Characterization of the Aminotransferase ThdN from Thienodolin Biosynthesis in Streptomyces albogriseolus

In Streptomyces albogriseolus the indolethiophen alkaloid thienodolin is derived from tryptophan. The first step in thienodolin biosynthesis is the regioselective chlorination of tryptophan in the 6‐position of the indole ring. The second step is catalyzed by the aminotransferase ThdN. ThdN shows sequence homology (up to 69 % similarity) with known pyridoxal 5′‐phosphate‐dependent aminotransferases of the aspartate aminotransferase family from Gram‐positive bacteria. thdN was heterologously expressed in Pseudomonas fluorescens, and the enzyme was purified by nickel‐affinity chromatography. ThdN is a homodimeric enzyme with a mass of 90 600 kDa and catalyzes the conversion of l ‐tryptophan and a number of chlorinated and brominated l ‐tryptophans. The lowest K_M values were found for 6‐bromo‐ and 6‐chlorotryptophan (40 and 66 μm , respectively). For l ‐tryptophan it was 454 μm, which explains why thienodolin is the major product and dechlorothienodolin is only a minor component. The turnover number (k_cat) for 7‐chlorotryptophan (128 min^?1) was higher than that for the natural substrate 6‐chlorotryptophan (88 min^?1).     

Multifunctional Silver Nanoparticles-Decorated Silica Functionalized with Retinoic Acid with Anti-Proliferative and Antimicrobial Properties

The paper describes a rapid and simple method for preparing a multifunctional biomaterial based on retinoic acid covalently bound on silica@Ag particles. Monodispersed SiO₂ particles were prepared by Stöber method and further used for loading the Ag nanoparticles on their surface. This composite was further functionalized with retinoic acid. Characterization of the hybrid materials was made by UV–Visible spectroscopy, Transmission electron microscopy, Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Thermal analysis. The biological evaluation of the obtained materials revealed their potential use for multiple biomedical applications, from anti-proliferative agents to novel antimicrobial and antibiofilm strategies.     

Inhibition of para‐Hydroxyphenylpyruvate Dioxygenase by Analogues of the Herbicide Nitisinone As a Strategy to Decrease Homogentisic Acid Levels,the Causative Agent of Alkaptonuria

Alkaptonuria (AKU) is a rare multisystem metabolic disease caused by deficient activity of homogentisate 1,2‐dioxygenase (HGD), which leads to the accumulation of homogentisic acid (HGA). Currently, there is no treatment for AKU. The sole drug with some beneficial effects is the herbicide nitisinone ( 1 ), an inhibitor of p‐hydroxyphenylpyruvate dioxygenase (4‐HPPD). 1 has been used as a life‐saving drug in infants with type I tyrosinemia despite severe side effects due to the buildup of tyrosine. Four clinical trials of nitisinone to treat AKU have shown that 1 consistently decreases HGA levels, but also caused the accumulation of tyrosine in blood serum. Moreover, the human preclinical toxicological data for 1 are incomplete. In this work, we performed pharmacodynamics and toxicological evaluations of 1 , providing the first report of LD₅₀ values in human cells. Intracellular tyrosinemia was also evaluated. Three additional 4‐HPPD inhibitors with a more favorable profile than that of 1 in terms of IC₅₀, LD₅₀, and tyrosine accumulation were also identified among commercially available compounds. These may be promising starting points for the development of new therapeutic strategies for the treatment of AKU.     

Kinetic study of the electrochemical mineralization of phenols in thin-layer condition

Electrochemical oxidation of p-nitrophenol (PNP) and p-methoxyphenol (PMP) at Bi-doped PbO₂ electrodes under thin-layer condition was studied by Fourier transform infrared spectroelectrochemistry (FTIR) as a function of electrode potential and the initial concentration of organic compound. The results show that complete mineralization of the organic species was achieved at potentials more positive than 1.4 V vs. SCE and the mineralization process was not determined by the concentration of phenols. From the electric charge transferred during thin-layer controlled potential electrolysis, we found that PNP and PMP electrooxidation follow Langmuir-Hinshelwood kinetics.     

