RESUMO
Several recent computational studies have tried to explain the observed selectivity in radical damage to proteins. In this work we use Density Functional Theory and Transition State Theory including tunnelling corrections, reaction path degeneracy, the effect of diffusion, and the role of free radicals to get further insights into this important topic. The reaction between a leucine derivative and free radicals of biological significance, in aqueous and lipid media, has been investigated. Both thermochemical and kinetic analyses, in both hydrophilic and hydrophobic environments, have been carried out. DPPH, ËOOH, ËOOCH3, ËOOCH2Cl, ËOOCHCl2 and ËOOCHCH2 radicals do not react with the target molecule. The reactions are proposed to be kinetically controlled. The leucine gamma site was the most reactive for the reactions with ËN3, ËOOCCl3, ËOCH3, ËOCH2Cl, and ËOCHCl2 radicals, with rate constants equal to 1.97 × 10(5), 3.24 × 10(4), 6.68 × 10(5), 5.98 × 10(6) and 8.87 × 10(8) M(-1) s(-1), respectively, in aqueous solution. The ËCl, ËOH and ËOCCl3 radicals react with leucine at the beta, gamma, and delta positions at rates close to the diffusion limit with the alpha position which is the slowest path and the most thermodynamically favored. The presented results confirm that the Bell-Evans-Polanyi principle does not apply for the reactions between amino acid residues and free radicals. Regarding the influence of the environment on the reactivity of the studied series of free radicals towards leucine residues, it is concluded that hydrophilic media slightly lower the reactivity of the studied radicals, compared to hydrophobic ones, albeit the trends in reactivity are very similar.
Assuntos
Radicais Livres/química , Leucina/análise , Proteínas/química , Interações Hidrofóbicas e Hidrofílicas , Cinética , Lipídeos/química , Modelos Moleculares , Estresse Oxidativo , Termodinâmica , Água/químicaRESUMO
A 13 year old girl with hypertension (170/140 mmHg), hyperkalemia (7.3 mmol/L), hyperchloremic metabolic acidosis and normal glomerular filtration rate (creatinine clearance 128 mL/min/1.73 m2), had low plasmatic renin activity (0.20 ng/mL/h), the levels of plasma aldosterone was low (5.5 ng/100mL) and very low transtubular potassium concentration gradient. Other forms of the secondary hypertension were discarded. The patient was treated with salt restriction, oral salbutamol and furosemide, with satisfactory evolution. At present her blood pressure is 130/85 mmHg and potassium, plasmatic levels of 5.3 mmol/L.
Assuntos
Hiperpotassemia , Hipertensão , Adolescente , Feminino , Taxa de Filtração Glomerular , Humanos , Hiperpotassemia/diagnóstico , Hipertensão/diagnóstico , SíndromeRESUMO
We studied the adsorption of sodium fluoride, ammonium fluoride, tin fluoride and sodium monofluorophosphate to synthetic hydroxiapatite in function of the pH (pH 4.7, 5.5 and 6.1). In two models; in a first model was eluted the fluorides of the hydroxiapatite column with artificial saliva; in the second model were incubated the fluoride with bufferized hydroxiapatite to the above pH. The fluoride determination was done by potentiometric method with a specific ion activity electrode. The results in the elution indicated that the sodium and tin fluorides give elution levels different at the pH studied. By other hand ammonium fluoride did not present differences. The results with incubation demonstrated that ammonium fluoride gives the greater adsorption, the sodium fluoride is slightly lower, and the sodium monofluorophosphate the lowest. Also, was observed that the adsorption decrease with the increase of the pH for the three fluorides. The comparison of both models showed that the incubation presented higher values of adsorption than the elution for the pH studied.