Biomedical subjects

M Quirós

Publications and source records attributed to M Quirós.

9 recordsLinked to original sources

PubMed2001

Tuning lipase enantioselectivity in organic media using solid-state buffers.

The enantioselectivity exhibited by Candida antarctica lipase B (CALB) in predominantly organic media has been studied for different enzyme protonation states. Alcoholysis of (+/-)-2-phenyl-4-benzyloxazol-5(4H)-one (1) using butan-1-ol as the nucleophile in low-water organic solvents was used as a model reaction. Using either organo-soluble bases or the newly introduced solid-state buffers of known pK(a), the protonation state of the lipase was altered. By choice of the appropriate solid-state buffer or organic base, the enantioselectivity could be selectively tuned. Both Et(3)N and the solid-state buffer pair CAPSO/CAPSO.Na were found to increase the enantioselectivity of the reaction catalyzed by CALB and that of another lipase (Mucor miehei). Significant differences to both the enantioselectivity and catalytic rate were observed, especially under hydrated conditions where byproduct acid was formed.

Buffers↗

PubMed2000

Dediazoniation of p-hydroxybenzenediazonium ion in a neutral aqueous medium.

The dediazoniation of p-hydroxybenzenediazonium ion (PDQ) in a neutral aqueous medium has been studied under controlled experimental conditions to prevent photochemical and/or heterolytic side-reactions. Oxygen increased the dediazoniation rate of PDQ and caused the appearance of quinone and hydroquinone. An accumulation of quinone deriving from the reduction of PDQ by hydroquinone was also observed. In ESR analyses with different spin traps, the most stable signal was identified as belonging to the adduct of the p-hydroxyphenyl radical, even in the presence of dimethylsulfoxide or ethanol. A general scheme is proposed including three pathways for the homolytic dediazoniation of PDQ. Pathway 1 represents dediazoniation induced by a hydroxyl ion, a slow process at neutral pH and an even slower one with deaerated samples; a favored quinoid structure is put forward to explain these results. In pathway 2, the formation of a semiquinone radical via the reaction of an aryl radical with oxygen is put forward to justify the increase in the dediazoniation rate in the presence of oxygen. In pathway 3, hydroquinone, produced by semiquinone dismutation, may act as a reducing agent.

Diazonium Compounds↗

PubMed2000

Longipinene derivatives from Santolina viscosa.

The neutral fraction of the hexane extract of the aerial parts of Santolina viscosa afforded eight new longipinene derivatives (1-8), oblongifolidiol (9), and several other known compounds. The structures of 1-8 were established by spectroscopic methods and chemical transformations. The vulgarone A-type structure previously reported for oblongifolidiol has been reassigned as the longipinene derivative 9 using 2D NMR, chemical correlations, and X-ray diffraction.

Magnetic Resonance Spectroscopy↗

PubMed1991