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Stroke has a high incidence and disability rate, and rehabilitation is an effective means to reduce the disability rate of patients. To systematize rehabilitation assessment, which is the foundation for rehabilitation therapy, we summarize the assessment methods commonly used in research and clinical applications, including the various types of stroke rehabilitation scales and their applicability, and related biomedical detection technologies, including surface electromyography (sEMG), motion analysis systems, transcranial magnetic stimulation (TMS), magnetic resonance imaging (MRI), and combinations of different techniques. We also introduce some assessment techniques that are still in the experimental phase, such as the prospective application of artificial intelligence (AI) with optical correlation tomography (OCT) in stroke rehabilitation. This review provides a useful bibliography for the assessment of not only the severity of stroke injury, but also the therapeutic effects of stroke rehabilitation, and establishes a solid base for the future development of stroke rehabilitation skills.

To systematically review studies using remote ischemia postconditioning (RIPostC) for ischemic stroke in experimental models and obtain factors that significantly influence treatment outcomes.Peer-reviewed studies were identified and selected based on the eligibility criteria, followed by extraction of data on potentially influential factors related to model preparation, postconditioning, and measure time based on outcome measures including infarct size, neurological scales, and cell tests with autophagy, apoptosis, normal-neuron, and damaged-neuron counting. Then, all data were preprocessed, grouped, and meta-analyzed with the indicator of the standardized mean difference.Fifty-seven studies with 224 experiments (91 for infarct size, 92 for neurological scales, and 41 for cell-level tests) were included. There was little statistical difference between different model preparations, treated body parts, number of treatments, and sides. And treatment effect was generally a positive correlation with the duration of conditioning time to stroke onset with exceptions at some time points. Based on infarct size, the number of cycles per treatment, duration of occlusion, and release per cycle showed significant differences. Combined with the effect sizes by other measures, the occlusion/release duration of 8-10 min per cycle is better than 5 min, and three cycles per treatment were most frequently used with good effects. Effect also varied when measuring at different times, showing statistical differences in infarct size and most neurological scales. RIPostC is confirmed as an effective therapeutic intervention for ischemic stroke, while the RIPostC-mediated autophagy level being activated or inhibited remained conflicting.Conditioning time, number of cycles per treatment, duration of occlusion, and release per cycle were found to influence the treatment effects of RIPostC significantly. More studies on the relevant influential factors and autophagy mechanisms are warranted.

Rationale and Objectives To use machine learning-based magnetic resonance imaging radiomics to predict metachronous liver metastases (MLM) in patients with rectal cancer. Materials and Methods This study retrospectively analyzed 108 patients with rectal cancer (54 in MLM group and 54 in nonmetastases group). Feature selection were performed in the radiomic feature sets extracted from images of T2-weighted image (T2WI) and venous phase (VP) sequence respectively, and the combining feature set with 2058 radiomic features incorporating two sequences with the least absolute shrinkage and selection operator method. Five-fold cross-validation and two machine learning algorithms (support vector machine [SVM]; logistic regression [LR]) were utilized for predictive model constructing. The diagnostic performance of the models was evaluated by receiver operating characteristic curves with indicators of accuracy, sensitivity, specificity and area under the curve, and compared by DeLong test. Results Five, 8, and 22 optimal features were selected from 1029 T2WI, 1029 VP, and 2058 combining features, respectively. Four-group models were constructed using the five T2WI features (ModelT2), the 8 VP features (ModelVP), the combined 13 optimal features (Modelcombined), and the 22 optimal features selected from 2058 features (Modeloptimal). In ModelVP, the LR was superior to the SVM algorithm (P = 0.0303). The Modeloptimal using LR algorithm showed the best prediction performance (P = 0.0019–0.0081) with accuracy, sensitivity, specificity, and area under the curve of 0.80, 0.83, 0.76, and 0.87, respectively. Conclusion Radiomics models based on baseline rectal magnetic resonance imaging has high potential for MLM prediction, especially the Modeloptimal using LR algorithm. Moreover, except for ModelVP, the LR was not superior to the SVM algorithm for model construction.

