Polymers and oligomers derived from pyrrole and N-hydroxymethylpyrrole: A theoretical analysis of the structural and electronic properties

This work reports a theoretical investigation about the structural and electronic properties of polymers constituted by pyrrole and N-hydroxymethylpyrrole in both neutral and p-doped states. Ab initio quantum mechanical calculations were performed on neutral and positively charged oligomers to evaluate the bond length alternation pattern in the π-system, the molecular conformation, the π-π* transition energies and the ionization potential. Results, which have been extrapolated to infinite polymer chains, allow analyze the influence of N-hydroxyalkylation of polypyrrole on these properties.     

Polyurea microcapsules with different structures: Preparation and properties

Polyurea microcapsules were formed by carrying out an interfacial polycondensation reaction in emulsion globules between various diisocyanates and ethylenediamine to investigate the effects of the chemical structure on various characteristics. FTIR showed that very reactive aromatic 2,4‐toulene diisocyanate produced many more hydrogen‐bonded N—H groups than did other aliphatic diisocyanates. All the microcapsules in this study had prominent thermal stabilities from the results of DSC and TG. It was evident that both the molecular weight and the reactivity of diisocyanates determined the mean diameter and particle‐size distribution at the same time. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 894–898, 2000     

QM/MM through the 1990s: The First Twenty Years of Method Development and Applications

The 2013 Nobel Prize in Chemistry was awarded to the authors of the first two publications utilizing the concept of combined quantum mechanical and molecular mechanical (QM/MM) methods. In celebrating this great event in computational chemistry, we review the early development of combined QM/MM techniques and the associated events that took place through the mid-1990s. We also offer some prospects for the future development of quantum mechanical techniques for macromolecular systems.     

Photophysics of Structurally Modified Flavin Derivatives in the Blue‐Light Photoreceptor YtvA: A Combined Experimental and Theoretical Study

The light‐induced processes of two flavin mononucleotide derivatives (1‐ and 5‐deaza flavin mononucleotide, 1DFMN and 5DFMN), incorporated into the LOV domain of YtvA protein from Bacillus subtilis, were studied by a combination of experimental and computational methods. Quantum mechanics/molecular mechanics (QM/MM) calculations were carried out in which the QM part was treated by density functional theory (DFT) using the B3LYP functional for geometry optimizations and the DFT/MRCI method for spectroscopic properties, whereas the MM part was described by the CHARMM force field. 1DFMN is incorporated into the protein binding site, yielding a red‐shifted absorption band (λ_max=530 nm compared to YtvA wild‐type λ_max=445 nm), but does not undergo any LOV‐typical photoreactions such as triplet and photoadduct formation. QM/MM computations confirmed the absence of a channel for triplet formation and located a radiation‐free channel (through an S₁/S₀ conical intersection) along a hydrogen transfer path that might allow for fast deactivation. By contrast, 5DFMN‐YtvA‐LOV shows a blue‐shifted absorption (λ_max=410 nm) and undergoes similar photochemical processes to FMN in the wild‐type protein, both with regard to the photophysics and the formation of a photoadduct with a flavin‐cysteinyl covalent bond. The QM/MM calculations predict a mechanism that involves hydrogen transfer in the T₁ state, followed by intersystem crossing and adduct formation in the S₀ state for the forward reaction. Experimentally, in contrast to wild‐type YtvA, dark‐state recovery in 5DFMN‐YtvA‐LOV is not thermally driven but can only be accomplished after absorption of a second photon by the photoadduct, again via the triplet state. The QM/MM calculations suggest a photochemical mechanism for dark‐state recovery that is accessible only for the adduct with a C4a? S bond but not for alternative adducts with a C5? S bond.     

