Desorption/ionization on porous silicon mass spectrometry (DIOS) of model cationized fatty acids

Desorption/ionization on porous silicon (DIOS) is a very useful technique in the case of small molecular weight compounds, compared to the matrix-assisted laser desorption ionization (MALDI). This is because MALDI generates matrix-related ions that overlap with the mass range of interest. The aim of our work was to investigate the suitability of the DIOS technique in the case of fatty acids in negative ion mode. The analysis of the chosen fatty acid models, nonadecanoic acid (C(19)H(38)O(2)) and heneicosanoic acid (C(21)H(42)O(2)), gave rise to the observation of the deprotonated monomeric species and selective cationized multimeric species. This cation selectivity was further elucidated by complementary studies based on the addition of various metals such as Ag(I), Zn(II), Fe(II), and also Cu(II). Specific behavior, depending upon the introduced metal, was highlighted by different redox reaction processes and also metastable decompositions (in PSD mode).     

Fluorescence and Mass Spectrometry Studies of Meta-tetra(hydroxyphenyl)chlorin Photoproducts

The meta-tetra(hydroxyphenyl)chlorin (m-THPC), a second-generation sensitizer used in photodynamic therapy (PDT), is currently under clinical trial. In vivo fluorometry provides direct evidence that photobleaching processes are induced at the tumor site during PDT. Photoproduct formation has thus to be taken into account to fully understand PDT treatment. A preliminary step is to determine the fluorescence characteristics of photoproducts formed in solution. Solutions of m-THPC irradiated at 514 nm have been separated by HPLC using absorption and fluorescence detection. Six main photoproducts have been isolated. According to matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOFMS) results, five fluorescent photoproducts emitting at 652 nm have been attributed to three mono-, one di- and one tri-hydroxy derivatives (m/z 697, 713 and 729, respectively). Fluorescence characteristics of mono-hydroxy forms were found to be similar to those of m-THPC, whereas fluorescence yields in di- and tri-hydroxy derivatives were very low. Another product, corresponding to a MALDI-TOF MS main signal at m/z 542, showed an absorption spectrum maximum at 522 nm while a weak fluorescence was detected at 480 nm. The loss of the Soret band suggests that this photoproduct results from the opening of the reduced pyrrole ring. The part played by each of these products in the photobleaching phenomenon of m-THPC is discussed.     

A Polycationic Metallodendrimer with 24 [Fe(η5-C5Me5)(η6-N-Alkylaniline)]+ Termini That Recognizes Chloride and Bromide Anions

Pronounced dendritic effects are shown by the title compound 1 in the recognition of Cl⁻ and Br⁻—this is shown by the comparison with a mononuclear compound with one dendrimer arm and a trinuclear compound with a tripodal dendrimer branch. Thus, 1 differs distinctly from 24-ferrocene dendrimers of comparable topology.     

De novo synthesis of sugar-aza-crown ethers via a domino Staudinger aza-Wittig reaction

A short and highly efficient route to sugar-aza-crown (SAC) ethers has been developed. The key step of the transformation is a one-pot cyclodimerization of C-glycosyl azido aldehydes via a domino Staudinger aza-Wittig reaction. This process allows the preparation of various orthogonally protected SAC ethers, from both alpha- and beta-C-glycosyl azido aldehydes.     

Semiclassical variational transition state calculations for the reactions of H and D with thermal and vibrationally excited H2

We present calculations of the rate constants for the title reactions on a new accurate potential energy surface with a 9.65 kcal mol^?1 barrier and a carefully fitted long-range attraction. The low-temperature thermal rate constant decreases from the previously calculated value, corresponding to a surface with a barrier of 9.80 kcal mol^?1, which is opposite to the direction of change expectedbecause of the change in barrier height. This demonstrates the sensitivity of tunneling contributions to more global characteristics of the surface. The excited-state (n = 1) rate constants alsochange slightly, but not nearly enough to settle the controversial disagreement of theory with experiment for these rate constants.     

Synthesis,storage, and transfer of [210Pb]-(CH3)3PbCl across tomato fruit cuticle

An improved synthetic route to [²¹⁰Pb]-(CH₃)₃PbCl is described in which chelated ²¹⁰Pb²⁺ is methylated to [²¹⁰Pb]-(CH₃)₄Pb with methylmagnesium bromide (CH₃MgBr) in the presence of methyl iodide. Controlled oxidation of the product with anhydrous hydrochloric acid and purification of the crude product by reversed-phase high-pressure liquid chromotography (HPLC) resulted in [²¹⁰Pb]-(CH₃)₃PbCl in 71% radiochemical yield. Whereas storage of the purified product at ?10 °C resulted in complete conversion to Pb²⁺ during one year, storage in 20% acetic acid at 4 °C resulted in less than 15% decomposition during six months. Periodic complexometric extractions to remove ²¹⁰Pb radioactive daughters (²¹⁰Bi, 100% β, E_max = 1.16 MeV; ²¹⁰Po, 100% α, E = 5.305 MeV) from the storage solution did not alter the rate of decomposition. The rate of translocation of [²¹⁰Pb]-(CH₃)₃Pb⁺ across an isolated tomato cuticle was approximately twice the rate of transfer of inorganic lead(II) and was not influenced by the presence of increasing amounts of disodium ethylenediamine-tetra-acetate.     

Exact solution of the generalized routing problem through graph transformations

In the general routing problem, the aim is to determine a least cost traversal of a subset of edges, arcs and vertices of a graph. The problem can be transformed into an equivalent traveling salesman problem or rural postman problem and solved optimally. Computational results are reported.     

FLUORESCENCE QUANTUM YIELD DETERMINATION OF PYRIMIDINE (6-4) PYRIMIDONE PHOTOADDUCTS

Abstract An extensive study of the fluorescence characteristics of pyrimidine (6-4) pyrimidone photoadducts, a major class of far-UV-induced DNA lesions, was carried out on dinucleoside monophosphate (6-4) photoadducts, including thymidylyl-(3'→ 5')-thymidine (TpT), 2'-deoxycytidylyl-(3'-5')-thymidine, thymidylyl-(3'→ 5')-2'-deoxy-cytidine, 2'-deoxyuridylyl-(3'→ 5')-thymidine, 5-methyl-2'-deoxycytidylyl-(3'-5')-thymidine (6-4) photoadducts and the corresponding base (6-4) photoadducts, 6-4'-(5'-methylpyrimidin-2'-one) thymine (TT), 5-hydroxy-6-4'-(5'-methylpyrimidin-2'-one)-5,6-dihydrothymine (CT), 5-amino-6-4'-(pyrimidin-2'-one)-5,6-dihydrothymine (UC) obtained by mild acidic hydrolysis of the former derivatives. The fluorescence quantum yield (Φ_F) of these compounds was found to depend on one hand, on the nature of the two bases involved and the base substituent and, on the other hand, on the presence of the phosphate group. The hydrolysis of the phosphodiester bond was shown to enhance Φ_F, the larger effect being observed in the case of the thymine-thymine photoadducts with a seven-fold increase of the Φ_F value in the case of TT as compared to TpT (0.21 and 0.03, respectively). These results are discussed in terms of structural considerations.