IR spectroscopic study of the conformational lability of 4′-ethyl-4-cyanobiphenyl

The conformational lability of 4-ethyl-4-cyanobiphenyl molecules in solid crystal (SC) and isotropic liquid (IL) states was investigated by IR spectroscopic techniques (experiment and theory). IR absorption spectra were measured at 28°C–95°C in the frequency range 400 cm^–1–4000 cm^–1. Spectrum simulation was performed using the fragment method with allowance for the conformational fluctuations of molecules. The experimental and calculated spectra were compared and analyzed, and it was shown that in the IL, the samples are mixtures of conformers. The temperature changes in the spectra in the stated range are caused by the conformational lability of molecules.Original Russian Text Copyright © 2004 by L. M. Babkov, I. I. Gnatyuk, G. A. Puchkovskaya, and S. V. TrukhachevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 398–405, May–June, 2004.     

Structural study of oriented non-crystalline PET by CDF method

The two-dimensional wide angle X-ray scattering (WAXS) intensities of oriented non-crystalline polyethylene terephthalate (PET) films extended umaxially are collected by the symmetrical transmission method; he-sides,the overlapped non-crystalline peaks at WAXS intensity curves,I(K) obtained at different azimuthal angles are also separated by computer,resulting in two peaks caused by interchain atomic scattering in the reciprocal space,KA(K=0.122),KB(K=0.171),and the other two peaks from intracham atomic scattering,Kc(K=0.310) and KD(K=0.548); their cylindrical distribution functions (CDF),CDF(R,α) in the real space are further calcu lated from the intensity functions,IE(K) using sampled transforms,thereof arising in turn the peaks in the real space as,RA(R=0.658),RB(R=0.456),RC(R=0.253) and RD(R=0.152),corresponding to KA,KP,K,and KD The equivalent relationships and distribution characteristics of the above-mentioned corresponding peaks in the reciprocal and real space,as well as their sources of struc     

Multi-dimensional energetic performance modeling of an aircraft engine with the aid of enhanced least–squares estimation based genetic algorithm method

Journal of Thermal Analysis and Calorimetry - Aircraft must have reliable and sustainable sources of power systems and must use energy efficiently. Aircraft engine advances have dramatically...     

Time-effective and reliable solid-state structure evaluation of selected peracetylated β-maltose derivatives by means of grid search,genetic algorithm and DFT calculations

Efficient solid-state structure evaluation of β-maltose octaacetate (1), methyl β-maltoside heptaacetate (2), and ethyl 1-thio-β-maltoside heptaacetate (3) was performed. The search for the best conformers for 1–3 was conducted in three consecutive steps: grid search, genetic algorithm refinement and DFT study. The use of a genetic algorithm caused a spectacular time shortening of the calculations. The obtained theoretical conformation for 1 resembled its XRD refinement almost perfectly. Although XRD analysis was impossible to perform for 2 and 3 (they form improper crystals), their reliable conformations were obtained. It was proved by the use of ¹³C CP/MAS NMR spectroscopy.     

Temperature–pressure shuffling outlier flooding method enhances the conformational sampling of proteins

Outlier flooding method (OFLOOD) is an efficient conformational sampling method developed by the authors. In the present study, to further enhance the conformational sampling efficiency, a set of parameters (temperatures and pressures) specified as inputs in the original OFLOOD were shuffled before restarting the short-time molecular dynamics (MD) simulations. Because of the diversity of these parameters, it was confirmed that the extended OFLOOD becomes superior to the original one in finding the folding pathways of Trp-cage. © 2019 Wiley Periodicals, Inc.     

