Cyclic Hydroxylamines as Monitors of Peroxynitrite and Superoxide-Revisited

There is a considerable need for methods that allow quantitative determination in vitro and in vivo of transient oxidative species such as peroxynitrite (ONOOH/ONOO–) and superoxide (HO2•/O2•−). Cyclic hydroxylamines, which upon oxidation yield their respective stable nitroxide radicals, have been suggested as spin probes of peroxynitrite and superoxide. The present study investigated this approach by following the kinetics of peroxynitrite decay in the absence and presence of various 5-membered and 6-membered ring hydroxylamines, and comparing the yield of their respective nitroxides using electron paramagnetic spectroscopy. The results demonstrate that hydroxylamines do not react directly with peroxynitrite, but are oxidized to their respective nitroxides by the radicals formed during peroxynitrite self-decomposition, namely •OH and •NO2. The accumulated nitroxides are far below their expected yield, had the hydroxylamines fully scavenged all these radicals, due to multiple competing reactions of the oxidized forms of the hydroxylamines with •NO2 and ONOO–. Therefore, cyclic hydroxylamines cannot be used for quantitative assay of peroxynitrite in vitro. The situation is even more complex in vivo where •OH and •NO2 are formed also via other oxidizing reactions systems. The present study also compared the yield of accumulated nitroxides under constant flux of superoxide in the presence of various cyclic hydroxylamines. It is demonstrated that certain 5-membered ring hydroxylamines, which their respective nitroxides are poor SOD-mimics, might be considered as stoichiometric monitors of superoxide in vitro at highest possible concentrations and pH.

Investigation of the relative reactivity of volatile organic compounds in the air plasma of a pulsed corona discharge by the method of competing reactions

A method for determining the relative reactivity of volatile organic compounds (VOCs) with respect to the air plasma of a pulsed corona discharge is proposed. It is based on the use of specially selected mixtures of organic compounds. The approach is based on the method of competing reactions: all components of the mixture are in equal conditions, so the relative reactivity can be determined with high accuracy using the gas chromatography. The parameters of scaling processes are proposed – plasma chemical yield, relative reactivity, formal reagent as a set of plasma components. In this paper, using the example of a number of VOCs, we demonstrate the extended capabilities of the method using a special technique for processing experimental data. More accurate data on the relative reactivity of a number of VOCs of wide application have been obtained. It is proposed to use the energy yield of ozone as a criterion for the energy efficiency of a plasma chemical installation.

PROPELLANS – PERSPECTIVE FRAME COMPOUNDS FOR THE CREATION OF HIGH-ENERGY SUBSTANCES

Важной задачей современной органической химии является открытие новых, ранее не известных науке веществ, которые могли бы расширить область наших знаний и пополнить номенклатуру высокоэнергетических или биологически активных продуктов. 3,7,10-Триоксо-2,4,6,8,9,11-гексааза[3.3.3|пропеллан и его нитропроизводные являются новейшими продуктами класса гетероциклов, их азотсодержащая полициклическая структура предполагает наличие интересных и полезных свойств, что обусловливает проявленный интерес к данной работе. Химия 3,7,10-триоксо-2,4,6,8,9,11-гексааза[3.3.3|пропеллана малоизучена и представлена лишь двумя алкилпроизводными и теоретическими расчетами энергетических характеристик нитропроизводных. В статье преставлены результаты исследования нитрования 3,7,10-триоксо-2,4,6,8,9,11-гексааза[3.3.3]пропеллана (THAP) концентрированнойазотной кислотой. Установлено, что в процессе нитрования наблюдается протекание двух конкурирующих реакций – лактам-лактимной перегруппировки и нитрования. Было показано, что продукты реакции сильно зависят от температуры реакционной массы. Установлено, что температуре -40 ºС протекает образование лактимной формы ТНАР, тогда как при постепенном увеличении температуры сначала образуется мононитропроизводное пропеллана, а при температуре 40 ºС идёт селективное образование 3,7,10-триоксо-2,6-динитро-2,4,6,8,9,11-гексааза[3.3.3]пропеллана с выходом 30%. An important task of modern organic chemistry is the discovery of new substances previously unknown to science, which could expand the area of our knowledge and replenish the range of high-energy or biologically active products. 3,7,10-Trioxo-2,4,6,8,9,11-hexaaza[3.3.3]propellane and its nitro derivatives are the newest products of the class of heterocycles; interest in this work. The chemistry of 3,7,10-trioxo-2,4,6,8,9,11-hexaaza[3.3.3]propellane is poorly understood and is represented by only two alkyl derivatives and theoretical calculations of the energy characteristics of nitro derivatives. The article presents the results of a study of the nitration of 3,7,10-trioxo-2,4,6,8,9,11-hexaaza[3.3.3]propellane (THAP) with concentrated nitric acid. It was found that in the process of nitration, there are two competing reactions - lactam-lactam rearrangement and nitration. It was shown that the reaction products strongly depend on the temperature of the reaction mixture. It was found that at a temperature of -40 ºС the formation of the lactimic form of THAP proceeds, whereas with a gradual increase in temperature, a mononitro derivative of propellane is first formed, and at a temperature of 40 ºС, the selective formation of 3,7,10-trioxo-2,6-dinitro-2,4,6,8,9,11-hexaaza[3.3.3]propellane in 30% yield.

