Tyrosinase immobilized magnetic nanobeads for the amperometric assay of enzyme inhibitors: application to the skin whitening agents

The immobilization of tyrosinase onto glutaraldehyde activated streptavidine magnetic particles and subsequent retention onto a magnetized carbon paste electrode for the amperometric assay of tyrosinase inhibitors is described. Tyrosine was used as substrate as it is the first substrate in the melanogenesis process. The sensing mode is based on monitoring the decrease of the amperometric signal corresponding to the electrochemical reduction of dopaquinone enzymatically generated. This current decrease is due to the presence of inhibitors acting directly on the enzyme or inhibitors acting on the product of the enzymatic reaction, i.e. dopaquinone. The methodology is designed for the evaluation of the inhibitory potency of the most frequently used active substances in cosmetic marketed products against hyperpigmentation such as kojic acid, azelaic acid and benzoic acid. These compounds bind to the tyrosinase active center. Ascorbic acid is also investigated as it interrupts the synthesis pathway of melanin by reducing the melanin intermediate dopaquinone back to l-dopa. By comparing the obtained IC₅₀, under the same experimental conditions, the order of their inhibitory potency was: kojic acid (IC₅₀ = 3.7 × 10⁻⁶ M, K_i = 8.6 × 10⁻⁷ M), ascorbic acid (IC₅₀ = 1.2 × 10⁻⁵ M), benzoic acid (IC₅₀ = 7.2 × 10⁻⁵ M, K_i = 2.0 × 10⁻⁵ M) and azelaic acid (IC₅₀ = 1.3 × 10⁻⁴ M, K_i = 4.2 × 10⁻⁵ M) in close agreement with literature spectrophotometric inhibition data using the soluble tyrosinase.     

A Comparative Study of the Dynamic-Mechanical Properties of Styrene Butadiene Rubber/Epoxidized Natural Rubber Dual Filler Nanocomposites Cured by Sulfur or Electron Beam Irradiation

The properties of (50/50?wt%) styrene butadiene rubber/epoxidized (50%) natural rubber (SBR/ENR50) blends containing nanoclay (NC, 5 or 10phr) without and with carbon black (CB 20phr) cured by sulfur or by electron beam (EB) irradiation (50 and 100kGy), were compared. A sulfur cured compound containing 35phr CB was prepared as a reference sample. Dynamic mechanical thermal analysis (DMTA) indicated that the sulfur cured sample containing 10phr NC and 20phr CB and the 100kGy irradiated sample with 5phr NC and 20phr CB had higher crosslink density, storage modulus, and tensile strength, and less loss factor and loss modulus, compared to the reference sample. Scanning electron microscopy (SEM) images of cryo- fractured surfaces confirmed the DMA and crosslink density results. We suggest a light weight 100kGy irradiated sample containing the lowest amount of NC and 20phr CB with a uniform distribution of the –C–C– bonds crosslinks, for high thermal stability applications and also for passenger cars tire treads, for its ice grip and wet skid properties especially for icy and wet roads, with improvements of 23% and 20%, respectively as compared to the reference sample.     

Nicotinium Dichromate (=3‐Carboxypyridinium Dichromate; NDC) as an Efficient Reagent for the Oxidative Deamination of Amines and Aminophosphonates

A new method for the efficient synthesis of aldehydes, ketones, and oxophosphonates from various types of amines (primary and secondary) and aminophosphonates via oxidative deamination by nicotinium dichromate (=3‐carboxypyridinium dichromate; NDC) is described.     

Resource allocation and power control for underlay device-to-device communication in fractional frequency reuse cellular networks

The current state of device-to-device (D2D) communication in the presence of cellular network addresses two major challenges of interference as well as throughput inadequacy. Specifically, a D2D communication underlaying fractional frequency reuse (FFR) cellular network exhibits rather high interferences due to higher occurrence of band crossing within a shared spectrum. However, due to the considerable impact of D2D communications on spectral efficiency and system capacity, the remedy for those issues may include efficient techniques of interference mitigation and average spectral efficiency maximization. In this paper, we propose a resource block (RB) allocation scheme to reduce the co-channel interference by providing and maintaining adequate distance between D2D user equipment (DUE) and cellular user equipment (CUE), and between the macrocell base station and DUEs that are using the same RB. In the proposed scheme, we initially introduce a plan with one omnidirectional and three directional antennas be used to serve the CUE in the inner and outer regions of the FFR cell, respectively. In addition, DUE in each region uses the RBs that are orthogonal to those used by CUE. It is shown that by using two different ranges for inner region of cellular and D2D communication, the overall performance is improved. Furthermore, we formulate an optimization problem for maximizing average spectral efficiency while guaranteeing CUE signal-to-interference-plus-noise-ratio and achieve efficient solutions to the different average spectral efficiency maximization problems. The results demonstrate the efficiency of the proposed scheme. In addition, it is shown that significant improvement in system spectral efficiency is obtained through the optimization of DUE power. That is, the achieved throughput is much higher than that of the random resource allocation and 1.5–2 times of the previous works.     

Characterization of the structural changes of human serum albumin upon interaction with single-walled and multi-walled carbon nanotubes: spectroscopic and molecular modeling approaches

Research on Chemical Intermediates - Through the incorporation of spectorescopic and molecular methods of modeling, the researchers investigated the interaction between Carbon Nanotubes (CNTs) and...     

