HEPT类化合物的QSAR研究

为定量结构／活性相关性研究提取了量子化学参数,拓扑指数Am,分子连接性指数^mxt及疏水性常数,同时应用正交变换和最佳变量子集算法（Leaps-and-Bonds)进行了变量压缩和选择,进而实施了多元回归分析,并由此结果进行了HEPT类化合物（1－[(2-hydroxyethoxy)methyl]-6-(phenylthio)-thymine derivatives)的结构／活性关系的理论解释,进行了人工神经网络法对于该类化合物的活性预测,其结构明显好于多元回归法。     

Investigation of the influence of the polarity of the solvent on the composition of the extractive substances and post-extraction residues of the bark ofAbies sibirica

The chemical compositions of the initial bark of the Siberian firAbies sibirica and of the solid residues after extraction with carbon dioxide, water, and alcohol have been studied. On successive extraction, the yield of extractive substances amounted to 25.05% of the absolutely dry bark. The carbon dioxide, aqueous, and alcoholic extracts obtained have been investigated. The carbon dioxide extract was found to contain 34.97% of essential oil, while only traces of it were detected in the aqueous and alcoholic extracts.Krasnoyarsk State Technological Academy. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 42–45, January–February, 1996. Original article submitted August 14, 1995.     

From the Micro- to the Macro-: Managing the Conservation of the Warship,Vasa

Sweden's famous warship, Vasa, sank on her maiden voyage in August 1628, and remained on the bottom of Stockholm harbour for 333 years. Raised in 1961, she became the first large-scale wooden object to be treated with polyethylene glycol (PEG). In the summer of 2000 a number of acidic salt precipitations were noticed on the surface of the ship and on wooden artefacts in the storerooms. An international research project has been established to look into the causes of this problem and suggest possible re-treatments. Meanwhile projects are underway to monitor movements in the ship, to build a better support system, and to replace the thousands of iron bolts holding the structure together, while a sophisticated new climate system has recently been installed in the museum.     

Effect of the pH of the medium on the chemical shifts in the PMR spectra and on the distribution of the π-electron density

The dependence of the chemical shift of the ring protons on the pH of the medium for a number of 3-hydroxyquinoline derivatives was studied by PMR spectroscopy. The regions of ionization of the molecules, which correspond to the ranges of acidic, neutral, and alkaline media, were found. In D₂O, 3-hydroxyquinoline is present only in the uncharged hydroxy form. The presence of intramolecular hydrogen bonding in 4-dimethylaminomethyl-3-hydroxyquinoline has a substantial effect on the character of the dependence of the chemical shift on the pH of the medium; the existence of separate protonation of the nitrogen atoms of the ring and the side chain of 4-dimethylaminomethyl-3-hydroxyquinoline was established. The distribution of the -electron density in the 3-hydroxyquinoline molecule is in good agreement with its chemical behavior during electrophilic substitution.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1540–1545, November, 1971.     

Effect of the pH of the medium on the chemical shifts in the PMR spectra and on the distribution of the π-electron density

The dependence of the chemical shifts of the ring protons on the pH of the medium for a number of 4-hydroxyquinoline derivatives was studied by means of PMR spectroscopy. The dipolar and uncharged hydroxy forms exist in equilibrium in aqueous solutions. The effect of intramolecular hydrogen bonding on the character of the dependence of the chemical shift on the pH of the medium in the case of 3-piperidinomethyl-4-hydroxyisoquinoline was investigated. The possibility of the separate protonation of the ring nitrogen and the side-chain nitrogen in 3-piperidinomethyl-4-hydroxyisoquinoline was established. The distribution of the -electron density in 4-hydroxyisoquinoline is in good agreement with its chemical behavior.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1546–1549, November, 1971     

On the quality of the hardness kernel and the Fukui function to evaluate the global hardness

An approximated hardness kernel, which includes the second derivative with respect to the density of the kinetic energy, the electron-electron coulomb repulsion, and the exchange density functionals, has been tested for the calculation of the global hardness. The results obtained for a series of 40 cations and neutral systems and 16 anions represent in most cases an improvement of the results obtained using the HOMO-LUMO gap approach and indicate the viability of this approach to evaluate global hardness. In addition, the relevance of the Fukui function approximation and the role of the three components of the hardness kernel in the evaluation of the global hardness have been analyzed.     

