Fil: Perez Calderon, John Freddy. Provincia de Buenos Aires. Gobernacion. Comision de Investigaciones Cientificas. Centro de Investigacion y Desarrollo en Criotecnologia de Alimentos. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Centro de Investigacion y Desarrollo en Criotecnologia de Alimentos. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigacion y Desarrollo en Criotecnologia de Alimentos; Argentina
Fil: Recupero, Francisco. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Centro de Investigacion y Desarrollo en Ciencias Aplicadas Dr. Jorge J. Ronco. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigacion y Desarrollo en Ciencias Aplicadas; Argentina
Fil: Muzzio, Nicolas Eduardo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Instituto de Investigaciones Fisicoquimicas Teoricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquimicas Teoricas y Aplicadas; Argentina
Mercury concentration was measured in the hair of people who live and work in centres were rocks and minerals are processed to recover gold by amalgamation with mercury. Hair samples were analysed for total mercury (T-Hg) by CVAAS (cold vapour atomic absorption spectrometry) in males (n= 104) and females (n= 11) aged 2 - 68 years. T-Hg ranged between 1.0 and 186.4 μg.g-1. The highest value was found in a 34 year woman, the other members of her family had between 5.0 and 83.0 μg.g-1. Males had an arithmetic mean of 8.15 μg.g-1 (min = 1.0 μg.g-1. max = 83.95 μg.g-1), which is less than the value found for females of 33.6 μg.g-1.(min = 1.0 μg.g-1. max = 186.4 μg.g-1). The 27 % of females hair samples exceeded the limit of 10 μg.g-1 that the World Health Organization consider as the non observed adverse effects levels (NOAEL). For males this proportion was only 4 % with a NOAEL of 50 μg.g-1. There was no statistical difference in T-Hg between the first four age groups, but the group > 50 years showed the highest mean (7.5 μg.g-1) differing significantly from other age groups. It was also found that samples of the most consumed carnivorous fishes have Hg levels above the value of 0.5 μg.g-1. In general, results showed the presence of Hg in individuals with concentrations in hair similar to those reported for other mining areas in South America.
The characteristics of the aggregation of the aqueous mixed system dodecyltrimethylammonium bromide - didodecyldimethylammonium bromide were studied by several techniques. The mixed systems show a coexistence of small spherical micelles, and a polydisperse mixture of vesicles and aggregates of micelles. The charge and size of aggregates were studied as a function of the mixture composition.
Two different types of interactions affecting both J(C,H) and longer range J(C,H) spin-spin coupling constants, SSCCs, are studied from a theoretical point of view in model compounds. The study, based on the DFT methodology, was supplemented with measurements of several J(C,H) couplings. The studied interactions are, on the one hand, those of electrostatic origin caused by proximity of either an electronegative atom or of an H atom and a C⎯H bond on the corresponding J(C sp2 ,H) SSCC. In agreement with previous observations it was determined that the former interaction yields an increase while the latter a decrease in the corresponding J(C,H) SSCC. Both of these changes are notably shielded by the dielectric effect of the solvent. On the other hand, the influence of the strong negative hyperconjugative interactions that take place in the aldehyde moiety on the corresponding J(C C ,H f ) and J(C,H f ) SSCCs, are studied. These negative hyperconjugative interactions are inhibited by, for instance, the intramolecular hydrogen bond in salicylaldehyde, the dielectric effect of the solvent, or the electrostatic effect of an aproximate electronegative atom close to the formyl proton of the H f ⎯C C bond.
An Euclidean graph associated with a molecule is defined by a weighted graph with adjacency matrix M = [d ij ], where for i#j, d ij is the Euclidean distance between the nuclei i and j. In this matrix d ii can be taken as zero if all the nuclei are equivalent. Otherwise, one may introduce different weights for distinct nuclei.In this paper, the automorphism group of the Bis Benzene Chromium(0) with D 6d point group symmetry is computed. We also find an euclidean graph with an odd number of automorphisms. This solved a problem posed by the author in an earlier paper. Resumen Un grafico euclidiano asociado a una molecula es definido por un grafico con matriz adyacente M = [d ij ] donde para i#j, d ij es la distancia euclidiana entre los nucleos i y j. En esta matriz d ii puede ser tomada como cero si todos los nucleos son equivalentes.De otra manera, se pueden introducir diferentes pesos para distintos nucleos. En este trabajo se calcula el grupo de automorfismo del Bis Benceno Cromo(0) con simetria D 6d . Se encontro tambien un grafico euclidiano con un numero impar de automorfismos. Este resultado resuelve un problema planteado por el autor en un articulo publicado previamente.
