A frustrated-Lewis-pair approach to catalytic reduction of alkynes to cis-alkenes

Frustrated Lewis pairs are compounds containing both Lewis acidic and Lewis basic moieties, where the formation of an adduct is prevented by steric hindrance. They are therefore highly reactive, and have been shown to be capable of heterolysis of molecular hydrogen, a property that has led to their use in hydrogenation reactions of polarized multiple bonds. Here, we describe a general approach to the hydrogenation of alkynes to cis-alkenes under mild conditions using the unique ansa-aminohydroborane as a catalyst. Our approach combines several reactions as the elementary steps of the catalytic cycle: hydroboration (substrate binding), heterolytic hydrogen splitting (typical frustrated-Lewis-pair reactivity) and facile intramolecular protodeborylation (product release). The mechanism is verified by experimental and computational studies

Kvantum molekuladinamikai szimulációk: elmélet és alkalmazások az elektrontranszfer folyamatok vizsgálatára = Quantum Molecular Dynamics Modelling: Theory and Applications to Electron-Transfer Processes

Kutatásunk során kondenzált fázisú kémiai reakciók és relaxációs folyamatok alapvető összefüggéseit tanulmányoztuk egyszerű modellek kevert kvantumos klasszikus molekuladinamikai szimulációjával. A szimulációk alkalmazása mellett a kevert kvantumos klasszikus módszer elemzésével és fejlesztésével is foglalkoztunk. Pszeudopotenciál elméleti analízist hajtottunk végre az elektron-vízmolekula potenciálon, melynek során a hidratált elektron hagyományos üreg-modelljét megkérdőjelező modellek komoly hiányosságaira mutattunk rá. Hasonló érvelés alkalmazása segítségével kidolgoztunk egy új elektron-metanol molekula potenciált is. Negatívan töltött víz és metanol molekulafürtök tulajdonságainak vizsgálata során elemeztük a legfontosabb kölcsönhatásokat, konfigurációkat, és a rendszerek egyensúlyi és nem-egyensúlyi dinamikai viselkedését. Az alapállapot elemzésén túlmenően a molekulafürt negatív töltését adó felesleg elektron gerjesztését, majd az alapállapotba történő relaxáció mechanizmusát és sebességét is megvizsgáltuk. Szimulációs eredményeink a kísérleti mérésekkel kiváló összhangban állnak és a kísérletek egy teljesen új interpretációját teszik lehetővé. Kutatásunk során lehetőségünk nyílt a hidratált elektronnal kapcsolatos elméleti eredményeket összefoglaló tanulmányok megírására is mind angol, mind magyar nyelven. | We investigated the basic physical properties of simple systems modeling condensed phase chemical reactions and relaxation processes by the application of mixed quantum-classical molecular dynamics simulations. Besides performing simulations we also examined the methodology and improved important ingredients of the mixed quantum classical simulation technique. Pseudopotential theory based theoretical analysis of the electron-water molecule potential lead us to conclude that pseudopotentials questioning the traditional cavity model of the hydrated electron suffer from serious deficiencies. Based on similar arguments we developed a new electron-methanol molecule potential. We examined the physical properties of negatively charged water and methanol clusters starting from their most important interactions and configurations to their equilibrium and non-equilibrium dynamical behavior. In addition to analyzing the ground state properties, we simulated the excitation of an excess electron in water and methanol cluster anions, and examined the mechanism and calculated the rate of the electronic relaxation back to the ground state. The simulation results are in excellent agreement with experimental measurements, but at the same time offer a completely different interpretation of the data. In the research period we also had the opportunity to review the theoretical results on the hydrated electron subject both in Hungarian and English

Interior- and Surface-Bound Excess Electron States in Large Water Cluster Anions

We present the results of mixed quantum/classical simulations on relaxed thermal nanoscale water cluster anions,(H_2O)^-_n, with n=200, 500, 1000 and 8000. By using initial equilibration with constraints, we investigate stable/metastable negatively charged water clusters with both surface-bound and interior-bound excess electron states. Characterization of these states is performed in terms of geometrical parameters, energetics, and optical absorption spectroscopy of the clusters. The calculations provide data characterizing these states in the gap between previously published calculations, and experiments, on smaller clusters and the limiting cases of either an excess electron in bulk water, or an excess electron at an infinite water/air interface. The present results are in general agreement with previous simulations and provide a consistent picture of the evolution of the physical properties of water cluster anions with size over the entire size range, including results for vertical detachment energies and absorption spectra that would signify their presence. In particular, the difference in size dependence between surface-bound and interior-bound state absorption spectra is dramatic, while for detachment energies the dependence is qualitatively the same

