Based on the molecular theory of non-linear viscoelasticity with constrained entanglements in polymer melts, the material functions in simple shear flow were formulated, the theoretical relations between. eta((gamma) ...Based on the molecular theory of non-linear viscoelasticity with constrained entanglements in polymer melts, the material functions in simple shear flow were formulated, the theoretical relations between. eta((gamma) over dot), psi (10)((gamma) over dot) and shear rate ((gamma) over dot), and topologically constrained dimension number n ' and a were derived. Linear viscoelastic parameters (eta (0) and G(N)(0)) and topologically constrained dimension number (n ' a and <(<upsilon>)over bar>) as a function of the primary molecular weight (M-n), molecular weight between entanglements (M-C) and the entanglement sites sequence distribution in polymer chain were determined. A new method for determination of viscoelastic parameters (eta (0), psi (10), G(N)(0) and J(e)(0)), topologically constrained dimension number (n ', a and v) and molecular weight (M-n, M-c and M-e) from the shear flow measurements was proposed. It was used to determine those parameters and structures of HDPE, making a good agreement between these values and those obtained by other methods. The agreement affords a quantitative verification for the molecular theory of nonlinear viscoelasticity with constrained entanglement in polymer melts.展开更多
The microscopic moleeular theory for electron transfer in a model solvent ishahr developed. The nonlinear response of the solvent molecules is be computedquanitatively in a new way. Adopting computer simulation daa an...The microscopic moleeular theory for electron transfer in a model solvent ishahr developed. The nonlinear response of the solvent molecules is be computedquanitatively in a new way. Adopting computer simulation daa and choosingappropriate reaction coordinae, a reasonable free energy dinram is constructed and thercorganhaion energy for the product state is calculated.展开更多
Fractional molecular field theory(FMFT)is a phenomenological theory that describes phase transitions in crystals with randomly distributed components,such as the relaxor-ferroelectrics and spin glasses.In order to ver...Fractional molecular field theory(FMFT)is a phenomenological theory that describes phase transitions in crystals with randomly distributed components,such as the relaxor-ferroelectrics and spin glasses.In order to verify the feasibility of this theory,this paper fits it to the Monte Carlo simulations of specific heat and susceptibility versus temperature of two-dimensional(2D)random-site Ising model(2D-RSIM).The results indicate that the FMFT deviates from the 2D-RSIM significantly.The main reason for the deviation is that the 2D-RSIM is a typical system of component random distribution,where the real order parameter is spatially heterogeneous and has no symmetry of space translation,but the basic assumption of FMFT means that the parameter is spatially uniform and has symmetry of space translation.展开更多
The critical _d vahues ( _ ) of the γ/(γ+σ).γ/(γ+μ) and γ/(γ+γ') phase boundaries in some ternar alloy phase diagrams at various temperatures are calculated by averaging the _d values of sererai selecte...The critical _d vahues ( _ ) of the γ/(γ+σ).γ/(γ+μ) and γ/(γ+γ') phase boundaries in some ternar alloy phase diagrams at various temperatures are calculated by averaging the _d values of sererai selected characteristic points at the phase boundaries.Approxmate equations for the temperature dependence of the critical _d of γ/(γ+σ).γ/(γ+μ) and γ/(γ+γ') phase boundaries are established.The accuracy of the analysis is discussed in detail. It is found for the first time that the average value of the bond order _ at the phase boundaries ts also approximatelr a constant and therefore a critical average bond order _ like - can be introduced for the analysts of phase stability展开更多
Basea on the new model and concept of mtramolecular orientational order parameter, a molecular field theory was built up for main chain liquid crystalline polymer (MC-LCPs) with flexible spacers. The theory takes acco...Basea on the new model and concept of mtramolecular orientational order parameter, a molecular field theory was built up for main chain liquid crystalline polymer (MC-LCPs) with flexible spacers. The theory takes account of orientational correlation among all mesogens in a polymer chain and the relationship between the intramolecular orientation and spatial orientation of the mesogens. The free energy, temperature and entropy of the nematic-isotropic transition were determined with the theory and compared with experiments in current work. It was found that many unique transition properties of the MC-LCPs comprising flexible spacer are correctly predicted by the theory and the agreement of the theory with the experiments is impressive.展开更多
