The effect of the position of methyl substituents on photophysical and photochemical properties of [Ru(x,x'-dmb)(CN)4]2- complexes: experimental confirmation of the theoretical predictions

The molecular geometry, electronic structure and electronic spectra and the energy levels of the molecular orbitals responsible for the photophysical characteristics of a series of solvent tunable [Ru(x,x'-dmb)(CN)(4)](2-) complexes (where x,x'-dmb = x,x'-dimethyl-2,2'-bipyridine) were calculated by density-functional theory-based quantum chemical methods, with the purpose of proposing for experimental study the best candidate for sensitizing electron- and energy transfer processes or for light induced structural changes in the molecule. The methods applied include geometry optimization using the B3LYP functional combination and various basis sets, time-dependent density functional theory with the B3LYP and PBE0 functionals, with and without explicit inclusion of coordinated solvent H(2)O molecules and the conductor-like polarizable continuum model for solvation. The accuracy of the theoretical predictions was tested by experiments: the model compounds have been synthesized and characterized by various spectroscopic methods, such as (1)H-NMR, UV-Vis absorption and emission spectroscopy and by cyclic voltammetry. Excellent correlation was found between the theoretically calculated and the experimentally determined photophysical and photochemical characteristics. The electronic transition energies measured in water are superbly reproduced by TD-PBE0 and well by TD-B3LYP, but the performance of both functionals is worse if the solvent is acetonitrile.     

What does an ionic liquid surface really look like? Unprecedented details from molecular simulations

We present the first intrinsic analysis of the surface of the [bmim][PF(6)] room-temperature ionic liquid. Our detailed analysis reveals unprecedented details about the structure of the interface by providing the relative prevalence of different molecular orientations. These results suggest that experimental data should be reinterpreted considering a distribution of molecular arrangements.     

Role of chemical structure in stereoselective recognition of beta-blockers and H1-antihistamines by human serum transferrin in capillary zone electrophoresis

Studies on chiral resolution of beta-blocker and H1-antihistamine drugs by CZE using human serum transferrin are described. The drugs with different structures passed a pseudostationary protein zone in a coated capillary applying the partial filling method for the chiral separation. In this study we screened 15 compounds; most of them showed longer migration time, indicating an interaction with transferrin. Stereoselective interaction was observed only for five beta-blockers (celiprolol, talinolol, mepindolol, bopindolol, and oxprenolol) and for one H1-antihistamine (brompheniramine). The most important finding was that very small differences in the chemical structure of the drug resulted in significant changes in the stereoselective recognition. Resolution of mepindolol enantiomers was observed showing the essential role of one methyl group compared to pindolol, which is not resolved by transferrin. Bopindolol, also a derivative of pindolol having bigger difference in the structure, showed more experienced separation. The very slight difference between alprenolol and oxprenolol was also revealed with these methods, since only oxprenolol enantiomers, having an extra oxygen in the structure, are resolved. Determining the migration order of the eutomers and distomers (chlorpheniramine, brompheniramine) we can deduct conclusions about the role of serum proteins in the delivery of drugs within the body.     

Heterocyclische Verbindungen aus Zuckern,XV: Zur Konfiguration chiraler C-2-substituierter 4-Thiazolidincarbonsäuren. Chiralitätstransfer auf C-3 in 3,4-Dihydro-1H-pyrrolo[1,2-c]thiazolen

Summary 5-Substituted 3,4-dihydro-pyrrolo[1,2-c]thiazole-6,7-dicarboxylic acid esters3 are obtained from 2-substituted-3-acyl-1,3-thiazolidine-4-carboxylic acids,1 in [3+2]-cycloaddition reactions via mesoionic oxazolone (münchnone) intermediates. The chirality at C-4 of the starting carboxylic acids1 is eliminated in the products3, and the chirality at C-3 (C-2 in the starting carboxylic acids1) can thus be determined through chiroptical measurements. Several representatives of the ring system3 have been characterised through¹H- and CD-spectra and the molecular structure of (3S)-3da has been determined by X-ray crystallography.

     

Determination of <Superscript>237</Superscript>Np, <Superscript>93</Superscript>Zr and other long-lived radionuclides in medium and low level radioactive waste samples

The majority of long-lived radionuclides produced in the nuclear fuel cycle can be regarded as “difficult-to-measure” nuclides, hence chemical separation is needed before the nuclear measurement of them. A combined radiochemical procedure that enables the simultaneous determination of some “difficult-to-measure” nuclides in medium and low level radioactive wastes has been developed in our laboratory. Recently, this method has been extended for determination of ²³⁷Np and ⁹³Zr. ²³⁷Np and ⁹³Zr are pre-concentrated by co-precipitation on iron(II) hydroxide and zirconium oxide, separated by extraction chromatography using UTEVA, and measured by inductively coupled plasma mass spectrometry (ICP-MS). As even traces of polyatomic ions and isotopes at m/z 237 or 93 cause considerable interferences during ICP-MS detection, a purification step by extraction chromatography was needed. Analyzing real samples (evaporation concentrates of a nuclear power plant) 66–99% and 31–99% chemical yields were achieved for Np and Zr, respectively.     

