Showing papers by "University of São Paulo published in 1985"

Effect of friction on electron transfer in biomolecules

Abstract: In biological and chemical electron transfer, a nuclear reaction coordinate is coupled to other nuclear and/or ‘‘solvent’’ coordinates. This coupling, or friction, if strong enough, may substantially slow down motion along the reaction coordinate, and thus vitiate the assumption of electron transfer being nonadiabatic with respect to the nuclei. Here, a simple, fully quantum mechanical model for electron transfer using a one mode treatment which incorporates this coupling is studied. Path integral methods are used to study the dependence of the reaction rate on friction, and the limits of the moderate and the high friction are analyzed in detail. The first limit will prevail if the reaction coordinate is, e.g., an underdamped nuclear vibration, whereas the second limit will prevail if it corresponds to a slow or diffusive degree of freedom. In the high‐friction limit, the reaction rate is explicitly shown to vary between the nonadiabatic and adiabatic expressions as the tunneling matrix element and/or the friction are varied. Starting from a path integral expression for the time evolution of the reduced density matrix for the electron and reaction coordinate, a Fokker–Planck equation is obtained which reduces in the high‐friction limit to a Smoluchowski equation similar to one solved by Zusman.

Presence of laminin receptors in Staphylococcus aureus.

Abstract: A characteristic feature of infection by Staphylococcus aureus is bloodstream invasion and widespread metastatic abscess formation. The ability to extravasate, which entails crossing the vascular basement membrane, appears to be critical for the organism's pathogenicity. Extravasation by normal and neoplastic mammalian cells has been correlated with the presence of specific cell surface receptors for the basement membrane glycoprotein laminin. Similar laminin receptors were found in Staphylococcus aureus but not in Staphylococcus epidermidis, a noninvasive pathogen. There were about 100 binding sites per cell, with an apparent binding affinity of 2.9 nanomolar. The molecular weight of the receptor was 50,000 and pI was 4.2. Eukaryotic laminin receptors were visualized by means of the binding of S. aureus in the presence of laminin. Prokaryotic and eukaryotic invasive cells might utilize similar, if not identical, mechanisms for invasion.

Flutuacoes do nivel relativo do mar durante o quaternario superior ao longo do litoral brasileiro e suas implicacoes na sedimentacao costeira

Abstract: Evidence of relative sea-level fluctuations during the Upper Quaternary are represented by numerous geological, biological, and pre-historical (shell-middens) records found along the Brazilian coast line. About 700 of these records, dated mostly by the radiocarbon method, are distributed through the States of Alagoas, Sergipe, Bahia, Espirito Santo, Rio de Janeiro, Sao Paulo, Parana, and Santa Catarina. The coastal plains of these states, representing about 50% of the Brazilian coast, have been geologically mapped, in part or entirely during the last 10 years. The geological maps are accompanied by sea level fluctuation curves for the past 7,000 years for the States of Bahia (Salvador, Ilheus, and Caravelas sectors), Rio de Janeiro (Angra dos Reis sector), Sao Paulo (Santos and Cananeia-Iguape sectors), Parana (Paranagua sector) and Santa Catarina (Itajai-Laguna sector). These informations allowed us to know that the relative sea level fluctuations during the last thousand years played a very important role in the construction of the Brazilian Coastal plains. It was also demonstrated that the relative sea level fluctuations during the Upper Quaternary have been important for the construction of the river mouth coastal plains of Sao Francisco (SE/AL), Jequitinhonha (BA), Doce (ES) and Paraiba do Sul (RJ) rivers, whose evolutionary histories were quite different in relation to the classical delta plains presented in the geological literature.

Gas-phase Nucleophilic Displacement Reactions

Abstract: Publisher Summary This chapter reviews that gas-phase nucleophilic displacement reactions constitute a mature field of physical organic chemistry. It is a field that provides some unusual insights into the world of solvent-free chemistry, although many experiments remain to be rationalized on a more quantitative basis. The extent to which the understanding of gas-phase reactivity provides an insight into solution behavior by appropriate extrapolation of salvation effects has been under attack recently, and it is a subject of lively discussion. The chapter discusses that the most important lesson that can be derived from these examples is that significantly different chemistry can be generated in ionic reactions in the gas phase. This aspect is one which most theoretical and experimental chemists find intellectually stimulating and a challenge to be pursued.

Trypanosoma cruzi: Interaction with Host Cells

Abstract: The flagellate protozoan Trypanosoma cruzi (order Kinetoplastida) is the aetiological agent of Chagas’ disease The disease, predominantly rural, affects approximately 10–12 million people living in Latin America Thus, from the medical point of view, T cruzi is the most important trypanosomatid in the New World

In vivo and in vitro characteristics of six Paracoccidioides brasiliensis strains.