The single reference second order Brillouin-Wigner perturbation theory recently developed, which eliminates its size-extensivity error, has been generalized to state-specific, multi-reference （SS-MR）, BWPT2 providin...The single reference second order Brillouin-Wigner perturbation theory recently developed, which eliminates its size-extensivity error, has been generalized to state-specific, multi-reference （SS-MR）, BWPT2 providing a size-extensive correction to the electron correlation problem for systems that demand the use of a multi-reference function. Illustrative numerical tests of the size-extensivity corrections are made for widely used molecules in their ground states, which are pronounced multi-reference characteristics. We have implemented two-reference and three-reference cases for CH2, BH and bond breaking process in the ground states of HF molecules. The results are compared with the rigorously size-extensive methods such as the M^ller-Plesset perturbation theory, i.e., MP2, full configuration interaction （Full-CI） and allied methods using the same basis sets.展开更多
The temperature dependent magnetization of the (Ce,Nd) 2(Fe,Si,Mn) 17 intermetallic compounds were measured and analyzed by molecular field theory (MFT). The relationship between T C and the intrasublattic...The temperature dependent magnetization of the (Ce,Nd) 2(Fe,Si,Mn) 17 intermetallic compounds were measured and analyzed by molecular field theory (MFT). The relationship between T C and the intrasublattice coupling interactions was discussed. The two sublattice MFT model can well describe the temperature dependence of the magnetization for all the compounds investigated. Ce ion in (Ce,Nd) 2Fe 17 compounds does not simply dilute the magnetic structure, but is likely present in a mixed valence state. The substitution of Si for Fe strongly raises T C and the mean Fe moment remains unchanged for Ce 2(Si,Fe) 17 compounds, and the 3d exchange coupling constant J FF increases linearly. Mn decreases T C of Nd 2(Mn, Fe) 17 compound by reducing J FF .展开更多
Elemene, derived from Curcuma wenyujin, one of the "8 famous genuine medicinal materials of Zhejiang province," exhibits remarkable antitumor activity. It has gained wide recognition in clinical practice for...Elemene, derived from Curcuma wenyujin, one of the "8 famous genuine medicinal materials of Zhejiang province," exhibits remarkable antitumor activity. It has gained wide recognition in clinical practice for effectiveness on tumors. Dr. XIE Tian introduced the innovative concept of "molecular compatibility theory" by combining Chinese medicine principles, specifically the "monarch, minister, assistant, and envoy" theory, with modern biomedical technology. This groundbreaking approach, along with a systematic analysis of Chinese medicine and modern biomedical knowledge, led to the development of elemene nanoliposome formulations. These novel formulations offer numerous advantages, including low toxicity, well-defined composition, synergistic effects on multiple targets, and excellent biocompatibility. Following the principles of the "molecular compatibility theory", further exploration of cancer treatment strategies and methods based on elemene was undertaken. This comprehensive review consolidates the current understanding of elemene's potential antitumor mechanisms, recent clinical investigations, advancements in drug delivery systems, and structural modifications. The ultimate goal of this review is to establish a solid theoretical foundation for researchers, empowering them to develop more effective antitumor drugs based on the principles of "molecular compatibility theory".展开更多
In this paper, we use a molecular theory to study the anomalous switching of ssDNA monolayers. Here, both ssDNA- water and water-water hydrogen bonds and their explicit coupling to the ssDNA conformations are consider...In this paper, we use a molecular theory to study the anomalous switching of ssDNA monolayers. Here, both ssDNA- water and water-water hydrogen bonds and their explicit coupling to the ssDNA conformations are considered. We find that hydrogen bonding becomes a key element in inducing the anomalous switching of ssDNA monolayers. This finding accords well with the experimental observations. Based on our theoretical model, we predict that the anomalous switching induced by water vapor will be applicable to a wide range of hydrogen bonds polymers, and ssDNA-water hydrogen bonds and water-water hydrogen bonds hybridization will lead to the hydrogen-bond network formation of 3D ssDNA monolayers.展开更多
