Study of the Crystal Structure and Hydrogen Bonding during Cold Crystallization of Poly(trimethylene 2,5-furandicarboxylate).

Here, we present a detailed description of the in situ isothermal crystallization of poly(trimethylene 2,5-furandicarboxylate)(PTF) as revealed by real-time Fourier transform infrared spectroscopy (FTIR) and grazing incidence wide-angle X-ray scattering (GIWAXS). From FTIR experiments, the evolution of hydrogen bonding with crystallization time can be monitored in real time, while from GIWAXS, crystal formation can be followed. Density functional theory (DFT) calculations have been used to simulate FTIR spectra for different theoretical structures, enabling a precise band assignment.

Estimation of diffusion coefficients during carrots cooking in arsenious solution at different temperatures.

This study is based on an investigation of the transport phenomenon, specifically the quantification of arsenic diffusion in carrots within a temperature range of 89 °C-99 °C using a thin plate model. Studying the diffusion of arsenic in carrots is important due to its toxicity, as it can concentrate during cooking. The World Health Organization considers arsenic as one of the ten chemical substances of public health concern.

Effects of confinement and vaccination on an epidemic outburst: A statistical mechanics approach.

This work describes a simple agent model for the spread of an epidemic outburst, with special emphasis on mobility and geographical considerations, which we characterize via statistical mechanics and numerical simulations. As the mobility is decreased, a percolation phase transition is found separating a free-propagation phase in which the outburst spreads without finding spatial barriers and a localized phase in which the outburst dies off. Interestingly, the number of infected agents is subject to maximal fluctuations at the transition point, building upon the unpredictability of the evolution of an epidemic outburst.

Energetics and structures of the tilted phases of fatty acid Langmuir monolayers.

Langmuir monolayers are monomolecular deep films composed of amphiphilic molecules which are typically confined to a water/air interface in a bi-dimensional structure. Due to the important applications in many research areas, they have been studied for many years. Their phase diagrams present several condensed phases, showing untilted or tilted structures at low values of surface pressure.

Iodide conversion to iodate in aqueous and solid aerosols exposed to ozone.

The aqueous-phase and surface reactions of ozone (O) with iodide (I) in/on seawater have been recently found to be a strong atmospheric source of iodine. In addition, ozone also reacts with I in solid and aqueous sea-salt aerosol. However, the primary products of the heterogeneous reactions of ozone with I have not been clarified.

Energetics and structure of Langmuir monolayers of palmitic acid: a DFT study.

Langmuir monolayers are monomolecular wide films composed of amphiphilic molecules with a bi-dimensional structure typically formed at the air-water interface. They have been studied for many years because these monolayers have important applications in many research fields. Their phase diagrams present several condensed phases whose atomic structure is not yet completely known.

A revisit of the interaction of gaseous ozone with aqueous iodide. Estimating the contributions of the surface and bulk reactions.

The main source of atmospheric iodine is the heterogeneous reaction of aqueous iodide (I-) with ozone (O3), which takes place in surface seawater and probably in sea-salt aerosols. However, there are seemingly contradictory conclusions about whether this heterogeneous reaction occurs in the bulk of the aqueous phase, via O3 dissolution, or at the aqueous surface, via O3 adsorption. In this work, the ozone uptake coefficient has been calculated as a function of the concentration of aqueous iodide ([I-]aq) and gaseous ozone near the aqueous surface ([O3]gs) by estimating parameters of the resistor model using results of previous studies.

A theoretical study on the reaction of ozone with aqueous iodide.

Atmospheric iodine chemistry plays a key role in tropospheric ozone catalytic destruction, new particle formation, and as one of the possible sinks of gaseous polar elemental mercury. Moreover, it has been recently proposed that reaction of ozone with iodide on the sea surface could be the major contributor to the chemical loss of atmospheric ozone. However, the mechanism of the reaction between aqueous iodide and ozone is not well known.

Metastable Nitric Acid Trihydrate in Ice Clouds.

The composition of high-altitude ice clouds is still a matter of intense discussion. The constituents in question are ice and nitric acid hydrates, but the exact phase composition of clouds and its formation mechanisms are still unknown. In this work, conclusive evidence for a long-predicted phase, alpha-nitric acid trihydrate (alpha-NAT), is presented.

Theoretical model of the interaction of glycine with hydrogenated amorphous carbon (HAC).

A theoretical model of hydrogenated amorphous carbon (HAC) is developed and applied to study the interaction of glycine with HAC surfaces at astronomical temperatures. Two models with different H content are tried for the HAC surface. The theory is applied at the Density Functional Theory (DFT) level, including a semiempirical dispersion correlation potential, d-DFT or Grimme DFT-D2.

The formation of carbamate ions in interstellar ice analogues.

Carbon dioxide and ammonia are two of the most abundant species in astrophysical media, where they can react in the solid phase under certain conditions. This contribution presents a study of this reaction both in the presence of water and for anhydrous samples. It is shown that after deposition at 15 K, the reaction can start by warming the deposit, and the process continues on up to a temperature of 220 K.

