Thermochemistry of Surfactant-Templating of USY Zeolite

With the aim of understanding the thermochemistry of the introduction of mesoporosity in zeolites by using surfactants, high temperature oxide melt solution calorimetry was used to determine the change in the enthalpy of formation of USY zeolite before and after the introduction of mesoporosity. Our results confirm that this process only slightly destabilizes the zeolite by the additional surface area. However, this can be overcome by the stabilizing effect of the interactions between the surfactant and the zeolite framework.     

Antibacterial activity of agave fructans against salmonella typhimurium

Abstract

The objective of this study was to evaluate the antimicrobial effect of Agave fructans against the Salmonella Typhimurium in “in vitro” experiments. The result of the antimicrobial activity was 263.89?±?0, 414.95?±?12.83, 494.54?±?13.88, 522.29?±?0, 580.41?±?14.92?AU for 10, 20, 30, 40 and 50% of Agave fructans (AF) respectively. In addition, there is a significant effect on the growth of the bacteria with all the percentages of AF evaluated (p?<?0.001, R2?=?0.859) with respect to the control. The growth rate of Salmonella with 25% AF was statistically significant compared to the control (?0.7353?±?0.586, 0.0079?±?0.002?D.O./h, respectively; p?>?0.01). Agave fructans could be an alternative to prevent the infections caused by Salmonella.     

Clustering versus percolation in the assembly of colloids coated with long DNA

We report an experimental study in which we compare the self-assembly of 1 mum colloids bridged through hybridization of complementary single-stranded DNA (ssDNA) strands (12 bp) attached to variable-length double-stranded DNA spacers that are grafted to the colloids. We considered three different spacer lengths: long spacers (48 500 bp), intermediate length spacers (7500 bp), and no spacers (in which case the ssDNA strands were directly grafted to the colloids). In all three cases, the same ssDNA pairs were used. However, confocal microscopy revealed that the aggregation behavior is very different. Upon cooling, the colloids coated with short and intermediate length DNAs undergo a phase transition to a dense amorphous phase that undergoes structural arrest shortly after percolation. In contrast, the colloids coated with the longest DNA systematically form finite-sized clusters. We speculate that the difference is due to the fact that very long DNA can easily be stretched by the amount needed to make only intracluster bonds, and in contrast, colloids coated with shorter DNA always contain free binding sites on the outside of a cluster. The grafting density of the DNA decreases strongly with increasing spacer length. This is reflected in a difference in the temperature dependence of the aggregates: for the two systems coated with long DNA, the resulting aggregates were stable against heating, whereas the colloids coated with ssDNA alone would dissociate upon heating.     

Interaction of giant extracellular Glossoscolex paulistus hemoglobin (HbGp) with zwitterionic surfactant N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS): effects of oligomeric dissociation

The present work focuses on the interaction between the zwitterionic surfactant N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and the giant extracellular hemoglobin of Glossoscolex paulistus (HbGp). Electronic optical absorption, fluorescence emission and circular dichroism spectroscopy techniques, together with Gel-filtration chromatography, were used in order to evaluate the oligomeric dissociation as well as the autoxidation of HbGp as a function of the interaction with HPS. A peculiar behavior was observed for the HPS–HbGp interaction: a complex ferric species formation equilibrium was promoted, as a consequence of the autoxidation and oligomeric dissociation processes. At pH 7.0, HPS is more effective up to 1 mM while at pH 9.0 the surfactant effect is more intense above 1 mM. Furthermore, the interaction of HPS with HbGp was clearly less intense than the interaction of this hemoglobin with cationic (CTAC) and anionic (SDS) surfactants. Probably, this lower interaction with HPS is due to two factors: (i) the lower electrostatic attraction between the HPS surfactant and the protein surface ionic sites when compared to the electrostatic interaction between HbGp and cationic and anionic surfactants, and (ii) the low cmc of HPS, which probably reduces the interaction of the surfactant in the monomeric form with the protein. The present work emphasizes the importance of the electrostatic contribution in the interaction between ionic surfactants and HbGp. Furthermore, in the whole HPS concentration range used in this study, no folding and autoxidation decrease induced by this surfactant were observed. This is quite different from the literature data on the interaction between surfactants and tetrameric hemoglobins, that supports the occurrence of this behavior for the intracellular hemoglobins at low surfactant concentration range. Spectroscopic data are discussed and compared with the literature in order to improve the understanding of hemoglobin–surfactant interaction as well as the acid isoelectric point (pI) influence of the giant extracellular hemoglobins on their structure–activity relationship.     