Surface characterization and dissolution study of biodegradable calcium metaphosphate coated by sol–gel method

Coatings of biomedical implant surfaces by a bioactive calcium phosphate film render bioactivity to the implant surface and shorten the healing time. In this present study, calcium metaphosphate (CMP) sol was synthesized by sol–gel method and coated onto the titanium alloys (Ti-6Al-4V). CMP sol was first synthesized by reacting Ca(NO₃)₂4H₂O (Sigma–Aldrich 99%, USA) with (OC₂H₅)₃P (Fluka 97%, Japan) in methyl alcohol. A stoichiometric Ca/P ratio of 0.5 was obtained by varying the amounts of the reactants. Sol was then coated on Ti-6Al-4V substrates by spin coating. The coated-specimens were then dried at 70 °C for 24 h, followed by a heat treatment at 650 °C for 1 h. Structural and chemical properties of the coatings were evaluated using XRD, SEM, and EPMA. The dissolution property of the coated-CMP layer was investigated by immersing the samples in the simulated body fluid (SBF) for 1, 3, 7 and 21 days. The concentration of Ca²⁺ released was measured using ICP. After heat treatment, SEM indicated a smooth and uniform CMP layer, with CMP grains of approximately 100 nm. The CMP phase was identified with δ-CMP (JCPDS #9-363). After immersion in SBF, coatings were observed to be roughened and porous. The concentration of Ca²⁺ in SBF was observed to increase over time, indicating continuous dissolution. The presence of titanium oxide phosphate compounds were also observed on CMP surfaces after immersion. It was thus concluded that the ability to control coating properties as well as the need for low heat treatment temperature offers advance for the use of CMP coating by sol–gel process on Ti-6Al-4V implant surfaces.     

Rational synthesis and X-ray structural study of manganese–pyridine–alcohol derivatives

Systematic syntheses of manganese derivatives with 2-pyridineethanol, 2-pyridinemethanol and 2,6-pyridinedimethanol as chelating ligands have been undertaken to produce [trans-Mn(C₅H₄N-2-CH₂CH₂OH)₂Cl₂] (1), [cis-Mn₂(μ-Cl)₂(Cl)₂(C₅H₄N-2-CH₂CH₂OH)₂(OH₂)₂] (2), [cis-Mn₂(μ-Cl)₂(C₅H₄N-2-CH₂OH)₄]Cl₂ (3) and [MnCl{η₃-C₅H₃N-2,6-(CH₂OH)₂}{η₂-(C₅H₃N-2,6-(CH₂OH)₂)}]Cl (4). The complexes were characterized by single-crystal X-ray diffraction. The oxidation state of the manganese ions in these complexes is 2+. Magnetic data are measured down to 2?K; in dimer complexes (2 and 3) a significant antiferromagnetic interaction is observed between two manganese ions.     

Kinetic simulation of oxidative coupling of methane over perovskite catalyst by genetic algorithm： Mechanistic aspects

The reaction kinetics of oxidative coupling of methane catalyzed by perovskite was studied in a fixed bed flow reactor. At atmospheric pressure, the reactions were carried out at 725, 750 and 775 ℃, inlet methane to oxygen ratios of 2 to 4.5 and gas hourly space velocity (GHSV) of 100 min-1. Correlation of the kinetic data has been performed with the proposed mechanisms. The selected equations have been regressed with experimental data accompanied by genetic algorithm (GA) in order to obtain optimized parameters. After investigation the Langmuir-Hinshelwood mechanism was selected as the best mechanism, and Arrhenius and adsorption parameters of this model were obtained by linear regression. In this research the Marquardt algorithm was also used and its results were compared with those of genetic algorithm. It should be noted that the Marquardt algorithm is sensitive to the selection of initial values and there is possibility to trap in a local minimum.     

Comparative study of the thermal behavior of Sr–Cu–O gels obtained by sol–gel and microwave-assisted sol–gel method

Journal of Thermal Analysis and Calorimetry - In the literature data, several papers reported the synthesis by various chemical or physical methods of the SrCu2O2 (SCO) having possible applications...     

Quantum algebraic–combinatoric study of the conformational properties of n‐alkanes. I

Based on quantum chemical calculation results, four rules were previously derived for the numbers and the sequences of the conformers of free alkane molecules. This paper builds up first an algebra to handle the conformational problem of alkanes. Partitioning the set of all sequences, the whole problem is then subdivided into three independent subcases. With the help of an equivalence relation, the sequences can be classified. According to the quantum chemical rules, certain equivalence classes do not represent conformers. A welldefined subcase of the whole problem is solved.