Objectives To discriminate low grade (Fuhrman I/II) and high grade (Fuhrman III/IV) clear cell renal cell carcinoma (CCRCC) by using CT-based radiomic features. Methods 161 and 99 patients diagnosed with low and high grade CCRCCs from January 2011 to May 2018 were enrolled in this study. 1029 radiomic features were extracted from corticomedullary (CMP), and nephrographic phase (NP) CT images of all patients. We used interclass correlation coefficient (ICC) and the least absolute shrinkage and selection operator (LASSO) regression method to select features, then the selected features were constructed three classification models (CMP, NP and with their combination) to discriminate high and low grades CCRCC. These three models were built by logistic regression method using 5-fold cross validation strategy, evaluated with receiver operating characteristics curve (ROC) and compared using DeLong test. Results We found 11 and 24 CMP and NP features were independently significantly associated with the Fuhrman grades. The model of CMP, NP and Combined model using radiomic feature set showed diagnostic accuracy of 0.719 (AUC [area under the curve], 0.766; 95% CI [confidence interval]: 0.709-0.816; sensitivity, 0.602; specificity, 0.838), 0.738 (AUC, 0.818; 95% CI:0.765-0.838; sensitivity, 0.693; specificity, 0.838), 0.777(AUC, 0.822; 95% CI: 0.769-0.866; sensitivity, 0.677; specificity, 0.839). There were significant differences in AUC between CMP model and Combined model (P = 0.0208), meanwhile, the differences between CMP model and NP model, NP model and Combined model reached no significant (P = 0.0844, 0.7915). Conclusions Radiomic features could be used as biomarker for the preoperative evaluation of the CCRCC Fuhrman grades.

Purpose To evaluate the performance of machine learning (ML)-based computed tomography (CT) radiomics analysis for discriminating between low grade (WHO/ISUP I-II) and high grade (WHO/ISUP III-IV) clear cell renal cell carcinomas (ccRCCs). Methods A total of 164 low grade and 107 high grade ccRCCs were retrospectively analyzed in this study. Radiomic features were extracted from corticomedullary phase (CMP) and nephrographic phase (NP) CT images. Intraclass correlation coefficient (ICC) was calculated to quantify the feature’s reproducibility. The training and validation cohort consisted of 163 and 108 cases. Least absolute shrinkage and selection operator (LASSO) regression method was used for feature selection. The machine learning (ML) classifiers were k-NearestNeighbor (KNN), Logistic Regression (LR), multilayer perceptron (MLP), Random Forest (RF), and support vector machine (SVM). The performance of classifiers was mainly evaluated and compared by certain metrics. Results Seven CMP features (ICC range, 0.990-0.999) and seven NP features (ICC range, 0.931-0.999) were selected. The accuracy of CMP, NP and the combination of CMP and NP ranged from 82.2%–85.9 %, 82.8%–94.5 % and 86.5%–90.8 % in the training cohort, and 90.7%–95.4%, 77.8%–79.6 % and 91.7%–93.5 % in the validation cohort. The AUC of CMP, NP and the combination of CMP and NP ranged from 0.901 to 0.938, 0.912 to 0.976, 0.948 to 0.968 in the training cohort, and 0.957 to 0.974, 0.856 to 0.875, 0.960 to 0.978 in the validation cohort. Conclusions ML-based CT radiomics analysis can be used to predict the WHO/ISUP grade of ccRCCs preoperatively.

The compatibility of the blend systems for olyactic acid (PLA)/tributyl citrate (TBC) and PLA/glycerol has been studied by molecule and mesoscopic dynamics methods. The results from glass transition temperature simulations showed that the compatibility of PLA/TBC system was better than that of PLA/glycerol, which were consistent with the conclusion obtained from the pair correlation functions. Besides, the behaviors of phase state distribution and evolution process were investigated by mesoscopic dynamics method as well. The results indicated that citrate ester was a better plasticizer than glycerol for PLA.

