Molecular dynamics simulations of the hydration of poly(vinyl methyl ether):Hydrogen bonds and quasi-hydrogen bonds

Atomistic detailed hydration structures of poly(vinyl methyl ether)(PVME) have been investigated by molecular dynamics simulations under 300 K at various concentrations. Both radial distribution functions and the distance distributions between donors and acceptors in hydrogen bonds show that the hydrogen bonds between the polymer and water are shorter by 0.005 nm than those between water molecules. The Quasi-hydrogen bonds take only 7.2% of the van der Waals interaction pairs. It was found the hydrogen bonds are not evenly distributed along the polymer chain,and there still exists a significant amount(10%) of ether oxygen atoms that are not hydrogen bonded to water at a concentration as low as 3.3%. This shows that in polymer solutions close contacts occur not only between polymer chains but also between chain segments within the polymer,which leads to inefficient contacts between ether oxygen atoms and water molecules. Variation of the quasi-hydrogen bonds with the concentration is similar to that of hydrogen bonds,but the ratio of the repeat units forming quasi-hydrogen bonds to those forming hydrogen bonds approaches 0.2. A transition was found in the demixing enthalpy at around 30% measured by dynamic testing differential scanning calorimetry(DTDSC) for aqueous solutions of a mono-dispersed low molecular weight PVME,which can be related to the transition of the fractions of hydrogen bonds and quasi-hydrogen bonds at ～27%. The transition of the fractions of hydrogen bonds and quasi-hydrogen bonds at ～27% can be used to explain the demixing enthalpy transition at 30% at a molecular scale. In addition,at the concentration of 86%,each ether oxygen atom bonded with water is assigned 1.56 water molecules on average,and 'free' water molecules emerge at the concentration of around 54%.     

CLOUD POINT CURVES OF POLY(ETHYLENE GLYCOL)/POLY(PROPYLENE GLYCOL) MIXTURES AND THEIR THERMODYNAMIC EXPLANATION

In the study of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) mixtures not only a bimodal shape but also a reverse trend of the dependence on molecular weight of the cloud point curves were observed.This trend indicates that the miscibility of the studied mixtures decreases as the molecular weight of one component decreases. The excess volumes of the mixtures show that the interaction parameter between two components decreases at first and increases after passing a minimum as the concentration of one component increases. This supports the explanation of Koningsveld on the bimodal shape of cloud point curves. Based on a binary interaction model a formula was derived revealing that the interaction between PPG and the end group of PEG and the hydrogen bonding interaction between ether and hydroxy end group inner or inter PEG molecules are not favorable for mixing. The latter interaction is an "attractive" force in PEG molecules. The two interactions are responsible for the observed abnormal dependence.     

Theoretical studies on the substitution effect of fluorine on ethylene

The substitution effect of fluorine on ethylene is investigated by means of studyingthe properties of the charge distribution at the bond critical points with the theory of atomsin molecules.It is found that fluorine atom acts not only as a σ electron acceptor,but also asa π electron donor,and these double effects are reflected in the quantity of ellipticity,Lap-lacian and the charge density of charge distribution at the bond critical points.For C—C,C—Fbonds,the major axis of elliptical contours is perpendicular to the molecular plane,but forC—H bond,it is parallel to the molecular plane.Other effects originating from the substi-tution have also been discussed.     

Studies on organophosphorus compounds 52.Structure-reactivity studies of organophosphorus compounds by MNDO calculations

MNDO and MM2(85)methods were used to study the conformation and the structure-reactivity relationship of neutral and acidic phosphorus esters.The calculation results indicate thatfor the most stable conformation,the charge density of phosphoryl oxygen(q_O)is determined notonly by the electronegativity of the substituents,but also by the conformation of the alkoxyl groupson the phosphorus atom.Meanwhile,the conformation of the alkoxyl group provides,as a rule,more important influence on the charge density of the phosphoryl oxygen.However,the energy ofthe highest occupied molecular orbital(EHOMO)is basically dependent on the eletronegativity of thesubstituents,while the donating ability or the withdrawing ability of the neutral phosphorus com-pounds is mainly governed by the EHOMO but not the q_O.This is also true for other kinds of theneutral oxygen-containing compounds.     

Influence of temperature on the structure of liquid water

Molecular dynamics simulations have been carried out for liquid water at 7 different temperatures to understand the nature of hydrogen bonding at molecular level through the investigation of the effects of temperature on the geometry of water molecules. The changes in bond length and bond angle of water molecules from gaseous state to liquid state have been observed, and the change in the bond angle of water molecules in liquid against temperature has been revealed, which has not been seen in literature so far. The analysis of the radial distribution functions and the coordinate numbers shows that, on an average, each water molecule in liquid acts as both receptor and donor, and forms at least two hydrogen bonds with its neigbors. The analysis of the results also indicates that the water molecules form clusters in liquid.     

