Development of minimized mixing molecular orbital method for designing organic ferromagnets

Predicting the high spin stability of organic radicals correctly for designing organic ferromagnets remains a significant challenge. We have developed a method with an index (L_min) for predicting the high spin stability of conjugated organic radicals at the restricted open‐shell Hartree–Fock level. Unitary transformations were performed for localizing the coefficients of nonbonding molecular orbitals, and subsequently the localized coefficients were used to calculate L_min that indicates the high spin stability of conjugated organic radicals. This method can be combined with the elongation method to treat huge high spin open‐shell systems. Thus, this method is useful for designing organic ferromagnets. © 2015 Wiley Periodicals, Inc.     

Predicting the chemical reactivity of organic materials using a machine-learning approach

Stability and compatibility between chemical components are essential parameters that need to be considered in the selection of functional materials in configuring a system. In configuring devices such as batteries or solar cells, not only the functionality of individual constituting materials such as electrodes or electrolyte but also an appropriate combination of materials which do not undergo unwanted side reactions is critical in ensuring their reliable performance in long-term operation. While the universal theory that can predict the general chemical reactivity between materials is long awaited and has been the subject of studies with a rich history, traditional ways proposed to date have been mostly based on simple electronic properties of materials such as electronegativity, ionization energy, electron affinity and hardness/softness, and could be applied to only a small group of materials. Moreover, prediction has often been far from accurate and has failed to offer general implications; thus it was practically inadequate as a selection criterion from a large material database, i.e. data-driven material discovery. Herein, we propose a new model for predicting the general reactivity and chemical compatibility among a large number of organic materials, realized by a machine-learning approach. As a showcase, we demonstrate that our new implemented model successfully reproduces previous experimental results reported on side-reactions occurring in lithium–oxygen electrochemical cells. Furthermore, the mapping of chemical stability among more than 90 available electrolyte solvents and the representative redox mediators is realized by this approach, presenting an important guideline in the development of stable electrolyte/redox mediator couples for lithium–oxygen batteries.

Stability and compatibility between chemical components are essential parameters that need to be considered in the selection of functional materials in configuring a system.     

Joint QSAR analysis using the Free-Wilson approach and quantum chemical parameters

A new quantitative structure-activity relationship (QSAR) technique combining the Free-Wilson method and constructed quantum chemical parameters was used to simulate the aqueous solubility (Sw), 1-octanol/water partition coefficient (Kow) of 14 new synthesized benzanilide derivatives and their 96 h acute toxicity (EC50) to Daphnia magna. The mode of action of the 14 selected compounds to Daphnia magna was shown to be a complex process involving a physical partition stage and a bio-chemical reaction stage. The results also indicated that the joint (QSAR) analysis was much effective than the original Free-Wilson method and Hansch method not only in predicting properties/toxicity, but also in investigating the mode of action of chemicals.     

Search for tetrylene structures that can exhibit catalytic activity: a quantum chemical approach

We present the results of a quantum chemical study of a series of tetrylenes (silylenes, germylenes, and stannylenes), aimed at identifying structural and electronic factors affecting the width of the HOMO—LUMO energy gap. Compounds considered in this work contain atoms of Group 14 elements in both di- and tricoordinate states due to additional transannular interaction. They bear substituents bonded to the atom of the Group 14 element through atoms with and without lone electron pairs. It was found that tetrylenes stabilized by both additional transannular interaction and direct bonds between the atom of the Group 14 element and the heteroatom containing a lone electron pair (in this situation the ligand acts as n-donor) are characterized by wide HOMO—LUMO energy gaps, the gap in stannylenes always being narrower than in the related silylenes and germylenes. Localization of the HOMO and LUMO in certain tetrylenes is analyzed.

     

Adsorption of organic substances on broken clay surfaces: a quantum chemical study

Hydrogen-bonded interactions between local defect structures on broken clay surfaces modeled as molecular clusters and the organic molecules acetic acid, acetate, and N-methylacetamide (NMA) have been investigated. Density functional theory and polarized basis sets have been used for the computation of optimized interaction complexes and formation energies. The activity of the defect structures has been characterized as physical or chemical in terms of the strength of the hydrogen bonds formed. Chemical defects lead to significantly enhanced interactions with stronger hydrogen bonds and larger elongation of OH bonds in comparison to the physical defects. The type of interaction with the defect structure significantly influences the planarity of the model peptide bond in NMA. Both cases, enhancement of the planarity by increase of the CN double bond character and strong deviations from planarity, are observed.     

