Peptide and protein folding Chasse, Gregory Adam; Rodriguez, Ana Maria; Mak, Melody L.; Deretey, E.; Perczel, András; Sosa, Carlos P.; Enriz, Ricardo Daniel; Csizmadia, Imre Gyula Ab initio peptide folding, and its role in the reductionistic approach towards the understanding of protein folding are discussed from the points of view of past, present and possible future developments. It is believed that after the initial holistic approach, we are now at a new epoch, which will be dominated by reductionism. New quantitative mathematical models will be the result of the reductionistic approach that will lead toward a new, more sophisticated holistic era.

Morphometric diversity of the pulmonate limpet Siphonaria lessoni in different coastal environments Tablado, Alejandro; López Gappa, Juan José Siphonaria lessoni (Blainville, 1824) is the most abundant marine gastropod in the rocky intertidal zone of Buenos Aires Province, Argentina. The morphology of this species was studied in 6 sites near the city of Quequén, differing in intertidal height and degree of exposure to wave action and pollution. Shell length, width, height, and the distance from apex to posterior shell margin were measured, as well as the dry weight of both the shell and limpet body. A data matrix of 600 individuals (100 limpets per site) by 6 variables was analyzed by Principal Component Analysis (PCA) and Discriminant Analysis (DA) in order to compare size and shape differences among sites. As expected, axis I of the PCA explained a very high percentage (87.7%) of total variance, and can be interpreted as a size factor. Axis II, which summarised 6.9 %, may be regarded as expressing shell shape. Limpets not exposed to wave action within Quequén Harbour showed the highest values in all variables, whereas individuals living within the Brachidontes rodriguezi (d'Orbigny, 1846) community were very small and highly variable. Limpets heavily exposed to sewage at mid intertidal levels had a subcentral shell apex and were relatively very low. Classification of individuals by DA showed that the most characteristic morphology corresponded to limpets living at mid intertidal level close to a sewage outfall, or within Quequén Harbour (94 and 97 % correct reallocations, respectively). The influence of different physical and biotic factors on the morphology of Siphonaria lessoni is discussed.

Simulation of granular compacts in two dimensions Vidales, Ana Maria; Kenkre, Vasudev M.; Hurd, Elizabeth A. Simulations of granular packings in 2-D by throwing disks in a rectangular die are performed. Different size distributions as bimodal, uniform and gaussian are used. Once the array of particles is done, a relaxation process is carried on using a large-amplitude, low-frequency vertical shaking. This relaxation is performed a number N of times. Then, we measure the density of the package, contact distribution, coordination number distribution, entropy and also the disks size distribution vs. height. The dependence of all these magnitudes on the number N of "shakings" used to relax the packing and on the size distribution parameters are explored and discussed.

The D2 receptor is critical in mediating opiate motivation only in opiate-dependent and withdrawn mice Dockstader, Colleen L.; Rubinstein, Marcelo; Grandy, David K.; Low, Malcolm J.; Van Kooy, Derek Der According to the dual systems model for opiate reward, dopamine mediates opiate motivation when an animal is in a deprived motivational state (i.e. opiate-dependent and in withdrawal) and not when an animal is in a nondeprived state (i.e. previously drug-naive). To determine the role of the D2 dopamine receptor subtype in mediating opiate motivation, we examined the behaviour of N5 congenic D2 receptor knockout mice and their wild-type siblings in opiate-naive and opiate-dependent and withdrawn place conditioning paradigms. Opiate-naive D2 receptor knockout mice demonstrated acquisition of morphine-conditioned place preference but failed to acquire place preference when conditioned in the deprived state. We propose that D2 receptor function is critical in mediating the motivational effects of opiates only when the animal is in an opiate-dependent and withdrawn motivational state. These findings also underscore the important influence of the genetic background to a given phenotype, as evidenced by the observation that increasing the allelic contribution from the 129/SvJ strain abolishes morphine place preference in C57BL/6 wild-type mice.

