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J M Leal

Publications and source records attributed to J M Leal.

At least 19 recordsLinked to original sources
PubMed2006

Intercalation of ethidium into triple-strand poly(rA).2poly(rU): a thermodynamic and kinetic study.

The kinetics and equilibria of the interaction of ethidium bromide (EB) with the triple-stranded RNA, poly(rA).2poly(rU), have been investigated by stopped-flow, absorption, fluorescence, and circular dichroism methods; to properly assess the effect of the third strand on the polymer molar properties, molar volumes, adiabatic compressibilities, and heats of melting have also been measured for both poly(rA).2poly(rU) and poly(rA).poly(rU). The melting experiments reveal that ethidium tends to destabilize the triplex, whereas it stabilizes the duplex; however, the triplex/ethidium system in 0.1 M NaCl is stable below 37 degrees C. The static titrations reveal that one ethidium ion binds every three base triplets of the polymer; on the basis of the excluded-site model, this feature suggests intercalation, as in the duplex, but the binding affinity for the triplex is weaker compared to that for the duplex. The kinetic experiments displayed a two-phase behavior, which was rationalized assuming the sequence D + S right arrow over left arrow DS(I), DS(I) + S right arrow over left arrow DS(II) + S (D = drug, S = site), the second step involving direct transfer of the drug between strands. Comparison with the duplex/EB system reveals that the additional strand of poly(U), present in the triplex, hinders the formation of the intermediate complex DS(I), while stabilizing the structure of the final DS(II) complex by hampering the partial slipping out of the dye from the triplex cavity.

Binding Sites↗
PubMed2006

Hydrolysis mechanisms for indomethacin and acemethacin in perchloric acid.

The acid-catalyzed hydrolysis reactions of the antiinflammatory drugs indomethacin and acemethacin were investigated at 25.0 degrees C in a number of strongly concentrated perchloric acid media. The reaction rates were evaluated by UV measurements, and the intermediate species were detected by UV-vis, 1H NMR, 13C NMR, and mass spectroscopy measurements. A switchover from an A-2 to an A-1 mechanism as a function of the medium acidity is reported for the acid-catalyzed hydrolyses of the amide group of both indomethacin and acemethacin. In the A-2 hydrolysis, two water molecules are involved in the rate-determining step. An analysis of the kinetic data collected for acemethacin by the different techniques used reveals a complex mechanism, indomethacin being a metabolite intermediate species in the hydrolysis of acemethacin. The rate constants for the hydrolysis of the acemethacin ester group were considerably larger compared to those of the amide group.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2005

Characterization and preferential solvation of the hexane/hexan-1-ol/methylbenzoate ternary solvent.

The thermophysical properties of the hexane/hexan-1-ol/methylbenzoate ternary system and its binary constituents were studied at 298.15 K over the whole composition range. The excess and mixing properties calculated from the experimental values combined with the mixture activity coefficients deduced from the UNIFAC group contribution method were used to calculate the integrals of the Kirkwood-Buff fluctuation theory for the ternary system and the binary constituents. Also the local composition and the excess or deficit number of molecules around a central molecule have been determined. The volumetric properties for the ternary system and its binary constituents were correlated and predicted successfully with several cubic equations of state combined with two simple mixing rules. The structural and intermolecular interactions of the mixtures were analyzed on the basis of the measured and derived properties.

Journal Article↗
PubMed2001

Hydroxamic acids as weak base indicators: protonation in strong acid media.

The protonation equilibria of N-phenylbenzohydroxamic, benzohydroxamic, salicylhydroxamic, and N-p-tolylcinnamohydroxamic acids have been studied at 25 degrees C in concentrated sulfuric, hydrochloric, and perchloric acid media; the UV-vis spectral measurements were analyzed using the Hammett equation and the Bunnett-Olsen and excess acidity methods. The medium effects observed in the UV spectral curves were corrected with the Cox-Yates and vector analysis methods. The H(A) acidity function based on benzamides provided the best results. The range of variation of the solvation coefficient m is similar to that of amides, this indicating similar solvation requirements for amides and hydroxamic acids. For the same substrate, the observed variations of pK(BH)(+) with the mineral acid used was justified by formation of solvent-separated ion pairs; for the same mineral acid, the observed changes in pK(BH)(+) can be explained by the solvation of BH(+). The change of the pK(BH)(+) values was in reasonably good agreement with the sequence of the catalytic efficiency of the mineral acids used, HCl > H(2)SO(4) > HClO(4).

Acid-Base Equilibrium↗
PubMed2000

Theoretical and experimental study of the acetohydroxamic acid protonation: the solvent effect.