By employing molecular theory, we systematically investigate the shift of solubility of poly（N-isopropylacrylamide）（PNIPAM） brushes in sodium halide solutions. After considering PNIPAM–water hydrogen bonds, water...By employing molecular theory, we systematically investigate the shift of solubility of poly（N-isopropylacrylamide）（PNIPAM） brushes in sodium halide solutions. After considering PNIPAM–water hydrogen bonds, water–anion hydrogen bonds, and PNIPAM–anion bonds and their explicit coupling to the PNIPAM conformations, we find that increasing temperature lowers the solubility of PNIPAM, and results in a collapse of the layer at high enough temperatures. The combination of the three types of bonds would yield a decrease in the solubility of PNIPAM following the Hofmeister series： Na Cl＆gt;Na Br＆gt;Na I. PNIPAM–water hydrogen bonds are affected by water–anion hydrogen bonds and PNIPAM–anion bonds. The coupling of polymer conformations and the competition among the three types of bonds are essential for describing correctly a decrease in the solubility of PNIPAM brushes, which is determined by the free energy associated with the formation of the three types of bonds. Our results agree well with the experimental observations, and would be very important for understanding the shift of the lower critical solution temperature of PNIPAM brushes following the Hofmeister series.展开更多
Using a molecular theory, we investigate the temperature-dependent self-assembly of single-stranded DNA（ss DNA）tethered to a charged nanoparticle surface. Here the size, conformations, and charge properties of ss DN...Using a molecular theory, we investigate the temperature-dependent self-assembly of single-stranded DNA（ss DNA）tethered to a charged nanoparticle surface. Here the size, conformations, and charge properties of ss DNA are taken into account. The main results are as follows： i） when the temperature is lower than the critical switching temperature, the ss DNA will collapse due to the existence of electrostatic interaction between ss DNA and charged nanoparticle surface; ii）for the short ss DNA chains with the number of bases less than 10, the switching of ss DNA cannot happen, and the critical temperature does not exist; iii） when the temperature increases, the electrostatic attractive interaction between ss DNA and charged nanoparticle surface becomes weak dramatically, and ss DNA chains will stretch if the electrostatic attractive interaction is insufficient to overcome the elastic energy of ss DNA and the electrostatic repulsion energy. These findings accord well with the experimental observations. It is predicted that the switching of ss DNA will not happen if the grafting densities are too high.展开更多
The chemisorption properties of N^18O adsorption on TiO2(110) surface were investigated by experimental and theoretical methods. The results of temperature programmed desorption (TPD) indicated that the temperatures o...The chemisorption properties of N^18O adsorption on TiO2(110) surface were investigated by experimental and theoretical methods. The results of temperature programmed desorption (TPD) indicated that the temperatures of the three desorption peaks of the main N2 molecules were at (low) temperature of 230 K, 450 K, and (high) temperature of 980 K. This meant that N^18O decomposed and recombined during the process of N2 desorption after N^18O was exposed. Analysis of thestable combination and orbital theory calculation of the surface reaction of NO adsorption on the TiO2(110) cluster modelshowed that there was clear preference for the Ti-NO orientation.展开更多
The Ti-Supported MnO_2 electrode was modified by introducing SnO_2+RuO_2+MnO_2 as an intermediate layer into the Ti/MnO_2 interface. The anodic polarization curves were measured at various temperatures ranging from 30...The Ti-Supported MnO_2 electrode was modified by introducing SnO_2+RuO_2+MnO_2 as an intermediate layer into the Ti/MnO_2 interface. The anodic polarization curves were measured at various temperatures ranging from 30 to 80℃ and the activation energy for the oxygen evolution reaction was evaluated. The experimental activation energy increased linearly with increasing the overpotential. The activation energy at the equilibrium potential was linearly correlated with the difference between the crystal field stabilization energies of Mn^(4+) at initial state and Mn^(4+) at transition state. The electrocatalysis characteristics of the anode were discussed by means of the mechanism of the substitution reaction of the ligand(S_N1 and S_N2) and molecular orbital theory. The results show that the anode has better electrocatalystic characteristics.展开更多