Curing kinetics of epoxy-urethane copolymers Stefani, Pablo Marcelo; Moschiar, Stella Maris; Aranguren, Mirta Ines The cure of the epoxy resin diglycidyl ether of bisphenol A (Araldyt GY9527) with a mixture of cycloaliphatic amines (Distraltec) was studied, and the focus was on the effect of the copolymerization with a commercial polyurethane (PU) elastomer (Desmocap 12). A simplified phenomenological model was proposed to represent the copolymerization reaction. It considered the effect of the temperature and the concentration of the elastomer on the reaction rate, and it was simple enough to be included in models of processing conditions. A nonlinear regression analysis of the experimental conversion data obtained from differential scanning calorimetry was utilized to find the best fitting parameters to Kamal's equation for the chemically controlled part of the reaction (short times) under isothermal and constant heating-rate conditions. The Rabinowitch approach together with the Addam–Gibbs theory was utilized to introduce the effect of diffusion control at the end of the reaction on the overall constant for the reaction rate. The Di Benedetto equation was used to predict the conversion at which vitrification takes place for each run. Experimental results for conversions higher than this critical conversion were utilized to obtain information about the diffusion kinetic constant using a nonlinear regression analysis as previously. The overall model obtained was used to calculate a calorimetric conversion and reaction rate as functions of time, which was in excellent agreement with the experimental results. The addition of PU elastomers affected the values of the activation energies of the chemically and diffusion controlled parts of the reaction, as well as the final conversion reached by the epoxy–amine system. The proposed model allowed prediction of all the observed features using parameters that were independent of the temperature of the curing reaction.

Perfect fluid cosmologies with varying light speed Chimento, Luis Pascual; Jakubi, Alejandro S. We have found exact constant solutions for the cosmological density parameter using a generalization of general relativity that incorporates a cosmic time-variation of the velocity of light in vacuum and the Newtonian gravitation constant. We have determined the conditions when these solutions are attractors for an expanding universe and solved the problems of the Standard Big Bang model for perfect fluids.

Protective role of medroxyprogesterone acetate on N-methyl-N-nitrosourea-induced lymphomas in BALB/c female mice Pazos, Patricia; Lanari, Claudia Lee Malvina; Molinolo, Alfredo In a previous paper we reported the occurrence of a high incidence of lymphomas in N-methyl-N-nitrosourea (MNU)-treated mice, in the course of an experiment of combined chemical-hormonal carcinogenesis in mammary gland, in which we used medroxyprogesterone acetate (MPA) and MNU in different treatment protocols. In this report we have analyzed the action of MPA in the leukemogenic effects of MNU, by specifically selecting for the analysis experimental groups in which only few mammary carcinomas had developed. A high incidence of lymphomas (65%, median latency: 176 days) was registered in MNU-treated mice, and the administration of MPA was associated with a significant reduction in the incidence of lymphomas (P<0.001) in all protocols.

Determination of the pore size distribution of correlated mesoporous networks López, Raúl Horacio; Vidales, Ana Maria; Zgrablich, Giorgio In the present work we study how the adsorption desorption hysteresis loop of a mesoporous disordered medium represented by a 3-dimensional Dual Site-Bond Model (DSBM) is affected by percolation. Site and bond distributions are assumed to be gaussians. The behavior of the threshold pressure for the evaporation processe suggests a method to determine the site and bond distributions from experimental adsorption-desorption hysteresis curves. Traditional methods developed for non-correlated networks are tested and evaluated against our simulation results showing the discrepancy mainly for highly correlated networks. Results of the prediction capability of our method are shown.

Increased AT 1 receptor expression and mRNA in kidney glomeruli of AT 2 receptor gene-disrupted mice Saavedra, Juan M.; Häuser, Walter; Ciuffo, Gladys Maria; Egidy, Giorgia; Hoe, Kwang Lae; Jöhren, Olaf; Sembonmatsu, Takaaki; Inagami, Tadashi; Armando, Inés The proposed feedback between angiotensin II AT2 and AT1 receptors prompted us to study AT1 receptor expression in kidneys of male AT2 receptor-gene disrupted mice (agtr2 −/y). In wild-type (agtr2 +/y) mice, AT1 receptor binding and mRNA is abundant in glomeruli, and AT1 receptor binding is also high in the inner stripe of the outer medulla. AT2 receptors are scarce, primarily associated to cortical vascular structures. In agtr2 −/y mice, AT1 receptor binding and mRNA were increased in the kidney glomeruli, and AT1 receptor binding was higher in the rest of the cortex and outer stripe of the outer medulla, but not in its inner stripe, indicating different cellular regulation. Although AT2 receptor expression is very low in male agtr 2 +/y mice, their gene disruption alters AT1 receptor expression. AT1 upregulation alone may explain the AT2 gene-disrupted mice phenotype such as increased blood pressure, higher sensitivity to angiotensin II, and altered renal function. The indirect AT1/AT2 receptor feedback could have clinical significance because AT1antagonists are widely used in medical practice.

