Formation of double cubanes [Sn(7)(NR)(8)] in the reactions of pyridyl and pyrimidinyl amines with Sn(NMe(2))(2): a synthetic and theoretical study

In contrast to the reactions of Sn(NMe(2))(2) with unfunctionalized primary amines (RNH(2)), which yield the simple imido Sn(II) cubanes [SnNR](4), the reactions of 2-pyridyl or 2-pyrimidinyl amines give the mixed-oxidation-state Sn(II)/Sn(IV) double cubanes [Sn(7)(NR)(8)]. In addition to [Sn(7)[2-N(5-Mepy)](8)] x 2thf (1 x 2thf) (py = pyridine) and [Sn(7)[2-N(pm)](8)] x 0.33thf (2 x 0.33thf) (pm = pyrimidine), which were communicated previously, the syntheses and structures of the new complexes [Sn(7)[2-N(4-Mepm)](8)] x 2thf (3 x 2thf), [Sn(7)[2-N(4,6-Me(2)pm)](8)] x 4thf (4 x 4thf), [Sn(7)[2-N(4-Me-6-MeO-pm)](8)] (5), and [Sn(7)[2-N(4-MeO-6-MeO-pm)](8)] (6) are reported. Model DFT calculations on the reactions of Sn(NMe(2))(2) with 2-pmNH(2) or PhNH(2), producing the cubanes [Sn[2-N(pm)]](4) and [SnNPh](4) (respectively), and the corresponding double cubanes [Sn(7)[2-N(pm)](8)] and [Sn(7)(NPh)(8)], show that the presence of intramolecular Sn...N bonding which spans the cubane halves of the complexes is crucial to the formation of the double-cubane structure.     

Gamma2-, gamma3-, and gamma(2,3,4)-amino acids, coupling to gamma-hexapeptides: CD spectra, NMR solution and X-ray crystal structures of gamma-peptides

There are numerous possible gamma-amino acids with different degrees of substitution and with various constitutions and configurations. Of these the gamma4- and the like- and unlike-gamma(2,4)-amino acids have been previously used as building blocks in gamma-peptides. The synthesis of gamma2-, gamma3-, and gamma(2,3,4)-peptides is now described. The corresponding amino acids have been prepared by Michael addition of chiral N-acyl-oxazolidinone enolates to nitro-olefins, with subsequent reduction of the NO2 to NH2 groups. Such additions to E-2-methyl-nitropropene provide (2R,3R,4R)-2-alkyl-3-methyl-4-amino-pentanoic acid derivatives (9, 10, 11). Stepwise coupling and fragment coupling lead to gamma-di-, tri-, and hexapeptides (12-23), which were fully characterized. The crystal structures of one of the gamma-amino acids (2,3-dimethyl-4-amino-pentanoic acid x HCl, 9a), of a gamma(2,3,4)-di- and a gamma(2,3,4)-tetrapeptide (20, 22) are described, and the NMR solution structure in MeOH of a gamma(2,3,4)-hexapeptide (3) has been determined (using TOCSY, COSY, HSOC, HMBC and ROESY measurements and a molecular dynamics simulated-annealing protocol). A linear conformation (sheet-like), a novel (M) helix built of nine-membered hydrogen-bonded rings, and (M) 2.6(14) helices have thus been identified. NMR measurements at different temperatures (298-393 K) and H/D-exchange rates obtained for the gamma(2,3,4)-hexapeptide are interpreted as evidence for the stability of the 2.6(14) helix (no "melting") and for its non-cooperative folding mechanism. CD Spectra of the gamma-peptides have been measured in MeOH and CH3CN, indicating that only the protected and unprotected gamma(2,3,4)-hexapeptide is present as the 2.6(14) helix in solution. The structures of the gamma2- and gamma3-hexapeptides (1, 2) could not be determined.     

