Synthesis of macromolecular systems via lipase catalyzed biocatalytic reactions: applications and future perspectives.

Enzymes, being remarkable catalysts, are capable of accepting a wide range of complex molecules as substrates and catalyze a variety of reactions with a high degree of chemo-, stereo- and regioselectivity in most of the reactions. Biocatalysis can be used in both simple and complex chemical transformations without the need for tedious protection and deprotection chemistry that is very common in traditional organic synthesis. This current review highlights the applicability of one class of biocatalysts viz."lipases" in synthetic transformations, the resolution of pharmaceutically important small molecules including polyphenols, amides, nucleosides and their precursors, the development of macromolecular systems (and their applications as drug/gene carriers), flame retardants, polymeric antioxidants and nanocrystalline solar cells, etc.

Influence of EDA-pi interactions in drug encapsulation using nanospheres.

We have evaluated the influence of aromatic and hydrophobic interactions on the strength and selectivity of encapsulation using polymeric nanospheres.

"Green"-enzymatic synthesis of pegylated phenolic macromer and polymer.

Environmentally benign synthesis of novel pegylated polyphenolics, by combining the extraordinary selectivities of a lipase and an oxidase to develop polymeric electrolytes for applications in dye sensitised solar cells.

Synthesis of covalently attached hexadecaanilines on carbon nanotubes: toward electronic nanocarbon preparation.

We describe the direct covalent-grafting synthesis of well-defined aniline oligomers, such as tetraaniline (A(4)) and hexadecaaniline (A(16), major)/eicosaaniline (A(20), minor), on the sidewalls of carbon nanotubes (CNTs), via dediazonization reaction, for achieving highly soluble nanomaterials suitable for printing purposes, with long-term physical stability. Chemically grafting a layer of electroactive hexadecaanilines on CNTs resembles semiconductive encapsulation of functionalized CNTs. The resulting covalent nanoconjugates SWNT-(A(4))(x), MWNT-(A(4))(x), SWNT-(A(16/20))(x), and MWNT-(A(16/20))(x) were characterized by various spectroscopic and microscopic mapping methods. The combination of transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) analyses provided direct evidence for A(16/20) attachment to the CNTs, giving confirmation of the presence of heteroatoms surrounding the CNTs that was absent in the parent CNTs. Subsequent atom mapping in the vicinity of the tube structure allowed us to illustrate the 3D distribution of heteroatoms along the CNT surface.

Optical and electrochemical detection of saccharides with poly(aniline-co-3-aminobenzeneboronic acid) prepared from enzymatic polymerization.

Boronic acid-based sensors for saccharides have been developed via biocatalysis. The self-doped copolymer of poly(aniline-co-3-aminobenzeneboronic acid) [poly(aniline-co-AB)], with various mole ratios of two components, was synthesized by oxidative enzymatic polymerization using a natural biocatalyst such as horseradish peroxidase together with an anionic polyelectrolyte template (sulfonated polystyrene) under mild conditions (pH 4.5). Poly(aniline-co-AB), having an aniline boronic acid-to-aniline ratio of 1:2 on average, gave rise to a green doped polymer with absorption maxima at 745 nm. The potentiometric detection of saccharides using poly(aniline-co-AB) is presented. Characteristics of both transient and steady-state response associated with the complex formation of poly(aniline-co-AB) with various saccharides were monitored by UV-vis spectroscopy and cyclic voltammetry (CV). The results obtained from UV-vis spectroscopy and CV show that the sensitivity of enzymatically synthesized water-soluble poly(aniline-co-AB) for various saccharides was improved significantly compared to the chemically synthesized counterpart. A possible mechanism for the sensitive detection of sugar molecules by boronic acid is proposed on the basis of UV-vis and IR spectrophotometry, and four-point probe conductivity measurements.

Biomimetic synthesis of water-soluble conducting copolymers/homopolymers of pyrrole and 3,4-ethylenedioxythiophene.

A novel biomimetic route for the synthesis of electrically conducting homopolymers/copolymers of pyrrole and 3,4-ethylenedioxythiophene (EDOT) in the presence of a polyelectrolyte, such as polystyrene sulfonate (SPS), is presented. A poly(ethylene glycol)-modified hematin (PEG-hematin) was used to catalyze the homopolymerization of pyrrole and EDOT as well as copolymerization of EDOT and pyrrole in the presence of SPS to yield homopolymers of polypyrrole/SPS and PEDOT/SPS as well as a polypyrrole-co-poly(3,4-ethylenedioxythiophene)/SPS complex. Spectroscopic characterization [UV-visible, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS)], thermal analysis, (TGA), and electrical conductivity studies for these complexes indicated the presence of a stable and electrically conductive form of these polymers. Furthermore, the presence of SPS that serves as a charge-compensating dopant in this complex provides a unique combination of properties such as processability and water solubility.

