Theoretical study on the photooxygenation and photorearrangement reactions of 3-hydroxyflavone

The mechanisms of three photodegradation reactions of 3-hydroxyflavone – its photosensitized oxygenation, photooxygenation with 3O2 and photorearrangement into an indanedione derivative – have been investigated by computing the free energy profiles.</p

Spectroscopy of laser-induced carbon plasma with nanosecond time resolution

Emission spectra in the visible spectral range generated by a Nd:YAG laser shining on graphite targets were taken with time-averaging and time resolution. The analyses of the components and temperature of the plasma components were performed in helium environment using the LIBS (Laser Induced Breakdown Spectroscopy) technique. The vibration-rotation temperature of the C2 radical in the plasma initiates around 8000 K and drops exponentially with time. The rate coefficient of the exponential emission decay is 0.0018 ns-1. Thus, the expected lifetime of the C22 Swan emission under our experimental conditions is 555 ns. In addition to C22, singly and doubly ionized carbon, and in the first phase of the plasma, a continuum electron radiation was also observed

Amino acid recognition by fine tuning the association constants: Tailored naphthalimides in pillar[5]arene-based indicator displacement assays

Three aminonaphthalimide derivatives were synthesized bearing different anchoring groups in their 4-position in order to adjust the supramolecular interactions with carboxylato-pillar[5]arene (WP5), an anionic, water-soluble host. The modification of the anchor groups resulted in varying association constants embracing three orders of magnitude (Ka from ∼103 to ∼106) in buffered water. Since the fluorophore responded significantly to the electronic environment, large fluorescence quenching was observed with the anionic WP5 host. The naphthalimide indicator-WP5 supramolecular assemblies were used to detect arginine and lysine with complete selectivity over other non-basic α-amino acids by turn-on fluorescence. The same assemblies proved to be highly sensitive fluorescence displacement assays for the detection of cadaverin

Optical spectroscopic studies on the complexation of stilbazolium dyes with a water soluble pillar[5]arene

The host-guest interactions of a water soluble carboxylato-pillar[5]arene (WPA5) and three stilbazolium dyes (containing 9-anthryl, 1-pyrenyl and 4-dimethylaminophenyl groups) were studied by UV-Vis and fluorescence spectroscopy giving a detailed description of the spectral changes. A different spectroscopic response was observed in each case, with the most significant result of 28-fold fluorescence enhancement and intense color change in the case of 4-dimethylaminostyryl-N-methylpyridinium iodide (DAST, G3). In addition, a FID (fluorescence indicator displacement) system comprised of WPA5 and G3 was shown to detect paraquat by turn-off fluorescence in aqueous solution

CONCENTRATION-MODULATED ABSORPTION SPECTROSCOPY AND THE TRIPLET STATE: SATURATION EFFECTS IN LONG-LIVED TRIPLETS

The theory and technique of the pump and probe method of Concentration Modulated Absorption Spectroscopy (COMAS) has been extended to species with high triplet yields. In the experiments erythrosin B and rose bengal have been applied as model compounds. Using continuous wave laser sources and a modulated pump beam the large COMAS signal expected from the formation of long-lived triplets is shown to be dramatically reduced as a result of strong saturation effects. A gain expression is derived which takes into account such saturation effects and which describes satisfactorily the interaction of coinciding focused Gaussian pump and probe beams with the sample solution. Based on this theory, singlet and triplet concentration profiles in the focal region in the sample can also be evaluated. Such a treatment will be of value in modelling the refractive index gradients that arise from the differing molecular polarisabilities of singlet and triplet molecular species and from the energy conversion of electronic excitation to heat

Synthesis and recognition properties of α-d-glucose-based fluorescent crown ethers incorporating an acridine unit

Two new chiral glucopyranoside-based crown ethers incorporating acridine fluorescent signalling units, 15-membered ligand 1 and 21-membered ligand 2 were synthesized. Their complexation properties toward alkali and alkali earth metal ions, and their enantioselectivity towards chiral ammonium salts were studied by absorption and fluorescence spectroscopic experiments. Macrocycle 1 formed 1:1 complexes with all the metal ions selected and the stability constants were low (lg K < 2.3). The cavity-size of 2 allowed only the complexaton of organic ammonium ions. Crown 2 showed chiral discrimination in case of all the four ammonium salts used as model guest compounds; the highest enantioselectivity (K(R)/K(S) ~3) was observed for the enantiomers of phenylethyl ammonium perchlorate. Ligand 2 forms much more stable complexes with metal ions; the highest stability constant was obtained for the Ca2+ complex (lg K = 6.15). The coordination of metal ions by ligand 2 was accompanied by marked fluorescence enhancement, whereas the binding of ammonium ions by the same species resulted in significant fluorescence quenching. © 2014 Springer Science+Business Media Dordrecht

