Spatial profiling invertebrate ganglia using MALDI MS

The ability of MALDI TOF MS to spatially map peptides and proteins directly from a tissue is an exciting advance to imaging mass spectrometry. Recent advances in instrumentation for MS have resulted in instruments capable of achieving several micron spatial resolution while acquiring high-resolution mass spectra. Currently, the ability to obtain high quality mass spectrometric images depends on sample preparation protocols that often result in limited spatial resolution. A number of sample preparation and matrix deposition protocols are evaluated for spatial profiling of Aplysia californica exocrine gland and neuronal tissues. Such samples are different from mammalian tissues, but make good targets for method optimization because of the wealth of biochemical information available on neuropeptide processing and distribution. Electrospray matrix deposition and a variety of freezing methods have been found to be optimum for these invertebrate tissues, with the exact protocols being tissue dependent.     

Covalent Schiff base catalysis and turnover by a DNAzyme: a M2+ -independent AP-endonuclease mimic

A DNAzyme, synthetically modified with both primary amines and imidazoles, is found to act as a M2+ -independent AP lyase-endonuclease. In the course of the cleavage reaction, this DNAzyme forms a covalent Schiff base intermediate with an abasic site on a complementary oligodeoxyribonucleotide. This intermediate, which is inferred from NaCNBH3 trapping as well as cyanide inhibition, does not evidently accumulate because the second step, dehydrophosphorylative elimination, is fast compared to Schiff base formation. The 5'-product that remains linked to the catalyst hydrolyzes slowly to regenerate free catalyst. The use of duly modified DNAzymes to perform Schiff base catalysis demonstrates the value of modified nucleotides for enhancing the catalytic repertoire of nucleic acids. This work suggests that DNAzymes will be capable of catalyzing aldol condensation reactions.     

Investigation of the asymmetric ionic Diels-Alder reaction for the synthesis of cis-decalins

The ionic Diels-Alder reaction, whereby an alpha,beta-unsaturated acetal in combination with a Lewis or Bronsted acid forms an equilibrium concentration of an activated dienophile, has been developed to provide an enantioselective synthesis of cis-decalins. Cyclohex-2-enone type chiral acetals of (2R,3R)-butane-2,3-diol have been screened against Lewis and Br?nsted acids with a variety of dienes and are efficient for the synthesis of a limited subset of cis-decalin structures. Diastereoselectivities of 73% and 82% have been found for the asymmetric ionic Diels-Alder reaction between the chiral acetal derivatives of cyclohex-2-enone (6) and 2-methylcyclohex-2-enone (18) with 2,3-dimethyl-1,3-butadiene (7). Terminal substituents on the diene partner in general render the system unreactive. However a synthetically useful cis-decalin 31, derived from the reaction of 2-methylcyclohex-2-enone and Z-3-t-butyldimethyl-silyloxypenta-1,3-diene has been prepared in enantiomerically pure form in 74% isolated yield using this asymmetric ionic Diels-Alder protocol.     

Development of a liquid chromatographic time-of-flight mass spectrometric method for the determination of unlabelled and deuterium-labelled alpha-tocopherol in blood components

A method is described for the analysis of deuterated and undeuterated alpha-tocopherol in blood components using liquid chromatography coupled to an orthogonal acceleration time-of-flight (TOF) mass spectrometer. Optimal ionisation conditions for undeuterated (d0) and tri- and hexadeuterated (d3 or d6) alpha-tocopherol standards were found with negative ion mode electrospray ionisation. Each species produced an isotopically resolved single ion of exact mass. Calibration curves of pure standards were linear in the range tested (0-1.5 microM, 0-15 pmol injected). For quantification of d0 and d6 in blood components following a standard solvent extraction, a stable-isotope-labelled internal standard (d3-alpha-tocopherol) was employed. To counter matrix ion suppression effects, standard response curves were generated following identical solvent extraction procedures to those of the samples. Within-day and between-day precision were determined for quantification of d0- and d6-labelled alpha-tocopherol in each blood component and both averaged 3-10%. Accuracy was assessed by comparison with a standard high-performance liquid chromatography (HPLC) method, achieving good correlation (r(2) = 0.94), and by spiking with known concentrations of alpha-tocopherol (98% accuracy). Limits of detection and quantification were determined to be 5 and 50 fmol injected, respectively. The assay was used to measure the appearance and disappearance of deuterium-labelled alpha-tocopherol in human blood components following deuterium-labelled (d6) RRR-alpha-tocopheryl acetate ingestion. The new LC/TOFMS method was found to be sensitive, required small sample volumes, was reproducible and robust, and was capable of high throughput when large numbers of samples were generated.     

Asymmetric synthesis of (1R,2S,3R)-gamma-methyl-cis-pentacin by a kinetic resolution protocol

The asymmetric synthesis of (1R,2S,3R)-3-methyl-2-amino-cyclopentane carboxylic acid has been achieved via kinetic resolution of racemic tert-butyl 3-methyl-cyclopentene-1-carboxylate with homochiral lithium (S)-N-benzyl-N-alpha-methylbenzylamide.     