Theoretical study of the reaction of H atoms with vibrationally highly excited HF molecules

Vibrationally highly excited molecules react extremely fast with atoms and probably with radicals. The phenomenon can be utilized for selectively enhancing the rate of reactions of specific bonds. On the basis of quasiclassical trajectory calculations, the paper analyzes mechanistic details of a prototype reaction, H + HF(v). At vibrational quantum numbers v above 2, the reaction exhibits capture-type behavior, that is, the reactive cross section diverges as the relative translational energy of the partners decreases, both for the abstraction and for the exchange channel. The mechanism of the reaction for both channels is different at low and at high translational energy. At low vibrational energy, the reaction is activated, which is switched to capture-type at high excitation. The reason is an attractive potential that acts on the attacking H atom when the HF molecule is stretched. In contrast to the 6-SEC potential surface of Mielke et al., the switch cannot be observed on the Stark-Werner potential surface, due to a small artificial barrier at high H-HF separation, preventing the reactants from obeying the attractive potential and also proving the importance of the latter. The exchange reaction can be observed even when the total energy available for the partners is below the exchange barrier, because at low translational energies the product F atom of a successful abstraction step can re-abstract that H atom from the intermediate product H2 molecule that was originally the attacker.     

Determination of orthophthalaldehyde in air using 2,4-dinitrophenylhydrazine-impregnated silica cartridge and high-performance liquid chromatography

A new method is described for the determination of orthophthalaldehyde in air which is used for the disinfection of various instruments (e.g. endoscopes) in hospital. Orthophthalaldehyde in air was collected with a silica gel cartridge impregnated with acidified 2,4-dinitrophenylhydrazine (DNPH-cartridge) and derivatives were analyzed by high-performance liquid chromatography (HPLC). In this study, the derivatization was examined by comparing the process with three phthalaldehyde isomers (ortho-, iso- and tere-). In the case of iso- and tere-phthalaldehyde, derivatives synthesized with excess of aldehyde consisted mainly of mono-derivatives, and derivatives synthesized with excess of DNPH consisted mainly of bis-derivative. In the case of orthophthalaldehyde, derivative consisted of only bis-derivative and mono-derivative was never observed under any conditions. Orthophthalaldehyde was completely retained by the DNPH-cartridge during air sampling, however, the derivatization reaction was incomplete and unreacted orthophthalaldehyde was flushed from the cartridge during the subsequent solvent extraction process. Unreacted orthophthalaldehyde and DNPH reacted again in the extraction solvent solution. Immediately after the solvent extraction, both mono- and bis-DNPhydrazone derivatives of orthophthalaldehyde were present in the solution. However, over time, the mono-derivative decreased and bis-derivative increased until only the bis-derivative was left allowing accurate determination of the orthophthalaldehyde concentration. The transformation of mono-derivative to bis-derivative was faster in polar aprotic solvents such as acetonitrile, dimethyl sulfoxide and ethyl acetate. Transformation was found to occur most quickly in acetonitrile solvent and was completed in 4 h in this case. It was possible to measure orthophthalaldehyde in air as bis-derivative using a DNPH impregnated silica cartridge and HPLC analysis.     

Metal-Free Twofold Electrochemical C−H Amination of Activated Arenes: Application to Medicinally Relevant Precursor Synthesis

The efficient production of many medicinally or synthetically important starting materials suffers from wasteful or toxic precursors for the synthesis. In particular, the aromatic non-protected primary amine function represents a versatile synthetic precursor, but its synthesis typically requires toxic oxidizing agents and transition metal catalysts. The twofold electrochemical amination of activated benzene derivatives via Zincke intermediates provides an alternative sustainable strategy for the formation of new C−N bonds of high synthetic value. As a proof of concept, we use our approach to generate a benzoxazinone scaffold that gained attention as a starting structure against castrate-resistant prostate cancer. Further improvement of the structure led to significantly increased cancer cell line toxicity. Thus, exploiting environmentally benign electrooxidation, we present a new versatile and powerful method based on direct C−H activation that is applicable for example the production of medicinally relevant compounds.     

What is the ‘Solvent’ effect on the electronic spectra of a solute in a polymer matrix?

The theory of solvent-induced shifts of the absorption and fluorescence band spectra of a solute is well known and has been tested for a multitude of systems. However, there are only few applications to polymers. By a direct comparison of the spectral shifts in liquid solvents with those in polymers it is possible to determine the microenvironment of the solutes in polymers within the frame of this theory. Polyethylene terephthalate as fabric and film was chosen as model polymer. The spectral shifts of 15 fluorescing solutes in this polymer as well as in 10 solvents with widely differing refractive indices n and permittivities ? were measured and fitted to the equations given by the theory of the solvent effect. It is found that interactions with the permanent dipoles of polyethylene terephthalate may be neglected within the limits of accuracy attainable for this polymer and the chosen solutes. Dispersion forces dominate the solvent effect. The refractive indices effective at the site of the solute molecules are n = 1.66 for the fabric and n = 1.70 for the film.     

Syntheses of dictyopterene B (hormosirene) and its enantiomer via asymmetric ScN′ reactions

Stereocontrolled syntheses of dictyopterene B (hormosirene) (1) and its enantiomer (ent-1) are reported. Key steps are highly stereoselective S_cN′ reactions of esters of alcohols 2 and 5 derived from (+)-camphor.