Antimicrobial finishing of acrilan fabrics with cetylpyridinium chloride: Affected properties and structures

Durable antimicrobial acrilan fabrics were prepared by using cetylpyridinium chloride (CPC) in a chemical finishing process. The CPC could form ionic interactions with anionic groups on acrilan fibers, which contribute to durable antimicrobial functions. Reaction conditions such as pH, temperature, and time of the chemical treatment affected exhaustion of CPC and antimicrobial properties. However, the pH conditions of the finishing bath also impacted mechanical properties and color of the fabrics, particularly under alkaline conditions. Although a more alkaline condition is preferred for durable antimicrobial functions, high pH reduces tensile strength and results in yellowing of acrilan fibers. The yellowing of the acrilan fibers is caused by the hydrolysis of acrylonitrle groups and induced formation of conjugated C?N systems in the polymers. The conjugated systems were characterized by FTIR. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1227–1236, 2005     

Structural properties,electronic structures and optical properties of WB2 with different structures: A theoretical investigation

The structural, electronic and optical properties of six WB₂ diborides with hP3, hP6, hP12, oP6, hR9 and hR18 structures were systematically investigated using the first-principles calculation based on density functional theory. The optimized atomic coordinates and lattice parameters agree well with the corresponding experimental and theoretical results. All WB₂ are energetically stable, and hP6-WB₂ has the best phase stability and hP3-WB₂ shows the worst phase stability. The results of density of states and the charge density differences indicate that WB₂ have the strong W–B and B–B covalent bonds. The hardness was obtained from the Mulliken population. The predicted values of absorption coefficient α(ω) and reflectivity R(ω) reveal that the laser with a longer wavelength is recommended during the synthesis of WB₂ coatings on the substrate surface using the Nd-YAG laser. Finally, the anisotropy in optical properties for WB₂ was discussed via the polycrystalline and directional static dielectric constants ε₁(0) and static refractive indexes n(0).     

Computer Simulations of Deep Eutectic Solvents: Challenges,Solutions, and Perspectives

Deep eutectic solvents (DESs) are one of the most rapidly evolving types of solvents, appearing in a broad range of applications, such as nanotechnology, electrochemistry, biomass transformation, pharmaceuticals, membrane technology, biocomposite development, modern 3D-printing, and many others. The range of their applicability continues to expand, which demands the development of new DESs with improved properties. To do so requires an understanding of the fundamental relationship between the structure and properties of DESs. Computer simulation and machine learning techniques provide a fruitful approach as they can predict and reveal physical mechanisms and readily be linked to experiments. This review is devoted to the computational research of DESs and describes technical features of DES simulations and the corresponding perspectives on various DES applications. The aim is to demonstrate the current frontiers of computational research of DESs and discuss future perspectives.     

Electronic structures and molecular properties of FLBDOB and its derivatives: A combined experimental and theoretical study

Theoretical studies on a new unsymmetrical electrolyte salt, lithium [3-fluoro-1,2-benzenediolato(2-)-o,o′ oxalato]borate (FLBDOB), and its derivatives, lithium bis[3-fluoro-1,2-benzenediolato(2-)-o,o]borate (FLBBB), and lithium bis(oxalate)borate (LBOB) are carried out using density functional theory (DFT) method and B3LYP theory level. Bidentate structures involving two oxygen atoms are preferred. Based on these conformations, a linear correlation is observed between the highest occupied molecular orbital (HOMO) energies and the limiting oxidation potentials measured by linear sweep voltammetry, which supports experimental results that strongly electron-withdrawing substituent anions are more resistant against oxidation. The correlations are also observed between ionic conductivity and binding energy, solubility and theoretical set of parameters of anion, thermal stability and the hardness (η). Wave function analyses are performed by natural bond orbital (NBO) method to further investigate the cation-anion interactions.     

