Intelligent gene delivery systems based on physiologically triggered reversible shielding technology have evinced enormous interest due to their potential in vivo applications. In the present work, an acid-labile block copolymer consisting of poly(ethylene glycol) and poly(2-(dimethylamino)ethyl methacrylate) segments connected through a cyclic ortho ester linkage (PEG- a-PDMAEMA) was synthesized by atom transfer radical polymerization of DMAEMA using a PEG macroinitiator with an acid-cleavable end group. PEG- a-PDMAEMA condensed with plasmid DNA formed polyplex nanoparticles with an acid-triggered reversible PEG shield. The pH-dependent shielding/deshielding effect of PEG chains on the polyplex particles were evaluated by zeta potential and size measurements. At pH 7.4, polyplexes generated from PEG- a-PDMAEMA exhibited smaller particle size, lower surface charge, reduced interaction with erythrocytes, and less cytotoxicity compared to PDMAEMA-derived polyplexes. At pH 5.0, zeta potential of polyplexes formed from PEG- a-PDMAEMA increased, leveled up after 2 h of incubation and gradual aggregation occurred in the presence of bovine serum albumin (BSA). In contrast, the stably shielded polyplexes formed by DNA and an acid-stable block copolymer, PEG- b-PDMAEMA, did not change in size and zeta potential in 6 h. In vitro transfection efficiency of the acid-labile copolymer greatly increased after 6 h incubation at pH 5.0, approaching the same level of PDMAEMA, whereas there was only slight increase in efficiency for the stable copolymer, PEG- b-PDMAEMA.

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Thin films of 1,6-diisocyanohexane (DICH) can be formed on Au and Pt surfaces by immersion of clean substrates in 0.001-1.0 M solutions of DICH. Infrared transitions for both Au-bound and free isocyanide functionalities are observed after Au surfaces have been placed in methanolic solutions with DICH concentrations > 0.001 M, indicating that some portion of the DICH layer is composed of molecules with only one of the isocyanide moieties bound to the Au surface. In addition, poly(DICH) layers are formed on Au as noted by the presence of imine bands in the reflection-absorption infrared (RAIR) spectra of such surfaces and the time-dependent nature of the band intensities of the imine and methylene modes. The resulting DICH-coated Pt and Au surfaces are effective transport barriersssubstantially diminished redox responses of various solution probes are observed at such modified electrodes. In particular, the DICH films on Pt prevent 95% oxidation of the underlying metal surface. It is found that the remaining free isocyanide groups on the DICH-coated surfaces can be further polymerized (cross-linked) to various extents by exposure to oxygenated aqueous Ni 2+ solutions, allowing for control of film permeability. These results point to the possible application of poly(DICH) films in the fields of chemical sensing and corrosion protection.