V. N. Rajasekharan Pillai

Membrane-encapsulated controlled-release urea fertilizers based on acrylamide copolymers

About 40–70% of the applied urea fertilizer is lost to the environment, causing serious pollution. Controlled-release technology is useful in increasing the efficiency of fertilizer urea as well as in checking environment pollution. Four laboratory-level controlled-release urea fertilizers were formulated based on polymers which are soil conditioners and then evaluated for their slow-release property. Urea was coated with the copolymer of acrylamide and divinylbenzene/N,N′-methylenebisacrylamide /tetraethyleneglycol diacrylate or pentaerythritol triacrylate and sealant materials (wax and polystyrene). Urea coated with co-polymer of acrylamide-tetraethyleneglycol diacrylate was found to be having a better slow-release property among the systems prepared.

Gel-phase peptide synthesis on a new high-capacity tetraethyleneglycol diacrylate-crosslinked polystyrene support: Synthesis of pardaxin 16–33.

An insoluble but highly solvating copolymer composed of tetraethyleneglycol diacrylate (TTEGDA)-crosslinked polystyrene has been prepared in beaded form by free-radical suspension polymerization of the monomers and employed as a new solid support for gel-phase peptide synthesis. This new polymer support has comparable physical and mechanical properties as that of the divinylbenzene (DVB)-crosslinked polystyrene support permitting identical manipulation such as shaking and filtration when used as a support for solid-phase peptide synthesis. This polystyrene-TTEGDA crosslinked polystyrene resin undergoes much more effective swelling and solvation than DVB-crosslinked polystyrene in a range of solvents with widely varying polarity which are commonly employed synthesis. The resin can be easily chloromethylated under controlled conditions to prepare resins of varying capacity ranging from low (0.15 meq/g) to high capacity (3.5meq/g). A high capacity resin with 1.5 meq/g chlorine capacity was used for synthesis of hydrophilic C-terminal 18-residue peptide of pardaxin from Pardachirus Pavoninus. The peptide was cleaved from the polymeric support by trifluoroacetic acid at 37°C and purified by Fast Protein Liquid Chromatography (FPLC). The purified peptide was shown to be homogeneous by HPLC and the identity of the 18-residue peptide was confirmed by amino acid analysis. The free peptide possesses a disordered conformation as revealed by the CD measurement.

Polymer-metal complexes of amino functionalized divinylbenzene-crosslinked polyacrylamides

Abstract The complexation of amino functions supported on polyacrylamides with 2–20 mol% of divinylbenzene (DVB) crosslinks was investigated towards Co(II), Ni(II), Cu(II), Zn(II) and Hg(II) ions. With increasing extent of DVB-crosslinking, the metal ion intake decreased in the order: Hg(II) >> Cu(II) > Zn(II) > Ni(II) > Co(II). The polymeric ligand and the derived metal complexes were characterized by their typical i.r. absorptions and from the e.s.r. spectra. The i.r. absorptions of the polymeric ligands were shifted by complexation. The e.s.r. parameters suggested the distorted tetragonal geometry of the Cu(II) complexes. The change in surface morphology on complexation was followed by scanning electron microscopy. The thermal stability varied with the incorporation of metal ions. The activation energy values and the extent of crosslinking in Cu(II) complexes fit into the general equation for a cubic polynomial. The time-course and kinetics of complexation and the adsorption characteristics of complexation were also followed. The swelling characteristics varied with the extent of crosslinking, and the extent of swelling was lower for the complexed resins. The complexed resins can be recycled several times, and the Cu(II)-desorbed resin showed specificity to the Cu(II) ion in the presence of other metal ions.

3-Nitro-4-Aminomethylbenzoylderivate von Polyethylenglykolen: Eine neue Klasse von Photosensitiven löslichen Polymeren Trägern zur Synthese von C-terminalen Peptidamiden

Zusammenfassung Die Synthese von 3-Nitro-4-aminomethylbenzoylpolyethylenglykol und seine Anwendung in der Flussigphasenpeptidsynthese wird beschrieben. Vollgeschutzte Peptide konnen durch Photolyse als C-terminale Amide quantitativ vom polymeren Trager abgespalten werden.

Crosslinked polystyrene-supported dithiocarbamates as metal complexing agents

Dithiocarbamate functions were introduced into divinylbenzene (DVB)-crosslinked polystyrene matrices in different structural environments and their complexation behaviour with various metal ions was investigated. The reactions involved introduction of the amino functionality into the polystyrene matrix through a number of different heterogeneous amination procedures. These aminopolystyrene derivatives which contain the amino functions in different steric environments were converted to the respective dithiocarbamates by reaction with carbondisulphide in the presence of alkali. The metal complexing ability of the resulting insoluble polystyrene-dithiocarbamates was investigated towards Fe(III), Ni(II), Cu(II) and Zn(II) ions. The structural factors characteristic of the polymer matrix like the molecular character and extent of crosslinking were found to exert influence on the metal complexing ability. The spectral characterization and the relative thermal stabilities of the complexes were also investigated.