Influence of lysine content and PH on the stability of alanine based copolypeptides Vila, Jorge Alberto; Ripoll, Daniel R.; Scheraga, Harold A. To account for the relative contributions of lysine and alanine residues to the stability of α‐helices of copolymers of these two residues, conformational energy calculations were carried out for several hexadecapeptides at several pHs. All the calculations considered explicitly the coupling between the conformation of the molecule and the ionization equilibria as a function of pH. The total free energy function used in these calculations included terms that account for the solvation free energy and free energy of ionization. These terms were evaluated by means of a fast multigrid boundary element method. Reasonable agreement with experimental values was obtained for the helix contents and vicinal coupling constants (3JHNα). The helix contents were found to depend strongly on the lysine content, in agreement with recent experimental results of Williams et al. (Journal of the American Chemical Society, 1998, Vol. 120, pp. 11033–11043) In the lowest energy conformation computed for a hexadecapeptide containing 3 lysine residues at pH 6, the lysine side chains are preferentially hydrated; this decreases the hydration of the backbone CO and NH groups, thereby forcing the latter to form hydrogen bonds with each other in the helical conformation. The lowest energy conformation computed for a hexadecapeptide containing 6 lysine residues at pH 6 shows a close proximity between the NHurn:x-wiley:00063525:media:BIP1001:tex2gif-stack-1 groups of the lysine side chains, a feature that was previously observed in calculations of short alanine‐based oligopeptides. The calculation on a blocked 16‐mer of alanine shows a 7% helix content based on the Boltzmann averaged vicinal coupling constants computed from the dihedral angles ϕ, consistent with previous experimental evidence on triblock copolymers containing a central block of alanines, and with earlier theoretical calculations.

Metasomatism and Melting in Carbonated Peridotite Xenoliths from the Mantle Wedge: The Gobernador Gregores Case (Southern Patagonia) Laurora, Angela; Mazzucchelli, Maurizio; Rivalenti, Giorgio; Vannucci, Riccardo; Zanetti, Alberto; Barbieri, María Adelaide; Cingolani, Carlos Alberto Spinel-facies mantle xenoliths occur in a diatreme cutting through the Neogene Southern Patagonia Plateau at Gobernador Gregores (Santa Cruz Province, Argentina). This plateau is in a back-arc position with respect to the Chile trench. Xenoliths differ in their whole-rock composition from other South America occurrences, having higher CaO/Al2O3 ratios and, in some samples, TiO2 enrichment, whereas the Na2O/Al2O3 variation range is similar. Three assemblages can be distinguished. Assemblage 1, in anhydrous protogranular lherzolites and harzburgites, contains clinopyroxene with a depleted major and trace element composition, indicating pre-metasomatic depletion processes. This assemblage fully recrystallized to Assemblage 2 (amphibole ± phlogopite ± Cl-apatite-bearing) during a metasomatic episode. This causes clinopyroxene to acquire geochemical characteristics often attributed to carbonate-melt metasomatism. Noticeably, amphibole is markedly enriched in Nb (up to 298 ppm), especially when depleted in Ti. A further event, related to decompression during xenolith uplift to the surface, induces closed-system (perhaps with the exception of CO2 addition) disequilibrium melting of Assemblage 2, dominantly of amphibole. It is found in pockets (where amphibole is a residual phase) consisting of Na–Si-rich glass and carbonate (Mg-rich calcite) drops, and in veins originating from the pockets (Assemblage 3). Euhedral olivine, clinopyroxene and spinel crystallize only in the silicate glass. So do new, euhedral apatite crystals when glass is in contact with previous Assemblage 2 apatite. Textural evidence and comparison with experimental work suggest that silicate glass and carbonates are the result of unmixing of a former homogeneous melt. Because of the different flow rates of carbonate and silicate melt, the xenoliths become enriched in carbonate, which is found in the veins during their migration. Thus, the high CaO/Al2O3 ratio of whole rocks provides inconclusive evidence of carbonatite metasomatism. This factor, and other minor deviations from the expected results of carbonatite metasomatism, lead us to hypothesize an aqueous, Cl-rich fluid, possibly slab derived, as an alternative agent. Amphibole, resulting from reactive porous flow of this agent in the mantle, could fully explain the observed geochemical features, as indicated by estimates of its partition coefficients.

