1-Alkoxycarbonyl- and 1-acyl-v-triazolo[4,5-b]-pyridine/hydrogen peroxide oxygenating systems

Epoxidation of alkenes and oxidation of thioanisole to the corresponding sulfoxide was achieved using the 1-alkoxycarbonyl- or 1-acyl-v-triazolo[4,5-6]pyridine/hydrogen peroxide systems. High yields of epoxide or sulfoxide were observed when some amide-type triazolides were employed for the oxidizing method.     

A new route to N2- and N3-substituted-2,3-diaminopyridines. Synthesis of 1- and 3-alkoxycarbonyl-v-triazolo[4,5-b]pyridines

Selective protection of the 3-amino group of 2,3-diaminopyridine with benzyl chloroformate allows a new synthesis of 3-methylamino- and 3-amino-2-alkylaminopyridines. The preparation of 1- and 3-alkoxycarbonyl-v-triazolo[4,5-b]pyridines is also reported.     

Reflection and refraction at elastic-viscoelastic interfaces

Summary A detailed investigation is performed of reflection and refraction at a plane interface between an elastic body and a viscoelastic one. The incident wave in the elastic body is supposed to be homogeneous while the transmitted waves are necessarily inhomogeneous. After setting up the general expressions for the determination of angles and amplitudes, an approximation procedure is developed which regards the dissipative effects as perturbative quantities and hence only the leading terms are kept. Then angles and amplitudes are derived explicitly and the behaviourvs. the frequency is examined. The numerical results show how this behaviour determines the time constant of an exponential-type relaxation function.

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Riassunto Si effettua un'analisi dettagliata della riflessione e della rifrazione su una superficie piana di separazione tra un mezzo elastico e uno viscoelastico. L'onda incidente, proveniente dal mezzo elastico, è assunta omogenea mentre le onde trasmesse sono necessariamente inomogenee. Dopo aver elaborato le espressioni generali per la determinazione di angoli e ampiezze, si sviluppa un processo di approssimazione in cui gli effetti dissipativi sono riguardati come una perturbazione e quindi si considerano solo i termini principali. In tal modo angoli e ampiezze sono determinati esplicitamente e se ne esamina il comportamento al variare della frequenza. I risultati numerici mostrano come tale comportamento individui la costante di tempo per una funzione di rilassamento di tipo esponenziale.

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Резюме Подробно исследуются отражение и преломление на =qpлоской границе раздела между упругим и упруговязким телами. Падающая волна на упругое тело предполагается однородной, тогда как прошедшие волпы обязательно являются неоднородными. После получения общих выражений для определения углов и амплитуд предлагается приближенная процедура, в которой диссипативные эффекты рассматриваются как возмущения, и поэтому сохраняются только главные члены. Затем в явном виде определяются углы и амплитуды и исследуются зависимость от частоты. Численные результаты показывают, что эта зависимость определяет временную постоянную для функции релаксации экспоненциального типа.

     

Metal chelation aptitudes of bis(o-azaheteroaryl)methanes as tuned by heterocycle charge demands

We describe the synthesis of a number of 1,3-azol-2-yl-, 1,3-benzazol-2-yl-, and azinyl-based bis(o-azaheteroaryl)methanes (LH, L(-) = Het(2)CH(-)) and their coordinating properties toward divalent transition metals (Zn, Cu, Co, Ni, Hg, Pd). This extended investigation includes both symmetrical and unsymmetrical ligands based on several substituted and/or unsubstituted thiazole, benzothiazole, benzoxazole, benzimidazole, pyridine, and quinoline derivatives. Depending on the structure and electron properties of the ligand, a vast set of neutral chelates ML(2) were obtained, where the ligand is present in its carbanionic form L(-). Additionally, we have prepared salt complexes [M(LH)(n)]X(m), where the ligand is present as a neutral system. Neutral chelates were typically obtained by the reaction of the ligand with metal acetates in alcoholic solution; salt complexes were formed by reaction with other metal salts such as chlorides. By exploring the coordinating properties of several bisheteroarylmethane ligands based on heteroaromatics of variable pi-electron structure and substitution pattern, we demonstrate that the formation of neutral chelates is strictly dependent on the electron-withdrawing capacity (charge demand) of the heteroaromatic moiety. The latter primarily dictates the efficiency by which the negative charge of the anionic ligand L(-) is stabilized by delocalization in ML(2) and, therefore, the stability of the chelate itself. On the basis of the large number and the variable nature of the nitrogen ligands used, we confirm the general validity of the charge-demand-dependent formation of chelates. This key factor can therefore be used for the efficient design of new pi-deficient heteroaromatic nitrogen ligands in chelates of great potential in many synthetic, catalytic, and technological fields.     