On the role of the conserved aspartate in the hydrolysis of the phosphocysteine intermediate of the low molecular weight tyrosine phosphatase

The usual rate-determining step in the catalytic mechanism of the low molecular weight tyrosine phosphatases involves the hydrolysis of a phosphocysteine intermediate. To explain this hydrolysis, general base-catalyzed attack of water by the anion of a conserved aspartic acid has sometimes been invoked. However, experimental measurements of solvent deuterium kinetic isotope effects for this enzyme do not reveal a rate-limiting proton transfer accompanying dephosphorylation. Moreover, base activation of water is difficult to reconcile with the known gas-phase proton affinities and solution phase pK(a)'s of aspartic acid and water. Alternatively, hydrolysis could proceed by a direct nucleophilic attack by a water molecule. To understand the hydrolysis mechanism, we have used high-level density functional methods of quantum chemistry combined with continuum electrostatics models of the protein and the solvent. Our calculations do not support a catalytic activation of water by the aspartate. Instead, they indicate that the water oxygen directly attacks the phosphorus, with the aspartate residue acting as a H-bond acceptor. In the transition state, the water protons are still bound to the oxygen. Beyond the transition state, the barrier to proton transfer to the base is greatly diminished; the aspartate can abstract a proton only after the transition state, a result consistent with experimental solvent isotope effects for this enzyme and with established precedents for phosphomonoester hydrolysis.     

Effect of the nature of the solvent and the temperature on the frequency and intensity of the stretching vibration of the Ge-H bond in the IR spectra of 1-hydrogermatranes

Conclusions The Ge-H stretching vibration in the IR spectra of 1-hydrogermatranes varies under the influence of the solvent and the temperature as a result of the presence of the transannular Ge N bond. The change in the length of this bond with variation in the polarity of the solvent and the temperature of the solutions is smaller in germatranes than for the Si N bond in the isostructural silatranes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1758–1761, August, 1985.     

Koopmans-like approximation in the Kohn-Sham method and the impact of the frozen core approximation on the computation of the reactivity parameters of the density functional theory

A Koopmans-like approximation is introduced in the spin-polarized version of the Kohn-Sham (KS) density functional theory to obtain a relation between KS orbital energies and vertical ionization potential and electron affinity. Expressions for reactivity indexes (like electronegativity, hardness, electrophilicity, and excitation energies) include KS frontier orbital energies and additional contributions associated with the self-interaction correction. Those reactivity parameters were computed with different exchange-correlation functionals to test the approach for a set of small molecules. The results show that the present approximation provides a better way to estimate hardness, electronegativity, and electrophilicity than just the use of frontier orbital energy values. However KS HOMO and LUMO energy gap gives a better agreement with excitation energies.     

On the theory underlying the Car-Parrinello method and the role of the fictitious mass parameter

The theory underlying the Car-Parrinello extended-Lagrangian approach to ab initio molecular dynamics (CPMD) is reviewed and reexamined using "heavy" ice as a test system. It is emphasized that the adiabatic decoupling in CPMD is not a decoupling of electronic orbitals from the ions but only a decoupling of a subset of the orbital vibrational modes from the rest of the necessarily coupled system of orbitals and ions. Recent work [J. Chem. Phys. 116, 14 (2002)] has pointed out that, due to the orbital-ion coupling that remains once adiabatic decoupling has been achieved, a large value of the fictitious mass mu can lead to systematic errors in the computed forces in CPMD. These errors are further investigated in the present work with a focus on those parts of these errors that are not corrected simply by rescaling the masses of the ions. It is suggested that any comparison of the efficiencies of Born-Oppenheimer molecular dynamics (BOMD) and CPMD should be performed at a similar level of accuracy. If accuracy is judged according to the average magnitude of the systematic errors in the computed forces, the efficiency of BOMD compares more favorably to that of CPMD than previous comparisons have suggested.     

Copper-containing dendromesogens: the influence of the metal on the mesomorphism

The synthesis and liquid crystalline behaviour of the first and second generations of a dendrimeric structure based on poly(propyleneimine)(DAB-dendr(NH₂)_x) are reported. 4-(4-n-Alkoxybenzoyloxy)salicylaldehydes are used as mesogenic moieties attached at the peripheral amino groups of the dendrimers giving rise to dendromesogens with four and eight mesogenic branches. From these dendromesogens, considered as organic ligands, were prepared six metal-containing dendrimers which incorporate two or four copper atoms in their structures. All the dendrimeric ligands and three of the metal-containing dendrimers exhibit liquid crystalline properties which were studied by optical microscopy, DSC, X-ray diffraction and EPR spectroscopy.     

