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Singlet fission is a photophysical process in organic matter, in which one absorbed photon is converted in two triplet excitons. Discovered over 50 years ago, today singlet fission attracts scientific interest because it opens new horizons for the development of highly efficient organic-based solar cells beyond the Shockley–Queisser limit. However, a relatively small amount of singlet fission chromophores is available and, with respect to molecular design, little is known about the relationship between compounds’ structure and singlet fission propensity. Here, we report the molecular design of new singlet fission materials based on dimers of N-heterocyclic carbenes (NHC) and their ‘locked’ analogues. The study applies the recently introduced spin-flip simplified time-dependent density functional theory (SF-sTD-DFT) approach, which allows the modelling of sizeable molecules with diradical character like most of the successful singlet fission chromophores. To motivate the choice of method for the study NHC-based chromophores, the SF-sTD-DFT results are benchmarked against high level calculations using the equation-of-motion spin-flip coupled-cluster method with single and double substitutions. Armed with a reliable computational strategy, we have explored in detail the singlet fission propensity variation of the compounds due to the following structural factors: topology, type of substituents, cis-trans conformation, extension of the conjugation and modulation of the heterocyclic aromaticity, as well as the length of the latch in the ‘locked’ analogues. The results reveal new strategies for the design of singlet fission materials and contribute to the deeper understanding of the excited state tunability at the molecular level.

Organic batteries are promising alternatives to the present rechargeable battery technologies, mainly due to projected lower fabrication costs, less environmental impact, more versatility, and chemical and mechanical flexibility. In this study we investigate potential organic battery electrodes composed of an electronically conductive graphene monolayer functionalized with redox-active anthraquinone (AQ). The combination overcomes common drawbacks of organic batteries: (i) the solubility of the organic redox-active materials in the electrolyte is mitigated by anchoring onto graphene and (ii) the need for a large amount of conductive additives in the composite electrode is circumvented by the high conductivity of graphene. The electrodes are modelled by various density functional theory (DFT) based approaches and their fundamental promise as part of Li, Ca, and Al based batteries are outlined. We model the design of the electrodes, such as AQ attachment and loading, the thermodynamics of accepting mono to trivalent ideal charge carriers from the electrolyte, i.e. Li+, Ca2+, and Al3+, and the kinetics of ion diffusion at the electrode surface by assessment of the activation barriers. From the calculated multi-step electrode potential profiles, the theoretical electrode energy densities, with respect to the redox-active part, are 570 and 512 W h kg−1 for Li and Ca, respectively, which is quite comparable to the active materials of inorganic medium voltage lithium-ion battery electrodes. As the average potentials are in the range 0.5–1.2 V vs. Mn+/M0 these materials are either to be used as negative electrodes, combined with a high or medium potential positive electrode, or as positive electrodes vs. metal electrodes, for low voltage battery application.

To create both greener and high-power metal-ion batteries, it is of prime importance to invent an unprecedented electrode material that will be able to store a colossal amount of charge carriers by a redox mechanism. Employing periodic DFT calculations, we modeled a new metal-organic framework, which displays energy density exceeding that of conventional inorganic and organic electrodes, such as Li- and Na-rich oxides and anthraquinones. The designed MOF has a rhombohedral unit cell in which an Ni(II) node is coordinated by 2,5-dicyano

Hybrid Li–Na ion batteries (HLSIBs) have become attractive because they combine the high energy density of lithium-ion batteries with the safety and low cost of sodium-ion batteries. However, the p...

We demonstrate the relationship between the topology (the way in which the atoms are connected), open-shell character, and singlet fission (SF) propensity in a series of diboron-doped anthracenes and phenanthrenes. The study is performed by using high-level wave-function-based quantum-chemical calculations. The results show that the molecular topology plays a crucial role for the optical properties and, respectively, for the SF propensity of the studied compounds. The topology-derived correlations between the structure and properties are interpreted in the light of the Kekule hydrocarbons concept and serve as molecular design guidelines for the discovery of new SF materials. Finally, several boron-doped polycyclic aromatic hydrocarbons are proposed as SF chromophores for organic solar cells.