改性化合物对聚酰胺膜材料亲水性及抗污染性能影响的分子力学计算与实验研究

以反渗透技术应用于海水淡化为背景,采用分子力学方法计算聚酰胺反渗透膜材料PA及3种改性化合物(PEGMA,SPM,AMPS)与水分子、典型有机污染物海藻酸AA形成各种氢键复合物的相互作用能、生成几率与平均相互作用能,以此为基础选择适宜的膜改性化合物,增加膜表面亲水性,降低海藻酸污染。分子力学计算表明,PA及三种改性化合物与水分子结合的强弱顺序为：PEGMA＞PA＞SPM＞AMPS;它们与海藻酸AA分子结合的强弱顺序为：AMPS＞PA＞SPM＞PEGMA。将PEGA“链接”到聚酰胺膜SW30表面,制得改性聚酰胺膜MSW30。实验表明,改性聚酰胺膜MSW30的亲水性能及抗污染性能均较原膜SW30有显著提高,实验结果与分子力学计算结果一致。     

Poly(ester amide)s derived from tartaric and succinic acids: Changes in structure and properties upon hydrolytic degradation

The changes in structure and properties taking place in a set of tartaric acid‐based polyamides and poly(ester amide)s upon hydrolytic degradation were examined. Poly(hexamethylene 2,3‐di‐O‐methyl‐L ‐tartaramide)s, either pure or containing minor amounts of succinate ester groups (≤10%), were exposed to humidity or incubated in buffered water at pH 7.4 and 37°C, and their thermal and mechanical properties were evaluated as a function of time. Both moisture uptake and hydrolysis induced a noticeable decay in the tensile properties of polymers. These effects were greatly enhanced by the presence of ester groups, whereas no large differences were noticed for changes in the enantiomeric composition. Variations in the glass transition temperatures and melting points appeared to be slight, whereas crystallinity clearly increased with incubation time. The latter effect was most apparent in poly(ester amide)s with a nearly racemic composition, in which a crystal‐to‐crystal transition was observed to take place upon degradation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 486–494, 2000     

On the correlation of some theoretical and experimental parameters in polycondensation cross-linked networks

The use of the equation f = km/αE, correlating number of degrees of freedom m of polymer segments between cross-linking nodes in polycondensation networks to the energy of interaction polymer segment/polymer segment, both within the same polymer and at different polymers interfaces, through measures of deflection in bending by dynamic thermomechanical analysis, yields a number of consequences of interest in the field of polycondensation-hardened networks and of their process of hardening. From this equation, regression equations correlating only two parameters are obtained, which render easier the determination of the parameters that are more difficult or lengthy to obtain by experimental means. The process of networking, hence of the reaction of polycondensation between the gel point and complete hardening of the network, can be followed by the determination of the average number of degrees of freedom m of the polymer segments between cross-linking nodes obtained through these equations. Even the equation of Carrothers can be adapted through the use of the average number of degrees of freedom of polymer segments between cross-linking nodes to describe the course of the polycondensation after the gel point and up to complete stable networking. The dependence from the temperature of m can be connected to both the rate constant of advancement of the network and to the correlation of the value of m of the system to its glass transition temperature. Peculiarities in gel point forecasting by Flory's and Carrothers' theories, which depend on the well-known existence of reactions of cyclization during polycondensation and by a thermodynamic temperature dependence not previously recognized, indicate that the gel point predicted by each theory fails to consider the existence of one and one only of these effects for each theory. On this theoretical basis, the combination of the two theories into a single, simple equation, which can still be used with ease at the applied level, leads to much better precision of forecasting of the gel point than any of the two theories from which the equation is derived and than any of the more complex theories in this field. © 1996 John Wiley & Sons, Inc. J Appl Polym Sci 63: 603–617, 1997     

Acid-base properties of copper oxides and fluorides by means of band calculations: Relevance to metal-polymer adhesion

Classification of acids and bases in the Lewis sense implies electronic participation and it is extendable to non-protonic solvent interactions as well as solventless reactions. In many microelectronic applications, interfacial interactions between a polymer and a metal occur and contribute to the resulting adhesion of the bond. In the practical sense, metal surfaces are either oxidized or can be chemically altered by process conditions; therefore, the interaction is through a modified surface. The present study shows how tight binding calculations of the extended Hückel type can be used to estimate the relative acid strengths of copper, its oxides and fluorides. The trends obtained from bulk and surface layers in each case were related to the Fermi level of the crystal and the number of empty states derived from the copper 3d orbitals. Our results show the relative acid strengths follow the trend: CuF₂ > CuO > CuF ~ Cu₂O > Cu The methods used here can be directly applicable to classify the relative acid strengths of other metal-based substrates.     

