Perturbation-graph theory—I: Resonance energies of heteroannulene π systems

Perturbation theory and the graph-theoretical definition of resonance energy are combined and applied to π systems substituted with heteroatoms and external substituents. The systems investigated are monocyclic and contain 3–6 atoms with 2–8 π electrons. In general, heteroatoms are calculated to exert their effects on resonance energy through two separable mechanisms, due either to the electronegativity (h parameter) or the conjugative ability (k parameter) of the substituent atom. There is no first-order effect of electronegativity in species containing 4n+2 (n= integer) π electrons. All electronegative or electropositive substituents are predicted to stabilize 4n π electron systems. Enhanced conjugation stabilizes 4n+2 systems and destabilizes 4n systems. Several examples of ions and molecules are given that qualitatively conform to these rules.     

Structure,bonding, and spectra of cyclic dithia radical cations: a theoretical study

Ab initio molecular orbital and hybrid density functional theory methods are employed to characterize the structure, bonding and properties of several cyclic dithia radical cation systems, particularly in the context of intra molecular two-center three-electron (2c-3e) bonding between two sulfur atoms. The calculated results are able to interpret the time-resolved transient optical spectra obtained from pulse radiolysis technique for these positively charged dithia systems in aqueous solution. Visualization of the appropriate molecular orbital (MO) in the systems is able to depict the presence of a 2c-3e bond between two sulfur atoms and its sigma character. Geometry optimizations of these doublet systems are carried out at restricted open shell Becke's half-and-half (BHH) nonlocal exchange and Lee-Yang-Parr (LYP) nonlocal correlation functionals (BHHLYP) with 6-311+G(d,p) basis set including solvent effects adopting Onsager's reaction field model. Hessian calculations are done at the same level to check the nature of the equilibrium geometry. Energy data are further improved by performing MP2/6-311+G(d,p) calculations on these radical cation systems. Excited-state calculations are done following configuration interaction with single-electron excitation (CIS) method and the optical transition wavelength from the highest doubly occupied molecular orbital (HDOMO) to the lowest singly occupied molecular orbital (LSOMO) is seen to correspond and match to the position of the absorption maxima (lambda(max)) obtained from the experimental spectra for all these radical cation systems in aqueous solution. These calculations are able to resolve a long-standing ambiguity in the assignment of intra molecular 2c-3e bonding in the case of the 3-methyl-2,4-dithiapentane radical cation system and to provide new insights into bonding features of this odd electron system as well as of other cyclic dithia systems studied.     

Fluorescence of intramolecular electron donor—acceptor systems; the importance of through-bond interaction

Intramolecular electron donor—acceptor (EDA) systems have been studied in which D and A are separated by three carboncarbon sigma bonds. With D = (di)methoxyphenyl and A = 1,1-dicyanomethylene, such systems are found to show intramolecular charge-transfer (CT) type emission from a polar excited state even when the interconnecting sigma bonds are part of a rigid framework which prevents close approach between D and A. Through-bond interaction is proposed to provide the coupling between the ground state and the polar excited state in these systems.     

Detection of slightly soluble systems by means of organized media in flow-injection analysis

Species that are slightly soluble in water (reagents, analytes or reaction products can be used in hydrodynamic analytical systems by means of a judicious choice of an appropriate organized medium allowing one to operate in homogeneous media with the attendant advantages. In addition, these systems allow one to improve existing analytical methods and to develop new analytical procedures. Results obtained with two types of insoluble systems are presented: those provided by 1-(2-pyridylazo)-2-naphthol (PAN) and those originating from Arsenazo III in a strongly acid medium. Detection in these systems is possible by working with an organized medium. New methods for the determination of thorium, uranium and rare-earth elements are proposed.     

Potential of multisyringe flow-based multicommutated systems

This work is aimed at emphasizing the potential of the multicommutated systems based on the multisyringe flow injection analysis (MSFIA) modality. First, the characteristics, advantages and withdraws offered by flow analysis systems based on the different non-segmented modalities are briefly described. In these systems, multicommutation and computer control of the analytical process occupy a predominant place, as in the case of sequential injection analysis (SIA), multicommutated flow injection analysis (MCFIA), MSFIA and multipumping flow systems (MPFS). Next, several examples are given and different aspects of the implementation of analysers based on MSFIA designs for the construction of different analysis systems, including intelligent (smart) systems, use of sample pre-treatment automatic systems, for chromatographic and non-chromatographic determinations as well as use of monolithic or capillary electrophoresis columns are considered.     

