KINETIC ISOTOPIC EFFECT: STATIC RAYLEIGH EQUATION AND BASIC DYNAMIC ISOTOPE EQUATION FOR THE SUBSTRATE IN THE DESCRIPTION OF NITRITE-DEPENDENT ANAEROBIC OXIDATION OF METHANE

The article analyzes the results of modeling the dynamics of nitrite-dependent methane oxidation (N-DAMO) by Methylomirabilis oxyfera microorganisms using the standard isotope dynamic equations. Without specifying a specific function of the rate of the process, the traditional static Rayleigh equation is derived from the basic dynamic isotope equation. Thus, the equation of the 1st order in terms of the substrate is only a special case in the derivation of the Rayleigh equation. It was shown that the dominant fractionation of carbon isotopes occurs in the process of the microbiological reaction of anaerobic oxidation of methane by nitrite, and not in the physical process of mass transfer of dissolved methane into the gas phase. In contrast to the static Rayleigh equation, the dynamic description of the process of fractionation of stable isotopes is important when describing the parallel transformations of the substrate.

A neural network potential energy surface for the F + H2O ↔ HF + OH reaction and quantum dynamics study of isotopic effect

A global potential energy surface for the F + H2O ↔ HF + OH reaction has been constructed using the neural networks method based on ~24,000 ab initio energies calculated...

A robust and tunable halogen bond organocatalyzed 2-deoxyglycosylation involving quantum tunneling

The development of noncovalent halogen bonding (XB) catalysis is rapidly gaining traction, as isolated reports documented better performance than the well-established hydrogen bonding thiourea catalysis. However, convincing cases allowing XB activation to be competitive in challenging bond formations are lacking. Herein, we report a robust XB catalyzed 2-deoxyglycosylation, featuring a biomimetic reaction network indicative of dynamic XB activation. Benchmarking studies uncovered an improved substrate tolerance compared to thiourea-catalyzed protocols. Kinetic investigations reveal an autoinductive sigmoidal kinetic profile, supporting an in situ amplification of a XB dependent active catalytic species. Kinetic isotopic effect measurements further support quantum tunneling in the rate determining step. Furthermore, we demonstrate XB catalysis tunability via a halogen swapping strategy, facilitating 2-deoxyribosylations of D-ribals. This protocol showcases the clear emergence of XB catalysis as a versatile activation mode in noncovalent organocatalysis, and as an important addition to the catalytic toolbox of chemical glycosylations.

Isotopic effect of macro- and microelements in ecosystems

Isotopic effects occurring in living organisms due to metabolism are analyzed. The phenomenon of metabolism is considered in the classical sense as a combination of biochemical reactions (mainly enzyma­tic) that take place in the cells of living beings and provide the cleavage, synthesis and interconversion of complex compounds. The scope of use of natural isotopes is wide and diverse. Isotopes are carriers of information about the birth and transformation of molecules, and isotope fractionation is a chemical characteristic of a substance. Isotope metabolism consists in the intermolecular fractionation of isotopes at separate stages of biochemical reactions, namely the cleavage, synthesis and interconversion of complex compounds caused by differences in the structure and fundamental properties of isotope nuclei. It is proved that the fractionation of isotopes in chemical and biochemical reactions due to isotopic effects is based on two fundamental properties of atomic nuclei — mass and magnetic moment. The kinetic (mass-depen­ dent) isotopic effect distributes the isotopic nuclei by their masses, and the magnetic one fractionates the nuclei by their magnetic moments. The kinetic isotopic effect depends on the magnitude of the difference in the masses of isotopic molecules, temperature and the difference in the activation energies of isotopic forms. The magnetic isotope effect depends on the reaction rate in a single cell, its projection, magnetic moment and energy of electron-nuclear interaction. It is determined that the fractionation of isotopes in living organisms is that the relative content of one of the isotopes in this compound increases by reducing its content in the other. As a result, there is a fractionation of isotopes within one biological object.

Role of stable hydrogen isotope variations in water for drug dissolution managing

In the present work, we provide the results of defining by utilizing Laser diffraction spectroscopy, the kinetic isotopic effect of solvent and constant of dissolution rate κ, s−1 of аn active pharmaceutical ingredient (API) in water with a different content of a stable _2^1{\rm{H}} isotope on the basis of the laws of first-order kinetics. This approach is based on the analysis of the light scattering profile that occurs when the particles of the dispersion phase in the aquatic environment are covered with a collimated laser beam. For the first time, the dependence of the rate of dissolution is demonstrated not only on the properties of the pharmaceutical substance itself (water solubility mg/ml, octanol–water partition coefficient log P oct/water, topological polar surface area, Abraham solvation parameters, the lattice type), but also on the properties of the solvent, depending on the content of stable hydrogen isotope. We show that the rate constant of dissolution of a sparingly hydrophobic substance moxifloxacin hydrochloride (MF · HCl) in the Mili-Q water is: k=1.20±0.14∙10−2 s−1 at 293.15 K, while in deuterium depleted water, it is k=4.24±0.4∙10−2 s−1. Consequently, we have established the development of the normal kinetic isotopic effect (kH/kD >1) of the solvent. This effect can be explained both by the positions of the difference in the vibrational energy of zero levels in the initial and transition states, and from the position of water clusters giving volumetric effects of salvation, depending on the ratio D/H. The study of kinetic isotopic effects is a method that gives an indication of the mechanism of reactions and the nature of the transition state. The effect of increasing the dissolution of the API, as a function of the D/H ratio, we have discovered, can be used in the chemical and pharmaceutical industries in the study of API properties and in the drug production through improvement in soluble and pharmacokinetic characteristics.

Cross Section Measurements of (n,p) Reactions on Ge Isotopes

The 72,73Ge(n,p)72,73Ga reaction cross sections were measured at the 5.5MV HV Tandem accelerator of NCSR “Demokritos”, at neutron energies 17.7 and 19.3 MeV by using the activation method. The contamination from the (n,d) and (n,np) reactions on 73Ge and 74 Ge, leading to the 72Ge and 73Ge residual nuclei, respectively, has been taken into account, implementing the corresponding cross sections from TENDL-2017. A systematic investigation of the isotopic effect on all Ge isotopes is also presented, from threshold up to 20MeV, using the present data along with existing data in literature