Abstract: The yeast-like forms of six P. brasiliensis strains were characterized and compared using in vitro (growth curve determination) and in vivo (pathogenicity to sensitive inbred mice) criteria. Strains Pb 18 and Pb 265 which behaved similarly in vitro, showing low counts of fungi and long mean generation times, were respectively the most and the least pathogenic strains. Strains Pb 2052 and IVIC Pb 267, which grow abundantly in vitro were, respectively virulent and avirulent. Strains Pb SN and IVIC Pb 9 behaved similarly both in vitro and in vivo displaying an intermediate pattern of virulence and growing conditions.

Very large and isotypically atypical polyclonal plaque-forming cell responses in mice infected with Trypanosoma cruzi.

Abstract: Normal C3H/HeJ mice, acutely infected with T. cruzi, develop large numbers of splenic Ig-secreting plaque-forming cells (PFC). IgG2a, IgG2b and IgG1 PFC account for over 90% of all PFC, while the numbers of IgG3- and IgA-secreting PFC are lower than in normal animals. These effects appear to be due to both T helper-dependent regulation and to a mitogenic activity associated with the parasites themselves.

Vertical structure of the Brazil Current

Abstract: Recent interest in world climate and interaction of the ocean and atmosphere have led to studies of the meridional fluxes of fresh water and heat in the ocean1,2. Several such studies3,4 have noted the asymmetry of heat fluxes between the North and South Atlantic oceans. In particular, the fluxes across both 24° N and 24° S appear to be northward. Crucial to all of the direct calculation techniques is an accurate estimate of the transport of the western boundary currents. In the North Atlantic, useful measurements in the Florida Current5 over a long period of time are available. For the much less studied South Atlantic no comparable time series has been made. The direct measurements of Brazil Current velocities near 23° S reported here show southward flow of warm water above 400 m depth and northward flow of Antarctic Intermediate Water below that. The upper layer transport was ∼6 × 106 m3 s−1 towards the south offshore of the 200-m isobath, with an indication of comparable flow on the shelf.

Pathology of the human pulmonary paracoccidioidomycosis.

Abstract: Lungs of twelve patients with chronic paracoccidioidomycosis (Pb) were studied in an attempt to understand the pathogenesis of the pulmonary disease. Ribbons of the lung parenchyma including the hilar region and directed towards apical, basal and lateral regions were subdivided into sections from the hilar, intermediate and peripheral segments. The following histopathological reactions directly or indirectly related to P. brasiliensis were described and analysed in relation to the number of slides studied and the pulmonary region involved: pneumonic reaction; early granulomatous formation; mature and healed granulomata; mixed pattern (early and mature granuloma in the same pulmonary area visualized in the slide); pulmonary fibrosis. It was concluded that chronic pulmonary Pb is a recurrent disease affecting equally both lungs. Fibrosis was connected mainly with the progressive evolution of the granulomata towards cicatrization and to a lesser degree probably to a direct induction by the fungi. Based chiefly on the tendency of the fibrosis to run around bronchi and to make up septa interconnecting bronchi and vessels it was hipothesized that these findings were the result of a previous chronic specific lymphangitis by the fungi. Hilar fibrosis would be the result of this lymphangitis and/or of the progression of the specific granulomatous reaction seen in the hilar lymph nodes. Non specific forms of arteritis and areas of destructive emphysema related to granulomatous inflammation and fibrosis were described. Three cases developed pulmonary hypertension.

The American Herpetofauna and the Interchange

Abstract: Amphibians and reptiles are treated together in this chapter because, overall, they have similar and complementary Zoogeographic patterns with respect to the faunal interchange of the Americas We are each interested in amphibian and reptilian zoogeography, but because we are not systematic specialists in both groups, we have written this Chapter together The basic amphibian data are discussed by Heyer and the reptile data by Vanzolini

Effect of material bulk and undercuts on the accuracy of impression materials

Abstract: A truncated cone-shaped chromium steel die was used to determine the influence of the bulk of elastomeric impression material and size of undercut on the dimension of stone dies. It was found that both conditions affect the accuracy of stone dies. The possible clinical implications of the inaccuracies were discussed.

Abdominoperineal endoanal pull-through resection. A comparative study between immediate and delayed colorectal anastomosis.

Abstract: Abdominoperineal endoanal pull-through resection with colorectal anastomosis was performed on 728 patients—primarily those with chagasic megacolon and cancer of the rectum. Intestinal continuity was reestablished through immediate anastomosis (Swenson procedure) in 229 patients and through delayed anastomosis (Cutait-Turnbull procedure) in 499. Comparative studies showed: that the incidence of leakage was 31.9 percent in immediate and only 2.2 percent in delayed anastomosis; that presacral infection occurred in 27.9 percent in immediate and in 6.8 percent in delayed anastomosis; that stenosis was observed in 4.4 percent in immediate and 1.8 percent in delayed anastomosis; that mortality was 6.1 percent in immediate and 2.2 percent in delayed anastomosis; that anal continence was good in both procedures and that sexual disturbances were rare in benign and frequent in malignant lesions in both procedures. The final conclusion is that, in abdominoperineal endoanal pull-through resection with colorectal anastomosis, complications and mortality are less frequent in delayed than in immediate anastomosis and that continence and sexual behavior are identical in both procedures.

