Jyotirekha G. Handique

Polyphenolic compounds: an overview

A comprehensive review on the polyphenolic compounds is presented. The emphasis is placed on the structural and functional implications on the regiochemistry as well as on the stereochemistry of oligomeric polyphenols. A correlation between the natural polyphenolic compounds and the synthetic ones is highlighted by making a general classification of polyphenolic compounds. The uses and applications of polyphenolic compounds are discussed in detail.

A THEORETICAL STUDY ON THE ANTIOXIDANT PROPERTY OF GALLIC ACID AND ITS DERIVATIVES

We analyze the antioxidant property of four phenolic compounds i.e., gallic acid, methyl gallate, ethyl gallate, and 4, 5-dihydroxy 3-methoxy benzoic acid through the determination of bond dissociation enthalpy (BDE), vertical ionization potential (IPv) in gas phase as well as in six different solvent medium. The theoretical trends of these phenolic compounds, based on BDE and IP, is compared with the scavenging activity towards HOCl. In addition, we compute and analyze the values of the density-based reactivity descriptors such as chemical potential, hardness, electrophilicity, and local softness.

The oligomer of 1,6-naphthalenediol as a support in oxidative reactions of cis-bisglycinato copper(II) and hydrogenperoxide

Abstract Oxidative oligomerization of 1,6-naphthalenediol by cis-bisglycinato copper(II)monohydrate with hydrogenperoxide gives C–O bonded oligomer. Further reactivity of this oligomer with hydrogen peroxide and organic substrate shows improvement in the yield of oxidative and hydrolytic reactions. For example the oligomer along with cis-bisglycinato copper(II) catalyses hydrolytic reaction of benzamide to benzoic acid.

Participation of self-generated polyaniline support in copper(II) catalysed oxidative reaction of phenyl aldimines

Aromatic aldimines, aldoximes and aldehydes can be converted to the corresponding carboxylic acid on reaction with catalytic amount of cis-bisglycinato copper(II) monohydrtae in the presence of copper(II) catalyst. The reactions are facilitated by addition of polyaniline as support. In the case of aldimines, evidences on participation of self-generated polyaniline is observed. The mechanistic aspect involving an oxy radical attached to copper(II) is presented with ESR evidence.

Oxidative oligomerisation of 2-naphthol by cis-bis(glycinato)copper(II)

The reaction of 2-naphthol with tert-butylhydroperoxide by cis-bis(glycinato)copper(II) oligomerises 2-naphthol. One of the isolated tetramer A contains a tert-butyloxy group. Similar reaction of 2-naphthol with hydrogen peroxide in the presence of cis-bis(glycinato)copper(II) oligomerises 2-naphthol gives tetramer through hydroxylative oligomerisation. The oligomers are bound to oxo-bridged copper cores to give B and C. These oligomers exhibit thermal sensing property. The oligomer (B) converts benzamide to benzoic acid, as well as catalyses oxidation of aromatic aldehydes such as benzaldehyde to corresponding acids.

The oligomer of 1,2,3-trihydroxybenzene with benzaldehyde

Abstract A linear oligomer of benzaldehyde with 1,2,3-trihydroxybenzene was synthesised and characterized. The oligomer has a quinonic end group that leads to a solvatochromic property and interacts with a variety of amines. In aprotic medium the oligomer has two non-equivalent intra -molecular H-bonded quinonic states arising from keto – enol tautomerism, one having the carbonyl and olefinic group at the 1,4-disposition ( X ) whereas in the other the carbonyl and olefinic groups are at the 1,2-disposition ( Y ). Thus, in acetonitrile both forms exist and the X and Y states have their characteristic absorption maximum at 500 and 427 nm, respectively. In protic medium a highly ordered structure with the hydrophobic and hydrophilic part projecting apart produces a structure ( Z ) having inter -molecular hydrogen-bonding with solvent which has a characteristic absorption at 475 nm. Non-stoichiometric amounts of various primary, secondary and tertiary amines interact with the oligomer providing stability to either of the forms or generating an anion by which the absorption maximum changes. For example, the oligomer interacts with t -butylamine, and this interaction changes the absorption maximum to 566 nm. The solution on further treatment with mineral acid (HCl) gives a new absorption maximum at 475 nm with a distinct color change. The absorptions can be changed back and forth by alternate addition of hydrochloric acid and t -butylamine. However, the characteristic changes that take place in the optical spectra of the oligomer in acetonitrile with different amines are highly substrate-dependent. For example the amines like ammonia, ethylamine, iso -propylamine, n -butyl amine, t -butyl amine, ethylenediamine, and pyridine cause loss of absorption at 427 and 500 nm and lead to growth of new absorption at 566 nm; whereas amines like benzidine, o -diaminobenzene, m -iodoaniline, m -nitroaniline, and p -hydroxyaniline enhance the original absorbance at 427 nm at the cost of absorption at 500 nm without leading to a new absorption. Some amines like 1-naphthylamine, 1,7-diaminonaphthalene, p -iodoaniline, and p -methoxyaniline increase the absorbances at 427 and 500 nm, whereas aniline, o -methylaniline, m -methylaniline, and diphenylamine do not significantly affect the spectra of the oligomer. The electrochemical study of the oligomer with 1,4-phenylenediamine shows that redox potentials of the bound state of the oligomer with 1,4-phenylenediamine shifts from the unbound state, for example, 1,4-phenylenediamine with the oligomer has two quasireversible couples at E 1/2 at 259 and 822 mV in contrast to the two reversible couples of free 1,4-phenylenediamine at 334 and 863 mV, respectively.

