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Abstract: Films obtained by radio-frequency sputtering of monocrystalline polydiacetylene (PDA) are under study. The structure is studied by Raman spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. It is shown that the obtained films have a heterogeneous structure containing agglomerates of nanosized inclusions of the initial PDA and irregular sp/sp2hybridized carbon chain fragments.

Staphylococcus aureusis an extremely infectious and malignant pathogen among many bacteria species. The aim of this work is to provide a robust classification model that would be able to identify S. aureusindependent of the culture growth stage and the variations in bacteria concentration in suspension and also one that would be able to identify the pathogen among both taxonomically close species of the same genus and taxonomically distant species of different genera, using Fourier transform infrared spectroscopy (FTIR). In total, the spectra of 141 isolates of 17 bacteria have been used. Based on a combination of principal component analysis (PCA) and linear discriminant analysis (LDA), an identification model providing 100% sensitivity and 98% specificity was built. Inherent reliability and flexibility of the model have been shown. The proposed method of analysis allows us to get closer to the diagnostic requirements in the field of clinical microbiology, and it can be utilized for typing of other pathogenic bacteria species.

Raman signal enhancement by laser crater production was systematically studied for 785 nm continuous wave laser pumping. Laser craters were produced in L-aspartic acid powder by a nanosecond pulsed solid state neodymium-doped yttrium aluminum garnet laser (532 nm, 8 ns, 1 mJ/pulse), while Raman spectra were then acquired by using a commercial spectrometer with 785 nm laser beam pumping. The Raman signal enhancement effect was studied in terms of the number of ablating pulses used, the lens-to-sample distance, and the crater-center-laser-spot offset. The influence of the experiment parameters on Raman signal enhancement was studied for different powder materials. Maximum Raman signal enhancement reached 11 fold for loose powders but decreased twice for pressed tablets. Raman signal enhancement was demonstrated for several diverse powder materials like gypsum or ammonium nitrate with better results achieved for the samples tending to give narrow and deep craters upon the laser ablation stage. Alternative ways of cavity production (steel needle tapping and hole drilling) were compared with the laser cratering technique in terms of Raman signal enhancement. Drilling was found to give the poorest enhancement of the Raman signal, while both laser ablation and steel needle tapping provided comparable results. Here, we have demonstrated for the first time, to the best of our knowledge, that a Raman signal can be enhanced 10 fold with the aid of simple cavity production by steel needle tapping in rough highly reflective materials. Though laser crater enhancement Raman spectroscopy requires an additional pulsed laser, this technique is more appropriate for automatization compared to the needle tapping approach.

Raman signal enhancement by multiple scattering inside laser crater cones was observed for the first time, to the best of our knowledge. Laser crater enhanced Raman spectroscopy (LCERS) yielded a 14-fold increase in the Raman spectra bands due to efficient multiple scattering of laser irradiation within the laser crater walls. The same pulsed Nd:YAG laser (532 nm, 10 ns) was used for both laser crater formation and Raman scattering experiments by varying the output pulse energy. First, powerful pulses are used to produce the laser crater; then low-energy pulses are used to perform Raman scattering measurements. The laser crater profile and its alignment with the laser beam waist were found to be the key parameters for the optimization of the Raman spectrum intensity enhancement. Raman intensity enhancement resulted from increased surface scattering area at the crater walls, rather than spatially offset Raman scattering. The increased signal-to-noise ratio resulted in limits of detection improvement for quantitative analysis using LCERS.

Abstract: The joint action of cationic surfactants and transition metal acetylacetonates on the oxidation of limonene (1-methyl-4-isopropenyl-1-cyclohexene) was studied. All mixed compositions exhibited a synergistic effect, i.e., the oxygen absorption rate in the presence of both components was several times the sum of the rates of oxidation catalyzed by the surfactant alone and the transition metal compound alone. The strongest synergistic effect was observed for the CTABr-Co(II) and CTACl-Cu(II) combinations. A detailed study of the limonene oxidation kinetics in the presence of CTABr and Co(acac)2 has shown that the synergy mechanism consists in that Co(acac)2 and the primary oxidation product hydroperoxide form mixed micelles in which hydroperoxides are activated and Co(acac)2 is concentrated.