Human immunodeficiency virus-1 (HIV-1) glycoprotein 120 (gp120) is one of the key targets for treatment of acquired immunodeficiency syndrome. A large number of inhibitors are being designed for this target in order to find safe and effective drugs. In the present study, quantitative structure activity relationship (QSAR) models established on 128 gp120 indole-based attachment inhibitors have been developed using suitable molecular descriptors. Chemometrics techniques including multiple linear regression (MLR), artificial neural network (ANN) and support vector machine (SVM) methods were used to set up QSAR models in order to explain the structural requirements of HIV-1 gp120 inhibitory activity. The prediction performance of each developed model was evaluated. The results obtained, for both the training and test sets, were encouraging. These results reveal that the predictive power of the SVM model is slightly superior to those of the MLR and ANN models. Further, the docking process was used not only to identify the most probable position and orientation of an inhibitor within the gp120 but also to assess its affinity with this target. This study could help researchers, particularly those working in the field of the pharmaceutical industry, to identify and discover more potent, active, and selective HIV-1 attachment inhibitors. Therefore, the established models could improve, diversify, and accelerate the drug development process and reduce the use of the trial and error approach in the search of new drug targets for the treatment of HIV.

A combined theoretical/experimental study of the photoreactivity of two flavylium-derived chalcones, 2,4,4′-trihydroxychalcone and 2,4′-dihydroxychalcone, at the multiconfigurational wavefunction level of theory (CASSCF//CASPT2) in vacuo and in an implicit solvent (water, treated as a polarisable continuum) and by means of linear absorption spectroscopy is presented. The photosensitivity of flavium salts is expressed in the ability of their chalcone form to undergo a cis-trans isomerisation which has found application in logical networks. Despite a considerable amount of experimental data documenting the dependence of the isomerisation on solvent, pH and temperature, the knowledge of how chalcones process energy under various conditions at the molecular level is still scarce. On the example of 2,4,4′-trihydroxychalcone we unravel the complex excited state deactivation mechanism in vacuo involving ultrafast decay through conical intersections, formation of twisted intramolecular charge transfer species, intramolecular proton transfer and inter system crossings. Furthermore, we rationalise the observed discrepancies in the linear absorption spectra of 2,4,4′-trihydroxychalcone and 2,4′-dihydroxychalcone, thereby establishing a link between the functionalisation pattern and the observed spectral properties.

Compounds able to adsorb at the interface of two immiscible liquids are of high importance for numerous chemical, physical and biological processes. Deeper understanding of the interfacial phenomena in such systems can contribute significantly to the rational practical application of small amphiphiles in electrochemistry, extraction, stabilization of emulsions, and drug design. Particularly interesting are the oil-water formulations, where the aqueous and the hydrophobic phases tend to express different molecular structure and characteristics under identical conditions. Surfactant behaviour in such environments is known to differ distinctly from the one observed in bulk water or oil or at the gas-liquid interface. It has been demonstrated that the free energy of adsorption and transfer of amphiphiles across water-oil interfaces can be decomposed into specific contributions of molecular fragments. The models developed so far do not provide information about the specifics of the functional groups contributions. To elaborate further on this topic, classical molecular dynamics simulations, combined with umbrella sampling calculations and weighted histograms method analysis are applied to reconstruct the free energy profile for several water-oil-amphiphile models along a relocation coordinate normal to the interface. Normal pentane, hexane, and heptane are chosen as models of the hydrophobic liquids and three short-chained normal alcohols⿿as low-molecular-weight amphiphiles. Gibbs energies of transfer and adsorption, as well as the average contributions per unit of elongation of the alkyl chain, are estimated and compared to experimental data and empirical results. The experimental trends of all quantities are reproduced correctly. Some quantitative differences are discussed. A detailed analysis of the free energy change vs. position of alcohol molecules shows that the transfer process can be decomposed into several stages. Such more precise stratification of the interfacial region is employed to determine and rationalize the free energy contributions of the separate alkanol functional groups.

All possible monohydroxycoumarin derivatives are modeled using density functional theory computations in order to investigate the role of the hydroxyl group position for the radical-scavenging and antioxidant activity of these compounds. Geometry optimization is performed using the B3LYP functional with the 6-311++G(d,p) basis set. The enthalpy changes are assessed in gas phase and in implicit water using the polarized continuum model. Structure-reactivity patterns are delineated. The most reactive isomers as well as the most probable mechanism of interaction between monohydroxycoumarins and free radicals are outlined.

