Matrix-Isolation Study and Ab Initio Calculations of the Structure and Spectra of Hydroxyacetone

The structure of hydroxyacetone (HA) isolated in an argon matrix (at 12 K) and in a neat solid phase (at 12−175 K) was characterized by using infrared (IR) spectroscopy. The interpretation of the experimental results was supported by high-level quantum chemical calculations, undertaken by using both ab initio (MP2) and density functional theory methods. A potential-energy surface scan, carried out at the MP2/6-311++G(d,p) level of theory, predicted four nonequivalent minima, Cc, Tt, Tg, and Ct, all of them doubly degenerate by symmetry. The energy barriers for conversion between most of the symmetrically related structures and also between some of the nonequivalent minima (e.g., Tg → Tt and Ct → Tt) are very small and stay below the zero-point vibrational level associated with the isomerization coordinate in the higher-energy form in each pair. Therefore, only Cc and Tt conformers have physical significance, with populations of 99 and 1%, respectively, in gas phase at room temperature. For the matrix-isolated compound, only the most stable Cc conformer was observed. On the other hand, the polarizable continuum model calculations indicated that in water solution, the population of Tt and Ct conformers might be high enough (ca. 6 and 11%, respectively) to enable their experimental detection, thus supporting the conclusions of a previous IR spectroscopy study [Spectrochim. Acta A 2005, 61, 477] in which the presence of more than one HA conformer in aqueous solution was postulated. The signatures of these minor conformers, however, do not appear in the spectra of the neat HA crystal, and the crystal structure was rationalized in terms of centrosymmetric hydrogen-bonded dimers consisting of two Cc-like units. Finally, we calculated 1H, 13C, and 17O NMR chemical shifts at different levels of theory and found them to agree with available experimental data

IR-Induced Photoisomerization of Glycolic Acid Isolated in Low-Temperature Inert Matrices

Glycolic acid (HO−CH2−COOH) monomers isolated in low-temperature argon and krypton matrices were studied using FTIR spectroscopy. The most stable SSC conformer of the compound dominated in the matrices immediately after their deposition. Upon broadband infrared irradiation, two minor conformers (GAC and AAT) were photogenerated. No other forms of glycolic acid were populated, either thermally or photochemically. Systematic monitoring of the progress of the IR-induced phototransformations (over a time scale of 20−140 min) allowed one to distinguish between the primary (GAC) and secondary (AAT) photoproducts. The assignment of experimental spectra to the different conformers was based on the results of IR irradiation of the samples and was assisted by the theoretical calculations carried out at the MP2/aug-cc-pVDZ level. Theoretical pathways for intramolecular rotation in the glycolic acid monomer were investigated at the MP2/6-31++G(d,p) level. Lack of conformers other than SSC, GAC, and AAT in the IR-irradiated matrices was explained in terms of energy barriers separating different forms of the compound

Assessing the Health Impact of Disinfection Byproducts in Drinking Water

This study provides a comprehensive investigation of the impact of disinfection byproducts (DBPs) on human health, with a particular focus on DBPs present in chlorinated drinking water, concentrating on three primary DBP categories (aliphatic, alicyclic, and aromatic). Additionally, it explores pivotal factors influencing DBP formation, encompassing disinfectant types, water source characteristics, and environmental conditions, such as the presence of natural materials in water. The main objective is to discern the most hazardous DBPs, considering criteria such as regulation standards, potential health impacts, and chemical diversity. It provides a catalog of 63 key DBPs alongside their corresponding parameters. From this set, 28 compounds are meticulously chosen for in-depth analysis based on the above criteria. The findings strive to guide the advancement of water treatment technologies and intelligent sensory systems for the efficient water quality surveillance. This, in turn, enables reliable DBP detection within water distribution networks. By enriching the understanding of DBP-associated health hazards and offering valuable insights, this research is aimed to contribute to influencing policy-making in regulations and treatment strategies, thereby protecting public health and improving safety related to chlorinated drinking water quality

Thermal and Photoinduced Control of Relative Populations of 4-Methoxybenzaldehyde (p-Anisaldehyde) Conformers

