Continuous flow enzyme-catalyzed polymerization in a microreactor

Enzymes immobilized on solid supports are increasingly used for greener, more sustainable chemical transformation processes. Here, we used microreactors to study enzyme-catalyzed ring-opening polymerization of ε-caprolactone to polycaprolactone. A novel microreactor design enabled us to perform these heterogeneous reactions in continuous mode, in organic media, and at elevated temperatures. Using microreactors, we achieved faster polymerization and higher molecular mass compared to using batch reactors. While this study focused on polymerization reactions, it is evident that similar microreactor based platforms can readily be extended to other enzyme-based systems, for example, high-throughput screening of new enzymes and to precision measurements of new processes where continuous flow mode is preferred. This is the first reported demonstration of a solid supported enzyme-catalyzed polymerization reaction in continuous mode.     

Layer-by-layer assembly of thiol-capped au nanoparticles on a water surface and their deposition on H-terminated Si(001) by the Langmuir-Blodgett method

A monolayer of dodecanethiol-encapsulated Au nanoparticles when compressed laterally transforms into layer-by-layer assemblies on water surface. These layer-by-layer assemblies of Au nanoparticles have been deposited on H-terminated Si(001) substrates by using one down-up cycle (two strokes) in the Langmuir-Blodgett (LB) method. The transformation from monolayer to layer-by-layer assembly on a water surface is irreversible; i.e., if the compressed film is decompressed the layer-by-layer structure cannot regenerate the monolayer structure. Unlike layer-by-layer growth, only odd numbers of layers grow from the monolayer on the H-terminated Si(001) substrates by using different numbers of down-up cycles. Z-type LB deposition occurs only in the first down-up cycle of the hydrophobic substrate, whereas Y-type LB deposition takes place in the successive cycles. Such layer-by-layer assemblies of Au nanoparticles, which are made on bare silicon surfaces and where thickness can be controlled at the nanoscale level, are very promising for their novel applications in the field of nanoscience.     

Silanylidene and Germanylidene Anions: Valence‐Isoelectronic Species to the Well‐Studied Phosphinidene

The reduction of TipMCl₃ (Tip=2,4,6‐triisopropylphenyl) (M=Si, Ge) with KC₈ in the presence of cyclic alkyl(amino) carbene (cAAC) afforded the acyclic silanylidene and germanylidene anions in the form of potassium salt [K(cAAC)MTip]₂ (M=Si ( 1 ); Ge ( 2 )). The silanylidene and germanylidene anions are valence‐isoelectronic to the well‐studied phosphinidene and are a new class of acyclic anions of Group 14. Compounds 1 and 2 were isolated and well characterized by NMR and single‐crystal X‐ray structure analysis. Furthermore, the structure and bonding of compounds 1 and 2 was investigated by computational methods.     

Modular Functionalization of Arenes in a Triply Selective Sequence: Rapid C(sp2) and C(sp3) Coupling of C−Br,C−OTf,and C−Cl Bonds Enabled by a Single Palladium(I) Dimer

Full control over multiple competing coupling sites would enable straightforward access to densely functionalized compound libraries. Historically, the site selection in Pd⁰‐catalyzed functionalizations of poly(pseudo)halogenated arenes has been unpredictable, being dependent on the employed catalyst, the reaction conditions, and the substrate itself. Building on our previous report of C?Br‐selective functionalization in the presence of C?OTf and C?Cl bonds, we herein complete the sequence and demonstrate the first general arylations and alkylations of C?OTf bonds (in <10 min), followed by functionalization of the C?Cl site (in <25 min), at room temperature using the same air‐ and moisture‐stable Pd^I dimer. This allowed the realization of the first general and triply selective sequential C?C coupling (in 2D and 3D space) of C?Br followed by C?OTf and then C?Cl bonds.     

Identification of inhibitors of DNA topoisomerase II from a synthetic library of glycoconjugates

A library of 24 glycoconjugates related to glycosylated beta-amino acid derivative (I) was been prepared and screened against DNA topoisomerase-II of the filarial parasite S. cervi. Among these, compound 6 was found to be a potent inhibitor of DNA topoisomerase-II with 95% inhibition at 1.09 microM. Furthermore, compound 6 was at least three times more potent than the lead compound, glycosylated beta-amino acid derivative I.     

