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Biomedical subjects

L M Molina

Publications and source records attributed to L M Molina.

15 recordsLinked to original sources
PubMed2005

Oxygen adsorption at anionic free and supported Au clusters.

The structure, stability, and O2 adsorption properties of anionic Au(n) (n=1-11) clusters either free or supported at defected MgO100 surfaces are investigated using density-functional theory. O2 adsorption is strong whenever unpaired electrons are present, except for at some small, supported, planar, high-band-gap clusters. These clusters have the unpaired electrons pinned by the Madelung potential of the support. Larger clusters (starting at Au7-Au8) become three dimensional and metallic. This ensures that while one cluster orbital is pinned to the defect, another orbital at comparable energy can undergo depletion, thus binding O2 with charge transfer.

Journal Article↗
PubMed2004

Growth of unidirectional molecular rows of cysteine on Au(110)-(1 x 2) driven by adsorbate-induced surface rearrangements.

Using scanning tunneling microscopy we have studied the nucleation and growth of unidirectional molecular rows upon adsorption of the amino acid cysteine onto the anisotropic Au(110)-(1 x 2) surface under ultrahigh vacuum conditions. By modeling a large variety of possible molecular adsorption geometries using density-functional theory calculations, we find that in the optimum, lowest energy configuration, no significant intermolecular interactions exist along the growth direction. Instead the driving force for formation of the unidirectional molecular rows is an adsorbate-induced surface rearrangement, providing favorable adsorption sites for the molecules.

Journal Article↗
PubMed2004

Adsorption of O2 and oxidation of CO at Au nanoparticles supported by TiO2(110).

Density functional theory calculations are performed for the adsorption of O2, coadsorption of CO, and the CO+O2 reaction at the interfacial perimeter of nanoparticles supported by rutile TiO2(110). Both stoichiometric and reduced TiO2 surfaces are considered, with various relative arrangements of the supported Au particles with respect to the substrate vacancies. Rather stable binding configurations are found for the O2 adsorbed either at the trough Ti atoms or leaning against the Au particles. The presence of a supported Au particle strongly stabilizes the adsorption of O2. A sizable electronic charge transfer from the Au to the O2 is found together with a concomitant electronic polarization of the support meaning that the substrate is mediating the charge transfer. The O2 attains two different charge states, with either one or two surplus electrons depending on the precise O2 adsorption site at or in front of the Au particle. From the least charged state, the O2 can react with CO adsorbed at the edge sites of the Au particles leading to the formation of CO2 with very low (approximately 0.15 eV) energy barriers.

Journal Article↗
PubMed2004

Adsorption, diffusion, and dissociation of molecular oxygen at defected TiO2(110): a density functional theory study.

The properties of reduced rutile TiO2(110) surfaces, as well as the adsorption, diffusion, and dissociation of molecular oxygen are investigated by means of density functional theory. The O2 molecule is found to bind strongly to bridging oxygen vacancies, attaining a molecular state with an expanded O-O bond of 1.44 A. The molecular oxygen also binds (with somewhat shortened bond lengths) to the fivefold coordinated Ti atoms in the troughs between the bridging oxygen rows, but only when vacancies are present somewhere in the surface. In all cases, the magnetic moment of O2 is lost upon adsorption. The expanded bond lengths reveal together with inspection of electron density and electronic density of state plots that charging of the adsorbed molecular oxygen is of key importance in forming the adsorption bond. The processes of O2 diffusion from a vacancy to a trough and O2 dissociation at a vacancy are both hindered by relative large barriers. However, we find that the presence of neighboring vacancies can strongly affect the ability of O2 to dissociate. The implications of this in connection with diffusion of the bridging oxygen vacancies are discussed.

Journal Article↗
PubMed2003

Active role of oxide support during CO oxidation at Au/MgO.

The oxidation of CO at MgO supported gold aggregates is studied by means of density functional theory calculations. In addition to serving as a structural promoter holding the gold particles, the supporting oxide also takes an active role in the bonding and activation of adsorbates bound to the gold. The oxide stabilizes a peroxolike reaction intermediate, CO.O2, and causes steric repulsion to CO. The most reactive site at Au/MgO appears where the gold shelters the MgO thereby creating a cavity where several low-coordinated Au atoms and Mg2+ cations from the substrate can interact simultaneously with an adsorbate.

Journal Article↗
PubMed1993

Presence of glucagon and glucagon-like peptide-1-(7-36)amide receptors in solubilized membranes of human adipose tissue.

