ab initio molecular dynamics, was further carried out to depict the trajectories for methyl rotation of NMA. Moreover, trajectories for methyl rotation of NMA complexed with water molecules were also calculated, and water molecules at the two different sites of NMA were found to reverse or cease the rotational direction of the methyl groups of NMA. This finding that microenvironment can not only control rotational direction of methyl groups but can also cease the rotation may be of significant importance for the control of molecular machines.     

Characterization of intensity-dependent optical rotation phenomena in chiral molecules in solution

The rotation of the plane of polarization of linearly polarized light by chiral molecules in solution is due to a forward scattering event. Ordinary optical rotation, a single-photon effect, is independent of intensity. As the light intensity is increased, other effects can appear, such as two-photon scattering or alignment of the molecule by one photon and scattering with a change of polarization by another. Both of these effects result in intensity-dependent (or nonlinear) optical rotation. A polarimeter was used to measure the nonlinear optical rotation of solutions in a heterodyne experiment. No nonlinear optical rotation was found in molecules lacking an absorption band near the laser frequency. In the three pyrimidine nucleosides studied, which do have such an absorption band, a nonlinear optical rotation was identified that was cumulative with each laser pulse. The effect persisted with a time constant that was on the order of seconds and characteristic of the molecule.     

Simple formulas for rotation averages of spectroscopic intensities

We give a self-contained exposition of the “ensemble method”, a rule for calculating rotation averages of spectroscopic absorption intensities. The rule is mathematically exact and conceptually simple and applies to rotation averages for several axes of rotation occurring in helical and superhelical symmetry. A measure of dichroism, D_I, is introduced which has a simple multiplicative property relative to axes of rotation. There are several applications to linear dichroism spectroscopy.     

Rotation of water in solid parahydrogen and orthodeuterium

The far-infrared spectra of solid orthodeuterium and solid normal deuterium are presented and compared to the corresponding spectra of solid parahydrogen and solid normal hydrogen. Spectra of water in orthodeuterium are compared to spectra of water in parahydrogen. The water rotation constants in orthodeuterium are approximately 80% of the rotation constants of water in parahydrogen. The S(0)(0) band of orthodeuterium gets a strong satellite in the presence of water. The position and width of the satellite depends on the isotopic composition of the water present. If there is a corresponding satellite in parahydrogen it is weak and closer to the S(0)(0) band of the matrix. The conclusion of the paper is that interaction between guest rotation and the rotation of matrix molecules must be taken into account to explain the reduction of the rotation constants in orthodeuterium.     

Quantification of Ocular Biologically Effective UV Exposure for Different Rotation Angle Ranges Based on Data from a Manikin

Human outdoor activities are randomly orientated at different angles to the sun. To quantify the ocular UV and biologically effective UV (UVBE; i.e. the ocular UV irradiance exposure for photokeratitis (UVpker), photoconjunctivitis (UVpcon), and cataract (UVcat)) exposure for different rotation angle ranges, a rotating manikin was used to monitor the ocular UV exposure at different rotation angles in clear skies during July 2010 in Sanya, China. As a result, the ocular UV and UVBE irradiance was directly influenced by the rotation angle variations, primarily for the 120° rotation angle ranges facing the morning and afternoon sun when the solar elevation was lower than 60°; during these times, the UV and UVBE spectral irradiance decreased as the rotation angle increased. When compared to the 360° rotation angle ranges (which were considered to be the average exposure situation), the cumulative ocular UVBE for 60°, 120° and 180° rotation angle ranges were maximally 91% (UVcat), 94% (UVpker) and 121% (UVpcon); 71% (UVcat), 74% (UVpker) and 95% (UVpcon); 42%(UVcat), 45%(UVpker) and 55% (UVpcon) higher respectively. Meanwhile, the cumulative ocular UVBE for the 180° rotation angle ranges facing away from the sun were 46% (UVpker), 59% (UVpcon) and 45% (UVcat) lower.     

Anomalous Lehmann Rotation of Achiral Nematic Liquid Crystal Droplets Trapped under Linearly Polarized Optical Tweezers

Continuous rotation of a cholesteric droplet under the heat gradient was observed by Lehmann in 1900. This phenomenon, the so-called Lehmann effect, consists of unidirectional rotation around the heat flux axis. We investigate this gradient heat effect using infrared laser optical tweezers. By applying single trap linearly polarized optical tweezers onto a radial achiral nematic liquid crystal droplet, trapping of the droplet was performed. However, under a linearly polarized optical trap, instead of stable trapping of the droplet with slightly deformed molecular directors along with a radial hedgehog defect, anomalous continuous rotation of the droplet was observed. Under low power laser trapping, the droplet appeared to rotate clockwise. By continuously increasing the laser power, a stable trap was observed, followed by reverse directional rotation in a higher intensity laser trap. Optical levitation of the droplet in the laser beam caused the heat gradient, and a breaking of the symmetry of the achiral nematic droplet. These two effects together led to the rotation of the droplet under linearly polarized laser trapping, with the sense of rotation depending on laser power.     

