Computational studies of peripheral ring twisting in meso-N-methyl pyridyl-substituted porphyrins

Semiempirical molecular orbital calculations for the porphyrins tetrakis(4-N-methyl pyridyl)porphine (H₂TMpyP-4) and tetrakis(2-N-methyl pyridyl)porphine using the MNDO and AM -1 Hamiltonians suggest that twisting one or more of the pyridinium rings results, at considerable energy expense, in highly nonplanar macrocycle configurations as the exocyclic ring(s) approach coplanarity. The results imply that the mechanism of intercalation of H₂TMpyP-4 into DNA cannot require twisting the exocyclic rings anywhere close to coplanarity with the central porphine core, but involves, instead, the inherent flexibility of DNA itself. © 1993 John Wiley & Sons, Inc.     

Resonance states in 12C and α-particle condensation

The states with J^π = 0⁺, 2⁺, and 4⁺ of ¹²C with excitation energies less than about 15 MeV are investigated with the alpha condensate wave function with spatial deformation and by using the method of ACCC (analytic continuation in the coupling constant) which is necessary for a proper treatment of resonance states. The calculated energy and width of the recently observed 2₂⁺ state are found to be well reproduced. The obtained 2₂⁺ wave function has a large overlap with a single condensate wave function of 3α gas-like structure. The density distribution is shown to be almost the same as that of the 0₂⁺ state that is regarded as a 3α Bose-condensed state, if the energy of the 2₂⁺ state is scaled down to the same value as the one of the 0₂⁺ state. Furthermore, the kinetic energy, nuclear interaction energy, and Coulomb interaction energy of the calculated 2₂⁺ state are shown to be very similar to those of the 0₂⁺ state. We conclude that the 2₂⁺ state has a structure similar to the 0₂⁺ state of Bose-condensate character with a dilute 3α gas-like structure. In addition, the resonance states, 0₃⁺, 0₄⁺, 4₂⁺, are also discussed.     

Congener-specific identification of technical PCB mixtures by capillary gas chromatography on a n-octyl-methyl silicone phase (SB-Octyl 50) with electron capture- and mass-selective detection

Summary The technical PCB mixtures Aroclor 1242, Aroclor 1254 and Aroclor 1260 have been analyzed by capillary gas chromatography using the new methyl n-octylpolysiloxane phase (SB-Octyl 50) with electron capture- and mass-selective detection. The selectivity of this new stationary phase in the separation of PCB is superior to that of the methyl-polysiloxanes. A pronounced separation according to the out-of-plane orientation of the PCB congeners is observed.

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Kongeneren-spezifische Identifizierung der technischen PCB-Gemische durch HRGC/ECD und HRGC/MSD mit einer n-Octyl-methyl-silicon-Phase

     

Some Boolean Algebras with Finitely Many Distinguished Ideals I

We consider the theory Th_prin of Boolean algebras with a principal ideal, the theory Th_max of Boolean algebras with a maximal ideal, the theory Th_ac of atomic Boolean algebras with an ideal where the supremum of the ideal exists, and the theory Th_sa of atomless Boolean algebras with an ideal where the supremum of the ideal exists. First, we find elementary invariants for Th_prin and Th_sa. If T is a theory in a first order language and α is a linear order with least element, then we let Sentalg(T) be the Lindenbaum-Tarski algebra with respect to T, and we let intalg(α) be the interval algebra of α. Using rank diagrams, we show that Sentalg(Th_prin) ? intalg(ω⁴), Sentalg(Th_max) ? intalg(ω³) ? Sentalg(Th_ac), and Sentalg(Th_sa) ? intalg(ω² + ω²). For Th_max and Th_ac we use Ershov's elementary invariants of these theories. We also show that the algebra of formulas of the theory Tx of Boolean algebras with finitely many ideals is atomic.     

Synthesis,characterization, crystal structure and catalytic property of [Cu(SalAHE)2] (SalAHE = salicylaldehydeimine-1-hydroxyethane) complex for the oxidation of 3,5-di-tert-butylcatechol

The crystal structure, spectroscopic properties and catalytic property of the copper(II) complex, prepared by the reaction between copper(II) diacetate with the bidentate Schiff base, SalAHE (SalAHE = salicylaldehydeimine-1-hydroxyethane), are reported. This complex is able to oxidize 3,5-di-tert-butylcatechol to the respective o-quinone. The oxidation reaction was studied in CH₃CN with molecular oxygen at 0, 5, 15 and 25 °C. The progress of the catalytic reaction was followed by gas chromatographic analyses (GC).     

Solving the Combined Zoning and Location Problem for Several Emergency Units

This paper discusses methods for the solution of the combined zoning and location problem for several emergency units. This is a stochastic optimization problem. The stochastic aspects include ordered preference of servers. A constraint of equal workload for the servers is also dealt with. Non-linear programming techniques are adapted for its solution.     

Mode coupling theory for the description of two particle-two hole states of208Pb

It is shown that for²⁰⁸Pb the 1p-1h space decouples from the 2p-2h space to a very high degree at least for the more collective states. We then calculate the low-lying 2p-2h spectrum of²⁰⁸Pb in a mode-coupling approach that seems to be very well justified in this case. For the particle-particle interaction we use theG-matrix of Herling and Kuo and for the particle-hole force we take the effective density-dependent interaction of Ring and Speth.     

The Chemistry of Stable Carbenes. Part 2. Benzoin-type condensations of formaldehyde catalyzed by stable carbenes

Stable carbenes derived from thiazole, 1H-imidazole, and 4H-1,2,4-triazole are efficient catalysts for benzointype condensations of formaldehyde. Catalysts derived from N-substituted thiazolium salts trimerize formaldehyde to dihydroxyacetone ( II ). Catalysts based on 1,4-disubstituted 4H-1,2,4-triazol-1-ium salts give glycolaldehyde ( I ) as the main product and no II , whereas N,N′-disubstituted 1H-imidazol-3-ium salts yield mixtures of both products. The isolation of several intermediates in the catalytic cycle provide a better insight into the reaction mechanism.     

Some properties of bivariate Gumbel Type A distributions with proportional hazard rates

We call a set of univariate distributions with the same mathematical form but different parameter values a family $\text{J}$. Consider a bivariate Gumbel Type A survival distribution, S₁₂(x₁, x₂), defined in (2.1), for which both marginal distributions, S₁(x₁), S₂(x₂), belong to the same family, $\text{J}$ of distributions. It is proved in this paper that subject to weak conditions, the crude hazard rates, h₁(t) and h₂(t), are proportional if and only if the marginal hazard rates, λ₁(t) and λ₂(t), are proportional (Theorem 1). It is also shown that the survival functions of W = min(X₁, X₂), and of the identified minimum, W_i = X_i, for X_i < X_j, j ≠ i, belong to the same family $\text{J}$ as do S₁(x₁), S₂(x₂) (Corollary 1). Counter-examples of distributions other than Gumbel Type A, for which these properties do not hold, are given. Some applications to the analysis of competing risks, using a family of Gompertz distributions, are discussed.