Oligonol inhibits UVB-induced COX-2 expression in HR-1 hairless mouse skin--AP-1 and C/EBP as potential upstream targets

Oxidative stress and inflammatory tissue damage are two major events frequently implicated in carcinogenesis. Numerous polyphenolic compounds derived from plants possess antioxidant and anti-inflammatory activities and are hence effective in preventing cancer. Oligonol is a polyphenol formulation enriched with catechin-type oligomers. As an initial approach to assess the chemopreventive potential of oligonol, we have determined its effects on inflammatory as well as oxidative damage in mouse skin irradiated with UVB. Topical application of oligonol onto the dorsal skin of male HR-1 hairless mice 30 min prior to UVB exposure diminished epidermal hyperplasia and formation of 4-hydroxynonenal, a biochemical hallmark of lipid peroxidation. Topical application of oligonol also significantly inhibited UVB-induced cyclooxygenase (COX-2) expression in mouse skin. Oligonol diminished the DNA binding of activator protein-1 (AP-1) and CCAAT/enhancer binding protein (C/EBP), and the expression of C/EBPdelta in mouse skin exposed to UVB. Our study also revealed that oligonol attenuated UVB-induced catalytic activity as well as expression of p38 mitogen-activated protein (MAP) kinase. Moreover, UVB-induced phosphorylation of another upstream kinase Akt was attenuated by oligonol. Taken together, oligonol showed antioxidative and anti-inflammatory effects in UVB-irradiated mouse skin by inhibiting COX-2 expression via blockade of the activation of AP-1 and C/EBP, and upstream kinases including p38 MAP kinase and Akt.     

Optimisation of physical and mechanical properties of rubber compounds by response surface methodology--Two component modelling using vegetable oil and carbon black

Response surface methodology was used for predicting the optimal composition of vegetable oil and carbon black in rubber compounding. Central composite rotatable design for two variables at five levels was chosen as the experimental design. The data obtained from measurement of properties was fitted as a two variable second order equation and were plotted as contour plots using programme developed in MATLAB v.5. It is observed from the contour plots that the increase in cross-link density caused by the formation of rubber mono-layer from its multi-layer on increasing the carbon black loading upto the central point (50 phr) of experimental region increases 300% modulus and elongation at break and reduces the ultimate properties like tear strength and tensile strength. On the other-hand hardness increases with increase in solid inclusion of carbon black. From the contours it is observed that the addition of vegetable oil upto 2-3 phr, cross-link density increases due to its coupling action leading to increase in hardness and modulus and lowering of ultimate properties like tensile strength and elongation at break. Addition of further amount of vegetable oil shows less coupling and more plasticising effect leading to increase in tear strength, tensile strength and elongation at break and decrease in hardness and 300% modulus.     

Production of Siderophores by an Apple Root-Associated Streptomyces ciscaucasicus Strain GS2 Using Chemical and Biological OSMAC Approaches

Apple Replant Disease (ARD) is a significant problem in apple orchards that causes root tissue damage, stunted plant growth, and decline in fruit quality, size, and overall yield. Dysbiosis of apple root-associated microbiome and selective richness of Streptomyces species in the rhizosphere typically concurs root impairment associated with ARD. However, possible roles of Streptomyces secondary metabolites within these observations remain unstudied. Therefore, we employed the One Strain Many Compounds (OSMAC) approach coupled to high-performance liquid chromatography-high-resolution tandem mass spectrometry (HPLC-HRMSⁿ) to evaluate the chemical ecology of an apple root-associated Streptomyces ciscaucasicus strain GS2, temporally over 14 days. The chemical OSMAC approach comprised cultivation media alterations using six different media compositions, which led to the biosynthesis of the iron-chelated siderophores, ferrioxamines. The biological OSMAC approach was concomitantly applied by dual-culture cultivation for microorganismal interactions with an endophytic Streptomyces pulveraceus strain ES16 and the pathogen Cylindrocarpon olidum. This led to the modulation of ferrioxamines produced and further triggered biosynthesis of the unchelated siderophores, desferrioxamines. The structures of the compounds were elucidated using HRMSⁿ and by comparison with the literature. We evaluated the dynamics of siderophore production under the combined influence of chemical and biological OSMAC triggers, temporally over 3, 7, and 14 days, to discern the strain’s siderophore-mediated chemical ecology. We discuss our results based on the plausible chemical implications of S. ciscaucasicus strain GS2 in the rhizosphere.