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Biomedical subjects

Luis Sánchez

Publications and source records attributed to Luis Sánchez.

18 recordsLinked to original sources
PubMed2006

Molecular panels for energy transduction in C60-based conjugates.

Light-harvesting C(60)-based dyads endowed with a truxene fluorophore unit have been synthesized. Their photophysical studies in solution reveal a singlet-singlet energy transfer deactivation mechanism that confirms the actuation of the latter as an efficient molecular panel for light absorption and energy transduction. Those processes strongly depend on the nature of the linker connecting both chromophores, such as C(60) and truxene, owing to the overlapping degree between their respective orbitals. [structure: see text]

Journal Article↗
PubMed2006

[Burden of rotavirus-related disease among children under five, Colombia, 2004].

OBJECTIVES: To establish an in-hospital surveillance system for diarrhea in children under five, to estimate the burden of rotavirus-related disease, and to identify the most common rotavirus genotypes. METHODS: Included in the study were children who were hospitalized for serious complications of diarrhea in three medical care facilities in Bogotá, Barranquilla, and Cali, Colombia. A solid-phase enzyme-linked immunosorbent assay (ELISA) was used to detect rotavirus, and reverse-transcriptase polymerase chain reaction (RT-PCR) was the genotyping method employed. The frequencies, central tendency, and dispersion of the variables were determined. Stratified analysis and bivariate analysis were performed by applying a chi squared test or Fisher's exact test, or a chi squared test for trends, depending on the type of data analyzed. Relative risks were established. For analyzing trends we performed linear regression and calculated correlation coefficients and P values. RESULTS: Between December 2003 and November 2004, 893 children were hospitalized in the three participating centers included in the study. Of these children, 68% were between 6 and 23 months of age; 2.7% of hospitalized patients showed clinical signs of hypovolemic shock, and 1.2% died. Only 57% of the mothers had given their children an oral rehydration solution before hospitalization. Rotavirus infection was the cause of 50% of hospitalizations (correlation coefficient [r] > 0.8) and was linked to an inability to hold down orally-ingested fluids (relative risk [RR] = 1.45; 95% confidence interval [95% CI]: 1.24 to 1.69; P < 0.0000) and to intractable vomiting (RR = 1.47; 95% CI: 1.16 to 1.86; P < 0.01). Rotavirus infection led to one death per 2 000 children; 16 hospitalizations per 1 000 children, and 631 medical visits per 1 000 children. A seasonal trend was noted for G1P[8], G2P[4], and G3P[8] rotavirus genotypes, and this did not vary as a result of geographic distance or differences in temperature, humidity, and rainfall among cities. CONCLUSIONS: Rotavirus infection is an important cause of morbidity and mortality from diarrhea, particularly during the first years of life, when children are more susceptible to serious complications. It is important for prevention strategies to have a high impact before 6 months of age, and vaccination against rotavirus can be a good complementary intervention strategy. No description was found in the international scientific literature of the seasonal variations in rotavirus genotypes. It is important to carry out cost-effectiveness studies in order to promote the investment of resources in accordance with population needs, and to continue surveillance activities so as to better understand how the virus behaves.

Child, Preschool↗
PubMed2005

Light harvesting tetrafullerene nanoarray for organic solar cells.

A light absorbing pi-conjugated oligomer-tetrafullerene nanoarray has been synthesized and its photophysical study reveals the presence of an intramolecular energy transfer. A phototovoltaic device fabricated from this nanoarray and poly(3-hexylthiophene) shows an external quantum efficiency of 15% at 500 nm.

Journal Article↗
PubMed2005

Hydrogen-bonding motifs in fullerene chemistry.

The combination of fullerenes and hydrogen-bonding motifs is a new interdisciplinary field in which weak intermolecular forces allow modulation of one-, two-, and three-dimensional fullerene-based architectures and control of their function. This Minireview aims to extend the scope of fullerene chemistry to a truly supramolecular level from which unprecedented architectures may evolve. It is shown that electronic communication in C(60)-based hydrogen-bonded donor-acceptor ensembles is at least as strong as that found in covalently connected systems and that hydrogen-bonding fullerene chemistry is a versatile concept for the construction of functional ensembles.

