Modeling the motion of a bright spot in jets from black holes M87* and SgrA*

General Relativity and Gravitation - In previous work, we established theoretical results concerning the effect of matter shells surrounding a gravitational wave (GW) source, and we now apply these...     

The Cytotoxic Effect of α-Synuclein Aggregates

Parkinson's disease is a neurodegenerative disorder involving a functional protein, α-synuclein, whose primary function is related to vesicle trafficking. However, α-synuclein is prone to form aggregates, and these inclusions, known as Lewy bodies, are the hallmark of Parkinson's disease. α-synuclein can alter its conformation and acquire aggregating capacity, forming aggregates containing β-sheets. This protein's pathogenic importance is based on its ability to form oligomers that impair synaptic transmission and neuronal function by increasing membrane permeability and altering homeostasis, generating a deleterious effect over cells. First, we establish that oligomers interfere with the mechanical properties of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) membrane, as demonstrated by nanoindentation curves. In contrast, nanoindentation revealed that the α-synuclein monomer's presence leads to a much more resistant lipid bilayer. Moreover, the oligomers’ interaction with cell membranes can promote lactate dehydrogenase (LDH) release, suggesting the activation of cytotoxic events.     

Condensation of all-cis-tetraphenylcyclotetrasiloxanetetraol in ammonia: new method for preparation of ladder-like polyphenylsilsesquioxanes

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Thermally induced solid-state transformation of cimetidine. A multi-spectroscopic/chemometrics determination of the kinetics of the process and structural elucidation of one of the products as a stable N3-enamino tautomer

Exposure of cimetidine (CIM) to dry heat (160–180 °C) afforded, upon cooling, a glassy solid containing new and hitherto unknown products. The kinetics of this process was studied by a second order chemometrics-assisted multi-spectroscopic approach. Proton and carbon-13 nuclear magnetic resonance (NMR), as well as ultraviolet and infrared spectroscopic data were jointly used, whereas multivariate curve resolution with alternating least squares (MCR-ALS) was employed as the chemometrics method to extract process information. It was established that drug degradation follows a first order kinetics.     

Multicriteria decision making under uncertainty

Formalization for problems of multicriteria decision making under uncertainty is constructed in terms of guaranteed and weak estimates. A relevant definition of the vector maximinimax value is given. Parameterization and approximation of maximum, minimax, and maximinimax values based on the inverse logical convolution are suggested. An application for multicommodity networks is considered. Received: December 13, 2000 / Accepted: August 21, 2001?Published online May 8, 2002     

Hydrophilic segmented block copolymers based on poly(ethylene oxide) and monodisperse amide segments

Segmented block copolymers based on poly(ethylene oxide) (PEO) flexible segments and monodisperse crystallizable bisester tetra‐amide segments were made via a polycondensation reaction. The molecular weight of the PEO segments varied from 600 to 4600 g/mol and a bisester tetra‐amide segment (T6T6T) based on dimethyl terephthalate (T) and hexamethylenediamine (6) was used. The resulting copolymers were melt‐processable and transparent. The crystallinity of the copolymers was investigated by differential scanning calorimetry (DSC) and Fourier Transform infrared (FTIR). The thermal properties were studied by DSC, temperature modulated synchrotron small angle X‐ray scattering (SAXS), and dynamic mechanical analysis (DMA). The elastic properties were evaluated by compression set (CS) test. The crystallinity of the T6T6T segments in the copolymers was high (>84%) and the crystallization fast due to the use of monodisperse tetra‐amide segments. DMA experiments showed that the materials had a low T_g, a broad and almost temperature independent rubbery plateau and a sharp flow temperature. With increasing PEO length both the PEO melting temperature and the PEO crystallinity increased. When the PEO segment length was longer than 2000 g/mol the PEO melting temperature was above room temperature and this resulted in a higher modulus and in higher compression set values at room temperature. The properties of PEO‐T6T6T copolymers were compared with similar poly(propylene oxide) and poly(tetramethylene oxide) copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4522–4535, 2007     

