A comparative study of the self-assembly of achiral and chiral hairy nanoparticles with polystyrene cores and poly(2-hydroxyethylmethacrylate) hairs.

Hairy nanoparticles with polystyrene cores (PS cores) and poly(2-hydroxyethylmethacrylate) (PHEMA) shells were synthesized by combining living anionic polymerization and atom transfer radical polymerization (ATRP). The structural characterization was carried out by FT-IR and NMR spectroscopy (1H NMR, 13C NMR, APT 13C NMR and 1H 13C HMQC). The thermal stability of the PS cores was not affected by grafting PHEMA on their surfaces. A differential scanning calorimetry (DSC) thermogram of the HNPs showed two distinct transition temperatures indicating microphase separation. Chiral HNPs were prepared by inducing chirality in the achiral HNPs by complexation with R- or S-mandelic acid. The circular dichroism (CD) spectroscopy of complexes of the HNPs/R- or S-mandelic acid indicated the formation of enantiomeric chiral structures. The self-assembled structures formed from the achiral HNPs show different surface morphologies, porous and zigzag, dependent on the solvents used. Blends of polystyrene functionalized with hydroxyl groups and PHEMA show different morphology and thermal properties compared with the core-shell HNP system. The chiral HNPs self-assembled into donut like structures or toroids with sizes in the range between 200 to 5000 nm. The study suggests that chirality can be utilized to develop interesting self-assembled structures.

Fabrication of Bioactive Surfaces by Functionalization of Electroactive and Surface-Active Block Copolymers.

Biofunctional block copolymers are becoming increasingly attractive materials as active components in biosensors and other nanoscale electronic devices. We have described two different classes of block copolymers with biofuctional properties. Biofunctionality for block copolymers is achieved through functionalization with appropriate biospecific ligands. We have synthesized block copolymers of electroactive poly(3-decylthiophene) and 2-hydroxyethyl methacrylate by atom transfer radical polymerization. The block copolymers were functionalized with the dinitrophenyl (DNP) groups, which are capable of binding to Immunoglobulin E (IgE) on cell surfaces. The block copolymers were shown to be redox active. Additionally, the triblock copolymer of α, ω-bi-biotin (poly(ethylene oxide)-b-poly (styrene)-b-poly(ethylene oxide)) was also synthesized to study their capacity to bind fluorescently tagged avidin. The surface-active property of the poly(ethylene oxide) block improved the availability of the biotin functional groups on the polymer surfaces. Fluorescence microscopy observations confirm the specific binding of biotin with avidin.

Synthesis of optically active helical poly(2-methoxystyrene). Enhancement of HeLa and osteoblast cell growth on optically active helical poly(2-methoxystyrene) surfaces.

Poly(2-methoxystyrene)s (P2MS) were synthesized using n-BuLi in THF and toluene at various temperatures. At -20 degrees C and higher temperatures, toluene was an effective polymerization solvent for synthesizing poly(2-methoxystyrene). Under these conditions, polymers with good yields and reasonable molecular weight distributions were obtained. Polymers synthesized under all conditions were isotactic; the most highly isotactic polymer was obtained in toluene at -20 degrees C. The m (isotactic dyad) content of the polymers synthesized in toluene at 0 degrees C and -20 degrees C was 0.65 and 0.74, respectively. Optically active helical (+) and (-) P2MS were synthesized by asymmetric polymerization utilizing (+) or (-) [2,3-dimethoxy1,4(dimethylamino)butane] (DDB)/tolyl lithium initiating complex in toluene. Asymmetric polymerizations were also carried out at 0 degrees C to synthesize optically active polymers. The optical rotations of the polymers were found to be dynamic and reversible, strongly suggesting contribution of the chiral higher ordered structure to the overall optical rotation. Geometry optimization carried out using various force fields such as MM+, AMBER and CHARMM suggests that isotactic P2MS form low energy stable helical conformations. HeLa cells showed better growth on surfaces prepared using chiral polymers compared to the surfaces prepared with achiral polymers. Similarly, chiral P2MS surfaces were also more effective as supports for mouse and human osteoblast cells. The cell attachment and growth data demonstrate that chiral P2MS surfaces were better supports compared to achiral P2MS surfaces. Atomic force microscopy (AFM) studies on surfaces prepared using chiral poly(2-methoxystyrene) showed more discrete topography features compared to surfaces prepared with achiral polymers. Thus, the surface topography may play a role in determining polymer-cell interactions.

