Molecular and crystal structure of bis-quinolizidine immonium salts,III: Δ1(6)-dehydrosparteinium diperchlorate

¹⁽⁶⁾-Dehydrosparteinium diperchlorate, [C₁₅H₂₆N₂]²⁺·2ClO ₄ ^– , is tetragonal; space groupP4₃,a=9.368(1),c=21.719(3) Å,Z=4,V _c =1906.1(5) ų,D _x =1.51g cm^–3,(CuK)=35.0 cm^–1. The finalR=0.055 for 1259 independent reflections. Atoms C(3) and C(4), which are trans-annular to the immonium bond in ringA, are disordered, as was observed for other bis-quinolizidine immonium salts. RingsB, C, andD have sofa, chair and chair conformations, respectively. The quinolizidinium and quinolizidine moieties have planar and cis configurations. The title compound was obtained by mercuric acetate dehydrogenation of sparteine to ⁵-dehydrosparteine and protonation of the latter with methanolic solution of perchloric acid to pH=2.0. From¹³C NMR measurements in DMSO-²H₆ and in²H₂O it is evident that in solution the chair/chair cis-ring fusion is present within the protonated quinolizidine moiety-identical to that found in the crystalline state by X-ray analysis.     

Spectroscopic Investigation of the Electronic Structure of YN: The XΣ Ground State and the New B1, C1 and D1 Excited Electronic States

YN molecules were produced in a free jet molecular beam apparatus by a laser vaporizing yttrium metal in the presence of He doped with NH₃. Laser excitation spectra were observed in the range 18 250-19 850 cm⁻¹. The ground state was confirmed to have ¹Σ⁺ symmetry. The fundamental vibration in the ground state was measured to be 650.6(1) cm⁻¹. Three new electronic states, B1, C1, and D1, were observed at 18 974.7(1), 19 023.3(1), and 19 824.0(1) cm⁻¹, respectively. The fundamental vibrations and equilibrium internuclear distances were found to be 718.3(1) cm⁻¹ and 1.939(8) for the B1 state and 723.5(1) cm⁻¹ and 1.9194(3) for the C1 state. Two additional electronic states were identified with the help of a deperturbation procedure, one of which is either the ¹Σ⁺ or the ³Σ₀⁻ state. The newly observed electronic states cannot be accounted for based on the existing ab initio results. We expect that these states correlate with the excited asymptote Y(4d¹5s²²D)+N(²D).     

Surface-plasmon-coupled emission of quantum dots

We studied surface plasmon-coupled emission (SPCE) of semiconductor quantum dots (QDs). These QDs are water-soluble ZnS-capped CdSe nanoparticles stabilized using lysine cross-linked mercaptoundecanoic acid. The QDs were spin-coated from 0.75% PVA solution on a glass slide covered with 50 nm of silver and a 5-nm protective SiO(2) layer. Excited QDs induced surface plasmons in a thin silver layer. Surface plasmons emitted a hollow cone of radiation into an attached hemispherical glass prism at a narrow angle of 48.5 degrees. This directional radiation (SPCE) preserves the spectral properties of QD emission and is highly p-polarized irrespective of the excitation polarization. The SPCE spectrum depends on the observation angle because of the intrinsic dispersive properties of SPCE phenomenon. The remarkable photostability can make QDs superior to organic fluorophores when long exposure to the intense excitation is needed. The nanosize QDs also introduce a roughness near the metal layer, which results in a many-fold increase of the coupling of the incident light to the surface plasmons. This scattered incident illumination transformed into directional, polarized radiation can be used simultaneously with SPCE to develop devices based on both quantum dot emission and light scattered from surface plasmons on a rough surface.     

SITE-TO-SITE DIFFUSION IN PROTEINS AS OBSERVED BY ENERGY TRANSFER AND FREQUENCY-DOMAIN FLUOROMETRY *

Abstract We report measurements of the site-to-site diffusion coefficients in proteins and model compounds, which were measured using time-dependent energy transfer and frequency-domain fluorometry. The possibility of measuring these diffusion coefficients were shown from simulations, which demonstrate that donor (D)-to-acceptor (A) diffusion alters the donor frequency response, and that this effect is observable in the presence of a distribution of donor-to-acceptor distances. For decay times typical of tryptophan fluorescence, the simulations indicate that D-A diffusion coefficients can be measured ranging from ^?7 to ^?5 cm²/s. This possibility was verified by studies of a methylenechain linked D-A pair in solutions of varying viscosity. The D-A diffusion was also measured for two labeled peptides and two proteins, melittin and troponin I. In most cases we used global analysis of data sets obtained with varying amounts of collisional quenchers to vary the donor decay time. Unfolding of troponin I results in more rapid D-A diffusion, whereas for melittin more rapid diffusion was observed in the α-helical state but over a limited range of distances.     

