Condensed thiolane 1,1-dioxide systems. 3. Two modes of cyclization of N-substituted trans-3-chloro-4-thioureidothiolane 1,1-dioxides

Reaction of trans-3-chloro-A-aminothiolane 1,1-dioxide hydrochloride with aryl isothiocyanates gives, according to the base involved, cis-perhydrothieno[3,4-d]imidazole-2-thione 5,5-dioxides or the hitherto undescribed cis-2-aryliminoperhydrothieno 3,4-d] thiazole 5,5-dioxides.For Part 2, see [1].Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1420–1423, October, 1988.     

Electron transfer,equilibrium, and protonation in the system of cis- and trans-stilbene in 2-propanol

Spectrophotometric pulse radiolysis experiments with cis- and trans-stilbene (S_c and S_t) in 2-propanol show that both isomers react with the solvated electron with a rate constant of 4.5 × 10⁹ M^?1 s^?1. The absorption spectra of the two anion radicals have maxima at 496 and 486 nm, respectively. The absorbances at 400–550 nm disappear exponentially corresponding to a pseudo first order protonation of the anion radicals. The rate constants for the protonation of the cis isomer is 6.4 × 10⁵ and of the trans isomer 0.7 × 10⁵ s^?1. In mixtures of cis- and trans-stilbene the electron transfer

has a forward rate constant of 9 × 10⁷ M^?1 s^?1 while the back reaction has a rate constant of 2.15 × 10⁷ M^?1 s^?1. An equilibrium constant K = 4.2 is calculated.     

Using spin dynamics of covalently linked radical ion pairs to probe the impact of structural and energetic changes on charge recombination

We have synthesized a series of structurally related, covalently linked electron donor-acceptor triads having highly restricted conformations to study the effects of radical ion pair (RP) structure, energetics, and solvation on charge recombination. The chromophoric electron acceptor in these triads is a 4-aminonaphthalene-1,8-dicarboximide (6ANI), in which the 4-amine nitrogen atom is part of a piperazine ring. The second nitrogen atom of the piperazine ring is part of a para-substituted aniline donor, where the para substituents are X = H, OMe, and NMe(2). The imide group of 6ANI is linked to a naphthalene-1,8:4,5-bis(dicarboximide) (NI) electron acceptor across a phenyl spacer in a meta relationship. The triads undergo two-step photoinduced electron transfer to yield their respective XAn(*)(+)-6ANI-Ph-NI(*)(-) RP states, which undergo radical pair intersystem crossing followed by charge recombination to yield (3)NI. Time-resolved electron paramagnetic resonance experiments on the spin-polarized RPs and triplet states carried out in toluene and in E-7, a mixture of nematic liquid crystals (LCs), show that for all three triads, the XAn(*)(+)-6ANI-Ph-NI(*)(-) RPs are correlated radical pairs and directly yield values of the spin-spin exchange interaction, J, and the dipolar interaction, D. The values of J are all about -1 mT and show that the LC environment most likely enforces the chair conformation at the piperazine ring, for which the RP distance is larger than that for the corresponding boat conformation. The values of D yield effective RP distances that agree well with those calculated earlier from the spin distributions of the radical ions. Within the LC, changing the temperature shows that the CR mechanism can be changed significantly as the energy levels of the RPs change relative to that of the recombination triplet.     

PHOTOCHEMISTRY OF REDUCED LUMIFLAVIN IN ITS ACIDIC FORM

Abstract— The photooxidation of reduced lumiflavin in its acidic form, LfH 3 ⁺, takes place in two consecutive steps. Upon illumination of LfH 3 ⁺ in its absorption band at 313 nm the semiquinone, LfH 3 ⁺, is formed. Two LfH 2 ⁺ ions are consumed for every LfH 2 ⁺ formed. Illumination of the semiquinone in its absorption band at 495 nm causes further oxidation so that the oxidized LfH⁺ ion is formed. In this reaction one LfH 3 ⁺ ion is photolyzed for every LfH⁺ formed. In addition, a hydrogen atom is released in the photooxidation of LfH 2 ⁺. Mechanisms for the two photoreactions are proposed.     