On the volume-dependence of the index of refraction from the viewpoint of the complex dielectric function and the Kramers-Kronig relation

How indices of refraction n(omega) of insulating solids are affected by the volume dilution of an optical entity and the mixing of different, noninteracting simple solid components was examined on the basis of the dielectric function epsilon(1)(omega) + iepsilon(2)(omega). For closely related insulating solids with an identical composition and the formula unit volume V, the relation [epsilon(1)(omega) - 1]V = constant was found by combining the relation epsilon(2)(omega)V = constant with the Kramers-Kronig relation. This relation becomes [n(2)(omega) - 1]V = constant for the index of refraction n(omega) determined for the incident light with energy less than the band gap (i.e., h omega < E(g)). For a narrow range of change in the formula unit volume, the latter relation is well approximated by a linear relation between n and 1/V.     

Copper-containing dendromesogens: the influence of the metal on the mesomorphism

The synthesis and liquid crystalline behaviour of the first and second generations of a dendrimeric structure based on poly(propyleneimine)(DAB-dendr(NH₂)_x) are reported. 4-(4-n-Alkoxybenzoyloxy)salicylaldehydes are used as mesogenic moieties attached at the peripheral amino groups of the dendrimers giving rise to dendromesogens with four and eight mesogenic branches. From these dendromesogens, considered as organic ligands, were prepared six metal-containing dendrimers which incorporate two or four copper atoms in their structures. All the dendrimeric ligands and three of the metal-containing dendrimers exhibit liquid crystalline properties which were studied by optical microscopy, DSC, X-ray diffraction and EPR spectroscopy.     

Structure of the xylan from the stems of the cotton plant

Summary 1. The structure of the aldobiuronic acid isolated from the xylan of cotton-plant stems has been established by its reduction and the hydrolysis of the reduced product.2. From a study of the products of the hydrolysis of the methylated xylan from cotton-plant stems the positions of attachment of the side chains in the molecule of the xylan and their structure have been determined, and a most probable structure for the xylan molecule has been put forward.V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 432–435, July–August, 1974.     

A boxmodel development to study the relationships between the photo-oxidants and the particles formation in the troposphere

The model BAGS (Boxmodel for Aerosol and Gasphase Simulations) has been developed. It is composed of two major modules: the first one describes the system of the chemical reactions in the gaseous phase, the second one calculates the aerosol chemical composition and the dimensional distribution of the particles. The boxmodel has been developed with the introduction of new chemical and physical processes, not previously included, in particular the formation of Secondary Organic Aerosol. The other implemented processes are a module for the dynamic of the particle population, nucleation, coagulation and dry deposition. The last phase of the work has been a check of the BAGS capabilities by a series of tests, that have permitted to compare it with other models (MAPS and MADM). The tests in particular have concerned the aerosol water content prediction, the photochemistry, the condensation of the inorganic compounds and the formation of Secondary Organic Aerosol.     

Influence of the errors made in the measurement of the extra-column volume on the accuracies of estimates of the column efficiency and the mass transfer kinetics parameters

The influences of the errors made in the measurement of the extra-column volume of an instrument on the accuracies of the estimates made of the column efficiency and of the parameters of the mass transfer kinetics were investigated from an experimental point of view. A standard HP1090 apparatus (extra-column volume, approximately 50 micro L) was used to measure the efficiency of a Sunfire-C(18) RPLC column (column hold-up volume, approximately 1.50 mL). The first and second moments of the peaks of phenol (a retained compound) and of thiourea (a practically non-retained compound) were measured at six different temperatures between 22 and 78 degrees C, for flow rates between 0.10 and 4.70 mL/min (i.e., for linear velocities between 0.025 and 1.179 cm/s). Each series of measurements was successively made with the instrument being fitted with and without the column. The experimental HETP data must be corrected for the solute dispersion in the connected tubes in order properly to assess the true column efficiency. Even with a modern, high performance instrument, the dispersion of a non-retained compound is essentially due to the band broadening phenomena that take place in the extra-column volumes, the sum of all these extra-column band broadening contributions accounting for more than 80% of the total band broadening measured. The contribution of the sampling device is particularly deleterious since, for a 2 mu L injection, the maximum solute concentration in the peak that enters into the column is nearly ten-fold lower than that of the sample. Nevertheless, the impact of the extra-column volumes on the estimates of the kinetic parameters (e.g., molecular diffusion coefficient D(m) and effective particle diffusivity D(e)) remains negligible. Obviously, the relative error made on the column efficiency of a retained compound depends much on its retention factor. It decreases from 8 to 1% when the retention factor increases from 5 to 17.     