Characterization of synthetic carrier ampholytes for isoelectric focusing.

The synthesis of carrier ampholytes suitable for isoelectric focusing is described. The mixture of hexamethylenetetramine (HMTA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA) and pentaethylenehexamine (PEHA) ampholytes closely resembles commercial Ampholine, and covers the pH range 3-9.5. We have been able to detect focused ampholytes in a gel slab, taking advantage of their different refractive indices, and to assess their relative amounts along the pH gradient. PEHA ampholytes contain up to 20% of chromophoric structures, with two UV peaks at 368 and 315 nm, in a pH-dependent equilibrium, associated with a very weak nitrogen function having a pK of 1.1. This could be the pK6 of the last amino group in PEHA. However, NMR spectra failed to reveal any nitrogen heterocyclic structure formed during the synthesis. This mixture of ampholytes exhibits good conductivity, produces smooth pH gradients and allows sharp protein separations in the pH range 3-9.5. Their synthesis is very easy and their cost is extremely low. Their availability sould make feasible large-scale preparative isoelectric focusing, and attract more interest to continuous-flow techniques, where large amounts of ampholytes are required.     

Guidelines for buckwheat enriched bread

Thermal analysis was used to check the role of the main components of buckwheat flour (polysaccharides and proteins) to assess guidelines for novel recipes for bread from wheat and buckwheat flour blends with improved nutritional properties. The structure-related poor protein quality, namely, the lack of network-forming links, severely limits the use of buckwheat flours in bread-making. Data from TG and DSC analysis indicate that the introduction of a de-hulling step in the buckwheat milling diagram and the addition of some buckwheat polysaccharide fractions, isolated from the buckwheat husk, that contribute to the formation of the crumb structure thanks to their effect on the phase separation driven by the thermodynamic incompatibility with wheat gluten proteins, allows one to tune opposite effects and obtain bread from de-hulled buckweat/wheat flour blends with alveolar distribution much close that of the wheat bread.     

Evaluation of partial least-squares with second-order advantage for the multi-way spectroscopic analysis of complex biological samples in the presence of analyte-background interactions

The combination of unfolded partial least-squares (U-PLS) with residual bilinearization (RBL) has not been properly exploited to process experimental second-order spectroscopic information, although it is able to achieve the important second-order advantage. Among other desirable properties, the technique can handle incomplete calibration information, i.e., when only certain analyte concentrations are known in the training set. It can also cope with analyte spectral changes from sample to sample, due to its latent variable structure. In this work, U-PLS/RBL has been successfully applied to experimental fluorescence excitation-emission matrix data aimed at the quantitation of analytes in complex samples: these were the antibiotic tetracycline and the anti-inflammatory salicylate, in both cases in the presence of human serum, where significant analyte-background interactions occur. The interactions of the analyte with the serum proteins modify their spectral fluorescence properties, making it necessary to employ training sets of samples where the biological background is present, possibly causing analyte spectral changes from sample to sample. The predictive ability of the studied model has been compared with that of parallel factor analysis (PARAFAC), as regards test samples containing different sera, and also other pharmaceuticals which could act as potential interferents.     

Universal local symmetries and nonsuperposition in classical mechanics

In the Hilbert space formulation of classical mechanics, pioneered by Koopman and von Neumann, there are potentially more observables than in the standard approach to classical mechanics. In this Letter, we show that actually many of those extra observables are not invariant under a set of universal local symmetries which appear once the Koopman and von Neumann formulation is extended to include the evolution of differential forms. Because of their noninvariance, those extra observables have to be removed. This removal makes the superposition of states in the Koopman and von Neumann formulation, and as a consequence also in classical mechanics, impossible.     

Dehydration of β-Hydroxy-α-amino Acid Derivatives With Phenyltriflimide

Conversion of N-protected β-hydroxy-α-amino esters to corresponding didehydroamino esters has been achieved using phenyltriflimide/triethylamine as a mild dehydrating agent. The selective formation of didehydroalanine derivatives from dipeptides containing, beside a serine residue, another β-hydroxy-α-amino acid, is also described.