Complexes of Tb(III) with the biscoumarin derivative 3,3′-[(4-hydroxyphenyl)methyl]bis-(4-hydroxy- 2H -chromen-2-one) are synthesized by using a solution of tetraethylammonium hydroxide, [(C 2 H 5 ) 4 N]OH, in water as deprotonating base. Elemental analysis, IR- and fluorescence spectroscopy are used to characterize the samples obtained. The complexes have good fluorescent properties and show the characteristic emission bands of the Tb(III) ion. The triplet state of the mono-deprotonated ligand H 2 L − was determined. The optimised geometries of the ligand and the complexes were obtained by means of molecular modelling with first principles (DFT) methods.

Tetrahydroimidazo[4,5,1jk][1,4]benzodiazepines (TIBO), as non-nucleoside analogues, constitute potent inhibitors of HIV-1 reverse transcriptase. In the present study, classification structure-activity relationship (SAR) models are developed to distinguish between high and low anti-HIV-1 inhibitors in this class of compounds. Different classifiers, such as support vector machines, artificial neural networks, random forests and decision trees have been established by using ten molecular descriptors. All models were validated using several strategies: internal validation, Y-randomization, and external validation. The correct classification rate ranges from 97% to 100% and from 70% to 90% for the training and test sets, respectively. A comparison between all methods was done in order to evaluate their performances. The contribution of each descriptor was evaluated to understand the forces governing the activity of this class of compounds.

Crystallization water plays an important role in the self-organization of oligomer chains in conducting polyaniline. In order to quantify the interaction between emeraldine salt and such a water, models containing a tetramer in bipolaronic or polaronic form, chloride counterions, and an explicit water molecule are used. Different initial positions of water with respect to the oligomer chain-tangential and vertical-are considered. Various media are simulated by introducing an implicit solvent continuum of decreasing polarity. The DFT-D3/PCM computational approach is employed to examine the behavior of the systems in several aspects-the role of the explicit water position and the effect of the environment polarity on the spatial structure, energetics, charge distribution, and the frontier molecular orbital energies. The strength of hydrogen bonding and the patterns of charge redistribution invoked by the water molecule are discussed. The study establishes trend lines in the variation of the molecular characteristics upon change of milieu as a tool for control of the self-assembly process. The results show that chains interact more efficiently with tangentially placed water. The influence of the environment polarity is minor and is mainly expressed in slight shortening of the intermolecular distances and mild decrease of the group charges of the system components with reduction of polarity.

The structuring of water molecules at the water/vapour interface is an object of scientific interest for decades. After the first successful attempts to explore liquid water with the help of theoretical chemistry, the number of studies on this topic grows progressively. Most of them are focused on bulk water but there is still need of a more detailed research on surface water. In addition, interfaces with alkanes are interesting as being instructive from both biological and industrial perspectives. Since in both bio- and industrial applications water/air and water/oil interfaces are mediated by amphiphiles, the role of a surfactant monolayer on surface water structuring deserves more attention as well. In the present study several atomistic water models were chosen—non-polarisable (SPC, TIP3P, and TIP4P) and polarisable (SW-RIGID-ISO, SWM4-NDP, and COS/G2) and classical molecular dynamics simulations were carried out on bulk water, water/vapour and water/alkane (from pentane to nonane) systems, as well as on water/DLPC/vapour and water/DLPC/octane models. In all cases the temperature was kept at 298 K. Several structural properties of bulk and surface layers were examined by means of radial distribution functions and Voronoi analysis. Dipole moments, surface tension and hydrogen bonding were addressed too. The objective was to estimate the impact of accounting for polarisability on the water properties of interest and to select a cost-efficient water model for describing them, as well as to add new data to the existing knowledge about interfacial water structuring.