Fullerenes↗
PubMed2005

C(60)-exTTF-C(60) Dumbbells: cooperative effects stemming from two C(60)s on the radical ion pair stabilization.

[structure: see text] The presence of a second C(60) cage in C(60)-exTTF-C(60) triads [exTTF = 9,10-bis(1,3-dithiol-2-ylidene)-9,10-anthraquinone] has beneficial effects on the stabilization of the radical ion pair formed upon irradiation in comparison with the related C(60)-exTTF dyad. Although C(60)-exTTF-C(60) ensembles show no electronic interaction between the electroactive units in the ground state, their irradiation leads to C(60)(*)(-)-exTTF(*)(+)-C(60) species with lifetimes on the order of 600 ns in benzonitrile; these lifetimes are twice those determined for the analogous C(60)-exTTF dyad.

Journal Article↗
PubMed2005

The first spiroconjugated TTF- and TCNQ-type molecules: a new class of electroactive systems?

[Structure: see text] Spiroconjugated TTF-type electron donors (13a-c) and TCNQ-type electron acceptors (10, 11) have been prepared from spiroquinone 9. Cyclic voltammetry reveals a relatively weak accepting ability for 10 and 11, and a strong electron-donor character for 13a-c. Whereas the spiroconjugation introduces a destabilization of the LUMO for compounds 9-11, the opposite is observed for compound 13, thus justifying the redox potential values.

Journal Article↗
PubMed2005

Simultaneous second-stage norwood operation and tracheoplasty.

Tracheal stenosis is a rare complication that follows operations for congenital heart disease in the newborn period. We report the case of an infant with hypoplastic left heart syndrome who developed symptomatic tracheal stenosis 5 months after a first-stage Norwood operation. The combined surgical procedure of a bidirectional Glenn anastomosis and a tracheoplasty under cardiopulmonary bypass was undertaken.

Cardiac Surgical Procedures↗
PubMed2003

Hydrogen bonding interfaces in fullerene*TTF ensembles.

Novel thermodynamically stable supramolecular donor-acceptor dyads have been synthesized. In particular, we assembled successfully C(60), as an electron acceptor, with the strong electron donor TTF through a complementary guanidinium-carboxylate ion pair. Two strong and well-oriented hydrogen bonds, in combination with ionic interactions, ensure the formation of stable donor-acceptor dyads. The molecular architecture has been fine-tuned by using chemical spacers of different lengths (i.e., phenyl versus biphenyl) and functional groups (i.e., ester versus amide), thus providing meaningful incentives to differentiate between through-bond and through-space electron-transfer scenarios. In electrochemical studies, both the donor and acceptor character of the TTF and C(60) units, respectively, have been clearly identified. Steady-state and time-resolved emission studies, however, show a solvent-dependent fluorescence quenching in C(60)*TTF dyads as well as the formation of the C(60)(*)(-)*TTF(*)(+) radical ion pairs, for which we determined lifetimes that are in the range of hundred of nanoseconds to microseconds. The complex network that connects C(60) with TTF in the dyads and the flexible nature of the spacer result in through-space electron-transfer processes. This first example of electron transfer in C(60)-based dyads, connected by strong hydrogen bonds, demonstrates that this approach can add outstanding benefits to the construction of artificial photosynthetic systems that bear a closer resemblance to the natural one.

Journal Article↗
PubMed2003

Controlling short- and long-range electron transfer processes in molecular dyads and triads.

Novel pi-extended tetrathiafulvalene (exTTF)-based donor acceptor hybrids-dyads and triads-have been synthesized following a multistep synthetic procedure. Cyclic voltammetry and absorption spectroscopy, conducted in room temperature solutions, reveal features that are identical to the sum of the separate donor and acceptor moieties. Steady-state and time-resolved photolytic techniques confirm that upon photoexcitation of the fullerene chromophore, rapid (1.25 x 10(10) s(-1)) and efficient (67 %) charge separation leads to long-lived, charge-separated radical pairs. Typical lifetimes for the dyad ensembles range between 54 and 460 ns, with the longer values found in more polar solvents. This indicates that the dynamics are located in the 'normal region' of the Marcus curve. In the triads, subsequent charge shifts transform the adjacent radical pair into the distant radical pair, for which we determined lifetimes of up to 111 micros in DMF-values never previously accomplished in molecular triads. In the final charge-separated state, large donor-acceptor separation (center-to-center distances: approximately 30 A) minimizes the coupling between reduced acceptor and oxidized donor. Analysis of the charge recombination kinetics shows that a stepwise mechanism accounts for the unusually long lifetimes.

