Anisotropic line tension of domains in lipid monolayers.

We formulate a simple effective model to describe molecular interactions in a lipid monolayer and calculate the line tension between coexisting domains. The model represents lipid molecules in terms of two-dimensional anisotropic particles on the plane of the monolayer. These particles interact through forces that are believed to be relevant for the understanding of fundamental properties of the monolayer: van der Waals interactions originating from lipid chains and dipolar forces between dipole groups in the molecular heads.

Molecular Ordering in Lipid Monolayers: An Atomistic Simulation.

We report on atomistic simulations of DPPC lipid monolayers using the CHARMM36 lipid force field (and also the Slipid force field as a control case), combined with a four-point OPC water model. The entire two-phase region where domains of the "liquid-condensed" (LC) phase coexist with domains of the "liquid-expanded" (LE) phase has been explored. The simulations are long enough that the complete phase-transition stage, with two domains coexisting in the monolayer, is reached in all cases.

Genetic analysis of age at onset variation in spinocerebellar ataxia type 2.

Objective: To examine heritability of the residual variability of spinocerebellar ataxia type 2 (SCA2) age at onset (AO) after controlling for CAG repeat length.

Methods: From 1955 to 2001, dates of birth, CAG repeat lengths, AO, sex, familial inheritances, and clinical manifestations were collected for a large Cuban SCA2 cohort of 382 affected individuals, including 129 parent-child pairs and 69 sibships. Analyses were performed with log-transformed AO in the GENMOD procedure to predict AO using repeat length, taking into account family structure.

[Importance of quality control of baciloscopy in laboratories that perform diagnosis of tuberculosis].

Background: Baciloscopy is the primary tool for pulmonary tuberculosis diagnosis, being this technique the most used internationally in the search for infectious cases. Quality control is the process of the rechecking smears by a highly qualified observer.

Aim: To evaluate and highlight the importance of quality control of smear microscopy in the Provincial Laboratories diagnosticians of Tuberculosis in Cuba.

Solid-solid transitions induced by repulsive interactions revisited.

We revisit a problem already studied 15 years ago by us in collaboration with Stell and Hemmer: the isostructural solid-solid transitions induced by repulsive particle interactions exhibited by classical systems interacting via the Stell-Hemmer potentials. The full phase diagram in the crystal region is obtained by applying a perturbation theory for classical solids used during our collaboration with Stell. Also, the performance of such a theory is now tested by comparing the perturbative phase diagram with that obtained from computer simulations.

[Isolation frequency of the Mycobacterium genus in urine samples].

Kidney infections caused by Mycobacterium genus are torpid and chronic evolution. In this study were analyzed 177 urine samples (included 110 from HIV patients) received between January 2006 and July 2014 in the National Reference Laboratory of Tuberculosis at Tropical Medicine Institute "Pedro Kourí" (IPK). The results were 17 isolates Mycobacterium tuberculosis, and 30 isolates of nontuberculous mycobacteria were detected.

Robust Modeling and Scaffold Hopping: Case Study Based on HIV Reverse Transcriptase Inhibitors Type-1 Data.

Background: Human immunodeficiency virus type 1 (HIV-1) is the causative agent of AIDS occurs across mucosal surfaces or by direct inoculation.

Objective: The objective of this study was to consider chemically diverse scaffold sets of HIV-1 Reverse Transcriptase Inhibitors (HIV-1 RTI) subjected to ideal oriented QSAR with large descriptor space.

Method: We generated a four-parameter QSAR model based on 111 data points, which provided an optimum prediction of HIV-1 RTI for overall 367 experimentally measured compounds.

Hard-body models of bulk liquid crystals.

Hard models for particle interactions have played a crucial role in the understanding of the structure of condensed matter. In particular, they help to explain the formation of oriented phases in liquids made of anisotropic molecules or colloidal particles and continue to be of great interest in the formulation of theories for liquids in bulk, near interfaces and in biophysical environments. Hard models of anisotropic particles give rise to complex phase diagrams, including uniaxial and biaxial nematic phases, discotic phases and spatially ordered phases such as smectic, columnar or crystal.

[Surveillance of resistance to antitubercular drugs in Cuba, 2000-2009].

Objective: Determine the prevalence of resistance to antitubercular drugs in Cuba in the 2000-2009 decade.

Methods: A prospective longitudinal study was conducted. The sample group consisted of 2,285 Mycobacterium tuberculosis isolates obtained from throughout the country in the period from 1 January 2000 to 31 December 2009.

Subtle rapid eye movement sleep abnormalities in presymptomatic spinocerebellar ataxia type 2 gene carriers.

Rapid eye movement (REM) sleep disorders are commonly associated to patients with spinocerebellar ataxia type 2 (SCA2); however, these abnormalities have not been studied in presymptomatic gene carriers. To determine whether the REM sleep pathology is detectable before clinical manifestation of SCA2 and evaluate it as a preclinical biomarker, we studied 36 presymptomatic SCA2 individuals and 36 controls by video-polysomnography (VPSG) and sleep questionnaires. Presymptomatic subjects showed significant decrease of REM sleep percentage, REMs density, total sleep time, and sleep efficiency.

Structural studies of cord factors from Mycobacterium simiae related to the capacity for tumour necrosis factor alpha (α-TNF) induction.

The structure of cord factor was studied in several strains of Mycobacterium simiae, including 'habana' TMC 5135, considered as highly immunogenic in experimental tuberculosis and leprosy. The mycolic acids liberated from cord factor were identified in all cases as α'-, α- and keto-mycolates. According to the general NMR and MS data, α'-mycolates were mono-unsaturated and contained from 64 to 68 carbon atoms, whereas α-mycolates mainly presented two 2,3-disubstituted cyclopropane rings and a chain length of 80-91 carbon atoms; keto-mycolates mostly contained one cyclopropane ring and 85-91 carbon atoms.