International audience; Structural characteristics of model monolayers of dilauroyl phosphatidylcholine (1,2-dilauroyl-sn-glycerol-3-phosphatidylcholine [DLPC]) adsorbed at the water/vapors and water/octane interfaces were studied by means of computational chemistry methods. Coarse-grained, followed by all-atom molecular dynamics simulations were used to obtain the monolayers equilibrium structures at room temperature at both fluid interfaces. The analysis of the polar head orientation, polar region thickness, tail lengths, and NMR order parameter revealed that the different interface composition affects only the tail lengths and their orientation with respect to the interface. At the octane/water boundary the DLPC tails are less extended than the tails at the water/vacuum interface and are rather significantly tilted or multiply folded. Very similar structuring of the polar DLPC region at both studied boundaries was established. Dynamic C-13 NMR chemical shift values, (C-13) computed with density functional theory allowed to identify the interface effect on the DLPC molecular structure and the intramolecular motions in the adsorbed monolayer at the room temperature equilibrium. Detailed analysis of these dynamic (C-13) values compared with available experimental data and static (C-13) estimates of one DLPC low-energy conformer are presented and discussed.

Olygo(ethylene glycol) alkyl ethers – C x E y are well known for their high surface activity and rich phase behavior. These substances exhibit some unusual aggregation characteristics in aqueous solution even at concentrations well below CMC attributed to the formation of pre-aggregates of small size, e.g., dimers. To verify this, a series of C 12 E 3 dimers with initial geometries taken from coarse-grained molecular dynamics simulations is subject to geometry optimization with two quantum chemical methods: DFT and ONIOM in implicit water solvent. The resulting structures are classified into groups based on structural parameters. Their stability is assessed by relative and binding energy and rationalized in terms of molecular characteristics. All studied dimers are stable and various mutual alignments of the surfactants therein are feasible. The loss of surface area is outlined as the predominant stabilizing factor. Substantial number of the structures is suitable for further aggregation.

In order to afford in a controlled fashion fine-tuning of the color and the intensity of the emitted light of potential fluorophores for organic light-emitting diodes (OLED), directed molecular design based on a donor-spacer-acceptor model is undertaken. One way of increasing emission efficiency is triplet harvesting. This can be achieved by thermally activated delayed fluorescence (TADF) when triplet and singlet excited states are quasi degenerate. Molecular building units are selected and bound in a specific pattern to allow for increase in emission performance, also due to TADF. Using time-dependent density functional theory, the relevant singlet-singlet and triplet-singlet energy gaps corresponding to absorption or emission transitions of the compounds are computed to simulate the electroluminescent spectrum. The results are analyzed in depth and relations between some spectral and structural properties are proposed. The best suited molecules are delineated as potential OLED building blocks. Guidelines for systematic improvement of the molecular characteristics are outlined.

Nonionic surfactants, such as poly(ethylene glycol) alkyl ethers (abbreviated as CyEx) show a rich phase behavior in aqueous solution, i.e., they form micellar, lamellar, cubic, and so forth phases depending on experimental parameters such as the hydrophobic and hydrophilic chain lengths, temperature, or concentration. The aim of the present study is to determine the nature of the preaggregates, which are inferred to exist before the actual self-assembly process in aqueous solution, and to assess the aptitude to their formation. The target molecules are C12E3, C12E4 and C12E5, surfactants of moderate water solubility. Coarse-grained and all-atom molecular dynamics simulations (NPT/293 K) of two molecules of each species with explicit water in periodic boundary conditions are carried out to estimate the mutual orientation and the interaction between the surfactants in their dimers. The force fields are MARTINI and Amber99, the latter with self-derived parameters for the ether groups. The change in the orientation and distance between the molecules in the dimers are discussed based on different structural parameters. In addition, the interaction between the surfactants is evaluated from quantum chemistry calculations in terms of binding energy for the average structures from the cluster analysis. The solvent-solute interaction is quantified by the mean number of hydrogen bonds formed between them. On the basis of combined analysis, a series of different structures for subsequent study of the possible self-assembly patterns of C12E3, C12E4, and C12E5 is outlined.

Control of the size and agglomeration of micellar systems is important for pharmaceutical applications such as drug delivery. Although shape-related transitions in surfactant solutions are studied experimentally, their molecular mechanisms are still not well understood. In this study, we use coarse-grained molecular dynamics simulations to describe micellar assemblies of pentaethylene glycol monododecyl ether (C12E5) in aqueous solution at different concentrations. The obtained size and aggregation numbers of the aggregates formed are in very good agreement with the available experimental data. Importantly, increase of the concentration leads to a second critical micelle concentration where a transition to rod-like aggregates is observed. This transition is quantified in terms of shape anisotropy, together with a detailed structural analysis of the micelles as a function of aggregation number.