The mechanism of the protonation of acetohydroxamic acid is investigated comparing experimental results and ab initio calculations. Experimentally, the UV spectral curves were recorded at different temperatures, at constant dioxane/water concentration, and at very high concentrations of strong mineral acids. The process is followed by monitoring the changes in the UV curves with increasing acid concentration. The molecular structures and the solvation energies were calculated with the RHF, B3LYP, and MP2 methods. The solvent is treated as a continuum of uniform dielectric constant. The isolated molecule of acetohydroxamic acid exhibits two protonation sites, the carbonyl oxygen and the nitrogen atom. In dioxane/water mixture, the RHF calculations predict the existence of a third cation of low stability, where the proton is bonded to the OH oxygen. With the MP2 ab initio calculations, the free energies of the formation processes in solution of the two most stable cations, CH3COH-NHOH+ (O3H+) and CH3CO-NH2OH+ have been evaluated to be -160.2 kcalmol(-1) and -157.6 kcal mol(-1). The carbonyl site is the most active center in solution and in the gas phase. The carbonyl site is also the most active center in the UV measurements. Experimentally, the ionization constant was found to be pK(O3H+) = -2.21 at 298.15 K, after the elimination of the medium effects using the Cox-Yates equation for hight acidity levels. Experiments and ab initio calculations indicate that K(O3H+) decreases with the temperature.

Cations↗
PubMed1984

Immediate, early, and late postsurgical management of upper-limb amputation.

This series is composed of 47 patients who underwent immediate, early, or late postoperative prosthetic fitting after upper-limb amputation. The purpose of this review was to analyze the impact of rapid postoperative fitting on upper-limb amputation, and to assess general prosthetic prescription and guidelines for upper-limb amputees. It would appear that in adult amputations there is a "Golden Period" of fitting for upper-limb prosthetic devices and this period appears to be within the first month after amputation. There appears to be no difference in ultimate prosthetic acceptance rate or use patterns as a function of the type of prosthesis initially provided. Based upon this combined review between the Tucson and Atlanta VA Medical Centers, the authors would suggest that all upper-limb amputees be fitted as rapidly as possible (within 30 days) with conventional prosthetic devices, and when they have shown motivation and skill in the use of conventional devices, then to re-evaluate them for appropriate externally powered prosthetic components.

Adolescent↗
PubMed1982

Brachial plexus injury management through upper extremity amputation with immediate postoperative prostheses.

Management of patients with brachial plexus injuries requires a team approach so that all aspects of their care are addressed simultaneously. This report examines elective amputation and prosthetic rehabilitation in a patient with brachial plexus avulsion of the left arm. The best possibility for good prosthetic rehabilitation is the early application of prosthetic devices with intensive occupational therapy. Using this type of approach, we have achieved significant improvement in amputation rehabilitation of upper extremity amputees treated with immediate postoperative conventional electric and myoelectric prostheses.

Adult↗
PubMed1981

Rehabilitation for lower extremity amputation.

The results of rehabilitation for lower-extremity amputation were analyzed to assess the impact of a center that used a coordinated team combined with modern surgical and prosthetic techniques. Data for group 1 patients (amputated between July 1, 1975, and June 30, 1977) demonstrated a healing rate of 63%, a mean rehabilitation time of 128 days, a mean hospitalization time of 68 days, and a rehabilitation rate of 69% for those who could walk prior to amputation. Data for group 2 (amputated between July 1, 1977, and July 30, 1979) demonstrated an amputation healing rate of 97%, an average rehabilitation time of 30.8 days, a mean hospitalization time of 38 days, and a rehabilitation rate of 100% for those patients who could walk before amputation. There was no difference between groups 1 and 2 in surgical mortality; all other variables, however, showed significant improvement for group 2 patients. Comparison within the same institution of the results of rehabilitation for lower-extremity amputation before and after the initiation of a dedicated amputation center clearly demonstrated the superiority of the center concept.

Adult↗
PubMed1980

Pulpectomy: immediate root canal filling with calcium hydroxide. Concept and procedures.

From the clinical aspect the endodontic treatment is divided into two groups: (1) teeth with pulp vitality (biopulpectomy) and (2) pulpless teeth (necropulpectomy). The authors point out the necessity of knowing the clinical pathologic conditions and the macroscopic aspect of the dental pulp before endodontic treatment. They describe the clinical procedures that must be performed in cases when the tooth presents pulp vitality (biopulpectomy), emphasizing (1) the necessity of a field of operation in an aseptic condition; (2) the necessity of a noninjuring instrumentation; (3) the use of cytophylactic substances and not cytotoxic substances; and (4) the use of a root canal--filling technique that respects the limits of the pulp stump, employing calcium hydroxide, a substance that maintains its vitality and induces and accelerates the apical closure by hard-tissue deposition.

Calcium Hydroxide↗