324 research outputs found
Parahydrogen-induced polarization in H<sub>2</sub> activations and hydrogenations mediated by metal-free catalysts
No full textAbstractThe aim of this thesis is to study the metal-free activation of parahydrogen and the subsequent effects of parahydrogen-induced polarization (PHIP). PHIP is a nuclear spin hyperpolarization method that dramatically increases the sensitivity in NMR by enhancing signals in the spectrum. Typically, PHIP experiments involve catalysts based on metal complexes to activate parahydrogen. However, a recent discovery has shown that metal-free H2 activators can also lead to the spin hyperpolarization. At the same time, there were no reports about metal-free catalytic hydrogenations yielding in hyperpolarized products.The first part of the thesis focuses on metal-free hydrogenations of alkynes mediated by the ansa-aminoborane-based catalyst HCAT. In this research, we performed hydrogenations of various alkynes in a high magnetic field using parahydrogen. During these reactions, HCAT interacted with alkynes to form HCAT-alkyne adducts, which activated the parahydrogen molecules and resulted in the corresponding alkenes. Consequently, we observed enhanced signals of HCAT-alkyne-H2 intermediates, and most importantly, the alkene products. This represents the first example of PHIP effects on the hydrogenation products using a metal-free catalyst. Additionally, by applying PHIP, we studied and confirmed the proposed reaction mechanism.Next, we proceeded to further investigate metal-free hydrogenations utilizing parahydrogen. In the second paper, we examined hydrogenation of imines facilitated by the catalyst QCAT. These experiments resulted in enhanced signals in amine products. Additionally, we demonstrated the reversibility of a catalytic cycle, wherein the amines could interact with QCAT and parahydrogen, showcasing hyperpolarization of the NH group hydrogens. This study highlights the significance of PHIP experiments in providing valuable mechanistic insights into metal-free hydrogenations.Finally, we significantly expanded the range of biradicaloid-based metal-free parahydrogen activators. Namely, pnictogen biradicaloids represent another class of metal-free parahydrogen activators, following the ansa-aminoboranes, that exhibit PHIP effects. In our third paper, we employed four- and five-membered biradicaloids containing P or/and As radical centers. Significant findings were achieved with the four-membered As-P biradicaloid, which exhibited a high enhancement factor exceeding three orders of magnitude at 9.4 T, which is a particularly high level for metal-free systems. Furthermore, the reversibility of parahydrogen addition enabled the hyperpolarization of the biradicaloids themselves, thereby demonstrating the example of SABRE-like (Signal Amplification By Reversible Exchange) effect with metal-free catalytic systems.Original papersOriginal papers are not included in the electronic version of the dissertation.Zakharov, D. O., Chernichenko, K., Sorochkina, K., Yang, S., Telkki, V.-V., Repo, T., & Zhivonitko, V. V. (2022). Parahydrogen‐induced polarization in hydrogenation reactions mediated by a metal‐free catalyst. Chemistry – A European Journal, 28(8), e202103501. https://doi.org/10.1002/chem.202103501Self-archived versionZakharov, D. O., Chernichenko, K., Sorochkina, K., Repo, T., & Zhivonitko, V. V. (2022). Parahydrogen-induced polarization study of imine hydrogenations mediated by a metal-free catalyst. Dalton Transactions, 51(36), 13606–13611. https://doi.org/10.1039/D2DT02178ASelf-archived versionZhivonitko, V. V., Beer, H., Zakharov, D. O., Bresien, J., & Schulz, A. (2021). Hyperpolarization effects in parahydrogen activation with pnictogen biradicaloids: Metal‐free phip and sabre. ChemPhysChem, 22(9), 813–817. https://doi.org/10.1002/cphc.202100141Self-archived versionOsajulkaisutOsajulkaisut eivät sisälly väitöskirjan elektroniseen versioon.Zakharov, D. O., Chernichenko, K., Sorochkina, K., Yang, S., Telkki, V.-V., Repo, T., & Zhivonitko, V. V. (2022). Parahydrogen‐induced polarization in hydrogenation reactions mediated by a metal‐free catalyst. Chemistry – A European Journal, 28(8), e202103501. https://doi.org/10.1002/chem.202103501Rinnakkaistallennettu versioZakharov, D. O., Chernichenko, K., Sorochkina, K., Repo, T., & Zhivonitko, V. V. (2022). Parahydrogen-induced polarization study of imine hydrogenations mediated by a metal-free catalyst. Dalton Transactions, 51(36), 13606–13611. https://doi.org/10.1039/D2DT02178ARinnakkaistallennettu versioZhivonitko, V. V., Beer, H., Zakharov, D. O., Bresien, J., & Schulz, A. (2021). Hyperpolarization effects in parahydrogen activation with pnictogen biradicaloids: Metal‐free phip and sabre. ChemPhysChem, 22(9), 813–817. https://doi.org/10.1002/cphc.202100141Rinnakkaistallennettu versioAcademic dissertation to be presented with the assent of the Doctoral Training Committee of Technology and Natural Sciences of the University of Oulu for public discussion in the Auditorium IT115, Linnanmaa, on November 17th, 2023, at 12 o’clock noonAbstract
The aim of this thesis is to study the metal-free activation of parahydrogen and the subsequent effects of parahydrogen-induced polarization (PHIP). PHIP is a nuclear spin hyperpolarization method that dramatically increases the sensitivity in NMR by enhancing signals in the spectrum. Typically, PHIP experiments involve catalysts based on metal complexes to activate parahydrogen. However, a recent discovery has shown that metal-free H2 activators can also lead to the spin hyperpolarization. At the same time, there were no reports about metal-free catalytic hydrogenations yielding in hyperpolarized products.