Photo-cross-linked immobilization of polyelectrolytes for enzymatic construction of conductive nanocomposites.

Horseradish peroxidase has been demonstrated to catalyze the oxidative polymerization of aniline to form conductive polyaniline. This process is facilitated by the presence of a macromolecular template with sulfonic acid groups that provide a unique environment for the formation of the conducting polymer. Here we report the use of a photo-cross-linkable thymine-based polymer with phenylsulfonate groups as a templating substrate. This allows for an aqueous-based environmentally benign photopatterning of a conductive material. A description and results of this process are presented.

Biocatalytic synthesis of the conjugated bridging ligand tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2'",3'"-j]phenazine (tpphz) and a dinuclear ruthenium complex.

We have synthesized a fully conjugated aromatic bridging ligand, tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2' ",3'"-j]phenazine (tpphz), and a dinuclear ruthenium complex using Hematin as a biocatalyst.

Helical conformational specificity of enzymatically synthesized water-soluble conducting polyaniline nanocomposites.

A novel template guided enzymatic approach has been developed to synthesize optically active conducting polyaniline (PANI) nanocomposites in the presence of H2O2 as an oxidant, using (+) and (-) 10-camphorsulfonic acid (CSA) as a dopant and chiral inductor. The formation of chiral polyaniline in the nanocomposites was confirmed by circular dichroism (CD). Interestingly, the CD spectra of nanocomposites formed either with (+) or with (-) CSA show the enzyme itself plays a critical role in controlling the stereospecificity of the polyaniline (PANI) in the nanocomposite. The enzyme used for the polymerization of aniline in the nanocomposite was horseradish peroxidase (HRP). It was shown that this enzyme prefers a specific helical conformation, regardless of whether induced chirality in the complex CSA-aniline is from (+) or (-) CSA. UV-vis spectra show that the polyaniline is in the conducting form, and transmission electron micrographs (TEM) show that the nanocomposites are dispersed nicely with particle size dimensions in the range of 20-50 nm. Electron diffraction patterns of these chiral polymer nanocomposites suggest that these nanocomposites are in both crystalline and amorphous states.

Enzymatic synthesis of multi-component copolymers and their structural characterization.

The use of enzymes in synthetic applications has increased dramatically in the recent years and the field of polymer science is part of this trend. Synthesis of a variety of polymers using lipase catalyzed (Candida antarctica) polymerization reactions has led to a variety of new materials with interesting properties in our laboratories. This paper describes the synthesis of multi-component polyesters and mixed polymers having polyester and polyamide linkages under solvent-less conditions using Candida antarctica lipase B. The effect of a third component, i.e. a series of 1,omega-alkanediols (1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol, 1,14-tetradecanediol and 1,16-hexadecanediol) on the copolymerization reaction of dimethyl 5-hydroxyisophthalate with poly(ethylene glycol 600) has been studied and the mechanism for the incorporation of the third component is proposed. We have also studied the effect of different functional groups during terpolymerization reaction of dimethyl 5-hydroxyisophthalate with poly(ethylene glycol) by adding a third component having different functionalities (1,6-hexanediol, 1,6-hexanediamine or 1,6-hexanedithiol) and compared the effect of hydroxyl, amine and thiol groups on the polymerization reactions.

Solvent specified conformation in poly(alpha-L-glutamic acid) thin films.

The ability to control conformational properties of polypeptides in their films is of considerable interest for many possible applications of these materials. By rational choice of the solvent system for film fabrication, control over the conformation of the main chain, the intermolecular hydrogen bonding in the side chain is easily achieved in poly(alpha-L-glutamic acid) (PLGA) thin films. The spectral data from circular dichromism (CD), FT-IR, and solid state (13)C NMR spectroscopies suggest that the beta-sheet conformation is dominant in PLGA films cast from trifluoroacetic acid (TFA) solution, whereas the right-handed alpha-helix is dominant in those cast from pyridine or DMF solution. In comparison with films cast from TFA solutions, the films fabricated from pyridine or DMF solutions exhibit strong intermolecular hydrogen bondings between -COOH groups and have a more ordered arrangement of side chains. Moreover, the extent of alpha-helix conformation of the PLGA backbone in films cast from pyridine or DMF solution is several times higher than that observed in the PLGA powder precipitated from aqueous solution at pH 4. All spectroscopic studies indicate clearly that the solvents (used for casting these films) play a crucial role in directing the organization of PLGA in these thin films.

