Santu Sarkar

Unique emission from norbornene derived terpyridine—a selective chemodosimeter for G-type nerve agent surrogates

A new chemodosimeter for a G-type agent that exploits norbornene derived terpyridine (NDT)-lanthanide unique emission is reported. The unusual emission between terpyridine and norbornene motifs of NDT is attributed to the significant difference in the position of the HOMO and LUMO wave functions that prevents the non-radiative relaxation pathway. An interesting magenta emission from NDT along with Eu(III) is utilized as a new fluorometric chemodosimeter that selectively detects (by changing the observed magenta emission to blue) G-type agent surrogates. A detection limit of 40 ppb is obtained and the selectivity for reactive surrogates over a variety of other close chemical analogs is demonstrated.

Magnetic Norbornene Polymer as Multiresponsive Nanocarrier for Site Specific Cancer Therapy

A site-specific, stimuli-responsive nanocarrier has been synthesized by conjugating folate, magnetic particles and doxorubicin to the backbone of norbornene polymer. Monomers, namely, cis-5-norbornene-6-(diethoxyphosphoryl)hexanote (mono 1), norbornene grafted poly(ethyleneglycol)-folate (mono 2), and norbornene derived doxorubicin (mono 3) are carefully designed to demonstrate the smart nanorcarrier capabilities. The synthesis and complete characterization of all three monomers are elaborately discussed. Their copolymerization is done by controlled/living ring-opening metathesis polymerization (ROMP) to get the triblock copolymer PHOS-FOL-DOX. NMR spectroscopy and gel permeation chromatography confirm the formation of the triblock copolymer, while FT-IR spectroscopy, thermogravimetric analysis, along with transmission electron microscope confirm the anchoring of iron particle (Fe3O4) to the PHOS-FOL-DOX. Drug release profile shows the importance of having the hydrazone linker that helps to release the drug exactly at the mild acidic conditions resembling the pH of the cancerous cells. The newly designed nanocarrier shows greater internalization (about 8 times) due to magnetic field. Also, increased intracellular DOX release is observed due to the folate receptor. From these results, it is clear that PHOS-FOL-DOX has the potential to act as a smart nanoreservoir with the magnetic field guidance, folate receptor targeting, and finally pH stimulation.

Norbornene-Derived Poly-d-lysine Copolymers as Quantum Dot Carriers for Neuron Growth

Synthesis of norbornene derived phosphonate (1), poly-D-lysine (2), and phopholipid (3) monomers and their complete characterizations are studied. Ring-opening metathesis polymerizations (ROMP) of monomers (1-3) produce well-defined copolymers, CP(1) and CP(2). (1)H NMR along with FT-IR spectroscopy characterization confirms the copolymer formation, while gel permeation chromatography (GPC) analysis suggests the formation of polymers with fairly narrow molecular weight distributions. Upon following the well-known ligand exchange methods these copolymers produce CdSe-bound copolymers, CP(3) and CP(4). Dynamic light scattering and transmission electron microscopy measures the size of these CdSe bound copolymers, while (31)P NMR suggests the formation of CP(3) and CP(4). The results from the experiments of these copolymers on Neuro2A cells suggest that the novel PDL-anchored nanomaterial show their ability to polarize neuronal growth and differentiation.

Unique norbornene polymer based 'in-field' sensor for As(III)

We report the synthesis of norbornene derived rhodamine (Nor-Rh) and thiol (Nor-Th) monomers and their polymerizations. The response of Nor-Rh against As(III) in the presence of potassium iodate and hydrochloric acid is monitored through UV and fluorescence spectroscopy. The observed colorimetric as well as fluorometric changes are attributed to the redox reaction involved in the unique design. Cyclic voltammogram measurements confirm the oxidation of As(III) to As(V) during the sensing event. The response of the sensing event is instantaneous. This novel design is able to sense ppb levels of As(III) very selectively in an aqueous environment. As(III) is trapped when it is passed through a column containing Nor-Th polymers. As(III) free water is tested using a calibration curve from the Nor-Rh response.

An efficient method to prepare a new class of regioregular graft copolymer via a click chemistry approach

Herein, we report the synthesis of a novel regioregular poly-norbornene anhydride-g-(3-hexyl thiophene) (PNBA-g-PHT) graft copolymer. Grignard metathesis polymerization was used to obtain a PHT homopolymer. Then, PHT-N3 was prepared via a chemical modification reaction of the hydroxyl terminated PHT. A click chemistry approach was then used to synthesis MM 1. Finally, ring-opening metathesis polymerization (ROMP) of MM 1 produced the final copolymer. NMR and COSY studies clearly showed that the regioregularity was retained in the newly synthesized copolymer.