Polymer-supported synthesis of protected peptide segments on a photosensitive o-nitro(a-methyl)bromobenzyl resin

Abstract The preparation of a new polystyrene support containing the photodetachable o -nitro(α -methyl)benzyl anchoring group and its application in the solid phase synthesis of fully protected C-terminal peptides are described, The preparation of the photosensitive resin involves a 4-step polymer-analogous reaction starting from 1 %-divinyl benzene crosslinked polystyrene. Amino acid units were incorporated into this resin following standard solid phase peptide synthetic methodology and the peptides were cleaved from the support by photolysis under neutral conditions at 350 nm, in 40–50 % overall yield. The attachment of the peptide through a secondary ester linkage In o -position to the nitro group is the factor permitting the photolytic cleavage of the peptides from the support.

Synthesis of Acyl Carrier Protein Fragment 65–74 on a Flexible Cross-linked Polystyrene Support: Comparison with Merrifield Resin

Abstract A novel 1,6-hexanediol diacrylate-cross-linked polystyrene support was prepared by suspension polymerization. The new support was used for synthesis of a difficult sequence-acyl carrier protein fragment 65–74 (ACP 65–74). The quantity and purity of peptide obtained from the new support were higher than when Merrifield resin was used. The reason for the high synthetic efficiency of the new support was found to be its ability to suppress the β-sheet formation of the growing peptide.

Polymer-supported analogues of t-butyl hypohalites. Preparation and applications in synthetic organic chemistry

Crosslinked polymer-supported analogues of t-butyl hypochlorite and t-butyl hypobromite were prepared and developed as a new class of recyclable solid-phase oxidizing and halogenating reagents. The preparation of these new reagents involved a three-step polymer-analogous reaction starting from styrene-divinylbenzene crosslinked polymer. A ketone functional group was introduced into the copolystyrene-2% divinylbenzene resin beads by a Friedel-Crafts reaction with bromoacetone. This functional group was then converted to a tertiary alcoholic function on the polymer support by a Grignard reaction with methylmagnesium iodide. The treatment of this tertiary alcohol resin with sodium hypochlorite or sodium hypobromite yielded the polymeric t-butyl hypochlorite or hypobromite. These hypohalites were estimated iodometrically. These reagents were found to oxidize primary and secondary alcohols to the corresponding carbonyl compounds in high yields. They were also found to be suitable for halogenation of carbonyl compounds and amides. The spent polymeric reagent after the oxidation or halogenation step can be easily removed by filtration and can be regenerated many times by treating with the sodium hypohalite without any loss of capacity.

Divinylbenzene-crosslinked polyacrylamide-supported dithiocarbamates as metal complexing agents

SummaryDithiocarbamate (DTC) functions were incorporated into divinylbenzene-crosslinked (2–20 mole %) polyacrylamides by a two-step polymer-analogous reaction. The complexations of these resins with DTC functions in different structural environments were investigated towards Co(II), Ni(II), Cu(II), Zn(II) and Hg(II) by batch equilibration technique. The metal ion intake decreased with the extent of the DVB content in the order Hg(II)>>Cu(II)>Zn(II)>Ni(II)>Co(II). The time-course on complexation, swelling behaviours of the uncomplexed and complexed resins, recyclability, IR and thermogravimetric characterisation of the complexes were carried out. The swelling of the resins decreased on complexation with metal ions and the thermal stability increased.

Solid-phase synthesis of C-terminal peptide amides using a photoremovable α-methylphenacylamido anchoring linkage

Polymer-supported solid-phase synthetic procedures have been developed for the synthesis of C-terminal peptide amides using a new photolytically removable α-methylphenacylamido anchoring linkage between the polymeric support and the growing peptide. The preparation of this new polymeric support involves a four-step polymer-analogous reaction starting from 2%-divinylbenzene-crosslinked polystyrene resin. The steps involved are (i) Friedel-Crafts reaction with 2-bromopropionyl chloride to give the 2-bromopropionyl resin, (ii) reaction of the 2-bromopropionyl resin with potassium phthalimide to give the phthalimidomethyl resin, (iii) hydrolysis with alcoholic potash to give the partially hydrolysed phthalamido resin and (iv) treatment with alcoholic HCl to give the 2-aminopropionyl resin. N-protected amino acids undergo coupling with this amino resin by the dicyclohexylcarbodiimide-mediated coupling. The acylated resins on irradiation at 350 nm in DMF released the attached carboxyl function in the C-terminal amide form. The mechanism of the photolytic deprotection involves a radical scission of the amide linkage adjacent to the phenacyl group. The synthetic utility of the new resin has been illustrated by the preparation of several N-protected amino acid amides and the C-terminal peptide amides, Boc-Pro-Val-NH2, Boc-Gly-Phe-Pro-NH2 and Boc-Leu-Ala-Gly-Val-NH2 in 70–74% yield.