Conversion of 1,4-naphthalenediol to 1,4-naphthoquinone by 1,4-benzoquinone

Abstract 1,4-Naphthalenediol gets converted to 1,4-naphthoquinone on reaction with 1,4-benzoquinone. In the reaction, 1,4-benzenediol is formed. The reaction passes through charge delocalisation in the equivalent keto and enol forms. The spectroscopic and electrochemical studies discern the role of equivalent charge transfer complex derived from 1,4-naphthoquinone with 1,4-benzenediol (A). The conversion of 1,4-naphthalenediol to 1,4-naphthoquinone in the presence of oxidants such as hydrogen peroxide and t-butylhydroperoxide are catalysed by 1,4-benzoquinone

A theoretical study on antioxidant activity of ferulic acid and its ester derivatives

Phenolic compounds play a very crucial role as antioxidant that can prevent various diseases caused by free radicals in human body. Although, lots of natural phenolic compounds having antioxidant activity are available nowadays, the modeling of compounds with naturally available phenolics as building blocks is very important in order to get enhanced antioxidant activity. In this study, Ferulic acid (FA), one natural phenolic acid present in coffee, apples, orange, etc., is taken as building block and its ester derivatives with different alkyl groups are subjected to measure the antioxidant activity by using density functional theory (DFT). Various parameters like bond dissociation enthalpy (BDE), vertical ionization potential (IPv), reactivity descriptors, metal chelation ability, etc. are used to measure the antioxidant activity. All the parameters suggest that the ester derivatives are superior antioxidants to the parent FA. Since FA has been reported to be present as esters in many herbs and plants, hence our study provides a route to study the structure activity relationship of this class of natural phenolics with antioxidant activity.

Synthesis of Series of Low Band Gap Small Organic Molecules and Evaluation of their Solar Cell Activity

Solar energy has been identified round the globe as an area of significance in providing solutions to the problem of meeting future energy needs. Today the most promising tool to make use of solar energy is its direct conversion into electrical energy in photovoltaic cells. But until now the photovoltaic cell have been dominated by solid state junction devices, often made of silicon. Though the power conversion efficiency of inorganic solar cells has gone up to 44.7 % in lab [1], their high energy consumption at fabrication and cost intensiveness has created a snag to their use in research and development. The limitations of the inorganic solar cells has been challenged by a new generation of photovoltaics based on organic compounds. Organic solar cells with π-conjugated materials as active layer has attracted much attention as a renewable energy source owing to their low energy consumption at fabrication, compatibility with flexible substrates, environment friendly and unlimited variability [2-5]. The recent surge in organic/polymer solar cell research began with the pioneering work by Tang [6] who developed bilayer organic semiconductors with an efficiency of around 1 %. Subsequently, Spanggaard and Krebs devised the first polymer/ C60 based cell [7]. But the power conversion efficiency of organic solar cells is only 8.4 % in lab and tandem organic solar cell, 11.5 % thereby opening up room for further research [8,9]. Synthesis of Series of Low Band Gap Small Organic Molecules and Evaluation of their Solar Cell Activity