Electrochemical self-assembly of alkanethiolate molecules on Ni(111) and polycrystalline Ni surfaces

In this work, the electrochemical formation of alkanethiolate self-assembled monolayers (SAMs) on Ni(111) and polycrystalline Ni surfaces from alkanethiol-containing aqueous 1 M NaOH solutions was studied by combining Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), electrochemical techniques, and density functional theory (DFT) calculations. Results show that alkanethiolates adsorb on Ni concurrent with NiO electroreduction. The resulting surface coverage depends on the applied potential and hydrocarbon chain length. Electrochemical and XPS data reveal that alkanethiolate electroadsorption at room temperature takes place without S-C bond scission, in contrast to previous results from gas-phase adsorption. A complete and dense monolayer, which is stable even at very high cathodic potentials (-1.5 V vs SCE), is formed for dodecanethiol. DFT calculations show that the greater stability against electrodesorption found for alkanethiolate SAMs on Ni, with respect to SAMs on Au, is somewhat related to the larger alkanethiolate adsorption energy but is mainly due to the larger barrier to interfacial electron transfer present in alkanethiolate-covered Ni. A direct consequence of this work is the possibility of using electrochemical self-assembly as a straightforward route to build stable SAMs of long-chained alkanethiolates on Ni surfaces at room temperature.     

Improved hollow-fibre membranes for dye-affinity chromatography

Hollow-fibre membranes with different degrees of surface hydrophilicity were obtained by grafting mixtures of glycidyl methacrylate (GMA) and dimethyl acrylamide (DMAA) in various proportions, and Cibacron Blue F3G-A was attached to them through ammonia or glucamine spacers. Membrane hydrophilicity increased with the amount of dimethyl acrylamide in the grafted polymer. As the hydrophilicity increased the permeability decreased from 352 mL/cm2 min MPa for membranes grafted with GMA with ammonia spacer to 12.7 mL/cm2 min MPa for membranes grafted with GMA/DMAA 1/3 with glucamine spacer. Membranes grafted with GMA/DMAA 1/3 with ammonia spacer showed the best performance for BSA and lysozyme adsorption: maximum capacity was 15.3 +/- 2.2 mg BSA/mL membrane and 58.3 +/- 6.6 mg lysozyme/mL membrane while dissociation constants were 0.27 +/- 0.16 and 0.13 +/- 0.12 mg/mL, respectively. Over 80% of adsorbed proteins could be eluted with 2 M NaCl + 20% isopropanol in 20 mM sodium phosphate buffer, pH 7.0.     

Microcomputer program based on the Beierbeck-Saunders approach for the prediction of 13C-NMR chemical shifts in acyclic hydrocarbons

A microcomputer program based on the Beierbeck-Saunders approach for estimating ¹³C-NMR chemical shifts in acyclic hydrocarbons is described. It is shown to be applicable in cases of asymmetric alkanes with diastereotopic carbon atoms induced by chirality, side-chains attached to fixed rings, and solid-state analyses of hydrocarbons, for which rules based on conformationally-averaged solution data are unsatisfactory.     

Photocycloadditions of electron poor olefins to 2-aryl-1-pyrrolinium salts

Photocycloadditions of the electron poor olefins, acrylonitrile and methyl acrylate to a series of $\text{para}$-substituted 2-phenyl-1-pyrrolinium perchlorates have been explored as part of studies designed to test new synthetic methods.     

A novel series of nickel(II)-dppe-arylazoimidazole complexes. Synthesis and spectroscopic characterization

Reaction of [Ni(dppe)Cl₂/Br₂] with AgOTf in CH₂Cl₂ medium following ligand addition leads to [Ni(dppe)(OSO₂CF₃)₂] and then [Ni(dppe)(RaaiR)](OSO₂CF₃)₂ [RaaiR′ = p–R–C₆H₄–N=N–C₃H₂–NN-1–R′,(1–3), abbreviated as N,N′-chelator, where N(imidazole) and N(azo) represent N and N′, respectively; R = H (a), Me (b), Cl (c) and R′ = Me (1), CH₂CH₃ (2), CH₂Ph (3), OSO₂CF₃ is the triflate anion]. ³¹P{¹H}-NMR confirm that stable bis-chelated square planar Ni(II) azoimine–dppe complex formation with one sharp peaks. The ¹H NMR spectral measurements suggest azoimine link is present with lot of phenyl protons in the aromatic region. Considering all the moities there are a lot of different carbon atoms in the molecule which gives many different peaks in the ¹³C(¹H)-NMR spectrum. In the ¹H-¹H COSY spectrum in the present complexes and contour peaks in the ¹H-¹³C-HMQC spectrum in the present complexes, assign the solution structure and stereoretentive conformation in each complexes.     

Equation of state of a seven-dimensional hard-sphere fluid. Percus-Yevick theory and molecular-dynamics simulations

Following the work of Leutheusser [Physica A 127, 667 (1984)], the solution to the Percus-Yevick equation for a seven-dimensional hard-sphere fluid is explicitly found. This allows the derivation of the equation of state for the fluid taking both the virial and the compressibility routes. An analysis of the virial coefficients and the determination of the radius of convergence of the virial series are carried out. Molecular-dynamics simulations of the same system are also performed and a comparison between the simulation results for the compressibility factor and theoretical expressions for the same quantity is presented.     

