Application of the maximum entropy principle to determine ensembles of intrinsically disordered proteins from residual dipolar couplings.

We present a method based on the maximum entropy principle that can re-weight an ensemble of protein structures based on data from residual dipolar couplings (RDCs). The RDCs of intrinsically disordered proteins (IDPs) provide information on the secondary structure elements present in an ensemble; however even two sets of RDCs are not enough to fully determine the distribution of conformations, and the force field used to generate the structures has a pervasive influence on the refined ensemble. Two physics-based coarse-grained force fields, Profasi and Campari, are able to predict the secondary structure elements present in an IDP, but even after including the RDC data, the re-weighted ensembles differ between both force fields. Thus the spread of IDP ensembles highlights the need for better force fields. We distribute our algorithm in an open-source Python code.

El tabaco: la epidemia del siglo veinte / No disponible

El tabaquismo es sin duda la gran epidemia del siglo veinte. En principio, el hábito tabáquico no se consideró nocivo y es a partir de la introducción de tabaco en las raciones de los soldados en la Primera Guerra Mundial cuando su consumo experimenta un crecimiento exponencial en toda Europa. Son varias las especialidades que abarcan las enfermedades relacionadas con el abuso del tabaco. En los últimos 50 años se ha acumulado gran número de evidencias de gran consistencia científica que avalan el hecho de que el tabaco está directamente relacionado con el incremento de una amplia variedad de neoplasias. Asimismo existen suficientes pruebas que demuestran que el consumo de tabaco incrementa el riesgo cardiovascular y los procesos respiratorios crónicos. En 1999 se ha estimado que la mortalidad mundial esperada como consecuencia del tabaquismo alcanzará la cifra de 520 millones de adultos durante la primera mitad del siglo veintiuno y que se vería reducida en 180 millones si se lograra la mitad de los adultos fumadores dejaran de fumar durante ese período. En los últimos años se ha demostrado que el consumo ocasional de tabaco conduce a un consumo crónico y que la mayoría de los fumadores crónicos cumplen criterios de “dependencia del tabaco” enfermedad que ha sido enumerada por la OMS. Es importante instaurar algún tipo de tratamiento de deshabituación tabáquica a los pacientes fumadores. Las investigaciones recientes han abarcado tanto estrategias para la prevención del consumo como para el abandono del mismo (AU)

Smoking is certainly the grand epidemic of the 20th century. At the beginning, smoking was not considered as an harmful habit. The introduction of tobacco in the food ration of the first world war solders resulted in its wide consumption all over Europe. Various medical specialties attribute many diseases to tobacco abuse. Over the last 50 years, consistent scientific evidences, of large number, have proved that smoking is directly associated with increased risk of various neoplasm’s. At the same time, sufficient data demonstrates that tobacco consumption increases the risk of cardiovascular and chronic respiratory disease. In 1999, it was estimated that the expected world mortality during the first half of the 21st century because of smoking could reach 520 millions adults and it could be reduced to 180 millions if half of smokers give demonstrated that occasional tobacco consumption leads to chronic consumption and the mayor part of smokers satisfy the recognized and listed by the WHO. It is important to facilitate treatments for smokers to help them to give up smoking. The recent investigations have offered various strategies for prevention of tobacco consumption and its giving up (AU)

The ozonolysis of acetylene--a quantum chemical investigation.

