Ramaswamy Nagarajan

Nanoreactors for the enzymatic synthesis of conducting polyaniline

The mechanistic role of template in the enzymatic synthesis of conducting polyaniline has been investigated using micelles and DNA as ionic templates. These studies show the existence and importance of a molecular local environment where the pH and charge density near the template molecule is different form that of the bulk solution. This local environment serves as a type of nanoreactor that ultimately controls the type of polyaniline that is produced enzymatically. When DNA is used as the template, an electro-responsive polyaniline/DNA complex is formed where the conformation of the DNA may be controlled through the electronic state of the polyaniline.

Biocatalytically Oligomerized Epicatechin with Potent and Specific Anti-proliferative Activity for Human Breast Cancer Cells

Catechins, naturally occurring flavonoids derived from wine and green tea, are known to exhibit multiple health benefits. Epigallocatechin gallate (EGCG) is one of the most widely investigated catechins, but its efficacy in cancer therapy is still inconsistent and limited. The poor stability of EGCG has contributed to the disparity in the reported anti-cancer activity and other beneficial properties. Here we report an innovative enzymatic strategy for the oligomerization of catechins (specifically epicatechin) that yields stable, water-soluble oligomerized epicatechins with enhanced and highly specific anti-proliferative activity for human breast cancer cells. This one-pot oxidative oligomerization is carried out in ambient conditions using Horseradish Peroxidase (HRP) as a catalyst yielding water-soluble oligo(epicatechins). The oligomerized epicatechins obtained exhibit excellent growth inhibitory effects against human breast cancer cells with greater specificity towards growth-inhibiting cancer cells as opposed to normal cells, achieving a high therapeutic differential. Our studies indicate that water-soluble oligomeric epicatechins surpass EGCG in stability, selectivity and efficacy at lower doses.

POLYMERIZATION OF WATER-SOLUBLE CONDUCTIVE POLYPHENOL USING HORSERADISH PEROXIDASE

Template assisted enzymatic polymerization of phenol has been carried out in aqueous media at room temperature. The templates used to facilitate this reaction, were polystyrene sulfonate, lignin sulfonate and dodecyl benzene sulfonate. The enzyme, horseradish peroxidase, proved to be an active catalyst for the polymerization, yielding a phenolic polymer that is permanently complexed with the template used. These polyphenol complexes are high molecular weight, soluble in water and/or mixed organic solvents and show good thermal stability. Under certain conditions, physical SPS-polyphenol gels can be formed in water that have high ionic conductivity. UV-vis, FTIR and electro-absorption spectroscopy show the presence of significant backbone conjugation and NLO properties. This novel enzymatic approach is a simple, inexpensive and environmentally friendly way to prepare processable polyphenolic materials with interesting electrical and optical properties. †Deceased.

Enzymatic Template Synthesis of Polyphenol

An alternative, biocatalytic approach for the synthesis of a new class of water soluble and processable polyphenols is presented. In this approach, the enzyme horseradish peroxidase (HRP) is used to polymerize phenol in the presence of an ionic template. The template serves as a surfactant that can both emulsify the phenol monomer and growing polyphenol chains and provide water solubility of the final polyphenol/template complex. This approach is a simple, one step synthesis where the reaction conditions are remarkably mild and environmentally compatible. The final product is a water soluble, high molecular weight complex of polyphenol and the template used. The approach is also very versatile as numerous templates may be used to build in specific functionalities to the final polyphenol complex. Polystyrene sulfonates (SPS), lignin sulfonate and dodecyl benzene sulfonates (micelles) are the templates investigated in this study. Thermal analysis and UV-Vis spectroscopy shows that these complexes have exceptional thermal stability and a high degree of backbone conjugation. Electrical conductivities on the order of 10 −5 S/cm and third order nonlinear optical susceptibilities (χ (3) ) of 10 −12 esu are also observed. In the case of the SPS template, under certain conditions, a sol gel complex may be formed. This enzymatic approach offers interesting opportunities in the synthesis and functionalization of a new class of processable polyphenolic materials.

PEROXIDASE, HEMATIN, AND PEGYLATED-HEMATIN CATALYZED VINYL POLYMERIZATIONS IN WATER

Horseradish peroxidase-, hematin- and pegylated-hematin mediated polymerization of sodium styrene sulfonate and sodium acrylate in water is reported. Molecular weight and yields were influenced by the concentrations of hydrogen peroxide and initiator, 2,4-pentanedione. Hematin and pegylated-hematin were studied in lieu of peroxidase at pH 11.0 and 7.0 in aqueous solution, respectively. Polymer with a high molecular weight (Mn = 223,520) was formed when the pegylated-hematin was used as the catalyst. The results demonstrate vinyl polymerizations in an all aqueous process in high yield and molecular weight catalyzed by peroxidase as well as biomimetic catalysts.