Calculations for model oligomers of the emeraldine salt with UBLYP/6-31G*/PCM are performed. The models differ in number of monomers, in the position of the counterions (Cl-), and in multiplicity. The molecular features affected most prominently by the protonation, namely, structure, energetics, and electron and spin density partitioning are analyzed. The results show unequivocally that the studied molecular characteristics are essentially size independent. The octamer profiles of all parameters are repeated in the dodecamer and the hexadecamer. The bipolaronic forms are energetically more favorable than the polaronic ones within the chosen protocol. The electronic structure in the intermediate multiplicities differs from the bipolaronic and polaronic periodicity. The geometrical changes and electron density redistribution upon increase of multiplicity illustrate the pathway of intramolecular bipolaron-polaron conversion. The orbital analysis rationalizes the observed behavior of the oligomers. © 2011 American Chemical Society.

Quantum mechanical simulations of a variety of inorganic and organic emeraldine salts (doping agents HCl, HBr, H2SO4, MSA, BSA, and CSA) in bipolaron and polaron form with account of solvents of different polarity (chloroform, m-cresol, and water) are reported for the first time. The models are based on tetramers, and the calculations are performed with the DFT method. The polarizable continuum model is used for the treatment of solute-solvent interaction. The effect of the different dopants and polarity of the solvents on the electronic structure and properties of the salts is evaluated and interpreted from the standpoint of the available experimental data. © 2010 Wiley Periodicals, Inc.

The interaction of Li atoms with BN- and B-substituted hydrocarbons was examined. A substantial number of prescreened stable BN- and B-isomers of anthracene and phenanthrene at all possible degrees of doping were used as models for adsorption of a Li-atom. The energy of the Li/substrate systems was calculated with the UMP2/6-31G∗ method. The total and the binding energies (BSSE and ZPE corrected) at each adsorption position of Li over the substituted hydrocarbons were evaluated. On the basis of the energy estimates and analysis of the molecular orbitals and electron density distribution, factors governing the preferred locations of the Li-atom on BN- and B-substituted anthracenes and phenanthrenes with different degrees of doping were outlined. Li positioned closer and bonded tighter to the substituted than to the pristine hydrocarbons. Optimal parameters ensuring minimum irreversible capacity of the substrate were defined: medium binding of Li combined with maximum charge transfer – requirements met by BN-anthracenes and B-phenanthrenes at low degree of doping and B-anthracenes with higher B-contents, the two latter being more prospective. The results provide valuable information for the molecular design of anode materials for Li-ion batteries with improved performance.

The aim of this theoretical study is the investigation of hydrocarbon stability as a function of BN- and B-substitution degree. The targets are anthracene and phenanthrene because they resemble the zig-zag and armchair peripheries of graphene sheets. The computations are made at the RHF and MP2 level with various basis sets. The conclusions drawn are based on the results from calculations for more than 600 different structures created in a systematic way where pairs of carbon atoms are replaced by the respective number of B and N, or solely B-atoms. A common feature of all stable substituted molecules is the tendency for least fragmentation of the carbon skeleton, particularly, for preservation of maximum number of intact carbon aromatic cycles. The major dissimilarity between the BN- and B-substituted molecules are the preferred doping patterns and positions: the favorable structures feature alternation of B and N in the BN-derivatives and disjoint borons separated by C 2 fragments in the B-ones; the nitrogen atoms substitute predominantly secondary carbons, while borons prefer tertiary sites in the BN-substituted hydrocarbons and secondary positions in the B-modified structures. Overall, the anthracene isomers are more stable. The energy and AO contributions to the LUMOs of the studied species are rationalized in terms of electron-accepting properties of the latter, estimating their potential performance as oxidants. Energy depression of LUMOs is achieved mainly in B-substituted hydrocarbons due to large coefficients on the borons causing pronounced delocalization of the orbital. The findings can be used for directed synthesis of novel modified carbon-based materials for practical purposes.