Single strand mRNA differential display (SSDD) applied to the identification of serine/threonine phosphatases regulated during cerebellar development Vilá Ortiz, Guillermo J.; Radrizzzani, Martín; Carminatti, Hector; Idoyaga Vargas, Victor Pastor; Santa Coloma, Tomás Antonio Differential display is a used widely and useful technique for the study of differentially expressed genes. However, very poor results have been obtained in the past when particular gene families were studied. Initially, we attempted to study the mRNA expression of catalytic subunits of serine/threonine phosphatases, using two primers specific to consensus sequences of these phosphatases. When differential display was applied, two wide, unresolved bands were isolated that contained cDNA of several phosphatases, together with that of many other unrelated transcripts. To overcome this problem, we used an alternative strategy, referred to as single strand differential display (SSDD), which is a combination of differential display and single strand conformation polymorphism (SSCP). After initial PCR amplification with specific primers, we ran a polyacrylamide (or agarose) gel, pre-selecting the region that contained fragments of the size expected for the consensus region (250-350 bp). The DNA eluted from this zone was then separated on a non-denaturing (SSCP) gel. Using this approach, we were able to characterize the expression of five ser/thr phosphatases, and a previously unreported splice variant of one of them, PP1γ. All these phosphatases show varying levels of expression during development, indicating a very complex regulation of protein phosphorylation-dephosphorylation during the period of synaptogenesis in the mouse cerebellum.

From direct to inverse GMR: Introduction of Cr in Fe/Cu superlattices Milano, Julian; Llois, Ana Maria It is well known that layered systems can present giant magnetoresistance (GMR). Particularly, the multilayers FeN/Cu8/Fe M/Cr/ FeM/Cu8 show inverse GMR. That is, the electrical conductivity decreases with the applied magnetic field. In the most common multilayers the conductivity increases with the applied field and this kind of GMR is called direct. In general the GMR is attributed to spin-dependent scattering in the bulk and mainly at interfaces. In this work we calculate the electronic band contribution to the GMR for Fe3/Cu 4/Fe/Cr/Fe/Cu4 and Fe3/Cu4 multilayers within the semiclassical approximation. The electrical conductivity is obtained in the ballistic and diffusive regimes. The results show a large change in the GMR behavior when one layer of Cr is introduced within the Fe layers. The GMR calculated in the CPP configuration (current flowing perpendicular to layers) of Fe3/Cu4 is of the direct type, with a value of about 40% while that obtained for Fe3/Cu 4/Fe/Cr/Fe/Cu4 is inverse and of the order of 45%. In the CIP configuration (current flowing parallel to the layers) the calculated GMR is direct with a value of about 35% for the system without Cr while, by the introduction of Cr, we obtain also a direct GMR but of about 3%. © 2001 Published by Elsevier Science B.V.

