Critical Effect of Film Thickness on Preconcentration Electroanalysis with Oriented Mesoporous Silica Modified Electrodes

Electrogenerated silica thin films exhibiting a regular hexagonal packing of vertically‐aligned mesopore channels are promising for preconcentration electroanalysis. This work demonstrates the critical role of film thickness on their sensing performance using paraquat as a model analyte, based on mesoporous silica films prepared by electrochemically assisted self‐assembly performed for various deposition times. Films prepared with too short synthesis times (<10 s) led to deposits covering partially the electrode surface and suffered from rather poor sensing performance. Then, uniformly deposited films were obtained (between 10 and 15 s), and sensitivity rose up by increasing deposition times, whereas some limitations started to occur with much thicker films (>15 s deposition times) as a result of less electrochemically accessible paraquat accumulated far away from the electrode surface and restricted mass transport through the whole film thickness. These limitations were also confirmed on the basis of multi‐layered mesoporous silica films, suggesting a behavior that might be typical for other types of film‐modified electrodes.     

Activation of C-H bonds in saturated hydrocarbons. The catalytic functionalisation of cycloöctane by means of some soluble iridium and ruthenium polyhydride systems

Homogeneous catalytic dehydrogenation of cycloöctane into cycloöctene has been effected by means of a variety of iridium and ruthenium polyhydrides, at 150°C, in the presence of an olefin as the hydrogen acceptor; best results (45–70 catalytic turnovers) have been achieved with (iPr₃P)₂IrH₅, [($\text{p}$-F-C₆H₄)₃P]₂IrH₅ and [($\text{p}$-F-C₆H₄)₃P]₃RuH₄.     

Synthesis of 3H-naphtho[2.1-b]pyran-2-carboxamides from cyclocoupling of β-naphthol,propargyl alcohols and isocyanide in the presence of Lewis acids

3H-Naphtho[2.1-b]pyran-2-carboxamides (3H-Benzo[f]chromene-2-carboxamides) can be synthesized from a three-component cyclocoupling reaction of β-naphthol, propargyl alcohols and isocyanide in the presence of ZnI₂ and FeCl₃ under air atmosphere. The reaction is proposed to involve the formation of aryl-zinc (II) σ-bond and its α-addition to isocyanide.     

Investigating Chaperone like Activity of Green Silver Nanoparticles: Possible Implications in Drug Development

Protein aggregation and amyloidogenesis have been associated with several neurodegenerative disorders like Alzheimer’s, Parkinson’s etc. Unfortunately, there are still no proper drugs and no effective treatment available. Due to the unique properties of noble metallic nanoparticles, they have been used in diverse fields of biomedicine like drug designing, drug delivery, tumour targeting, bio-sensing, tissue engineering etc. Small-sized silver nanoparticles have been reported to have anti-biotic, anti-cancer and anti-viral activities apart from their cytotoxic effects. The current study was carried out in a carefully designed in-vitro to observe the anti-amyloidogenic and inhibitory effects of biologically synthesized green silver nanoparticles (B-AgNPs) on human serum albumin (HSA) aggregation taken as a model protein. We have used different biophysical assays like thioflavin T (ThT), 8-Anilino-1-naphthalene-sulphonic acid (ANS), Far-UV CD etc. to analyze protein aggregation and aggregation inhibition in vitro. It has been observed that the synthesized fluorescent B-AgNPs showed inhibitory effects on protein aggregation in a concentration-dependent manner reaching a plateau, after which the effect of aggregation inhibition was significantly declined. We also observed meaningful chaperone-like aggregation-inhibition activities of as-synthesized florescent B-AgNPs in astrocytes.     

