Transverse NMR relaxation as a probe of mesoscopic structure

Transverse NMR relaxation in a macroscopic sample is shown to be extremely sensitive to the structure of mesoscopic magnetic susceptibility variations. Such a sensitivity is proposed as a novel kind of contrast in the NMR measurements. For suspensions of arbitrary-shaped paramagnetic objects, the transverse relaxation is found in the case of a small dephasing effect of an individual object. Strong relaxation rate dependence on the objects' shape agrees with experiments on whole blood. Demonstrated structure sensitivity is a generic effect that arises in NMR relaxation in porous media, biological systems, as well as in kinetics of diffusion limited reactions.     

Bifunctionalized Allenes,Part IX: An Efficient Method for Regioselective Synthesis of 4‐Heteroatom‐Functionalized Allenecarboxylates

An efficient method for regioselective synthesis of 4‐heteroatom‐functionalized allenecarboxylates by an atom economical [2,3]‐sigmatropic rearrangement of the mediated 2‐heteroatom‐functionalized alk‐3‐ynecarboxylates is described. Alkyl 4‐(dimethoxyphosphoryl), (diphenylphosphinoyl), (benzenesulfinyl), or (methanesulfonyl)‐alka‐2,3‐dienoates can be readily prepared via reactions of alkyl 2‐hydroxy‐alk‐3‐ynoates with dimethylchlorophosphite, chlorodiphenylphosphine, benzensulfanyl chloride, or methanesulfinyl chloride, respectively, in the presence of a base.     

Tandem transformations of tetrahydrobenzothieno[2,3-c]pyridines in the presence of activated alkynes

The reactivity of some new tetrahydrothienopyridines towards activated alkynes was investigated. A novel cascade cleavage-spiroannulation process, leading to the formation of previously unreported derivatives of 1′H-spiro[1-benzothiophene-3,4′-pyridine] was discovered and studied.     

Simple and efficient preparation of 3-substituted 6-(4-chlorophenyl)-9-methyl-12H-[1]benzofuro[3,2-e][1,2,4]triazolo[4,3-b][1,2]diazepines via a silylation–amination reaction

Abstract  

A series of new 3-substituted 6-(4-chlorophenyl)-9-methyl-12H-[1]benzofuro[3,2-e][1,2,4]triazolo[4,3-b][1,2]diazepines was synthesized from the corresponding bicyclic 1-(4-chlorophenyl)-3,5-dihydro-8-methyl-4H-[1]benzofuro[2,3-d][1,2]diazepin-4-one. The synthesis strategy makes use of silylation–amination as the key step, allowing a wide range of derivatives to be prepared.     

Polyplexes of poly(methylaminophosphazene): energetics of DNA melting

The interaction of DNA with a synthetic biocompatible and biodegradable cationic polymer, poly(methylaminophosphazene) hydrochloride (PMAP·HCl), was investigated by high-sensitivity differential scanning calorimetry under conditions of strong and weak electrostatic interactions of the macroions. Thermodynamic parameters of the DNA double-helix melting were determined as a function of pH and the PMAP·HCl/DNA weight ratio. PMAP·HCL was shown to reveal two functions with respect to DNA: the polyelectrolyte function and the donor-acceptor one. The first function stabilizes the helical conformation of DNA, and the second one destabilizes it. The stabilizing effect of PMAP·HCl is of entropic origin, related to a displacement of mobile counterions from the DNA's nearest surroundings by the poly(methylaminophosphazene) charged groups. The donor-acceptor function of poly(methylaminophosphazene) dominates when its electrostatic interaction with DNA is either saturated (in the complex coacervate phase at high poly(methylaminophosphazene) concentrations) or completely suppressed (in a salt medium when the polycation carries a small charge). Under these conditions, poly(methylaminophosphazene) destabilizes DNA. It preferentially binds to the DNA coil form likely via the formation of multiple labile hydrogen bonds with the donor-acceptor groups of DNA.     

Surface-to-volume ratio with oscillating gradients

Restrictions to diffusion result in the dispersion of the bulk diffusion coefficient. We derive the exact universal high-frequency behavior of the diffusion coefficient in terms of the surface-to-volume ratio of the restrictions. This frequency dependence can be applied to quantify structure of complex samples with NMR using oscillating field gradients and static-gradient CPMG. We also demonstrate the inter-relations between different equivalent diffusion metrics, and describe how to calculate the effect of restrictions for arbitrary gradient waveforms.     

Anomalous Beckmann Reaction of 4-Aryl-2,7,7-trimethyl-5-oxo-5,6,7,8-tetrahydroquinoline Oximes in Polyphosphoric Acid. 1. New Synthesis of 1-Ethoxycarbonyl-2,5,5-trimethyl-5,6-dihydro-4H-pyrido[2,3,4-k,l]acridines

Transformations of oximes of 4-aryl-2,7,7-trimethyl-5-oxo-5,6,7,8-tetrahydroquinolines in PPA have been studied. It is shown that the reaction, depending on substituent at position 4 of quinoline ring, can occur in three directions: aromatization of the saturated ring (Semmler-Wolff aromatization), formation of azepinones - normal products of Beckmann rearrangement, and formation of pyridoacridines.     

Modulo image encryption with fractal keys

An encryption technique based on the modulo operation is proposed. The technique is a one-to-one encryption–decryption single key algorithm. Fractal images are proposed to be used as a source of randomness to generate strong keys. The use of the proposed method is verified, both in the single image encryption–decryption, and in a real-time streaming application. The described algorithm provides a mechanism for controlling the strength of the keys. The advantages of the proposed method are discussed. A video setup is built and GUI software implemented to practically test this method. Numerical results of the test are provided and analyzed. Overall, the theoretically anticipated results are achieved, and the algorithm proven to be adept for real world cryptographic applications.