On Cubic Graphs Admitting an Edge-Transitive Solvable Group

Using covering graph techniques, a structural result about connected cubic simple graphs admitting an edge-transitive solvable group of automorphisms is proved. This implies, among other, that every such graph can be obtained from either the 3-dipole Dip₃ or the complete graph K ₄, by a sequence of elementary-abelian covers. Another consequence of the main structural result is that the action of an arc-transitive solvable group on a connected cubic simple graph is at most 3-arc-transitive. As an application, a new infinite family of semisymmetric cubic graphs, arising as regular elementary abelian covering projections of K _3,3, is constructed.     

Stabilization of a subvalent oxidation state of bismuth in N,N-dimethylthioformamide solution: an EXAFS, UV-Vis, IR, and cyclic voltammetry study

At the dissolution of anhydrous bismuth(III) trifluoromethanesulfonate in N,N-dimethylthioformamide (DMTF) a deep red-orange complex, lambda(max) = 457 nm, is formed. Bismuth(III) is reduced by the solvent to a low-valent oxidation state stabilized by the sulfur-coordinating solvent DMTF. The obtained complex is weakly solvated seen by a low EXAFS amplitude and a slightly higher absorption energy of the L(III) edge than of the DMTF-solvated bismuth(III) ion. The EXAFS data reveal a dimeric bismuth complex solvated by a single DMTF molecule, which sulfur atom bridges the bismuth atoms. The Bi-S bond distance is 2.543(2) A, and the Bi...Bi distance is 3.929(7) A giving a Bi-S-Bi angle of 101.2(4) degrees. The very low number of coordinated solvent molecule shows that the lone electron pairs of the reduced bismuth ions are stereochemically active. Cyclic voltammetry investigations provide evidence that at least one bismuth atom in the dimer exists in an oxidation state lower than +III, seen by two peaks at approximately -0.36 and -0.57 V in the reduction half-cycle. The absence of EPR signals excludes the presence of bismuth(II) radicals.     

Factor analysis of deuterium isotope effects on 13C NMR chemical shifts in Schiff bases

We have analyzed deuterium isotope effects on (13)C chemical shifts in a series of o-hydroxy Schiff bases by applying factor analysis. Two orthogonal factors were obtained that explain about 80 and 10 % of the variance of the data. The numerical values of these factors can be related to 1H NMR chemical shifts of the proton involved in the intramolecular bonds delta(XH) (X = O or N). Such a relation allows one to identify clusters of compounds with different tautomeric forms of hydrogen bonding. Application of a similar approach to solution 13C NMR chemical shifts produces three important factors, which have a different structure to factors describing isotope effects. This illustrates well the different nature of chemical shifts and isotope effects. The three factors explain about 54, 15, and 13 % of variance. They can be rationalized and are strongly related to the electronic properties and location of substituents.     

Cores,cutsets and the fixed point property

The purpose of this paper is the analysis and application of the concepts of a core (a pair of chains) and cutset in the fixed point theory for posets. The main results are:

1. (Theorem 3) If P is chain-complete and (*), it contains a cutset S such that every nonempty subset of S has a join or a meet in P, then P has the fixed point property (FPP),
2. (Theorem 5) If P or Q is chain-complete, Q satisfies (*) and both P and Q have the FPP, then P x Q has the FPP.
3. (Theorem 6) Let P or Q be chain-complete and there exist p∈P and a finite sequence f ₁, f ₂, ..., f _n of order-preserving mappings of P into P such that $$\left( {\forall x\varepsilon P} \right)x \leqslant f_1 \left( x \right) \geqslant f_2 \left( x \right) \leqslant \cdots \geqslant f_n \left( x \right) \leqslant p$$ If P and Q have the FPP then P x Q has the FPP.
4. (Theorem 7) If T is an ordered set with the FPP and {P _t :t∈T} is a disjoint family of ordered sets with the FPP then its ordered sum ∪{P _t :t∈T} has the FPP.

     

Asymmetric photocycloaddition between furan and chiral alkyl glyoxylates

High-pressure mercury lamp irradiation of chiral alkyl glyoxylates [R(?)-menthyl,R(?)- andS(+)-2-octyl,R(?)-andS(+)-2, 2-dimethyl-3-butyl] with furan led to alkyl 2,7-dioxabicyclo-[3.2.0] hept-3-ene-6-car?ylates (13a–e) exhibiting low (2.5–7.3%) optical purity. Compounds13a–e were isomerized to alkyl 3-furylglycolates (14a–e) in good yield. ConfigurationS was assigned to levorotary methyl 3-furlymethoxyacetate. Two interpretations of the results of asymmetric synthesis were proposed.     