Protonation and reactivity towards carbon dioxide of the mononuclear tetrahedral zinc and cobalt hydroxide complexes, [Tp(Bu)t(,Me)]ZnOH and [Tp(Bu)t(,Me)]CoOH: comparison of the reactivity of the metal hydroxide function in synthetic analogues of carbonic anhydrase

The tris(3-tert-butyl-5-methylpyrazolyl)hydroborato zinc hydroxide complex [Tp(Bu)t(,Me)]ZnOH is protonated by (C(6)F(5))(3)B(OH(2)) to yield the aqua derivative [[Tp(Bu)t(,Me)]Zn(OH(2))][HOB(C(6)F(5))(3)], which has been structurally characterized by X-ray diffraction, thereby demonstrating that protonation results in a lengthening of the Zn-O bond by ca. 0.1 A. The protonation is reversible, and treatment of [[Tp(Bu)t(,Me)]Zn(OH(2))](+) with Et(3)N regenerates [Tp(Bu)t(,Me)]ZnOH. Consistent with the notion that the catalytic hydration of CO(2) by carbonic anhydrase requires deprotonation of the coordinated water molecule, [[Tp(Bu)t(,Me)]Zn(OH(2))](+) is inert towards CO(2), whereas [Tp(Bu)t(,Me)]ZnOH is in rapid equilibrium with the bicarbonate complex [Tp(Bu)t(,Me)]ZnOC(O)OH under comparable conditions. The cobalt hydroxide complex [Tp(Bu)t(,Me)]CoOH is likewise protonated by (C(6)F(5))(3)B(OH(2)) to yield the aqua derivative [[Tp(Bu)t(,Me)]Co(OH(2))][HOB(C(6)F(5))(3)], which is isostructural with the zinc complex. The aqua complexes [[Tp(Bu)t(,Me)]M(OH(2))][HOB(C(6)F(5))(3)] (M = Zn, Co) exhibit a hydrogen bonding interaction between the metal aqua and boron hydroxide moieties. This hydrogen bonding interaction may be viewed as analogous to that between the aqua ligand and Thr-199 at the active site of carbonic anhydrase. In addition to the structural similarities between the zinc and cobalt complexes, [Tp(Bu)t(,Me)ZnOH] and [Tp(Bu)()t(,Me)]CoOH, and between [[Tp(Bu)t(,Me)]Zn(OH(2))](+) and [[Tp(Bu)t(,Me)]Co(OH(2))](+), DFT (B3LYP) calculations demonstrate that the pK(a) value of [[Tp]Zn(OH(2))](+) is similar to that of [[Tp]Co(OH(2))](+). These similarities are in accord with the observation that Co(II) is a successful substitute for Zn(II) in carbonic anhydrase. The cobalt hydroxide [Tp(Bu)()t(,Me)]CoOH reacts with CO(2) to give the bridging carbonate complex [[Tp(Bu)t(,Me)]Co](2)(mu-eta(1),eta(2)-CO(3)). The coordination mode of the carbonate ligand in this complex, which is bidentate to one cobalt center and unidentate to the other, is in contrast to that in the zinc counterpart [[Tp(Bu)t(,Me)]Zn](2)(mu-eta(1),eta(1)-CO(3)), which bridges in a unidentate manner to both zinc centers. This difference in coordination modes concurs with the suggestion that a possible reason for the lower activity of Co(II)-carbonic anhydrase is associated with enhanced bidentate coordination of bicarbonate inhibiting its displacement.     

Activation of C-H bonds in saturated hydrocarbons. The selective,catalytic functionalisation of methyl groups by means of a soluble iridium polyhydride system

The selective, catalytic conversion of methylcyclohexane into methylenecyclohexane at 100°C, and of n-hexene into 1-hexene at 45°C, has been effected using bis(triisapropylphosphine)iridium pentahydride and an olefin (neohexene) as a hydrogen acceptor; with this system, approximate relative reactivities of C-H bonds in saturated hydrocarbons are: sec-alkyl-H, 1; iso-alkyl-H, 8; n-alkyl-H, > 60.     

