The thermal degradation kinetics of dextran and pullulan

The effect of molar mass and, in the case of dextran, of the degree of branching on the thermal degradation kinetics of dextran and pullulan was studied in the presence and absence of oxygen. Although the initial mass loss of the dextran samples occurred at higher temperatures than that of the pullulan samples, the overall thermal degradation activation energies were lower for dextran than for pullulan. In the case of dextran the thermal stability was found to decrease with molar mass and degree of branching. The molar mass of pullulan, in the range of 10⁴ to 10⁵ g/mol, appeared to have no significant influence on the thermal characteristics of the samples.     

Determination of structure and 13C chemical shift assignments of the nitration products of 2-chloro-10-methylphenothiazine. X-Ray molecular structure of 2-chloro-7-nitro-10-methylphenothiazine 5-oxide

Nitration of 2-chloro-10-methylphenothiazine, 1 , yields two mono-nitro compounds identified as sulfoxide 2 and sulfone 3 . The nmr analyses of the ¹³C spectra of 2 and 3 establish unequivocally that in both compounds substitution has occurred at the seven position. This is supported by the X-ray crystal structure of one of the compounds 2-chloro-7-nitro-10-methylphenothiazine 5-oxide, 2 , which also shows that the sulfoxide group is in the “pseudo-axial” configuration. Crystals of 2 are monoclinic, space group P2₁/n, a = 11.606(4), b = 13.970(4)Å, c = 9.837(2), β = 127.49(2)° and Z = 4. The structure has been refined by full-matrix least-squares to R = 0.033 and R_w = 0.035, using 1704 observed reflections.     

Some elucidations to the concept of the effective resonance energy\bar E_r

The concept of the effective resonance energy , formerly introduced as a parameter in the absolute (e.g. k₀-) standardization methodology of (n, ) activation analysis, is elucidated with respect to dimensioning, accuracy and usefulness.     

Kinetic vortex chain solution in the drift-wave plasma regime

A fully nonlinear Bernstein-Greene-Kruskal stationary solution is found in the form of a quasi-three-dimensional chain of electron holes coupled to hydrodynamic vortices. This new coherent structure is enabled by the trapping and depletion of resonant particles, and the cyclotron dissipation of the singular current sheets. It is expected to play an important role in the collisionless magnetic field line reconnection in the drift-wave plasma regime, where it represents a plausible saturated state.     

Nuclear forensic analysis with laser ablation inductively coupled plasma mass spectrometry in CMX-6

Journal of Radioanalytical and Nuclear Chemistry - The 6th Collaborative Materials Exercise, CMX-6, was organized by the Nuclear Forensic International Technical Working Group in 2018 and 2019. Two...     

The Enzyme-Free Release of Nucleotides from Phosphoramidates Depends Strongly on the Amino Acid

Phosphoramidates composed of an amino acid and a nucleotide analogue are critical metabolites of prodrugs, such as remdesivir. Hydrolysis of the phosphoramidate liberates the nucleotide, which can then be phosphorylated to become the pharmacologically active triphosphate. Enzymatic hydrolysis has been demonstrated, but a spontaneous chemical process may also occur. We measured the rate of enzyme-free hydrolysis for 17 phosphoramidates of ribonucleotides with amino acids or related compounds at pH 7.5. Phosphoramidates of proline hydrolyzed fast, with a half-life time as short as 2.4 h for Pro-AMP in ethylimidazole-containing buffer at 37 °C; 45-fold faster than Ala-AMP and 120-fold faster than Phe-AMP. Crystal structures of Gly-AMP, Pro-AMP, βPro-AMP and Phe-AMP bound to RNase A as crystallization chaperone showed how well the carboxylate is poised to attack the phosphoramidate, helping to explain this reactivity. Our results are significant for the design of new antiviral prodrugs.     

Trace analysis of uranium ore concentrates using laser ablation inductively coupled plasma mass spectrometry for nuclear forensics

Journal of Radioanalytical and Nuclear Chemistry - We present a laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) method for trace-element analysis of uranium ore concentrates...     

Electrochemical and surface characterization of pH sensor based on bisulfate-doped poly(pyrrole)

Pyrrole was electrochemically polymerized on glassy carbon support in NaHSO₄ solutions under different conditions (method applied, concentration of monomer, concentration of the main solution, thickness of the film). These variables were used to study the preparation effect on the resulting properties, in particular on the potentiometric response of the PPy-HSO₄ electrodes. The electrodes were characterized by cyclic voltammetry, as well as by STM and AES techniques. Utilities of the polymer application as a sensor were studied by direct potentiometric measurements. The results obtained show that poly(pyrrole) doped with bisulfate ions can serve as pH sensor, with the slope of E/pH curves approaching the theoretical value.     

Fixed set search applied to the multi-objective minimum weighted vertex cover problem

Journal of Heuristics - The Fixed Set Search (FSS) is a novel metaheuristic that adds a learning mechanism to the Greedy Randomized Adaptive Search Procedure (GRASP). In recent publications, its...