Coumarin derivatives for dye sensitized solar cells: a TD-DFT study.

Time dependent density functional theory (TD-DFT) calculations have been carried out to study the electronic structure and the optical properties of five coumarin based dyes: C343, NKX-2311, NKX-2586, NKX-2753 and NKX-2593. We have found out that the position and width of the first band in the electronic absorption spectra, the absorption threshold and the LUMO energy with respect to the conduction band edge are key parameters in order to establish some criteria that allow evaluating the efficiency of coumarin derivatives as sensitizers in Dye Sensitized Solar Cells (DSSC). Those criteria predict the efficiency ordering for the coumarin series in good agreement with the experimental evidence. Presumably, they might be used in the design of new efficient organic based DSSC.

Molecular modification of coumarin dyes for more efficient dye sensitized solar cells.

In this work, new coumarin based dyes for dye sensitized solar cells (DSSC) have been designed by introducing several substituent groups in different positions of the NKX-2311 structure. Two types of substitutions have been considered: the introduction of three electron-donating groups (-OH, -NH(2), and -OCH(3)) and two different substituents with steric effect: -CH(2)-CH(2)-CH(2)- and -CH(2)-HC=CH-. The electronic absorption spectra (position and width of the first band and absorption threshold) and the position of the LUMO level related to the conduction band have been used as theoretical criteria to evaluate the efficiency of the new dyes. The introduction of a -NH(2) group produces a redshift of the absorption maximum position and the absorption threshold, which could improve the cell efficiency. In contrast, the introduction of -CH(2)-CH(2)-CH(2)- does not modify significantly the electronic structure of NKX-2311, but it might prevent aggregation. Finally, -CH(2)-HC=CH- produces important changes both in the electronic spectrum and in the electronic structure of the dye, and it would be expected as an improvement of cell efficiency for these dyes.

Influence of the degree of oligomerization of surfactants on the DNA/surfactant interaction.

The interaction between calf thymus DNA, ctDNA, and a series of oligomeric surfactants derived from N-benzyl-N,N-dimethyl-N-(1-dodecyl)ammonium chloride is investigated. The influence of the surfactants' degree of oligomerization (2, 3 and 4) on the ctDNA/surfactant interaction is studied, as well as the effect of the structure of the spacer group linking the individual surfactant fragments. In particular, the effect of the distance between the positive charges and the hydrophobic chains within the oligomers on these interactions was examined, by using the three positional isomers (i.e., ortho-, meta-, and para-) with the rigid xylidene moiety as spacer. Results show that the dimeric ("gemini") surfactants are much more efficient in the inversion of the nucleic acid charge than the single-chained (monomeric) surfactant. Whereas the ortho - isomer causes a partial condensation, the meta - and para - isomers can completely condense ctDNA. The meta - and para - isomers of the trimeric surfactants can also completely condense the polynucleotide. In contrast, the tetrameric surfactant investigated does not change the morphology of the nucleic acid from an elongated coil into a compacted form, in spite of effectively inverting the nucleic acid's charge in their complex. Accordingly, the capacity for ctDNA compaction of oligomeric surfactants is not simply correlated to their degree of oligomerization, but depends on a complex balance of the number and relative distance of cationic charges and/or hydrophobic tails in the surfactants for effectively interacting with the nucleic acid to form the appropriate complex. This information will help to design more effective cationic surfactants as non-viral vectors for gene therapy.

V@Au12-: an improved novel catalyst for CO oxidation?

The catalytic properties toward CO combustion of an encapsulated cluster, V@Au12-, have been explored by means of plane-wave pseudopotential density-functional theory calculations. Single adsorption of both O2 and CO as well as coadsorption have been considered. The adsorption energy for the O2 molecule is about 0.3-0.4 eV which limits its use to low temperatures. However, in contrast to what happens for pure gold clusters, this system shows a remarkable capacity to bind a high number of oxygen molecules. Moreover, its icosahedral cluster is able to bind 12 CO molecules, since all of the gold atoms are available. The bond between the metal cluster and the oxygen molecule mainly arises from a charge transfer from the metal toward the pi(g) antibonding O2 orbitals, while in the case of CO molecule, the classical sigma-donation pi-back-donation mechanism is observed. Finally, no coadsorption effects are found when both molecules are adsorbed, the interaction properties between the cluster and the substrates remain basically unaltered.

