Orientation and dynamics of benzyl alcohol and benzyl alkyl ethers dissolved in nematic lyotropic liquid crystals. 2H NMR and molecular dynamics simulations.

Most drugs have to cross cell membranes to reach their final target. A better understanding of the distribution, interactions, and dynamics of biologically active molecules in model bilayers is of fundamental importance in understanding drug functioning and design. 2H NMR quadrupole splittings (delta nu(Q)) and longitudinal relaxation times (T1) from the aromatic ring of benzyl alcohol-d5 (C0), a commonly used anesthetic, and a series of linear alkyl benzyl-d5 ethers with chain lengths from 1 to 12 carbon atoms (C1-C12), were measured. The molecules were dissolved in a nematic discotic lyotropic liquid crystal solution made of tetradecyltrimethylammonium chloride (TTAC)/decanol (DeOH)/NaCl/H2O. Values of delta nu(Q) and T1 from 1,1-dideuteriodecanol (15% enriched) and DHO (H2O with 0.2% D2O) were also measured. Delta nu(Q) of DeOH and DHO remained constant throughout the series. The value of delta nu(Q) of the para position of the ring (delta nu(p)) in C1 is 30% smaller than the delta nu(p) of C0. This is attributed to the existence of an H-bond between the alcohol hydroxyl proton and the solvent, which influences the average orientation of the ring. The relaxation data show that T1o,m is always longer than T1p and both decrease with the increase in alkyl chain length. Molecular dynamics simulations of the experimentally studied systems were performed. The aggregate was represented as a bilayer. The distribution, average orientation, and order parameters of the aromatic ring of the guest molecules in the bilayer were examined. Rotational correlation functions of all the C-D bonds and the OH bond from H2O were evaluated, allowing an estimate of the correlation times and T1. According to these results all spins relax in extreme narrowing conditions, except DeOH. Experimental and calculated T1 values differ at most by a factor of 3. However, the order of magnitude and the observed trends are well reproduced by the calculations. The aromatic ring of C0 possesses a unique average orientation in the bilayer. For the ether series, the orientation is modified and the C2 symmetry axis of the aromatic ring is exchanging between two orientations averaging the quadrupole splittings from the ortho and meta positions. The simulation supports the existence of an H-bond between C0 and the solvent not found in the ethers, which should be responsible for the observed differences.

Structure and aggregation number of a lyotropic liquid crystal: a fluorescence quenching and molecular dynamics study.

The structure and aggregation number of a discotic lyotropic liquid crystal, prepared from tetradecyltrimethylammonium chloride (TDTMACl)/decanol (DeOH)/NaCl/H2O, have been examined using fluorescence quenching of pyrene by hexadecylpyridinium chloride and molecular dynamics (MD). The fluorescence method gives an aggregation number of 258 +/- 25 units (DeOH + TDTMACl). From the MD simulation, a lower limit for the aggregate dimension of 130 units of DeOH + TDTMACl is predicted. A stable oblate aggregate of 240 units was studied in detail. A strong polarization between the ammonium headgroups and chloride ions is observed from the calculated trajectory. DeOH headgroups are located, on average, 0.3 nm more to the interior of the aggregate than the TDTMACl headgroup and contribute to widening the interface by forming H-bonds with water. The radial distribution function of the ammonium headgroup shows that there are 16 water molecules in the first solvation sphere. The diagonal elements of the order parameter tensor of the tail atoms of both surfactants indicate that the interior of the micelle preserves about the same degree of order as at the interface, up to the last three atoms of the aliphatic chain, where the order starts to decrease.