Two Interrelated Strategies for Cephalotaxine Synthesis

Studies of two interrelated strategies for the synthesis of members of the cephalotaxus alkaloid family have culminated in a concise route for the preparation of the parent member cephalotaxine (1). As part of efforts exploring the use of an SET-promoted photocyclization reaction of aryl-substituted silylallyliminium salts to generate the spirocyclic DE unit of the target, we noted that attempts to generate the pentacyclic amino ketone 23 by deacylation of the enol ester 20 led to production of a mixture of 23 and the macrocyclic amino enone 24. A rapid equilibrium was shown to exist between 23 and 24, favoring the latter ring-opened form. This contrasts with the behavior of desmethylcephalotaxinone (22), a key late intermediate in several earlier cephalotaxine syntheses, which is known to exist in a ring-closed form. These observations led to the design of a second generation strategy which relies on transannular cyclization of the macrocyclic amino enedione 28. In practice, the sequence following this design transforms the known iodopiperonylethanol derivative 4 to 22 in 13 steps and a 12% overall yield and, thus, corresponds to an efficient formal synthesis of cepahalotaxine.     

Electrochemistry of Tris(1,10-phenanthroline)iron(II) inside a polymeric hydrogel. Coupled chemical reactions and migration effects

The retention, release, and detection of metallic complexes in polymeric hydrogels are of interest in drug delivery, analytical chemistry, and water remediation. The electrochemistry of the redox complexes inside the hydrogel could be affected by the viscoelastic properties of the gel, local ionic force and pH, and interactions (e.g., hydrophobic) between the complex and the polymer chains. In this work, it is shown that a simple setup, consisting of a disk electrode pressed on the hydrogel, allows to perform electrochemistry of a redox couple: Tris(1,10-phenanthroline)iron(II) (Fe(phen)₃ ²⁺) inside a hydrogel matrix. The behavior is compared with the same couple in solution, and it is found that the electrochemical properties of the redox couple are strongly affected by the presence of the hydrogel matrix. The cyclic voltammogram of the hydrogel loaded with complex shows a response, which suggests electrochemical-chemical mechanism. The chemical step is likely linked to a catalytic oxidation of free hydrated Fe²⁺ ions present inside the hydrogel together with the redox complex. Since Fe²⁺ ions have small charge transfer constants on the glassy carbon electrodes, only the catalytic current is observed. Indeed, when excess ligand (phenanthroline) is absorbed inside the hydrogel, the measured cyclic voltammograms show a single reversible oxidation/reduction step. It seems that the complexation equilibrium shifts toward the complex, making the free iron concentration negligible. Accordingly, the cyclic voltammetry shape and peak potential difference agree with a reversible oxidation/reduction. Additionally, the peak currents of the cyclic voltammograms show a linear dependence with the square root of time, as predicted by a Randles-Sevcik equation. However, the measured currents are smaller than the simulated ones. The differences are in agreement with simulations of the cyclic voltammograms where the migration of the redox species is considered. Chronoamperometry is used to measure the mass transport of redox species inside the hydrogel. It is found that the current transients still obey Cottrell’s equation, but the diffusion coefficients obtained from the slopes of Cottrell’s plots have to be corrected for migration effects. The effective diffusion coefficient of Fe(phen)₃ ²⁺ measured inside the hydrogel (D _Red-hydrogel = 5.5 (±0.5) × 10^?8 cm² s^?1) is ca. 80 times smaller than the one measured in solution (D _Red-solution = 4.4 (±0.5) × 10^?6 cm² s^?1). The simple setup has a true semi-infinite boundary condition, which allows characterizing the hydrogel in the same condition as the bulk material and easily changing both the redox species and the hydrogel structure.     

Polyethyleneimine‐Coated Gold Nanoparticles: Straightforward Preparation of Efficient DNA Delivery Nanocarriers

A novel one‐pot method for the synthesis of polyethyleneimine (PEI)‐coated gold nanoparticles (AuPEI‐NPs) that combines the reductant–stabilizer properties of PEI with microwave irradiation starting from hydrogen tetrachloroaurate acid (HAuCl₄) and branched PEI 25 kDa (b25kPEI) was explored. The method was straightforward, green, and low costing, for which the Au/PEI ratio (1:1 to 1:128 w/w) was a key parameter to modulate their capabilities as DNA delivery nanocarriers. Transfection assays in CHO‐k1 cells demonstrated that AuPEI‐NPs with 1:16 and 1:32 w/w ratios behaved as effective DNA gene vectors with improved transfection efficiencies (twofold) and significantly lower toxicity than unmodified b25kPEI and Lipofectamine 2000. The transfection mediated by these AuPEI‐NP–DNA polyplexes preferentially used the caveolae‐mediated route for intracellular internalization, as shown by studies performed by using specific internalization inhibitors as well as colocalization with markers of clathrin‐ and caveolae‐dependent pathways. The AuPEI‐NP polyplexes preferentially used the more efficient caveolae internalization pathway to promote transfection, a fact that supports their higher transfection efficiency relative to that of Lipofectamine 2000. In addition, intracellular trafficking of the AuPEI‐NPs was studied by transmission electron microscopy.