Two almost isoenergetic conformers of 4-methoxybenzaldehyde (p-anisaldehyde), O-trans and O-cis, are nearly equally populated in gas phase at room temperature. The existence of these two conformers of similar energy makes p-anisaldehyde an attractive molecule for conformational investigations, in which the relative populations of the two forms might be subjected to optical control. In the present study, monomers of the compound were trapped from the room-temperature gas phase into cryogenic argon and xenon matrices. The initial relative amount of the two conformers present in the freshly deposited matrices is shifted slightly in favor of the O-trans conformer. The ratio of the two forms could be reversibly varied by irradiating the sample with UV light in different wavelength ranges or by using the temperature variation. Increasing the temperature of the xenon matrix up to ca. 57 K led to conversion of the less stable O-cis form into the O-trans conformer, shifting the O-cis/O-trans ratio to ca. 1:7. A series of UV irradiations with different long-pass cutoff filters was carried out. UV excitation induced transformation of O-cis and O-trans conformers into each other. These transformations were leading to the UV-wavelength-specific photostationary equilibria characterized by the O-cis/O-trans ratios of about 1:2.2, 1:1.4, 1:1.1, and 1:0.89 for λ > 328, 295, 288, and 234 nm cutoff filters, respectively. The isomerization processes were probed by infrared spectroscopy and supported by quantum chemical calculations. The absorption bands observed in the infrared spectra of p-anisaldehyde isolated in argon and xenon matrices were assigned to the theoretically predicted normal modes

Positive Identification of UV-Generated, Non-Hydrogen-Bonded Isomers of o-Hydroxybenzaldehyde and o-Hydroxyacetophenone

Non-hydrogen-bonded isomers were photogenerated by UV (λ > 335 nm) irradiation of o-hydroxybenzaldehyde (salicylaldehyde) and o-hydroxyacetophenone monomers isolated in low-temperature Ar matrixes. These photoisomerizations were found to be photoreversible. Upon shorter wavelength (λ > 235 nm or λ > 270 nm) UV irradiation, the initial forms of the compounds (with intramolecular hydrogen bonds) were partially repopulated. The structures of the photogenerated non-hydrogen-bonded isomers of both compounds were positively identified by comparison of their IR spectra with the spectra theoretically calculated [at the DFT(B3LYP)/6-311++G(2d,p) level] for all possible non-hydrogen-bonded isomers of the studied compounds. The experimental IR spectra of the photoproducts generated from o-hydroxybenzaldehyde and o-hydroxyacetophenone are very well reproduced only by the theoretical spectra predicted for the isomers with both OH and formyl (or acetyl) groups rotated by 180°, with respect to the initial, most stable hydrogen-bonded conformer. Excellent agreement between experiment and theoretical prediction provides a basis for a very reliable identification of the photoproduced isomers of o-hydroxybenzaldehyde and o-hydroxyacetophenone

Підсистема обробки вибірок даних активної та реактивної потужності трансформаторної підстанції

