The computation of the representation matrices of the generators of the unitary group

A method is presented for the efficient computation of the representation matrices of the unitary group, U(n) in the Gelfand—Tsetlin basis (corresponding to the usual spin-symmetry adapted basis for an N electron CI). The present scheme is conceptually and computationally attractive in that it is formulated directly in terms of Weyl tableaux and also that it permits simultaneous basis vector generation and matrix element evaluation. In addition the basis vectors are ordered so that subsequent restriction to the three dimensional rotation group is facilitated. An illustrative example is also presented.Taken in part from a thesis submitted to the University of London in partial fulfilment of the requirements for the degree of PhD.     

On the nature of the anhydride of the lactam of guanidinoglutaric acid

When glutamic acid is amidinated, guanidinoglutaric acid is formed. This is readily converted by boiling in water to its lactam [2-imino-4-oxo-5-(3′-propane acid) imidazolidine; GGAL]. In the present study GGAL is dehydrated to form a second lactam, anhydro-GGAL (AGGAL), with trifluoroacetic anhydride. The molecular weight of this compound was ascertained gravimetrically by precipitation with flavianic acid and by mass spectrography to be 153.14. UV and infrared spectra and hydrogen and ¹³C NMR studies determined its structure as an imidazolidine ring fused to a pyrrol ring, 2-imino-4-oxo-imidazolidine-1,5-pyrrolidone-8. On paper electrophoresis, GGAL traveled to the anode, while AGGAL traveled to the cathode. On TLC plates (butanol 60, H₂O 25, acetic 15), the R_f value of GGAL was 0.42 and that of AGGAL was 0.38, confirming that AGGAL was more basic than GGAL. The preparation of 1,3-di-(phenylcarbamoyl)-GGAL is also described.     

On the Neglect of the Philosophy of Chemistry

In this paper I present a historiography of the recent emergence of philosophy of chemistry. Special attention is given to the interest in this domain in Eastern Europe before the collapse of the USSR. It is shown that the initial neglect of the philosophy of chemistry is due to the unanimous view in philosophy and philosophy of science that only physics is a proper science (to put in Kant's words). More recently, due to the common though incorrect assumption that chemistry can in principle be reduced to physics, the neglect continued, even when interest in sciences such as biology and psychology entered more strongly in philosophy of science. It is concluded that chemistry is an autonomous science and is perhaps a more typical science than physics.     

Synthesis of the Stereoisomers of the Sex Pheromones of the Southern Corn Rootworm

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Simulation of the condenser of the seawater greenhouse

A theoretical model is developed in Part I of this study to simulate the physical process of condensation of the humid air in the condenser of an existing seawater greenhouse that is located in Muscat, Oman. Application is conducted in this part to validate the theoretical developments. Comparisons are made between the predictions and the existing experimental results. The results indicate that the comparison is well consistent. The effect of the relative humidity, the dry bulb temperature and the solar radiation are also discussed to see their effects on the condensate values.     

Synthesis of the naphthalene portion of the rubromycins

[reaction: see text]. A synthesis of a reduced version of the naphthazarin found in the rubromycin class of natural products is reported. The naphthalene ring system is formed via a D?tz reaction with a symmetrical alkyne. Differentiation between the C1' and C3' groups of the D?tz adduct is achieved by selective oxidation since the two methylene groups possess different oxidation potentials.     

The effect of the order of the autocatalysis on the transverse stability of reaction fronts

A linear stability analysis of planar reaction fronts to transverse perturbations is considered for a system based on an autocatalytic reaction of general order p. Dispersion curves, plots of the growth rate sigma against a transverse wavenumber k, are obtained for a range of values of p and D, where D is the ratio of the diffusion coefficients of autocatalyst and substrate. A value D(0) of D, dependent on p, is found at which sigma(max), the maximum value of sigma in the unstable regime, is largest, with D(0) increasing as p is increased. An asymptotic analysis for small wavenumbers is derived, which enables the region in the (p, D) parameter space for instability to be determined. An analysis for D small is undertaken, which leads to upper bounds on the wavenumber for a possible instability.     

Effect of the sequence of the introduction of foreign substances on the action of papain

Summary In general, aniline, aniline hydrochloride, aniline sulfate, and triethylamine act as inhibitors in the hydrolysis of casein or of a suspension of flour from grain of Cicer arietinum by means of papain. The order in which the enzyme and the substrate is added to the inhibitor often has a significant effect. As a rule, there is a greater retardation when the enzyme is added last to a complex of the substrate and the inhibitor.     

On the application of the modeling of the relaxation spectrum to the prediction of linear viscoelastic properties of surfactant systems

 In this work, the linear viscoelastic properties of cetyl-trimethylammonium tosilate–water system are predicted by the modeling of the relaxation spectrum. The modeled spectrum of relaxation times is of the “wedge-box” type where the “wedge” portion is located at the short-time scale of relaxation times and the “box” part covers the long-time scale. The linear viscoelastic properties are calculated through the exact relationships with the suggested spectrum. Agreement between the calculated expressions and experimental data of the moduli and the stress relaxation function is found. Comparison is also made with predictions of the empirical expressions of the Cole–Cole and the Williams–Watts models. Received: 17 December 1996 Accepted: 1 July 1997     

On the application of the geometric approximation to the calculation of ring-current properties

Burrows' formula giving an upper bound for the error in the geometric approximation is applied to the calculation of the ring-current contribution to the diamagnetic anisotropies of conjugated molecules. It is also emphasized that this approximation is easily applied in practice.     