Anodic electrodeposition of cobalt oxides from an alkaline bath containing Co-gluconate complexes on glassy carbon. An electroanalytical investigation

In this study an electrodeposition procedure of cobalt oxides operating under anodic condition and directly from 0.5 M NaOH solutions containing 12 mM gluconate and 12 mM CoCl₂ was defined for the modification of glassy carbon surface electrode. Different experimental approaches based on cyclic voltammetry, steady-state potentiostatic technique, chronoamperometry and scanning electron microscopy were used to characterize the deposited cobalt oxide films and to evaluate the kinetics and mechanism of electrodeposition. Some aliphatic aldehydes were tested as compound model in order to evaluate the electroanalytical properties of the electrodeposited cobalt film as active redox material for amperometric applications in strong alkaline aqueous solutions. Interesting results in terms of surface electrode modification “in situ” of glassy carbon substrate with cobalt oxides were obtained and critically discussed.     

Behaviour of the antioxidant tert-butylhydroquinone on the storage stability and corrosive character of biodiesel

The behaviour of the antioxidant tert-butylhydroquinone (TBHQ) on the storage stability of biodiesel was investigated. Storage conditions were simulated through static immersion corrosion tests in biodiesel (with and without TBHQ) using copper coupons. Measurements of oxidation stability (Rancimat induction period) and metal release at different stages of corrosion were performed. After 24 h of the static immersion test, the neat and TBHQ-doped biodiesels presented induction times below the EN 14214 limit (6 h). Copper release was more intense in the neat biodiesel which evidenced that TBHQ retarded the corrosion process as a corrosion inhibitor. Ion trap–time-of-flight mass spectrometry (IT–TOF-MS) revealed the presence of considerable amounts of tert-butylquinone (TBQ) in the TBHQ-doped biodiesel exposed to the corrosion process. As TBHQ molecules adsorb at the copper surface to inhibit corrosion, these molecules are catalytically oxidised to TBQ. IT–TOF-MS also indicated the formation of new molecules of high molecular weight only presented in the TBHQ-doped biodiesel deteriorated by the corrosion process. MS² spectra gave clear evidence of the formation of new complexes between free radicals of long-chain molecules (fatty acid derivatives) and TBQ radicals during biodiesel deterioration.     

Synthesis and Biological Evaluation of RGD and isoDGR–Monomethyl Auristatin Conjugates Targeting Integrin αVβ3

This work reports the synthesis of a series of small-molecule–drug conjugates containing the α_Vβ₃-integrin ligand cyclo[DKP-RGD] or cyclo[DKP-isoDGR], a lysosomally cleavable Val-Ala (VA) linker or an “uncleavable” version devoid of this sequence, and monomethyl auristatin E (MMAE) or F (MMAF) as the cytotoxic agent. The conjugates were obtained via a straightforward synthetic scheme taking advantage of a copper-catalyzed azide–alkyne cycloaddition as the key step. The conjugates were tested for their binding affinity for the isolated α_vβ₃ receptor and were shown to retain nanomolar IC₅₀ values, in the same range as those of the free ligands. The cytotoxic activity of the conjugates was evaluated in cell viability assays with α_vβ₃ integrin overexpressing human glioblastoma (U87) and human melanoma (M21) cells. The conjugates possess markedly lower cytotoxic activity than the free drugs, which is consistent with inefficient integrin-mediated internalization. In almost all cases the conjugates featuring isoDGR as integrin ligand exhibited higher potency than their RGD counterparts. In particular, the cyclo[DKP-isoDGR]-VA-MMAE conjugate has low nanomolar IC₅₀ values in cell viability assays with both cancer cell lines tested (U87: 11.50±0.13 nm ; M21: 6.94±0.09 nm ) and is therefore a promising candidate for in vivo experiments.