Structure sensitivity and in-situ activation of benzene combustion on Pt/Al2O3 catalysts Garetto, Teresita Francisca; Apesteguia, Carlos Rodolfo The structure sensitivity and in situ activation of benzene combustion on Pt/Al2O3 catalysts of different platinum and chlorine loadings were studied. The catalyst activities were evaluated through both conversion versus temperature (light-off curves) and conversion versus time catalytic tests. The light-off curves shifted to lower temperature with increasing Pt particle size, thereby suggesting that benzene combustion is a structure sensitive reaction. Kinetically-controlled catalytic tests confirmed that benzene oxidation turnover rates are preferentially promoted by larger Pt crystallites. Kinetic studies showed that the reaction orders and the apparent activation energy are not changed by changing the metallic dispersion. Results are explained by considering that benzene oxidation proceeds via a Langmuir–Hinshelwood mechanism which involves the rapid and strong adsorption of benzene on metallic platinum and assumes that the rate constant of oxygen adsorption is very low compared to the rate constant of the surface reaction. The number of PtO bonds of lower binding energy, i.e. the site density of more reactive surface oxygen, increases on larger Pt particles. Low-conversion catalytic tests performed at constant temperature showed that on well-dispersed Pt/Al2O3 catalysts the benzene conversion increases with time, irrespective of the chlorine content on the sample. TEM examination and hydrogen chemisorption measurements suggested that the activity increase parallels a concomitant increase in the platinum particle size. In contrast, sintered samples (platinum dispersions lower than 10%) did not exhibit initial activation periods. It is proposed that the initial in situ activation of well-dispersed Pt catalysts is caused by the sintering of the metallic phase. Hot-spots on the metallic particles together with the presence of gaseous water cause the formation of larger Pt crystallites, even at mild reaction conditions. As a result, the benzene conversion increases with time until the formation of larger steady state Pt particles is completed.

A boundary value problem of a semilinear second order ODE Amster, Pablo Gustavo; Mariani, Maria Cristina; Sabia, Juan Vicente Rafael We solve by topological methods a Dirichlet problem for the genera.l scmilinear second order ODE. We also prove the uniqueness of the solutions. Moreover, we develop an iterative method in order to find a solution in certain cases, for which the usual Picard iteration is riot appliable.

Fórmulas de tratamiento y cortesía en las relaciones amorosas de la novela de caballería (siglo XVI) Rígano, Mariela Elizabeth El objetivo de este trabajo es analizar la evolución de las fórmulas de tratamiento de uso vocativo empleadas para manifestar cortesía en el marco del vínculo amoroso en la novela de caballería del siglo XVI. En tal sentido, empleamos como fuentes dos de las obras más importantes de este género en la literatura española: el Amadís de Gaula y Palmerín de Oliva. El análisis se encuadra en el enfoque de la sociolingüística histórica y el material se analiza, siempre que sea posible, empleando la metodología propuesta por la etnografía del habla (véase Rigatuso, 1986, 1992 a y b, 1993 y 1995). Asimismo, en el procesamiento de los datos, trabajamos con un enfoque sociolingüístico e interaccional. Consideramos también las dimensiones de poder y solidaridad, según lo propuesto por Roger Brown y Albert Gilman para los estudios sobre tratamientos (1960). Por otra parte, en los aspectos contemplados en el análisis de los tratamientos, seguimos la propuesta de Elizabeth M. Rigatuso en su estudio sobre las fórmulas de tratamiento en la relación amorosa del español bonaerense entre 1830 y 1930, considerando la evolución en el uso de los tratamientos a lo largo de las distintas instancias de una relación de pareja: primer encuentro, declaración, noviazgo, después del matrimonio.

Analysis of a styrene-divinylester copolymerization: Reaction heats, double bond conversions and average sequence lengths Auad, Maria Lujan; Aranguren, Mirta Ines; Borrajo Fernandez, Julio A simple model, based on the free radical copolymerization theory of Mayo and Lewis, is developed to predict reaction heats, calorimetric and molar conversions and average sequence lengths, during the crosslinking reaction between a monounsaturated monomer (M1) and a multiunsaturated comonomer (M2). The M2-double bonds are assumed to react independently with equal initial reactivities. The input variables of the model are the initial reactivity ratios (r10, r20) and their variation with the global molar conversion, the initial composition of the reactive mixture (f10) and the molar heat of formation of the different bonds formed during the copolymerization (ΔH11, ΔH22, ΔH12). The application of this model allows to calculate the overall molar and calorimetric double bond conversions (P(m) and P(c)), the heat developed during the reaction (ΔH(T)), the conversions corresponding to each type of unsaturations (P(c1), P(c2), P(m1), P(m2)), and the average sequence lengths of the reacted bonds ( and ). Published data of experimental comonomers conversions in the system styrene-divinylester (SDVER) were satisfactorily reproduced by including a functionality of both reactivity ratios with the overall conversion. Finally, it was shown that the assumption implicitly made in most published kinetic studies from the differential scanning calorimetric (DSC) data, that P(c) and P(m) are equivalent, is not general and this feature must be investigated in order to perform correct kinetic calculations.