Biomimetic synthesis of a water soluble conducting molecular complex of polyaniline and lignosulfonate.

A new biomimetic route for the synthesis of a conducting molecular complex of polyaniline (Pani) and a natural polyelectrolyte, lignosulfonate (LGS) is presented. A poly(ethylene glycol) modified hematin (PEG-hematin) was used to catalyze the polymerization of aniline in the presence of LGS to form a Pani/LGS complex. UV-vis, FTIR, conductivity and TGA studies for the LGS-polyaniline complex indicate the presence of a thermally stable and electrically conductive form of polyaniline. Also the presence of LGS in this complex, an inexpensive byproduct from pulp processing, provides a unique combination of properties such as electronic conductivity, processability and biodegradability. The use of this conductive complex for corrosion protection is also proposed.

Supramolecular assemblies based on copolymers of PEG600 and functionalized aromatic diesters for drug delivery applications.

A chemoenzymatic approach has been developed to synthesize poly(ethylene glycol)-based amphiphilic copolymers under mild reaction conditions that self-assemble in aqueous media to form polymeric nanomicelles in the range of 20-50 nm. The supramolecular organization of polymeric nanomicelles was studied by 1H NMR longitudinal relaxation time (T1) and light scattering techniques (static and dynamic). Interestingly, the enzyme novozyme-435 plays an important role in controlling the polymerization and distribution of polymer chains, which is critical for the formation of nanomicelles with unimodal distributions. The methodology developed is highly flexible as it allows the introduction of various functionalities in the polymeric nanomicelles. These self-organized nanomicelles are highly efficient drug delivery vehicles for hydrophobic and partially hydrophilic drugs, both transdermally and orally, as they have the ability to encapsulate guest molecules during self-organization. In vivo studies by encapsulating anti-inflammatory agents (aspirin and naproxen) in these polymeric nanomicelles and by applying topically resulted in significant reduction in inflammation. The % reduction in inflammation using polymeric nanomicelles containing aspirin and naproxen was 62 and 64%, respectively.

Synthetic and novel biocatalytic resolution studies on (+/-)-5/6/7-acetoxy-4-aryl-3,4-dihydrocoumarins.

Eleven (+/-)-5/6/7-acetoxy-4-aryl-3,4-dihydrocoumarins have been synthesised in two steps starting from the coupling of cinnamic acid/substituted cinnamic acid with appropriate phenols, followed by acetylation in 50-83% overall yields. All hydroxy- and acetoxycoumarins were unambiguously identified on the basis of their spectral data. Candida antarctica lipase-catalysed deacetylation of these racemic acetoxydihydrocoumarins in dioxane occurred with moderate enantioselectivity. This is one of the rare examples of resolution using phenolic ester moiety as a remote handle for chiral recognition by a lipase.

Synthesis, characterization and in vitro anti-invasive activity screening of polyphenolic and heterocyclic compounds.

Invasion is the hallmark of malignant tumors, and is responsible for the bad prognosis of the untreated cancer patients. The search for anti-invasive treatments led us to screen compounds of different classes for their effect in an assay for invasion. Thirty-nine new compounds synthesized in the present study along with 56 already reported compounds belonging mainly to the classes of lactones, pyrazoles, isoxazoles, coumarins, desoxybenzoins, aromatic ketones, chalcones, chromans, isoflavanones have been tested against organotypic confronting cultures of invasive human MCF-7/6 mammary carcinoma cells with embryonic chick heart fragments in vitro. Three of them (a pyrazole derivative, an isoxazolylcoumarin and a prenylated desoxybenzoin) inhibited invasion at concentrations as low as 1 microM; instead of occupying and replacing the heart tissue within 8 days, the MCF-7/6 cells grew around the heart fragments and left it intact, when treated with these compounds. At the anti-invasive concentration of 1 microM, the three compounds did not affect the growth of the MCF-7/6 cells, as shown in the sulforhodamine B assay. Aggregate formation on agar was not stimulated by any of the three anti-invasive compounds, making an effect on the E-cadherin/catenin complex improbable. This is an invasion suppressor that can be activated in MCF-7/6 cells by a number of other molecules. Our data indicate that some polyphenolic and heterocyclic compounds are anti-invasive without being cytotoxic for the cancer cells.