Proteome analysis using isoelectric focusing in immobilized pH gradient gels followed by mass spectrometry

Over the past several years, a large effort has been focused on improvements of two-dimensional (2-D) gel electrophoresis-based proteomics technology, and on development of novel approaches for proteome analysis. Here, we describe the application of an alternative strategy for the analysis of complex proteomes. The strategy combines isoelectric focusing in immobilized pH gradient strips (in-gel IEF), mass spectrometry (MS), and bioinformatics. A protein mixture is separated by in-gel IEF, and the entire strip is cut into a set of gel sections. Proteins in each gel section are digested with trypsin, and the tryptic peptides are subjected to liquid chromatography-nanoelectrospray-quadrupole ion-trap tandem mass spectrometry (LC-ESI-MS/MS). The LC-ESI-MS/MS data are used to identify the proteins through searches of a protein sequence database. Using this in-gel IEF-LC-MS/MS strategy, we have identified 127 proteins from a human pituitary. This study demonstrates the potential of the in-gel IEF-LC-MS/MS approach for analyses of complex mammalian proteomes.     

UV-induced unscheduled DNA synthesis in human skin: dose response, correlation with erythema, time course and split dose exposure in vivo

Unscheduled DNA synthesis (UDS) has been shown to be saturated above a threshold dose of UV-C in human fibroblasts in vitro. We have investigated by autoradiography whether a similar saturation occurs in human skin in vivo with UV-B and whether this phenomenon correlates with the erythemal response. In addition, we determined the time course of UDS at 24 h after exposure and the effect of dual exposures separated by 24 h. The dose-response curve was established by exposure to 1/16, 1/8, 1/4, 1/2, 1, 2, 3, 4 and 6 MEDs UV-B. For the time-course study, areas exposed to 1/2 and 2 MEDs were biopsied after 1, 3, 6, 12 and 24 h. Autoradiography was performed in vitro. The dose-response curve showed a significant increase in UDS from 1/16 to 1 minimal erythema dose (MED), whereas no significant difference was observed between 1 MED and the higher UV-B doses tested. The 24 h time sequence revealed a gradual decrease in UDS activity. The 1/2 MED curve declined more rapidly and reached the zero-level between 12 h and 24 h, whereas about 50% of the initial UDS value was still retained 24 h after 2 MEDs. The dual-dose study revealed that a second hit of fractions of the MED resulted in lower levels of UDS than induced by these fractions alone in previously untreated areas. UDS increases with the erythemal dose between 1/16 and 1 MED. It reaches a plateau after 1 MED and cannot be increased by doses up to 6 MEDs, suggesting a saturation of excision repair in vivo. Time course studies support such a saturation phenomenon. The failure to increase significantly UDS by a second irradiation 24 h after the first exposure needs further clarification. Since persistence of DNA lesions may lead to an accumulation after repeated exposures, additional mechanisms other than excision repair may protect human skin by error-free removal of possibly mutagenic sites. Photoreactivation may be important in this respect.     

The effect of cyclohexene, a preservative in dichloromethane on the liquid-liquid extraction and analysis of chlorinated drinking water

Liquid-liquid extraction with dichloromethane is the Environmental Protection Agency's (EPA) method of choice for the analysis of acid or base neutral organic chemicals in water. Free radical chlorination and oxidation products of cyclohexene (the solvent preservative) in dichloromethane have been observed in extracts of chlorinated drinking water (after 10(5) fold concentration) by gas chromatography and gas chromatography-mass spectrometry. The chlorinated cyclohexene derivatives limit the quantitative and qualitative analysis of compounds eluting at Kovát's index less than 700-1000 and the use of these extracts for organoleptic and mutagenic studies. The effect of residual free chlorine in water on the cyclohexene present in the solvent was studied. Over ten cyclohexene derivatives were produced in every case when any residual free chlorine was present in the water. When chlorine is reduced to chloramine, the cyclohexene derivatives were greatly reduced in number and amount.     