Abstract: The copolymers of ethylene with 5-ethylidene-2-norbornene containing 10–65% of the cyclic comonomer have been prepared with the use of three ansa-metallocene catalysts, namely, Et[Ind]2ZrCl2-methylaluminoxane, Et[IndH4]2ZrCl2-methylaluminoxane, and Me2Si[Ind]2ZrCl2-methylaluminoxane. Side groups >C=CH-CH3 capable of participation in the ozonolysis reaction have been incorporated into polymer chains via the copolymerization of ethylene with the cyclic comonomer. As evidenced by DSC, and X-ray diffraction, and very cold neutron scattering measurements of the supramolecular structure of the copolymers, the enrichment of the copolymer with the cyclic comonomer causes transformation of the ethylene-5-ethylidene-2-norbornene copolymer from the semicrystalline state to the amorphous state. This effect is accompanied by an increase in the density and optical transparency of the material and a rise in its glass transition temperature. Among the copolymers under study, the highest T g (83�C) is exhibited by the copolymer synthesized with the Et[Ind]2ZrCl2-methylaluminoxane catalyst and containing 30 mol % 5-ethylidene-2-norbornene.

A series of previously unknown unsymmetrical difluoroaromatic compounds, viz., p-fluorobenzoylphenyl(p-fluorophenyl)-substituted imidazoles, pyrazines, and quinoxalines, were synthesized according to multistep procedures with the use of chloral as the key compound. The reactivities of the resulting difluoroaromatic compounds were estimated based on 19F and 13C NMR spectral data and the results of quantum-chemical calculations. The calculated charge densities on the Cipsoatoms correlate linearly with the experimental chemical shifts in the 19F and 13C NMR spectra. Difluoroaromatic compounds, which are characterized by δF> –110 and δC> 163 and by the charge density on the Cipsoatom higher than 0.08 e, are sufficiently activated to be used for the preparation of high-molecular-weight polyethers.

The temperature dependence of the ESR spectra of the radical-cations of the N-derivatives of phenothiazine were studied in the range of 200-393 K (o-xylene). It was established that at temperatures of 323-333 K the nature of the HFS varies from doublet to quartet with approximate intensity ratios of 1:2:2:1, and this transformation is irreversible. A hypothesis explaining the results is proposed. IR spectroscopy was used to confirm the proposed mechanism of localization of the unpaired electron.

Abstract: A new monomer of the ABA type, 2,5-diphenyl-3,4-bis[p-(phenylethynyl)phenyl]-cyclopentadienone, was synthesized. The Diels-Alder homocondensation of the monomer resulted in a highly branched polyphenylene (M w=160000), readily soluble in organic solvents. The polymer obtained is thermally stable up to 600 °C (in argon atmosphere) and has a glass transition of 280°C. The structure of the monomer and polymer was confirmed by1H NMR,13C NMR, IR Fourier, and Raman Fourier spectroscopy.

Abstract: N-Substituted amides of 2-cyanopenta-2E,4-dienoic acid were synthesized by condensation ofN-substituted cyanoacetamides with acrolein in a dioxane-DMSO solution in the presence of Zn(OAc)22H2O as a condensing agent. X-ray diffraction study of 3-methylanilide of 2-cyanopenta-2E,4-dienoic acid (2d) demonstrated that the crystal structure of this compound is similar to that of 2-cyanopenta-2E,4-dienoic acid studied previously. However, the presence of themeta-tolyl substituent in molecule2d apparently results in the fact that the β-structure, which is typical of 2-cyanopenta-2E,4-dienoic acid, does not exist in the crystalline phase of2d.

Abstract: The Diels-Alder reactions of 4,4′-bis(2,4,5-triphenylcyclopentadienon-3-yl)benzophenone with carboxylic anhydrides containing multiple carbon-carbon bonds afforded novel tetracarboxylic dianhydrides.

Vibratonal spectra of 2-acetyltetronic acid (ATA) (3-acetyloxolane-2,4-dione) were investigated in different aggregate states.Ab initio quantum chemical calculations (3-21G basis set) of 2-formyltetronic acid as analogue of ATA and semi empirical calculation of ATA were carried out. The tautomeric forms of ATA can be arranged in the following series with respect to thermodynamic stability (in decresing order):1a,1b,2a,2b.