Mössbauer study of the structure of liquid nanophases trapped in porous silicate and solid microemulsion matrix

Mössbauer spectra of liquid solutions fixed as submicroscopic (nanosize) droplets in solid carriers were taken at room temperature and 77 K. A porous silicate (“thirsty glass”) and microemulsions prepared with a paraffin/naphthalene mixture as dispersion medium served as carriers. Solutions of Mössbauer-active tin(IV) and iron(II) complexes were incorporated in these carriers as nanosize droplets. The Mössbauer effect was observed at temperatures above the freezing point of the solutions. For comparison, the systems were also studied in frozen state. Depending on the nature of the system (carrier-solute-solvent) the presence of three types of species was shown in the droplets on the basis of the Mössbauer parameters: (a) situated in bulk position with no interaction with the walls; (b) adsorbed on the internal surface of the holes in the carrier and (c) in bulk position, but with Mössbauer parameters reflecting the influence of the carrier. In some cases surface-bound and bulk species were present together in the sample. The appearance of the Mössbauer effect in liquid state reveals that the Mössbauer-active atoms are fixed in the nanosize pores by a network of hydrogen bonds which form between the solvent molecules, between solvent and solute molecules and between the solvent molecules and the walls of the pores in the carrier. The main parameters determining the rigidity of the network and the situation of the probe molecules are the hydrogen-bonding ability and the polarity of the components of the system. On the basis of the above observations, a new procedure was elaborated for the Mössbauer study of solutions fixed as nanosize droplets in rigid carriers. The analysis of the Mössbauer parameters gives a qualitative picture regarding the solution structure in the interior of the pores, and the adsorption and wetting properties of the system.     

Comparison between thermal analysis and mass spectroscopic studies of uranyl oxinates

The 5,7-dichloro, 5,7-dibromo, 5,7-diiodo and 5,6-dinitro derivatives of oxine (ligandsL ₁,–L ₄) were used to prepare uranyl chelates (A ₁–A ₄). Thermal analysis (DTA) and mass spectroscopic studies were performed. The stoichiometries of the chelates were determined by elemental analysis, molecular weight determination applying an -spectroscopic liquid scintillation counter and mass spectral measurements. The uranylligand ratios were found to be 11 for A₁, 13 for A₂, 12 (monohydrate) for A₃, and 12 forA ₄. The correlation between the thermal analysis and mass spectra was examined. The activation energy required for each step of thermal degradation of the ligands and chelates was calculated. The natures of most of the molecular ions obtained in the mass spectra were also explained.     

Anionic bulk oligomerization of ethylene and propylene carbonate initiated by bisphenol‐A/base systems

When the bulk oligomerization of 1,3‐dioxolan‐2‐one (ethylene carbonate, EC) and 4‐methyl‐1,3‐dioxolan‐2‐one (propylene carbonate, PC) with the 2,2‐bis(4‐hydroxyphenyl)propane (bisphenol‐A, BPA)/base system (bases such as KHCO₃, K₂CO₃, KOH, Li₂CO₃, and t‐BuOK) was investigated at elevated temperature, significant differences were observed. Oligomerization of EC initiated by BPA/base readily takes place, but the oligomerization of PC is inhibited. The very first propylene carbonate/propylene oxide unit readily forms a phenolic ether bond with the functional groups of BPA phenolate, but the addition of the second monomer unit is rather slow. The oligomerization of EC yields symmetrical oligo(ethylene oxide) side chains. According to IR studies the oligomeric chains formed from PC with BPA contain not only ether but also carbonate bonds. The in situ step oligomerization of the BPA dipropoxylate was also identified by SEC, and a possible reaction mechanism is proposed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 545–550, 1999     

Simultaneous GC-MS quantitation of acids and sugars in the hydrolyzates of immunostimulant, water-soluble polysaccharides of basidiomycetes

Summary The simultaneous quantitation of acids and sugars as their trimethyl silyl (TMS) derivatives has been extended in order to identify and quantitate the simple acid and sugar constituents in the hydrolyzates of various immunostimulant, water-soluble polysaccharides obtained from various Basidiomycetes, such as Armillariella mellea, Auricularia auricula-judae, Coriolus versicolor, Flammulina velutipes, Fomes fomentarius, Ganoderma applanatum, Ganoderma lucidum, Pleurotus ostreatus, Schizophyllum commune, Trametes hirsuta. Optimum hydrolysis conditions, performed with 2 M trifluoroacetic acid (TFAA) for five hrs, proved the presence of several sugars and acids with maximum recovery. (i) the total sugar/sugar alcohol content of polysaccharides varied between 20- and 65% and consisted of arabitol (0.01–10.2%), arabinose (0.09–1.3%), ribose (0.2–1.8%), fucose (0.3–1.2%), mannitol (0.01–5.3%), sorbitol (0.01–0.05%), galactiol (0.04%), fructose (0.08–0.8%), galactose (0.9–29%), glucose (10–53%), uronic acids (0.14–3.7%), sucrose (0.03–2%), trehalose (0.2–1%), cellobiose (0.01–0.6%), maltose (0.2–1.9%), other disaccharides (0.2–8%). (ii) The total of acids varied from 1.5 to 30% including o-phosphoric (1.3–19%), malic (0.08–4.7%), citric (0.08–4.7%), isocitric; (3%) and C₁₆−C₁₈ fatty acids (1–6%).     

Electron impact ionisation and UV absorption study of α- and β-pinene

We have performed a coordinated set of experiments to measure the electron impact ionisation and UV photoabsorption cross sections of α- and β-pinene. The adiabatic ionisation energies of α- and β-pinene were derived from experiment and found to be 8.3 and 8.6 eV which compared well with high-level quantum chemical calculations (G3MP2) yielding values of 8.29 and 8.41 eV. Additionally, vertical ionisation energies of 8.62 and 8.96 eV were calculated using an OVGF method. UV photoabsorption cross sections were measured using a high-resolution synchrotron radiation source and electronic states interpreted on the basis of the TD quantum chemical methods.