Siau-Gek Ang

Observations on the quantitation of the phosphate content of peptides by fast-atom bombardment mass spectrometry

Equimolar mixtures of the phosphorylated and dephosphorylated forms of several peptides have been subjected to fast-atom bombardment mass spectrometry (FABMS), to investigate whether the stoichiometry of phosphorylation can be determined from the relative molecular-ion abundances of the phospho and dephospho derivatives. It is concluded that quantitation can be achieved for peptides with large positive or negative hydrophobicity/hydrophilicity indices (delta F values) where addition of a phosphate group does not alter the distribution of the peptide within the matrix significantly. For peptides with small positive or negative delta F values, phosphopeptides tend to be partially suppressed by their dephosphorylated counterparts. Suppression can be partially or totally overcome by conversion of the peptide to a hydrophobic derivative, and by the selection of an appropriate matrix. Alternatively, addition of a very strong acid, perchloric acid, can even reverse the original suppression effect. This last effect is believed to be due to the increased ionic strength in the matrix, which forces a relatively hydrophilic analyte to the matrix surface; and the ability of such a phosphorylated analyte to form a more stable gas-phase cation.

Chromatographic analysis of low-molecular-mass copper-binding ligands from the crab species Syclla serrata and Portunis pelagicus

Two copper-binding proteins and a zinc-binding ligand were isolated from the hepatopancreas of the crab Portunus pelagicus. The copper-binding proteins behave similarly to those from the crabs Carcinus maenas and Scylla serrata, and were shown to be metallothioneins. Reversed-phase high-performance liquid chromatographic (HPLC) analysis confirmed the relative purity of both proteins with only cross-contamination between the two different forms of metallothioneins, and offers a good method to separate the two forms of metallothioneins. The vast difference in the retention times (and hence the hydrophobicity) in reversed-phase HPLC indicates that the two proteins could be conformationally very different.

The reactions of bis(trifluoromethyl) phosphine and arsine with trinuclear ruthenium carbonyl cluster: molecular structures of the trinuclear and double-linked trinuclear clusters [Ru3(CO)8)(μ-H)2{μ-P(CF3)2}2] and [{Ru3(CO)10(μ-H)}2{μ-P(CF3)2}2]

Abstract Reactions of (CF3)2EH (E=P, As) with [Ru3(CO)12] under varying conditions result in hydrogen transfer from ligand to cluster to form trinuclear cluster [Ru3(CO)8(μ-H)2{μ-P(CF3)2}2] 1, double-linked trinuclear clusters [{Ru3(CO)10(μ-H)}2{μ-E(CF3)2}2] (2: E=P; 3: E=As), flat butterfly cluster [Ru4(CO)13{μ-P(CF3)2}2] 4, butterfly clusters [Ru4(CO)12(μ-H)3{μ-E(CF3)2}] (5: E=P; 6: E=As), open-chain clusters [Ru4(CO)14{μ-E(CF3)2}2] (7: E=P; 8: E=As) and square pyramidal clusters [Ru5(CO)15(μ4-ECF3)] (9: E=P; 10: E=As). Cluster 1 contains a triangular Ru plane with two short RuRu bonds bridged by a phosphido and a hydride, respectively. Cluster 2 consists of two coplanar Ru3 triangles linked by two phosphido groups.

Triosmium carbonyl cluster derivatives containing pentameric phenyl cyclopolyphosphine

Abstract The reactions of the pentaphenylcyclopentaphosphine with [Os 3 (CO) 10 (NCCH 3 ) 2 ] afforded a pair of inversion isomers, ( 1 ) and ( 2 ). [Os 3 (CO) 11 (C 6 H 5 P) 5 ] ( 3 ) and [{Os 3 (CO) 11 } 2 (C 6 H 5 P) 5 ] ( 4 ) were obtained by the treatment of the same ligand with [Os 3 (CO) 11 (NCCH 3 )]. The four new triosmium clusters have been shown by X-ray crystallography to contain an intact cyclopolyphosphine ring in each case.

Reactions of the linear triosmium cluster [Os3H(CO)11(η2-C6F5NNNC6F5)] with [Os3(CO)12–n(NCMe)n](n= 1 or 2): crystal structures of [Os4(µ-H)(CO)14(η2-C6F5NNNC6F5)] and [Os5(µ-H)(CO)17(η2-C6F5NNNC6F5)]

Reaction of the linear triosmium carbonyl cluster [Os3H(CO)11(η2-C6F5NNNC6F5)] with [Os3(CO)11(NCMe)] in hexane at 60 °C under vacuum afforded the ‘spiked’ tetraosmium cluster [Os4(µ-H)(CO)14(η2-C6F5NNNC6F5)]1. Reaction with [Os3(CO)10(NCMe)2] in CH2Cl2 at room temperature gave the ‘spiked’ hexaosmium cluster [Os6(µ-H)(CO)21(NCMe)(η2-C6F5NNNC6F5)]2. Cluster 2 is reactive and converts into the ‘spiked’ pentaosmium cluster [Os5(µ-H)(CO)17(η2-C6F5NNNC6F5)]3 and a known cluster [Os5(CO)16] respectively when heated with and without C6F5NNNHC6F5. Clusters 1 and 3 were characterized by single-crystal X-ray crystallography. The structure of 1 consists of a triangular unit with a Os(CO)3(η2-C6F5NNNC6F5) portion ‘spiked’ equatorially to it. The two nitrogen atoms in the triazenide ligand occupy an axial and an equatorial position in the Os(CO)3(η2-C6F5NNNC6F5) group. The hydride ligand bridges, in a cis manner, the Os–Os edge where the Os(CO)3(η2-C6F5NNNC6F5) portion is attached. The structure of 3 adopts a ‘4 + 1 spiked’ geometry hitherto unknown. Its metal core consists of a planar ‘kite-like’ Os4 unit with the Os(CO)3(η2-C6F5NNNC6F5) portion ‘spiked’ to one of the equatorial co-ordination sites of an osmium atom. The two nitrogen atoms in the triazenide ligand and the hydride are bonded as in cluster 1. Based upon 13C NMR studies, the structure of cluster 2 in solution was also deduced to have a ‘spiked’ feature with the linear triosmium fragment Os3(CO)11(η2-C6F5NNNC6F5) bound to one atom in the osmium triangle at an eqatorial co-ordination site. The transformation of cluster 2 and the formation of cluster 1 are also briefly discussed.

