Synthesis of Polylactide: Effect of Dispersion of the Initiator

The ring opening polymerization of L-lactide was studied in bulk using stannous octoate as initiator. In some experiments, triphenylphosphine, a Lewis base was also used as co-initiator. The polymerization was carried out at 130°C up to 29 h. The monomer was used after recrystallizing three times with dry toluene. Experiments were carried out using a wide range of monomer to initiator ratio. The averages and distributions of molar masses of resulting PLA have been determined by means of size exclusion chromatography, SEC. It is shown that the (mode, process) procedure of dispersion of the catalyst in polymerization system affects the molar mass distribution of the product as is evidenced by the bimodality or even trimodality observed in the SEC chromatograms.     

A sensitive solid-phase fluoroimmunoassay for detection of opiates in urine

An automated flow fluorometer designed for kinetic binding analysis was adapted to develop a solid-phase competitive fluoroimmunoassay for urinalysis of opiates. The solid phase consisted of polymer beads coated with commercial monoclonal antibodies (MAbs) raised against morphine. Fluorescein-conjugated morphine (FL-MOR) was used as the fluorescein-labeled hapten. The dissociation equilibrium constant (K _D ) for the binding of FL-MOR to the anti-MOR MAb was 0.23 nM. The binding of FL-MOR to the anti-MOR MAb reached steady state within minutes and was displaced effectively by morphine and other opiates. Morphine-3-glucuronide (M3G), the major urinary metabolite of heroin and morphine, competed effectively with FL-MOR in a concentration-dependent manner for binding to the antimorphine MAb and was therefore used to construct the calibration curve. The sensitivity of the assay was 0.2 ng/mL for M3G. The assay was effective at concentrations of M3G from 0.2 to 50 ng/mL, with an IC₅₀ of 2 ng/mL. Other opiates and heroin metabolites that showed >50% crossreactivity when present at 1 μg/mL included codeine, morphine-6-glucuronide, and oxycodone. Methadone showed very low crossreactivity (<5%), which is a benefit for testing in patients being treated for opiate addictions. The high sensitivity of the assay and the relatively high cutoff value for positive opiate tests allows very small sample volumes (e.g., in saliva or sweat) to be analyzed. A double-blind comparison using 205 clinical urine samples showed good agreement between this single-step competitive assay and a commercially performed enzyme multiplied immunoassay technique for the detection of opiates and benzoylecgonine (a metabolite of cocaine).     

Synthesis,characterization, DNA cleavage and in vitro antimicrobial activities of copper(II) complexes of Schiff bases containing a 2,4-disubstituted thiazole

Six Cu(II) complexes of Schiff base ligands of arylidene-2-(4-(4-bromo/methoxy-phenyl)thiazol-2-yl) hydrazines have been synthesized, characterized and screened for DNA cleavage and antimicrobial activities. The chemical structures of the complexes were deduced by physicochemical and spectroscopic methods. Elemental analyses indicated that the stoichiometry of the complexes is CuL₂ (L = Schiff base ligand). The DNA cleavage activities of the complexes were evaluated by agarose gel electrophoresis in the presence and absence of oxidant (H₂O₂) and free radical scavenger (DMSO). All the six complexes showed significant nuclease activity in the presence of H₂O₂, and two of the complexes showed moderate nuclease activity even in the absence of oxidant. The complexes did not show nuclease activity in the presence of free radical scavenger. The compounds were tested for activity against selected bacteria and fungi.     

Polymerization of lactide and synthesis of block copolymer catalyzed by copper(Ⅱ) Schiff base complex

In the present investigation, the novel copper Schiff base complex was synthesized and its catalytic activity was evaluated for the ring-opening polymerization (ROP) of lactide and block polymerization of poly(lactide) with poly(ethylene glycol)methyl ether.     