Mechanism of the cyclization of dimethyl diethynyl silane with selenium tetrabromide: Computational and structural studies, and monitoring

The structure of 2,4-dibromo-2-dibromomethyl-3,3-dimethyl-1-selena-3-silacyclopentene-4, formed by regioselective electrophilic addition of SeBr₄ to dimethyl diethynyl silane, has been determined using X-ray analysis technique. Quantum chemistry methods were used to study elementary stages of the reaction. It was found that the first stage consisted of SeBr₄ conversion into bimolecular complex Br₂?SeBr₂, initiated by dimethyl diethynyl silane. Possible formation of five-membered and six-membered heterocycles involves different cyclization mechanisms. The formation of only five-membered heterocycle is explained by kinetically preferable ring closure through four-center transition state. The conclusions obtained by calculations were confirmed by monitoring of the reaction using ¹H NMR method.     

Electrochemical and spectral studies on the reductive nitrosylation of water-soluble iron porphyrin

The reaction of iron(III) (meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (Fe(III)TMPyP) with nitric oxide (NO) was studied by electronic absorption spectroscopy, ESR, and electrochemical and spectroelectrochemical techniques in aqueous solutions with pH from 2.2 to 12.0. Fe(III)TMPyP has been found to undergo a reductive nitrosylation in all pHs, and the product of nitric oxide binding to the porphyrin has been determined as iron(II) porphyrin nitrosyl complex ([Fe(II)(NO)TMPyP]). The rate of the reductive nitrosylation exhibits a tendency to get faster with increase in pH. An intermediate species was observed around neutral pH by spectroelectrochemical technique and was proposed to be the iron(II) nitrosyl complex of the mu-oxo dimeric form of FeTMPyP, which is known to be a predominant in neutral solutions.     

Separation strategy for acidic chiral pharmaceuticals with capillary electrochromatography on polysaccharide stationary phases

The effect of five factors on the capillary electrochromatographic enantioseparation of acidic compounds was studied using an experimental design. The studied factors were pH, acetonitrile content in the mobile phase, temperature, buffer concentration, and applied voltage. These experiments allowed defining a generic separation strategy applicable on acidic compounds with chemical and structural diversity. The starting screening conditions consist of a 45 mM ammonium formate electrolyte at pH 2.9 mixed with 65% acetonitrile, an applied voltage of 15 kV, and a temperature of 25 degrees C. The screening phase occasionally can be followed by an optimization procedure. Evaluation of the proposed strategy pointed out that it allows achieving baseline resolution within a relatively short time when a beginning of separation is obtained at the starting conditions. This strategy revealed enantioselectivity for 11 compounds out of 15, of which 10 could be baseline-separated after the proposed optimization steps.     

Synthesis of hydroporphyrins based on comparative studies of palladium-catalyzed and non-catalyzed approaches

Hydroporphyrins have been synthesized using both Pd-catalyzed and non-catalyzed approaches. Comparative studies of the reaction of tetrasubstituted porphyrins with organolithium reagents in the presence of and without palladium catalysts showed that depending on reagents, the catalyst structure and reactivity of the corresponding porphyrins, chlorins (β-hydroporphyrins) and/or porphodimethenes (meso hydroporphyrins) of 5,10-type can be prepared in reasonable yields. In the absence of Pd catalysts, the formation of chlorins is predominant in the reactions with aliphatic RLi while porphodimethenes are the main products in reactions with PhLi. The use of a palladium catalyst resulted in the formation of both types of hydroporphyrins and the selective formation of either β-mono- or disubstituted chlorins. Of special interest was the reaction of octaethylporphyrin. Here, reaction with t-BuLi in the presence of Pd(PPh₃)₄/CuI proceeded with complete regioselectivity for 5,10-porphodimethenes.