Stereochemical and biochemical aspects of organoboron(III) compounds of hydrazonecarboxamides and hydrazonecarbothioamides

Hydrazonecarboxamides and hydrazonecarbothioamides and their derivatives have important pharmacodynamic significance. In the search for better fungicides and bactericides, organoboron(III) compounds derived from these ligands were screened for their antifungal and antibacterial activities. The heterocyclic aldimines were prepared by the condensation of (2-furanyl)methanal, (2-thienyl)methanal, (2-pyridinyl)methanal, (1H-indol-3-yl)methanal or 3-phenyl-2-propenal with hydrazinecarboxamide or hydrazine-carbothioamide. Unimolar and bimolar reactions between phenyldihydroxyborane and these ligands have produced PhB(OH)(NO), PhB(NO)₂, PhB(OH)(NS) and PhB(NS)₂ types of biologically active compounds. Structural assignment has been made through UV, IR and NMR (¹H, ¹¹B and ¹³C) spectroscopy. TGA and XRD of a representative compounds have also been carried out. The compounds were tested in vitro against a number of fungal and bacterial strains and were found to possess moderate to good toxicity.     

The steric course of proton elimination in conversion of a tricarbonylcyclohexadieneiron carbinol into an endocyclic cation

Tricarbonyl-1-carbomethoxy-5α²H-cyclohexadieneiron (3) reacts with MeLi to tricarbonyl-1(1¹ -hydroxy-1¹ -methyl-ethyl)-5α²H-cyclohexadiene- iron (1) which yields with acid the salt tricarbonyl-1(1¹ -methyl-ethyl)-5₂H- cyclohexadienyliron(+)-PF₆ (?) (4). Retention of ²H demonstrates the stereochemistry of the elimination of the ring proton as β-(endo).     

Carbon-13 NMR spectra of some labdane diterpenoids

Carbon-13 signal assignments of the labdane diterpenoids phlogantholide-A, its diacetate and isophlogantholide-A are reported. The assignments of the ¹³C NMR signals of 14-deoxyandrographolide and its diacetate, made earlier, have now been confirmed by lanthanide shift studies on the former and also by ¹³C spectral studies on anhydroandrographolide diacetate and 14-deoxy-11,12-didehydroandrographolide diacetate.     

Electrochemical properties of columns in capillary electrochromatography. I. Ohm's law, resistivity and field strength

The most commonly used type of column in capillary electrochromatography (CEC) consists of a packed segment and an open (but buffer-filled) segment. The two segments differ importantly in two respects: firstly, their electrical resistivity; and secondly, their zeta potentials at a multitude of solid-liquid interfaces. Determination of the magnitude of these properties for each segment cannot be made using only results from the column as a whole. Instead, measurements of resistivity and zeta potentials of an entirely open, unpacked column can be used in conjunction with those of the CEC column to determine the electrochemical nature of both segments. This review of basic electrochemical properties will describe simple procedures that can be used to determine resistance, resistivity, conductivity, conductance, and field strength in each segment. In addition, it will be shown how the properties of each segment add together to give the same properties of the CEC column as a whole. The equations so derived will be applied to data from the literature and conclusions drawn from the results.     

Merging C(sp3)–H activation with DNA-encoding

DNA-encoded library (DEL) technology has the potential to dramatically expedite hit identification in drug discovery owing to its ability to perform protein affinity selection with millions or billions of molecules in a few experiments. To expand the molecular diversity of DEL, it is critical to develop different types of DNA-encoded transformations that produce billions of molecules with distinct molecular scaffolds. Sequential functionalization of multiple C–H bonds provides a unique avenue for creating diversity and complexity from simple starting materials. However, the use of water as solvent, the presence of DNA, and the extremely low concentration of DNA-encoded coupling partners (0.001 M) have hampered the development of DNA-encoded C(sp³)–H activation reactions. Herein, we report the realization of palladium-catalyzed C(sp³)–H arylation of aliphatic carboxylic acids, amides and ketones with DNA-encoded aryl iodides in water. Notably, the present method enables the use of alternative sets of monofunctional building blocks, providing a linchpin to facilitate further setup for DELs. Furthermore, the C–H arylation chemistry enabled the on-DNA synthesis of structurally-diverse scaffolds containing enriched C(sp³) character, chiral centers, cyclopropane, cyclobutane, and heterocycles.

DNA-compatible C(sp³)–H activation reactions of aliphatic carboxylic acids, amides, and ketones were developed for efficient access to DEL synthesis.     

Olefin cross-metathesis as a tool in natural product degradation. The stereochemistry of (+)-falcarindiol

[reaction: see text] There are conflicting reports in the literature concerning the absolute sterochemistry at C-3 of the common plant polyacetylene oxylipin (+)-falcarindiol. We have employed olefin cross-metathesis using Grubbs' second generation catalyst and ethylene gas to degrade falcarindiol to the symmetrical 1,9-decadiene-4,6-diyne-3,8-diol. The reaction is completely selective for net removal of the aliphatic side chain. Degradation of (+)-falcarindiol from Tetraplasandra hawaiiensis yields a meso product as shown by chiral HPLC. Hence, (+)-falcarindiol from this source has a (3R,8S)-configuration.     

A Review on Carbon Quantum Dot Based Semiconductor Photocatalysts for the Abatement of Refractory Pollutants

Photocatalysis is a green approach frequently utilised to eliminate a variety of environmentally hazardous refractory pollutants. Accordingly, the modification of semiconductor photocatalysts with Carbon Quantum Dots (CQDs) is of great importance for the treatment of such pollutants due to their attractive physical and chemical properties. CQDs are a perfect candidate to handle photocatalysts of high-performance since they operate as co-catalysts and as visible light harvesters. The higher separation rate of electron-hole pairs in the photocatalytic system is attributable to better photodegradation efficiency. This review classifies CQD based photocatalysts as pure, doped and composite materials and discusses the specific advantages of CQDs in visible light-driven photocatalysis. In this work, the versatile roles of CQDs in CQD-based photocatalytic systems are thoroughly discussed and summarised.