Quenching of Singlet Oxygen by a Carotenoid–Cyclodextrin Complex: The Importance of Aggregate Formation

The Girard's reagent P derivative of canthaxanthin ((GRP)₂-canthaxanthin), a dicationic carotenoid, forms a highly water-dispersible complex with (2-hydroxypropyl)-γ-cyclodextrin. The UV–visible light spectrum of the complex is consistent with some degree of aggregation, but the spectrum is independent of concentration from 7.5 to 750 μ m . Stern-Vomer plots for singlet-oxygen quenching by the complex are linear over a concentration range of 0–20 μ m . In the presence of 1 m m (2-hydroxypropyl)-γ-cyclodextrin, the singlet-oxygen quenching constant for the complex is 7.9 ± 0.9 × 10⁸  m ⁻¹s⁻¹. This is about an order of magnitude lower than the singlet-oxygen quenching constants for (GRP)₂-canthaxanthin in various organic solvents. The properties of the complex are also compared with the properties of (GRP)₂-canthaxanthin solubilized in neat water and in water containing various detergents. The singlet-oxygen quenching constant for (GRP)₂-canthaxanthin in micelles depends strongly on the specific detergent used, varying from 9.4 × 10⁸  m ⁻¹s⁻¹ for hexadecyltrimethylammonium bromide (CTAB) to 1.24 ± 0.4 × 10¹⁰  m ⁻¹s⁻¹ for sodium dodecyl sulfate. The small quenching constant in CTAB micelles correlates with spectroscopic evidence for aggregation of the (GRP)₂-canthaxanthin in this detergent.     

Shallow hydroxyapatite coatings pulsed laser deposited onto Al2O3 substrates with controlled porosity: correlation of morphological characteristics with in vitro testing results

We studied the influence of porous Al₂O₃ substrates on Ce-stabilized ZrO₂-doped hydroxyapatite thin films morphology pulsed laser deposited on their top. The porosities of substrates were monitored by changing sintering temperatures and measured with a high pressure Hg porosimeter.The depositions were conducted in 50 Pa water vapors by multipulse ablation of the targets with an UV KrF* (λ = 248 nm, τ ∼ 25 ns) excimer laser. The surface morphology of synthesized nanostructures was investigated by scanning electron microscopy and atomic force microcopy. Ca/P ratio within the range 1.67-1.70 was found for hydroxyapatite coatings by energy dispersive spectroscopy.The films were further seeded with mesenchymal stem cells for in vitro tests. The cells showed good attachment and spreading uniformly covering the entire surface of samples. The complexity of film morphology which is increasing with substrate porosity was shown to have a positive influence on cultivated cells density.     

PHOTOCHEMICAL OXIDATION OF VINDOLINE and 16-O-ACETYLVINDOLINE

Abstract— Photooxidation of 16-O-acetylvindoline in methanol using chlorpromazine-HCl as a photosensitizing agent produces nearly quantitative yields of an iminium derivative. The 16-O-acetylvindol-ine-iminium product was characterized spectrally by proton NMR and mass spectrometry; and by chemical reduction with sodium borodeuteride. Proton NMR and mass spectral analyses of the reduced product revealed that deuterium was stereospecifically incorporated into the 3-a-position. The iminium product formed by photochemical oxidation is identical to that produced by copper oxidases and peroxidase. Photochemical oxidation provides direct evidence for the involvement of free radicals in Aspidosperma alkaloid transformations.     

Novel magnetic nanoparticles with morpholine tags as multirole catalyst for synthesis of hexahydroquinolines and 2-amino-4,6-diphenylnicotinonitriles through vinylogous anomeric-based oxidation

Research on Chemical Intermediates - A new heterogeneous nanomagnetic catalyst bearing morpholine tags was synthesized and characterized. The formation of the nanomagnetic catalyst was fully...     

Simple synthesis of the novel Cu-MOF catalysts for the selective alcohol oxidation and the oxidative cross-coupling of amines and alcohols

A novel porous metal–organic framework {Cu₂(bbda)_0.5(Hbbda)_1.5(OAc)_1.5.8H₂O} (UoB-5) was synthesized under ultrasound irradiation by employing a new Schiff base ligand H₂bbda (4,4′(1,4-phenylene bis (azanylylidene)) bis (methanylylidene))dibenzoic acid) and was fully characterized. The microporous nature of UoB-5 was confirmed by gas-sorption measurements. This framework acted as a highly effective heterogeneous catalyst for the alcohol oxidation reaction with tert-butyl hydroperoxide (t-BuOOH) as an oxidant. The presence of coordinatively unsaturated metal sites in UoB-5 could be the reason for high performance in this reaction. Furthermore, using the long linker with the free -NC group and uncoordinated -N atom on the wall of the pores created UoB-5 an excellent candidate for the catalytic activities without activation of the framework. It was confirmed with the heterogeneous catalytic experiments on the one-pot tandem synthesis of imines from benzyl alcohols and anilines. Eventually, the new Cu-MOF (UoB-5) could be an alternative catalyst as a more economically favorable and environmentally friendly in the catalysis field.