DIRECT RECORDING OF THE INITIALLY EXCITED AND THE SOLVENT RELAXED FLUORESCENCE EMISSION SPECTRA OF TRYPTOPHAN BY PHASE SENSITIVE DETECTION OF FLUORESCENCE

Abstract Phase sensitive detection of fluorescence was used to directly record the initially excited and the solvent-relaxed emission spectra of N-acetyl-L-tryptophanamide in propylene glycol. Emission from the initially excited state was suppressed by adjusting the phase sensitive detector to be out of phase with the emission on the short wavelength side of the fluorescence spectrum. Then, the phase sensitive intensities revealed the emission spectrum of the solvent relaxed state. Similarly, the emission from the solvent relaxed state was suppressed by adjusting the detector to be out of phase with the emission on the long wavelength side of the spectrum, allowing the spectrum of the initially excited state to be directly recorded. Distinct emission spectra could be recorded when the solvent relaxation time was comparable to the fluorescence lifetime. At higher or lower temperatures, emission occurs predominantly from a single state, and suppression of the fluorescence signal at any arbitrary wavelength resulted in suppression of the entire emission. A simple theory is described which allows the spectral relaxation times to be estimated from the phase sensitive intensities. From this analysis we obtained an activation energy for spectral relaxation of 3 kcal/mol. This activation energy is smaller than that found for the temperature dependence of fluorescence depolarization, 7.8 kcal/mol. We attribute this difference to the smaller molecular motions required for spectral relaxation.
The method of phase sensitive detection of fluorescence shows excellent resolving power and sensitivity, and this method should facilitate measurement of spectral relaxation around tryptophan residues in proteins.     

Physicochemical Properties,Fatty Acid Composition,Volatile Compounds of Blueberries,Cranberries, Raspberries,and Cuckooflower Seeds Obtained Using Sonication Method

Every year, thousands of tons of fruit seeds are discarded as agro-industrial by-products around the world. Fruit seeds are an excellent source of oils, monounsaturated fatty acids, and n-6 and n-3 polyunsaturated essential fatty acids. This study aimed to develop a novel technology for extracting active substances from selected seeds that were obtained after pressing fruit juices. The proposed technology involved sonification with the use of ethyl alcohol at a low extraction temperature. Seeds of four species—blueberry (Vaccinium myrtillus L.), raspberry (Rubus idaeus), cranberry (Vaccinium macrocarpon), and cuckooflower (Cardamine pratensis)—were used for extraction. Following alcohol evaporation under nitrogen, the antioxidant activity, chemical composition, and volatile compounds of the obtained extracts were analyzed using chromatographic methods, including gas chromatography (GC)–mass spectrometry (MS) (GC–MS/MS), and high-performance liquid chromatography–MS. We analyzed physicochemical properties, fatty acid, and volatile compounds composition, sterol and tocochromanol content of blueberry, cranberry, raspberry, and cuckooflower seed oils obtained by sonication. This method is safe and effective, and allows for obtaining valuable oils from the seeds.     

Novel Lipophilic Fluorophores with Highly Acidity-Dependent Two-Photon Response

Lipophilic fluorophores are widely implemented in nonlinear microscopy; however, few existing membrane-specific probes combine the high brightness of two-photon excited fluorescence (2PEF) with pH sensitivity. Herein we describe four novel two-photon excited fluorophores, based on a coumarin 151 core structure, where lipophilicity is induced by a covalently attached phosphazene moiety. Changing the environmental acidity using trifluoromethanesulfonic (triflic) acid leads to profound changes in the linear fluorescence and 2PEF characteristics, due to chromophores’ switching between neutral- and protonated forms. We characterize this dependence by measuring the two-photon absorption (2PA) spectra over the region λ_2PA=550–1000 nm, observing 2PA cross sections of σ_2PA=10–20 GM, with an associated 2PEF brightness of 10–13 GM, in neutral solutions of both acetonitrile and n-octanol. Although quantum chemical modelling and NMR measurements show that, at high chromophore concentrations, protonation may be accompanied by a dimerization process, these dimers likely do not form at the lower concentrations used in optical spectroscopy.