Comparability graphs and electronic spectra of condensed benzenoid hydrocarbons

A systematic topological approach to the search for regularities in molecular properties has been proposed on the basis of the so-called comparability graphs of isomeric classes of molecules. It is shown that the ordering of the isomeric benzenoid hydrocarbons in the comparability graphs coincides with that of the longest wavelenght in the p band of their electronic spectra.     

A machine learning approach to computer-aided molecular design

Summary Preliminary results of a machine learning application concerning computer-aided molecular design applied to drug discovery are presented. The artificial intelligence techniques of machine learning use a sample of active and inactive compounds, which is viewed as a set of positive and negative examples, to allow the induction of a molecular model characterizing the interaction between the compounds and a target molecule. The algorithm is based on a twofold phase. In the first one — the specialization step — the program identifies a number of active/inactive pairs of compounds which appear to be the most useful in order to make the learning process as effective as possible and generates a dictionary of molecular fragments, deemed to be responsible for the activity of the compounds. In the second phase — the generalization step — the fragments thus generated are combined and generalized in order to select the most plausible hypothesis with respect to the sample of compounds. A knowledge base concerning physical and chemical properties is utilized during the inductive process.     

The BCR programme and measurements for food and agriculture

Summary The importance of accurate and comparable measurements to the removal of technical barriers to trade and the achievement of the single European Market is well established. The BCR Programme is recognized as having an important role in this area, a fact reflected in a substantial increase in the programme in recent years.There has been a consequential expansion of its activities for food and agricultur measurements which currently involves some 50 projects and will lead to the issue of a further 25 CRMs in the next 12 months.Topics covered include:Nutritional properties — fatty acids, sterols, total fat, protein, carbohydrates, dietary fibre, oil and fat soluble vitamins, and major elements.Undesirable substances — PAHs, PCBs, shellfish toxins, mycotoxins, heterocyclic amines, nitrate, pesticides and toxic element in food and animal feed.Technological properties — bread making quality of flour (farinograph, extensograph, etc.), determination of gluten in wheat, rapid NMR methods and reference materials for the oil content of rapeseed, reference colour tiles for calibration of colorimeters for tomato paste, and characterisation of natural products by isotopic determination (NMR and MS).For agriculture particular emphasis has been placed on methodology and RMs for the analysis of the very wide range of growth promoting compounds in farm animals (organs and fluids). Other projects concern amino-acids in feed and rapid method (XRF) for glucosinolates in rapeseed. Although most of the projects lead to CRMs, the common feature and indeed, the objective of the work, is the establishment of reliable reference values which form the basis for the accuracy and comparability of the results of these measurements.The work of the BCR Programme in this area is reviewed and the steps taken to ensure that the reference values are accurately certified with an acceptably small uncertainty are illustrated with examples taken from current projects.     

On the Existence and Hydrolytic Stability of Titanosiloxane Bonds in the System: Glycidoxypropyltrimethoxysilane-Water-Titaniumtetraethoxide

Heterometal materials based on glycidoxypropyltrialkoxysilane and titaniumalkoxide are used for optical applications and require a high homogeneity on the molecular level. The presence of heterometal titanosiloxanes, their distribution and hydrolytic stability should influence the homogeneity of these materials. 29Si and 17O NMR spectroscopy has been used to investigate sols with molar ratios Si : Ti = 1 and H2O : OR (H) = 0.5 – 2.0 and their gels after heat treatment at 130°C. The presence of Si—O—Ti bonds in sols with a low water content (H < 0.2) and in the corresponding gels was identified by the high-field shift of the 29Si NMR signals of T1 and T2 units of up to 2–3 ppm compared to corresponding signals of homo-condensed Si—O—Si bonds. The existence of Si—O—Ti bonds in the sols is supported by 17O NMR spectra which show a characteristic signal around 340 ppm. A cleavage of the Si—O—Ti bonds occurs with increasing water/OR ratio in the sols. The cleavage of the heterometal bonds and the building up of homo-condensed species leads to a separation into areas with predominantly Ti—O—Ti and Si—O—Si bonds resulting in a decreased molecular homogeneity of the materials.     

Photo‐induced thiol‐ene polysulfide‐crosslinked materials with tunable thermal and mechanical properties

Photo‐induced thiol‐ene crosslinked polymeric networks have been extensively explored in constructing a variety of new materials with enhanced mechanical properties for optical, biomedical, and sensing applications. Toward the broad applications, however, tunable mechanical properties are greatly desired. Here, an effective approach utilizing high‐molecular‐weight methacrylate copolymers having pendant thiol and vinyl groups (MCPsh and MCPenes) to modulate thermal and mechanical properties of photo‐induced thiol‐ene crosslinked materials is reported. The MCP copolymers are synthesized by an industrially friendly polymerization method, followed by post‐modification including either a facile coupling reaction or reductive cleavage. Upon UV irradiation, thiol‐ene reactive blends of MCPsh and MCPenes yield highly crosslinked materials through the formation of flexible sulfide linkages. These polysulfide‐crosslinked materials based on rigid MCP backbones exhibit enhanced mechanical properties. Further, their thermal and mechanical properties are tuned by modulating monomer compositions of MCPs as well as varying numbers of pendant SH or vinyl groups (i.e., extent of crosslinking densities). This approach is versatile and effective for development of high performance polymeric materials. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3060–3068     