Zur Synthese von Aminocaprolactam

α-Amino-?-caprolactam (I), an intermediate for the synthesis of L-lysine, has been synthesized by BECKMANN -rearrangement of α-amino-cyclohexanoneoxime (XII) in concentrated sulfuric acid (13% yield) or oleum (34% yield). Cyclisation of α-amino-?-bromocaproamide hydrobromide (VIII) did not yield I but an isomer of I of unknown structure (compound X). Upon hydrolysis X gave a compound XI which was similar to lysine in its chromatographic and electrophoretic behavior.     

Spin dephasing in impurity induced states in molecular solids

Spin coherence experiments are used to determine the energy level structure, physical geometry, and exciton dynamics of a series of impurity-induced traps in 1,2,4,5-tetrachlorobenzene. The trap, a pertubed host molecule, is shown to be caused by an adjacent, translationally equivalent chemical impurity whose triplet energy may lie above or below the host exciton, but above the trap. The slow rates of thermal processes within the trap are interpreted as weak coupling between the lattice phonons and localized phonons induced at the trap by the impurity.     

Novel rhenium(I) polypyridine biotin complexes that show luminescence enhancement and lifetime elongation upon binding to avidin

While most biotin-fluorophore conjugates suffer from significant emission quenching upon binding to avidin due to resonance energy-transfer, three novel rhenium(I) polypyridine biotin complexes have been designed in view of their characteristic photophysical properties, in particular their large Stokes shifts. In contrast to most biotin-fluorophore conjugates, the (3)MLCT emission intensities and lifetimes of these rhenium(I) complexes are increased upon binding to avidin, rendering them luminescent probes for avidin and biotinylated species.     

Syntheses, structures and magnetic properties of Mn(II) dimers [CpMn(micro-X)]2(Cp = C5H5; X = RNH, R1R2N, C[triple bond]CR)

Manganocene, Cp(2)Mn, has been employed as a precursor in the synthesis of a range of Mn(II) dimers of the type [CpMn(micro-X)](2)[X = 8-NHC(9)H(6)N (1), N(Ph)(C(5)H(4)N)(2), N(4-EtC(6)H(4))(C(5)H(4)N)(3) and C[triple bond]CPh (4)] as well as the bis-adduct [Cp(2)Mn[HN=C(NMe(2))(2)](2)](5). The solid-state structures of 1-5 are reported. Variable-temperature magnetic measurements have been used to assess the extent of Mn(micro-X)Mn communication within the dimers of 1-4 as a function of the bridging ligands (X).     

Analysis of the human lumbar cerebrospinal fluid proteome

Idiopathic low back pain has no known cause, and the molecular basis is unknown. Neuropeptidergic systems have been previously studied, and proteomics methods have been applied in this present study. Proteomics combines high-resolution two-dimensional (2-D) gel electrophoresis, high-sensitivity mass spectrometry, and continuously expanding protein databases. Proteomics offers a comprehensive, bird's-eye view to analyze, at a systems level, all of the proteins in cerebrospinal fluid (CSF) that might contribute to idiopathic low back pain. CSF contains a high salt concentration and low protein concentration. In order to obtain a high-quality 2-D pattern, several sample preparation methods were tested to remove salts - protein precipitation with either acetone or trichloroacetic acid/acetone, or sample treatment with a Bio-Spin column. More spots were visualized on the 2-D gel of human CSF, and a relatively high protein recovery was obtained when a Bio-Spin column was used to process a human CSF sample. Sixty-one protein spots, obtained from 2-D gels with a pH range of either 3-10 or 4-7, were identified by matrix assisted laser desorption/ionization-mass spectrometry (MALDI-MS) and MALDI-post-source decay (PSD)-MS. These 61 protein spots represent 22 proteins; six of those proteins were not annotated in any previously published 2-D maps. Those six proteins are PRO2619, pigment epithelium-derived factor, albumin homolog, kallikrein-6 precursor, DJ717I23.1, and AMBP protein precursor. These protein-mapping data will contribute to the database that will be used in the future to compare the proteomes obtained from the CSF of controls and low back pain patients, to characterize differentially expressed proteins, and to elucidate the biological markers for idiopathic low back pain.