Investigating inclusion complexes using quantum chemical methods

Quantum chemistry has firmly established itself as a reliable method for investigating present-day problems in biological and materials chemistry. Understanding inclusion complexes represents one of the cutting edges of simulation sciences. In this tutorial review, we focus on the role and composition of non-covalent interactions, which are essential when studying inclusion complexes. A selected set of recently developed pragmatic methods used to study inclusion complexes are then surveyed including e.g. dispersion corrected DFT, double-hybrid functionals and spin-component scaled MP2. Finally, three case studies are outlined: (a) endohedral fullerene complexes, (b) buckyball catcher and (c) resorcinarene capsule. These case studies were carefully chosen to help illustrate how one may accurately investigate inclusion complexes, at a modest computational cost, using state-of-the-art quantum chemical methods (67 references).     

A new pyrolysis—mass spectrometry approach to organic marine chemistry using chemical ionization

A new approach is being developed to obtain a great deal of information about the organic chemicals in the marine environment as rapidly as possible. The sample, after drying, is pyrolyzed at four different temperatures and the resulting pyrolyzates are swept into a mass spectrometer operating under chemical ionization conditions to obtain maximum sensitivity while at the same time maintaining to a large extent the integrity of the molecular structure of the pyrolyzates. This results in at least four different pyrogram peaks each composed of at least 100 different ion species. A sample size of only 200 μl is required and the analysis is completed in less than 10 min.Minimal sample manipulation decreases drastically the chance for contamination. Resulting data are computer processed. Possible uses for this approach are water mass differentiation, water mass tracing, determination of covariation between organics and a process of interest, and monitoring the interaction of organics with a process of interest. The chief advantage of this approach is that our interpretation of the role that organics play in the marine environment will be less limited by the availability of sample, personnel, and time. The chief limitation is our inadequate understanding of pyrolysis mechanisms and how pyrolyzates behave under chemical ionization-mass spectrometric conditions. This should rapidly improve with more research.The approach was tested successfully by looking at the similarities and differences between two coastal bodies of water, one more influenced by terrestrial run-off than the other.     

A subsystem density-functional theory approach for the quantum chemical treatment of proteins

We present an extension of the frozen-density embedding (FDE) scheme within density-functional theory [T. A. Wesolowski and A. Warshel, J. Phys. Chem. 97, 8050 (1993)] that can be applied to subsystems connected by covalent bonds, as well as a practical implementation of such an extended FDE scheme. We show how the proposed scheme can be employed for quantum chemical calculations of proteins by treating each constituting amino acid as a separate subsystem. To assess the accuracy of the extended FDE scheme, we present calculations for several dipeptides and for the protein ubiquitin.     

Metallization of a thiol-terminated organic surface using chemical vapor deposition

The deposition and the subsequent decomposition of an organometallic precursor, (eta (3)-allyl)(eta (5)-cyclopentadienyl)palladium [Cp(allyl)Pd], on an organic surface exposed by self-assembled monolayers (SAM) was studied using X-ray photoelectron spectroscopy (XPS) and infrared reflection absorption spectroscopy (IRRAS). The interfacial chemical reactions of the vapor-deposited metal precursor with the pendant thiol group of the SAMs made from oligophenyldithiols, which are either prepared directly (terphenyldimethyldithiol, TPDMT) or by a deprotection route from SAMs formed by a monoacylated derivative of biphenyldimethyldithiol (dep. BPDMAc-1) have been studied in detail. When the TPDMT-SAMs were exposed to Cp(allyl)Pd vapor, a Pd (2+)/allyl-terminated SAM surface was obtained (to a lower extent this was also the case for dep. BPDMAc-1 SAMs), which was stable against exposure to H 2 gas. Reduction to Pd (0) by H 2 was only observed when small amounts of Pd (0) were already present, for example, after prolonged exposure to the precursor. The catalytic activity of the small Pd (0) particles also caused a decomposition of the SAMs upon exposure to air.     