Structure elucidation of a glycopeptide antibiotic, OA-7653

The structure of a vancomycin-type antibiotic, OA-7653, isolated from Streptomyces hygroscopicus subsp. hiwasaensis subsp. nov. Nishida, has been elucidated by a combination of classical chemical methods, mass spectrometry, and nuclear magnetic resonance spectroscopy. The interaction of OA-7653 with the peptide cell wall analogues N-acetyl-D-alanyl-D-alanine, and di-N-acetyl-L-lysyl-D-alanyl-D-alanine, in solution in aqueous dimethyl sulphoxide, has been examined by n.m.r. and u.v. difference spectroscopy.

Fabrication of CuTAPc polymer nanowires and nanotubes by electropolymerization

Poly-copper tetraaminophthalocyanine (CuTAPc) nanowires and nanotubes were successfully fabricated on porous alumina templates by electropolymerization and characterized using field-emission scanning electron microscopy (FE-SEM), energy-dispersive x-ray spectroscopy (EDX), transmission electron microscopy (TEM) and Raman microscopy. The lengths of these nanostructures could be controlled by the number of cycles applied and the monomer concentrations, while their diameters are confined by the pore size of the template. The product of electropolymerization (whether as nanowires or nanotubes) is a function of the monomer concentrations. The morphology of electropolymerized nanowires was found to be sensitive to the changes in scan rates and monomer concentrations. These organometallic nanostructures may have applications in micro-electronics, chemical sensing, and catalysis.

Reactions of spiked and open chain cluster hydrides with Au complexes: skeletal rearrangement and crystal structures of heterometallic clusters [Au2Ru4(CO)12(μ4-PCF3)(PMe3)2] and [Au2Ru4(CO)12(μ3-PCF3)2(PPh3)2]

Abstract Treatment of the spiked cluster [Ru 4 (CO) 13 (μ-H) 2 (μ 4 -PCF 3 )] with [Au(PMe 3 )Cl] in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) results in deprotonation and metal core rearrangement from spiked to butterfly, yielding the heterometallic cluster [Au 2 Ru 4 (CO) 12 (μ 4 -PCF 3 )(PMe 3 ) 2 ] 1 . Reaction of the open chain cluster [Ru 4 (CO) 12 (μ-H) 2 (μ 3 -PCF 3 ) 2 ] with [Au(PPh 3 )Cl] under similar conditions gives [Au 2 Ru 4 (CO) 12 (μ 3 -PCF 3 ) 2 (PPh 3 ) 2 ] 2 where the hydrides are simply replaced by AuPPh 3 fragments. Clusters 1 and 2 are characterised by spectroscopy and X-ray crystallography.

Restriction of the Inversion Process of the 1,3-Bridged Ring in the Rigid Conformer of 24-Methyl-2,17-Dithia[3.3](2,2′)Biphenyleno(1,3)Cyclophane

Abstract The title compound 3 was prepared via a cyclization reaction between two known precursors. It is confirmed that the inversion process of the 1,3-bridged ring in the 2,17-dithia[3.3](2,2′)biphenyleno(1,3)cyclophane system was restricted with a conformational energy barrier of >84 kJ mol−1. The adopted rigid conformation is represented by 3a (or 3b) having the methyl protons located above the cavity of one of the benzene rings. This is consistent with the preferred conformation derived from semiempirical molecular orbital PM3 calculations. All the protons in this rigid conformer could be assigned by its COSY spectra and results from a series of NOE experiments.

Structural and two-dimensional phosphorus-31 nuclear magnetic resonance studies of derivatives from (RP)5(R = Et or Ph) and activated triosmium clusters [Os3(CO)10X2](X =µ-H or NCMe)

The reaction of the cyclophosphane (EtP)5 with the activated triosmium cluster [Os3(µ-H)2(CO)10] at 80 °C gave [Os3(µ-H)(CO)8(µ-η3-P5Et5H)]1 and [Os3(CO)10{1,3-(PEt)5}]2. The compound (PhP)5 reacted with [Os3(µ-H)2(CO)10] at room temperature to give [Os3(µ-H)(CO)8(µ-η3-P5Ph5H)]3. Treatment of (EtP)5 with [Os3(CO)10(NCMe)2] at room temperature afforded [Os3(CO)10{1,2-(PEt)5}]4, while the reaction at 80 °C yielded only 2. All the reaction products have been characterized by elemental analysis and IR, 1H and 31P NMR spectroscopy. The solid-state structures of compounds 1, 2 and 4 established by single-crystal X-ray diffraction showed that the phosphorus ring in 1 has undergone one P–P bond cleavage while those in 2 and 4 are intact. The solution structure of 3 has been fully characterized by two-dimensional 31P NMR spectroscopy.