Chemistry

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Shiv Nadar University

We report a study of photoinduced charge separation in poly(1,4-phenylenevinylene) (PPV) derivatives with enhanced exciton dissociation using light-induced electron paramagnetic resonance (EPR). Four polymers were studied; all contained alkoxy and fluorenyl side chain units, and two of them also contained a nitro group on the 7-positon of the fluorenyl moieties. Pulsed EPR detected a light induced polaron for all the polymers with the intensity significantly higher for those with nitro groups. A second center was observed for these materials and spectra could be fitted assuming a radical anion was localized on the nitro groups. The fraction of radical anion and polaron centers was comparable, consistent with intramolecular exciton dissociation for the PPV derivatives containing the nitro groups. © 2008 Elsevier B.V. All rights reserved.

World University root node

(SoNS) School of Natural Sciences

Organic Electronics

Photoinduced charge separation in poly(1,4-phenylenevinylene) derivatives studied by electron paramagnetic resonance

During crystallization experiments two new polymorphs of the highly-active organic nonlinear optical (NLO) material 3-methyl-4-methoxy-4′- nitrostilbene (MMONS) have been discovered. Crystallization conditions of all three polymorphs and their characterization via crystal structure determination from single crystal X-ray diffraction data at 100 K have been discussed in detail. Two of the polymorphs exhibit different conformations, while a third polymorph incorporates both conformers as well as disorder. Comparisons between various types of intermolecular contacts in these three polymorphic forms have been quantified via Hirshfeld surface analysis. © The Royal Society of Chemistry.

Fulltext

CrystEngComm

Polymorphism in 3-methyl-4-methoxy-4′-nitrostilbene (MMONS), a highly active NLO material

Data fusion originally referred to the process of combining multi-sensor data from different sources such that the resulting information/model is in some sense better than would be possible when these sources where used individually. In this paper the data fusion concept is extended to molecular drug design. Rather than using data from different sensor sources, different descriptor sets are used to predict activities or responses for a set of molecules. Data fusion techniques are applied in order to improve the predictive (QSAR) model on test data. In this case this type of data fusion is referred to as auto-fusion. An effective auto-fusion functional model and alternative architectures are proposed for a predictive molecular design or QSAR model to model and predict the binding affinity to the human serum albumin. © Springer-Verlag Berlin Heidelberg 2007.

Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)

Data fusion and auto-fusion for Quantitative Structure-Activity Relationship (QSAR)

The structure of l-ornithine hydrochloride, C5H13N2O Cl-, has been redetermined at 100 K by single-crystal X-ray diffraction within a project that aims to generate accurate bond-distance restraints for the invariom refinement of proteins. The high-resolution data were subject to an invariom and a multipole refinement, and the resulting electron densities on a grid were compared. Improvements in the conventional R factor obtained by multipole modelling were smaller than in other structures containing solely the elements CHNO owing to Cl core scattering. Cruickshanks diffraction-component precision index and Stevens &amp; Coppens suitability factor are discussed. © International Union of Crystallography 2007.

Acta Crystallographica Section B: Structural Science

Redetermination, invariom-model and multipole refinement of L-ornithine hydrochloride

Although reliable determination of the molecular dipole moment from experimental charge density analyses on molecular crystals is a challenging undertaking, these values are becoming increasingly common experimental results. We collate all known experimental determinations and use this database to identify broad trends in the dipole moment enhancements implied by these measurements as well as outliers for which enhancements are pronounced. Compelling evidence emerges that molecular dipole moments from X-ray diffraction data can provide a wealth of information on the change in the molecular charge distribution that results from crystal formation. Most importantly, these experiments are unrivalled In their potential to provide this information in such detail and deserve to be exploited to a much greater extent. The considerable number of experimental determinations now available has enabled us to pinpoint those studies that merit further attention, either because they point unequivocally to a considerable enhancement in the crystal (of 50% or more), or because the experimental determinations suggest enhancements of 100% or more - much larger than independent theoretical estimates. In both cases further detailed experimental and theoretical studies are indicated. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.

ChemPhysChem

Dipole moment enhancement in molecular crystals from X-ray diffraction data

We describe the use of dipole lattice sums to estimate the electric field experienced by a molecule in a crystal, and apply it iteratively to ab initio calculations on a number of molecules of interest for nonlinear optical applications. The results demonstrate that it represents an efficient and reliable route to estimating molecular dipole moments in crystals. Typical dipole moment enhancements are in the range of 10-40%, agreeing well with the range resulting from partitioning of crystal Hartree-Fock electron densities, but much less than has been suggested in some previous work, and in particular from charge density analysis of X-ray diffraction data. © 2007 Elsevier B.V. All rights reserved.

Chemical Physics Letters

The use of dipole lattice sums to estimate electric fields and dipole moment enhancement in molecular crystals

An intramolecular Schmidt reaction strategy for the synthesis of various derivatives of crispine A using azido-ketone as a key intermediate is described.

Beilstein Journal of Organic Chemistry

Synthesis of crispine A analogues via an intramolecular Schmidt reaction

Titanium(ii) solutions, prepared by dissolving titanium wire in triflic acid + HF, contain equimolar quantities of Ti(iv). These preparations react readily with oxidizing species such as VO2+, substituted benzoquinones, and the biguanide complex of Mn(iv). Reactions with excess Ti(ii) yield Ti(iii). Reductions of 1,4-benzoquinones and the Mn(iv) complex are catalyzed by added Ti(iv) but stoichiometry is unaffected. Rate laws for the Ti(iv)-catalyzed reactions are consistent with formation of a Ti II-TiIV complex (Kformation 4 × 10 2 M-1), which, in some cases, also partakes in contributing deprotonated and halogen-catalyzed paths. © The Royal Society of Chemistry.

Dalton Transactions

Reductions of oxo species by aquatitanium(ii) as catalyzed by titanium(iv)

The Quantum Theory of Atoms in Molecules: From Solid State to DNA and Drug Design

QTAIM in Drug Discovery and Protein Modeling

The crystal structure of the N,N,N′,N′- tetramethylethylenediammonium dithiocyanate salt has been examined by experimental charge density studies from high-resolution X-ray diffraction data. The corresponding results are compared with multipole refinements, using theoretical structure factors obtained from a periodic density functional theory calculation at the B3LYP level with a 6-31G** basis set. The salt crystallizes in space group P1̄ and contains only a single ion pair with an inversion center in the cation. The salt has thus one unique classical N +-H⋯(NCS)- hydrogen bond but also has six other weaker interactions: four C-H⋯S, one C-H⋯N, and one C-H⋯Cπ. The nature of all these interactions has been examined topologically using Bader's quantum theory of "atoms in molecules" and all eight of the Koch-Popelier criteria. The experimental and theoretical approaches agree well and both show that the inter-ion interactions, even in this simplest of systems, play an integrated and complex role in the packing of the ions in the crystal. Electrostatic potential maps are derived from experimental charge densities. This is the first time such a system has been examined in detail by these methods. © 2007 American Chemical Society.

Journal of Physical Chemistry A

Investigation of inter-ion interactions in N,N,N′N′- tetramethylethylenediammonium dithiocyanate via experimental and theoretical charge density studies