Purpose. Apply statistical analysis to the volumetric samples of electricity consumption parameters to reduce the amount of network node capacity that will be stored. Methodology. Using the statistical data methods processing in the graphical programming system LabVIEW. Findings. Electricity is one of the energy types, the generation volume, transportation, distribution and use of  which is constantly growing. At all these stages, the control of the change rate parameters of electrical energy – power occurs. Power is characterized by certain parameters that are subject to continuous monitoring. The change capacity in the conditions of industrial enterprises has a complex character with certain stochastic components. The need to record detailed information causes an increase in the data amount to be stored. As a result, there is a processing data problem on electric energy volumes and electric power parameters with reduction data volume and informativeness preservation. Based on the statistical normal distribution concept, in the graphical programming environment the data processing subsystem on sampling intervals of active and reactive powers of low voltage section the step-down substation is constructed. Using the indicators of the characteristics of the normal distribution of active and reactive power, the analysis of their semi-daily samples was performed. Selected intervals at which the indicators of normal distribution differ significantly, which allowed to form conclusions about the presence of modes close to idling Originality. It is established that due to the difficulty covering long time periods under the fixing condition data on electric power parameters, there is a dilemma regarding the resulting information amount and its detailing, to avoid information loss, a procedure based on the law of normal data sampling is the resulting data to be stored, with the possibility recording significant deviations in terms of excess and  sample asymmetry. Practical value. Applying the proposed method in the monitoring system for long-term monitoring electrical power parameters, it is possible to reduce significantly the amount of data during the transmission basic information, power level and range, and, if necessary, use additional information about changes in observation intervals expressed through excess and asymmetry.Цель работы. Применение статистического анализа на объемные выборки данных параметров потребления электрической энергии, для уменьшения объема данных о мощности узла сети, которые будут храниться. Методы исследования. Использование методов статистической обработки данных, в системе графического программирования LabVIEW. Полученные результаты. Электрическая энергия является одним из видов энергии объемы генерации, транспортировки, распределения и использования которой постоянно растут. На всех указанных этапах происходит контроль параметров скорости изменения электрической энергии - мощности. Мощность характеризуется определенными параметрами подлежащих непрерывном мониторинге. Изменение мощности в условиях промышленных предприятий имеет сложный характер с определенными стохастическими составляющими. Необходимость фиксации детальной информации вызывает рост объема данных, подлежащих хранению. Как следствие, возникает задача обработки данных об объемах электрической энергии и параметры электрической мощности с уменьшением объема данных и сохранением информативности. Основываясь на статистической концепции нормального распределения, в среде графического программирования построено подсистему обработки данных на интервалах выборки активной и реактивной мощностей секции низкого напряжения понижающей пидстанции.З использованием показателей характеристики нормального распределения активной и реактивной мощностей, выполнен анализ их Полусуточная выборок. Выделенные интервалы, на которых существенно различаются показатели нормального распределения, что позволило сформировать выводы о наличии режимов, приближенных к холостого хода. Научна новизна. Установлено, что из-за сложности охвата больших промежутков времени при фиксации данных о параметрах электрической мощности, возникает дилемма относительно объема результирующей информации и ее детализации, во избежание потерь информации предложена процедура, основанная на законе нормального распределения выборки данных, и в длительных процессах снижает объем результирующих данных, подлежащих хранению, с возможностью фиксации существенных отклонений по показателям эксцесса и асимметрии соответствующей выборки. Практическая ценность. Применяя в системе мониторинга при долгосрочном наблюдении за параметрами электрической мощности предложенный метод может значительно уменьшить количество данных при передаче основной информации, уровня мощности и диапазона колебаний, а также, при необходимости, использовать дополнительную информацию об изменениях в интервалах наблюдения, выраженные через эксцесс и асимметрию.Мета роботи. Застосування статистичного аналізу на об’ємні вибірки даних параметрів споживання електричної енергії, для зменшення обсягу даних про потужності вузла мережі, які зберігатимуться. Методи дослідження. Використання методів статистичної обробки даних, в системі графічного програмування LabVIEW. Отримані результати. Електрична енергія є одним з видів енергії обсяги генерування, транспортування, розподілу та використання якої постійно зростають. На всіх зазначених етапах відбувається контроль параметрів швидкості зміни електричної енергії – потужності. Потужність характеризується певними параметрами що підлягають безперервному моніторингу. Зміна потужності в умовах промислових підприємств має складний характер з певними стохастичними складовими. Необхідність фіксації детальної інформації викликає зростання обсягу даних, які підлягають зберіганню. Як наслідок, виникає завдання обробки даних про обсяги електричної енергії та параметри електричної потужності зі зменшенням обсягу даних та збереженням інформативності. Ґрунтуючись на статистичній концепції нормального розподілу, в середовищі графічного програмування побудовано підсистему обробки даних на інтервалах вибірки активної та реактивної потужностей секції низької напруги знижуючої підстанції. З використанням показників характеристики нормального розподілу активної та реактивної потужностей, виконано аналіз їх напівдобових вибірок. Виділені інтервали на яких суттєво розрізняються показники нормального розподілу, що дозволило сформувати висновки про наявність режимів наближених до холостого ходу. Наукова новизна. Встановлено, що через складність охоплення великих проміжків часу за умови фіксації даних про параметри електричної потужності, виникає дилема щодо обсягу результуючої інформації та її деталізації, для уникнення втрат інформації запропоновано процедуру, що базується на законі нормального розподілу вибірки даних, та в тривалих процесах знижує обсяг результуючих даних, які підлягають зберіганню, з можливістю фіксації суттєвих відхилень за показниками ексцесу та асиметрії відповідної вибірки. Практична цінність. Застосовуючи в системі моніторингу при довгостроковому спостереженні за параметрами електричної потужності запропонований метод можливо значно зменшити кількість даних під час передачі основної інформації, рівня потужності та діапазону коливань, а також, за необхідності, використати додаткову інформацію про зміни в інтервалах спостереження, виражені через ексцес та асиметрію

Photoinduced transformation of matrix-isolated methyl 2-pyrone-3-carboxylate into methyl 2-pyrone-5-carboxylate via intramolecular hydrogen shift in open-ring aldehyde-ketene