In silico theoretical molecular modeling for Alzheimer's disease: the nicotine-curcumin paradigm in neuroprotection and neurotherapy

The aggregation of the amyloid-β-peptide (AβP) into well-ordered fibrils has been considered as the key pathological marker of Alzheimer's disease. Molecular attributes related to the specific binding interactions, covalently and non-covalently, of a library of compounds targeting of conformational scaffolds were computed employing static lattice atomistic simulations and array constructions. A combinatorial approach using isobolographic analysis was stochastically modeled employing Artificial Neural Networks and a Design of Experiments approach, namely an orthogonal Face-Centered Central Composite Design for small molecules, such as curcumin and glycosylated nornicotine exhibiting concentration-dependent behavior on modulating AβP aggregation and oligomerization. This work provides a mathematical and in silico approach that constitutes a new frontier in providing neuroscientists with a template for in vitro and in vivo experimentation. In future this could potentially allow neuroscientists to adopt this in silico approach for the development of novel therapeutic interventions in the neuroprotection and neurotherapy of Alzheimer's disease. In addition, the neuroprotective entities identified in this study may also be valuable in this regard.     

Molecular and Electronic Structures of Neutral Polynitrogens: Review on the Theory and Experiment in 21st Century

The data on the existence and physicochemical characteristics of uncharged single element chemical compounds formed by nitrogen atoms and containing more than two nuclides of this element (from N₄ to N₁₂₀, oligomeric and polymeric polynitrogens) have been systematized and generalized. It has been noticed that these data have a predominantly predictive character and were obtained mainly using quantum chemical calculations of various levels (HF, DFT, MP, CCSD etc.). The possibility of the practical application of these single element compounds has been considered. The review mainly covers articles published in the last 25 years. The bibliography contains 128 references.     

微孔膜法油水分离——表面性质及微观结构的研究进展

石油炼制和化工过程存在大量油水混合物体系,影响生产过程稳定性,也会造成环境污染,亟需高效低成本的油水分离技术。与气浮、离心、化学混凝等传统油水分离技术相比,微孔膜技术通过油或水的选择性渗透实现分离,具有操作简单、分离效率高、运行成本低等众多优点。然而,微孔膜处理油水混合物的分离效率和加工能力同时取决于膜材料的表面性质（表面浸润性能）和微孔结构（分离通道的尺寸效应）。本文首先基于表面润湿现象和尺寸筛分机制介绍了膜法油水分离的原理,然后从上述两个角度出发综述了近年来微孔膜法油水分离的相关研究进展,最后指出微孔膜法油水分离在迈向工业化应用的过程中还需解决的一些问题,并对未来膜材料表面性质和微孔结构的研究进行了展望。     

Application of FTIR spectroscopy to determine transport properties and water-polymer interactions in polypropylene (PP)/poly(ethylene-co-vinyl alcohol) (EVOH) blend films: Effect of poly(ethylene-co-vinyl alcohol) content and water activity

This paper reports the use of FTIR spectroscopy along with gravimetric analysis to simultaneously study water sorption, transport properties and water-polymer interactions in PP/EVOH films at 25 °C, as a function of EVOH content and water vapour activity. The results indicate the existence of two different mechanisms, below (dual-mode) and above a critical concentration value close to the clustering limit activity. Several spectroscopically distinguishable “types” of sorbed water molecules with different diffusion rates have been detected, and their evolution as a function of the penetrant concentration followed. The main changes in the water structure take place from the clustering limit activity onwards. Significant differences both in the state of water and diffusion sequence of free/bound water have been found between 90/10 PP/EVOH films and blends with EVOH content ≥20%, suggesting not only composite-dependence but also morphology-dependence.     

