Proteins immobilization on the surface of modified plant viral particles coated with hydrophobic polycations.

Two hydrophobic cations based on poly-N-ethyl-vinylpyridine were used to produce biologically active complexes. The complexes obtained from tobacco mosaic virus (TMV) spherical particles (SPs), hydrophobic polycation, and a model protein were stable and did not aggregate in solution, particularly at high ionic strengths. The nucleic acid-free SPs were generated by thermal remodeling of the TMV (helical rod-shaped plant virus). The model protein preserved its antigenic activity in the ternary complex (SP-polycation-protein). Immobilization of proteins on the surface of SPs coated with hydrophobic cation is a promising approach to designing biologically active complexes used in bionanotechnologies.

Polymer migration among phospholipid liposomes.

Complexation of phospholipid lipsomes with a cationic polymer, poly(N-ethyl-4-vinylpyridinium bromide) (PEVP), and subsequent interliposomal migration of the adsorbed macromolecules, have been investigated. Liposomes of two different charge types were examined: (a) a liposomal system, with an overall charge near zero, consisting of zwitterionic phosphatidylcholine (egg lecithin, EL) with added doubly anionic phospholipid, cardiolipin (CL(2-)), and cationic dihexadecyldimethylammonium bromide (HMAB(+)), in a CL(2-)/HMAB(+) charge-to-charge ratio of 1:1; (b) an anionic liposomal system composed of an EL/CL(2-) mixture plus polyoxyethylene monocetyl ether (Brij 58). Both three-component systems were designed specifically to preclude liposomal aggregation upon electrostatic association with the PEVP, a phenomenon that had complicated analysis of data from several two-component liposomes. PEVP macromolecules were found from fluorescence experiments to migrate among the charge-neutral EL/CL(2-)/HMAB(+) liposomes. In the case of anionic EL/CL(2-)/Brij liposomes, a combination of fluorescence and laser microelectrophoresis methods showed that PEVP macromolecules travel from liposome to liposome while being electrostatically associated with anionic lipids.

Biomembrane sensitivity to structural changes in bound polymers.

Anionic liposomes containing a 4:1 molar ratio of neutral to anionic phospholipids were treated with an excess of five zwitterionic polymers differing only in the spacer length separating their cationic and anionic moieties. Although the polymers do not disrupt the structural integrity of the liposomes, they can induce spacer-dependent molecular rearrangements within the liposomes. Thus, the following were observed: spacer length = 1, no binding to the liposomes; spacer length = 2, adsorption to the liposomes, but no molecular rearrangement; spacer length = 3, lateral lipid segregation but little or no flip-flop; spacer length = 4 or 5, lateral lipid segregation and flip-flop. These diverse behaviors are relevant to the use of biomedical formulations where polyelectrolytes play a role.

Polyelectrolyte-coated liposomes: stabilization of the interfacial complexes.

Anionic liposomes, composed of egg lecithin (EL) or dipalmitoylphosphatidylcholine (DPPC) with 20 mol% of cardiolipin (CL(2-)), were mixed with cationic polymers, poly(4-vinylpyridine) fully quaternized with ethyl bromide (P2) or poly-L-lysine (PL). Polymer/liposome binding studies were carried out using electrophoretic mobility (EPM), fluorescence, and conductometry as the main analytical tools. Binding was also examined in the presence of added salt and polyacrylic acid (PAA). The following generalizations arose from the experiments: (a) Binding of P2 and PL to small EL/CL(2-) liposomes (60-80 nm in diameter) is electrostatic in nature and completely reversed by addition of salt or PAA. (b) Binding can be enhanced by hydrophobization of the polymer with cetyl groups. (c) Binding can also be enhanced by changing the phase state of the lipid bilayer from liquid to solid (i.e. going from EL to DPPC) or by increasing the size of the liposomes (i.e. going from 60-80 to 300 nm). By far the most promising systems, from the point of view of constructing polyelectrolyte multilayers on liposome cores without disruption of liposome integrity, involve small, liquid, anionic liposomes coated initially with polycations carrying pendant alkyl groups.

What is the effective charge of TGA-stabilized CdTe nanocolloids?

The surface charge of semiconductor nanoparticles, Q, is an important parameter which determines their electrokinetic behavior, stability in water and polar solvents, functions of optical and electronic devices, self-assembly properties, and interactions with cell membranes. We have developed a simple method for quantitative determination of Q in their native aqueous environment. The method does not require the knowledge of exact atomic structure or make assumptions about effects of drying on charge distribution. The method is based on titration of nanoparticle dispersion with a solution of oppositely charged polyelectrolyte. The point of complete neutralization is recognized as an inflection point on the dependence of fluorescence intensity on the amount of polyelectrolyte added. Thioglycolic acid-stabilized CdTe nanoparticles 2 nm in diameter were found to carry an average Q from -2.6 to -5.5 for pH 7.5 to 10, respectively. This charge is found to be smaller than that calculated theoretically for an analogous structure (i.e., Q = -8), presumably due to adsorption of Cd(2+) ions on the stabilizer shell and on Te atoms with unsaturated valence located on the side planes of CdTe tetrahedrons.

Aqueous dispersions of single-wall and multiwall carbon nanotubes with designed amphiphilic polycations.

Poor solubility of single-walled and multiwalled carbon nanotubes (NTs) in water and organic solvents presents a considerable challenge for their purification and applications. Macromolecules can be convenient solubilizing agents for NTs and a structural element of composite materials for them. Several block copolymers with different chemical functionalities of the side groups were tested for the preparation of aqueous NT dispersions. Poly(N-cetyl-4-vinylpyridinium bromide-co-N-ethyl-4-vinylpyridinium bromide-co-4-vinylpyridine) was found to form exceptionally stable NT dispersions. It is suggested that the efficiency of macromolecular dispersion agents for NT solubilization correlates with the topological and electronic similarity of polymer-NT and NT-NT interactions in the nanotube bundles. Raman spectroscopy and atomic force and transmission electron microcopies data indicate that the polycations are wrapped around NTs forming a uniform coating 1.0-1.5 nm thick. The ability to wind around the NT originates in the hydrophobic attraction of the polymer backbone to the graphene surface and topological matching. Tetraalkylammonium functional groups in the side chains of the macromolecule create a cloud of positive charge around NTs, which makes them hydrophilic. The prepared dispersions could facilitate the processing of the nanotubes into composites with high nanotube loading for electronic materials and sensing. Positive charge on their surface is particularly important for biological and biomedical applications because it strengthens interactions with negatively charged cell membranes. A high degree of spontaneous bundle separation afforded by the polymer coating can also be beneficial for NT sorting.

Self-organized, highly luminescent CdSe nanorod-DNA complexes.

DNA molecules are useful building blocks and nanotemplates for controllable fabrication of various bioinorganic nanostructures due to their unique physical-chemical properties and recognition capabilities and the synthetic availability of desired nucleotide sequences and length. We have synthesized novel DNA complexes with positively charged, highly luminescent CdSe nanorods that can be self-organized into filamentary, netlike, or spheroidal nanostructures. DNA-CdSe-nanorod filaments possess strongly linearly polarized photoluminescence due to the unidirectional orientation of nanorods along the filaments.