Mohan Gopalkrishna Kulkarni

Polydentate disulfides for enhanced stability of AuNPs and facile nanocavity formation

Stabilization of gold nanoparticles (AuNPs) on a unique polydentate disulfide ligand, poly(DSDMA) synthesized by selective polymerization of bis(methacryloyl hydroxyethyl)disulfide (DSDMA), results in 2.2 nm monodisperse AuNPs, which exhibit Coulomb blockade at room temperature. A higher graft density (1.8 chains nm−2) of the polydentate ligand results in additional stability in DMF up to one year and competitive exchange against DTT (100 mM) up to 72 h. Crosslinking of the polymer remarkably enhances the thermal stability up to 140 °C for 4 h and also during selective etching by methyl iodide which results in nanocapsules as confirmed by TEM and AFM.

One pot room temperature synthesis of robust gold nanochains

We report a room temperature reduction and stabilization of gold nanoparticles (AuNPs) from auric chloride in the presence of 1.5 and 3 mM linear poly(amidoamine) (PAmAm), which leads to 1D assembly of AuNPs. At higher concentrations, isolated AuNPs are formed. Detailed investigations show that the morphology is governed primarily by pH rather than concentration. This is the first report to demonstrate the stability of nanochains against pH switching. The nanochains are robust as revealed by stability at higher temperature, salt concentration, thiol exchange, and would be useful in developing electronic devices for biological applications.

Secondary patents in the pharmaceutical industry: missing the wood for the trees?

ABSTRACT Introduction: The critics of the Innovator pharmaceutical industry allege that secondary patents are trivial modifications over the primary patent, which extend its term and delay the entry of the generics in the market place. The protagonists regard secondary patents a result of continuous research and development (R&D), which help them introduce and protect new, differentiated products. Areas covered: The areas covered are Product life cycle management (PLCM), Drug approval process, Orange book (OB) listed patents, US patent data. Expert opinion: Our analysis of the patents and products of four innovators viz., AstraZeneca, Takeda, Eisai and Wyeth in the field of proton pump inhibitors (PPI’s) and Merck and Pfizer in the field of Statins shows that secondary patents help innovators sustain competition against other innovators in the specific product segment. The number of secondary patents listed in OB per NCE depends on the innovators interest in exploiting the NCE, the success of R & D effort and product lifecycle management strategy in the wake of market competition. Market entry decisions of innovators are strategic rather than a mere fallout of the secondary patents granted. Entry of another innovator is more unpredictable and hurts the first entrant more vis a vis the entry of generics who can enter the market when the patents protecting a product are no more enforceable, and hence more predictable. Generic entry in the field of PPI’s shows that the term of the primary patent is not extended by the secondary patents.

pH Sensitive graft copolymers for zero order drug release: a mechanistic analysis.

Aliphatic polyesters containing pendent unsaturation were synthesized by the polycondensation of a diol, dicarboxylic acid and glycidyl methacrylate. Grafting methacrylic acid (MAA) resulted in graft copolymers containing polyester backbone and MAA grafts. Depending on composition, the polymers swelled extensively and eroded or dissolved at near neutral pH but remained in collapsed state at acidic pH. Three representative drugs differing in solubility, viz., Diltiazem hydrochloride (DH), Indomethacin (IM) and Verapamil hydrochloride (VH) were released at constant rate from tablets made by compressing spray-dried microparticles. The release of DH at constant rate has been attributed to increase in diffusion coefficient of the drug from the swollen layer of matrix. The release of IM and VH at constant rate was governed by erosion and was enhanced in matrices which undergo dissolution. The release rate was enhanced with increasing MAA content and the frequency of grafts along the polyester backbone. Once a day dosage forms for drugs differing in solubility have been developed using a single polymer matrix which is easy to manufacture.

Template assisted highly ordered novel self assembly of micro-reservoirs and its replication

A novel method is developed for template assisted fabrication of a regular assembly of microcavity arrays. Simple micropatterns on PDMS mold are used to create complex geometries via solvent vapor back pressure in a biodegradable polymer. Cavities are in turn replicated in complimentary PDMS mushroom like microstructures.