Alpo4 and Alpo4-Al2O3 as New Heterogeneous Catalysts for the Solvent-Free Tetrahydropyranylation of Alcohols and Phenols

OH-protection of alcohols and phenols by heating the hydroxylated compound with 3,4-dihydro-2H-pyrane in the presence of an AlPO₄ or AlPO₄-Al₂O₃ heterogeneous acid catalyst is described. Isolated yields, not optimized, were in the range 50–99%.     

Bandgap Modulation in Efficient n‐Thiophene Absorbers for Dye Solar Cell Sensitization

Five new sensitizers for dye sensitized solar cells have been designed consisting of conjugated thienylenevinylene units threaded with alkyl chains to improve solubility and cyanoacetic acid as anchoring group. The conjugation length was increased from 2 to 6 thienylenevinylene units, which resulted in a red‐shift of the optical absorption of the dyes from 550 to 750 nm, improving the spectral overlap with the solar spectrum. The photovoltaic performance of these dyes as sensitizers in mesoporous TiO₂ solar cells shows a clear correlation of increasing photocurrent with the extension of the conjugation up to an optimal length. Further extension of the conjugation increases the absorption but additional effects like self‐quenching or recombination processes reduce the photocurrent and photovoltages and consequently the overall efficiency of the DSC.     

Theoretical study of {Au3(CH3NCOCH3)3}n·{2,4,7‐trinitro‐9‐fluorenone} (n = 1,2) complexes

The interaction between {Au₃(CH₃N?COCH₃)₃} and {2,4,7‐trinitro‐9‐fluorenone} and the electronic structure and spectroscopic properties of {Au₃(CH₃N = COCH₃)₃}_n·{2,4,7‐trinitro‐9‐fluorenone} (n = 1,2) are studied at the HF, MP2, and PBE levels. Secondary π‐interactions (Au‐fluorenone) were found to be the main contribution to short‐range stability in the {Au₃(CH₃N?COCH₃)₃}_n·{2,4,7‐trinitro‐9‐fluorenone} complex. At the MP2 and PBE levels, Au‐C equilibrium distances of 292.3 and 304.0 pm and interaction energies of 105.3 and 24.9 kJ/mol were found, respectively. The absorption spectra of these complexes were calculated by the single excitation time‐dependent method at the PBE level. The theoretical values obtained are in agreement with the experimental range. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Capillary electrophoresis/mass spectrometry for the separation and characterization of bovine Cu,Zn‐superoxide dismutase

The native form of Cu,Zn‐superoxide dismutase (SOD‐1) is a homodimer that coordinates one Cu²⁺ and one Zn²⁺ per monomer. Cu²⁺ and Zn²⁺ ions play crucial roles in enzyme activity and structural stability, respectively. In addition, dimer formation is essential for SOD‐1 functionality, and in humans several SOD‐1 mutant isoforms have been associated with certain types of amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disorder. In this paper we used capillary electrophoresis and mass spectrometry to study the different structures of bovine SOD‐1. The metal ions of the native enzyme (Cu₂,Zn₂‐dimer SOD‐1) were released in acidic medium in order to obtain apo‐SOD‐1, which is a monomer. Both substances were analyzed by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) and capillary electrophoresis with ultraviolet and electrospray ionization mass spectrometry detection (CE/UV and CE/ESI‐MS, respectively). With MALDI‐TOF‐MS, using matrices of sinapinic acid (SA) or 2,5‐dihydroxybenzoic acid (DHB) with or without trifluoroacetic acid (TFA), similar mass spectra were obtained for the metalated and non‐metalated samples. In both cases, an average molecular mass corresponding to the apo‐monomer SOD‐1 was calculated. This finding indicated that the metals were released from the Cu₂,Zn₂‐dimer SOD‐1 during sample preparation or ionization. For CE/UV and CE/ESI‐MS, two background electrolytes (BGEs) potentially compatible with ESI‐MS detection were used, namely 1 M of acetic acid (pH 2.3) and 10 mM of ammonium acetate (pH 7.3). Using a sheath liquid of 2‐propanol/water (60:40 v/v), with or without 0.1% v/v of formic acid, CE/ESI‐MS sensitivity was enhanced when the acidic BGE and the acidic sheath liquid were used. However, the electrophoretic profiles and the mass spectra obtained suggested that the metals of Cu₂,Zn₂‐dimer SOD‐1 were released, which generated the apo‐monomer during the electrophoretic separation. The neutral BGE provided enhanced conditions for the detection of the native enzyme. The differences between the mass spectra obtained for the Cu₂,Zn₂‐dimer and the apo‐monomer forms were significant and the presence of formic acid in the sheath liquid affected only sensitivity. Our results highlight the importance of selecting appropriate non‐denaturing separation and detection conditions to obtain reliable structural information about non‐covalent protein complexes by CE/ESI‐MS. Copyright © 2010 John Wiley & Sons, Ltd.     