Evaluación de métodos diagnósticos para sífilis congénita / Evaluation of diagnostic methods for congenital syphilis

La sífilis congénita es un problema relevante en nuestro país. Actualmente no existen exámenes de uso rutinario que permitan confirmar su diagnóstico. En este estudio prospectivo multicéntrico se evaluaron 60 binomios madre-RN que presentaban test no treponémicos (TNT) reactivos. En todas las muestras se realizaron 2 TNT (VDRL y RPR) y 7 test treponémicos (TT): dos evaluaban IgM, uno IgG y cuatro IgM + IgG. La concordancia entre los tests que evaluaban IgG o IgG + IgM fue de 90 por ciento y entre los que evaluaban IgM fue de 87,5 por ciento. Un resultado IgG positivo se observó en 100 por ciento de los binomios cuyas madres presentaron sífilis durante el embarazo o portaban serología residual. La IgM fue positiva en 64 por ciento de las madres con sífilis adecuadamente tratada durante el embarazo, siendo sus neonatos todos IgM negativa. Aquellas madres con un tratamiento inadecuado tuvieron IgM positiva en 82.3 por ciento y sus RN tuvieron IgM positivas en 11,8 por ciento. En conclusión, la IgM materna no aporta al diagnóstico de sífilis congénita, pues su positividad no se correlaciona con el riesgo de que el RN presente este cuadro. La Igm en el RN es útil para el diagnóstico precoz de sífilis congénita, pero su ausencia no descarta esta patología

[Health status of the population in the vicinity of a waste recycling plant in Mexico]. / Condiciones de salud de la población vecina a una planta recicladora de residuos en México.

This study was conducted in Mexico among residents of an area near a recycling plant for zinc and other metallic dusts to find out if these substances produce various adverse health effects in the population that may come in contact with them. The plant is in a municipality close to Monterrey, which is Mexico's third most populous and second most industrialized city. A cross-sectional comparative design was used for the research, which took place from September to November 1994. By means of quota sampling, houses were selected in two areas--one exposed, by virtue of its proximity to the plant, and the other unexposed, which served as a control--until the desired sample size was reached (621 individuals, an average of five per household). In each dwelling, a trained psychology student administered a questionnaire to one of the older family members to gather data on the presence of acute and chronic illnesses, problems during pregnancy, and congenital illnesses among the household members. In the exposed population, 127 questionnaires were completed, providing information on 596 persons; in the unexposed population, data on 743 persons were gathered via 147 questionnaires. The sex and age distributions were similar in the two populations, and the length of residence in their respective area was slightly longer among unexposed individuals. The most frequently reported health problems in the exposed population were irritation of the eyes and upper respiratory tract, allergies, sleep disturbances, bronchitis, fatigue, skin problems, ear infections, and anemia. The prevalence ratios for the exposed versus unexposed populations were significant with regard to skin eruptions and other skin diseases, fatigue, sleep disturbances, upper respiratory infections, ear infections, bronchitis, and allergies. Women from the two groups did not show significant differences in the prevalence of obstetric problems, miscarriages, or children born with congenital deformities or low birthweight. The sensitivity of the questionnaire used to detect health problems was poor, which could have resulted in an underestimation of some disorders. Nevertheless, various types of information bias were controlled, permitting the conclusion that the exposed population had a greater risk of suffering certain diseases and disorders than the unexposed population.

[Health status of urban passenger transportation conductors in Mexico City]. / Las condiciones de salud de los conductores de autotransportes urbanos de pasajeros de la ciudad de México.

Between 1985 and 1988, a two-phase epidemiological study was conducted at the "Ruta 100" company in Mexico City to examine the harmful effects of the working conditions on drivers of urban transport vehicles. In the first phase, five groups of nine drivers each were interviewed regarding their opinions about their working conditions and possible work-related disorders. On the basis of this information, an epidemiological survey was developed and applied using a polytypic sampling design to some 200 drivers plus two other groups of approximately the same size, one consisting of maintenance workers and the other of office workers, which served as controls. The driver group showed a high prevalence of respiratory and neuropsychiatric disorders, diarrhea, myopia, arterial hypertension, urinary disorders, hemorrhoids, hearing loss, back pain, varicose veins, peptic ulcers, diabetes, cardiopathies, abdominal hernias, and appendicitis. For arterial hypertension, hemorrhoids, nervous disorders, and psychiatric disorders the prevalence ratios of drivers/maintenance workers and drivers/administrative workers were statistically significant.