Non-covalent nano-adducts of co-poly(ester amide) and poly(ethylene glycol): preparation, characterization and model drug-release studies.

Biodegradable, biocompatible poly(ester amide)s (co-PEAs), composed of amino acids, fatty diols and carboxylic acids, have been synthesized. To improve the performance of co-PEAs in Federal Drug Administration-approved solvents such as water and ethanol, these polymers were complexed with poly(ethylene glycol) (PEG) of 10 kDa molecular mass have been prepared by solution blending. The non-covalent adducts were purified by precipitation into hexanes. Co-PEAs are soluble in organic solvents but are insoluble in water and ethanol; however, the co-PEA/PEG (0.8:1, w/w) adducts are soluble in ethanol and slightly soluble in water. 2D-NOESY NMR spectroscopy suggests that the non-covalent adducts are held together by multiple non-covalent interactions between the -CH2- groups of the two polymers (co-PEA and PEG). Differential scanning calorimetry studies indicate that the two polymers are interacting in the non-covalent adducts; the thermal properties of the adducts are different from those of the pure polymers. The solid-state adduct structures have been determined by atomic force microscopy (AFM). By one sample preparation method, nanoscale pancake-like structures were observed with an average diameter of 260 nm and an average height of 16 nm. Films of co-PEAs and (co-PEA)/PEG adducts containing Rhodamine B Base (RhBB), a model hydrophobic drug, were prepared. From the adduct/RhBB film containing 3% RhBB, 20% of the total RhBB was released within the first 2 h. Film and adduct composition may be varied to obtain different release profiles. The studies reported here demonstrate that non-covalent conjugation is a relatively easy and effective approach in developing new materials for application as biomaterials.

Helical poly(3-methyl-4-vinylpyridine)/amino acid complexes: preparation, characterization, and biocompatibility.

Helical poly(3-methyl-4-vinylpyridine) (P3M4VP)/amino acid complexes have been prepared via acid-base reaction of the achiral polymer with D and L amino acids: alanine, leucine, valine, serine and phenylalanine. The circular dichroism (CD) spectra of P3M4VP/D- and L-alanine complexes in CH(3)OH/H(2)O show opposing (near mirror image) Cotton effect signals at 278.4, 274.8 and 270.8 nm, indicating the formation of enantiomeric secondary structures. The formation of the enantiomeric structures is supported by observed [alpha](D)(25) values of -3.0 and +3.0 for the P3M4VP/D-alanine and P3M4VP/L-alanine complexes, respectively. The preparation of helical P3M4VP/amino acid complexes has been carried out in CH(3)OH and H(2)O at pH 1.8 and 2.7. The intensities of the Cotton effect signals were good. For example, for the P3M4VP/L-alanine complexes in CH(3)OH/H(2)O and H(2)O (pH 1.8), the second Cotton effect signal around 275-277 nm show [theta;] values of 49 980 and 79 210 deg . cm(2) . dmol(-1), respectively. The formation of the helical secondary structure is rapid. The acid-base reaction between P3M4VP and L-alanine in CH(3)OH/H(2)O, in 10 min, show a CD spectrum with Cotton effect signals at 274 and 272 nm with [theta] values of 27,000 deg . cm(2) . dmol(-1) and -36,000 deg . cm(2) . dmol(-1), respectively. P3M4VP permits ready conformational reorientation on complexation with amino acids, but once the helical P3M4VP/amino acid complexes are formed, it is stable at room temperature. P3M4VP is not compatible with HeLa ovarian cancer cells, but the helical P3M4VP/amino acid complexes are compatible with HeLa cells. The complexes minimally interfere with the adhesion and growth of HeLa cells on complex surfaces. Helical poly(3-methyl-4-vinylpyridine)/D- and L-alanine complexes support the attachment and growth of HeLa cells. The micrographs shows HeLa cells after three days: left panel: on P3M4VP/L-alanine complex; right panel: on P3M4VP/D-alanine complex.