Determination of the population,depopulation and the anisotropic spin lattice relaxation rates in the photoexcited triplet state of phenazine. A light modulation-EPR study

The photoexcited triplet state of phenazine in toluene glasses at 35 K is investigated by light modulation-EPR spectroscopy. From the transient EPR spectra and the kinetics in the three canonical orientations (p = x, y, z) the rate parameters are determined. Thus, the depopulation rate constants k_p, the anisotropic spin lattice relaxation rate constants W_p, and the ratios between the population constants A_p are calculated: k_x = (2.2 ± 0.3) × 10² s^?1, k_y = (0.21 ± 0.04) × 10² s^?1, k_z = (0.06 ± 0.03) × 10² s^?1, W_x = (8.6 ± 0.9) × 10³ s^?1, W_y = (11.0 ± 1.0) × 10³ s^?1, W_z = (14.0 ± 1.4) × 10³ s^?1, and A_x: _Ay:A_z ≈ 1:0.04:0.02. It is concluded therefore that the in-plane spin state |τ_x > is the active one.     

Analysis of multiobjective decision problems by the indifference band approach

A new approach, based on indifference band, for analyzing problems with multiple objectives is described. The relations of this approach to some previous results are given. Methods for generating nondominated solutions are supplied.     

On The Parameterized Intractability Of Motif Search Problems*

We show that Closest Substring, one of the most important problems in the field of consensus string analysis, is W[1]-hard when parameterized by the number k of input strings (and remains so, even over a binary alphabet). This is done by giving a “strongly structure-preserving” reduction from the graph problem Clique to Closest Substring. This problem is therefore unlikely to be solvable in time O(f(k)•n^c) for any function f of k and constant c independent of k, i.e., the combinatorial explosion seemingly inherent to this NP-hard problem cannot be restricted to parameter k. The problem can therefore be expected to be intractable, in any practical sense, for k ≥ 3. Our result supports the intuition that Closest Substring is computationally much harder than the special case of Closest String, althoughb othp roblems are NP-complete. We also prove W[1]-hardness for other parameterizations in the case of unbounded alphabet size. Our W[1]-hardness result for Closest Substring generalizes to Consensus Patterns, a problem arising in computational biology. * An extended abstract of this paper was presented at the 19th International Symposium on Theoretical Aspects of Computer Science (STACS 2002), Springer-Verlag, LNCS 2285, pages 262–273, held in Juan-Les-Pins, France, March 14–16, 2002. † Work was supported by the Deutsche Forschungsgemeinschaft (DFG), research project “OPAL” (optimal solutions for hard problems in computational biology), NI 369/2. ‡ Work was done while the author was with Wilhelm-Schickard-Institut für Informatik, Universit?t Tübingen. Work was partially supported by the Deutsche Forschungsgemeinschaft (DFG), Emmy Noether research group “PIAF” (fixed-parameter algorithms), NI 369/4.     

Laser photolysis of zinc porphyrin dissolved in cyanohexylbiphenyl liquid crystal

A laser photolysis study of ZnTPP (P) oriented in nematic and isotropic cyanohexylbiphenyl (6CB) as a function of added 1.4-benzoquinone (Q) is reported. In the absence of Q, enhancement of triplet absorption below the clearing point (nematic phase) is observed. It is attributed to the improved alignment of the optical transition in the ordered matrix and also to the increase in the intersystem crossing efficiency. T−S₁. In the presence of Q in the nematic phase. An additional increase in triplet absorption is noticed. This result is interpreted in terms of a triplet radical pair [P^+√…Q^−√]^T,RP formation which is facilitated by the ordering in the liquid crystal, thus providing an additional channel for triplet formation. The triplet P^T in 6CB (nematic or isotropic) is quenched with a second-order rate of ≈10⁸ M⁻¹ s⁻¹ as compared to 2 × 10⁹ M⁻¹ s⁻¹ in toluene.     

General auxiliary problem and algorithm for a generalized multi-valued variational-like inequality problem in reflexive Banach spaces

In this article, some generalized multi-valued variational-like inequality problems and their related general auxiliary problems in real reflexive Banach spaces are introduced. An existence theorem for one of the general auxiliary problems is proved. Furthermore, by exploiting this theorem, an algorithm for the corresponding generalized multi-valued variational-like inequality problem is constructed. The theorems of this article generalize, improve and unify many known corresponding results.