流体力学半径对估算胶体微球聚集速率常数的影响

胶体粒子聚集速率常数实验值远低于理论值一直是被普遍关注的问题.聚集速率常数的理论推导是基于粒子的几何半径来考虑的,但决定粒子扩散速率及聚集速率的应该是粒子的流体力学半径(大于几何半径),因而它是使聚集速率常数实验值低于理论值的因素之一.影响流体力学半径的因素很多,其中,带电粒子在溶液中因表面存在双电层,会明显增大流体力学半径,造成聚集速率减慢.而双电层的厚度又随溶液中离子强度的不同而改变.本工作在聚集速率的公式中引入了修正因子,即几何半径与其流体力学半径之比,以修正由于用几何半径代替流体力学半径带来的误差.其中几何半径和流体力学半径可以分别用扫描电镜(SEM)和动态光散射(DLS)来测定.以两种粒径的聚苯乙烯带电微球为例,考察了在不同离子强度下,该误差的大小.结果发现,对于半径为30 nm的微球,用流体力学半径计算的慢聚集速率常数比理论值偏低约8%.该误差随离子强度增加而减少.对于快聚集情况,流体力学半径对聚集速率基本没有影响.     

Quantum field lability indexes of ligands for predicting some properties of platinum complexes

The state of a ligand in a molecule is discussed in terms of the quantum field theory operating with wave functions and occupation numbers in the Fock space. Following the basic concepts of the quantum theory, the state of a ligand is considered as an average weighed value of two ionic states given in the form of effective electron charge on ligand. A shift in the ligand state between the ionic states under the influence of an external field is estimated in terms of lability indexes arising as a result of the information statistical theory application to the problem of quantum parameter estimation. The proposed indexes combined with their energetic characteristics are used for predicting cis and trans effects in platinum(II) complexes forming the Werner–Miolatti series. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65 : 49–57, 1997     

Raman Spectra of Glycine and Their Modeling in Terms of the Discrete–Continuum Model of Their Water Solvation Shell

Optics and Spectroscopy - Raman spectra of glycine in a crystalline form and in a water environment have been obtained. B3LYP/6-311++G(3df,2p) quantum-chemical calculations have shown that an...     

Molecular fragmentation under the action of an instantaneous perturbation as exemplified by propane

The spectra of fragmentation of molecules under the action of pulsed laser radiation or ion beams are studied in the sudden-perturbation approximation. By the example of the fragmentation process of the propane molecular ion [C₃H₈]⁺, it is established by calculating the most significant potential-energy surface cross sections along the reaction pathway that there is a correlation between the probability of formation of ionic fragments and the breaking energetics of individual chemical bonds. A complex rearrangement of atoms in the methane detachment process is established. The fragmentation spectra are attributed to protons with an energy of approximately 10 keV.     

Synthetic magnetic opals

We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there exists no report in literature on any BiNi compound which is magnetic.     

Grignard Reaction as a Result of Tunneling of the Triplet Branch of the Reaction Through a Singlet Barrier

Quantum-chemical calculations were carried out to study the mechanism of the Grignard reaction Mg + CH₃F. The reaction between Mg, CH₃F gives rise to a triplet complex which has a lower energythan the corresponding singlet complex at MgFCH₃ angles ranging from 60 to 139°. The transition from thesinglet branch of the reaction to the nonequilibrium triplet branch results in decomposition of CH₃F with formation of various final products. A linear Grignard reagent CH₃-Mg-F is formed by simultaneous homolytic CH₃-F dissociation and ionic covalent interaction of the methyl group and the fluorine atom with the magnesium cation arising in the course of the reaction. Normal mode frequencies for the Mg + CH₃F complex at various MgFCH₃ are were calculated. The calculation results nicely agree with experimental data.     

DFT:B3LYP ab initio molecular dynamics study of the Zundel and Eigen proton complexes, H5O2+ and H9O4+, in the triplet state in gas phase and solution

DFT:B3LYP ab initio molecular dynamics (MD) approach is used to elucidate the properties of the Zundel and Eigen, H5O2+ and H9O4+, proton complexes in the triplet state. The simulation considers the complexes in the gas phase (isolated complexes) and inside the clusters composed of 32, 64, and 128 water molecules, mimicking the behavior of aqueous solutions. MD simulations reveal three distinct periods. For the complex in solutions, the periods are smoothed out. The H5O2+ and H9O4+ complexes in the triplet state undergo structural rearrangements, which eventually result in hydrogen elimination. For the H5O2+, the hydrogen is eliminated from the center of the water cluster, whereas for the H9O4+ it is removed from a near-surface water molecule. The rate of hydrogen elimination decreases with increasing the number of water molecules surrounding the complex.     

Proton Migration in a Chain of Tyrosine Residues

Proton migration in a tyrosine residue chain which is a model for a proton channel in a series ofproteins, including tubulin, has been studied. Magnesium(2+) complex within the guanosinetri phosphatemoiety favors dissociation one of the coordinated water molecules. The dissociation initiates proton shiftsalong the tyrosine chain composed of spatially separated tyrosine residues. The shifts are thermodynamicallyallowed (G298 < 0). The barrier to the proton shift does not exceed 3.15 kJ/mol. When applied, externalelectric field of low intensity, which mimicks the electret properties of some proteins, favors proton migrationby large distances.     

Reactive-field theory for molecules in the surface layer of a liquid

Analytic formulas are derived for the solvation energy of molecules adsorbed in the surface layer of a liquid. These are analogs of the Born and Onsager formulas for the bulk phase. Deriving the solvation energy involves decomposing the molecular characteristics, which is done by quantum-chemical calculation.St. Petersburg University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 2, pp. 3–10, March–April, 1993.     

Temperature hysteretic effect and its influence on colossal magnetoresistance of La0.33Nd0.33Ca0.33MnO3

Electrical resistance (R) measurements of a bulk La_0.33Nd_0.33Ca_0.33MnO₃ perovskite in magnetic fields up to 40 kOe have revealed anomalous temperature hysteretic effects both in 0 Oe and 20 kOe magnetic fields. The sharp peak observed in the R vs. T plot indicates the occurrence of metal-to-insulator (M-I) transition at a temperature of T _MI=110 K and 140 K, for cooling and warming paths, respectively. An applied magnetic field of 20 kOe reduces the resistance and shifts T _MI to 160 K and 185 K for cooling and warming, respectively. We have observed a much higher resistance in the cooling path than in the warming path leading to the hysteretic resistance ratio (R _cool/R _warm) of 200 at 110 K and 1.8 at 160 K for 0 Oe and 20 kOe, respectively. Record values of colossal magnetoresistance (CMR) have been achieved. The CMR value reaches nearly 99% in the temperature ranges of 90 K to 140 K and 90 K to 170 K for 20 kOe and 40 kOe magnetic fields in the cooling mode, respectively. The observed unusual behavior is attributed to the co-existence of La-rich and Nd-rich domains assumed to be distributed randomly in the compound.