In this article, we explored the noncovalent bonding interactions between OCS, SCS, F2CS, Cl2CS, and singlet carbene. Six chalcogen-bonded complexes were obtained. It is found that all the vibrational frequencies of CS bond presented a red shift character. Interaction energy, topology property of the electron density and its Laplacian, and the donor–acceptor interaction have been investigated. All these results show that there exists a weak nonbonded interaction between the chalcogen bond donor and CH2. An energy decomposition analysis was performed to disclose that the electrostatic interaction is the main stabilized factor in these nonbonded complexes. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

In this paper, we calculated a series of halogen-bonded complexes. The halogen bond donor is CFnH3−nCl, and the halogen bond acceptors are NH3, H2O, H2S, and Br−. Ten stable halogen-bonded complexes were obtained and the C–Cl bond length was contracted in all of these complexes. We carried out AIM and NBO analysis under the MP2/aug-cc-PVDZ optimized structures. The variation of the electron density at the bond critical point of C–Cl bond correlates well with Δr(C–Cl). A balance among intra- and inter-hyperconjugation and rehybridization determined the contracted C–Cl bond.

LCAC-SW method has been extended to study the reaction dynamics for ion-pair formation processes. M+ X2Mt + X2 reaction system involves two potential energy surfaces, i.e., the covalence state (M + X2) and the ionic state (M + X2) and their crossing effect. The working equations for calculating state-to-state probability have been derived based on the above two-state model, Satisfied results d collinear state-to-state probabilities for K+ I2 K+ + I2 ion-pair formation system have been obtained.

This paper has improved Hickman's nonadiabatic collision model by substituting Hickman's constant velocity classical straight line trajectory approximation with the solution of motion equation mR=−dV(R)/dR, and has calculated the cross sections of ion-pair formation Cs+O2Cs++O−2 with the improved nonadiabatic collision model (INCM). A comparison of our results with other theoretical and experimental results has been made.

LCAC-SW (linear combination of arrangement channel-scattering wavefunction) method was used to calculate collinear state-to-state reaction probabilities for the reaction F + H2(v = 0) HF(v′) + H on the 6SEC potential energy surface. The results show that reaction probabilities P02 and P03 [i. e., v′ = 2,3 for reaction F + H2 (v = 0) + HF(v′) + H] are primary, the population of product vibrational states is inverse and the reaction probabilities are oscillatory with collision energies, i.e., there is energy resonance in this reaction, which agrees with a new experiment.

The acetylation mechanisms of several selected typical substrates from experiments, including arylamines and arylhydrazines, are investigated with the density functional theory in this paper. The results indicate that all the transition states are characterized by a four-membered ring structure, and hydralazine (HDZ) is the most potent substrate. The bioactivity for all the compounds is increased in a sequence ofPABA≈4-AS<4-MA<5-AS≈INH

The peptide deformylase from Leptospira interrogans (LiPDF) shows many unusual characteristics. The substrate pocket of formate-bound complex adopts an open conformation. However, in the actinonin-bound LiPDF complex, a slightly open substrate pocket is observed. The opening is not large enough for the inhibitor, because the CD-loop restricts the access to the active site. To explore the conformational changes of the substrate pocket, we perform a 16,000 ps molecular dynamics simulation separately on the ligand-free LiPDF and actinonin-bound LiPDF. During the molecular dynamics simulations, extensive conformational changes have taken place. The comparison of the two MD results shows that the CD-loop, hydrophilic inhibitor, and hydrophobic cluster are necessary for the reopening of the substrate pocket. In addition, Tyr71 plays an important role in mediating the movements of CD-loop, and the transition of the substrate pocket from open to semi-open only occurs in the presence of an inhibitor, which are consistent with the experiment very well.

In the course of an extensive investigation aimed at understanding the detailed mechanism of a prototypical polyatomic reaction, several remarkable observations were uncovered. To interpret these findings, we surmise the existence of a reactive resonance in this polyatomic reaction. The concerned system is HO + CH4 H2O + CH3, of which the partial potential energy surface is constructed by the coupling between vibrational models and reactive coordinates. Then we explain the formation mechanism of the reactive resonance state by the partial potential energy surface. Finally, we estimated the lifetime of the resonance state, and it is about 45fs. The study of the reactive resonance in a polyatomic reaction is more than just an extension from a typical atom + diatom reaction. As shown here, it holds great promise to disentangle the elusive intramolecular vibrational dynamics of the transient collision complex in the critical transition-state region. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

In the course of an extensive investigation aimed at understanding the detailed mechanism of a prototypical polyatomic reaction, several remarkable observations were uncovered. To interpret these findings, we surmise the existence of a reactive resonance in this polyatomic reaction. The system of concern is X + H2O → XH + OH ( X = Cl, F, H ), and it belongs to a type of asymmetrical H exchanging reaction. Because the concerned electronic number is quite small, it is usually regarded as a template constructed the model of theory or experiment. In this paper, compared with the symmetrical systems, we constructed the partial potential surfaces of asymmetrical systems in order to research their resonance states. All results are in good agreement with previous theoretical and experimental works.