Development of a systems analysis approach for resolving the structure of biodegrading soil systems

An experimental and mathematical method is developed for the microbial systems analysis of polyaromatic hydrocarbon (PAH)-degrading mixed cultures in PAH-contaminated “town gas” soil systems. Frequency response is the primary experimental and data analysis tool used to probe the structure of these complicated systems. The objective is to provide a fundamental protocol for evaluating the performance of specific mixed microbial cultures on specific soil systems by elucidating the salient system variables and their interactions. Two well-described reactor systems, a constant volume stirred tank reactor (CSTR) and a plug flow differential volume reactor, are used in order to remove performance effects that are related to reactor type as opposed to system structure. These two reactor systems are well-defined systems that can be described mathematically and represent the two extremes of one potentially important system variable, macroscopic mass transfer. The experimental and mathematical structure of the protocol is described, experimental data is presented, and data analysis is demonstrated for the stripping, sorption, and biodegradation of napththalene.     

Liquid ion exchangers in paper chromatography of steoidal glucosiduronic acids. Influence of different exchangers on the mobility in chloroform-formamide and correlation of chromatographic data.

A group of 25 steroidal glucosiduronic acids was chromatographed on paper chloroform-formamide in the presence of several different liquid ion exchangers. Chromatograms were run also in three Bush-type systems. RF values were converted into RM values and the data were correlated by use of a series of regression equations of the type RM(Y) = a-RM(X) + b, in which X designates a standard system to which each other system (Y) is compared. The ratio of the slope a to the correlation coefficient r (i.e., a/r) is a measure of the resolving power of system Y relative to the standard system; intercept b, in association with slope a, is an indication of the polarity of system Y relative to X. The correlation coefficient r and the standard error of estimate sy-x are indications of whether solvent systems Y and X have very similar or relatively different resolving properties for a group of solutes. The regression equations are useful for correlating chromatographic data obtained from a group of compounds in several solvent systems. Properties of the chromatography systems are discussed and the relative importance of ion exchange and hydrogen bonding with the various solvent systems is pointed out. Delta RMg and delta RMr values are given for functional groups at several locations in the conjugates for ten of the chromatography systems.     

Synthesis,characterization and recent developments of liquid crystalline polymers

Recent developments of polymer liquid crystals (PLCs) are reviewed. The virial expansion method of Onsager and the lattice model used by Flory to appreciate the most relevant parameters in establishing mesomorphic behavior in polymeric systems are presented. These and other theoretical predictions are confirmed by numerous experiments. Both lyotropic (polymer solutions) and thermotropic (polymer melts) types of PLCs are considered with emphasis placed on the latter. The general properties of mesophases formed by such polymers are surveyed and some chemical structures capable of producing mesophases are classified in relation to their ability to form lyotropic and thermotropic systems. The synthetic routes, the effects of polymer structure on physical properties, and applications of two major classes of lyotropic systems (polypeptides, polyamides) and of a range of potentially important thermotropic polymers are discussed.     

Modeling of Liquid-Vapor Equilibrium in Systems Including a Light Oil-Gas Component and Aromatic and Polyaromatic Hydrocarbons

The Victorov-Smirnova's hole lattice quasichemical group-contribution model (HM) is used to simulate the vapor-liquid equilibrium in binary and ternary mixtures systems composed by aromatic (benzene, toluene) and polyaromatic (naphthalene, phenanthrene) hydrocarbons and light oil-gas components (carbon dioxide, hydrogen sulfide, nitrogen, methane, ethane, propane). Eighteen binary and two ternary systems are examined. New group parameters for these systems are estimated. The results of modeling are compared with the experimental data and those predicted by the Peng-Robinson equation of state.     

Effect of excess electron on structure,bonding, and spectral properties of sulfur/selenium based dichalcogen systems

First principle based quantum chemical methods are employed to characterize structure, bonding, and spectral properties of sulfur and selenium based dichalcogen systems in presence of an excess electron. Inter molecular two-center three-electron (2c-3e) bonding between two chalcogen (X) atoms is described in the systems of the type (R-X)₂^•- (R = Ph, PhCH₂ X = S, Se). In addition, effect of electron withdrawing (-NO₂) and electron donating (-CH₃) groups in phenyl ring on the stability of these 2c-3e bonded systems is also studied in water medium applying a macroscopic hydration model. Molecular parameters and binding energy of the neutral, (R-X)₂ and reduced, (R-X)₂^•- dichalcogen systems are compared. Search for minimum energy structures of these open shell doublet systems are carried out applying various density functionals with dispersion corrections and MP2 method considering 6-311++G (d,p) set of basis functions for all atoms. Effect of water medium is introduced through a macroscopic solvation model based on density (SMD). Frontier molecular orbitals based analysis is carried out for showing the definite presence of 2c-3e bond between two chalcogen atoms in these radical anions of sulfur and selenium based aromatic dichalcogen systems. Excited state calculations are performed on all these systems using Time Dependent Density Functional Theory (TDDFT). UV-Vis spectra are simulated and effect of solvent water on the absorption maximum of these radical anions is discussed. This study illustrates that the combination of electronic effect and geometrical flexibility decides the strength of two-center three-electron bond in these systems.     