Size-selective synthesis and stabilization of gold organosol in C(n)TAC: enhanced molecular fluorescence from gold-bound fluorophores

Gold nanoparticles of variable sizes have been synthesized in toluene employing two-phase (water-toluene) extraction of AuCl4- followed by its reduction with sodium borohydride in the presence of a series of cationic surfactants of a homologous series having the general formula C(n)TAC. The solubility features of the gold particles in the organic solvent have been accounted qualitatively by calculating the van der Waals interaction potential between the particles. The effect of thermal energy and medium dielectric constant on the stability of metal particles has been studied by measuring the surface plasmon resonance. The stabilization of surfactant-mediated gold particles as hydrosol or organosol has been elucidated by considering the double-layer interaction as a function of the dielectric constant of the solvent medium. The influence of the counterion of the phase transfer reagent and stabilizing ligand on the photochemical stability of the gold colloids has been investigated. The fluorescence probe 1-methylaminopyrene (MAP) was considered for the surface functionalization of the gold particles, and it has been found that there is an enhancement of molecular fluorescence from the gold-probe assembly.     

Unprecedented control over polymerization of n-hexyl isocyanate using an anionic initiator having synchronized function of chain-end protection

The living anionic polymerization of isocyanates carried out using conventional initiators is associated with side reactions due to rapid initiation rates as well as back-biting by the growing chain, resulting in a lack of control on the molecular weight (MW) and molecular weight distribution (MWD) of the polymers. Successful control over the reaction was possible by using additives that could prevent back-biting. We find an initiator in sodium benzanilide (Na-BA), which has a slow initiation rate combined with additive function, so that use of an external additive is eliminated. The initiator has resulted in polymers with high yields and an unprecedented control over the MW and MWD. It is possible to introduce a number of functionalities at the termini of the polymer by using Na-BA derivatives as well as suitable terminating agents, leading to macromonomer, reactive and chiral polymers, and chiral macromonomer in approximately 100% yields. In the process, the finding has expanded the scope of polyisocyanates in diverse applications.     

Solvent- and Substrate-Induced Chiroptical Inversion in Amphiphilic,Biocompatible Glycoconjugate Supramolecules: Shape-Persistent Gelation,Self-Healing,and Antibacterial Activity

We have shown solvent- and substrate-dependent chiral inversion of a few glycoconjugate supramolecules. (Z)-F-Gluco, in which d -glucosamine has been attached chemically to Cbz-protected l -phenylalanine at the C terminus, forms a self-healing hydrogel through intertwining of the nanofibers wherein the gelators undergo lamellar packing in the β-sheet secondary structures with a single chiral handedness. Dihybrid (Z)-F-gluco nanocomposite gel was prepared by in-situ formation of silver nanoparticles AgNPs in the gel; this enhances the mechanical properties of the composite gel through physical crosslinking without altering the packing pattern. In contrast, (Z)-L-gluco bearing an l -leucine moiety does not form a hydrogel but an organogel. Interestingly, the chiral handedness of the aggregates of (Z)-L-gluco can be reversed by choosing suitable solvents. In addition to self-healing behavior, (Z)-L-gluco gel revealed shape persistency. Further, (Z)-F-gluco hydrogel is benign, nontoxic, non-immunogenic, and non-allergenic in animal cells. AgNP-loaded (Z)-F-gluco hydrogel showed antibacterial activity against both Gram-positive and Gram-negative bacteria.     

Role of solvent in the compatibility of a vinylchloride–vinylacetate–maleic acid terpolymer and nitrocellulose blends

The compatibility of cast films of a vinylchloride–vinylacetate–maleic acid terpolymer (VMCH) and nitrocellulose (NC) blends is influenced by solvents. Transparent films of VMCH/NC blends are obtained when cast from solvents such as tetrahydrofuran or cyclohexanone, whereas hazy films are obtained when cast from solvents such as acetone or ethylacetate. Visible spectroscopy and phase morphology were used to analyse the compatibility–incompatibility of the blend. Differential scanning calorimetry (DSC) studies demonstrate that the transparent film is compatible, but the hazy film is incompatible. Fourier transform infra-red (FTIR) studies establish that a greater interaction is observed between the polymer pair in case of the compatible blend than in the case of the incompatible blend. A solvent dependency of blend compatibility is reflected in this study. The conformational state of the polymers in solution, which is responsible for the compatibility phenomena, may depend on the donor number and/or Taft-β value of the solvent. The greater the donor number and/or the Taft-β value, the higher may be the level of interaction between the solvent and the polymer molecules, which in turn may give a compatible blend after removal of the solvent.