Ab initio study of hydroxyl torsional barriers and molecular properties of mono- and di-iodotyrosine.

Phenol rings with one or two iodine atoms bonded to ortho carbons are the essential organic source of iodine for living organisms. The salvage of this halogen fundamental for a variety of biological functions is accomplished through enzymatic processes that rely on recognition of mono- and di-iodotyrosine (MIT and DIT, respectively). Ab initio quantum calculations are used to investigate molecular properties of MIT and DIT associated with their recognition by cognate proteins.

An infrared study of solid glycine in environments of astrophysical relevance.

The conversion from neutral to zwitterionic glycine is studied using infrared spectroscopy from the point of view of the interactions of this molecule with polar (water) and non-polar (CO(2), CH(4)) surroundings. Such environments could be found on astronomical or astrophysical matter. The samples are prepared by vapour-deposition on a cold substrate (25 K), and then heated up to sublimation temperatures of the co-deposited species.

Active Site, Catalytic Cycle, and Iodination Reactions of Vanadium Iodoperoxidase: A Computational Study.

A combined computational study using molecular surfaces and Poisson-Boltzmann electrostatic potentials for proteins and quantum calculations on complexes representing the vanadate cofactor throughout the catalytic cycle is employed to study the activity of vanadium iodoperoxidase (VIPO) from alga Laminaria digitata . A model structure of VIPO is compared with available crystal structures of chloroperoxidases (VClPOs) and bromoperoxidases (VBrPOs) focusing on properties of the active site that concern halogen specificity. It is found that VIPO displays distinctive features regarding electrostatic potentials at the site cavity and the local topography of the cavity entrance.

Clusters of atmospheric relevance: H(2)O/HCl/HNO(3). Prediction of IR & MW spectra.

Theoretical calculations at the B3LYP/aug-cc-pVQZ level are performed on ternary clusters of water, hydrogen chloride and nitric acid to predict their IR and MW spectra. The main IR spectral features and their changes in a set of 15 selected clusters are analyzed in terms of the different hydrogen bonding characteristics of the aggregates. The formation of these clusters in laboratory experiments and their possible identification based on their infrared and microwave spectral properties are discussed.

Interaction of CH4 and H2O in ice mixtures.

Ice mixtures of methane and water are investigated by means of IR spectroscopy in the 14-60 K range. The spectroscopic research is focused on the symmetry-forbidden nu(1) band of CH(4) and the dangling bond bands of water. The nu(1) band is visible in the spectra of the mixtures, revealing a distorted methane structure which co-exists with the normal crystalline methane.

Characterization of two types of intermolecular interactions on halogen monoxide monohydrates.

Monohydrates of halogen monoxides ClO.H2O and BrO.H2O have been studied by means of DFT (B3LYP) and ab initio (MP2) correlated calculations with aug-cc-pVnZ basis sets ranging from triple- up to quintuple-zeta.

Phases of solid methanol.

The solid phases of methanol were investigated using IR spectroscopy and numerical calculations with the SIESTA method. Improved spectra are reported of amorphous methanol at 90 K, and in particular of the alpha and beta phases at 130 and 165 K, respectively, with assignments of bands not previously measured. The main features of the spectra of each phase are discussed and compared.

Ices of CO2/H2O mixtures. Reflection-absorption IR spectroscopy and theoretical calculations.

Ice mixtures of CO2 and H2O are studied using Fourier transform reflection-absorption infrared (RAIR) spectroscopy. Mixtures are prepared by sequential deposition or co-deposition of the two components from the gas phase onto an Al plate kept at 87 K inside a low-pressure chamber. Two CO2 structures are found in most experiments: a crystalline form similar to pure CO2, which evaporates when warming at 105 K, and a noncrystalline species which remains embedded in amorphous water ice after warming.

Variation of atomic charges on proton transfer in strong hydrogen bonds: the case of anionic and neutral imidazole-acetate complexes.

The variation of atomic charges upon proton transfer in hydrogen bonding complexes of 4-methylimidazole, in both neutral and protonated cationic forms, and acetate anion, is investigated. These complexes model the histidine (neutral and protonated)-aspartate pair present in active sites of proteases where strong N--H..

A combined matrix isolation and ab initio study of bromine oxides.

Bromine oxides have been generated by passing a mixture of Br(2)/O(2)/Ar through a microwave discharge. The products were stabilized at 6.5 K in an excess amount of argon.

Immediate and delayed memory recall patterns of chronic hemodialysis adult hispanic patients.

Objective: To determine the most effective time to administer nutrition education to hemodialysis patients by evaluating memory recall scores before, during, and after treatment.

Design: Prospective, quasi experimental cohort.

Subjects: Sixty-two adult Hispanic hemodialysis patients (38 men and 24 women, 29 <65 years of age and 32 >65 years of age).