Gastroprotection by coxibs: what do the Celecoxib Long-Term Arthritis Safety Study and the Vioxx Gastrointestinal Outcomes Research Trial tell us?

Current evidence suggests that PPIs might be effective in maintaining patients in remission during continued NSAID use and that the combination of omeprazole plus diclofenac is as effective as treatment with celecoxib in preventing recurrent bleeding. Larger outcome studies comparing the combination of a PPI with other nonselective NSAIDs and a selective COX-2 inhibitor (and the combination of a selective COX-2 inhibitor with a PPI or misoprostol) are required to determine whether or not any regimen will further decrease or eliminate the risk of ulcer complications in high-risk individuals.

Gastric outlet obstruction as a consequence of a duodenal web masquerading as gastrinoma in an adult.

We present the case of a 24-year-old man with recurrent peptic ulcers and hypergastrinemia, in whom a multidisciplinary investigation for gastrinoma revealed a duodenal web. The affected duodenal segment was excised, and a gastroduodenostomy with highly selective vagotomy was performed. Postoperative serum gastrin levels returned to the normal range over the next 6 weeks. Congenital duodenal anomalies are unusual causes of gastric outlet obstruction in adults. Chronic gastric outlet obstruction secondary to an adult duodenal web can induce neurohumoral changes in gastric function, which enhance both acid output and gastrin secretion. This case reminds clinicians to consider congenital anomalies in adults presenting with recurrent peptic ulcers and hypergastrinemia.

Adsorption of Acetone onto MgO: Experimental and Theoretical Evidence for the Presence of a Surface Enolate.

A new band at 1640 cm-1 is revealed by diffuse reflectance FT-IR spectroscopy of acetone adsorbed on a MgO surface (shown schematically). On the grounds of ab initio quantum-mechanical calculations, this band is assigned to an adsorbed enolate species. This evidence proves the catalytic role of the metal oxide surface in the condensation reaction mechanism.

Biomimetic polymers of plant cutin: an approach from molecular modeling.

Biomimetics of materials is based on adopting and reproducing a model in nature with a well-defined functionality optimized through evolution. An example is barrier polymers that protect living tissues from the environment. The protecting layer of fruits, leaves, and non-lignified stems is the plant cuticle. The cuticle is a complex system in which the cutin is the main component. Cutin is a biopolyester made of polyhydroxylated carboxylic acids of 16 and 18 carbon atoms. The biosynthesis of cutin in plants is not well understood yet, but a direct chemical route involving the self-assembly of either molecules or molecular aggregates has been proposed. In this work, we present a combined study using experimental and simulation techniques on self-assembled layers of monomers selectively functionalized with hydroxyl groups. Our results demonstrate that the number and position of the hydroxyl groups are critical for the interaction between single molecules and the further rearrangement. Also, the presence of lateral hydroxyl groups reinforces lateral interactions and favors the bi-dimensional growth (2D), while terminal hydroxyl groups facilitate the formation of a second layer caused by head-tail interactions. The balance of 2D/3D growth is fundamental for the plant to create a protecting layer both large enough in 2D and thick enough in 3D.