In this Letter, we developed a new calculation method on the lifetime of reactive scattering resonance state. In the natural collision coordinate system, the core translational equation was solved by the numerical propagation method along the reaction coordinate of the partial potential energy surface. Then the resonance lifetime matrix of the reactive system was constructed by the wave function of the transient collision complex. This is a direct calculation method on the lifetime of the scattering resonance state. It is different from the former methods which estimated the resonance lifetime by the reaction probability curve or the integral cross-section as functions of the collision energy. For example, the lifetime of the first scattering resonance state of the I + HI( v ) → IH( v ′) + I reaction has been calculated by this method, and the result is in good agreement with previous theoretical and experimental works.

The hydrogen-transfer reaction of HCO + HNO2 → HCHO + NO2 has been studied using both the density function theory (DFT) and high-level ab initio method. Three complete reaction paths have been located for the transfer reaction. Geometry optimization and frequency calculation have been performed at the B3LYP/6-311++G** level. QCISD(T) and G3B3 methods have been used to verify the single-point energy. On the basis of the ab initio data, the rate constants have been deduced over a temperature range of 300–3000 K using the transition-state theory and canonical variational transition-state theory with small-curvature tunneling effect. The calculated rate constants have been compared with the previous reported values.Key words: density function theory, reaction mechanism, variational transition-state theory, rate constant.

DFT methods were used on the model molecular to determine the mechanism of β-lactamase inhibitor. The results show that the thiazole ring can be opened as well as β-lactam ring. The thiazole ring-open product can be formed via β-lactam ring-open product or tetrahedral intermediate directly. Those products, in imine or enamine form, can tautomerize via hydrogen migration. The sulforious form products may be transformed into sulfonyl ones. Water or hydroxyl group in residues on active site will help lower the activation energy of above reactions, and if structure permitted, they also effect the route selection of whole reaction system. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

Based on the vibrational potential curves coupled with the minimum energy reaction path, the partial potential energy surface of the reaction I+HIIH+I was constructed at the QCISD(T)//MP4SDQ level with pseudo potential method. And the formation mechanism of the scattering resonance states of this reaction was well interpreted with the partial potential energy surface. The scattering resonance states of this reaction should belong to Feshbach resonance because of the coupling of the vibrational mode and the translational mode. With the one-dimensional square potential well model, the resonance width and lifetime of the I+HI(=0)IH(=0)+I state-to-state reaction were calculated, which preferably explained the high-resolved threshold photodetachment spectroscopy of the IHI anion performed by Neumark et al..

The partial potential energy surface (PPES) of H + NO → N + OH or O + NH of 3A″ symmetry is first constructed using QCISD (T) method with 6-311++g** basis set, and then we speculate the existence of the scattering resonance states of these reactions. Finally, we estimate that the lifetime of scattering resonance state is about 1.5 ps, which is in agreement with Schatz's conclusion (~1.2 ps ). The scattering resonance states of the two reactions belong to the Feshbach type. The results are consistent with the probabilities calculations reported in the literatures.

The partial potential energy surface is constructed using ab initio method [QCISD (T)/6-311++G (2df, 2dp)] for F+CH 4 →HF+CH 3 reaction. It not only explains the reaction mechanism brought forward by D. Troya, but also successfully validates K.P. Liu's experimental phenomena about the existence of a reactive resonance. Finally, we estimate the lifetime of the scattering resonance state, which is about 0.07 ps. All these are in agreement with the experiments.