Comparability graphs and molecular properties III. C9 and C10 alkanes

The graph-theoretical approach recently developed for comparing and ordering isomeric chemical compounds is extended and applied to the calculation of various molecular properties of C₉ and C₁₀ alkanes (critical densities, volumes, and pressures; heats and entropies of vaporization; standard entropies in liquid and gas state). The key to the approach is in specifying subsets of comparable isomers which are located in the same paths in the so-called comparability graphs. Optimized samples for structure-property correlations are thus obtained.     

Optical Alignment of Organic Dopants in a Solid Gel Matrix: Dispersed and Grafted Rhodamine B Molecules

We study herein the rotational mobility of organic dye molecules and their ability to align on a strong optical electric field when they are encaged in the pores of an inorganic silica xerogel matrix. We compare the case of dye molecules simply dispersed in the pores of the gel—and possibly held by hydrogen bonds—to the case of molecules chemically grafted on the inner surface of these pores through covalent bonds. The study is led on hybrid silicon-zirconium based inorganic matrices doped with organic rhodamine B molecules. The stronger holding of the dopants when these are grafted to the matrix enhances the molecular alignment—and thus the induced anisotropy—as well as the remanence of this alignment. Furthermore, we show that submitting the samples to a supplementary drying at higher temperature tends to increase both the alignment anisotropy and its stability. We explain these results in terms of mobility of the molecules, in relation to their immediate environment.     

Self-assembly of “patchy” nanoparticles: a versatile approach to functional hierarchical materials

The solution-phase self-assembly or “polymerization” of discrete colloidal building blocks, such as “patchy” nanoparticles and multicompartment micelles, is attracting growing attention with respect to the creation of complex hierarchical materials. This approach represents a versatile method with which to transfer functionality at the molecular level to the nano- and microscale, and is often accompanied by the emergence of new material properties. In this perspective we highlight selected recent examples of the self-assembly of anisotropic nanoparticles which exploit directional interactions introduced through their shape or surface chemistry to afford a variety of hierarchical materials. We focus in particular on the solution self-assembly of block copolymers as a means to prepare multicompartment or “patchy” micelles. Due to their potential for synthetic modification, these constructs represent highly tuneable building blocks for the fabrication of a wide variety of functional assemblies.     

Auxiliary functions for Slater molecular integrals

Summary Some types of recurrence relations are modified to overcome the cases in which their conventional application is unstable in both the forward and backward directions. The original recurrence relations — connecting adjacent elements — are replaced by more general ones, where the non-adjacent elements are connected by coefficients obtained by new sets of relations derived from the original ones. This modification can be helpful for the calculation of the complicated molecular integrals with Slater Type Orbitals (STOs).As a simple test we prove that some auxiliary functions — previously evaluated by expensive expansions — appearing in two-center two-electron integrals can be thus calculated with very low computer cost and high accuracy.     

Synthesis,reactions, and properties of some selenides of the thiophene,furan, and selenophene series (review)

The review is devoted to the authors' research on the synthesis and study of the reactivities of selenides of the thiophene series, and, to a lesser extent, of selenides of the furan and selenophene series. The properties of the indicated compounds — their capacity for reaction with electrophilic agents and organolithium compounds — and their spectral characteristics are examined in order to compare them with the properties of the corresponding sulfides and alkoxy derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 723–737, June, 1972.     

The miscibility of dodecyltrihydroxyethylammonium bromide with cationic, nonionic and anionic surfactants in mixed monolayers and micelles

In this paper were analyzed the surface properties of surfactants and the miscibility and interactions between components of adsorbed monolayers and micelles formed from mixed systems. The investigated compounds differ in the structure of the polar head and represented cationic (dodecyltrihydroxyethylammonium bromide—DTEAB, dodecyltrimethylammonium bromide DTMAB), anionic (sodium dodecyl sulfate—SDS), and nonionic (dodecyl-β-d-glucoside—DG) surfactant. The experiments were based on the measurements of the surface tension of the aqueous solutions of the investigated compounds and their mixtures (cationic/nonionic—DTEAB/DG, cationic/cationic—DTEAB/DTMAB and cationic/anionic—DTEAB/SDS). The composition of the mixed films and micelles as well as the free energies of mixing values, which are a measure of the molecular interactions, was calculated basing on the equations resulting from the Motomura theory. The obtained results indicate that all the investigated systems mix nonideally both in the monolayers and micelles. The magnitude of the deviations from ideal behavior is strongly dependent on the type of the investigated mixture and increases in the following order: DTEAB/DTMAB < DTEAB/DG  DTEAB/SDS.     