A convenient synthesis and theoretical study of five CCK-functional dendrimers is described. The dendritic cores were linked with the CCK（Trp-Met-Asp（OBn）-PheNH2） fragment by forming amide bonds to give five targe...A convenient synthesis and theoretical study of five CCK-functional dendrimers is described. The dendritic cores were linked with the CCK（Trp-Met-Asp（OBn）-PheNH2） fragment by forming amide bonds to give five target molecules. The structures of CCK-functional dendrimers were characterized by NMR, MS spectrum and predicted using molecular mechanics and PM3 semi- empirical molecular orbital theory.展开更多
Water flooding is widely applied for pressure maintenance or increasing the oil recovery of reservoirs.The heterogeneity and wettability of formation rocks strongly affect the oil recovery efficiency in carbonate rese...Water flooding is widely applied for pressure maintenance or increasing the oil recovery of reservoirs.The heterogeneity and wettability of formation rocks strongly affect the oil recovery efficiency in carbonate reservoirs.During seawater injection in carbonate formations,the interactions between potential seawater ions and the carbonate rock at a high temperature can alter the wettability to a more water-wet condition.This paper studies the wettability of one of the Iranian carbonate reservoirs which has been under Persian Gulf seawater injection for more than 10 years.The wettability of the rock is determined by indirect contact angle measurement using Rise in Core technique.Further,the characterization of the rock surface is evaluated by molecular kinetic theory(MKT)modeling.The data obtained from experiments show that rocks are undergoing neutral wetting after the aging process.While the wettability of low permeable samples changes to be slightly water-wet,the wettability of the samples with higher permeability remains unchanged after soaking in seawater.Experimental data and MKT analysis indicate that wettability alteration of these carbonate rocks through prolonged seawater injection might be insignificant.展开更多
Ab initio molecular orbital calculations of doubly negative charged B16H162-(D2) and neutral B16H16(Td) have been done at the HF/6-31G level.They are predicted to be chemically and kinetically stable by vibrational an...Ab initio molecular orbital calculations of doubly negative charged B16H162-(D2) and neutral B16H16(Td) have been done at the HF/6-31G level.They are predicted to be chemically and kinetically stable by vibrational analyses on their respective energy hypersurface of the HF/6-31G level.The geometrical structure of the species B16H1622-(D2) was discussed.展开更多
Nine phthalates were calculated at the B3LYP/6-311G＊＊ level using DFT method. The corresponding linear relationship equations （R2 were 0.853 and 0.936 respectively） for the biodegradation rate （Kb） and half-life...Nine phthalates were calculated at the B3LYP/6-311G＊＊ level using DFT method. The corresponding linear relationship equations （R2 were 0.853 and 0.936 respectively） for the biodegradation rate （Kb） and half-life time （h/2） of biodegradation were obtained with the structural parameters as theoretical descriptors. Furthermore, CoMFA method was also applied to establish 3D models which revealed the fields influencing these properties. The relationship between the properties and the structure was obtained. The correlation coefficients of the models were 0.992 and 0.999, respectively. Analyses of 2D and 3D models demonstrated that the molecular volume was an important factor affecting the biodegradability of these compounds.展开更多
The micro-capsules used for drug delivery are fabricated using polylactic acid（PLA）,which is a biomedical material approved by the FDA.A coarse-grained model of long-chain PLA was built,and molecular dynamics（MD）s...The micro-capsules used for drug delivery are fabricated using polylactic acid（PLA）,which is a biomedical material approved by the FDA.A coarse-grained model of long-chain PLA was built,and molecular dynamics（MD）simulations of the model were performed using a MARTINI force field.Based on the nonlocal theory,the formula for the initial elastic modulus of polymers considering the nonlocal effect was derived,and the scaling law of internal characteristic length of polymers was proposed,which was used to adjust the cut-off radius in the MD simulations of PLA.The results show that the elastic modulus should be computed using nonlinear regression.The nonlocal effect has a certain influence on the simulation results of PLA.According to the scaling law,the cut-off radius was determined and applied to the MD simulations,the results of which reflect the influence of the molecular weight change on the elastic moduli of PLA,and are in agreement with the experimental outcome.展开更多