The first part of the thesis focuses on metal-free hydrogenations of alkynes mediated by the ansa-aminoborane-based catalyst HCAT. In this research, we performed hydrogenations of various alkynes in a high magnetic field using parahydrogen. During these reactions, HCAT interacted with alkynes to form HCAT-alkyne adducts, which activated the parahydrogen molecules and resulted in the corresponding alkenes. Consequently, we observed enhanced signals of HCAT-alkyne-H2 intermediates, and most importantly, the alkene products. This represents the first example of PHIP effects on the hydrogenation products using a metal-free catalyst. Additionally, by applying PHIP, we studied and confirmed the proposed reaction mechanism.
Next, we proceeded to further investigate metal-free hydrogenations utilizing parahydrogen. In the second paper, we examined hydrogenation of imines facilitated by the catalyst QCAT. These experiments resulted in enhanced signals in amine products. Additionally, we demonstrated the reversibility of a catalytic cycle, wherein the amines could interact with QCAT and parahydrogen, showcasing hyperpolarization of the NH group hydrogens. This study highlights the significance of PHIP experiments in providing valuable mechanistic insights into metal-free hydrogenations.
Finally, we significantly expanded the range of biradicaloid-based metal-free parahydrogen activators. Namely, pnictogen biradicaloids represent another class of metal-free parahydrogen activators, following the ansa-aminoboranes, that exhibit PHIP effects. In our third paper, we employed four- and five-membered biradicaloids containing P or/and As radical centers. Significant findings were achieved with the four-membered As-P biradicaloid, which exhibited a high enhancement factor exceeding three orders of magnitude at 9.4 T, which is a particularly high level for metal-free systems. Furthermore, the reversibility of parahydrogen addition enabled the hyperpolarization of the biradicaloids themselves, thereby demonstrating the example of SABRE-like (Signal Amplification By Reversible Exchange) effect with metal-free catalytic systems
Characteristics and Analysis of Speech Development Disorders in Early Children
No full textСтаття присвячена характеристиці та аналізу порушень мовленнєвого розвитку у дітей раннього віку. У кожній країні є діти з важкими порушеннями мовлення, якi потребують особливих умов навчання та виховання. На сьогоднi дуже актуальними є питання надання кваліфікованої корекційно-розвиткової допомоги таким дiтям. Розлади мовленнєвого розвитку знаходяться на вивченні у багатьох спеціальностей. Мовленнєва функція є основною та ключовою для розвитку мислення та інтелекту дитини, тому порушення формування мовлення неминуче тягне за собою відставання у розвитку інтелекту, мислення, порушення спілкування та соціалізації, виникнення поведінкових порушень. Порушення мовленнєвого розвитку можуть бути спричинені різноманітними захворюваннями, які зустрічаються в загальній педіатричній практиці. Одними із таких причин можуть бути порушення артикуляційного апарату, хронічні отити, що призводять до порушення слуху, епілепсія та епілептичні енцефалопатії, ДЦП та багато інших захворювань. У статті висвітлено проблематику, що в даний час логопеди – практики відчувають недостатність розроблених ефективних методик щодо подолання мовленнєвих порушень у дітей раннього віку. У зв'язку з цим необхідно вивчати розлади експресивного та імпресивного мовлення, які охоплюють всі сфери особистості дитини. У спеціальній педагогіці йде активний пошук найбільш оптимальних форм організації освітнього та корекційного-розвиткового середовища для цієї категорії дітей. У огляді наукової літератури проведено аналіз даних, що стосуються розладів мовленнєвого розвитку дітей раннього віку. Автор аналізує особливості міжнародних та вітчизняних класифікацій порушень розвитку мовлення в ранньому віці, найбільш часто зустрічаються клінічні варіанти цієї патології. Паралельно розглядається етіологія затримок розвитку мовлення в залежності від їх захворювання.The article is devoted to the characteristics and analysis of disorders of speech development in young children. Every country has children with severe speech disorders who require special conditions for education and upbringing. Today, the issue of providing qualified correctional and developmental assistance to such children is very relevant. Disorders of speech development are studied in many specialties. The speech function is the main and key for the development