The determination of Eu and Sm by application of X-ray spectrometry to isotope-source activation analysis

The use, for analysis, of K X-rays proceeding from metastable and beta-emitting radionuclides—produced by neutron activation—is an undeveloped aspect of activation analysis. Consequently, this study examines the feasibility of applying X-ray spectrometry to isotope source activation analysis and in particular the determination of Sm and Eu at low levels is described. Generally speaking, the sensitivity is seriously restricted by the thermal neutron flux of the source but in certain specific cases the analysis is favoured by the nuclear properties of the elements concerned. Therefore, the selection of elements was based largely on their demand for analysis and their ability to produce a practicable yield. Optimum signalto-noise ratios were attained by employing a detector that was particularly sensitive at energies below 150 keV. Analytical conditions are demonstrated for the elements of interest over a wide range of concentrations in small samples, and ultimately the applicability of the method was tested by the analysis of a typical monazite sample. The analytical potential of the method is thoroughly appraised and possible practical applications are discussed.     

Fatty acid-cyclodextrin complexes: Properties and applications

The complexation of fatty acids (both saturated and unsaturated) with various cyclodextrins and cyclodextrin derivatives greatly modifies their properties. Inclusion complex formation — depending upon the type of host cyclodextrin — may result in protection against the environment, in improved water solubility and bioavailability. Thus lipid complexation enables the preparation of more reliable diagnostic reagents, better chromatographic separations and higher yields in biotechnological processes. The relevant literature is reviewed with particular emphasis on the practical utility of the molecular encapsulation of fatty acids with cyclodextrins.     

Synthesis and properties of substituted 3-amino-2H-azirines (review)

Methods for the synthesis of and the results of studies of the chemical properties of 3-amino-2H-azirines — compounds that have a highly reactive three-membered nitrogen heteroring and an amidine system, which predetermines their multifaceted reactivity and wide use as convenient synthones for organic synthesis — are correlated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 867–887, July, 1990.     

Thermodynamic properties of the first to fifth generations of carbosilane dendrimers with allyl terminal groups

Temperature dependences of the specific heats, characteristic temperatures, and enthalpies of physical transformations of the first to fifth generations of carbosilane dendrimers with allyl terminal groups were studied using an adiabatic vacuum calorimeter in the temperature range 6—340 K. The error of measurements was, as a rule, about 0.2%. Thermodynamic characteristics of physical transformations of the dendrimers were determined and their thermodynamic functions C _p°(T), H°(T)—H°(0), S°(T)—S°(0), and G°(T)—H°(0) were calculated for the temperature range 0—340 K. The thermodynamic functions of the dendrimers are linearly related to their molecular weights, the number of allyl groups on their outer spheres, and the number of moles of diallylmethylsilane per mole of the dendrimers formed. Additive dependence of the properties of the dendrimers on their chemical composition and structure indicates that the energy of interaction between structural fragments of the dendrimers is independent of the dendrimer generation number. The fractal dimensions, D, of all dendrimers studied in this work are 1.2—1.3 in the temperature range 30—50 K, thus indicating a chain-layered structure of the dendrimer glasses.     

Structures and conformational behavior of phosphorothioites and their complexes with transition metals obtained from X-ray diffraction analysis

The data on the structures, conformational behavior, and coordination properties of phosphorothioites are summarized. Their complexes with transition metals are characterized by different modes of coordination depending on the nature of the metal atom, the substituents at the sulfur atoms, reaction conditions, and conditions of single-crystal growth. The principal differences in properties of phosphorothioites and their analogs containing the P—O and P—N bonds are analyzed.     

Theoretical study of Pu and Am tetracarbide molecules

The electronic structure and ground‐state molecular properties of Pu and Am tetracarbides have been investigated by relativistic multireference calculations using CASSCF/CASPT2 theory as well as by density functional theory in conjunction with relativistic pseudopotentials. The CASSCF/CASPT2 treatment has been extended by spin–orbit coupling effects for selected species using the CAS state‐interaction method. The five atoms can form various structural isomers, from which 12 ones have been identified in our study. The electronic ground state in both molecules corresponds to a planar fan‐type structure of C_2v symmetry, in which the actinide atom is connected to a bent C₄ moiety. The other structures are much higher in energy, the ones computed in this study appear between 250 and 1050 kJ/mol. The bonding characteristics in the most relevant structures have been analyzed on the basis of the valence molecular orbitals and natural bond orbital analysis. The most stable structures have been characterized by their spectroscopic (vibrational and electron) properties. © 2014 Wiley Periodicals, Inc.     

On the problem of directed signal transmission and energy transfer in molecular systems

A new physical interpretation of the mechanism of directed energy transfer and signal transmission in molecular systems along one-dimensional chains capable of successive isomerization is proposed. The photoacceptor—transmitting chain—reaction center system is considered as a model. Conditions under which the directed energy transfer occurs from the photoacceptor to the reaction center along the chain are analyzed. The time of signal transmission depends on the chain length, and the transmission coefficient is mainly determined by the characteristics of the initial and final elements in the whole system.