The 1,3-dipolar cycloaddition reactions of various substituted ynamines with hydrazoic acid were theoretically investigated with the high-accuracy CBS-QB3 method. Two regioisomers, 4-amine, and 5-amine substituted add...The 1,3-dipolar cycloaddition reactions of various substituted ynamines with hydrazoic acid were theoretically investigated with the high-accuracy CBS-QB3 method. Two regioisomers, 4-amine, and 5-amine substituted adducts, were obtained, with the former as the preferred yield. This regioselectivity is rationalized by the frontier molecular orbital theory. The reactivity and synchronicity are enhanced with the increase of the electron-withdrawing character of the substitute on ynamine fragment. The calculations also show that the effect of solvent increases the activation energy, and the reaction becomes even harder in polar solvent.展开更多
Modern computer simulations of biological systems often involve an explicit treatment of the complex interactions among a large number of molecules. While it is straightforward to compute the short-ranged Van der Waal...Modern computer simulations of biological systems often involve an explicit treatment of the complex interactions among a large number of molecules. While it is straightforward to compute the short-ranged Van der Waals interaction in classical molecular dynamics simulations, it has been a long-lasting issue to develop accurate methods for the longranged Coulomb interaction. In this short review, we discuss three types of methodologies for the accurate treatment of electrostatics in simulations of explicit molecules： truncation-type methods, Ewald-type methods, and mean-field-type methods. Throughout the discussion, we brief the formulations and developments of these methods, emphasize the intrinsic connections among the three types of methods, and focus on the existing problems which are often associated with the boundary conditions of electrostatics. This brief survey is summarized with a short perspective on future trends along the method developments and applications in the field of biological simulations.展开更多
基金The authors gratefully a.cknowledge financial supportfrom th6 Natiol-al Natural Science Foundatiol- of CI-h-a. The number of
文摘Based on the molecular theory of non-linear viscoelasticity with constrained entanglements in polymer melts, the material functions in simple shear flow were formulated, the theoretical relations between. eta((gamma) over dot), psi (10)((gamma) over dot) and shear rate ((gamma) over dot), and topologically constrained dimension number n ' and a were derived. Linear viscoelastic parameters (eta (0) and G(N)(0)) and topologically constrained dimension number (n ' a and <(<upsilon>)over bar>) as a function of the primary molecular weight (M-n), molecular weight between entanglements (M-C) and the entanglement sites sequence distribution in polymer chain were determined. A new method for determination of viscoelastic parameters (eta (0), psi (10), G(N)(0) and J(e)(0)), topologically constrained dimension number (n ', a and v) and molecular weight (M-n, M-c and M-e) from the shear flow measurements was proposed. It was used to determine those parameters and structures of HDPE, making a good agreement between these values and those obtained by other methods. The agreement affords a quantitative verification for the molecular theory of nonlinear viscoelasticity with constrained entanglement in polymer melts.
文摘The microscopic moleeular theory for electron transfer in a model solvent ishahr developed. The nonlinear response of the solvent molecules is be computedquanitatively in a new way. Adopting computer simulation daa and choosingappropriate reaction coordinae, a reasonable free energy dinram is constructed and thercorganhaion energy for the product state is calculated.
基金Project supported by the Open Project of the Key Laboratory of Xinjiang Uygur Autonomous Region,China(Grant No.2021D04015)the Yili Kazakh Autonomous Prefecture Science and Technology Program Project,China(Grant No.YZ2022B021).
文摘Fractional molecular field theory(FMFT)is a phenomenological theory that describes phase transitions in crystals with randomly distributed components,such as the relaxor-ferroelectrics and spin glasses.In order to verify the feasibility of this theory,this paper fits it to the Monte Carlo simulations of specific heat and susceptibility versus temperature of two-dimensional(2D)random-site Ising model(2D-RSIM).The results indicate that the FMFT deviates from the 2D-RSIM significantly.The main reason for the deviation is that the 2D-RSIM is a typical system of component random distribution,where the real order parameter is spatially heterogeneous and has no symmetry of space translation,but the basic assumption of FMFT means that the parameter is spatially uniform and has symmetry of space translation.
