Fractionation of nitrogen stable isotopes by ion exchange chromatography

The ion exchange chromatography displacement technique was used for the enrichment of ¹⁵N. The runs were conducted in laboratory and bench scales using two systems of columns filled with Wofatit KPS ion exchange resin (medium porosity type). Ammonia NH₄ ⁺/NH₃ aq. was chosen as the isotopic exchange system. The ammonium bands formed in the columns were eluted by means of sodium hydroxide solution. Hydrodynamic patterns in the column beds was evaluated in terms of dimensionless Reynolds number. The results show that separation process can be performed in the turbulent or laminar flow regime.     

Additions of enantiopure alpha-sulfinyl carbanions to (S)-N-sulfinimines: asymmetric synthesis of beta-amino sulfoxides and beta-alphamino alcohols

The addition of the lithium anions derived from (R)- and (S)-methyl and -ethyl p-tolyl sulfoxides to (S)-N-benzylidene-p-toluenesulfinamide provides an easy access route to enantiomerically pure beta-(N-sulfinyl)amino sulfoxides. Stereoselectivity can be achieved when the configurations at the sulfur atoms of the two reagents are opposite (matched pair), thus resulting in only one diastereoisomer, even for the case in which two new chiral centers are created. The N-sulfinyl group primarily controls the configuration of the carbon bonded to the nitrogen, whereas the configuration of the alpha-sulfinyl carbanion seems to be responsible for the level of asymmetric induction, as well as for the configuration of the new stereogenic C-SO carbon in the reactions with ethyl p-tolyl sulfoxides. An efficient method for transforming the obtained beta-(N-sulfinyl)amino sulfoxides into optically pure beta-amino alcohols, based on the stereoselective non-oxidative Pummerer reaction, is also reported.     

Multi-element Saha–Boltzmann and Boltzmann plots in laser-induced plasmas

A multi-element Saha–Boltzmann plot method is proposed for the determination of the temperature and the relative number density in laser-induced plasmas, assuming local thermodynamic equilibrium and stoichiometry conservation. The method has been applied to the characterization of a plasma generated with a Cu–Fe–Ni–Mn alloy, using a Nd:YAG laser in air at atmospheric pressure. Spectra of the local emissivity have been obtained by spatial deconvolution of the intensity spectra, obtained with spatial resolution. Saha–Boltzmann plots obtained from the emissivities of 58 spectral lines of Fe I, Fe II, Ni I, Ni II, Mn I and Mn II have been fitted to linear behavior with high correlation, which shows the validity of the equation proposed. Radial distributions of the temperature and number densities of neutral atoms and ions have been determined. The results obtained reinforce the initial considerations of local thermodynamic equilibrium and conservation of stoichiometry. The proposed equation can also be applied to only one ionization species (multi-element Boltzmann plot). Spatially-integrated measurements of the plasma emission have also been performed to show that, in this case, the application of the method to the line intensities provides the two different apparent temperatures for neutral atoms and ions.     

(Z)-3-p-tolylsulfinylacrylonitrile as a chiral dienophile: diels-alder reactions with furan and acyclic dienes

The behavior of (Z)-3-p-tolylsulfinylacrylonitrile (1) as a chiral dienophile has been evaluated from its reactions with furan and acyclic dienes. Electrostatic interactions of the cyano group with the sulfinyl one restrict the conformational mobility around the C-S bond, thus controlling the pi-facial selectivity, which is almost complete in all cases, the approach of the diene from the less-hindered face of the dienophile (that bearing the lone electron pair) in the predominant rotamer being the favored one. The regioselectivity is also completely controlled by the cyano group. Additionally, the reactivity of compound 1 as well as its endo-selectivity are both higher than those observed for the corresponding (Z)-3-sulfinylacrylates, thus proving the potential of sulfinylnitriles as chiral dienophiles.     