Importance of the diamine reactant in the production of polyphosphonamides by the interfacial technique

The stirred interfacial polycondensation of phenylphosphonic dichloride and 1,6-hexanediamine has been studied as a function of several reaction variables. The reaction is rapid, being completed in less than 1 min. When organic solvent is varied and reactant molar ratio is varied with an excess of the acid chloride, yield is constant. When reactant molar ratio is varied polymer yield increases with increase in amine concentration. When reactant concentration is increased yield increases. With the addition of a soluble salt in the aqueous phase yield is increased. The above indicates that the diffusion of the amine to the reaction zone is of primary importance in determining polymerization rate and that the diffusion of the acid chloride is relatively unimportant. Polymer yield was found to be dependent on the pH of the amine in the aqueous phase. The observed trend is related to the apparent solubility of the amine in the aqueous phase such that the greater the apparent solubility of the amine, the less the polymer yield. Polymer molecular weight is found to be independent of reaction variables tested. Polymer was also formed from the condensation of phenylphosphonic dichloride with p-phenylenediamine, H₂N-D-NH₂ (where D is a 36-carbon hydrocarbon chain), 1,3-di-4-piperidylpropane, and 4-aminomethylpiperidine; phenyl phosphorodichloridate with 1,6-hexanediamine; chloromethyl phosphonic dichloride with 1,6-hexanediamine.     

Influence of the polarity of the microenvironment of pyrene on the intensity of its solid-phase luminescence

The sorption of pyrene by a filter paper modified with lead acetate is studied by luminescence methods. Based on changes in the vibrational structure of fluorescence spectra of pyrene, it was found that the polarity of the microenvironment of pyrene adsorbed from solutions in ethanol increases with the concentration of acetic or hydrochloric acid in these solutions. It was revealed that, when an acid is added, pyrene fluoresces and phosphoresces more intensely at room temperature. It is shown that this is associated with a more efficient sorption of pyrene by the filter paper from acid solutions in ethanol.     

On the origin of the splitting of the second maximum in the radial distribution function of amorphous solids

The splitting of the second maximum of the radial distribution function of an irregular atomic packing is regarded as an indication of the amorphous state of a substance. This paper describes the splitting-forming atomic configurations using Delaunay simplices, representing chains of elementary configurations. It is shown that the splitting is formed of chains in which all simplices are nearly regular tetrahedra and quartoctahedra. Translated fromZhumal Struktumoi Khimii, Vol. 38, No. 1, pp. 78–88, January–February, 1997.     

Identification of the Enzymes Mediating the Maturation of the Seryl-tRNA Synthetase Inhibitor SB-217452 during the Biosynthesis of Albomycins

Albomycin δ₂ is a sulfur-containing sideromycin natural product that shows potent antibacterial activity against clinically important pathogens. The l -serine-thioheptose dipeptide partial structure, known as SB-217452, has been found to be the active seryl-tRNA synthetase inhibitor component of albomycin δ₂. Herein, it is demonstrated that AbmF catalyzes condensation between the 6′-amino-4′-thionucleoside with the d -ribo configuration and seryl-adenylate supplied by the serine adenylation activity of AbmK. Formation of the dipeptide is followed by C3′-epimerization to produce SB-217452 with the d -xylo configuration, which is catalyzed by the radical S-adenosyl-l -methionine enzyme AbmJ. Gene deletion suggests that AbmC is involved in peptide assembly linking SB-217452 with the siderophore moiety. This study establishes how the albomycin biosynthetic machinery generates its antimicrobial component SB-217452.     

An improvement of the resolution of the identity approximation for the formation of the Coulomb matrix

A straightforward modification of the resolution of the identity (RI) approximation to the Coulomb interaction is described. In the limit of basis sets that are dominated by high angular momentum functions the observed speedups in realistic test systems reach a factor of 2 compared to the standard RI algorithm, and a factor of up to 300 compared to the standard algorithm to form the Coulomb matrix. More moderate savings on the order of 0-20% are obtained for the more commonly used smaller basis sets. A series of test calculations is reported to illustrate the efficiency of the algorithm.     

Determining the parameters of the potential of intermolecular interaction by the Zeno line

The method of determination of intermolecular interaction potential parameters by the Zeno line is proposed. The intermolecular interaction of ethane, propane, ethylene, and propylene is described using a model of site-site interactions and Karr-Konowalow potential. It is shown that the parameters of intermolecular interaction for this potential can be determined from a small number of experimental data in the single-phase area. It is noted that the final parameters allow us to describe the thermodynamic properties over a broad range of gas and liquid states with precision acceptable for practical use.     

Resonance nature of instabilities at the boundaries of the region of the electrode ideal polarizability

For the gallium metals, a model is proposed that explains the mechanism of an anomalous increase in the differential capacitance of the EDL dense part of the metal-electrolyte interface at limiting anodic and cathodic polarizations. The considerable increase in the capacitance is explained by the resonance interaction between electronic states of the metal and the adjacent layer of solvent molecules. The potential dependence of the capacitance is interpreted in terms of the Breit-Wigner parameters of a resonant scattering.     

On the validity of the BEBO method

The use of tha BEBO method proposed by Johnston and Parr is considered, taking into account the observations of Jordan and Kuafman. It is found that the original formulation is applicable even when the new values for noble gas pairs are employed,if an appropriate choice of the constant in Pauling's relation is made.     

On the Misleading Interpretation of the Properties of the f-Electron Elements

The aim of the paper is to elucidate the problem of the regular changes in the properties of f-elements represented by the double-double effect. It is pointed out that because of the half-filled shell and double-double effects the f-element properties cannot be plotted as a linear function of the L -quantum number, as suggested by Sinha [1][2].     

On the chain nature of the third self-ignition limit of the detonating mixture

It is demonstrated by numerical simulation that neglect of branched chains at the third self-ignition limit of the detonating mixture is in conflict with actual observations.