Identification of decomposition reactions for HMDSO organosilicon using quantum chemical calculations

Hexamethyldisiloxane [HMDSO, (CH₃)₃-SiOSi-(CH₃)₃] is an important precursor for SiO₂ formation during flame-based silica material synthesis. As a result, HMDSO reactions in flame have been widely investigated experimentally, and many results have indicated that HMDSO decomposition reactions occur very early in this process. In this paper, quantum chemical calculations are performed to identify the initial decomposition of HMDSO and its subsequent reactions using the density functional theory at the level of B3LYP/6-311+G (d, p). Four reaction pathways—(a) Si O bond dissociation of HMDSO, (b) Si C bond dissociation of HMDSO, (c) dissociation and recombination of Si O and Si C bonds, and (d) elimination of a methane molecule from HMDSO—have been examined and identified. From the results, it is found that the barrier of 84.38 kcal/mol and Si O bond dissociation energy of 21.55 kcal/mol are required for the initial decomposition reaction of HMDSO in the first pathway, but the highest free energy barrier (100.69 kcal/mol) is found in the third reaction pathway. By comparing the free energy barriers and reaction rate constants, it is concluded that the most possible initial decomposition reaction of HMDSO is to eliminate the CH₃ radical by Si C bond dissociation.     

Self-adapting computer program system for designing organic syntheses

The computer program SCANSYNTH is designed to assist in planning organic syntheses. The system features a new mode of data input/output, and is self-adapting, with simultaneous generation of possible synthesis schemes in the forward and reverse directions. Operational options include modeling of individual reactions, one-step reactions and multi-step reactions.     

Determination of organic additives in mortars by near-IR spectroscopy. A novel approach to designing a sample set with high-variability components

Industrial mortars consist primarily of a mixture of cement and an aggregate plus a small amount of additives that are used to modify specific properties. Using too high or too low additive rates usually results in the loss of desirable properties in the end product. This entails carefully controlling the amounts of additives added to mortar in order to ensure correct dosing and/or adequate homogeneity in the final mixture. Near-IR (NIR) spectroscopy has proved effective for this purpose as it requires no sample pretreatment and affords expeditious analyses. The purpose of this work was to determine two organic additives (viz. Ad1 and Ad2) in mortars by using partial least squares regression multivariate calibration models constructed from NIR spectroscopic data. The additives are used to expedite setting and increase cohesion between particles in the mortar. In order to ensure that the sample set contained natural variability in the samples, we used a methodology based on experimental design to construct a representative set of samples. This novel design is based on a hexagonal antiprism that encompasses the concentration ranges spanned by the analytes and the variability inherent in each additive. The D-optimality criterion was used to obtain various combinations between Ad1 and Ad2 additive classes. The partial least squares calibration models thus constructed for each additive provided accurate predictions: the intercept and the slope of the plots of predicted values versus reference values for each additive were close to 0 and 1, respectively, and their confidence ranges included the respective value. The ensuing analytical methods were validated by using an external sample set.     

Local properties of quantum chemical systems: the LoProp approach

A new method is presented, which makes it possible to partition molecular properties like multipole moments and polarizabilities, into atomic and interatomic contributions. The method requires a subdivision of the atomic basis set into occupied and virtual basis functions for each atom in the molecular system. The localization procedure is organized into a series of orthogonalizations of the original basis set, which will have as a final result a localized orthonormal basis set. The new localization procedure is demonstrated to be stable with various basis sets, and to provide physically meaningful localized properties. Transferability of the methyl properties for the alkane series and of the carbon and hydrogen properties for the benzene, naphtalene, and anthracene series is demonstrated.     

The designing of nanometer-sized passive films at metal surfaces using organic inhibitors

Results of studies in the adsorption of carboxylic-acid salts (diftorant, mephenamic acid, fluphenamic acid and its compositions with benzotriazole) at iron and low-carbon steel surfaces from neutral borate buffer solution are presented. A link between adsorption and protective ability of these compounds is revealed. Anticorrosion protection of metals can be improved by formation of bi- or even multilayer nanocoatings of inhibitors in aqueous solutions or vapor phase.