Halogen-free ultra-high flame retardant polymers through enzyme catalysis

Over the past few years, the use of certain types of halogenated flame retardant additives such as decabromodiphenylether has come under intense scrutiny due to their toxicity, environmental persistence and bio-accumulation. There is an immediate need for the development of non-toxic alternative flame retardant materials and fire resistant polymers with comparable or better efficacies, obtained using benign synthetic approaches. Enzymatic polymerization is being used increasingly as an environmentally friendly alternative method for the synthesis of functional materials including polymers and additives. Here, we report a biocatalytic synthesis of a new class of thermally stable, ultra-fire resistant polyphenols based on deoxybenzoins. In calorimetric studies, these polyphenols exhibit very low heat release capacities (comparable to Nomex™) and form a large amount of carbonaceous char rendering them suitable for flame retardant applications.

NOVEL ENZYMATIC POLYETHYLENE OXIDE-POLYPHENOL SYSTEM FOR IONIC CONDUCTIVITY

Abstract Phenol formaldehyde resins are of interest for different industrial and electronic applications. However, the toxic nature of formaldehyde and the extreme reaction conditions for the synthesis of these polymers have severely limited their use in todays markets. We present here a novel, biocatalytic approach where the enzyme horseradish peroxidase is used to polymerize phenol in the presence of a template such as polyethylene oxide. Here the template assists as a surfactant that can both emulsify the phenol and polyphenol chains during polymerization and provide water/solvent solubility of the final polyphenol/template complex. The reactants and the reaction conditions of this method are mild and result in high molecular weight, electrically and optically active, water-solvent soluble complexes of polyphenol and the template used. High molecular weight water-soluble polyphenol/polyethylene oxide complexes were formed.

VARIATION IN THE STRUCTURE OF CONDUCTING POLYANILINE WITH AND WITHOUT THE PRESENCE OF TEMPLATE DURING ENZYMATIC POLYMERIZATION: A SOLID-STATE NMR STUDY

ABSTRACT Polyanilines (PANI) were synthesized from peroxidase-catalyzed polymerization of aniline with and without the presence of a template in the aqueous buffer solution of pH 4.3. The template used was poly(vinylphosphonic acid) (PVP). Solid-state 13C and 15N CP/MAS NMR techniques were applied to characterize the structure of polyaniline in its self-doped conducting, dedoped base, and redoped conducting form of PANI. The charge distribution along the polymer backbone in the protonated form of the polyaniline is also discussed. The structural features exhibited by a template assisted enzymatically synthesized PANI is the result of linear 1,4-coupling of aniline moiety while the PANI synthesized in the absence of template contains both 1,2- and 1,4-coupled products. Solid-state NMR studies on the enzymatically-synthesized polyaniline with the aid of template (PANI-PVP) confirmed the formation of a linear polymer chain containing alternate benzenoid-quinoid repeat units. The dedoped form is in the emeraldine base state of the polyaniline. The structural features in the spectra of the PANI synthesized without a template are quite different. Solid-state NMR data suggest that the PANI synthesized without aid of the template contains structures having C-C and C-N-C coupled products indicating the presence of branching in the polymer chain.

ENZYMATIC SYNTHESIS OF MOLECULAR COMPLEXES OF POLYANILINE WITH DNA AND SYNTHETIC OLIGONUCLEOTIDES: THERMAL AND MORPHOLOGICAL CHARACTERIZATION

The assembly of electronic and photonic materials on biomacromolecules is of tremendous interest for the development of biofunctional nanocomplexes as well as highly selective biosensors. In the context of the use of electrically conducting polymers for sensing, polyaniline (Pani) and polypyrrole have received considerable interest because of their well-known electrical properties. Recently, we have reported an enzyme catalyzed synthetic procedure involving horseradish peroxidase (HRP) for the polymerization of aniline on a calf thymus DNA matrix. The mild reaction conditions involved in the synthesis have provided opportunities for the use of more delicate biomacromolecules as templates. The complexation of Pani with DNA has been found to induce reversible changes in the secondary structure of DNA leading to the formation of an over-wound polymorph. The thermal characterization (melting behavior) of the DNA in the complex and the morphological properties of the complex have provided corroborative evidence for the wrapping of Pani around the DNA matrix. Scanning probe and electron microscopy studies have indicated that the formation of Pani causes the DNA-Pani strands to agglomerate, presumably due to the neutralization of charge on the phosphate groups by the partially charged Pani. We also report the synthesis of Pani on a synthetic oligonucleotide (Poly[dA-dC].poly[dG-dT]). Demonstration of the use of a new biomimetic catalyst, polyethylene glycol modified hematin (PEG-hematin), in these reactions will also be presented. These results indicate that this biocatalytic synthetic approach is generic, versatile and can be adopted for both genomic and synthetic nucleic acids. †Deceased.

Thermal analysis of energetic materials

Abstract Substances which undergo strongly exothermic chemical reactions may constitute hazards in various situations. The techniques of thermal analysis, in general, and differential scanning calorimetry (DSC) in particular, provide ways of examining such substances, in small quanitities under relatively safe conditions. A brief review of some developments in thermal explosion theory relevant to thermoanalytical studies is given. Extrapolation of the results obtained from thermoanalytical tests to more realistic situations has to be done with great care. The findings of some recent studies on energetic materials are reviewed.