In this paper, the partial potential energy surface (PPESs) of the Br + HBr and Br - + HBr systems including the minimum energy path and the vibrational potential curves were constructed at MP2/6-311++G** level, based on the conception and constructing approach of the PPESs previously proposed. These results obtained from the PPESs were compared with those from the high resolved threshold photodetachment spectrum of the BrHBr - anion measured by Neumark et al., J Phys Chem94, 1377–1388, 1990. On the basis of the PPESs, the scattering resonance states of the Br + HBr (v) → BrH (v′) + Br state-to-state reaction were studied and the satisfactory results were obtained. Subsequently, we calculated the width and lifetime of the resonance states in this reaction by the one-dimensional square potential well model, and obtained some results consistent to the experiments.

The neutral hydrolysis mechanisms of a simple β-phospholactam with and without water-assisted reaction have been studied by using quantum chemical method at HF/6-31G**, MP2/6-31G** and B3LYP/6-31G** levels, respectively. The reaction can proceed by two different mechanisms: concerted and stepwise. There are two pathways in stepwise, i.e. pathway a and b, and the energy barriers of them are close. The energy barriers of water-assisted hydrolysis of β-phospholactam are obviously lower than those of no-water-assisted hydrolysis system. The energy barriers of stepwise mechanism are much lower than those of the concerted pathway in both cases. The solvent effects have been considered by means of a polarizable continuum model. The hydrolysis mechanism of β-phospholactam with that of the β-lactam and β-sultam was compared.

The hydrolysis of N-benzyl 3-oxo-β-sultam and the general base catalysis by the neucleophile are investigated. Different possible mechanistic pathways of the reaction are proposed. Both B3LYP/6-31G* and B3LYP/6-311+G* were employed to calculate the reaction pathways. The results show that in the case of non-catalyzed hydrolysis the pathways producing N-benzyl-acylamide methyl sulfonate (P1) and N-benzyl-2-sulfonic acylamide acetic acid (P2) have very similar activation energies; they are competing reactions. However, in the case of catalyzed hydrolysis by a second water molecule, the break of C–N bond is preferred. The theoretical results are in good agreement with the recent experimental observations.

The aminolysis and the effect of water on the aminolysis processes of n-methyl β-sultam have been studied using density functional theory (DFT) method at the B3LYP/6-31G* level. The stationary structures and energies have been investigated for both reactions to find two different reaction channels. Specific and general solvent effects have been evaluated and the most favored pathway was found. The presence of solvent disfavors the reaction, whereas the participation of water in the aminolysis reaction plays a positive role and reduces the activation energy greatly. All transition states in the assisted aminolysis are 35–70 kJ/mol lower than those for the non-assisted reaction.

As a first step toward the understanding of the aminolysis reaction of β-sultam compounds, the ammonolysis and the effect of a second ammonia on the ammonolysis reactions of N -methyl β-sultam have been studied using Density Functional Theory (DFT) method at the B3LYP/6-31G* level. The exploration of the reaction processes proposed two different mechanisms: concerted and stepwise mechanisms. There is one pathway in concerted mechanism and two pathways in stepwise mechanisms: pathways a and b. The calculations of reaction energy barriers show that the nonconcerted route is the more favored one. Solvent effects were assessed by the PCM method. The results show that the pathway a in channel II is the most favorable in both cases. The presence of solvent disfavors the reaction, and the participation of ammonia in the ammonolysis reaction plays a positive role and reduces the active energy greatly. All transition states in the assisted ammonolysis are 45–65 kJ/mol lower than those for the non-assisted reaction. The results also show that the ammonolysis reaction have a higher energy barrier than the alcoholysis reaction. This low reactivity of amines is also observed in the reactions of N -benzoyl β-sultam and p-nitrophenyl toluene-p-sulfonate where there is a distinct preference towards oxygen nucleophiles.

The alcoholysis mechanisms of N-benzyl 3-oxo-β-sultam are investigated at B3LYP/6-31G* level. Different possible mechanistic pathways of the reaction are proposed. The results show that the cleavage of S–N bond producing P1 has a little lower energy barrier than does C–N bond producing P2. The inclusion of solvent effects by a polarizable continuum model (PCM) does not change the conclusions based on the gas-phase study.