1-(2-Hydroxyethyl)-2-imidazolidinone as corrosion inhibitor of mild steel in 0.5 M HCl solution: thermodynamic,electrochemical and theoretical studies

The inhibition effect of 1-(2-Hydroxyethyl)-2-imidazolidinone (2-HEI) on mild steel (MS) corrosion in 0.5?M HCl solution was investigated at different inhibitor concentration and temperature by electrochemical experiments, such as linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and quantum chemical calculations. The inhibitor adsorption process on mild steel in 0.5?M HCl system was studied at different temperatures (20?°C–50?°C). Furthermore, the surface morphology of MS was also investigated with SEM in the absence and the presence of inhibitor. The adsorption of 1-(2-Hydroxyethyl)-2-imidazolidinone on MS surface is an exothermic process and this process obeys the Langmuir adsorption isotherm. The Quantum chemical findings are good agreed with the empirical data.     

Pore-network modelling of combined molecular diffusion and gravity drainage mechanisms in a porous matrix block: The competitive role of driving forces

A large part of the world's hydrocarbon resources are located in fractured reservoirs, and mass transfer phenomena play a crucial role in enhanced hydrocarbon recovery from these reservoirs. Pore-network models have been widely used to study kinetic and pore-scale micro-mechanisms. Molecular diffusion involves mass transfer and liquid–vapour phase change and can be simulated by a modified invasion percolation model. Despite the existence of separate pore-scale studies on molecular diffusion and gravity drainage, no articles have been published that evaluate the combined effect of both mechanisms. This study investigates the competitive roles of the two phenomena and the effective factors controlling each mechanism with the aid of pore-network models. According to the results obtained, gravity drainage and molecular diffusion would have a synergic effect when they are simultaneously active. Although for a single-component liquid system, there would be a capillary holdup residual saturation in the pure gravity drainage process (between 11% and 14% for the evaluated cases) and a slow and lengthy evaporation in pure molecular diffusion (between 47% and 57% longer for the cases under study), our investigation revealed that when the two mechanisms coexist, a faster process with no residual liquid is expected. Our findings clarify that when the system is strongly gravity dominated, the liquid body remains integrated, gas–liquid contact recedes in a piston-like manner, and three-stage liquid desaturation is observed. Furthermore, highly clustered liquid saturation is observed in strongly capillary-dominated systems, and the liquid desaturation curve in a capillary-dominated model has two distinguishable stages. The competitive contribution of gravity drainage and molecular diffusion as the main driving forces of liquid extraction from a single-block model is quantified for the entire period of desaturation. Depending on the dominance of the production mechanisms, the process is either gravity-assisted molecular diffusion or diffusion-assisted gravity drainage.     

Deep eutectic solvents for efficient capture of cyclohexane in volatile organic compounds: Thermodynamic and molecular mechanism

Deep eutectic solvents (DESs) as promising green absorbents were first proposed to capture the condensable cyclohexane gas. Choline chloride–ethylene glycol (EG) (Ethaline) and choline chloride–urea (Reline) were prepared using choline chloride as the hydrogen-bond acceptor (HBA) and urea or EG as the hydrogen-bond donor (HBD). To explore the potential application of DESs in condensable gas capture, the COSMO-RS model was used to predict the solubility of cyclohexane in Ethaline and Reline. The thermodynamic properties, that is, Henry's constant and excess enthalpy, were estimated by correlating solubility data with Henry's law equation. Quantum chemical (QC) calculation was applied to understand the absorption mechanism at the molecular level. The results showed that the absorption performance of cyclohexane in Ethaline and Reline was dependent on the weak interaction between O of EG (or N of urea) and H of cyclohexane as well as the free volume effect of DESs.