Abstract Photochemical transformations of methyl 2-pyrone-3-carboxylate (mp3c) were studied by matrix-isolation technique. The dominating primary photoreaction induced by UV (k > 295 nm) light was a-bond cleavage leading to open-ring aldehyde-ketene. Another reaction characteristic of a-pyrones, isomerisation to the Dewar form, did not occur for mp3c. The ring-opening photoreaction was followed by intramolecular hydrogen shift and subsequent ring-closure reaction converting the aldehyde-ketene into methyl 2-pyrone-5-carboxylate (mp5c). Upon prolonged UV irradiation, mp3c completely transformed into mp5c and its Dewar isomer Dmp5c. Unequivocal identification of mp5c and Dmp5c photoproducts was enabled by exact knowledge of their experimental IR spectra, recorded in separate experiments

Minerals of Rare Earth Elements in High-Phosphorus Ooidal Ironstones of the Western Siberia and Turgai Depression

The aim of this research was to study the rare earth (REE) minerals in ooidal ironstone deposits of the West Siberian basin and the Turgai depression. Authigenic minerals (monazite and cerite) were described, and their main mineral form was identified as light rare earth element phosphate (LREE-phosphate) in this study. LREE-phosphate is included in ferruginous ooids, peloids, and oncoids and forms a consistent mineral association with Fe-hydroxides (goethite and its hydrated amorphous derivatives) and Fe-rich layered silicates (Fe-illite-smectite, chamosite, berthierine). The constancy of the mineral association in two deposits of different ages indicates a general mechanism behind the formation of these minerals. LREE-phosphates (authigenic monazite) are characterized by microscopic sizes (up to 24 ?m), diverse morphology (mainly spherical or xenomorphic), and occupy spaces between the micro-cortex in ferruginous spheroids. This mineral can be found in other deposits of ooidal ironstone. According to its mineralogical and chemical characteristics, LREE-phosphate mainly belongs to the authigenic (nodular or “gray”) monazite. However, the incomplete (not 100%) correspondence of Kikuchi bands with the reference monazite does not allow its reliable identification. Based on its small size, chemical leaching or bacterial interaction is recommended to extract REE from ooidal ironstone while predicting the associated removal of phosphorus from iron ore due to its dominant phosphate mineral form. Ooidal ironstone should be considered a complex deposit and an unconventional natural type of REE ores as an example of the largest Bakchar and Lisakovsk deposits

Sigmatropic rearrangements in 5-allyloxytetrazoles

Mechanisms of thermal isomerization of allyl tetrazolyl ethers derived from the carbocyclic allylic alcohols cyclohex-2-enol and 3-methylcyclohex-2-enol and from the natural terpene alcohol nerol were investigated. In the process of the syntheses of the three 1-aryl-5-allyloxytetrazoles, their rapid isomerization to the corresponding 1-aryl-4-allyltetrazol-5-ones occurred. The experiments showed that the imidates rearrange exclusively through a [3,3¢]-sigmatropic migration of the allylic system from O to N, with inversion. Mechanistic proposals are based on product analysis and extensive quantum chemical calculations at the DFT(B3LYP) and MP2 levels, on O-allyl and N-allyl isomers and on putative transition state structures for [1,3¢]- and [3,3¢]-sigmatropic migrations. The experimental observations could be only explained on the basis of the MP2/6-31G(d,p) calculations that favoured the [3,3¢]-sigmatropic migrations, yielding lower energies both for the transition states and for the final isomerization products

Photoisomerization and Photochemistry of Matrix-Isolated 3-Furaldehyde

3-Furaldehyde (3FA) was isolated in an argon matrix at 12 K and studied using FTIR spectroscopy and quantum chemistry. The molecule has two conformers, with trans and cis orientation of the O═C—C═C dihedral angle. At the B3LYP/6-311++G(d,p) level of theory, the trans form was computed to be ca. 4 kJ mol−1 more stable than the cis form. The relative stability of the two conformers was explained using the natural bond orbital (NBO) method. In fair agreement with their calculated relative energies and the high barrier of rotamerization (ca. 34 kJ mol−1 from trans to cis), the trans and cis conformers were trapped in an argon matrix from the compound room temperature gas phase in proportion 7:1. The experimentally observed vibrational signatures of the two forms are in a good agreement with the theoretically calculated spectra. Broad-band UV-irradiation (λ > 234 nm) of the matrix-isolated compound resulted in partial trans → cis isomerization, which ended at a photostationary state with the trans/cis ratio being ca. 1.85:1. This result was interpreted based on results of time-dependent DFT calculations. Irradiation at higher energies (λ > 200 nm) led to decarbonylation of the compound, yielding furan, cyclopropene-3-carbaldehyde, and two C3H4 isomers: cyclopropene and propadiene