Transforming Predictions into Testable Hypotheses: The Case of Polar Organic Reactivity

<p>Herbert Mayr’s research on reactivity scales tells a success story of how polar organic synthesis can be rationalized by a simple empirical relationship. In this work, we propose an extension to Mayr’s reactivity approach that is rooted in uncertainty quantification (UQ). It transforms the <i>unique</i> values of reactivity parameters (<i>s</i>_N, <i>N</i>, <i>E</i>) into value <i>distributions</i>. Through uncertainty propagation, these distributions can be exploited to quantify the uncertainty of bimolecular rate constants. Our UQ-based extension serves three purposes. First, predictions of polar organic reactivity can be transformed into testable hypotheses, which increases the overall reliability of the method and guides the exploration of new research directions. Second, it is also possible to quantify the discriminability of two competing reactions, which is particularly important if subtle reactivity differences matter. Third, since rate constant uncertainty can also be quantified for reactions that have yet to be observed, new opportunities arise for benchmarking computational chemistry methods (benchmarking <i>under uncertainty</i>). We demonstrate the functionality and performance of the UQ-extended reactivity approach at the example of the 2001/12 reference data set released by Mayr and co-workers [<i>J. Am. Chem. Soc.</i> <b>2001</b>, <i>123</i>, 9500; <i>J. Am. Chem. Soc.</i> <b>2012</b>, <i>134</i>, 13902]. As a by-product of the new approach, we obtain revised reactivity parameters for the electrophiles and the nucleophiles of the reference set.</p>

Transforming Predictions into Testable Hypotheses: The Case of Polar Organic Reactivity

<p>Herbert Mayr’s research on reactivity scales tells a success story of how polar organic synthesis can be rationalized by a simple empirical relationship. In this work, we propose an extension to Mayr’s reactivity approach that is rooted in uncertainty quantification (UQ). It transforms the <i>unique</i> values of reactivity parameters (<i>s</i>_N, <i>N</i>, <i>E</i>) into value <i>distributions</i>. Through uncertainty propagation, these distributions can be exploited to quantify the uncertainty of bimolecular rate constants. Our UQ-based extension serves three purposes. First, predictions of polar organic reactivity can be transformed into testable hypotheses, which increases the overall reliability of the method and guides the exploration of new research directions. Second, it is also possible to quantify the discriminability of two competing reactions, which is particularly important if subtle reactivity differences matter. Third, since rate constant uncertainty can also be quantified for reactions that have yet to be observed, new opportunities arise for benchmarking computational chemistry methods (benchmarking <i>under uncertainty</i>). We demonstrate the functionality and performance of the UQ-extended reactivity approach at the example of the 2001/12 reference data set released by Mayr and co-workers [<i>J. Am. Chem. Soc.</i> <b>2001</b>, <i>123</i>, 9500; <i>J. Am. Chem. Soc.</i> <b>2012</b>, <i>134</i>, 13902]. As a by-product of the new approach, we obtain revised reactivity parameters for the electrophiles and the nucleophiles of the reference set.</p>

Impact of environmental temperature on Covid-19 spread: Model and analysis of measurements recorded during the second pandemic in Cyprus

The paper investigates the effect of the environmental temperature on the spread of COVID-19. We study the daily numbers of the cases infected and deaths caused by Covid-19 during the second wave of the pandemic within 2020, and how they were affected by the daily average-high temperature for the districts of the Republic of Cyprus. Among the findings of the paper, we show that (i) the average ratio of the PCR to rapid positive tests is ∼2.57±0.25, as expected from the tests’ responses, indicating that PCR overestimates positivity by ∼2.5 times; (ii) the average age of deaths caused by Covid-19 increases with rate about a year of age per week; (iii) the probability of a person infected by Covid-19 to develop severe symptoms leading to death is strongly depended on the person’s age, while the probability of having a death on the age of ∼67 or younger is less than 1/1000; (iv) the number of infected cases and deaths declined dramatically when the environmental temperature reaches and/or climbs above the critical temperature ofTC=30.1±2.4 C0; (v) the observed negative correlation between the exponential growth rate of the infected cases and the environmental temperature can be described within the framework of chemical kinetics, with at least two competing reactions, the connection of the coronavirus towards the receptor and the dissolution of the coronavirus; the estimated activation energy difference corresponding to the competing chemical reactions, 0.212±0.25 eV, matches the known experimental value; and (vi) the infected cases will decline to zero, when the environmental temperature climbs above the critical temperature within the summery days of 2021, which is expected for the Republic of Cyprus by the 16thof May, 2021.

Исследование относительной реакционной способности ароматических соединений в воздухе под действием плазмы импульсного разряда

Based on the method of competing reactions, a method for determining the relative reactivity of aromatic vapors in relation to the plasma components of a pulsed corona discharge is developed. The parameters of the relative reactivity of aromatic compounds in the air and nitrogen stream were obtained using model mixtures based on benzene, toluene, and xylene with a content of 250-500 ppm. The effect of water vapor on the process is shown. The obtained data will be useful for optimizing the processes of plasma-chemical air purification from the vapors of toxic aromatic compounds.