文摘The critical _d vahues ( _ ) of the γ/(γ+σ).γ/(γ+μ) and γ/(γ+γ') phase boundaries in some ternar alloy phase diagrams at various temperatures are calculated by averaging the _d values of sererai selected characteristic points at the phase boundaries.Approxmate equations for the temperature dependence of the critical _d of γ/(γ+σ).γ/(γ+μ) and γ/(γ+γ') phase boundaries are established.The accuracy of the analysis is discussed in detail. It is found for the first time that the average value of the bond order _ at the phase boundaries ts also approximatelr a constant and therefore a critical average bond order _ like - can be introduced for the analysts of phase stability
文摘Basea on the new model and concept of mtramolecular orientational order parameter, a molecular field theory was built up for main chain liquid crystalline polymer (MC-LCPs) with flexible spacers. The theory takes account of orientational correlation among all mesogens in a polymer chain and the relationship between the intramolecular orientation and spatial orientation of the mesogens. The free energy, temperature and entropy of the nematic-isotropic transition were determined with the theory and compared with experiments in current work. It was found that many unique transition properties of the MC-LCPs comprising flexible spacer are correctly predicted by the theory and the agreement of the theory with the experiments is impressive.
基金Supported by the Scientific and Technological Research Council of Turkey(TUBITAK)under Grant No 2219-1/2013
文摘The single reference second order Brillouin-Wigner perturbation theory recently developed, which eliminates its size-extensivity error, has been generalized to state-specific, multi-reference （SS-MR）, BWPT2 providing a size-extensive correction to the electron correlation problem for systems that demand the use of a multi-reference function. Illustrative numerical tests of the size-extensivity corrections are made for widely used molecules in their ground states, which are pronounced multi-reference characteristics. We have implemented two-reference and three-reference cases for CH2, BH and bond breaking process in the ground states of HF molecules. The results are compared with the rigorously size-extensive methods such as the M^ller-Plesset perturbation theory, i.e., MP2, full configuration interaction （Full-CI） and allied methods using the same basis sets.
文摘The temperature dependent magnetization of the (Ce,Nd) 2(Fe,Si,Mn) 17 intermetallic compounds were measured and analyzed by molecular field theory (MFT). The relationship between T C and the intrasublattice coupling interactions was discussed. The two sublattice MFT model can well describe the temperature dependence of the magnetization for all the compounds investigated. Ce ion in (Ce,Nd) 2Fe 17 compounds does not simply dilute the magnetic structure, but is likely present in a mixed valence state. The substitution of Si for Fe strongly raises T C and the mean Fe moment remains unchanged for Ce 2(Si,Fe) 17 compounds, and the 3d exchange coupling constant J FF increases linearly. Mn decreases T C of Nd 2(Mn, Fe) 17 compound by reducing J FF .
文摘Elemene, derived from Curcuma wenyujin, one of the "8 famous genuine medicinal materials of Zhejiang province," exhibits remarkable antitumor activity. It has gained wide recognition in clinical practice for effectiveness on tumors. Dr. XIE Tian introduced the innovative concept of "molecular compatibility theory" by combining Chinese medicine principles, specifically the "monarch, minister, assistant, and envoy" theory, with modern biomedical technology. This groundbreaking approach, along with a systematic analysis of Chinese medicine and modern biomedical knowledge, led to the development of elemene nanoliposome formulations. These novel formulations offer numerous advantages, including low toxicity, well-defined composition, synergistic effects on multiple targets, and excellent biocompatibility. Following the principles of the "molecular compatibility theory", further exploration of cancer treatment strategies and methods based on elemene was undertaken. This comprehensive review consolidates the current understanding of elemene's potential antitumor mechanisms, recent clinical investigations, advancements in drug delivery systems, and structural modifications. The ultimate goal of this review is to establish a solid theoretical foundation for researchers, empowering them to develop more effective antitumor drugs based on the principles of "molecular compatibility theory".