Amibas de vida libre en seres humanos / Free-living amoebae in humans

Entre las enfermedades graves, peligrosas y de gran importancia epidemiológica se encuentran la meningitis y la encefalitis, que pueden llevar a invalidez o muerte. Los agentes etiológicos que las producen generalmente son bacterias, virus y hongos. En cuanto a los protozoos causantes de meningitis y encefalitis, se encuentran las amibas de vida libre. Los individuos infectados con estas amibas tienen como antecedente el haber tenido contacto con aguas contaminadas en días recientes, especialmente de piscinas o aguas termales. Naegleria fowleri parasita a individuos aparentemente saludables, niños o jóvenes y es la causante de meningoencefalitis amebiana primaria, que se caracteriza por su rápida evolución y luego la muerte. Algunas especies del género Acanthamoeba, Balamuthia mandrillaris, y recientemente Sappinia pedata, producen encefalitis amebiana granulomatosa, que se presenta de forma subaguda o crónica; generalmente parasitan a individuos inmunosuprimidos. Además, ciertas especies de Acanthamoeba producen queratitis, que se confunden con las producidas por Herpes simplex u hongos. Estas amibas también causan infecciones severas en pulmones, oídos, piel y nariz. El diagnóstico de estas amibas en la mayoría de los casos se hace después de la muerte de los individuos infectados. En cuanto a su tratamiento, se han empleado combinaciones de varios antimicrobianos con resultados poco alentadores. Estas amibas no son lo suficientemente conocidas por el personal de salud, por lo tanto, en esta revisión se pretende evidenciar los aspectos más relevantes de éstas, ya que puede haber subdiagnóstico o confusión con otros agentes etiológicos y no sospechar de la presencia de amibas de vida libre...

Meningitis and Encephalitis are amongst the most dangerous disabling or death causing diseases. The etiological causes of these diseases include bacterium, virus and fungi. Protozoan which causes Meningitis and Encephalitis tend to be free-living amoebae. Patients identified with these amoebae infections had recently been exposed to contaminated water in swimming pools or steam baths. Healthy children and youth are vulnerable to Naegleria fowleri which causes Primary Amoebic Meningoencephalitis which evolution rapidly, causing death. Some species of Acanthamoeba, Balamuthia mandrillaris and recently Sappinia cause Granulomatous Amoebic Encephalitis in both acute and sub-acute forms, primarily affecting case with immunosuppression. Furthermore, some species produce Keratitis, which is confounded with diseases caused by Herpes Simplex or fungi. These amoebae are also infection causing agents in the lungs, ears, skin and nose. In most cases, diagnosis of these amoebae is posthumous. Combinations of antimicrobial treatment have had little effect, combating infections. This study seeks to enhance approaches towards diagnosing diseases caused by these agents and overcoming confounding them with other etiological agents without doubting the presence of free living amoebae...

Colorectal cancer screening and familial risk: a survey of internal medicine residents' knowledge and practice patterns.

OBJECTIVE: Risk stratification is essential to the appropriate use of colorectal cancer screening recommendations. The principal objective of this study was to assess the knowledge and screening behavior of internal medicine (IM) residents regarding familial colorectal cancer. METHODS: We conducted a survey of IM residents in their second and third year of postgraduate training from two university-based programs (n = 127). The survey instrument assessed physician knowledge of screening recommendations and current practices for individuals with a family history of colorectal cancer, adenomatous polyps, familial adenomatous polyposis, and hereditary nonpolyposis colorectal cancer. The instrument also elicited data regarding familial risk assessment, documentation, and notification of at-risk family members. RESULTS: Eighty-one IM eligible residents (81%) completed the survey. Most respondents identified a family history of colorectal cancer as an important factor in assessing colorectal cancer risk and appropriately implemented relevant screening recommendations. However, for patients with a family history of adenomatous polyps diagnosed before age 60 yr, knowledge and adherence to recommendations advocating screening at age 40 was relatively poor. More importantly, for patients with familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer, respondents lacked the necessary risk assessment skills and knowledge to appropriately implement current recommendations. There were no consistent differences in knowledge or screening behavior when stratified on the basis of program site or postgraduate year status. CONCLUSION: Many IM residents are deficient in their knowledge, risk assessment skills, and screening practices for patients at familial risk of colorectal cancer. Effective educational strategies that promote awareness regarding familial risk, risk assessment skills, and appropriate use of relevant screening guidelines are needed.