Capture of nerve agents and mustard gas analogues by hydrophobic robust MOF-5 type metal-organic frameworks

In this communication, a series of observations and data analyses coherently confirms the suitability of the novel metal-organic framework (MOF) [Zn(4)(μ(4)-O)(μ(4)-4-carboxy-3,5-dimethyl-4-carboxy-pyrazolato)(3)] (1) in the capture of harmful volatile organic compounds (VOCs). It is worthy of attention that 1, whose crystal structure resembles that of MOF-5, exhibits remarkable thermal, mechanical, and chemical stability, as required if practical applications are sought. In addition, it selectively captures harmful VOCs (including models of Sarin and mustard gas, which are chemical warfare agents), even in competition with ambient moisture (i.e., under conditions mimicking operative ones). The results can be rationalized on the basis of Henry constant and adsorption heat values for the different essayed adsorbates as well as H(2)O/VOC partition coefficients as obtained from variable-temperature reverse gas chromatography experiments. To further strengthen the importance of 1, its performance in the capture of harmful VOCs has been compared with those of well-known materials, namely, a MOF with coordinatively unsaturated metal sites, [Cu(3)(btc)(2)] and the molecular sieve active carbon Carboxen. The results of this comparison show that coordinatively unsaturated metal sites (preferential guest-binding sites) are ineffective for the capture of VOCs in the presence of ambient moisture. Consequently, we propose that the driving force of the VOC-MOF recognition process is mainly dictated by pore size and surface hydrophobicity.     

Computer simulation of the thermodynamics of the B → Z-DNA transition: effect of the ionic size and charge

The B- to Z-DNA transition free energy as a function of the size and charge of added ions is investigated by Monte Carlo simulation for simple grooved B- and Z-DNA models. It is shown that the electrostatic contribution to the free energy depends almost linearly on the logarithm of the salt concentration for all the systems. The effect of increasing the size of the ions is to make the curves steeper, although its influence on the transition midpoint is more complex. Divalent cations markedly reduce both the slope and the transition midpoint with respect to monovalent ions. These conclusions are in agreement with the experimental findings. The effect of increasing the charge of the anions—not yet experimentally studied—is less pronounced.     

Concentration of Solutions for Some Singularly Perturbed Mixed Problems: Existence Results

In this paper,we study the asymptotic behavior of some solutions to a singularly perturbed problem with mixed Dirichlet and Neumann boundary conditions. We prove that, under suitable geometric conditions on the boundary of the domain, there exist solutions which approach the intersection of the Neumann and the Dirichlet parts as the singular perturbation parameter tends to zero.     

Gloriosaols A and B, two novel phenolics from Yucca gloriosa: structural characterization and configurational assignment by a combined NMR-quantum mechanical strategy

Gloriosaols A (1) and B (2), two novel phenolic derivatives characterized by unusual spirostructures made up of two C₁₅ units linked via a γ-lactone to a central stilbenic portion were isolated from the roots of Yucca gloriosa. On the basis of an extensive NMR analysis, the same basic structure was established for the two compounds but no further information about their structural difference could be deduced. Thus two hypotheses were formulated: (1) gloriosaols A and B could be atropisomers caused by a restriction of the free rotation around the double bond due to a steric congestion of the bulky phenolic portions; (2) gloriosaols A and B could be two configurational isomers, indicating, in this case, a nonstereoselective biogenetic formation of the stereogenic center C-2. Semi-empirical calculations of the potential energy surfaces on gloriosaols A and B, together with the ¹H NMR spectra recorded at various temperatures, allowed us to unambiguously exclude the hypothesis of two restricted rotational conformers of a single configurational isomer. Finally, quantum mechanical calculations of the geometries and of the ¹H chemical shifts on the gloriasols A and B in combination with the analysis of the ROE data allowed us to deduce a diastereomeric relation between the two compounds and to assess the relative configuration of the two diastereomers.     

Antioxidant bibenzyl derivatives from Notholaena nivea Desv

Four new bibenzyl derivatives were isolated, together with other known bibenzyls, by bioassay-guided fractionation of a CHCl?-MeOH extract of Notholaena nivea Desv. (Pteridaceae) aerial parts. The structures were elucidated by NMR, ESIMS and other spectral analyses. Their antioxidative effects towards superoxide, lipidic peroxidation and the 2,2'-azino-bis-3-ethilbenzothiazoline-6-sulfonic acid (ABTS) radical were assayed. Results showed that the compound 3,12-dihydroxy-5-methoxybibenzyl (6) is the most active compound in the ABTS free-radical scavenging test, while in the coupled oxidation of β-carotene and linoleic acid assay the compound 5,12-dihydroxy-3-methoxydibenzyl-6-carboxylic acid (1) exerted the highest activity after 1h. A superoxide anion enzymatic test was also carried out and the results were confirmed by an inhibition of xanthine oxidase activity assay. The putative protective role played by compounds 1 and 6 on the injurious effects of reactive oxygen metabolites on the intestinal epithelium, using a Caco-2 human cell line, was investigated. H?O?-induced alterations were prevented by preincubating the cells with compounds 1 and 6.     

High‐Fidelity Noncovalent Synthesis of Hydrogen‐Bonded Macrocyclic Assemblies

A hydrogen‐bonded cyclic tetramer is assembled with remarkably high effective molarities from a properly designed dinucleoside monomer. This self‐assembled species exhibits an impressive thermodynamic and kinetic stability and is formed with high fidelities within a broad concentration range.     

The effects of different cryoprotectants and the temperature of addition on the survival of red deer epididymal spermatozoa

With the aim of finding an ideal cryoprotectant in a suitable concentration for red deer epididymal spermatozoa conservation, we evaluated the effects of four most commonly used cryoprotectants (CPAs), Glycerol (G), Ethylene glycol (EG), Propylene glycol (PG), and Dimethyl sulfoxide (DMSO), on the sperm survival. Besides, the effects of two temperatures of CPA addition--22 degrees C (ambient temperature) and 5 degrees C--on sperm quality were also tested. For each temperature tested, sperm samples were evaluated after 0, 15, 30 and 60 min of spermatozoa exposition to CPAs. Thus, sperm quality was in vitro judged by microscopic assessments of individual sperm motility (SMI), and of plasma membrane (Viability) and acrosome (NAR) integrities. Overall, DMSO showed the highest toxicity for red deer epididymal spermatozoa, and glycerol the lowest. Thus, at 60 min of incubation SMI results showed that the toxicity to red deer epididymal spermatozoa of the four CPAs are in the following sequence: G approximately = EG approximately = PG < DMSO ('less than' symbol means P < 0.05, and approximate symbol means P = 0.08). Furthermore, our results also showed a differential response of acrosome membrane to temperature of CPAs addition. Regardless of the CPA used, statistically significant variations (P < 0.05) were found between the two temperatures of addition of CPAs for acrosome integrity, the best being 22 degrees C (NAR = 83.8% vs. 69.8%). These data indicate that sperm quality of red deer epididymal spermatozoa, in addition to be affected by the cryoprotectant, can also be influenced by the temperature at which CPAs are added prior to freezing.