The ozonolysis of acetylene was investigated using CCSD(T), CASPT2, and B3LYP-DFT in connection with a 6-311+G(2d,2p) basis set. The reaction is initiated by the formation of a van der Waals complex followed by a [4pi + 2pi] cycloaddition between ozone and acetylene (activation enthalpy DeltaH(a)(298) = 9.6 kcal/mol; experiment, 10.2 kcal/mol), yielding 1,2,3-trioxolene, which rapidly opens to alpha-ketocarbonyl oxide 5. Alternatively, an O atom can be transferred from ozone to acetylene (DeltaH(a)(298) = 15.6 kcal/mol), thus leading to formyl carbene, which can rearrange to oxirene or ketene. The key compound in the ozonolysis of acetylene is 5 because it is the starting point for the isomerization to the corresponding dioxirane 19 (DeltaH(a)(298) = 16.9 kcal/mol), for the cyclization to trioxabicyclo[2.1.0]pentane 10 (DeltaH(a)(298) = 19.5 kcal/mol), for the formation of hydroperoxy ketene 15 (DeltaH(a)(298) = 20.6 kcal/mol), and for the rearrangement to dioxetanone 9 (DeltaH(a)(298) = 23.6 kcal/mol). Compounds 19, 10, 15, and 9 rearrange or decompose with barriers between 13 and 16 kcal/mol to yield as major products formanhydride, glyoxal, formaldehyde, formic acid, and (to a minor extent) glyoxylic acid. Hence, the ozonolysis of acetylene possesses a very complicated reaction mechanism that deserves intensive experimental studies.

Tropospheric formation of hydroxymethyl hydroperoxide, formic acid, H2O2, and OH from carbonyl oxide in the presence of water vapor: a theoretical study of the reaction mechanism.

We have carried out a theoretical investigation of the gas-phase reaction mechanism of the H2COO+ H2O reaction, which is interesting for atmospheric purposes. The B3LYP method with the 6-31G(d,p) and 6-311 + G(2d,2p) basis sets was employed for the geometry optimization of the stationary points. Additionally, single-point CCSD(T)/6-311 + G(2d,2p) energy calculations have been done for the B3LYP/6-311 + G(2d,2p) optimized structures. The reaction begins with the formation of a hydrogen-bond complex that we have calculated to be 6 kcalmol(-1) more stable than the reactants. Then, the reaction follows two different channels. The first one leads to the formation of hydroxymethyl hydroperoxide (HMHP), for which we have calculated an activation barrier of deltaGa(298) = 11.3 kcalmol(-1), while the second one gives HCO + OH + H2O, with a calculated activation barrier of deltaGa(298) = 20.9 kcalmol(-1). This process corresponds to the water-catalyzed decomposition of H2COO, and its unimolecular decomposition has been previously reported in the literature. Additionally, we have also investigated the HMHP decomposition. We have found two reaction modes that yield HCOOH+H2O; one reaction mode leads to H2CO + H2O2 and a homolytic cleavage, which produces H2COOH + OH radicals. Furthermore, we have also investigated the water-assisted HMHP decomposition, which produces a catalytic effect of about 14 kcalmol(-1) in the process that leads to H2CO + H2O2.

Nosocomial infection in an intensive-care unit: identification of risk factors.

OBJECTIVE: To identify risk factors predictive of nosocomial infection in an intensive-care unit (ICU) and to identify patients with a higher risk of nosocomial infection using a predictive model of nosocomial infection in our ICU. DESIGN: Prospective study; daily concurrent surveillance of intensive-care-unit patients. SETTING/PATIENTS: All patients admitted for at least 24 hours to the ICU of a tertiary-level hospital from February to November 1994 were followed daily. METHODS: Variables measuring extrinsic and intrinsic risk factors for nosocomial infection were collected on each patient during their ICU stay, and the Cox Proportional Hazards multivariable technique was used to identify the variables significantly associated with infection. RESULTS: The population studied consisted of 944 patients. The main risk factors identified were intrinsic; the significant extrinsic risk factors identified were head of the bed in a horizontal (< 30 degrees) position (this variable presented the highest increase of the infection hazard ratio) and the use of sedative medication. Patients presenting the highest risk scores using the predictive model are those with the highest risk of nosocomial infection. CONCLUSIONS: The important preventive measures derived from our results are that underlying conditions suffered by the patient at the ICU admission should be corrected promptly, the depression of the patient's level of consciousness with sedatives should be monitored carefully, and the horizontal position of the head of the bed should be avoided totally. Patients with a high risk of infection can be the target of special preventive measures.