of a child's thinking and intelligence, therefore, a violation of the formation of speech inevitably entails a delay in the development of intelligence, thinking, communication and socialization disorders, and the emergence of behavioral disorders. Disturbances in speech development can be caused by a variety of diseases that occur in general pediatric practice. One of these reasons can be disorders of the articulation apparatus, chronic otitis media leading to hearing impairment, epilepsy and epileptic encephalopathies, cerebral palsy and many other diseases. The article highlights the problem that currently speech therapists - practitioners feel the insufficiency of developed effective methods for overcoming speech disorders in young children. In this regard, it is necessary to study disorders of expressive and impressive speech, which cover all spheres of the child's personality. In special pedagogy, there is an active search for the most optimal forms of organizing an educational and corrective-developmental environment for this category of children. In the review of scientific literature, an analysis of data related to disorders of speech development of young children was carried out. The author analyzes the features of international and domestic classifications of speech disorders at an early age, the most common clinical variants of this pathology. At the same time, the etiology of speech development delays depending on their disease is considered
Experimental synthetic approach to segment assessment of aggregate credit risk
No full textMultifaceted, multifactor and multicomponent nature of credit risk makes it possible to consider it as an integral hypothetical unit which consists of the autonomous diverse segments specifying risky situations. As the given article is focused on the mechanism of loan fund circulation within foreign currency loan the author considers the combination of credit, interest rate, foreign exchange and inflation risks within the aggregate (total, combined) credit risk. Foreign exchange and inflation risks generate special interest in relation to evaluation procedures as there can be statutory regulation of interest rate risk and well-functioning mechanism of debt capacity analysis as the main factor of credit risk. As commercial loans and bank credits taken by Russian companies are wide spread the authors of the article suggest an innovative procedure of aggregate credit risk assessment considering agricultural companies, as well as companies belonging to chemical and machine-building industries as «pure borrowers» (debtors). The research has a set sequence of procedures. During the first stage the authors structured a risky situation in the lending process, determined specific constituents and performed their further strategic agreement. The second stage implies the analysis of the possibilities and specific characteristics of the preliminary segment assessment of the risk level. The third stage involves the development of experimental synthetic approach to the segment assessment of the aggregate credit risk in case of foreign exchange rate and interest rate volatility when there are inflation expectations. The procedure considers the following scenarios: 1) isolated assessment of inflation risk; 2) isolated assessment of exchange rate risk; 3) complex assessment of inflation and exchange rate risks
Replacing C6F5 groups with Cl and H atoms in frustrated Lewis pairs : H-2 additions and catalytic hydrogenations
No full text2-(Dialkylamino) phenylboranes containing the BXZ group, where X, Z = C6F5, Cl, and H, were prepared in a few synthetic steps and demonstrated the cleavage of H-2 under mild conditions. Depending on the nature of the dialkylamino group, X, and Z, the stability of the produced zwitterionic H-2 adducts varies from isolated solids indefinitely stable in an inert atmosphere to those quickly equilibrating with the initial aminoborane and H-2. Using a combined experimental/computational approach on a series of isostructural aminoboranes (dialkylamino = 2,2,6,6-tetramethylpiperid-1-yl), it was demonstrated that the electro-negativity and the steric effect of the substituents generally follow the trend C6F5 similar to Cl >> H. This observation is useful for designing new FLPs for practical applications. As an example, we demonstrated the hydrogenation of alkynes to cis-alkenes under mild conditions that was catalyzed by a chloro-analogue of the C6F5-substituted aminoborane developed previously. The presence of a BHCl group in the amino-chloroboranes or in their H-2 adducts features facile redistribution of the H and Cl atoms and the formation of polychloro and polyhydrido species.Peer reviewe