Efectos de sustratos competitivos y de la insulina sobre la captación y el destino metabólico de la glucosa en corazón perfundido de ratas dislipémicas Chicco, Adriana Graciela; Montes, Monica; D'alessandro, Maria Eugenia Guadalupe; Pighín, Darío Gabriel; Lombardo, Yolanda La utilización de sustratos energéticos por el músculo cardíaco depende no sólo de la disponibilidad de los mismos sino del entorno metabólico y hormonal. En el presente trabajo nos propusimos analizar la captación y el destino metabólico de la glucosa en los corazones perfundidos de ratas en un modelo experimental de hipertrigliceridemia, elevados niveles de ácidos grasos circulantes y resistencia insulínica global. Los corazones de ratas alimentadas durante 15 semanas con una dieta rica en sacarosa (DRS) (63% p/p) fueron perfundidos durante 30 min con un medio adicionado de glucosa y ácido palmítico en concentraciones semejantes a las del entorno de los animales in vivo, en presencia o ausencia de insulina. Los resultados muestran: i) Una alterada captación y reducida utilización de la glucosa, ii) Una menor oxidación de la glucosa (estimada como la actividad del complejo PDH) principalmente debido a mayor actividad enzimática PDH quinasa y menor actividad del complejo PDH, iii) La adición de insulina in vitro incrementa la captación sin lograr normalizarla, pero no muestra un efecto significativo sobre la oxidación de la glucosa durante el período de perfusión. Estos resultados nos señalan que en los corazones de ratas alimentadas con DRS perfundidos con ácidos grasos y glucosa a niveles semejantes a los del plasma del animal in vivo, al menos dos mecanismos podrían contribuir al alterado metabolismo de la glucosa: 1) una menor captación y utilización de la glucosa a nivel basal y frente al estímulo de la insulina y 2) una incrementada disponibilidad y oxidación de lípidos (menor actividad PDHc y mayor actividad PDH quinasa) que a su turno disminuirían la captación de la glucosa y su utilización. Finalmente cabe señalar que este modelo animal experimental inducido nutricionalmente podría ser de gran utilidad para el estudio de algunos mecanismos fisiopatológicos involucrados en lesiones cardíacas tales como las observadas en individuos dislipémicos y en diabetes mellitus no insulino dependiente.

Determinación de las Concentraciones Letales de Diazinón para Haematobia Irritans (Diptera: Muscidae) Susceptibles a los Organo-Fosforados y su Aplicación para el Diagnóstico de Resistencia Castellino, Marta Elena; Volpogni, M.M.; Mangold, Atilio Jose; Guglielmone, Alberto Alejandro Se usaron papeles de filLro y frascos de vidrio lrarados con dislintas cooceutracio nes de diazinón para obtener la conc.cntración letal 50 (CL50) y 90 (Cl.90) de una población de Haenllltobio irrilnns susceptible a los órgano fosforados.

Bifurcation control: Theories, methods, and applications Chen, Guanrong; Moiola, Jorge Luis; Wang, Hua O. Bifurcation control deals with modification of bifurcation characteristics of a parameterized nonlinear system by a designed control input. Typical bifurcation control objectives include delaying the onset of an inherent bifurcation, stabilizing a bifurcated solution or branch, changing the parameter value of an existing bifurcation point, modifying the shape or type of a bifurcation chain, introducing a new bifurcation at a preferable parameter value, monitoring the multiplicity, amplitude, and/or frequency of some limit cycles emerging from bifurcation, optimizing the system performance near a bifurcation point, or a combination of some of these objectives. This article offers an overview of this emerging, challenging, stimulating, and yet promising field of research, putting the main subject of bifurcation control into perspective.