The catalytic mechanism of one-carbon unit transfer between 5-amino-4-carboxamide imidazole (AICA) and N10-formyl-tetrahydrofolate (10f-H4F) is investigated by ONIOM approach. There are two different channels for proton transfer in this reaction, resulting in two reaction pathways with different properties. Our results indicate that proton transfer process is the rate-limiting step, and the intermolecular H-bond contributes much to the activation energy. Furthermore, the influence of the substituent linked to C4 atom of AICA is also discussed. The results from our calculations are consistent with experiment very well.

The conception of partial potential energy surface (PPES) is presented in this paper. PPES can be abstracted from complete potential energy surface (CPES), therefore, it can be constructed with ab initio quantum chemical method. For the systems of H + H 2→ H 2+ H , I + HI → IH + I and I -+ HI → IH + I -, the construction and applications of PPES are proposed as typical examples. It can be seen that the applications of PPES demonstrate remarkable virtues in the analysis of reaction mechanism and the formation of scattering resonance states.

The mechanism of one-carbon unit transfer between 1-methyl-5-amino-4-carboxamide imidazole (M-AICA) and N1-methyl-N1-acryloyl-formamide (the model molecule of 10-f-H4F) is investigated by the Hartree–Fock and DFT methods, respectively, at the 6-31G* basis level. There are two different channels for the proton transfer, resulting in two reaction pathways with different properties. The results indicate that both channels can complete the reaction, but path a is slightly favored due to its lower active energy barrier. Furthermore, the influence of 4-carboxamindde in M-AICA is also discussed. This group can stabilize the reactant and intermediates, and reduce the active energy barrier through the intermolecular hydrogen bond. The intermolecular hydrogen bond results in an enlarged conjugation system and makes the transition states more stable. Our results are in agreement with experiments. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

The effects of water and alcohol on the alcoholysis mechanisms of N-methyl-1,2-thiazetidine-1,1-dioxide and the differences of these effects have been studied using the Density Functional Theory (D...

For the Cs + I2 collision system, a systematic theoretical study is first reported using the ab initio method. Three of eight possible channels are considered. The nonadiabatic coupling between the covalent state and the ionic one is calculated from different angles, especially the T-shape collision. The complete ion-pair formation potential energy surfaces of the T-shape collision in two electronic states (ionic 2B2 state and covalent 2A1 state) and the reactive surface of the linear collision are constructed at the QCISD(T)/SDD level. The main features of potential energy surfaces, such as the minimum energy reaction path, the crossing radius (Rc), and energy minimum geometries, are analyzed. The cross section of this titled system is calculated based on the harpoon mechanism and compared with the available experimental data and those obtained for the M + I2 (M = Li, Na) systems.Key words: ab initio two-state potential energy surfaces, nonadiabatic coupling, ion-pair formation, cross section.

Eight competing reaction pathways on the potential energy surface of C-methyl nitrone with acrlonitrile have been determined at the B3LYP/6-311++G** level using the density functional theory, and each of them, which has a double-peak-double-valley structure, consists of reactants, a prior complex, two transition states and two products. Accurate geometric structures, relative stabilities and harmonic vibrational frequencies of the stationary points have been investigated. The changes of enthalpy, entropy and Gibbs free energy for each reaction path are also calculated. The Boltzmann equilibrium distributions for the eight puckered envelope conformations have also been discussed qualitatively through the calculations of Gibbs free energy at 20-1000 K. The absolute rate constant calculation at the room temperature has been performed using conventional transition state theory, and as a result the most probable reaction path is determined. The exothermal energies of the possible reaction paths range from 26.11 to 51.75 kJ/mol. The first potential barrier heights vary from 72.28 to 105.62 kJ/mol while the barrier heights of isomerization vary from 1.37 to 17.05 kJ/mol. It is found that the formation of H-bond plays a critical role in the reaction. The intramolecular H-bond increases the stability of the trans-C-methyl nitrone, and the intermolecular H-bond between the C-methyl nitrone and acrlonitrile results in the formation of the prior complex, both of which reduce the reactivity of the title system. Moreover, the relative energies calculated by higher level computations, including the MP2, MP3, MP4SDQ, and QCISD(T) methods, are consistent with that obtained from the B3LYP method, which indicates that the B3LYP/6-311++G** level of theory can apply to this kind of systems. (C) 2004 Elsevier B.V. All rights reserved.