Recrystallized microstructures and mechanical properties of a C-containing CoCrFeNiMn-type high-entropy alloy
No full textThe effect of cold rolling to 80% thickness reduction and annealing at 973-1373 K for 1h our on the microstructure and mechanical properties of a C-containing CoCrFeNiMn high-entropy alloy was studied. Cold rolling significantly strengthened the alloy to the yield strength of 1310 MPa. Annealing at 973 K or 1073 K resulted in incomplete recrystallization of an fcc matrix and M23C6-type carbide precipitations aligned with highly elongated grains/subgrains. Complete recrystallization occurred during annealing at 1173-1373
Two Modifications Formed by “Sulflower” C<sub>16</sub>S<sub>8</sub> Molecules, Their Study by XRD and Optical Spectroscopy (Raman, IR, UV−Vis) Methods
No full textSublimation of sulflower, octathio[8]circulene C16S8 (1), on heating under high vacuum (∼10−5 Torr) leads to successive formation of two modifications: a white film (1W) and a red polycrystalline solid (1R). When kept at room temperature for several weeks, 1W spontaneously turns pink, reflecting the monotropic phase transition 1W → 1R. The accurate molecular and crystal structure of 1R has been studied using low-temperature (100 K) high-resolution single crystal X-ray analysis. The C16S8 molecule in crystal is strictly planar with nearly equalized bonds of each type (C−C, C−S, and CC). The point symmetry group of the free molecule is D8h, and the crystal space group is P21/n. These data allowed group-theoretical analysis of vibrational normal modes to be accomplished. Investigation of the charge density distribution of 1R including Bader’s AIM approach has revealed rather strong intermolecular S···S, S···C, and C···C interactions of charge transfer and π-stacking types with overall lattice energy of 28.5 kcal/mol. The charge transfer due to the S···S interactions is the reason for the red coloration of 1R. The latter is reflected by its UV−vis spectrum exhibiting absorption bands in the visible region which are absent from that of 1W. Both modifications were studied comparatively by vibrational (Raman, IR) and electronic spectroscopies as well as XRD powder diffraction. All the results obtained are fully consistent and show that 1W is much less ordered than 1R with significantly weakened intermolecular interactions. Rationalizing of these results has led to an idea that 1W could be soluble, in contrast to 1R. Indeed, 1W appeared soluble in common solvents; this finding opens the way to the study of the chemistry of 1 and investigation of its electrooptical properties
Kinetics of recrystallization and grain growth in an ultra-fine grained CoCrFeNiMn-type high-entropy alloy
No full textA novel high entropy alloy based on the CoCrFeMnNi system with substantial amounts of Al and C was studied. After cold rolling and annealing at 973-1273 K a duplex ultrafine grained structure composed of the recrystallized fcc grains and M23C6 and B2 particles was produced. Analysis of the coarsening behavior of grains and particles growth suggested that kinetics of both was controlled by volume diffusion. The apparent activation energy of structure coarsening during recrystallization was evaluate
Impact of heterocirculene molecular symmetry upon two-dimensional crystallization
No full textPeer reviewe
Measurement of Bottom Versus Charm as a Function of Transverse Momentum with Electron-Hadron Correlations in p plus p Collisions at s=200 GeV
No full textThe momentum distribution of electrons from semileptonic decays of charm and bottom quarks for midrapidity |y|< 0.35 in p+p collisions at s=200 GeV is measured by the PHENIX experiment at the Relativistic Heavy Ion Collider over the transverse momentum range 2 < p(T)< 7 GeV/c. The ratio of the yield of electrons from bottom to that from charm is presented. The ratio is determined using partial D/D -> e(+/-)K(-/+)X (K unidentified) reconstruction. It is found that the yield of electrons from bottom becomes significant above 4 GeV/c in p(T). A fixed-order-plus-next-to-leading-log perturbative quantum chromodynamics calculation agrees with the data within the theoretical and experimental uncertainties. The extracted total bottom production cross section at this energy is sigma(bb)=3.2(-1.1)(+1.2)(stat)(-1.3)(+1.4)(syst)mu b
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