In vitro digestibility of soybean β-conglycinin hydrolysates

The in vitro digestibility of alcalase enzymatic hydrolysates ofβ-conglycinin was studied.The results showed that the zeta potentials ofβ-conglycinin hydrolysates decreased and their electronegativity increased when digested with pepsin and trypsin.Furthermore,the content of peptides with molecular weight from 10 kDa to 20 kDa remained stable,while those with higher molecular weight(>20 kDa) decreased,and those with lower molecular weight(<10 kDa) increased.The proportion of highly hydrophobic peptides decreased in the process of the in vitro digestion,but no significant change in the surface hydropliobicity indices of digestion products was observed(P<0.05).These results indicate that theβ-congiycinin hydrolysates were degraded through in vitro digestion,but the degree of degradation was relatively low.Peptides with molecular weight from 10 kDa to 20 kDa in theβ-conglycinin hydrolysates resisted the digestion by pepsin and trypsin and they remained stable during the in vitro digestion processes.     

Observations of carbon–carbon coupling of 4,4'-dibromo-p-terphenyl on Cu(110) surface at molecular level

The carbon–carbon couplings of 4,4'-dibromo-p-terphenyl(DBTP) on Cu(110) surface have been investigated at a single molecular level by scanning tunneling microscopy. After annealing at 353 K, a mixture of parallel non-organometallic and organometallic intermediates of DBTP molecules along the[1–10] direction of the surface has been observed. Further annealing at 393 K causes one group of molecules to form oligomers with para-para and para-meta motifs via Ullmann reaction and the other group of molecules to synthesize oligomers with meta-meta motifs via direct carbon–carbon coupling reaction. Statistical results directly reveal that the occurrence of reaction type is strongly related to the initial binding configuration of DBTP molecules.     

Theoretical Study on Co^3＋ in Aqueous Solution in Terms of ABEEM/MM Model

A detailed theoretical investigation on Co^3＋ hydration in aqueous solution has been carded out by means of molecular dynamics （MD） simulations based on the atom-bond electronegativity equalization method fused into molecular mechanics （ABEEM/MM）. The effective Co^3＋ ion-water potential has been constructed by fitting to ab initio structures and binding energies for ionic clusters. And then the ion-water interaction potential was applied in combination with the ABEEM-7P water model to molecular dynamics simulations of single Co^3＋（aq.） solution, managing to reproduce many experimental structural and dynamical properties of the solution. Here, not only the common properties （radial distribution function, angular distribution function and solvation energy） obtained for Co^3＋ in ABEEM-7P water solution were in good agreement with those from the experimental methods and other molecular dynamics simulations but also very interesting properties of charge distributions, geometries of water molecules, hydrogen bond, diffusion coefficients, vibrational spectra are investigated by ABEEM/MM model.     

Mean Residence Time of CO2 Molecules in Flexible ZIF-8 Cages Explored by Molecular Dynamics Simulations

The adsorption sites and diffusion mechanism of CO2 molecules in the flexible Zn（MeIM）2 （MeIM=2-methylimidazole） （ZIF-8） have been investigated by grand canonical Monte Carlo and molecular dynamics simulations. A reasonable time correlation function is for the first time constructed to explore the mean residence time of CO2 molecules in the ZIF-8 cages, suggesting that C02 molecules can remain in the same cage for up to several tens of picoseconds. Furthermore, we find that the mean residence time almost linearly increases with the increasing pressure （or loading） at 273 and 298 K.     

Preparation of Highly Loaded PAA/PAH Layer-by-layer Films by Combining Acid Transformation and Templating Methods

Enhancing the molecular loading capability of layer-by-layer(LbL)method holds high importance in environmental and biomedical application.Here,we reported a strategy to prepare highly loaded poly(acrylic acid)(PAA)/poly(allylamine hydrochloride)(PAH)LbL films by combining the particulate templating strategy and acid treatment film transformation and realized tlae efficient loading of hydrophilic small molecules.The loaded molecules can be released in a pH-controlled manner.A slow release speed was observed in the acidic solutions with pH value of 3.Abrupt releases were observed at higher pH values(5 or 7).     

