Generalized bond orders

We introduce generalized bond orders defined in terms of weighted Kekule valence structures. The weights were determined by the contributions of linearly independent and minimal conjugated circuits in individual Kekule valence structure. When special values for the contributions of conjugated circuits of different size are assumed, one obtains quantities that show considerable similarity to the Pauling and the Clar's bond orders. Pauling bond orders are obtained when one assumes that all conjugated circuits make equal contribution to bond orders. © 1994 John Wiley & Sons, Inc.     

Eigenmobilities in background electrolytes for capillary zone electrophoresis: III. Linear theory of electromigration

A mathematical model of capillary zone electrophoresis (CZE) based on the conception of eigenmobilities, which are the eigenvalues of a matrix M tied to the linearized governing equations is presented. The model considers CZE systems, where constituents, either analytes or components of the background electrolyte (BGE), are weak electrolytes--acids, bases, or ampholytes. There is no restriction on the number of components nor on the valence of the constituents nor on pH of the BGE. An electrophoretic system with N constituents has N eigenmobilities. In most BGEs one or two eigenmobilities are very close to zero so their corresponding eigenzones move very slowly. However, there are BGEs where no eigenmobility is close to zero. The mathematical model further provides: the transfer ratio, the molar conductivity detection response, and the relative velocity slope. This allows the assessment of the indirect detection, conductivity detection and peak broadening (distortion) due to electromigration dispersion. Also, we present a spectral decomposition of the matrix M to matrices allowing the assessment of the amplitudes of system eigenpeaks (system peaks). Our model predicted the existence of BGEs having no stationary injection zone (or water zone, gap, peak, dip). A common practice of using the injection zone as a marker of the electroosmotic flow must fail in such electrolytes.     

Graph-theoretical analysis of molecular properties. Isomeric variations in nonanes

Paths of length two and three appear to dominate variations in isomers of alkanes when various physical and chemical molecular properties are compared. The regularities previously observed for octanes have been fully examined for the set of 35 nonane isomers C₉H₂₀. Such examinations are facilitated by construction of appropriate grid graphs with paths of length two and three, respectively, representing molecules and connecting such points along the grid axes. By ordering structures in the two-dimensional coordinate plane, various trends and regular changes in the relative magnitudes for the selected thermodynamic properties have been traced to molecular connectivity and topology.     

Survey of structural regularities in molecular properties. I. Carbon-13 chemical shifts in alkanes

Many regularities in properties among structurally related compounds are known but a systematic approach to investigate all such cases is rare. A plan is outlined for a systematic study of structural regularities that is based on use of selected graph invariants as prime auxiliary quantities. In this paper carbon-13 chemical shifts in alkanes are examined. Since NMR spectra of paraffins are well understood, the example provides a useful illustration of the approach, introduces basic concepts, and illustrates the kind of the results that the graph-theoretical scheme generates. Differences and similarities between graph-theoretical viewing of the problem of structural regularities and customary direct use of additivities are discussed in some detail.     

Selective additions of polyhalogenated compounds to chloro substituted ethenes catalyzed by a copper complex

The Cu complex Cu(L)_nCl (L=2-propylamine) has been found to be an advantageous catalyst for the addition of polyhalogenated compounds to chloro substituted ethenes; the 11 adducts were formed almost exclusively in up to 71% yield.

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, , Cu(L)_nCl (L=2-), ; 71% 11.

     

A photochemical method for patterning the immobilization of ligands and cells to self-assembled monolayers

This work describes a chemically well defined method for patterning ligands to self-assembled monolayers (SAMs) of alkanethiolates on gold. This method begins with monolayers presenting a nitroveratryloxycarbonyl (NVOC)-protected hydroquinone which is photochemically irradiated to reveal a hydroquinone group. The resulting hydroquinone is then oxidized to the corresponding benzoquinone, providing a site for the Diels-Alder mediated immobilization of ligands. The rate constant for the photochemical deprotection is 0.032 s(-1) (with an intensity of approximately 100 mW/cm(2) between 355 and 375 nm), corresponding to a half-life of 21 s. The hydroquinone is oxidized to the benzoquinone using either electrochemical or chemical oxidation and then functionalized by reaction with a cyclopentadiene-tagged ligand. Two methods for patterning the immobilization of ligands are described. In the first, the substrate is illuminated through a mask to generate a pattern of hydroquinone groups, which are elaborated with ligands. In the second method, an optical microscope fit with a programmable translational stage is used to write patterns of deprotection which are then again elaborated with ligands. This technique is characterized by the use of well-defined chemical reactions to control the regions and densities of ligand immobilization and will be important for a range of applications that require patterned ligands for biospecific interactions.     

Determination of diamine oxidase by a kinetic method with 2,2''-azino-di(3-ethylbenzthiazoline-6-sulfonate)

Hydrogen peroxide, the product of diamine oxidase-catalyzed putrescine or cadaverine oxidation, formed in proportion to the enzyme activity, is measured spectrophotometrically by using the above sulfonate (ABTS) and peroxidase. Only one reagent solution containing 3 mmol of putrescine or 10 mmol of cadaverine, 4 mmol of ABTS and 3000 U of peroxidase per litre of 0.2 mol l^-1 Tris—0.1 mol l^-1 HCl buffer pH 7.5 is needed. Absorbance changes are measured at 410 nm over the first 3 min of the reaction. This initial oxidation rate of the chromogen enables diamine oxidase activity up to 230 U l^-1 to be determined.     

Algebraic Kekulé structures of benzenoid hydrocarbons

An algebraic Kekulé structure of a benzenoid hydrocarbon is obtained from an ordinary Kekulé structure by inscribing into each hexagon the number of pi-electrons which (according to this Kekulé structure) belong to this hexagon. We show that in the case of catafusenes, there is a one-to-one correspondence between ordinary and algebraic Kekulé structures. On the other hand, in the case of perifusenes, one algebraic Kekulé structure may correspond to several ordinary Kekulé structures.