Concomitant Mycobacterium avium infection and Hodgkin's disease in a lymph node from an HIV-negative child.

We report a case of an immunocompetent child with simultaneously an infection with Mycobacterium avium and Hodgkin's disease in a cervical lymph node. A positive PCR result for M. avium on a biopsy of the lymph node directed the definitive diagnosis for both etiologies and avoided a possible dissemination of this infection after chemotherapy was started.

Topological defects in a two-dimensional liquid crystal confined in a circular nanocavity.

Using a microscopic theory based on excluded-volume interactions, we analyze the structure and thermodynamic stability of configurations in a two-dimensional liquid crystal confined into a (small) circular nanocavity. Weak homeotropic anchoring conditions are considered, and topological defects of total charge k=+1 are discussed. It is found that, for small cavity radii, the cavity is free of defects at the expense of surface free energy not being optimized.

Capillary and anchoring effects in thin hybrid nematic films and connection with bulk behavior.

By means of a molecular model, we examine hybrid nematic films with antagonistic anchoring angles where one of the surfaces is in the strong anchoring regime. If anchoring at the other surface is weak, and in the absence of wetting by the isotropic phase, the anchoring transition may interact with the capillary isotropic-nematic transition. For general anchoring conditions on this surface we confirm the existence of the steplike biaxial phase and the associated transition to the linear constant-tilt-rotation, configuration.

New variants of polar glycopeptidolipids detected in Mycobacterium simiae, including 'habana' strains, as evidenced by electrospray ionization-ion trap-mass spectrometry.

Aims: To determine the composition of polar glycopeptidolipids (pGPLs) of Mycobacterium simiae and, particularly, those of 'habana' strains, in a search for specific markers given the immunogenic potential of 'habana' TMC 5135 in experimental tuberculosis.

Methods And Results: pGPLs were determined in free lipid extracts using electrospray ionization-ion trap-mass spectrometry (ESI-IT-MS), working in both negative- and positive-ion mode. In the case of TMC 5135, the presence of the previously characterized GPL-II (containing 2,4-di-O-CH(3) glucuronic acid as distal sugar in the oligosaccharide antigenic moiety) and GPL-III (containing 4-O-CH(3) glucuronic acid as distal sugar) was confirmed using MS/MS and MS/MS/MS approaches.

Large attractive depletion interactions in soft repulsive-sphere binary mixtures.

We consider binary mixtures of soft repulsive spherical particles and calculate the depletion interaction between two big spheres mediated by the fluid of small spheres, using different theoretical and simulation methods. The validity of the theoretical approach, a virial expansion in terms of the density of the small spheres, is checked against simulation results. Attention is given to the approach toward the hard-sphere limit and to the effect of density and temperature on the strength of the depletion potential.

Analysis of the structure of mycolic acids of Mycobacterium simiae reveals a particular composition of alpha-mycolates in strain 'habana' TMC 5135, considered as immunogenic in tuberculosis and leprosy.

Structural analysis of mycolic acids from Mycobacterium simiae (including some 'habana' strains) was carried out using (1)H-NMR and MS. Results indicated that this species presents a general pattern of alpha-, alpha'- and keto-mycolates. alpha-Mycolates were composed of a complex mixture of 82 to 89 carbon atoms (C82-C89), with the predominant molecular species containing two di-substituted cyclopropane rings.

Depletion effects in smectic phases of hard-rod-hard-sphere mixtures.

It is known that when hard spheres are added to a pure system of hard rods the stability of the smectic phase may be greatly enhanced, and that this effect can be rationalised in terms of depletion forces. In the present paper we first study the effect of orientational order on depletion forces in this particular binary system, comparing our results with those obtained adopting the usual approximation of considering the rods parallel and their orientations frozen. We consider mixtures with rods of different aspect ratios and spheres of different diameters, and we treat them within Onsager theory.

Capillary effects in a confined smectic phase of hard spherocylinders: influence of particle elongation.

A system of hard rods confined into a pore with slit geometry (two parallel planar substrates) is studied theoretically in the regime of high packing fraction. In this regime the bulk system exhibits a nematic phase as well as a smectic-A (spatially layered) phase. When the system is confined, strong commensuration effects between the layer spacing and the pore width bring about a rich phenomenology, with a phase diagram showing layering and capillary transitions.

Orientational ordering in hard rectangles: The role of three-body correlations.

We investigate the effect of three-body correlations on the phase behavior of hard rectangle two-dimensional fluids. The third virial coefficient B3 is incorporated via an equation of state that recovers scaled particle theory for parallel hard rectangles. This coefficient, a functional of the orientational distribution function, is calculated by Monte Carlo integration, using an accurate parametrized distribution function, for various particle aspect ratios in the range of 1-25.

Smectic, nematic, and isotropic phases in binary mixtures of thin and thick hard spherocylinders.

A second-virial Onsager theory, based on Parsons-Lee rescaling and suitably extended to deal with multicomponent systems and smectic phases, has been used to calculate the phase diagram of a collection of binary mixtures of thin and thick hard spherocylinders. In particular, two types of phase diagrams are investigated. First, a number of binary mixtures where the two components have the same total length have been considered; in addition, the phase diagram of a binary mixture where the two components have the same volume has been calculated.

Lipids of 'Mycobacterium habana', a synonym of Mycobacterium simiae with vaccine potential.

'Mycobacterium habana' was proposed as a distinct species within the genus Mycobacterium; however, it is actually a synonym of Mycobacterium simiae and included in the serotype I of this species. The potential use of 'M. habana' as a vaccine in both leprosy and tuberculosis has led to the analysis of its lipid composition in an attempt to define distinctive markers that could be used in the quality control of true strains of this bacterium.