Determination of the enthalpy of fusion of K<Subscript>3</Subscript>TaO<Subscript>2</Subscript>F<Subscript>4</Subscript> and KTaF<Subscript>6</Subscript>

Areas of fusion and crystallization peaks of K₃TaO₂F₄ and KTaF₆ were measured using the DSC mode of a high-temperature calorimeter (SETARAM 1800 K). On the basis of these quantities, considering the temperature dependence of the calorimeter sensitivity, values of the fusion enthalpy of K₃TaO₂F₄ at the fusion temperature of 1181 K of (43 ± 4) kJ mol⁻¹ and of KTaF₆ at the fusion temperature of 760 K of (8 ± 1) kJ mol⁻¹ were determined.     

2,4‐Di­nitro­phenyl­hydrazones of 2,4‐di­hydroxy­benz­aldehyde, 2,4‐di­hydroxy­aceto­phenone and 2,4‐di­hydroxy­benzo­phenone

In 2,4‐di­hydroxy­benz­aldehyde 2,4‐di­nitro­phenyl­hydrazone N,N‐di­methyl­form­amide solvate {or 4‐[(2,4‐di­nitro­phenyl)­hydrazono­methyl]­benzene‐1,3‐diol N,N‐di­methyl­form­amide solvate}, C₁₃H₁₀N₄O₆·C₃H₇NO, (X), 2,4‐di­hydroxy­aceto­phenone 2,4‐di­nitro­phenyl­hydrazone N,N‐di­methyl­form­am­ide solvate (or 4‐{1‐[(2,4‐di­nitro­phenyl)hydrazono]ethyl}benzene‐1,3‐diol N,N‐di­methyl­form­amide solvate), C₁₄H₁₂N₄O₆·C₃H₇NO, (XI), and 2,4‐di­hydroxy­benzo­phenone 2,4‐di­nitro­phenyl­hydrazone N,N‐di­methyl­acet­amide solvate (or 4‐­{[(2,4‐di­nitro­phenyl)hydrazono]phenyl­methyl}benzene‐1,3‐diol N,N‐di­methyl­acet­amide solvate), C₁₉H₁₄N₄O₆·C₄H₉NO, (XII), the molecules all lack a center of symmetry, crystallize in centrosymmetric space groups and have been observed to exhibit non‐linear optical activity. In each case, the hydrazone skeleton is fairly planar, facilitated by the presence of two intramolecular hydrogen bonds and some partial N—N double‐bond character. Each molecule is hydrogen bonded to one solvent mol­ecule.     

“蒸馏酒”还是“发酵酒”——对《科学史导论》中“spirits” 和“distillation”的再思考

科学史奠基者乔治·萨顿在《科学史导论》第二卷的第一部分对我国宋代酿酒著作《北山酒经》予以了简要描述,出现了“spirits”“distillation”等字样;而《北山酒经》被众多学者认为其描述对象是发酵酒(黄酒)。本文从东西方蒸馏技术和相关著作的文本分析对《科学史导论》中提及的蒸馏技术和蒸馏酒存在的可能性提出了质疑。     

Projection of the liquidus surface of the Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>-Gd<Subscript>2</Subscript>Te<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> system

Phase equilibria in the Sb₂Te₃-Gd₂Te₃-Bi₂Te₃ ternary system have been studied using differential thermal analysis, namely, X-ray powder diffraction, microstructure examination, thermodynamic analysis, and microhardness and alloy density measurements. Phase diagrams of some polythermal joins and liquidus surface have been constructed. The regions of primary crystallization of phases and the coordinates of all invariant and univariant equilibria in the system under investigation have been established.     

Crystal structure of the synthetic analog of radtkeite Hg<Subscript>3</Subscript>S<Subscript>2</Subscript>Cl<Subscript>1.00</Subscript>I<Subscript>1.00</Subscript>

The results of structural studies of the synthetic analog of the radtkeite mineral Hg₃S₂Cl_1.00I_1.00 are analyzed. The crystal structure of the compound has been refined; the unit cell parameters are a _m = 16.827(4) , b _m = 9.117(1) , c _m = 13.165(5) , = 130.17(2)°, V = 1543.3(8) ³, space group C2/m, Z = 8, R = 0.0527. A possible transition a ₀ = a _m; b ₀ = a _m + 2c _m; c ₀ = –b _m to the pseudo-orthorhombic F cell previously determined for radtkeite, where one of the angles ( ₀ ) is slightly different from 90° (89.55°), has been found. Each sulfur atom in the structure is bonded to three mercury atoms, forming SHg₃ umbrellas with distances 2.240(6) –2.474(8) and angles HgSHg 94.7(2)°–102.9(2)°. The SHg₃ fragments are linked through Hg vertices to form corrugated [Hg₁₂S₈] layers. The halogen atoms lie inside and between the [Hg₁₂S₈] layers; the distances are Hg-Cl and Hg-I 2.783(7) , 2.961(7) , and 3.083(4) –3.311(3) , respectively.Original Russian Text Copyright © 2004 by N. V. Pervukhina, S. V. Borisov, S. A. Magarill, D. Yu. Naumov, V. I. Vasiliev, and B. G. NenashevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 755–758, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Physicochemical foundations of synthesis of new ferromagnets from chalcopyrites A<Superscript>II</Superscript>B<Superscript>IV</Superscript>C<Stack><Subscript>2</Subscript><Superscript>V</Superscript></Stack>

