Reductive opening of the thiazolidine ring. Selective N-methylation of cysteamines

The reaction of thiazolidines 2 and 7 with borane was investigated. It gave N-methylcysteamines 3 and 8 through thiazolidine ring opening. Sodium borohydride and lithium aluminum hydride were ineffective.     

Copper(II) complexes of N-terminal protected tri- and tetra-peptides containing histidine residues

Copper(II) complexes of peptides containing two or three histidyl residues (Ac-HisGlyHis-OH, Ac-HisGlyHis-NHMe, Ac-HisHisGlyHis-OH and Ac-HisHisGlyHis-NHMe) have been studied by potentiometric, UV-Vis, EPR and CD spectroscopic measurements. The imidazole nitrogen atoms are described as the primary metal binding sites of all ligands resulting in the formation of various macrochelates in the pH range 4 to 7. The (Nim, N-, Nim)-co-ordinated [CuH-1L]0+ complexes were mainly detected in samples containing free carboxylates at the C-termini, whilst the [CuH-2L]-(0) complexes were the predominant species in slightly alkaline solution and their binding modes were described via 4N-co-ordination (Nim, N-, N-, Nim) in (7,5,6)-membered fused chelate rings. Deprotonation and co-ordination of the third amide nitrogens were detected above pH approximately 9 in all cases.     

Synthesis of mixed metal decaosmium carbido clusters: The X-ray structures of the monoanions [Os10C(CO)24Cu(NCMe)]− and [Os10C(CO)24AuPPh3]−

The high nuclearity mixed metal cluster monoanions [Os₁₀C(CO)₂₄Cu(NCMe)]^? (I) and [Os₁₀C(CO)₂₄AuPPh₃]^? (II) have been obtained by reaction of the carbido-dianion [Os₁₀C(CO)₂₄]^2? (III) with one equivalent of [Cu(NCMe)₄] [BF₄] and Ph₃PAuCl, respectively, in CH₂Cl₂. X-ray analysis of the [PPh₃Me]⁺ salts of I and II show that the Cu and Au ligands have added to capping tetrahedra of the dianion III in μ₃- and μ₂-bridging positions, respectively.     

Solid-state supramolecular organization, established directly from powder diffraction data, and photoluminescence efficiency of rigid-core oligothiophene-S,S-dioxides

The "rigid-core" material 3,5-dimethyl-2,3'-bis(3-methylthiophene)-dithieno[3,2-b:',3'-d]thiophene-4,4-dioxide (DTTOMe4) has the highest photoluminescence ever reported for thiophene-based molecules in the solid state. We report the structure of this material, determined directly from powder X-ray diffraction data using the Genetic Algorithm method for structure solution, followed by Rietveld refinement, and the structural properties are discussed in relation to the structures of the corresponding subsystems DTTO and DTTOMe. While the crystal structures of the latter compounds contain cofacial dimers, the crystal structure of DTTOMe4 comprises layers of molecules aligned in an antiparallel fashion. Intermediate neglect of differential overlap with single configuration interaction (INDO/SCI) calculations on the intermolecular interactions in the three crystal structures show that the different solid-state photoluminescence efficiencies of DTTOMe4, DTTOMe, and DTTO cannot be correlated with the different types of dipole-dipole alignment in the solid state. Instead, photoluminescence efficiencies correlate well with the rate of formation of nonradiatively decaying charge-transfer pairs upon photoexcitation. Because of larger intermolecular distances in DTTOMe4, the photoluminescence is less effectively quenched by charge-transfer processes than in DTTOMe and DTTO.     

Cationic cobalt(I) carbonyl complexes containing secondary or tertiary phosphines. A direct synthesis from cobalt(II) salts

Cobalt(I) carbonyl complexes of formula [Co(CO)_n(P)_5?n]ClO₄ (n = 1, 2, 3; P = secondary or tertiary phosphine) have been prepared by reaction of CO under ambient conditions with Co(ClO₄)₂ · 6H₂O and phosphine in isopropyl alcohol. The chemical and spectroscopic properties of these complexes are described and the stoichiometry and mechanism of the carbonylation reaction discussed.     

Preparative and NMR studies of 1,3-dienecobalt(I) complexes

The synthesis and the characterization of cobalt(I) complexes of the type [Co(diene)(phosphine)₃]Y (diene = 1,3-butadiene and isoprene; phosphine = PMe₃, PMe₂Ph, and HPPh₂; Y = ClO₄, BF₄, or BPh₄) are reported. The fluxional nature of the five-coordinate cations [Co(diene)(phosphine)₃]⁺ is shown by variable-temperature NMR spectroscopy (¹H and ³¹P). Low-temperature spectra are consistent with a square-pyramidal structure in which the diene occupies two basal coordination sites.     

Solid-state versus solution preparation of two crystal forms of [HN(CH2CH2)3NH][OOC(CH2)COOH]2. Polymorphs or hydrogen bond isomers?

The reaction of [N(CH2CH2)3N] with malonic acid [HOOC(CH2)COOH] in the molar 1:2 ratio yields two different crystal forms of the salt [HN(CH2CH2)3NH][OOC(CH2)COOH]2 depending on the preparation technique and crystallization speed: form I, containing malonate anions with intramolecular hydrogen bonds, is obtained by solid-state co-grinding or by rapid crystallization, whereas form II containing intermolecular hydrogen bonds is obtained by slow crystallization. Form I and II do not interconvert, and form I undergoes an order-disorder phase transition on cooling.     

Rigid optically-active D2 and D3 macrocycles

The synthesis and characterization of novel optically-active macrocycles, obtained by esterification reaction from a binaphthyl-containing diol and phthalic or terephthalic acids, and possessing overall D2 or D3 symmetry, is described.     

Kinetic study of the reduction of hydroxylamine by Cu(I)

We have studied the reduction of Se^IV in acidic medium (1 M HCl and 1 M HClO₄) by classical and alternating current polarography and single sweep linear voltammetry with dropping mercury electrode and hanging mercury drop (HMDE). Two steps are observed distinctly: (1) The reduction of Se^IV→Se^o leads to a deposit of adsorbed elementary selenium. A mathematical expression is shown for the variation of current which is related to the surface covered at the HMDE. (2) The second step is the reduction of Se^o→Se^2? which takes place at more negative potentials. The accumulation of Se^o may be used for the determination of traces in trace analysis by cathodic stripping. It appears that the behavior of selenium in these two mineral acids is similar. But sometimes it behaves in a different manner, especially in a.c. polarography (in this connection the influence of frequency and demodulation angle are important).     

Rheology of asphalts modified with glycidylmethacrylate functionalized polymers

Asphalt is known to be a colloidal suspension in which asphaltenes are covered by a stabilizing phase of polar resins and form complex micelles that are dispersed in the oily maltenic phase. In order to enhance its mechanical properties (e.g., in road paving), asphalts are often loaded with polymeric materials, thereby obtaining blends that can have different physical or chemical structures, depending on the composition of the added polymer. Asphalts modified by the addition of reactive ethylene terpolymers were prepared and their dielectric and rheological properties were measured both before and after a cure at high temperature. Even if it is not possible to determine the exact nature of the chemical interactions between asphalt and polymer, master curves obtained from dynamic data clearly show that during the cure the material tends to the behavior of a cross-linked network.