Mixed-metal cluster chemistry. 19. Crystallographic, spectroscopic, electrochemical, spectroelectrochemical, and theoretical studies of systematically varied tetrahedral group 6-iridium clusters

A systematically varied series of tetrahedral clusters involving ligand and core metal variation has been examined using crystallography, Raman spectroscopy, cyclic voltammetry, UV-vis-NIR and IR spectroelectrochemistry, and approximate density functional theory, to assess cluster rearrangement to accommodate steric crowding, the utility of metal-metal stretching vibrations in mixed-metal cluster characterization, and the possibility of tuning cluster electronic structure by systematic modification of composition, and to identify cluster species resultant upon electrochemical oxidation or reduction. The 60-electron tetrahedral clusters MIr(3)(CO)(11-x)(PMe(3))(x)(eta(5)-Cp) [M = Mo, x = 0, Cp = C(5)H(4)Me (5), C(5)HMe(4) (6), C(5)Me(5) (7); M = W, Cp = C(5)H(4)Me, x = 1 (13), x = 2 (14)] and M(2)Ir(2)(CO)(10-x)(PMe(3))(x)(eta(5)-Cp) [M = Mo, x = 0, Cp = C(5)H(4)Me (8), C(5)HMe(4) (9), C(5)Me(5) (10); M = W, Cp = C(5)H(4)Me, x = 1 (15), x = 2 (16)] have been prepared. Structural studies of 7, 10, and 13 have been undertaken; these clusters are among the most sterically encumbered, compensating by core bond lengthening and unsymmetrical carbonyl dispositions (semi-bridging, semi-face-capping). Raman spectra for 5, 8, WIr(3)(CO)(11)(eta(5)-C(5)H(4)Me) (11), and W(2)Ir(2)(CO)(10)(eta(5)-C(5)H(4)Me)(2) (12), together with the spectrum of Ir(4)(CO)(12), have been obtained, the first Raman spectra for mixed-metal clusters. Minimal mode-mixing permits correlation between A(1) frequencies and cluster core bond strength, frequencies for the A(1) breathing mode decreasing on progressive group 6 metal incorporation, and consistent with the trend in metal-metal distances [Ir-Ir < M-Ir < M-M]. Cyclic voltammetric scans for 5-15, MoIr(3)(CO)(11)(eta(5)-C(5)H(5)) (1), and Mo(2)Ir(2)(CO)(10)(eta(5)-C(5)H(5))(2) (3) have been collected. The [MIr(3)] clusters show irreversible one-electron reduction at potentials which become negative on cyclopentadienyl alkyl introduction, replacement of molybdenum by tungsten, and replacement of carbonyl by phosphine. These clusters show two irreversible one-electron oxidation processes, the easier of which tracks with the above structural modifications; a third irreversible oxidation process is accessible for the bis-phosphine cluster 14. The [M(2)Ir(2)] clusters show irreversible two-electron reduction processes; the tungsten-containing clusters and phosphine-containing clusters are again more difficult to reduce than their molybdenum-containing or carbonyl-containing analogues. These clusters show two one-electron oxidation processes, the easier of which is reversible/quasi-reversible, and the more difficult of which is irreversible; the former occur at potentials which increase on cyclopentadienyl alkyl removal, replacement of tungsten by molybdenum, and replacement of phosphine by carbonyl. The reversible one-electron oxidation of 12 has been probed by UV-vis-NIR and IR spectroelectrochemistry. The former reveals that 12(+) has a low-energy band at 8000 cm(-1), a spectrally transparent region for 12, and the latter reveals that 12(+) exists in solution with an all-terminal carbonyl geometry, in contrast to 12 for which an isomer with bridging carbonyls is apparent in solution. Approximate density functional calculations (including ZORA scalar relativistic corrections) have been undertaken on the various charge states of W(2)Ir(2)(CO)(10)(eta(5)-C(5)H(5))(2) (4). The calculations suggest that two-electron reduction is accompanied by W-W cleavage, whereas one-electron oxidation proceeds with retention of the tetrahedral core geometry. The calculations also suggest that the low-energy NIR band of 12(+) arises from a sigma(W-W) --> sigma*(W-W) transition.     

Diamond and diamond-like carbon from a preceramic polymer

The synthesis of poly(hydridocarbyne), one of a class of carbon-based random network polymers and a structural isomer of polyacetlyene, is reported. The network backbone of this polymer is primarily composed of tetrahedrally hybridized carbon atoms, each bearing one hydride substituent and linked via three carbon-carbon single bonds into a three-dimensional random network of fused rings. This atomic-level carbon network backbone confers unusual properties on the polymer, including facile thermal decomposition to form diamond or diamond-like carbon high-quality films at atmospheric pressure, by direct deposition or by chemical vapor deposition (CVD), without the use of hydrogen or any other reagent.     

Isolation and Crystal Structure of Novel by-products Observed During the Formation of bis(thiosemicarbazones)

During the condensation of 4-methyl-4-phenyl-3-thiosemicarbazide (3) with 2,3-butanedione an unexpected by-product, 8a-methyl-6,8a-dihydro-8-methyl-2-[N-methyl-N-phenylamino]-5H-1,3,4-thiadiazolo[3,2-d][1,2,4]triazine-5-thione, (5) was obtained in addition to the desired bis(thiosemicarbazone) (4). An X-ray crystal structure was obtained and is presented together with a proposed mechanism for its formation. A brief investigation of the coordination chemistry of bicycle (5) was carried out. The formation of cyclic compounds during the synthesis of analogues with extended backbones is also described.     

Mechanism of o-xylene conversion on magnesium modifications of Y zeolite

o-Xylene conversions has been investigated in the presence of MgNaY zeolites with different Si/Al ratios and degrees of exchange. Disproportionation proceeds to a higher degree than does isomerization. The distribution of reaction products is attributed to geometric factors. The results are in agreement with a monomolecular mechanism of isomerization.

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- MgNaY Si/Al . , , . . .

     

Sparsely substituted chlorins as core constructs in chlorophyll analogue chemistry. II. Derivatization

Stable chlorins bearing few or no substituents have been subjected to a variety of reactions including demetalation, magnesium insertion, oxochlorin formation, and bromination followed by Suzuki coupling. The kinetics of deuteration also have been determined for two oxochlorins and a series of chlorins bearing 0, 1, 2, or 3 meso-aryl substituents.