基金Project supported by the National Natural Science Foundation of China(Grant Nos.21264016,11464047,and 21364016)the National Basic Research Program of China(Grant No.2012CB821500)the Natural Science Foundation of Xinjiang Uygur Autonomous Region,China(Grant No.2013211A053)
文摘In this paper, we use a molecular theory to study the anomalous switching of ssDNA monolayers. Here, both ssDNA- water and water-water hydrogen bonds and their explicit coupling to the ssDNA conformations are considered. We find that hydrogen bonding becomes a key element in inducing the anomalous switching of ssDNA monolayers. This finding accords well with the experimental observations. Based on our theoretical model, we predict that the anomalous switching induced by water vapor will be applicable to a wide range of hydrogen bonds polymers, and ssDNA-water hydrogen bonds and water-water hydrogen bonds hybridization will lead to the hydrogen-bond network formation of 3D ssDNA monolayers.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.21264016,11464047,and 21364016)the Joint Funds of Xinjiang Natural Science Foundation,China(Grant No.2015211C298)
文摘By employing molecular theory, we systematically investigate the shift of solubility of poly（N-isopropylacrylamide）（PNIPAM） brushes in sodium halide solutions. After considering PNIPAM–water hydrogen bonds, water–anion hydrogen bonds, and PNIPAM–anion bonds and their explicit coupling to the PNIPAM conformations, we find that increasing temperature lowers the solubility of PNIPAM, and results in a collapse of the layer at high enough temperatures. The combination of the three types of bonds would yield a decrease in the solubility of PNIPAM following the Hofmeister series： Na Cl＆gt;Na Br＆gt;Na I. PNIPAM–water hydrogen bonds are affected by water–anion hydrogen bonds and PNIPAM–anion bonds. The coupling of polymer conformations and the competition among the three types of bonds are essential for describing correctly a decrease in the solubility of PNIPAM brushes, which is determined by the free energy associated with the formation of the three types of bonds. Our results agree well with the experimental observations, and would be very important for understanding the shift of the lower critical solution temperature of PNIPAM brushes following the Hofmeister series.
基金Project supported by the Joint Funds of Xinjiang Natural Science Foundation,China(Grant No.2015211C298)
文摘Using a molecular theory, we investigate the temperature-dependent self-assembly of single-stranded DNA（ss DNA）tethered to a charged nanoparticle surface. Here the size, conformations, and charge properties of ss DNA are taken into account. The main results are as follows： i） when the temperature is lower than the critical switching temperature, the ss DNA will collapse due to the existence of electrostatic interaction between ss DNA and charged nanoparticle surface; ii）for the short ss DNA chains with the number of bases less than 10, the switching of ss DNA cannot happen, and the critical temperature does not exist; iii） when the temperature increases, the electrostatic attractive interaction between ss DNA and charged nanoparticle surface becomes weak dramatically, and ss DNA chains will stretch if the electrostatic attractive interaction is insufficient to overcome the elastic energy of ss DNA and the electrostatic repulsion energy. These findings accord well with the experimental observations. It is predicted that the switching of ss DNA will not happen if the grafting densities are too high.
文摘The chemisorption properties of N^18O adsorption on TiO2(110) surface were investigated by experimental and theoretical methods. The results of temperature programmed desorption (TPD) indicated that the temperatures of the three desorption peaks of the main N2 molecules were at (low) temperature of 230 K, 450 K, and (high) temperature of 980 K. This meant that N^18O decomposed and recombined during the process of N2 desorption after N^18O was exposed. Analysis of thestable combination and orbital theory calculation of the surface reaction of NO adsorption on the TiO2(110) cluster modelshowed that there was clear preference for the Ti-NO orientation.
基金Supported by the National Natural Science Foundation of China.
文摘The Ti-Supported MnO_2 electrode was modified by introducing SnO_2+RuO_2+MnO_2 as an intermediate layer into the Ti/MnO_2 interface. The anodic polarization curves were measured at various temperatures ranging from 30 to 80℃ and the activation energy for the oxygen evolution reaction was evaluated. The experimental activation energy increased linearly with increasing the overpotential. The activation energy at the equilibrium potential was linearly correlated with the difference between the crystal field stabilization energies of Mn^(4+) at initial state and Mn^(4+) at transition state. The electrocatalysis characteristics of the anode were discussed by means of the mechanism of the substitution reaction of the ligand(S_N1 and S_N2) and molecular orbital theory. The results show that the anode has better electrocatalystic characteristics.
文摘A convenient synthesis and theoretical study of five CCK-functional dendrimers is described. The dendritic cores were linked with the CCK（Trp-Met-Asp（OBn）-PheNH2） fragment by forming amide bonds to give five target molecules. The structures of CCK-functional dendrimers were characterized by NMR, MS spectrum and predicted using molecular mechanics and PM3 semi- empirical molecular orbital theory.