The isolation of intermediates in hydrogen halide additions to some iridium complexes

The complexes [Ir(cod)L_n]PF₆(I, L = PPh₃, PMePh₂; n = 2. L = PMe₂Ph; n = 3) react with HX to give [IrHX(cod)L₂]PF₆ (II, L = PMePh₂ or PMe₂Ph) or [IrHX₂(cod)(PPh₃)] (III). The intermediates [IrX(cod)L₂] have, in two cases (L = PMePh₂, X = I, Br), been directly isolated from the reaction mixtures at 0°C, and are also formed from I with KX (L = PPh₃, X = Cl; L = PMePh₂, X = Cl, Br, I); these intermediates protonate to give II (L = PMePh₂), or an equimolar mixture of III and I (L = PPh₃, X = Cl). Surprisingly, I₂ reacts with I in MeOH to give III (L = PPh₃). The stereochemistries of II and III were determined by < ¹H NMR and especially by new methods using ¹³C NMR spectroscopy. The complexes I exhibit a Lewis acid reactivity pattern.     

A cyclometallated iridium(III) dimethylphenylphosphine complex

[Ir(cod)Cl]₂ (cod = 1,5-cyclooctadiene) reacts with PMe₂Ph in CH₃CN to give the red cation [Ir(PMe₂Ph)₄]⁺. This complex in CH₃CN reacts with H₂ to give cis-[IrH₂(PMe₂Ph)₄]⁺, but on reflux for 6 h in the absence of H₂, it gives the first example of a cyclometallated PMe₂Ph complex fac-[IrH(PMe₂C₆H₄)(PMe₂Ph)₃]⁺, as shown by PMR spectroscopy and preliminary X-ray crystallographic data.     

Dihydridoiridium diolefin complexes as intermediates in homogeneous hydrogenation

Two isomeric series of dihydrido-diolefin complex cations, cis- and cis-trans- [IrH₂(cod)L₂]PF₆ (cod = 1,5-cyclooctadiene; L = tertiary phosphine)have been observed directly by PMR spectroscopy and in some cases have been isolated as crystalline solids. They are prepared by H₂ addition to a diolefin complex (unsaturated route) or by diolefin addition to a hydrido complex (hydride route), respectively. These complexes appear to be important intermediates in the catalytic hydrogenation of (cod) by the catalysts [Ir(cod)L₂]PF₆. The cis- isomers transfer hydrogen to the coordinated (cod) much more rapidly than the cis, trans isomers; the hydrogen transfer to the olefin seems to require a coplanar M(CC)H system. H₂ addition to [Ir(cod)₂]⁺ at ?80° C gives [IrH₂(cod)₂]⁺; electron-withdrawing substituents therefore do not deactivate the metal center with respect to oxidative addition.     

Radiation-induced grafting of styrene onto ultra-high molecular weight polyethylene powder and subsequent film fabrication for application as polymer electrolyte membranes: I. Influence of grafting conditions

Ultra-high molecular weight polyethylene (UHMWPE) powder was irradiated by gamma rays using a ⁶⁰Co source. Simultaneous and pre-irradiation grafting was performed in air and in inert atmosphere at room temperature. The monomer selected for grafting was styrene, since the styrene-grafted UHMWPE could be readily post-sulfonated to afford proton exchange membranes (PEMs). The effect of absorbed radiation dose and monomer concentration in methanol on the degree of grafting (DG) is discussed. It was found that the DG increases linearly with increase in the absorbed dose, grafting time and monomer concentration, reaching a maximum at a certain level. The order of rate dependence of grafting on monomer concentration was found to be 2.32. Furthermore, the apparent activation energy, calculated by plotting the Arrhenius curve, was 11.5 kJ/mole. Lower activation energy and high rate dependence on monomer concentration shows the facilitation of grafting onto powder substrate compared with film. The particle size of UHMWPE powder was measured before and after grafting and found to increase linearly with increase in level of grafting. FTIR-ATR analysis confirmed the styrene grafting. The grafted UHMWPE powder was then fabricated into film and post-sulfonated using chlorosulfonic acid for the purposes of evaluating the products as inexpensive PEM materials for fuel cells. The relationship of DG with degree of substitution (DS) of styrene per UHMWPE repeat unit and ion exchange capacity (IEC) is also presented.