The alcoholysis of N -methyl-1,2-thiazetidine-1,1-dioxide has been investigated using ab initio and density functional theory. The geometries, energies and frequencies of reactants, intermediates, transition states and products are calculated. Our results indicate the alcoholysis of N -methyl 1,2-thiazetidine 1,1-dioxide proceeds via two reaction channels. Channel I is the cleavage of bond C–S and producing N -methyl- N -ethyl amino-methyl sulfonate (P1, in Fig. 1) in which attacking of CH 3 OH and breaking of bond C–S are concerted. Channel II is the cleavage of bond S–N and producing 2-( N -methyl) taurine methyl ester (P2, in Fig. 1) in which there are two reaction processes with two different mechanism: concerted and stepwise. The most favorite pathway for alcoholysis of N -methyl 1,2-thiazetidine 1,1-dioxide was found. The energy barrier of the cleavage of C–S bond and producing P1 is the highest among them. We think that this may be the possible reason of having no experimental evidence on the formation of product P1.

The interaction of partially hydrolyzed polyacrylamide (HPAM) with dodecyl-oxypropyl-β-hydroxyl trimethyl-ammonium bromide (C12NBr) and nonyl-phenyl-oxypropyl-β-hydroxyl trimethyl-ammonium bromide (C9phNBr) in the solution was investigated by the Dissipative Particle Dynamics (DPD) method. The calculated interaction parameters between HPAM and C12NBr or C9phNBr showed that C12NBr is most likely to form polymer/surfactant complex with HPAM in contrast to C9phNBr. The experiment of binding isotherm was used to validate the DPD results via surfactant-selective electrode and equilibrium dialysis method. In DPD method, the mean square end-to-end distance of polymer chain firstly increased, then reduced, and finally increased again. In addition, some polymer/surfactant complexes were also shown. One conclusion is that mesoscopic simulation can be considered as an adjunct to experiments and provide otherwise inaccessible (or not easily accessible) information in the experiment.

The alcoholysis of 1,2-thiazetidine 1,1-dioxide has been investigated using ab initio and density functional theory at HF/6-31G*, MP2/6-31G*//HF/6-31G* and B3LYP/6- 31G* levels. The geometries, energies and frequencies of all stationary points were calculated in detail. Solvent effects have been considered by means of a polarizable continuum model (PCM). Our results indicate the alcoholysis of 1,2-thiazetidine 1,1-dioxide proceeds via concerted mechanism and stepwise mechanism. In the stepwise mechanism, two possible reaction pathways can be followed whilst one possible reaction pathway can be followed in the concerted mechanism. The most favorite pathway for alcoholysis of 1,2-thiazetidine 1,1-dioxide was found.

An extended LCAC-SW (linear combination of arrangement channels-scattering wavefunction) quantum scattering dynamic method combined with ab initio quantum chemical calculations has been used to study the formation mechanism of the resonance states for the ion-pair formation reaction Na + I 2 → Na + + I 2 -. Resonance energy and resonance width or lifetime for the first resonance peak were calculated. Resonance can be identified to Feshbach resonance, and the physical interpretation has been given.

The structure of eight-carbon monolayers on the H-terminated Si(111) surface was investigated by a molecular simulation method. Molecular mechanics calculations showed that the best substitution percentages on the Si(111) surface were 50% for octene or octyne-derived monolayers and 40% for the styrene or phenylacetylene-derived monolayers. These values are in good agreement with the experimental results. After a two-dimensional cell containing alkyl chains and four layers of Si atoms was constructed, the densely packed and well-ordered monolayer on the Si(111) surface can be shown at the molecular level. At the same time, the thickness of the monolayers and the tilt angle of the alkyl chain were also calculated. Additionally, the theoretical calculations showed that the CC bond of the alkyne only reacts once with the H-terminated Si(111) surface, that is only one Si–C bond per organic molecule is formed on the Si(111) surface, which verifies the experimental results. It is thus shown that molecular simulation can provide otherwise inaccessible microscopic information at the molecular level, and may be considered as a useful adjunct to experiments.