We report a theoretical study on the geometry characteristics and the electronic properties of bipolaron defects introduced in oligomers (tetramer to hexadecamer) of emeraldine salt. The main goal of the present investigation is to establish a quantum chemical method suitable for description of the target system and for determination of the oligomer segment perturbed by protonation. For the purpose, a series of first principles methods (HF and DFT) combined with different basis sets are tested and the influence of the medium (water) dielectric constant is estimated using PCM. It is shown that the optimized molecular geometry is critically dependent on the theoretical formalism applied. HF yields geometry of the tetramer substantially distorted from planarity and bipolaron, which is highly localized in the quinoid ring. The bipolaron produced by DFT tends to delocalize, thus enhancing the conjugation along the oligomer chain. The reliability of the separate methods is commented on the basis of a list of criteria such as reproducibility of available experimental geometry, spin contamination of wavefunctions and quantification of correlation effects. The BLYP/6-31G*/PCM method is outlined as the most appropriate. It is found that irrespective of the oligomer chain length and the degree of protonation (partial or full) a bipolaron spreads on three phenyl rings and the nitrogen atoms bound to them. © 2010 Elsevier B.V.

Quantitative Structure Activity Relationships (QSAR or SAR) have helped scientists to establish mathematical relationships between molecular structures and their biological activities. In the present article, SAR studies have been carried out on 89 tetrahydroimidazo[4,5,1-jk][1,4]benzodiazepine (TIBO) derivatives using different classifiers, such as support vector machines, artificial neural networks, random forests, and decision trees. The goal is to propose classification models that will be able to classify TIBO compounds into two groups: high and low inhibitors of HIV-1 reverse transcriptase. Each molecular structure was encoded by 10 descriptors. To check the validity of the established models, all of them were subjected to various validation tests: internal validation, Y-randomization, and external validation. The established classification models have been successful. The correct classification rates reached 100% and 90% in the learning and test sets, respectively. Finally, molecular docking analysis was carried out to understand the interactions between reverse transcriptase enzyme and the TIBO compounds studied. Hydrophobic and hydrogen bond interactions led to the identification of active binding sites. The established models could help scientists to predict the inhibition activity of untested compounds or of novel molecules prior to their synthesis. Therefore, they could reduce the trial and error process in the design of human immunodeficiency virus (HIV) inhibitors.

The simulations of emeraldine hydrochloride tetramers were performed for the first time in implicit water solvent using the polarisable continuum model (PCM) with the density functional theory (DFT) method. This approach should be more appropriate for the study of the conducting form of polyaniline as all known processes of synthesis and further transformations take place in polar medium. Our results confirm this hypothesis and clearly indicate that the geometry and electronic structure of the emeraldine salt depend on the dielectric properties of the medium. In polar environment the protons are bound tighter to the chains compared to vacuum and this leads to stronger impact of the dopant on the structural parameters of PANI. As a consequence, the density distribution in the emeraldine hydrochloride obtained by PCM is more realistic compared to vacuum estimates. The stability in polar medium of two possible salt configurations with respect to counterions position is assessed. Each configuration is simulated in singlet and triplet state (bipolaron and polaron). The results show that at the tetramer level the bipolaron form is always preferred in accordance to available experimental results.

Atomistic modeling of insoluble monolayers is currently used to inspect their organization and electric characteristics, providing a link between theory and experiment. Extensive molecular dynamics simulations at 300 K were carried out for model films of the lipids dipalmitoylphosphatidylcholine (DPPC) and dicaprin (DC) at the air/water interface. Surface concentrations corresponding to a set of points along the surface pressure/area isotherms of the surfactants were considered. The models contained 25 or 81 lipid molecules in hexagonal arrangement and explicit aqueous media (TIP3P) treated in periodic boundary conditions. Molecular dynamics simulations based on a classical force field (CHARMM27) were carried out and key characteristics of the studied films were estimated. The dielectric properties of the films in normal and tangential direction were quantified by means of dipole moment magnitude and orientation analysis and by monolayer dielectric permittivity. The contributions of lipids and interfacial water to each component of the considered characteristics were assessed and their variations upon film compression were discussed and compared for the two monolayers and to earlier results. The dielectric permittivity tensors were analyzed. Electrostatic potential profiles across the layers and surface pressure values were used for more detailed clarification of experimental measurements. The results show dissimilar behavior of the two lipids at the air-water interface. While the average electric and dielectric properties of DPPC monolayers result from opposite surfactant and water contributions, the two subsystems are synergetic in the DC films. The anisotropy of the monolayer dipole moment and dielectric permittivity is explained by domination of a different subsystem in the various components. Tangential characteristics turn out to be more sensitive to the size of the model and to the degree of film compression.