Excess Electron Relaxation Dynamics at Water/Air Interfaces

We have performed mixed quantum-classical molecular dynamics simulations of the relaxation of a ground state excess electron at interfaces of different phases of water with air. The investigated systems included ambient water/air, supercooled water/air, Ih ice/air and an amorphous solid water/air interfaces. The present work explores the possible connections of the examined interfacial systems to finite size cluster anions, and the three-dimensional infinite, fully hydrated electron. Localization site analyses indicate that in the absence of nuclear relaxation the electron localizes in a shallow potential trap on the interface in all examined systems in a diffuse, surface-bound (SB) state. With relaxation, the weakly bound electron undergoes an ultrafast localization and stabilization on the surface with the concomitant collapse of its radius. In the case of the ambient liquid interface the electron slowly (on the 10 ps timescale) diffuses into the bulk to form an interior-bound (IB) state. In each other case, the excess electron persists on the interface in surface-bound (SB) states. The relaxation dynamics occur through distinct SB structures which are easily distinguishable by their energetics, geometries, and interactions with the surrounding water bath. The systems exhibiting the most stable SB excess electron states (supercooled water/air and Ih ice/air interfaces) are identified by their characteristic hydrogen-bonding motifs which are found to contain double acceptor type water molecules in the close vicinity of the electron. These surface states correlate reasonably with those extrapolated to infinite size from simulated water cluster anions

Excess Electron Localization Sites in Neutral Water Clusters

We present approximate pseudopotential quantum mechanical calculations of the excess electron states of equilibrated neutral water clusters sampled by classical molecular dynamics simulations. The internal energy of the clusters are representative of those present at temperatures of 200 K and 300 K. Correlated electronic structure calculations are used to validate the pseudopotential for this purpose. We find that the neutral clusters support localized, bound excess electron ground states in about 50 % of the configurations for the smallest cluster size studied (n=20), and in almost all configurations for larger clusters (n>66). The state is always exterior to the molecular frame, forming typically a diffuse surface state. Both cluster size and temperature dependence of energetic and structural properties of the clusters and the electron distribution are explored. We show that the stabilization of the electron is strongly correlated with the pre-existing instantaneous dipole moment of the neutral clusters, and its ground state energy is reflected in the electronic radius. The findings are consistent with electron attachment via an initial surface state. The hypothetical spectral dynamics following such attachment is also discussed

Az árkos erózió szerepe Magyarország jelenkori felszínfejlődésében = The role of gully erosion in the present-day relief development of Hungary

A kutatás célja egy országos vízmosás kataszter, adatbázis készítése és kiértékelése, valamint az árkos erózió folyamatainak mintaterületi vizsgálata volt. Az 1:10 000 méretarányú térképek felhasználásával elkészült az ország vízmosás sűrűség térképe. A kataszterben közel 112.000 vízmosás szerepel, amelyek teljes hossza 22.000 km. A kataszter alapján veszélyeztetettségi térkép készült, eszerint az ország területének közel 5%-a tartozik az erősen veszélyeztetett kategóriába. Az országos és a mintaterületi vizsgálatok az árkos eróziót befolyásoló tényezők sokoldalú szerepét tárták fel. E tényezők hatása együttesen érvényesül. A földhasználat szerepe is sokarcú. Megállapítottuk, hogy a vízmosások nem elsősorban a legmeredekebb lejtőkön, nem a hegységek központi régióiban alakulnak ki, mivel e területeket jórészt erdő borítja. Érdekes ugyanakkor, hogy a vízmosások többsége erdőben található. Ez nem jelenti azt, hogy ott is alakult ki. A szántóföldön kialakult vízmosásokat vagy elegyelgetik, vagy ha ez már nem lehetséges ezek idővel beerdősödnek. A szántóföldi időszakos vízmosások nem szerepelnek a felhasznált topográfiai térképeken, ezeken csak a nagyobb, állandó vízmosások vannak feltüntetve. Megállapítottuk, hogy a vízmosások kialakulását a földhasználat mellett főként a domborzat és a talajképző kőzet befolyásolja, a talajtulajdonságok szerepe kevésbé fontos. A mintaterületi vizsgálatok a fenti megállapításokat árnyalják. | The objective of the project was the preparation and analysis of a national gully cadastre and database as well as the investigation of gully erosion processes in sample areas. 1:10 000 topographic maps were used for the compilation of the gully density map of Hungary containing 112 000 gullies with a total length of 22 000 km. A gully erosion risk map was also prepared and according to it high risk is present on nearly 5 % of the country area. The manifold role of the factors controlling gully erosion was revealed by the nationwide and the sample area investigations. These factors have a combined effect on gully development. Even the role of land use is multifaceted. It was established that in most cases gullies do not develop on the steepest slopes, i.e. in the central parts of the mountains because these areas are covered by forest. It is interesting, however, that most gullies can be found in the forest. It doesn’t mean that they were formed in the forest. Gullies on arable land will usually be levelled or if it is not possible any more, they will be forested after a time. Ephemeral gullies on arable land are not illustrated on topographic maps, only large and stable gullies are represented on them. It was established that gully formation beside land use the formation of gullies is controlled by relief and parent rock conditions and the role of soil characteristics is less important. Investigations in sample areas revealed the nuances of the above statements