Specific receptors for glucagon and for glucagon-like peptide-1 (GLP-1) (7-36)amide have been found in solubilized human adipose membranes. The 50% inhibition dose of the corresponding unlabeled peptide was near to their physiological levels [ID50, 0.5 nmol/L for glucagon and 1.0 nmol/L for GLP-1(7-36)amide;]. In both cases, the presence of high affinity receptors was evident [Kd, 0.5 and 0.7 nmol/L for glucagon and GLP-1(7-36)amide, respectively]; the high affinity maximal binding capacity for GLP-1(7-36)amide was higher than that for glucagon (893 and 117 fmol/mg solubilized fat membranes, respectively). Glucagon at 10(-6) mol/L did not compete with the [125I]GLP-1(7-36)amide binding, nor did GLP-1(7-36)amide (10(-6) mol/L) compete with that of [125I]glucagon. The relative abundance of GLP-1(7-36)amide receptors in human adipose tissue is further support for a direct and probably important action of this peptide in the metabolism of the fat cell.

Adipose Tissue↗
PubMed1988

Intestinal angiodysplasia: retrospective study of 18 cases.

Eighteen patients operated on for intestinal angiodysplasia are reported. Visceral angiography was the diagnostic procedure of choice, providing evidence in most cases of lesions in the right colon. Right hemicolectomy was the surgical treatment normally provided. Mortality in our series was nil. This report looks at the main clinical features of these lesions, paying particular attention to their etiopathogenesis.

Aged↗
PubMed1988

Operative choledochoscopy in biliary surgery.

Forty-six patients submitted to operative choledochoscopy during biliary surgery are presented. Forty-two had benign diseases, principally calculi (38 cases), with only four patients presenting with malignant neoplasms. Our results bear out the effectiveness of operative choledochoscopy as a complement to cholangiography and conventional exploration of the bile duct, in significantly reducing the number of retained stones found, and in aiding other surgical procedures in the biliary tract.

Cholangiopancreatography, Endoscopic Retrograde↗
PubMed1988

Obstruction of the bile duct by a papillary adenoma of the gallbladder.

A case of papillary adenoma of the gallbladder unassociated with cholelithiasis and showing detachment of part of the growth with obstruction of the common bile duct is described. One the basis of a search of the literature, it would appear that this is the first time such a case has been reported. The bibliography is discussed and a distinction drawn between this kind of adenoma and other benign tumors of the gallbladder.

Aged↗
PubMed1986

Influence of the conjoint administration of insulin and glucagon upon hepatic regeneration.

In noneviscerated rats, the influence of the conjoint administration of insulin and glucagon in the regenerative response triggered by 70 per cent hepatectomy using the incorporation of tritiated thymidine by nuclear deoxyribonucleic acid as a parameter has been demonstrated. The response was earlier and more intense in relation to animals not hormonally stimulated and stimulated only with glucagon (previously reported by us). Such a response has been comparatively greater both in the nonparenchymal cells and in the hepatocytes, especially in the latter, which are the main cause of the early peak of thymidine incorporation in the periportal zones indicating a greater regenerative activity than in the intermediate and centrolobular zones. In our opinion, this indicates the importance of certain extrahepatic humoral agents in the manifestation of the regenerative process. Therefore, the results of our study ascertain the determining role and synergistic action of the pancreatic hormones--insulin and glucagon--in hepatic regeneration.

Animals↗
PubMedDate not supplied

Tumor markers in pancreatic cancer: a comparative clinical study between CEA, CA 19-9 and CA 50.

Seventy-eight patients were evaluated to ascertain the usefulness of markers CA 19-9 and CA 50 in diagnosing pancreatic cancer, using a less specific marker (CEA) as reference. Three groups were considered: a) 36 controls; b) 22 patients with benign obstructive jaundice; c) 20 patients with pancreatic cancer. Preoperative blood samples were obtained to ascertain CEA (E.I.A.), CA 19-9 (R.I.A.) and CA 50 (T.R.-F.I.A.). Serum concentrations of the various markers were significantly higher for patients with pancreatic cancer in comparison with the other groups, at cut-offs of 10 ng/ml (CEA), 100 ng/ml (CA 19-9) and 170 U/ml (CA 50). The sensitivity of CA 19-9 (94%) and CA 50 (88%) was much greater than that of CEA (30%). The specificity of the three markers in patients with pancreatic cancer, with respect to the control group, was 100% and this figure is reduced with respect to the group suffering from benign obstructive jaundice (CEA: 90%; CA 19-9: 88% and CA 50: 87%). Diagnostic results (sensitivity, specificity, positive predictive value (P.P.V.) and negative predictive value (N.P.V.] did not significantly increase with respect to CA 19-9 and CA 50 when considered individually. It is concluded that the serum concentrations of CA 19-9 and CA 50 showed high sensitivity and specificity as markers of pancreatic cancer with respect to the other groups, pointing towards clinical routine clinical use of both markers. In addition, a comparative study of the literature has been made and prospects for short-term development and concrete applications for early and reliable diagnosis have been highlighted.

Aged↗
PubMedDate not supplied

Popliteal artery entrapment syndrome.

Three cases of popliteal artery entrapment syndrome, one of them bilateral, are presented with a review of the literature, with special reference to the embryological development of the popliteal space and the diagnostic and therapeutic problems presented by this syndrome.

Adolescent↗