Forma da correlação T-S de massas de água das regiões costeira e oceânica entre o Cabo de São Tomé (RJ) e a Ilha de São Sebastião (SP), Brasil

Abstract: Characteristics of the structure and sea water properties on the continental shelf and waters adjacent to the continental slope, were studied based on the temperature-salinity (T-S) relationships. The water sampling was carried out with standard methods in a network of hydrographie stations worked in five-time intervals (5-10 days), from January 1970 through February 1971. The classification review of the water masses used under regional conditions confirm that the Subtropical-Deep (STDW), Subtropical (STW) and South Atlantic Central (SACW) Water Masses are different nomenclature for the same water mass; the latter is suggested to indicate a water mass with a thermohaline index given by (20.0 oC; 36.36 ‰), observed underneath the Tropical Water Mass. This salinity value is slightly higher than the modified thermohaline index of the SACW (36.20 ‰), and can be used with great simplification in volumetric studies in the area. Polynomial expressions of the mean T-S curve, whose coefficients were computed with the least squares method, were given for practical applications. From these applications, alternative methods for the determination of the thermohaline derivative and constant density ratio (Rρ = αdT/βdS) were obtained.

Cyclic melanotropins. 9. 7-D-Phenylalanine analogues of the active-site sequence

Abstract: The cyclic melanotropin Ac-Ser1-Tyr2-Ser3-Cys4-Glu5-His6-Phe7-Arg8 -Trp9-Cys10-Lys11-Pro12-Val13-NH is a highly potent agonist as determined in several melanocyte bioassays. In linear melanotropins, a D-Phe7 substitution leads to increased potency and often prolonged biological activity. In order to determine if this substitution would have the same effect in cyclic melanotropins, we have prepared a series of these analogues. The D-Phe7-substituted cyclic melanotropins Ac-[Cys4,D-Phe7,Cys10]-alpha-MSH4-10-NH2 and Ac-[Cys4,D-Phe7,Cys10]-alpha-MSH4-11-NH2 were both more potent than their cyclic L-Phe7-containing counterparts in either the frog or lizard skin bioassay by more than a factor of 10. Neither peptide, however, exhibited prolongation of biological activity in either assay. Substitution of D-Phe7 into the cyclic 4-12 and 4-13 sequences led to a slight or no increase in potency in both assays relative to the L-Phe7 counterparts, but the activity of the melanotropins was ultraprolonged in each assay. Ac-[Cys4,D-Phe7,Cys10]-alpha-MSH4-12-NH2 was about equipotent to Ac-[Cys4,D-Phe7,Cys10]-alpha-MSH4-13-NH2, again demonstrating, as with certain linear and cyclic L-Phe7-containing melanotropins, that the C-terminal amino acid valine is not required for biological activity or for superpotency. Similar to the linear D-Phe7 analogues that possessed ultraprolonged melanotropic activity, the 4-12 and 4-13 cyclic D-Phe7 analogues also displayed the phenomenon of superagonism, which is a time-dependent increase in efficacy over that produced by an equipotent concentration of the native hormone. Cyclization of certain linear melanotropins resulted in analogues with increased resistance to biological degradation by serum enzymes or purified proteolytic enzymes. Further, incorporation of a D-Phe7 into in the cyclic analogues led to melanotropins that were totally resistant to enzymatic inactivation by trypsin.

On the mean-field Ising model in a random external field

Abstract: We use a method developed by van Hemmen to obtain the free energy of the mean-field Ising model in a random external magnetic field. Some results of previous mean-field calculations are confirmed and generalized. The tricritical point in the global phase diagram is discussed in detail. We also consider different probability distributions of the random fields and provide some proofs regarding the conditions for the existence of a tricritical point.

Diffusion, mobility and the einstein relation

Abstract: We investigate the Einstein relation σ = βD between the diffusion constant D and the “mobility”, of a “test particle” interacting with its environment: β−1 is the temperature of the system where D is measured and σE is the drift in a constant external field E The relation is found to be satisfied for all model systems in which we can find a unique stationary non-equilibrium State of the environment, as seen from the test particle in the presence of the field For some systems, eg infinite systems of hard rods in one dimension, we find non unique stationary states which do not satisfy the Einstein relation For some models in a periodic box the Einstein relation is the most direct way of obtaining D A precise macroscopic formulation of the Einstein relation which makes it mathematically very plausible is given