A molecular dynamics simulation was performed to investigate the aggregates of mixing and the interaction between different polymers in aqueous solution. These polymers include partially hydrolyzed polyacryamide (HPAM), hydroxyethylcellulose (HEC) and polyvinylpyrrolidone (PVP). The structures of mixed aggregates were analyzed from the dihedral angle distribution of: (1) pure HPAM; (2) HPAM in aqueous solution; (3) HPAM with small segments of PVP or HEC in aqueous solution. At the same time, the simulated IR spectra and the calculated interaction parameters were used to distinguish the different interactions between HPAM and PVP or HEC. In order to confirm the validity of the simulated predictions, experimental IR spectra of polymer systems were made, and the specific viscosity of the HPAM and PVP or HEC system was measured using capillary viscometry. It can be seen from the viscosity measurements that the viscosity of the HPAM/PVP system in aqueous solution decreases linearly with an increase in concentration of PVP, whereas a maximum viscosity value appears with the increase in concentration of HEC in the HPAM/HEC system. The conclusion was drawn that the interaction between HPAM and HEC is stronger than the one between HPAM and PVP, and that molecular simulation can be considered as an adjunct to experiments and can provide otherwise inaccessible (or, not easily accessible) microscopic information that experimentalists can use.

A simple model, i.e., sodium bis(2-ethylhexyl) sulfosuccinate (AOT) represented by one-head and two-tail beads tied together by a harmonic spring and water or iso-octane by one bead, was put forward via dissipative particles dynamics (DPD) simulation method. Using the changes of interfacial tension between water and oil phase, a ternary phase diagram of AOT/water/iso-octane system was drawn.

A quantitative structure–property relationship (QSPR) was used to predict the critical micelle concentration (cmc) of anionic surfactant in aqueous solution. Some conformational, electronic, spatial and thermodynamic properties were selected as descriptors to build a relationship between the macro-property (such as the cmc) and the micro-structures. These descriptors include the octanol/water partition coefficient, the total area of surfactant molecule and the dipole moment of the surfactant molecule. A general four-parameter structure-property relationship between the logarithm of cmc and the descriptors, which was developed for a set of 37 anionic surfactants of sodium alkyl sulfates (r 2=0.996, F-test=1838.773), can be used to predict the cmc of anionic surfactants.

The quantitative structure–property relationship was used to predict the critical micelle concentration (cmc) of a nonionic surfactant in aqueous solution. Several structural, electronic, spatial and thermodynamic properties were selected as descriptors to build the relationship between the macroscopic properties (such as the cmc) and microscopic structures. These descriptors include the octanol/water partition coefficient, the heat of formation, the volume of a molecule and the energy of the lowest unoccupied molecular orbital. A general four-parameter structure–property relationship between the logarithm of the cmc and the descriptors, which was developed for a set of 37 nonionic surfactants (r2=0.990, F-test=802.970), can be used to predict the cmc of nonionic surfactants without the experimental data. The success of this approach indicates that the prediction of the cmc for other surfactants, such as anionic, cationic and zwitterionic surfactants, as well as the prediction of other surfactant properties, can be obtained.

One-carbon unit transfer from 1-acetyl-3-methylimidazolinium to 1,2-diaminobenzene has been studied using PM3 method. The structures of the intermediates and transition states have been optimized. The results show that there are two pathways to transfer the one-carbon unit, and each pathway consists of six steps. They are the combination of two reactants, proton migration, splitting of five-membered ring, formation of benzimidazole ring, another proton migration and separation of C–N bond. And the proton migrating step is the rate limiting step.

The structures of a type of tetrahydrofolate cofactor models, asymmetric substituted imidazolinium, have been studied theoretically, and the relation of reactivities to the electronic structures of these compounds has been analyzed. It is found that the reactivity of one-carbon unit transfer of this type of tetrahydrofolate cofactor models has a tight relation to properties of the two nitrogen atoms that link to the transferring carbon atom. The followed regularity is obtained. With the group on the para-position of benzenesulfonyl changing from an electronic acceptor to an electronic donor, the difference between N3 and N6 is smaller step by step, and the model becomes more active to transfer one-carbon unit gradually. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001