Theoretical approaches to hybrid-spin systems aim at clarification of the nature of spin exchange between the metal ion and the organic radicals. This aids the molecular design, of novel materials based on studies of the relevant molecular fragments. The current investigations were focused on two isomeric complexes of CuII with acetylacetonate and organic radicals (3- and 4-N-oxyl-tretbutylaminopyridine), whose geometry and magnetic properties were known from, experimental data. A DFT approach based on the UB3LYP functional and basis sets of different size and quality were used in order to elaborate a computational protocol providing a reliable quantitative estimate of the spin-spin interaction. The computational scheme allows the elucidation of the role of various structural factors on the type and magnitude of the spin coupling, such as symmetry, spatial orientation of the radicals and type of the magnetic orbital of the metal ion. Proper symmetry assignment of the wavefunction proved to be critical for correct description of the magnetic behaviour of the complexes. The introduction, of extended basis sets did not justify the computational cost, as the 6-31G* results were sufficiently accurate for the purpose of the study. Detailed analysis of the energies, the natural orbitais and the spin density distribution, upon conformational changes was carried out. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.

Films of polyaniline (PANI) featuring about 80% crystallinity and characterised with strong π-π stacking alignment parallel to the film surface have been obtained directly after the original synthesis upon simple drying of the aqueous PANI suspension. A strong anisotropy in the growth of the nano-sized crystals produced during the synthesis results in the formation of micrometer-length fibrils perpendicular to the film surface in the course of water evaporation. The regular intercalation of water molecules between the PANI chains seems to be crucial for their ordering throughout the synthesis and film formation.

Photoexcitation as a novel route for obtaining delocalized polarons in conducting polyaniline is predicted theoretically and confirmed experimentally. Original model experiments and theoretical calculations on protonated emeraldine species with various chain alignments as well as of isolated chains were carried out. In addition, experimental models matching theoretical models of isolated and bulk polyaniline (PANI) chains were synthesized and their absorption and Raman spectra recorded. The detection of the photoexcited states was performed by conventional Raman scattering spectroscopy (generally employed for studying ground states), which is an attractive alternative for generating and characterizing photoexcited delocalized polarons in polyaniline. The occurrence of photoexcited delocalized polaronic species is favored by chain stacking.

Studies of insoluble monolayers built of phospholipids, various long-chained fatty acids, and their glycerin esters are the major source of our current knowledge about the relationship between monolayer composition and its physicochemical properties. Such are the surface pressure, dipole moment, dielectric permittivity, polarizability, refractivity, and other electrical and optical features governed by the surfactant structural specificity and solvent organization at the microscopic level. Therefore, model monolayers at the air/water interface of two surfactants that are distinctly different in composition and isotherm profile are investigated by means of a Monte Carlo/molecular mechanics computational procedure. The combination of experimental and theoretical results permits estimation of empirically unattainable quantities and a detailed insight in the interfacial molecular organization at different surface concentrations as well as an evaluation of the surfactant/water contributions to the overall monolayer characteristics. The employed theoretical approach provides a comprehensive description of phenomena at the molecular level where the traditional phenomenological investigations are ineffective. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

Investigations addressing correlation between antioxidant activity and theoretical descriptors are plentiful in the literature. This task is quite ambitious, bearing in mind the rather complicated interactions in living cells. In this study we have tried to simplify the problem by looking for direct correlations between calculated characteristics and scavenging activity, neglecting the specificity of cellular environment. To address the problem of antioxidant activity, a set of 20 phenolic compounds and their phenoxyl radicals were investigated at the unrestricted B3LYP level of theory using the 6-31+G(d,p) basis set. Three important descriptors of the considered compounds were related to the results of the DPPH scavenging activity. Significant linear correlations were obtained in several cases.

