Layer uniformity in glucose oxidase immobilization on SiO2 surfaces

The goal of this work was the characterization, step by step, of the enzyme glucose oxidase (GOx) immobilization on silicon oxide surfaces, mainly by means of X-Ray photoelectron spectroscopy (XPS). The immobilization protocol consists of four steps: oxide activation, silanization, linker molecule deposition and GOx immobilization. The linker molecule, glutaraldehyde (GA) in this study, must be able to form a uniform layer on the sample surface in order to maximize the sites available for enzyme bonding and achieve the best enzyme deposition. Using a thin SiO₂ layer grown on Si wafers and following the XPS Si2p signal of the Si substrate during the immobilization steps, we demonstrated both the glutaraldehyde layer uniformity and the possibility to use XPS to monitor thin layer uniformity. In fact, the XPS substrate signal, not shielded by the oxide, is suppressed only when a uniform layer is deposited. The enzyme correct immobilization was monitored using the XPS C1s and N1s signals. Atomic force microscopy (AFM) measurements carried out on the same samples confirmed the results.     

NMR studies of phenylbenzohydroxamic acid and kinetics of complex formation with nickel(II)

The behavior of N-phenylbenzohydroxamic acid (PBHA) in organic solvents has been investigated by (1)H and (13)C NMR spectroscopy. Measurements in acetone at different temperatures and concentrations enable one to individualized two signals, in a 20/80 area ratio, which were ascribed to partition of PBHA between two isomers, HZ (cis) and HE (trans). The dependence of the low-intensity peak on concentration and temperature strongly suggests dimer formation. Since only the HZ form can give dimers, it may be concluded that in acetone PBHA is present mainly in the HE form. (13)C NMR measurements in methanol yielded a 50/50 [HZ]/[HE] ratio. The equilibria and kinetics of complex formation in aqueous solutions between Ni(II) and PBHA were investigated by spectrophotometric and stopped-flow techniques at 25 degrees C and 0.2 M ionic strength. Two reaction paths, involving the binding of Ni(2+) to the neutral PBHA and to its anion, were observed. The rate constants of the forward and reverse steps are k(1) = (7.1 +/- 0.3) x 10(2) M(-)(1) s(-)(1) and k(-1) = (4.9 +/- 0.6) s(-)(1) for the step involving the undissociated PBHA and k(2) = (5.5 +/- 0.7) x 10(4) M(-)(1) s(-)(1) and k(-2) = (1.2 +/- 0.1) s(-)(1) for the step involving the anion. The k(2) value indicates that the PBHA anion reacts with Ni(2+) according to Eigen's mechanism and that in water the cis form prevails. The k(1) value is lower by a factor of 13 compared to the value estimated on the basis of Eigen's mechanism, suggesting that at least 90% of the neutral ligand is present in a nonreactive conformation.     

A Rhodium–Pentane Sigma‐Alkane Complex: Characterization in the Solid State by Experimental and Computational Techniques

The pentane σ‐complex [Rh{Cy₂P(CH₂CH₂)PCy₂}(η²:η²‐C₅H₁₂)][BAr^F₄] is synthesized by a solid/gas single‐crystal to single‐crystal transformation by addition of H₂ to a precursor 1,3‐pentadiene complex. Characterization by low temperature single‐crystal X‐ray diffraction (150 K) and SSNMR spectroscopy (158 K) reveals coordination through two Rh???H?C interactions in the 2,4‐positions of the linear alkane. Periodic DFT calculations and molecular dynamics on the structure in the solid state provide insight into the experimentally observed Rh???H?C interaction, the extended environment in the crystal lattice and a temperature‐dependent pentane rearrangement implicated by the SSNMR data.     

A simple and efficient highly enantioselective synthesis of alpha-ionone and alpha-damascone

An efficient highly enantioselective (ee > or =99%) synthesis of alpha-ionone and alpha-damascone is described. Both enantiomers of title compounds were synthesized through two straightforward pathways diverging from enantiopure (R)- or (S)-alpha-cyclogeraniol. These versatile building blocks were obtained by regioselective ZrCl(4)-promoted biomimetic cyclization of (6S)- or (6R)-(Z)-6,7-epoxygeraniol, respectively, followed by deoxygenation of the so formed secondary alcohol. The chiral information was encoded by a highly regioselecive Sharpless asymmetric dihydroxylation of inexpensive geranyl acetate.     

