Single peptide bonds exhibit poly(pro)II ("random coil") circular dichroism spectra

The far-UV circular dichroism spectra of a series of amino acid derivatives containing single peptide bonds have been measured. The N-acetyl-alanine displays a polyproline (PP) II-like spectrum, but alaninamide shows a very weak positive signal. Similarly Gly-Ala shows a PPII spectrum, but Ala-Gly does not. On heating, the spectrum shows a two-state transition also shown by long PPII polypeptides. Thus the characteristic PPII negative maximum at <200 nm results from the coupling of a peptide bond N-terminal to the chiral alpha-carbon, and therefore the simplest peptide bonds have a preferred conformation that defines the spectrum of disordered proteins of any size.     

Molecular dynamics simulation study of the influence of chirality on the stability of the smectic Q liquid crystal phase

The structure of smectic Q (SmQ) liquid crystal phase consisting of a dichiral molecule, called M7BBM7, was studied by submicrosecond molecular dynamics (MD) simulation. A detailed atomic model was used to study the stability of a model SmQ structure proposed by Levelut et al. (Levelut, A.-M.; Hallouin, E.; Bennemenn, D.; Heppke, G.; Lotzsch, D. J. Phys. II 1997, 7, 981) and its difference between (S,S)-, (S,R)-M7BBM7 and racemic mixture systems. Negative values of the fourth-rank orientational order parameter (), which characterize the model SmQ structure, were stably kept up to a 100 ns MD run only in the (S,S)-M7BBM7 system and lost in the other systems. The results correspond well to the marked chiral sensitivity in real systems where only the (S,S)-M7BBM7 system (among the three above-mentioned systems) shows the SmQ phase. Our simulation results imply that the asymmetric intramolecular potentials and resultant chirality-dependent molecular conformations are primarily responsible for keeping the negative values of and the model SmQ structure.     

Toxic CO detection by Li-encapsulated fullerene-like BeO

Structural Chemistry - We report adsorption energies, structures, energy gap (E g), charge transfer, and electronic properties of carbon monoxide (CO) on primary, cation Li-, Li-, and two...     

An enhancement on electrical properties of carboxymethyl cellulose-NH4Br based biopolymer electrolytes through impedance characterization

In this work, the formulation of biopolymer electrolytes (BEs) system has been accomplished by incorporating various plasticizers with carboxymethyl cellulose–NH₄Br through solution casting technique. The ionic conductivity at room temperature of BEs system was achieved at ～10^?4 S cm^?1 with addition of 25?wt% NH₄Br and enhanced to ～10^?3 S cm^?1 when plasticizers were added. The temperature-dependence of the BEs system exhibits Arrhenius behavior. Jonschers power law was used to study the electrical properties and shows that the highest conducting BEs system can be represented by overlapping overlapping a large polaron tunneling model for poly(ethylene glycol) system a, small polaron hopping model for glycerol system, and a quantum mechanical tunneling model for ethylene carbonate system.     

Synthesis,characterization, and catalytic activity of FeTiO3/TiO2 for photodegradation of organic pollutants with visible light

Research on Chemical Intermediates - High-purity ilmenite, FeTiO3, was prepared by the sol–gel method and calcination under nitrogen atmosphere. Several FeTiO3/TiO2 catalysts were prepared by...     

Ferrielectric and antiferroelectric chiral twin liquid crystals showing a stable chiral nematic phase

A homologous series of chiral twin liquid crystals possessing identical chiral moieties at both peripheral ends, i.e. optically active α,ω -bis{4-[(4′-(1-methylheptyloxycarbonyl)-4-biphenylyl)oxycarbony]phenoxy}alkanes, has been prepared and their liquid crystalline properties investigated. The homologues preferred to show the ferrielectric and/or antiferroelectric phase rather than the ferroelectric phase. With ascending central spacer length, the temperature range of the ferrielectric phase became narrow and eventually disappeared for the dodecyl homologue, suggesting that the coupling in motion and/or direction between two mesogenic parts of each twin molecule has an important effect on the stabilization of the ferrielectric phase. The octyl and dodecyl homologues showed a wide temperature range chiral nematic phase (ca. 10°C or more), so that these compounds were found to be the first examples showing antiferroelectric and/or ferrielectric phases with a broad temperature range of the chiral nematic phase. X-ray diffraction studies showed that the homologues tend to form a mono-layered structure. The formation of a relatively well defined layered structure was also indicated, which is considered to be important for generating anticlinic ordering in the antiferroelectric and ferrielectric phases. An isotropic-isotropic transition characterized by the emergence of a broad diffuse DSC peak was observed for the even-membered homologues.     

Soliton solutions and stability analysis for some conformable nonlinear partial differential equations in mathematical physics

This research presents soliton solutions and stability analysis to some conformable nonlinear partial differential equations (CNPDEs). The CNPDEs equations in this paper are conformable Cahn–Allen and conformable Zoomeron equations. The powerful sine-Gordon method is used to carry out the soliton solutions for these equations. The aspects of stability analysis for the considered equations is investigated using the linear stability technique. The sine-Gordon method proves to be efficient and effective for the extraction of soliton solutions for different types of CNPDEs.     

Intramolecular construction of trifluoromethyl group by the palladium-catalyzed reaction of 2,3,3-trifluoroallylic carbonates with O-nucleophiles

The synthesis of the trifluoromethyl group containing enol ethers by the palladium-catalyzed intermolecular reaction of 2,3,3-trifluoroallylic carbonates with oxygen nucleophiles was accomplished. The reaction proceeds through the intermolecular attack of oxygen nucleophiles on the C-2 carbon atom of the allylic unit, and the intramolecular fluorine atom shift from the C-2 position to the C-3 position. The reactions with several types of alcohols and phenols proceeded smoothly, and afforded the corresponding trifluoromethyl group containing enol ethers in good to high yields.     

Comparative Study of Reversed-Phase High-Performance Liquid Chromatography and Ultraviolet–Visible Spectrophotometry to Determine Doxorubicin in pH-Sensitive Nanoparticles

Analytical methods by reversed-phase high-performance liquid chromatography (HPLC) and ultraviolet–visible spectrophotometry were developed and validated to determine doxorubicin in pH-sensitive chitosan nanoparticles. Chromatographic separation was performed on a reversed-phase C₁₈ column, with ultraviolet detection at 254?nm and a mobile phase composed by 90% (v/v) acetonitrile in water and water pH 3.0 (33:67, v/v). The spectrophotometry method had the wavelength set at 480?nm and pH 3.0 water was used as a diluent. Calibration curves were linear from 1 to 30?µg/?mL (r?>?0.9995) and the specificity was demonstrated by verifying the absence of interferences from nanoparticle components. The values of accuracy and precision were within the acceptable limits, and robustness studies were performed by a two-level full factorial design. The validated methods were further tested to assess doxorubicin content in six different batches of pH-sensitive chitosan nanoparticles. The comparative analyses showed nonsignificant differences (p?>?0.05). Likewise, the HPLC method was successfully applied to determine the drug encapsulation efficiency as well as to measure doxorubicin during in vitro release assays and degradation kinetic studies under ultraviolet light C irradiation. Both methods fulfilled all validation parameters and were shown to be suitable for the characterization of doxorubicin-loaded pH-sensitive chitosan nanoparticles, without interferences from nanoparticle matrix.