The influence of iodide ions on the radiative and radiationless decay of the triplet state of aromatic hydrocarbons

An analysis of the influence of I^? ions on radiative and radiationless transitions from the lowest triplet state of aromatic hydrocarbons is presented. The distance dependence in the external heavy atom effects and the dependence of the enhancement of the T₁→S₀ radiative transition on the triplet energy is discussed in terms of perturbation theory.     

Synthesis of nucleoside-amino acid conjugates containing boranephosphate, boranephosphorothioate and boranephosphoramidate linkages

Conjugates of 3^′-azido-2^′,3^′-dideoxythymidine (AZT) and 2^′,3^′-didehydro-2^′,3^′-dideoxythymidine (D4T) with the hydroxyl group of tyrosine containing boranephosphate and boranephosphorothioate moieties were prepared via the oxathiaphospholane and dithiaphospholane methodology as a mixture of P-diastereomers. Their structures were confirmed by MS analysis and ¹H, ³¹P NMR spectroscopy. It has been shown that the boranephosphorothioate linkage is unstable under acidic conditions. The first nucleoside-alanine conjugates connected through a boranephosphoramidate linkage were also obtained.     

Oxathiaphospholane Approach to the Synthesis of Conjugates of Amino Acids Methyl Esters with Nucleosides

Based upon 1,3,2-oxathiaphospholane chemistry, 5'-O-derivatization of nucleosides with the O-methyl esters of amino acids was performed and corresponding conjugates were obtained in satisfactory yield.     

An Improved Synthesis of L-Homohistidine

Bloemhoff - Kerling's method of L-homohistidine synthesis was modified by employing formamidine acetate in liquid ammonia for imidazole ring formation. The improved procedure significantly shortened the synthetic pathway and resulted in enhanced yield.     

Probing plasmonic nanostructures by photons and electrons

We discuss recent developments for studying plasmonic metal nanostructures. Exploiting photons and electrons opens up new capabilities to probe the complete plasmon spectrum including bright and dark modes and related local optical fields at subnanometer spatial resolution. This comprehensive characterization of plasmonic properties of metal nanostructures provides new basic insight into the fundamental physics of “surface enhanced” spectroscopy in hottest hot spots and enables us to optimize plasmon supported processes and devices.     

Surface-enhanced Raman scattering: a new optical probe in molecular biophysics and biomedicine

Sensitive and detailed molecular structural information plays an increasing role in molecular biophysics and molecular medicine. Therefore, vibrational spectroscopic techniques, such as Raman scattering, which provide high structural information content are of growing interest in biophysical and biomedical research. Raman spectroscopy can be revolutionized when the inelastic scattering process takes place in the very close vicinity of metal nanostructures. Under these conditions, strongly increased Raman signals can be obtained due to resonances between optical fields and the collective oscillations of the free electrons in the metal. This effect of surface-enhanced Raman scattering (SERS) allows us to push vibrational spectroscopy to new limits in detection sensitivity, lateral resolution, and molecular structural selectivity. This opens up exciting perspectives also in molecular biospectroscopy. This article highlights three directions where SERS can offer interesting new capabilities. This includes SERS as a technique for detecting and tracking a single molecule, a SERS-based nanosensor for probing the chemical composition and the pH value in a live cell, and the effect of so-called surface-enhanced Raman optical activity, which provides information on the chiral organization of molecules on surfaces.     

Fragmentation of deprotonated d-ribose and d-fructose in MALDI—Comparison with dissociative electron attachment

We present a detailed, collaborative study on the fragmentation of deprotonated native d-ribose and d-fructose and the isotopically labelled 1-¹³C-d-ribose, 5-¹³C-d-ribose and C-1-d-d-ribose. The fragmentation is studied in a matrix assisted laser desorption/ionization time of flight mass spectrometer (MALDI ToF MS), both in in-source decay (ISD) and post-source decay (PSD) mode and compared with fragmentation through dissociative electron attachment (DEA). Fragmentation of deprotonated monosaccharides formed in the MALDI process, as well as their transient molecular anions formed upon electron attachment are characterized by loss of different numbers of H₂O and CH₂O units. Two different fragmentation pathways leading to cross-ring cleavage are identified. Metastable decay of deprotonated d-ribose proceeds either via an X-type cleavage yielding fragment anions at m/z = 119, 100 and 89, or via an A-type cleavage resulting in m/z = 89, 77 and 71. A fast and early metastable cross-ring cleavage of deprotonated d-ribose observed in in-source decay is dominated by X-type cleavage leading mainly to m/z = 100 and 71. For dissociative electron attachment to d-ribose a sequential dissociation was identified that includes metastable decay of the dehydrogenated molecular anion leading to m/z = 89. All other fragmentation reactions in DEA to d-ribose are likely to proceed directly and on a faster timescale (below 400 ns).     

Photopolymerization reactions initiated by a visible light photoinitiating system: Cyanine dye/borate salt/1,3,5‐triazine

New three‐component photoinitiating systems consisting of a cyanine dye, borate salt, and a 1,3,5‐triazine derivative were investigated by measuring their photoinitiation activities and through fluorescence quenching experiments. Polymerization kinetic studies based on the microcalorimetric method revealed a significant increase in polymerization rate when the concentration of n‐butyltriphenylborate salt or the 1,3,5‐triazine derivative were increased. The photo‐induced electron transfer process between electron donor and electron acceptor was studied by means of fluorescence quenching and SrEt change of the fluorescence intensity. The experiments performed documented that an increase of the n‐butyltriphenylborate salt concentration dramatically increases the rate of dye fluorescence quenching, whereas the increasing of the 1,3,5‐triazine derivative concentration slows down the consumption of the dye. We conclude that the primary photochemical reaction involves an electron transfer from the n‐butyltriphenylborate anion to the excited singlet state of the dye, followed by the reaction of the 1,3,5‐triazine derivative with the resulting dye radical to regenerate the original dye. This reaction simultaneously produces a triazinyl radical anion derived from the 1,3,5‐triazine, which undergoes the carbon‐halogen bond cleavage yielding radicals active in initiation of a free radical polymerization chain. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3626–3636, 2007     

Synthesis and X-ray structure of 11-N-benzylamido-9,10-dihydro-9,10-ethenoanthracene

As a part of studies on MDR reversing agents, the structure of a benzylamido-9,10-dihydro-9,10-ethenoanthracene is reported: C₂₄ H₁₉ N O; orthorhombic; space group: Pca2₁; a = 9.214(2), b = 18.624(4), c = 10.170(2) Å; 1745.2(6) ų; Z = 4. The three nonplanar rings from the 9,10-dihydro-9,10-ethenoanthracene skeleton of the molecule adopt a boat conformation. The benzamide side-chain is extended (conformation, trans-trans-gauche). The molecules in the crystal are joined by infinite chains of H-bonds N14–H14···O13.