Synthetic approaches to indolo[6,7-a]pyrrolo[3,4-c]carbazoles: potent cyclin D1/CDK4 inhibitors

Synthesis of indolo[6,7-a]pyrrolo[3,4-c]carbazoles 1, a new class of cyclin D1/CDK4 inhibitors, by oxidation of the corresponding aryl indolylmaleimides 2, will be described. Two approaches to the synthesis of 2 were identified that required new methods for the synthesis of 7-substituted indole acetamides 3 and N-methyl (indol-7-yl)oxoacetates 6. The chemistry developed enabled introduction of functionality (-OR, NR(2)) at C(12) and N(13) facilitating structure-activity relationship (SAR) evaluation of this indolocarbazole platform.     

Structure of dipotassium 5,6-dihydrouracil-6,6-disulfonate monohydrate

The title compound was synthesized and its crystal structure determined by single crystal X-ray diffraction techniques. It crystallizes in the monoclinic system witha=9.390(1),b=9.688(2),c=13.828(3)Å,=110.16(2)°, space groupP2₁/c,Z=4. The structure was solved by direct methods and refined by full-matrix least-squares calculations toR=0.032 for 1968 reflections withI>3(I) [MoK radiation]. The six-membered ring of the 5,6-dihydrouracil-6,6-disulfonate dianion displays an approximate skew-boat conformation, but the ring puckering differs from that commonly observed in 5,6-dihydrouracil derivatives. The coordination to two crystallographically independent K⁺ ions which exhibit different coordination geometries links anions, cations and water molecules in an infinite three-dimensional network.     

Preliminary studies of berberine and its semi-synthetic derivatives as a promising class of multi-target anti-parkinson agents

Parkinson’s disease (PD) is a neurodegenerative disorder bearing motor and nonmotor symptoms. The treatment today is symptomatical rather than preventive or curative and this leaves the field open for the search of both novel molecular targets and drug candidates. Interference with α-synuclein fibrillation, monoamine oxidase (MAO) inhibition, modulation of adenosine receptors and the inhibition of specific phosphodiesterase (PDE) isoforms are some of the currently pursued strategies. We synthesised and studied some semi-synthetic berberine derivatives using a set of in silico tools. We evaluated their drug-likeness and tested the compounds against a set of target proteins involved in the onset or progression of PD, with a particular attention to MAO-B. Preliminary in vitro assay on MAO-B confirmed our in silico predictions.     

In-water reactivity of nucleosides and nucleotides: one-step preparation and biological evaluation of novel ferrocenyl-derivatives

The reactivity in water of a series of nucleosides and nucleotides towards ferrocenemethanol was investigated. Several adducts incorporating the ferrocenemethyl moiety into the heterocyclic base were isolated and their activity was tested against HIV-1, HBV, YFV, BVDV and several bacteria. However, none of the new compounds showed significant antiviral activity nor cytotoxicity. The reaction with ferrocenemethanol of the model dinucleotide ^5′dCpdG^3′, for a direct comparison of the behaviour of purine versus pyrimidine bases, is also discussed.     

OsO4-Catalyzed oxidative cyclization of geranyl and neryl acetate to cis-2,5-bis(hydroxymethyl)tetrahydrofurans

OsO₄ catalyzes the oxidative cyclization of the 1,5-dienes geranyl acetate (1) and neryl acetate (2) to the cis-2,5-bis(hydroxymethyl)tetrahydrofurans 3 and 4 respectively, in the presence of NaIO₄ as cooxidant in DMF. The reaction is stereospecific and proceeds with the sequential syn addition to both double bonds of the starting materials. The observed stereoselectivity can be explained by invoking the intermediacy of a square-based pyramidal osmium (VI) diester (5) that has been isolated and characterized. Evidence is reported that this substance is indeed an intermediate in the transformation of 1 to 3.     

Spectroscopic,magnetic and conductivity measurements of manganese(II) complexes with 2,5-diphenyloxazole

Summary The Mn(PPO)_nX₂ complexes (where PPO is 2,5-diphenyloxazole, n = 1, 2 or 3 and X = Cl^–, Br^–, I^– or SCN^–) have been prepared from the corresponding metal salt with the ligand in methanolic solution or with the molten ligand in the appropriate reactant ratio and studied by chemical analysis, electronic and i.r. spectroscopy, magnetic and molar conductivity values at 25°. The complexes are generally nonconducting in DMF; they are high spin and hexacoordinated. The Mn(PPO)X₂ complexes are high polymers with both ligand and anions bridging. The Mn(PPO)₂X₂ species are polymeric with PPO monodentate N-bonded and halogens and thiocyanates bridging bonded; the Mn(PPO)₃X₂ derivatives have monodentate N-bonded ligands whereas the halogens and thiocyanates are terminal and bridging, respectively.