On the polymerisation of the epoxidised biodiesel: The importance of the epoxy rings position,the process and the products

Polyesters were prepared using epoxidised methyl esters of oleic acid (EP_OAME) and epoxidised biodiesel (mixture of methyl esters) from sunflower oil (EP_SOME) and linseed oil (EP_LOME) with cis-1,2-cyclohexanedicarboxylic anhydride and triethylamine. The kinetic of partial processes involved in the polymerisation were elucidated and related to epoxy rings position in the fatty acid chain. The activation energies (E_a) for the epoxy ring opening by the catalyst are 298, 216 and 136 kJ/mol for EP_OAME, EP_SOME and EP_LOME respectively. The reactions of the epoxy rings in the positions C9–C10, C12–C13 and C15–C16 with anhydride require average activation energies of 116, 32 and 22 kJ/mol, respectively. The compensation effect between activation energy and pre-exponential factor is observed. The polymerisation enthalpy, molecular weight, glass transition temperature and electrical properties were determined. The polyesters studied show promising properties for use in various technological applications.     

Concerning the deprotonation of the trimethylsulfonium ion by the dimethylsulfinyl anion

As shown by deuterium labelling experiments, the deprotonation of the trimethylsulfonium ion (1) by the dimsyl anion (8) is accompanied by extensive hydrogen exchange. This cannot be explained by an acid-base equilibrium between the trimethylsulfonium ion (1) and the dimsyl anion (8) on one side and dimethylsulfonium methylide (2) and DMSO on the other side, because for thermodynamic reasons this process is irreversible due to the limited life-time of 2. Therefore, the isotopic exchange that accompanies the deprotonation is an indicator of a more complex deprotonation process. It is suggested that in a kinetically controlled reaction, a proton of 1 is transferred to the O-atom of 8 rather than to the carbanionic centre. This means that instead of DMSO, its tautomer, hydroxy-methylsulfonium methylide (10), is obtained in the deprotonation process. Similarly, in the acid-base interaction between DMSO and its conjugate base 8, the formation of the DMSO tautomer 10 is kinetically favoured. The intermediate 10 produced in this way transfers a DMSO-derived proton to 1 when it intervenes in the back reaction 10 + 2→8 + 1. An alternative mechanism based on methyl group exchange between 1 and 8 could be excluded by a (13)C-labelling experiment. The hydrogen exchange according to the suggested scenario is taking place in competition with the reaction of dimethylsulfonium methylide (2) with electrophilic substrates. This explains the different degrees of isotopic exchange when compounds of different electrophilicities are used to scavenge 2 from the deprotonation-hydrogen distribution equilibria.     

Analysis and assessment of the occurrence, the fate and the behavior of nanomaterials in the environment

Nanomaterials have one dimension <100 nm and possess physico-chemical properties dictated by their unusually small size, large surface area, shape and chemical composition. New properties of nanomaterials have boosted their production and industrial applications in many fields (e.g., microelectronics, catalysis, fuel cells, materials science, textiles, biotechnology and medicine). In biomedical fields, nanomaterials are of the appropriate dimensions to interact with biological matter. However, they may also have negative effects on biological systems. Nanotechnology is a major, innovative, scientific and economic growth area, but the increasing production and use of nanomaterials have led to calls for more information regarding the potential impacts that their release may have on human health and the environment.This review addresses analytical approaches for characterization and quantification of nanomaterials in the environment and recent studies on their occurrence, fate and behavior.     

Using of the Agglomeration-in-liquid for the Technology of the Fine Materials

The content of the fine and ultrafine particles in the raw material results in difficulty of the separation, the loss of the valuable components and ecological contamination. Secondary using of the fine particles is impossible without their granulation. This problem has been solved by the agglomeration-in-liquid method.An agglomeration-in-liquid method is a process to produce agglomerates in a liquid phase from solid particles suspended in the liquid. The surface of solid particles and the binding liquid must be of identical polarity, but the continuous phase must be of the opposite polarity. The water solutions of the surfactant are the binding liquids or the organic liquids.