Synchrotron X-ray techniques for the investigation of structures and dynamics in interfacial systems

This review focuses on recent results obtained by synchrotron X-ray techniques applied to the characterization of interfacial systems, with main emphasis on flat interfaces and on colloidal systems. The techniques covered are, for structural determinations: X-ray reflectivity (XRR), grazing incidence X-ray diffraction (GIXRD) and grazing incidence X-ray excited fluorescence (GIXF), while dynamics are investigated by X-ray photon correlation spectroscopy (XPCS) mainly in the grazing-incidence geometry (GIXPCS).The systems reviewed are, in order of growing complexity, floating Langmuir monolayers, supported films of lipids and proteins, polymeric films, buried interfaces, colloidal systems and gels formed by colloids either in 3D or in the form of 2D interfacial layers. Recent results are critically discussed, and some interesting directions of development are outlined, having also in mind new technical developments such as X-ray free electron laser sources and micro-focused synchrotron beamlines.     

Nanoscale co-organization of quantum dots and conjugated polymers using polymeric micelles as templates

Hierarchical organization of light-absorbing molecules is integral to natural light harvesting complexes and has been mimicked by elegant chemical systems. A challenge is to attain such spatial organization among nanoscale systems. Interactions between nanoscale systems, e.g., conjugated polymers, carbon nanotubes, quantum dots, and so on, are of interest for basic and applied reasons. However, typically the excited-state interactions and dynamics are examined in rather complex blends, such as cast films. A model system with complexity intermediate between a film and a supramolecular system would yield helpful insights into electronic energy and charge transfer. Here, we report a simple and versatile approach to achieving spatially defined organization of colloidal CdSe, CdSe/ZnS core/shell, or PbS nanocrystals (quantum dots) with poly(3-hexylthiophenes) (P3HTs) using micelles of poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) as the main structural motif. We compare the characteristics of this system to those of natural light-harvesting complexes. Bulk heterojunction films (and related systems) are characterized by electronic interactions, and therefore dynamics of charge and energy transfer, at interfaces rather than between specific donor-acceptor molecules. Owing to structural disorder, such systems are inherently complex. Therefore, we expect that the spatially defined organization of the active components in the present system provides new opportunities for studying the complicated photophysics intrinsic to blends of nanoscale systems, such as bulk heterojunctions by establishing simplified and better controlled interfaces.     

Necessary and sufficient conditions for the appearance of extrema on concentration distribution curves in complex equilibrium systems

It is shown that species distribution curves with at least one minimum may be found in most equilibrium systems with three or more components. Whether such concentration minima are actually observed then depends on the values of the equilibrium constants and on the total (analytical) concentrations of the components. A general algorithm is given for the necessary and sufficient conditions for the appearance of extrema in multicomponent systems. Three-component systems are studied in more detail and special attention is given to the limiting case of a horizontal inflection, i.e., the point where the concentration minimum just disappears. Two well-studied chemical examples, the Cu(2+)-diethylenetriamine-OH(-) and Hg(2+)-Cl(-)-OH(-) systems are discussed, along with a simple model system showing as many as five extrema on a single distribution curve.     

钯配合物催化烯烃氧化合成酮类物质的研究进展

本文系统地评述了钯配合物催化烯烃氧化合成酮类物质的研究进展。综述了改进Wacker 类催化剂催化活性的几种方法。总结了烯烃氧化合成酮类物质反应的几种典型催化体系及其作用机理。着重介绍了Pd (Ⅱ) HPA (杂多酸)、Pd (Ⅱ) FePc (酞菁铁)、Pd (Ⅱ) HQ (氢醌) FePc、Pd (Ⅱ) HQHPA、Pd (Ⅱ) CuSO₄ HPA 等Wacker 类催化体系在烯烃氧化合成酮类物质中的应用; 对Pd (Ⅱ) LCoNO₂、PdCl₂(MeCN)₂ CuCl、Pd (OAc)₂ 吡啶、氟两相等非Wacker 类催化体系在烯烃氧化合成酮类物质中的应用也作了讨论。     

New topic of supercritical fluids: local activity coefficients of supercritical solvent and cosolvent around solute

The study of inhomogeneity in supercritical fluids (SCFs) is of great importance. In this work, we propose the concept of local activity coefficients in supercritical (SC) solutions, which link thermodynamics and inhomogeneity in SC systems. The local activity coefficients of CO(2)+acetonitrile+phenol blue and CO(2)+acetic acid+phenol blue systems are investigated at 308.15 K in critical region and outside critical region. To do this, the local compositions of CO(2)+acetonitrile and CO(2)+acetic acid mixed solvents around phenol blue are first estimated using UV-visible spectroscopy. Then it is considered that there exist bulk phase and local phase around phenol blue in the systems. The activity coefficients of CO(2) and the cosolvents (acetonitrile or acetic acid) in bulk phase are calculated using Peng-Robinson equation of state. The local activity coefficients of CO(2) and the cosolvents are then calculated on the basis of thermodynamic principles. It is demonstrated that in the critical region the local activity coefficients differ from bulk activity coefficients significantly and are sensitive to pressure. This can explain many unusual phenomena in SC systems in critical region thermodynamically.     