Divergent synthetic routes to biologically relevant types of compounds: chiral polyfunctional γ-lactams and amino acids

Divergent and versatile synthetic routes leading to the title compounds are described. They start from a common chiral precursor derived from (−)-(S)-verbenone and afford polyfunctional γ-lactams and γ- and ε-amino acids. The cyclobutane moiety in these molecules acts as a chiral and polyfunctional platform providing stereogenic centres with unambiguous absolute configuration that control the chirality of the newly produced asymmetric carbons. Furthermore, it affords functional groups and carbon chains suitable not only to create the basic skeleton of the desired products but additional functional groups. These features confer on these derivatives a great versatility for further uses in the development of new drugs and as synthetic building blocks.     

Tacrines as Therapeutic Agents for Alzheimer's Disease. V. Recent Developments

Herein we have reviewed our recent developments for the identification of new tacrine analogues for Alzheimer's disease (AD) therapy. Tacrine, the first cholinesterase inhibitor approved for AD treatment, did not stop the progression of AD, producing only some cognitive improvements, but exhibited secondary effects mainly due to its hepatotoxicity. Thus, the drug was withdrawn from the clinics administration. Since then, many publications have described non‐hepatotoxic tacrines, and in addition, important efforts have been made to design multitarget tacrines by combining their cholinesterase inhibition profile with the modulation of other biological targets involved in AD.     

Spin-singlet clusters in the ladder compound NaV2O5

The space group of alpha(')-NaV2O5 turns below T(c) = 34 K from Pmmn with all V sites equivalent, into Fmm2 with three independent vanadium sites per layer. This is incompatible with models of charge ordering into V4+ and V5+. Our structure determination indicates that the phase transition consists of a charge ordering with three distinct valence states, formally V4+, V4.5+, and V5+. The singlet formation is not associated with dimerization on the spin ladder, but with the formation of spin clusters. Finally, we ascribe the quadrupling of the c axis to the large polarizability of the V2O5 skeleton.     

Dependence of pulser driving responses on electrical and motional characteristics of NDE ultrasonic probes

Acoustic performance in ultrasonic transmitters can be improved by means of a suitable electrical driving response and matching/tuning networks. It is important to predict this electrical response, but doing so is not easy because it departs notably from the nominal pattern with the loading probes. In practice, the analysis of HV pulser spikes in NDE applications requires fairly complex models in the transient regime and, in addition, non-linear problems could arise, especially in the case of tuned transmitters. In this paper, the most relevant influences of loading characteristics of NDT ultrasonic probes on the pulser electrical driving responses are evaluated in time and frequency domains. Conventional pulse generators and typical NDE pulsers are considered. Driving responses are analysed across commercial ultrasonic probes and, alternatively, across similar purely electrical loads. Distinct influences on pulser responses from electrical and motional sections of the probes are identified. All these aspects are studied on the basis of experimental and computer results.     

Interaction between a Novel Oligopeptide Fragment of the Human Neurotrophin Receptor TrkB Ectodomain D5 and the C-Terminal Fragment of Tetanus Neurotoxin

This article presents experimental evidence and computed molecular models of a potential interaction between receptor domain D5 of TrkB with the carboxyl-terminal domain of tetanus neurotoxin (Hc-TeNT). Computational simulations of a novel small cyclic oligopeptide are designed, synthesized, and tested for possible tetanus neurotoxin-D5 interaction. A hot spot of this protein-protein interaction is identified in analogy to the hitherto known crystal structures of the complex between neurotrophin and D5. Hc-TeNT activates the neurotrophin receptors, as well as its downstream signaling pathways, inducing neuroprotection in different stress cellular models. Based on these premises, we propose the Trk receptor family as potential proteic affinity receptors for TeNT. In vitro, Hc-TeNT binds to a synthetic TrkB-derived peptide and acts similar to an agonist ligand for TrkB, resulting in phosphorylation of the receptor. These properties are weakened by the mutagenesis of three residues of the predicted interaction region in Hc-TeNT. It also competes with Brain-derived neurotrophic factor, a native binder to human TrkB, for the binding to neural membranes, and for uptake in TrkB-positive vesicles. In addition, both molecules are located together in vivo at neuromuscular junctions and in motor neurons.