Journal Article↗
PubMed2002

Ceramide promotes the death of human cervical tumor cells in the absence of biochemical and morphological markers of apoptosis.

C8-ceramide, a synthetic cell-permeable analog of endogenous ceramides, interfered with cell proliferation, and was cytotoxic to papilloma virus-containing human cervix carcinoma cells, CALO, INBL, and HeLa, that match two clinical stages of tumor progression. C8-ceramide (3 microM) markedly reduced the tumor cell number after 48 h of treatment, an effect that endured even after the removal of C8-ceramide. The carcinoma cells showed morphologic changes, characteristic of necrosis and released lactate dehydrogenase (LDH). A biologically inactive analog C8-dihydro-ceramide had no effect on cell viability in any of the cell lines tested. Seventy-two hours after C8-ceramide treatment none of the biochemical and morphological markers characteristic of apoptosis: (a) nuclear chromatin condensation, (b) DNA fragmentation, (c) proteolysis of the caspase-3 substrate poly-(ADP-ribose)-polymerase (PARP), and (d) appearance of phosphatidylserine on the external cell membrane, were observed. C8-ceramide had no effect on human cervix fibroblasts and induced a mild reduction (30%) in the proliferation of normal human cervix epithelia and HeLa cells (IV-B metastatic stage). The cytotoxicity of C8-ceramide was restricted to CALO (early II-B) and INBL (IV-A non-metastatic) carcinoma cells. The possible application of ceramide in the treatment of early stages of cervical cancer is discussed.

Antineoplastic Agents↗
PubMed2001

Functional interaction between the Ser/Thr kinase PKL12 and N-acetylglucosamine kinase, a prominent enzyme implicated in the salvage pathway for GlcNAc recycling.

PKL12 (STK16) is a ubiquitously expressed Ser/Thr kinase, not structurally related to the well known subfamilies, with a putative role in cell adhesion control. Yeast two-hybrid protein interaction screening was used to search for proteins that associate with PKL12 and to delineate signaling pathways and/or regulatory circuits in which this kinase participates. One positive clone contained an open reading frame highly similar to N-acetylglucosamine kinase (GlcNAcK) of several species. The PKL12/GlcNAcK interaction was further confirmed both in vitro and in vivo. Protein expression analysis of GlcNAcK using a specific rabbit antiserum displayed a ubiquitous pattern in cell lines and animal tissues. Subcellular localization studies showed that GlcNAcK is a cytoplasmic protein with a dual subcellular localization, distributed between the perinuclear and peripheral cell reservoirs. After overexpression, GlcNAcK localizes in vesicular structures associated mainly with the cell membrane and colocalizes with the PKL12 protein. GlcNAcK is not otherwise a substrate for PKL12 activity and PKL12 does not appear to influence GlcNAcK activity either in vitro or in vivo. In vitro kinase assays have nonetheless revealed that functional GlcNAcK, although not able to modulate autophosphorylation of PKL12, greatly influences PKL12 kinase activity on a defined substrate protein. These results are interpreted to indicate a potential in vivo role for GlcNAcK in PKL12 translocation and a tentative regulatory role for PKL12-mediated phosphorylation on substrate proteins.

3T3 Cells↗
PubMed1999

Synthesis, X-ray Structure, and Electrochemical Oxidative Coupling Reactions of 1,5- and 2,6-Bis(1,4-dithiafulven-6-yl)naphthalenes.