A theoretical and NMR lanthanide‐induced shift (LIS) investigation of the conformations of lactams.

Molecular mechanics (MM) with MMFF94 and MMX force fields and ab initio (RHF/6‐31G*,RHF/6‐311G**, and B3LYP/6‐311G**) calculations are used with lanthanide‐induced shift (LIS) to investigate the conformations of N‐methyl‐2‐pyrrolidone 1 , N‐methyl‐2‐piperidone 2 , ε‐caprolactam 3, γ‐valerolactam (1,5‐dimethyl‐2‐pyrrolidone) 4, 2 ‐ azetidinone 5 , 4‐methyl azetidinone 6 , 4‐phenyl azetidinone 7 , and N‐methyl‐4‐phenyl azetidinone 8 . The Yb(fod)₃ paramagnetic induced shifts of all the ¹H and ¹³C nuclei are measured and the corresponding diamagnetic complexation shifts obtained by the addition of Lu(fod)₃. The complexation model (two‐, three‐, or four‐site) used depends on the relative rates of the processes involved. The amide inversion is the same order as that of the 5‐ and 6‐membered lactam rings and much faster than the lanthanide complexation and the inversion of the 7‐membered ring. Both MM and ab initio calculations give an envelope conformation for 1 with C‐4 out of the ring plane in agreement with the LIS analysis. For the piperidone ring of 2 , the half‐chair is calculated as the most stable form. The LIS analysis confirms this but cannot exclude a small amount (<2%) of the boat conformation. For 3 , the LIS analysis gives a minimum for 90:10% chair to boat conformation, and 4 exists in two envelope conformations with the C₅‐Me ps‐eq and ps‐ax in an eq/ax ratio of 94:6%. In 2‐azetidinone 5 , the ab initio calculations gave both ring and nitrogen planar, but the MMFF94 calculations give a butterfly ring and pyramidal nitrogen. The LIS analysis for 5 gave good agreement (Rcryst 0.46%) for the MMFF94 geometry with endo NH but the planar ab initio geometries worse agreement (Rcryst = 1.1%). For 4‐methyl‐2‐azetidinone 6 , the MMFF94 geometry gave good agreement (Rcryst 0.96%) with two butterfly conformations with axial and equatorial methyl groups in 1:1 ratio. All the planar geometries gave worse agreement (Rcryst >1.5%). In 4‐phenyl azetidinone 7 , the MMFF94 geometry with 60% of the axial conformer gave Rcryst 1.2% but the other geometries Rcryst >1.5%. In contrast the N‐methyl‐4‐phenyl‐2‐azetidinone 8 gave good agreement for all the geometries. The butterfly conformation gave Rcryst 1.1% for 80% of the axial conformer and the planar geometries Rcryst 0.98%. The LIS results confirm the ab initio and MM optimised geometries, but the conformer energies at times differ from the calculated values. They also differ considerably from the corresponding values for the lactones studied previously, and possible reasons for this are discussed.     

The effect of temperature on the mechanical properties of a protein-based biopolymer network

Several studies have shown that eggshell membrane (ESM) is a suitable biomaterial with potential applications in biomedicine such as wound repair and cell culture. In order to control and improve the use of ESM for biomedical applications their physical and structural properties must be known. In this paper, we have studied the effect of temperature on the mechanical properties of the ESM. Atomic force microscopy was used to assess the morphology of the ESM. The mechanical properties of the membranes were studied by means of uniaxial tensile tests carried out at four different temperatures. Differential scanning calorimetry and thermo-gravimetrical analysis were used to assess the thermal transitions of the ESM and the influence of the water content on its thermal behavior. The Young’s modulus showed a linear inverse dependence with regard to the temperature of the sample. A peak associated to the thermal denaturation of collagen was observed in the DSC tests of the membrane. These peaks showed a dependence on the water content of the specimens.