Dual Responsive Regulation of Host–Guest Complexation in Aqueous Media to Control Partial Release of the Host

The regulation of the concentration of a wide range of small molecules is ubiquitous in biological systems because it enables them to adapt to the continuous changes in the environmental conditions. Herein, we report an aqueous synthetic system that provides an orchestrated, temperature and pH controlled regulation of the complexation between the cyclobis(paraquat-p-phenylene) host ( BBox ) and a 1,5-dialkyloxynaphthalene ( DNP ) guest attached to a well-defined dual responsive copolymer composed of N-isopropylacrylamide as thermoresponsive monomer and acrylic acid as pH-responsive monomer. Controlled, partial release of the BBox , enabling control over its concentration, is based on the tunable partial collapse of the copolymer. This colored supramolecular assembly is one of the first synthetic systems providing control over the concentration of a small molecule, providing great potential as both T and pH chromic materials and as a basis to develop more complex systems with molecular communication.     

Strong enhancement of extremely energetic proton production in central heavy ion collisions at intermediate energy

The energetic proton emission has been investigated as a function of the reaction centrality for the system (58)Ni + (58)Ni at 30A MeV. Extremely energetic protons (E(NN)(p) > or = 130 MeV) were measured and their multiplicity is found to increase almost quadratically with the number of participant nucleons, thus indicating the onset of a mechanism beyond one- and two-body dynamics.     

Aggregation of perfluoropolyether carboxylic salts in aqueous solutions. Fluorescence probe study

Aqueous solutions of anionic surfactants Cl(C3F6O)nCF2COOX, consisting of n = 2 and 3 perfluoroisopropoxy units and the counterion X = Na+ or NH4+, were studied by the method of fluorescence quenching with the use of (1-pyrenylbutyl)trimethylammonium bromide as a luminophore, and 1,1'-dimethyl-4,4'bipyridinium dichloride (methyl viologen) as a quencher. From the kinetics of fluorescence decay (time-resolved experiments) micellar aggregation numbers, N, and rate constants of the intramicellar quenching were determined for a wide range of surfactant concentrations, on the basis of the model developed by Infelta and Tachiya. The results are discussed in terms of the shape of the aggregates and the degree of counterion binding. The most important conclusions include: (i) a significant increase of N with increasing surfactant concentration suggests that spherical micelles formed at critical micellar concentration (CMC) transform into ellipsoidal aggregates, (ii) the degree of counterion binding to micelles is higher for NH4+ than for Na+, leading to higher N values in the case of the ammonium salt (n = 2), and (iii) at concentrations close to CMC the longer chain surfactant (n = 3) forms loose aggregates suggesting significant permeation with water molecules. An additional finding of this study is that the micelle-bound luminophore and quencher can form a ground-state complex, and for this reason the N values cannot be evaluated properly from the steady-state fluorescence intensity data using the equation proposed by Turro and Yekta.     

Lead validation and SAR development via chemical similarity searching; application to compounds targeting the pY+3 site of the SH2 domain of p56lck

Compound selection based on chemical similarity has been used to validate active "parent" compounds identified via database searching as viable lead compounds and to obtain initial structure-activity relationships for those leads. Twelve parent compounds that have inhibitory activity against the SH2 domain of the p56 T-cell tyrosine kinase (Lck) are the focus of this study. Lck is involved in the T-cell mediated immune response, and inhibitors of Lck protein-protein interactions could potentially be used to develop novel immunosuppressants. Similarity searches for each parent compound were performed using 2D structural fingerprints on a database containing 1,300,000 commercially available compounds. The inhibitory activity of the selected compounds was assessed using enzyme immunoassay (EIA). In general, the most active parent compounds yield the most high activity similar compounds; however, in two cases low activity parent compounds (i.e. inhibitory activity < 25% at 100 microM) yielded multiple similar compounds with activities > 60%. Such compounds may, therefore, be considered as viable lead compounds for optimization. Structure-activity relationships were explored by examining both ligand structures and their computed bound conformations to the protein. Functional groups common to the active compounds as well as key amino acid residues that form hydrogen bonds with the active compounds were identified. This information will act as the basis for the rational optimization of the lead compounds.     

Total reflection X-ray fluorescence and archaeometry: Application in the Argentinean cultural heritage

Archaeometry is an interdisciplinary research area involved in the development and use of scientific methods in order to answer questions concerned with the human history. In this way the knowledge of archaeological objects through advanced chemical and physical analyses permits a better preservation and conservation of the cultural heritage and also reveals materials and technologies used in the past. In this sense, analytical techniques play an important role in order to provide chemical information about cultural objects. Considering the non destructive characteristic of this study, analytical techniques must be adequate in order to prevent any alteration or damage and in addition to allow the conservation of their integrity. Taking into account the irreplaceable character of the archaeological and artistic materials considered in this study, analytical techniques must be adequate in order to prevent any alteration or damage and in addition to allow the conservation of their integrity.