Heavy-Atom Tunneling in the Covalent/Dative Bond Complexation of Cyclo[18]carbon–piperidine

Recent quantum chemical computations demonstrated the electron-acceptance behavior of this highly reactive cyclo[18]carbon (C18) ring with piperidine (pip). The C18–pip complexation exhibited a double-well potential along the N–C reaction coordinate, forming a van der Waals (vdW) adduct and a more stable, strong covalent/dative bond (DB) complex by overcoming a low activation barrier. By means of direct dynamical computations using canonical variational transition state theory (CVT), including the small-curvature tunneling (SCT), we show the conspicuous role of heavy atom quantum mechanical tunneling (QMT) in the transformation of vdW to DB complex in the solvent phase near absolute zero. Below 50 K, the reaction is entirely driven by QMT, while at 30 K, the QMT rate is too rapid (kT ~ 0.02 s-1), corresponding to a half-life time of 38 s, indicating that the vdW adduct will have a fleeting existence. We also explored the QMT rates of other cyclo[n]carbon–pip systems. This study sheds light on the decisive role of QMT in the covalent/DB formation of the C18–pip complex at cryogenic temperatures.

Solution-phase decomposition of ferrocene into wüstite-iron oxide core-shell nanoparticles

We report an improved method for the controlled solvent-phase decomposition of ferrocene into highly crystalline monodisperse iron oxide nanoparticles at relatively low temperatures. Solution-phase decomposition of ferrocene into nanoparticles has...

OPTIMIZATION EXTRACTION OF COFFEINE AND THEOBROMINE FROM VARIOUS VARIETIES OF TEA WITH PLURONIC BLOCK COPOLYMER

Контроль содержания алкалоидов в пищевых продуктах и напитках в соответствии с нормируемыми показателями – актуальная задача для биотехнологии. Рассмотрена экстракция кофеина и теобромина из растительного сырья – чая черного и зеленого с использованием в качестве экстрагента блок-сополимера плюроник, представляющего собой чередующиеся фрагменты этиленоксида (20 мономерных звеньев) и пропиленоксида (70 мономерных звеньев). Экстракционные системы на основе водорастворимых полимеров отвечают всем требованиям «зеленой» экстракции и могут применяться в технологических процессах, связанных с контролем качества исходного сырья. Исследованы условия процесса извлечения пуриновых алкалоидов, установлены его оптимальные параметры: концентрация экстрагента 0,25 г/см3, температура процесса 95°С, степень измельчения для черного и зеленого чая 0,4 и 0,8 мм соответственно, соотношение водной и органической фаз 10 : 1 соответственно. По результатам экстракции рассчитаны коэффициенты распределения и степень извлечения кофеина и теобромина, которая составляет 95–99% в зависимости от сорта чая. Содержание кофеина и теобромина в фазе органического растворителя после экстракции определяли методом капиллярного электрофореза по электрофореграммам образцов черного и зеленого чая. На основании разработанной экстракционно-электрофоретической методики определения кофеина и теобромина в различных сортах чая предложен механизм взаимодействия пуриновых алкалоидов с экстрагентом плюроник. Наличие в цепи полимера концевых НО-групп, а также в основной цепи атомов кислорода способствует взаимодействию полимера с аналитами с образованием водородных связей. Представленные схемы образования Н-связей подтверждают эффективность применения блок-сополимера плюроник в качестве экстрагента пуриновых алкалоидов. Monitoring the content of alkaloids in food and beverages in accordance with the normalized indicators is an urgent task for biotechnology. The extraction of caffeine and theobromine from vegetable raw materials – black and green tea using the pluronic block copolymer as an extractant is considered. The pluronic block copolymer consists of alternating fragments of ethylene oxide (20 monomer units) and propylene oxide (70 monomer units). Extraction systems based on water-soluble polymers meet all the requirements of «green» extraction and can be used in technological processes related to quality control of feedstock. The conditions of the purine alkaloid extraction process have been investigated, its optimal parameters have been established: the extractant concentration is 0,25 g/cm3, the process temperature is 95°C, the degree of grinding for black and green tea is 0,4 and 0,8 mm respectively, the ratio of aqueous and organic phases is 10 : 1 respectively. According to the extraction results, the distribution coefficients and the degree of extraction of caffeine and theobromine, which is 95–99%, depending on the tea variety, are calculated. The content of caffeine and theobromine in the organic solvent phase after extraction was determined by capillary electrophoresis from electrophoregrams of black and green tea samples. The presence of terminal HO-groups in the polymer chain, as well as in the main chain of oxygen atoms, promotes the interaction of the polymer with analytes with the formation of hydrogen bonds. The presented schemes for the formation of H-bonds confirm the effectiveness of using the pluronic block copolymer as an extractant of purine alkaloids.

Polymer-Assisted Condensation: A Mechanism for Hetero-Chromatin Formation and Epigenetic Memory

We consider the formation of droplets from a 2-component liquid mixture induced by a large polymer chain that has preferential solubility with one of the components. We assume that the liquid mixture is in a fully miscible state, but far above the critical interaction limit of the two species. We show that the polymer coil acts as a chemical potential trap, which can shift the mixture inside the polymer volume into the partially miscible state and thus triggers the formation of a polymer-bound droplet of the preferred solvent phase which we denote as polymer-assisted condensation (PAC). We propose a simple mean-field model which can predict the essential feature of PAC and perform molecular-dynamics simulations to show that the predicted phase behavior is robust against fluctuation effects. Our model aims to understand the formation of macromolecular condensates inside the cell nucleus, such as those formed by heterochromatin 1 (HP1). We propose that such droplets organize the spatial structure of chromatin into hetero- and euchromatin and ensure the propagation of epigenetic information through the cell generations.

Role of heteroatoms and substituents on the structure, reactivity, aromaticity, and absorption spectra of pyrene: a density functional theory study

Effect of heteroatoms viz. BN and substituents viz. –Me (methyl), –OH (hydroxyl), –NH2 (amine), –COOH (carboxyl), and –CN (cyano) on the structural parameters, global reactivity, aromaticity, and UV-visible spectra of pyrene are studied with the help of density functional theory (DFT). Global reactivity parameters such as global hardness (η) and electrophilicity (ω) are calculated using density functional reactivity theory (DFRT). Time dependent density functional theory (TD-DFT) is explored for interpreting the UV-visible absorption spectra. Aromaticity of the pyrene rings are predicted from the nucleus independent chemical shift (NICS) values. Presence of BN unit and substituent induces reasonable impact on the studied parameters. The observed absorption spectra lie predominantly within the UV-region (both blue and red shifts are observed in presence of BN and substituent). HOMO energy and absorption spectra are affected nominally in solvent phase.

Titrimetric Study of Solubility of Solute Benzoic Acid and Their Partition in Water and Benzene Solvents

The solubility and distribution coefficient (K) of solute in solvent is depends on temperature and solute-solvent interaction, where the solute is partitioned between two immiscible solvents phase and dissociated into ionic form. Here, we have reported the titrimetric study for solubility and partition or distribution coefficient of benzoic acid (solute) in aqueous water and in organic benzene which are using as solvents. The benzoic acid solubility (in g/100g of solvent) in water and in benzene solutions have determined by titrimetrically. There is partitioning and concentration of such acid in these solvent phase by shake-flask and acid-base titration method as well. The benzoic acid solubility and their distribution between water and benzene as in different pH buffer solutions have been analyzed at room temperature (25°C) in acidic, neutral and basic (pH 4.0, 7.0 and 9.0) medium, respectively.