The reaction mechanism for the organocatalytic ring-opening polymerization of l-lactide using a guanidine-based catalyst: hydrogen-bonded or covalently bound?

We have investigated two alternative mechanisms for the ring-opening polymerization of l-lactide using a guanidine-based catalyst, the first involving acetyl transfer to the catalyst, and the second involving only hydrogen bonding to the catalyst. Using computational chemistry methods, we show that the hydrogen bonding pathway is considerably preferred over the acetyl transfer pathway and that this is consistent with experimental information.     

Tagging alcohols with cyclic carbonate: a versatile equivalent of (meth)acrylate for ring-opening polymerization

Cyclic carbonate monomers based on a single biocompatible scaffold allow for incorporation of a wide range of functional groups into macromolecules via ring-opening polymerization.     

Layered Dendritic Block Copolymers

A star-shaped molecule and a layered structure are displayed by the title compound, where the layers consist of high molecular weight polymers. A core molecule that is functionalized by six hydroxyl groups acts as the initiator for the ring-opening polymerization of ε-caprolactone, leading to a six-arm star polymer. The second layer of the dendritic block copolymer with 12, 24, or 48 hydroxyl groups (depending on the dendron generation in use) is obtained by the linkage of chain ends with functionalized dendrons. These macromoleculse act as “macroinitiators” for the construction of a further layer of poly(ε-caprolatone), the third generation of dendritic block copolymers.     

Thermoresponsive Random Poly(ether urethanes) with Tailorable LCSTs for Anticancer Drug Delivery

A new class of thermoresponsive random polyurethanes is successfully synthesized and characterized. Poly(ethylene glycol) diol (M_n = 1500 Da) and 2,2‐dimethylolpropionic acid are reacted with isophorone diisocyanate in the presence of methane sulfonic acid catalyst. It is found that these polyurethanes are thermoresponsive in aqueous media and manifest a lower critical solution temperature (LCST) that can be easily tuned from 30 °C to 70 °C by increasing the poly(ethylene glycol) content. Their sharp LCST transitions make these random polyurethanes ideal candidates for stimuli‐responsive drug delivery applications. To that end, the ability of these systems to efficiently sequester doxorubicin (up to 36 wt%) by means of a sonication/dialysis method is successfully demonstrated. Additionally, it is also demonstrated that accelerated doxorubicin release kinetics from the nanoparticles can be attained above the LCST.

     

Galactose‐Functionalized Cationic Polycarbonate Diblock Copolymer for Targeted Gene Delivery to Hepatocytes

To mediate selective gene delivery to hepatocytes via the asialoglycoprotein receptors (ASGP‐Rs), we designed and synthesized well‐defined and narrowly dispersed galactose‐ and glucose‐functionalized cationic polycarbonate diblock copolymers (designated as Gal‐APC and Glu‐APC, respectively) using organocatalytic ring‐opening polymerization of functionalized carbonate monomers, with a subsequent quaternization step using bis‐tertiary amines to confer quaternary and tertiary amines for DNA binding and endosomal buffering, respectively. The sugar‐functionalized diblock copolymers effectively bound and condensed DNA to form positively charged nanoparticles (<100 nm in diameter and ≈30 mV zeta‐potential) that were stable under high physiological salt conditions. In comparison to the control Glu‐APC/DNA complexes, Gal‐APC/DNA complexes mediated significantly higher gene expression in ASGP‐R positive HepG2 cells with no significant difference observed in ASGP‐R negative HeLa cells. The co‐incubation of Gal‐APC/DNA complexes with a natural ASGP‐R ligand effectively led to a decrease in gene expression, hence providing evidence for the ASGP‐R mediated endocytosis of the polyplexes. Importantly, the Gal‐APC/DNA complexes induced minimal cytotoxicities in HepG2 cells at the N/P ratios tested. Taken together, the galactose‐functionalized cationic polycarbonate diblock copolymer has potential for use as a non‐viral gene vector for the targeted delivery of therapeutic genes to hepatocytes in the treatment of liver diseases.