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Nirmalya K Chaki

Publications and source records attributed to Nirmalya K Chaki.

6 recordsLinked to original sources
PubMed2006

Wolff rearrangement of alpha-diazoketones using in situ generated silver nanoclusters as electron mediators.

[reaction: see text] We report Wolff rearrangement of alpha-diazoketones by in situ generated silver nanoclusters (Ag(n)(), 2-4 nm) from silver(I) oxide (Ag(2)O) involving a nonclassical electron-transfer process. Our results show that Ag(n)()(+)/Ag(n)()(0) redox couple allows the initial removal of an electron from alpha-diazoketone and its back-donation after chemical reaction(s). Controlled potential coulometry (CPC) of various alpha-diazoketones results in the realization of Wolff-rearranged carboxylic acids in excellent yields.

Journal Article↗
PubMed2006

Silver nanocluster redox-couple-promoted nonclassical electron transfer: an efficient electrochemical Wolff rearrangement of alpha-diazoketones.

In this work we report the unique electrocatalytic role of benzoic acid protected silver nanoclusters (Ag(n), mean core diameter 2.5 nm) in the Wolff rearrangement (Scheme 1) of alpha-diazoketones. More specifically, the presence of a Ag(n) (0)/Ag(n) (+) redox couple facilitates a nonclassical electron-transfer process, involving chemical reaction(s) interposed between two electron-transfer steps occurring in opposite directions. Consequently, the net electron transfer between the electron mediator (Ag(n)) and alpha-diazoketone is zero. In-situ UV-visible studies using pyridine as a nucleophilic probe indicate the participation of alpha-ketocarbene/ketene as important reaction intermediates. Controlled potential coulometry of alpha-diazoketones using Ag(n) as the anode results in the formation of Wolff rearranged carboxylic acids in excellent yield, without sacrificing the electrocatalyst.

Journal Article↗
PubMed2004

Controlled interlinking of Au and Ag nanoclusters using 4-aminothiophenol as molecular interconnects.

This work describes the formation of interlinked gold and silver nanoclusters at controlled pH using 4-aminothiophenol (ATP) as a molecular interconnect. UV-visible spectra give on intercrystal plasmon resonance band in the region 550-580 nm. The crystalline heteroassembly formation is also evident from the transmission electron microscopic (TEM) images, whereas X-ray photoelectron spectroscopic (XPS) analysis of the aggregates shows the presence of charged -N species, indicating electrostatic interaction of -N with Ag nanoclusters. Furthermore, electrochemical studies of these heteroassembled systems suggest that silver nanoclusters are not fully passivated by the monolayers of ATP and are accessible for redox reactions.

Journal Article↗
PubMed2002

Self-assembled monolayers as a tunable platform for biosensor applications.

Considerable attention has been drawn during the last two decades to functionalize noble metal surfaces by forming ordered organic films of few nm to several hundred-nm thickness. Self-assembled monolayer (SAM) provides one simple route to functionalize electrode surfaces by organic molecules (both aliphatic and aromatic) containing free anchor groups such as thiols, disulphides, amines, silanes, or acids. The monolayer produced by self-assembly allows tremendous flexibility with respect to several applications depending upon their terminal functionality (hydrophilic or hydrophobic control) or by varying the chain length (distance control). For example, SAM of long chain alkane thiol produces a highly packed and ordered surface, which can provide a membrane like microenvironment, useful for immobilising biological molecules. The high selectivity of biological molecules integrated with an electrochemical, optical or piezoelectric transduction mode of analyte recognition offers great promise to exploit them as efficient and accurate biosensors. It is demonstrated with suitable examples that monolayer design plays a key role in controlling the performance of these SAM based biosensors, irrespective of the immobilisation strategy and sensing mechanism.

Biosensing Techniques↗