A series of new symmetrical and asymmetrical disubstituted diacetylenic monomers containing piperidine and carboline nitroxyl radicals were synthesized. These compounds are starting reagents for the synthesis of polyconjugated high-spin species.

An X-ray study of N-propargylcarbazole (I) and N-(3-iodopropargyl)carbazole (II) has been carried out. In the crystal II acetylenic groups form zigzag ladder-like infinite motives extended along the b axis. The motives are characterized by alternation of more close (and capable, in principle, of topochemical dimerization in crystal) and more distant pairs of acetylenic groups. A hypothetical possibility of topochemical polymerization in crystal II under uniaxial compression with formation of the ordered trans-polyacetylene is considered.

The paper compares the visible wavelengths excited resonance Raman and the near-infrared Fourier transform (NIR-FTR) Raman spectroscopy methods in terms of their convenience and informativeness for studies of diacetylenes (DA) and polydiacetylenes (PDA). It is shown that the combination of excellent precision with the reliability of measurements on the samples which are essentially transparent to both the exciting laser wavelength, 1064 nm, and the NIR-Raman photons makes NIR-FTR spectroscopy an ideal tool for quantitative measurements of the solid-state structural transformations in PDAs. In particular, thermally induced polymerization of a model DA, PTS has been reinvestigated in situ by the NIR-FTR method. The data so obtained suggest occurrence of a sharp but continuous and concerted structural transition during the polymerization of PTS. Other peculiarities, namely the apparent lack of both the intensity and frequency dispersions with the polymer π-conjugated length in the NIR-FTR spectra, as well as a non-trivial reasonant enhancement of the latter are noted.

Cooperative sensitisation of luminescence of Nd3+ ions at the 4F3/2 4I13/2, 4I9/2 transitions by Pr3+ ions was observed in a borate glass doped with Pr3+—Nd3+ ion pairs. The luminescence was excited by a 800-mW, 1.064-m Nd3+:YAG laser. Simultaneously, spontaneous Raman scattering was observed in glasses containing Pr3+—Nd3+ ion pairs or only Pr3+ ions. The Stokes shift from the 9398-cm–1 excitation line is 794 cm–1. The mechanism of nonradiative energy transfer is discussed.

Although the two polymorphic modifications, (I) and (II), of the title compound, C13H10N2O, crystallize in the same space group (P21/c), their asymmetric units have Z′ values of 1 and 2, respectively. These are conformational polymorphs, since the mol­ecules in phases (I) and (II) adopt different rotations of the phenyl ring with respect the central 2‐cyano­carboxy­amino­prop‐2‐enyl fragment. Calculations of crystal packing using Cerius2[Molecular Simulations (1999). 9685 Scranton Road, San Diego, CA 92121, USA] have shown that (I) is more stable than (II), by 1.3 kcal mol−1for the crystallographically determined structures and by 1.56 kcal mol−1for the optimized structures (1 kcal mol−1= 4.184 kJ mol−1). This difference is mainly attributed to the different strengths of the hydrogen bonding in the two forms.

Abstract: Reactions of new bis(α-diketones) with 1,3-diphenylacetone resulted in new bis(tetraarylcyclopentadienones).

We report the results of thermochromism, electroabsorption, and Raman scattering spectroscopy studies for trans- cis blend of 'soluble' polyacetylene. We have observed that the properties of the trans and cis isomers differ dramatically: the trans isomer reveals considerably higher Raman scattering activity, electroabsorption, thermochromism, and sensitivity of vibrational modes to temperature.

A viability of studies of thermally- and photo-induced polymerizations of diacetylenes (DA's) as well as of thermochromicity of polydiacetylenes (PDA's) by NIR-FT Raman spectroscopy is reported. High informativeness and intrinsic convenience of the method as well as usability of NIR-FTR bands parameters for quantitative work on PDA's are illustrated and advocated.

We report the results of thermochromism, electroabsorption, and Raman scattering spectroscopy studies for trans-cis blend of ’soluble’ polyacetylene. We have observed that the properties of the trans and cis isomers differ dramatically: the trans isomer reveals considerably higher Raman scattering activity, electroabsorption, thermochromism, and sensitivity of vibrational modes to temperature.

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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.