Since the cage substrate of 1-X;3-Y-bicyclo[1.1.1]pentanes is notably strained, it is expected that in compounds of this type important trans-cage spin-spin coupling constants, SSCCs, could be observed. Such SSCCs should be dominated to a great extent by the Fermi Contact, FC, contribution since this term, for long-range couplings, is transmitted by electron-transfer interactions, which in strained compounds are particularly enhanced. In this paper, both theoretically and experimentally, 4 J( 13 C α , 1 H 3 ) SSCCs in 1-Xbicyclo[1.1.1]pentanes, where the α−atom of group X is 13 C, are studied. Results are compared with similar trans-cage SSCCs in analogous compounds. Insights into electron delocalization interactions defining the experimental trends are obtained through the study of σ-hyperconjugative interactions of cage bonds. These interactions are studied using the Natural Bond Orbital, NBO, method. Results suggest that multipath additivity should hold in compounds where trans-cage SSCCs are determined by charge transfer interactions.
The ω cis-trans isomers, backbone conformers (α-L, e-L and γ-L) and syn-anty ring puckered structures of formyl L-prolinamide were studied at the RHF/3-21G, RHF/6-31G(d) and RB3LYP/6-31G(d) level of theory. In addition single point calculations using a more accurate and extended basis set (aug-cc-PVDZ) were carried out. The barrier heights for cis-trans isomerization fell in the range of 19.58 to 24.6 Kcal/mol and those for the interconversion between backbone conformations were in the range of 0.61-5.56 Kcal/mol. The barrier heights for syn-anty ring puckering were found within 1.79 to 7.46 Kcal/mol at the aug-cc-pVDZ//RHF/3-21G level of theory.
In this work is demonstrated that the Surface Resistance (SR) technique can be applied to study the different interactions of anions, such as, perchlorate, sulphate and benzenesulphonate and also a cation as Cu(II), with a gold film surface, even when the metal film surface is partially blocked with an electroactive polymer film. The electroactive polymer poly(o-aminophenol) (POAP) was employed to cover the surface of the gold film electrode. Resistometric changes were detected even after the metal surface was completely covered with the polymer. Dependence of the resistance change on the external electrolyte composition for polymer thicknesses lower than 0.25 mC cm –2 was attributed to a competition, at the gold film surface, between the redox process of the polymer and adsorption of different species in the electrolyte. This result points to a discontinuous character of the polymer for thicknesses lower than 0.25 mC cm –2 at the metal|polymer interface. For polymer thicknesses higher than 0.8 mC cm –2 , the resistometric response becomes independent of both the external electrolyte composition and the polymer thickness. Thus, polymer thicknesses higher than 0.8 mC cm –2 seem to be compact enough at the metal|polymer interface to prevent the interaction of species in the supporting electrolyte with the gold film surface. However, the resistometric changes observed, were attributed to the redox conversion of the polymer. In this connection, the redox conversion of POAP from amine to imine groups leads to an increase of the gold film resistance. This increase was explained as a transition from specular to diffuse scattering of the conduction electrons of gold at the gold|POAP interface due to a less compact distribution of oxidised sites (imine) as compared with those of the reduced centers (amine).
In this work we focused our interest on the study of the effect of the ionic strength of the solution on the properties of the lipids that form an asymmetric membrane composed by DPPC and DPPS - . The Molecular Dynamics Simulation was the simulation technique chosen to carry out the study. The asymmetry in the lipid bilayer was generated by placing the charged lipids (DPPS - ) in only one of the two leaflets of the membrane. In the opposite leaflet, the layer was composed only by neutral lipids (DPPC). The ionic strength of the aqueous solution was simulated at two different concentrations of NaCl, corresponding to 0.25 and 0.5 M. From the analysis of the simulated trajectories, information related to steady and dynamics properties of the system with atomic detail was obtained. Thus, the translational diffusion coefficient of the lipids, lipid head orientation, lipid hydration or the structure of the hydrocarbon zone of the membrane have been studied.
The effect of the syn-anti conformational isomerism and fluorination of methyl nitrite on the ultraviolet photoelectron spectra of methyl nitrite is predicted on the basis of Outer Valence Green Function calculations using the 6-311++G** basis set. The conformational space of methyl nitrite and its single, di- and tri-fluoromethyl derivatives have been explored with MP2 and B3LYP-DFT approaches. Only the fluoro-methyl nitrite shows minima with geometries compatible with bound systems, therefore the OVGF study has been limited to methyl nitrite and fluoro-methyl nitrite. A procedure has been devised to represent simulated spectra starting from the OVGF data and the experimental UPS spectrum taken from the literature. The He I experimental spectrum has been assigned at the OVGF level and the simulated spectra are discussed. It is predicted that the syn-anti conformational isomerism will affect less the spectrum of the fluorinated system than that of the methyl nitrite. The effects of fluorination will be larger for the second peak than for the first. Fluorination brings about changes of the general shape (e.g., peak shifts, changes in gap widths, positions, etc.) of the low ionization energies of the spectrum.