基金the financial support of Iranian Offshore Oil Company (IOOC)
文摘Water flooding is widely applied for pressure maintenance or increasing the oil recovery of reservoirs.The heterogeneity and wettability of formation rocks strongly affect the oil recovery efficiency in carbonate reservoirs.During seawater injection in carbonate formations,the interactions between potential seawater ions and the carbonate rock at a high temperature can alter the wettability to a more water-wet condition.This paper studies the wettability of one of the Iranian carbonate reservoirs which has been under Persian Gulf seawater injection for more than 10 years.The wettability of the rock is determined by indirect contact angle measurement using Rise in Core technique.Further,the characterization of the rock surface is evaluated by molecular kinetic theory(MKT)modeling.The data obtained from experiments show that rocks are undergoing neutral wetting after the aging process.While the wettability of low permeable samples changes to be slightly water-wet,the wettability of the samples with higher permeability remains unchanged after soaking in seawater.Experimental data and MKT analysis indicate that wettability alteration of these carbonate rocks through prolonged seawater injection might be insignificant.
文摘Ab initio molecular orbital calculations of doubly negative charged B16H162-(D2) and neutral B16H16(Td) have been done at the HF/6-31G level.They are predicted to be chemically and kinetically stable by vibrational analyses on their respective energy hypersurface of the HF/6-31G level.The geometrical structure of the species B16H1622-(D2) was discussed.
文摘Nine phthalates were calculated at the B3LYP/6-311G＊＊ level using DFT method. The corresponding linear relationship equations （R2 were 0.853 and 0.936 respectively） for the biodegradation rate （Kb） and half-life time （h/2） of biodegradation were obtained with the structural parameters as theoretical descriptors. Furthermore, CoMFA method was also applied to establish 3D models which revealed the fields influencing these properties. The relationship between the properties and the structure was obtained. The correlation coefficients of the models were 0.992 and 0.999, respectively. Analyses of 2D and 3D models demonstrated that the molecular volume was an important factor affecting the biodegradability of these compounds.
基金Project supported by the National Natural Science Foundation of China(no.11272360)the Natural Science Foundation of Guangdong Province(no.2014A030313793)+1 种基金the Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund(the second phase)National Supercomputer Center in Guangzhou
文摘The micro-capsules used for drug delivery are fabricated using polylactic acid（PLA）,which is a biomedical material approved by the FDA.A coarse-grained model of long-chain PLA was built,and molecular dynamics（MD）simulations of the model were performed using a MARTINI force field.Based on the nonlocal theory,the formula for the initial elastic modulus of polymers considering the nonlocal effect was derived,and the scaling law of internal characteristic length of polymers was proposed,which was used to adjust the cut-off radius in the MD simulations of PLA.The results show that the elastic modulus should be computed using nonlinear regression.The nonlocal effect has a certain influence on the simulation results of PLA.According to the scaling law,the cut-off radius was determined and applied to the MD simulations,the results of which reflect the influence of the molecular weight change on the elastic moduli of PLA,and are in agreement with the experimental outcome.
基金Ⅴ. ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China （No.20833008）.
文摘The 1,3-dipolar cycloaddition reactions of various substituted ynamines with hydrazoic acid were theoretically investigated with the high-accuracy CBS-QB3 method. Two regioisomers, 4-amine, and 5-amine substituted adducts, were obtained, with the former as the preferred yield. This regioselectivity is rationalized by the frontier molecular orbital theory. The reactivity and synchronicity are enhanced with the increase of the electron-withdrawing character of the substitute on ynamine fragment. The calculations also show that the effect of solvent increases the activation energy, and the reaction becomes even harder in polar solvent.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.91127015 and 21522304)the Open Project from the State Key Laboratory of Theoretical Physicsthe Innovation Project from the State Key Laboratory of Supramolecular Structure and Materials
文摘Modern computer simulations of biological systems often involve an explicit treatment of the complex interactions among a large number of molecules. While it is straightforward to compute the short-ranged Van der Waals interaction in classical molecular dynamics simulations, it has been a long-lasting issue to develop accurate methods for the longranged Coulomb interaction. In this short review, we discuss three types of methodologies for the accurate treatment of electrostatics in simulations of explicit molecules： truncation-type methods, Ewald-type methods, and mean-field-type methods. Throughout the discussion, we brief the formulations and developments of these methods, emphasize the intrinsic connections among the three types of methods, and focus on the existing problems which are often associated with the boundary conditions of electrostatics. This brief survey is summarized with a short perspective on future trends along the method developments and applications in the field of biological simulations.