Novel pi-extended tetrathiafulvalene (TTF) derivatives (12a-c, 13a-c, 15a-c) in which the two 1,3-dithiole units are connected through a naphthalene spacer have been prepared in high yields by Wittig-Horner olefination reaction from dialkoxy-substituted diformylnaphthalenes (11a,b, 14) and differently substituted phosphonate esters (10a-c). The electrochemical study revealed a similar behavior for the novel electron donor molecules (12a-c, 13a-c, 15a-c) regardless of the position of the 1,3-dithiole rings on the naphthalene core. The extended donors undergo an efficient electrooxidation process affording new oligomeric extended TTF species which exhibit lower oxidation potential values than their precursor donors. EPR experiments confirm the presence of the cation radical derived from the oligomeric TTF vinylogues and support an ECE process. The structural study has been carried out by X-ray analysis of 12a and semiempirical PM3 calculations and reveals a distorted geometry from the planarity with the naphthalene moiety forming an angle of approximately 35 degrees with the thiafulvalene rings. A good agreement was found between the experimental and calculated values, thus validating the PM3 method. The chemical oxidation of the synthesized donors (12a-c, 13a-c, 15a-c) with strong electron acceptors give rise to charge transfer complexes (CTC) which were characterized by UV-vis, FTIR, and EPR spectroscopy.

Journal Article↗
PubMed1998

Diels-Alder Cycloadducts of [60]Fullerene with Pyrimidine o-Quinodimethanes.

Novel organofullerenes bearing a pyrimidine nucleus covalently attached to the C(60) cage have been prepared by [4 + 2] cycloaddition reactions of C(60) and pyrimidine o-quinodimethanes generated "in situ" from the readily available cyclobutapyrimidines which are prepared in a one-pot procedure from cyclobutanone and alkyl or aryl nitriles. The reaction mechanism involves formation of a nitrilium cation with participation of two molecules of the respective nitrile. A side-product (16) formed from two cyclobutanone molecules is obtained together with the target cyclobutapyrimidines 4a-d. Compounds 4a-d are appropriate precursors for the generation of substituted pyrimidine o-quinodimethanes 5a-d which are efficiently trapped by the C(60) molecule in a cycloaddition reaction which according to theoretical calculations is controlled by the HOMO of the diene. (1)H NMR spectra indicate the presence of a dynamic process attributed to the boat-to-boat interconversion of the cyclohexene ring. The activation free energy has been measured by dynamic NMR experiments showing values DeltaG() approximately 16-17 kcal/mol for both methylene groups, depending upon the substituents on the pyrimidine unit. Theoretical calculations at the semiempirical PM3 level confirm the presence of a boat conformation for the cyclohexene ring which undergoes a rapid flipping motion resulting in an average C(s)() symmetry as it is observed in the (1)H NMR spectra. The cyclic voltammetry measurements show the presence of reduction waves cathodically shifted, related to C(60), due to the saturation of a double bond of the C(60) cage. A weak electronic interaction is observed between the pyrimidine moiety and the C(60) core.

Journal Article↗
PubMedDate not supplied

[ENDOGENOUS INTRAGASTRICAL MICROFLORA IN GASTRIC CANCER]

The aim of this prospective study was to identify the type of microbial flora and additionally to correlate the total number of microorganisms with factors such as age, tumoral area, and the pH gastric in unaffected gastric mucosal biopsies obtained during gastrojejunostomy (n=5) or gastrectomy (n=1) in patients with gastric adenocarcinoma (n=15) or lymphoma (n=1) at the Belen Hospital, Trujillo, Peru, between January 1, 1996 and April 30,1998. The mean age of the patients was 54.4 + 18.3 years (range: 20 to 79 years) with a male:female ratio of 1:2,2. Fifteen of the patients (93.7%) were colonized. Aerobic species found in 7/15 (46.7%), 5/15 (33.3%) showed a mixed aerobic and anaerobic bacterial growth, 1/15 (6.7%) had growths of aerobic microorganisms and yeasts, and only 2/15 (13.3%) of the patients harbored yeasts. Gram-negative aerobic and gram-positive species were present in 4/7 (57.1 %) and 3/7 (42.9%) of the patients, respectively. In those patients who had a mixed bacterial growth, peptostreptococcus were the most common findings in 5/5 (100%) of the patients, and Helicobacter pylori was isolated only in one case. A gastric pH of 4 or more was found in 14/16 of the patients examined and 12 of them (85%) had growth of microorganisms. There was no significant statistical correlation among the pH of the gastric juice, age or tumoral area and the total number of microorganisms/gram in mucosal biopsies of the 7 cases evaluated. Antibiotic agents used as a prophylaxis in gastric cancer surgery should cover both aerobic and anaerobic microorganisms, especially those patients with a pH of 4 or more.

Journal Article↗