Recently, there has been growing international interest regarding food safety. Unlike many physical elements, the impact of most chemical and biological hazards is complex and has not been fully characterized. Establishing a database of parameters associated with such molecular interactions would not only be beneficial for the scientific community, but may allow consumers to wisely choose certain food products. By examining the interaction between a simple phenol and the divalent magnesium ion, we propose a new approach to assess the interactions between biologically relevant compounds using widely accepted theoretical methods such as ab initio computations, while taking into consideration recent developments in the field. Certain theoretical cases were examined, while others were collected from scientific literature on phenols/phenolics. Experimental and theoretical methods should complement each other to provide a more complete picture of molecular interactions. A common database of interactions between common chemicals detectable in foodstuffs and human systems will enable consumers to make more informed decisions regarding their purchases.
The stability of the complex formed by one molecule of 1,2-dihydroxybenzene and one molecule of zinc acetate in solutions with different permittivity and temperature was investigated by means of spectroscopic and chromatographic methods. The Becke hybrid three-parameter nonlocal exchange functional combined with the Lee-Yang-Parr dynamic correlation functional method (B3LYP/6-31G(d)) and the isodensity polarized continuum model (IPCM) were used in the calculations. It was assumed that the formation of the complex takes place by a reaction between ions of opposite charges. It was also proposed an equation to explain the changes of the constant of the complexation equilibrium with the permittivity of the reaction medium. The calculations allowed us to prove that the increase of the hydrogen-bond donor ability of the solvents favours a higher thermodynamic stability of the reactants with respect to the complex and, as a result, a decrease of the corresponding equilibrium constants. The non-planar structure proposed for the complex is consistent with the experimentally observed hyperchromic shift. The plane, in the complex molecule, containing the aromatic ring is tilted by approximately 18o with respect to that of the zinc and oxygen atoms. It was concluded that the formation of the complex is an endothermic process.
Motivation. This paper outlines the utility of a 3D→1D transformation of peptide conformation. Although this transformation leads to a linearized notation of protein secondary and tertiary structures that may be used for an objective description and classification of protein folding, nevertheless, the method is intended to be descriptive and is not meant to be predictive. Method. It is established from first principles that the idealized 2D-Ramachandran potential energy surface must have nine minima. It is therefore an obvious question to ask whether all these nine conformations are actually occurring in proteins. An analysis is carried out on 258 proteins with known X-ray structure. These proteins contain 56 495 amino-acid residues with well-defined φ and ψ angles. The minima are identified with the aid of the nine minima of Ac-L-Ala-NHMe determined by ECEPP/2 method allowing a ±40° tolerance in the φ and ψ values. All nine conformations do occur in proteins. Results. L-conformation preference varies as: e > γ > α >> δ > β = 1. Pro is the amino acid with the greatest preference for L-conformation. L-conformation preference varies as: Pro >> Ile > Val > Leu > Thr > Met > Ala > Glu > Phe > Trp > Tyr > Gln > Lys > Ser > Cys > Arg > Asp > His > Asn > Gly. The results relative to achiral Gly shows that the trend-line slope varies as: α >> e > γ >> β = 0 ≈ δ. The strong Pro preference is in agreement with its character of strong α-helix and β-sheet breaker, and β-turn and random-coil former. Conclusions. In XX–XXI centuries, the secondary–tertiary structures of proteins, frequently referred to as protein folding, posed a major problem to medicine, biochemistry, pharmaceutical drug design and related fields. A method is formulated, via a 3D→1D transformation, which allows using a qualitative linearized notation for protein 3D structures, which is based on quantitative geometrical data. It appears that with the present objective method, there is no longer any need to refer to a particular protein segment as unordered, and the description– classification of protein secondary–tertiary structures is now within reach of all protein chemists. L-conformation preferences vary as: e > γ > α >> δ > β = 1, and as: Pro >> Ile > Val > Leu > Thr > Met > Ala > Glu > Phe > Trp > Tyr > Gln > Lys > Ser > Cys > Arg > Asp > His > Asn > Gly. The Pro preference is in agreement with its strong character of α-helix and β-sheet breaker, and β-turn and random-coil former. Availability. The original software used in the investigation is available from the author.
In order to better understand, at submolecular level, the minimal structural requirements for the recognition process in the inhibitor activity, N-aralkyl substituted 2-aminoindans were examined as D 2 dopamine receptor antagonist variants. Semiempirical (AM1) and ab- initio (RHF/3-21G and RHF/6-31G(d)) calculations were performed for a better understanding of the recognition process at submolecular level. Using the above-mentioned computational model, we were able to interpret the basic behavior and predict some additional features of N-aralkylsubstituted 2-aminoindans-Dopamine D 2 receptor interaction.