应用分子图形学、分子力学、量子化学及静电势研究农药分子结构与性能关系(X)──磺酰脲分子内旋转通道的分子力学研究

磺酞豚分子是一类极其重要的低毒超高效除草剂，有着十分重要的用途．研究分子的空间结构对于了解分子的构效关系十分重要．最近，我们测定的一系列分子的晶体结构［‘－’1表明，分子1、2、3晶体结构的空间群分别为PZ；儿、Pz、Pz，说明晶体中分别有对称元素（对称面或者对称中心），分子以对映体的形式存在于晶体中．由于磺酸豚分子本身不存在手性原子，由此推断磺酷服分子在晶体中存在的对映异构体是由内旋转阻碍产生的，因而应是构象异构体．本项研究工作的目的是应用分子力学方法，计算阻碍内旋转的能垒，从而找出分子内旋转时的最低…     

Keep It Flexible: Driving Macromolecular Rotary Motions in Atomistic Simulations with GROMACS

We describe a versatile method to enforce the rotation of subsets of atoms, e.g., a protein subunit, in molecular dynamics (MD) simulations. In particular, we introduce a "flexible axis" technique that allows realistic flexible adaptions of both the rotary subunit as well as the local rotation axis during the simulation. A variety of useful rotation potentials were implemented for the GROMACS 4.5 MD package. Application to the molecular motor F(1)-ATP synthase demonstrates the advantages of the flexible axis approach over the established fixed axis rotation technique.     

Recoil anisotropy following multiphoton dissociation via near-resonant intermediate states

Expressions are derived for the moments beta(n) of the anisotropy of fragment recoil following multiphoton dissociation. The results for all possible two- and three-photon excitation pathways from a sigma or pi initial state, with prompt dissociation, are listed in tabular and graphical form, thereby facilitating the identification of pathways compatible with experimental data. The consequence of possible interference between multiple-excitation pathways is discussed. In addition, allowance is made for rotation of the parent molecule in the dissociating state on the time scale of its dissociation, with specific equations for three cases: fully resolved rotation on excitation, significant but unresolved rotation, and the intermediate case of partially resolved excitation. Finally, expressions are given for the consequence of significant rotation in a near-resonant intermediate state. It is pointed out that the effects of rotation can lead to a strong variation of the anisotropic moments over an excitation band, and that the absence of rotational features does not necessarily imply that the effects of rotation on recoil anisotropy can be ignored. The application of the theory is illustrated for a number of model systems, restricted to diatomic molecules with possible rotation but subsequent axial recoil. However, the expressions are easily adapted to polyatomic systems, provided that any fragment rotation is unresolved.     

low-frequency dispersion of surface conducting particles as measured by means of electrorotation

Electrorotation of glutaraldehyde-fixed red blood cells (RBCs) has been investigated in the frequency range from 16 Hz to 30 MHz. Special emphasis has been given to the low-frequency range (16 Hz–2 kHz). In this region, a distinctly new type of co-field rotation peak was observed. Native RBCs also show low-frequency rotation, but much less pronounced. The low-frequency rotation is nonmonotonous with regard to conductivity. With increasing external conductivity, the low-frequency rotation speed reaches a maximum of around 3.5 mS/m and decreases again when the external conductivity is increased further. The low-frequency co-field rotation peak was observed between 30 Hz and 70 Hz except at very low conductivity almost independent of electrolyte concentration. Decreasing surface charge density by means of neuraminidase led to a reduction of the rotation speed in the low-frequency range. The position of the peak remained unaffected by changes of the surface charge density. These experimental results are not consistent with the typical Pauli–Schwan- and Maxwell–Wagner-dispersion. They rather suggest the presence of a concentration polarization mechanism responsible for the low-frequency electrorotation peak.     

Rotation in simplex optimization

A modification of the modified simplex method of optimization was tested. This modification involves rotation of the simplex when the standard simplex motion by reflection, expansion and contraction, fails to lead to continued progress of the simplex. Two other methods and several kinds of rotation are compared for four response surfaces. Certain rotations are shown to be superior to others and to two previously reported operations that do not involve rotation.     

The rotation and the phase transition in solid C60

The interaction between C60's in solid C60 has been calculated by (exp-6-1) potential, and the cause and the controlled factor of the high rapid rotations of C60 's were discussed. In order to describe the disordered degree of C60 rotation, an equivalent M is introduced. The phase transitions at the ~260 K and at the ~90 K are studied from the viewpoint of C60 rotation. The potential barriers of the ordered rotation below the ~260 K and the disordered rotation above the ~260 K have been given, and the effect of the external pressure on the temperature of phase transition has also been given.