On the basis of ab initio and density functional theory (DFT) calculations of the o-coumaric amide and thioamide, the latter is found to have better delocalization. It is demonstrated that the thioamide function features stronger attraction for electron density from the conjugated residue. Therefore, the electronic distribution in the thioamide favors stable phenoxyl radical formation. This is a reason to expect better antioxidant activity of the thioamide. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

Polyaniline (PANI) is one of the most studied conducting polymers. Obtained in its conducting form (known as "emeraldine salt") by chemical or electrochemical oxidation of aniline in aqueous acidic medium, this polymer manifests an array of attractive properties. Nevertheless, these properties still need to be described at the molecular level. Intense theoretical investigations during the past few years aim at explaining the chain organization, conductivity mechanism, and other structural and spectral characteristics. Most studies adopt simplified models in which hydration effect is underestimated, since all simulations are performed either in vacuum or in the presence of a limited number of water molecules. The present computational study sheds light on the molecular organization of a number of model PANI hydrated clusters with different alignment and multiplicity, which can explain the experimentally recorded UV/VIS spectra. The influence of hydration and interaction with adjacent oligomers is estimated. Short-chain doubly protonated emeraldine oligomers are used as model systems. The calculations are performed at the semi-empirical (AM1) and/or molecular mechanics (AMBER96) level. Proper configurations of the clusters are selected using Monte Carlo simulations. Electron correlation (CIS) is accounted for upon evaluation of the absorption spectra of the clusters. The relative strength of the interchain coupling is estimated by simulation of PANI clusters consisting of two PANI tetramers in water. Comparison to experimental results is made.

A new class of open-shell polymethine monoradicals, possessing nonbonding molecular orbitals (NBMO) and very low excitation energies, was investigated theoretically. The radicals are derivatives of the stable 2-azaphenalenyl radical. Since in the ground state the NBMO is strictly localized within a molecular fragment, the electron transitions are connected with a substantial charge-transfer. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

Polyaniline is among the most intensely investigated polymers because of its exceptional properties affording its current and potential applications. The structure and energy spectra of isolated oligomers and infinite chains in different oxidation states and degrees of protonation have been discussed at length from experimental and theoretical perspectives. The reaction environment effect, however, has received less attention and, particularly, the influence of monomer excess has been completely neglected in theoretical studies. Experimental measurements show that residual aniline is always detected in emeraldine samples obtained at low pH. Upon addition of oxidant to emeraldine PANI samples, post-polymerization due to the presence of excess monomers occurs. This is an indication of the formation of aniline-PANI complexes in the reaction medium. The presence of aniline monomers should affect the PANI chain arrangement and optical/conducting characteristics. Therefore, model clusters of aniline with neutral or singly protonated emeraldine tetramers in explicit water medium and periodic boundary conditions are addressed in this paper using a Monte Carlo/AMBER96/AM1 computational protocol to simulate the absorption spectra. The monomer impact on the structure, energy characteristics, and UV/vis spectra of the polymer are discussed.

The article describes the results of semiempirical quantum-chemical calculations for a series of 3',5'-esters of 5-bromo-2'-deoxyuridine with amino acids or peptides. These compounds were synthesized and tested for antiviral activity as potential prodrugs of the parent 5-bromonucleoside. It was not clear why only some of the compounds were active. On the basis of structure investigation and the calculated molecular descriptors, it was found that the determining factor for obtaining appropriate prodrugs of 5-bromo-2'-deoxyuridine is the lipophilicity of the esters.

Polyaniline (PANI) has attracted lasting interest due to its unconventional electronic, optical, and electro-optical properties. A rigid backbone polymer, PANI exhibits very strong intra- and intermolecular interactions governing its overall behavior. The purpose of this study is to investigate theoretically the contribution of the various inter- and intramolecular interactions to the process of organization of PANI macromolecules in aqueous environment. The structure and spectral conduct of oligoanilines (tetramers) in different oxidation states have been calculated at the Monte Carlo/Molecular Mechanics (MC/MM) and quantum chemical (QC) semiempirical level. The effect of protonation on the optical properties of partially and fully oxidized oligomers is discussed. The role of intermolecular interactions and the influence of water as a solvent are estimated for a number of hydrated clusters. Computed results and experimental spectra are compared. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006