Description of liquid—liquid extraction equilibria in exchange extractions of chelates: Part 3. Calculation of pH—pA Diagrams and Enrichment Factors in pH—pA Coordinates

Equilibrium values of free ligand concentration (pA) in extraction systems which contain comparable amounts of metal and extraction agents, particularly exchange extraction systems, can readily be calculated with a desk computer. The technique is applied in the treatment of extraction systems where step-wise complexation, hydrolysis, masking and polynuclear complex formation of the metal take place in the aqueous phase. Data of normalized coordinates are tabulated and proved to be useful in finding pA in extraction systems of chelates MA .... MA₄, of various compositions. The same mathematical approach is used to calculate enrichment factors for two-element separations as a function of pA and pH. Model systems of the Zn, Pb, Co(II), Co(III) and Fe(II) diethyldithiocarbamates and Fe(III) and Sc 8-quinolinolates serve as examples.     

D.C. voltammetry of ionic liquid-based capacitors: Effects of Faradaic reactions, electrolyte resistance and voltage scan speed investigated using an electrode of carbon nanotubes in EMIM-EtSO4

Carbon nanotube (CNT) electrodes in combination with ionic liquid (IL) electrolytes are potentially important for energy storage systems. We report electrochemical investigation of such a system involving a paper-electrode of multi-wall CNT (MWCNT) in the IL of 1-ethyl-3-methyl imidazolium ethylsulfate (EMIM-EtSO₄). Our study concentrates on the analytical aspects of cyclic voltammetry (CV) to probe the double layer capacitance of these relatively unconventional systems (that involve rather large charge-discharge time constants). Both theoretical and experimental aspects of CV for such systems are discussed, focusing in particular, on the effects of Faradaic side-reactions, electrolyte resistance and voltage scan speeds. The results are analyzed using an electrode equivalent circuit (EEC) model, demonstrating a method to account for the typical artifacts expected in CV of CNT-IL interfaces.     

Study of the nature and mechanism of the formation of paramagnetic species in nickel-based Brookhart-type catalytic systems

The catalytic systems NiBr₂(DPP-DAB) + 20 MAO and NiBr₂(DPP-BIAN) + 20 MAO (DPP-BIAN = bis(2,6-diisopropylphenyl)-bis(imino)-acenaphtene, MAO = methylaluminoxane), as well as a number of model systems, are studied under conditions of their activation and functioning. There are paramagnetic nickel complexes and radical-anion aluminum complexes in the systems under real conditions of activation and functioning. The highest activity is observed when the Ni(I) signal intensity in the ESR spectrum is maximal. A mechanism of paramagnetic species formation is proposed.     

Exploiting Co‐solubilization of Warfarin,Curcumin, and Rhodamine B for Modulation of Energy Transfer: A Micelle FRET On/Off Switch

Two new FRET pairs, warfarin (WF)–curcumin (CUR) and curcumin–rhodamine B (RhB), are explored by using surfactant‐based self‐assembled soft systems as scaffolds. The study is extended to design a two‐step concurrent FRET system based on these three fluorophores, which is an important mechanism to devise artificial light‐harvesting/antenna systems. Surfactant systems of varying nature (cationic, anionic, nonionic, and zwitterionic) are exploited to modulate the energy transfer in different FRET systems. Interestingly, micelle/water interfacial‐charge‐responsive FRET is observed owing to selective solubilization of the fluorophores during co‐solubilization. The step‐one FRET (WF→CUR) is switched on in cationic and zwitterionic media but switched off in anionic/nonionic media, whereas the step‐two FRET from CUR to RhB is switched on in anionic/nonionic and zwitterionic media. However, both the FRET steps (WF→CUR→RhB) are observed to be active only in zwitterionic medium. Co‐solubilized, appropriately mixed fluorophores having multistep FRET possibilities can be switched on/off selectively as and when required and energy efficiency can be tuned to an optimal level by varying the nature and geometry of the micellar scaffold. Thus, the two FRET pairs selectively acknowledge all types of media for their anticipated applications in biological systems, as structural tools, and for the development of artificial light‐harvesting/antenna systems and lasers.