The results of studying phase equilibria of ternary A^IIB^IVC^V systems have been reported. Physicochemical foundations have been developed for the synthesis of new ferromagnets with Curie temperatures above room temperature structurally compatible with basic semiconducting materials. Methods of synthesis and physicochemical properties of manganese-doped A^IIB^IVC₂^V ferromagnets have been described. The results of theoretical simulation of magnetic properties have been considered and basic approaches to the explanation of the emergence of ferromagnetism in A^IIB^IVC₂^V doped with 3d metals have been surveyed. The most promising ways to produce and study dilute magnetic semiconductors as spintronics materials have been presented.     

Calculations of thermodynamic stability of CpCoC<Subscript>2</Subscript>B<Subscript>9</Subscript>H<Subscript>11</Subscript> cobaltacarborane isomers

Quantum-chemical calculations of the geometry and energies of nine possible isomers of 12-vertex cobaltacarborane CpCoC₂B₉H₁₁ (1) were carried out by the DFT method (PBEPBE/DGDZVP/DGA1). Thermodynamic stability of the isomers increases with increasing distance between the carbon atoms in the cage and is virtually independent of the position of the CpCo vertex. The relative stabilities of the 1,2,3-(17.57 kcal mol⁻¹), 1,2,4-(3.72 kcal mol⁻¹), and 1,2,9-isomers of 1 (0 kcal mol⁻¹) are similar to the corresponding values for the ortho (17.61 kcal mol⁻¹), meta (3.21 kcal mol⁻¹), and para isomers (0 kcal mol⁻¹) of carborane C₂B₁₀H₁₂. The results of the present study confirm a close similarity of the CpCo and BH fragments in metallacarborane chemistry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1557–1559, July, 2005.     

Influence of composition on corroding process of Na<Subscript>2</Subscript>O-K<Subscript>2</Subscript>O-CaO-ZrO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> glasses

The corroding process of six glasses of the Na₂O-K₂O-CaO-ZrO₂-SiO₂ system with ZrO₂content 0–2.13 mass % by water was observed during static tests at 121°C and pressure of 0.25 MPa in steam sterilizer. Significant increase of Na⁺ and K⁺ content in leachates was observed after the addition of ZrO₂ into glass. Further increase of the content of ZrO₂ in glasses slowed down the rate of Na⁺ and K⁺ leaching. The leaching process of SiO₂ as well as Na⁺, K⁺, and Ca²⁺ ions was evaluated on the basis of comparison with model leaching processes. Variation of the concentrations of Na⁺, K⁺, Ca²⁺, and SiO₂ in leachates with time was described by empirical equation. Observed changes in the initial leaching rates of Na⁺, K⁺, Ca²⁺, and SiO₂ can be ascribed to the content of ZrO₂ in glasses. The presence of ZrO₂ in glasses reduced the overall rate of glass dissolution.     

Determination of the enthalpy of fusion of K<Subscript>3</Subscript>NbO<Subscript>2</Subscript>F<Subscript>4</Subscript>

Areas of fusion and crystallization peaks of K₃NbO₂F₄ were measured using the DCS mode of a high-temperature calorimeter (SETARAM 1800 K). On the basis of these quantities, considering the temperature dependence of the calorimeter sensitivity, the value of the fusion enthalpy of K₃NbO₂F₄ of (98 ± 6) kJ mol⁻¹ was determined at the fusion temperature of 1257 K.     

Ionic conduction of a high-temperature modification of Lu<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript>

A nanoceramic product of the composition Lu₂Ti₂O₇ is synthesized by a coprecipitation method with a subsequent sublimation drying and an annealing at 650–1650°C. The conduction of Lu₂Ti₂O₇ synthesized at 1650°C is ionic (10^–3 S cm^–1 at 800°C). Thus, a new material with a high ionic conduction has been discovered. The ordering in Lu₂Ti₂O₇ is studied by methods of RFA, RSA, IK spectroscopy, electron microscopy, and impedance spectroscopy. The existence of a low-temperature phase transition fluorite-pyrochlore at 800°C and a high-temperature conversion order-disorder at 1650°C are established.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 298–303.Original Russian Text Copyright © 2005 by Shlyakhtina, Ukshe, Shcherbakova.