Transition metal complexes with long-chain amines thermal behaviour and crystal structure of (n-CaH2a+1NH2)2ZnCl2

The thermal behaviour of (n-C_aH_2n+1NH₂)₂ZnCl₂ complexes with n = 6, 8, … 16 has been investigated by DSC and by temperature variable IR and X-ray powder diffraction techniques. Complexes with n = 12,14,16 show solid—solid phase transition which are “melting” transitions of the hydrocarbon regions of the structure. The crystal structure of both the low and the high temperature polymorphs is characterized by the piling of sandwiches, each formed by an “inorganic” layer sandwiched between two alkylammonium layers.     

Structural studies of the allelic wheat glutenin subunits 1Bx7 and 1Bx20 by matrix-assisted laser desorption/ionization mass spectrometry and high-performance liquid chromatography/electrospray ionization mass spectrometry

Structural studies of the high molecular mass (HMM) glutenin subunits 1Bx7 (from cvs Hereward and Galatea) and 1Bx20 (from cv. Bidi17) of bread wheat were conducted using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) and reversed-phase high-performance liquid chromatography/electrospray ionization mass spectrometry (RP-HPLC/ESI-MS). For all three proteins, MALDI-TOFMS analysis showed that the isolated fractions contained a second component with a mass about 650 Da lower than the major component. The testing and correction of the gene-derived amino acid sequences of the three proteins were performed by direct MALDI-TOFMS analysis of their tryptic peptide mixture. Analysis of the digest was performed by recording several MALDI mass spectra of the mixture at low, medium and high mass ranges, optimizing the matrix and the acquisition parameters for each mass range. Complementary data were obtained by RP-HPLC/ESI-MS analysis of the tryptic digest. This resulted in coverage of about 98% of the sequences. In contrast to the gene-derived data, the results obtained demonstrate the insertion of the sequence QPGQGQ between Trp716 and Gln717 of subunit 1Bx7 (cv. Galatea) and a possible single amino acid substitution within the T20 peptide of subunit 1Bx20. Moreover, the mass spectrometric data demonstrated that the lower mass components present in all the fractions correspond to the major components but lack about six amino acid residues, which are probably lost from the protein C-terminus. Finally, the results obtained provide evidence for the lack of glycosylation or other post-translational modifications of these subunits.     

Structural studies of glutenin subunits 1Dy10 and 1Dy12 by matrix-assisted laser desorption/ionisation mass spectrometry and high-performance liquid chromatography/electrospray ionisation mass spectrometry

Structural studies of the high molecular weight (HMW) glutenin subunits 1Dy10 and 1Dy12 of bread wheat were conducted using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) and reversed-phase high-performance liquid chromatography/electrospray ionisation mass spectrometry (RP-HPLC/ESI-MS). For both proteins, MALDI-TOFMS analysis showed that the isolated fractions contained a second component with a mass about 500-540 Da lower than the major component. The testing and correction of the gene-derived amino acid sequences of both proteins were performed by direct MALDI-TOFMS analysis of their tryptic peptide mixture and analysis of the digests was performed by recording several MALDI mass spectra of the mixture at low, medium and high mass ranges, optimising the matrix and the acquisition parameters for each mass range. Complementary data were obtained by RP-HPLC/ESI-MS analysis of the tryptic digest. This resulted in the coverage of the whole protein sequences except for two short fragments (T1 and T8), which are identical in the two homologous subunits, and for an additional dipeptide (T14) in subunit 1Dy12, which were not detected. It also demonstrated that, in contrast to the gene-derived data, the sequence of subunit 1Dy12 does not include the dipeptide Gly-Gln between residues Gln(454) and Pro(455), and that the lower mass components present in both fractions correspond to the same sequences lacking short peptides that are probably lost from the protein N- or C-termini. Finally, the results obtained provide evidence for the lack of a substantial level of glycosylation or other post-translational modifications of the two subunits, and demonstrate that mass spectrometric mapping is the most useful method presently available for the direct verification of the gene-derived sequences of HMW glutenin subunits and similar proteins.     

Mononuclear heterocyclic rearrangements. Part 4 Synthesis and characterization of the E-isomer phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole

3-Benzoyl-5-phenyl-1,2,4-oxadiazole (I) with phenylhydrazine in acetic acid gives the two geometrical isomers, phenylhydrazones II-Z and II-E, which have been characterized by uv-visible, ir, and nmr spectra. The possible II-E ? II-Z isomerization as well as the rearrangement of II-Z and of II-E into 2,5-diphenyl-4-benzoylamino-1,2,3-triazole (III) has been pointed out.     

Cluster and periodic DFT calculations of MgO/Pd(CO) and MgO/Pd(CO)(2) surface complexes

The bonding and vibrational properties of Pd(CO) and Pd(CO)(2) complexes formed at the (100) surface of MgO have been investigated using the gradient-corrected DFT approach and have been compared to the results of infrared and thermal desorption experiments performed on ultrathin MgO films. Two complementary approaches have been used for the calculation of the electronic properties: the embedded cluster method using localized atomic orbital basis sets and supercell periodic calculations using plane waves. The results show that the two methods provide very similar answers, provided that sufficiently large supercells are used. Various regular and defect adsorption sites for the Pd(CO) and Pd(CO)(2) have been considered: terraces, steps, neutral and charged oxygen vacancies (F and F(+) centers), and divacancies. From the comparison of the computed and experimental results, it is concluded that the most likely site where the Pd atoms are stabilized and where carbonyl complexes are formed are the F(+) centers, paramagnetic defects consisting of a single electron trapped in an anion vacancy.     

Synthesis, Chemical Characterization, and Molecular Structure of Au8{Fe(CO)4}4(dppe)2 and Au6Cu2{Fe(CO)4}4(dppe)2

The new Au₈{Fe(CO)₄}₄(P^P)₂ and Au₆Cu₂{Fe(CO)₄}₄(P^P)₂ (P^P=dppm, dppe) neutral cluster compounds were isolated in good yields by condensation of the [Au₃{Fe(CO)₄}₂(P^P)]^- anions with Au(SEt₂)Cl and CuCl, respectively, and have been characterized by IR, NMR and microanalyses. The molecular structures of Au₈{Fe(CO)₄}₄(dppe)₂ and Au₆Cu₂{Fe(CO)₄}₄(dppe)₂ have been determined by X-ray diffraction studies. Both molecules adopt a stereogeometry of the heavy atoms consisting of a triangulated and corrugated ribbon twisted around the elongation direction. Contrary to the expectations the latter displays the two copper atoms in the sites of highest connectivity. This implies that site exchange between copper and gold occurs during the synthesis.     

RuO4-promoted oxidative polycyclization of isoprenoid polyenes. A further insight into the stereochemistry of the process

Further studies on the RuO₄-catalyzed oxidative polycyclization of isoprenoid polyenes have been carried out. The configuration of the tris-THF product from the oxidation of geranylgeranyl acetate has been determined by a combination of spectral and chemical correlation methods. The oxidation of (E,Z)-farnesyl acetate, synthesized from nerol, has been carried out. This process stops at the first cyclization indicating that an E configuration of the Δ⁶ double bond is needed for the second cyclization to occur. The results are discussed in comparison with previous knowledge on the related Re(VII) polycyclization of polyenic bis-homoallylic alcohols.