Interference of surface plasmon resonances causes enhanced depolarized light scattering from metal nanoparticles

We show that the strongly depolarized light scattering from noble metal particles is a result of interference of two surface plasmon resonances on the same particle. The maximum depolarization occurs between two resonances. Under favorable conditions the anisotropy of the scattering light can be much lower than what is possible for dielectric particles. This explanation is discussed in relation to earlier published experimental measurements. Comparison of experimental results with theoretical calculations provides information on the shape distribution of metallic particles in the suspension.     

Substituent Reactivity and Tautomerism of Isoguanosine and Related Nucleosides

The substituent reactivity and tautomerism of isoguanine nucleosides is studied. Benzoylation or tosylation of isoguanine nucleosides (pyridine, room temperature) yields the 2-benzoyl derivatives 7c, 11 , and 12 or the 2-tosyl compounds 13 and 14 . The isobutyrylation of the 6-amino group which did not occur under these conditions was induced in the presence of Me₃SiCl. In the absence of Me₃SiCl, the reactivity of isoguanine substituents decreases in the order from 2-oxo → 5′-OH → 3′-OH → 6-NH₂. From isoguanine nucleosides, the N¹-( 2b ), N³-( 17 ), N⁶-( 15a,b ), and 2-O-alkylated ( 3b ) derivatives were prepared. Their pK_a values were determined and the UV and ¹³C-NMR spectra compared with regard to the alkylation position. Also the tautomeric forms of isoguanine nucleosides were determined UV-spectrophotometrically in aqueous and nonaqueous solution. Isoguanosine ( 1a ), its 2′-deoxy analogue 1b as well as the N⁶-methyl- and 8-substituted derivatives form lactam tautomers in aqueous solution, whereas the lactim form is present in dioxane.     

Determination of benzene alkyl derivatives in heavily loaded environmental aqueous samples by means of combination of distillation and purge and trap-gas chromatography-mass spectrometry

Simple distillation was used to prepare aqueous environmental samples (especially those with high content of accompanying dissolved and suspended organic and inorganic matter) for determination of benzene, toluene, ethylbenzene, and xylenes (BTEX) by means of purge and trap (PT) coupled to gas chromatography-mass spectrometry (GC-MS). The PT step was carried out with a laboratory-built device in which alalytes desorbed from a Primary trap (macrotrap) are focused in a microtrap (also with sorbent) and moisture is removed from purge gases by a Nafion tube (walls selectively permeable to water vapor). Recoveries, if only the first 10 ml distillate was collected, were of the order of 40% at optimum distillation parameters. At a probability level of 95% recoveries were independent of concentration in a studied concentration range of 0.50–30 ppb. Enrichment factors for distillation were of the order off 20. Real samples, i.e., raw and treated waste water were analyzedc for BTEX content by the developed medthod.     

Synthesis of Phosphonates and Oligodeoxyribonucleotides Derived from 2′-Deoxyisoguanosine and 2′-Deoxy-2-haloadenosines

Oligonucleotides containing 2′-deoxyisoguanosine ( 1 ) or 2-chloro-2′-deoxyadenosine ( 2a ) have been prepared by solid-phase synthesis. Suitably protected phosphonates 3a, 4a , and 4b as well as the phosphoramidite of 1 have been obtained from the nucleosides 1, 2a , or 2b via the (dimethylamino)methylidene derivatives 5–7 . 4,4′-Dimethoxytrityl groups were introduced to yield the base-protected derivatives 8–10 . Alternatively to the direct incorporation of 1 into oligonucleotides, they were also obtained by the photochemical conversion of a 2a residue within the oligonucleotide chain.     

Application of solid-phase microextraction for determination of organic vapours in gaseous matrices

This paper reviews the practical applications of solid-phase microextraction (SPME) in the analysis of organic vapours which are pollutants of atmospheric air, indoor air and workplace air. Applications to headspace of solids and liquids such as different waters, soils, food, etc., are also included. Problems related to calibration in SPME analysis of gaseous matrices are also dealt with. Calibration procedures and apparatus for generation of standard gaseous mixtures are described. Advantages and limitations of SPME based gas chromatographic methods of air organic pollutants are discussed.     

Determination of volatile aliphatic amines in air by solid-phase microextraction coupled with gas chromatography with flame ionization detection

Practical aspects of the application of solid-phase microextraction (SPME) to the determination of volatile aliphatic amines in air are described. Analytes included methylamine (MA), ethylamine (EA), dimethylamine (DMA), diethylamine (DEA), trimethylamine (TMA) and triethylamine (TEA). New SPME stationary phases were examined. The effects of relative humidity and temperature on analytes uptake were taken into account in analysis. Gas chromatography (GC) with flame ionization detector (FID) was used for the final analysis.