Nagy pontosságú modellek az elméleti kémiában és spektroszkópiai alkalmazások = High-accuracy models in theoretical chemistry and their applications to spectroscopy

A korábban kidolgozott nagy pontosságú kvantumkémiai módszerek számításigényének csökkentésével pontos kvantumkémiai modelleket fejlesztettünk ki, amelyek a korábbiaknál jóval nagyobb méretű molekulákra is alkalmazhatók. A számításigény mérséklését a módszerek egyenletiben szereplő numerikus paraméterek számának a csökkentésével valósítottuk meg ügyelve arra, hogy a módszerek pontossága ne romoljon. Jelentős lépéseket tettünk olyan kvantumkémiai módszerek kifejlesztésének irányába, amelyek helyesen írják a molekulákat egyensúlyi állapotuktól távol is. Korábban kidolgozott nagy pontosságú kvantumkémiai módszereinket relativisztikus közelítésekkel is kombináltuk, és így lehetővé vált a molekuláris tulajdonságok nagy pontosságú számítása nehezebb atomokból felépülő molekulákra is. Az elméleti modellek fejlesztése mellett ezeket a módszereket spektroszkópiai technikákkal kombinálva számos kémiai probléma megoldására is alkalmaztuk. | We have developed accurate quantum chemical approaches which are applicable to molecules significantly larger than before. This goal has been achieved through the reduction of the computational costs of high-precision quantum chemical calculations. The cost reduction has been accomplished by decreasing the number of numerical parameters to be optimized without sacrificing accuracy. A considerable amount of effort has been devoted to the development of quantum chemical models which behave correctly at distorted structures. Combining our previously developed high-accuracy models with relativistic approaches we have implemented a general-order relativistic electronic structure method, and thereby extended the applicability range of high-accuracy calculations to molecules containing heavier elements. Besides the development of theoretical models, we also applied these methods to real-life problems combined with spectroscopic techniques

Pillararene-based fluorescent indicator displacement assay for the selective recognition of ATP

The complexation of the cationic, water soluble ammonium pillar6arene was investigated with Dapoxyl sodium sulfonate. Large fluorescence enhancement was observed upon partial inclusion and the resulting complex was used as the first pillararene-based indicator displacement system for the selective recognition of adenosine-5'-triphosphate

Szupramolekuláris rendszerek fotofizikai és fotokémiai tulajdonságai = Photophisical and photochemical properties of supramolecular systems

Fotoaktív vegyületek (olyan anyagok, amelyek alkalmazása optikai tulajdonságain alapul) tulajdonságait tanulmányoztuk oldatfázisban és szupramolekuláris komplexekben, UV-látható abszorpciós, fluoreszcencia és CD spektroszkópiai mérésekkel, továbbá időfelbontásos lézerspektroszkópiai kísérletekkel. Az eredményeket több esetben kvantumkémiai számítások alapján értelmeztük. Kutatásaink eredményeként - új modellt állítottunk fel fluoreszkáló kationos festékek orientációs relaxációjára oldatban, - fluoreszcens próbaként alkalmazható vegyületek gerjesztett elektronállapotait vizsgálva tisztáztuk a dezaktíválódási folyamatok mechanizmusát, - jellemeztük fémionok optikai kimutatására szolgáló szupramolekuláris receptorok ionmegkötésének szelektivítását, és királis ligandumok megkötésére szolgáló szupramolekuláris receptorok enantioszelektivítását, - tanulmányoztuk kationos festékek megkötődését több kötéshelyű szupramolekuláris receptorokon, párhuzamos reakciókból álló reakció-modelleket állítottunk fel és kiszámítottuk az egyensúlyi állandókat, - meghatároztuk a fotodinamikus terápiában (PDT) potenciálisan hatóanyagként alkalmazható ftalocianinoknak a PDT-s hatás szempontjából érdekes fotofizikai/fotokémiai jellemzőit. | Photoactive compounds have been studied in solution and in supramolecular complexes by UV-VIS absorption, fluorescence and CD spectroscopy and by time-resolved laser spectroscopic experiments. The results have been interpreted with help of quantum chemical calculations. As results of the project - a new model has been created to describe the orientational relaxation of fluorescent cationic dyes, - the decay mechanism of the excited electronic states of some fluorescent probes has been clarified, - equilibrium constants characterizing the selectivity of new metal ion binding supramolecular receptors and the enantioselectivity of new chiral supramolecular receptors have been determined, - the binding of cationic dyes on supramolecular receptors with multiple binding sites has been studied, the results have been interpreted in terms of reaction models with simultaneous reactions, - the photophysical/photochemical characteristics of new phtalocyanines relevant of their application in photodynamic therapy, have been determined