Synthesis, characterization, adsorption, and interfacial rheological properties of four-arm anionic fluorosurfactants

Four-arm oligo(fluorooxetane) tetraols containing -CF3 and -C2F5 groups were prepared in reasonable yields by cationic, ring-opening polymerization of fluorinated oxetane monomers using a tetrafunctional, alkoxylated polyol as initiator and BF3.THF as catalyst. The tetraols were then converted to ammonium sulfate salts using oleum followed by neutralization with ammonium hydroxide in excellent yields. The four-arm oligo(fluorooxetane) sulfates (1=-CF3, 2=-C2F5) have an architecture characterized by a hydrophobic core of oligo(fluorooxetane) arms with a hydrophilic sulfate shell and initiator. The four-arm anionic oligo(fluorooxetane)s are surface active with critical micelle concentration values approximately 4.2x10(-6) and 2.4x10(-6) mol/L for 1 and 2, respectively. Surface tension isotherms in pH 8 buffered solution were measured and data fitted parametrically to the Davies surface tension isotherm equation. Molecular areas at saturation were estimated to be approximately 89 and approximately 85 A2 with DeltaGads=-12.7 and -13.2 kcal/mol for 1 and 2, respectively. The results are compared to two-arm, bolaamphiphilic analogues of 1 and 2 and a small molecule, long perfluoroalkyl-chain (-C8F17), anionic fluorosurfactant (Kausch, C. M.; Kim, Y.; Russell, V. M.; Medsker, R. E.; Thomas, R. R. Langmuir 2003, 19, 7182). Dynamic surface tension data for 1 and 2 were analyzed using the Ward-Tordai mass transport equation to yield concentration-dependent diffusion coefficients. In the concentration range approximately 10(-6) mol/L, diffusion coefficients were estimated to be approximately 1-3x10(-5) cm2/s. Dilational interfacial rheological parameters for 1 and 2 were measured. Values of |E| and E' were found to be larger than those of the two-arm analogues of the same perfluoroalkyl chain length while E' 'and phi were found to be smaller. The magnitude of these values reflects the difference in adsorption strength and mass transport and/or relaxation between the two different architectures.

[Preparation and characterization of a polyvinylpyrrolidone water-based magnetic fluid]

OBJECTIVE

To prepare a stable water-based magnetic fluid.

METHODS

A water-based magnetic fluid was prepared by addition of polyvinylpyrrolidone (PVP) as the coating agent for the magnetic particles. After preparation of Fe3O4 by co-precipitation method, PVP was added for its coating, followed by ultrasonic agitation and purification.

RESULTS

The magnetic nanoparticles of homogeneously small size and water-based magnetic fluid were obtained, which had good dispersion in water with strong magnetism.

CONCLUSION

PVP can be used as a surfactant to stabilize the magnetic fluid.

Synthesis of novel cationic bolaamphiphiles from vernonia oil and their aggregated structures

The present study describes the synthesis of a novel class of vesicle-forming bolaamphiphiles with choline ester head groups. These bolaamphiphiles were derived from vernonia oil, whose main constituent is vernolic acid, a fatty acid with a unique combination of epoxy, carboxy and unsaturated double bonds. A series of bolaamphiphiles containing amido or ester groups within the hydrophobic domain were synthesized from N,N'-alkylenebis (vernolamides) and alpha,omega-alkylene divernolate ester in a two-stage synthesis comprising opening of the epoxy ring with chloroacetic acid, followed by quaternization with N,N-dimethylaminoethyl acetate to form choline ester head groups. The products were characterized by FT-IR, (1)H and (13)C NMR, and ESI-MS. Vesicles prepared from these bolaamphiphiles have the potential to serve as a targeted drug delivery systems with selective decapsulation in the presence of the enzyme acetylcholine esterase, resulting in site-specific release of the drug.

Precise synthesis of poly(macromonomer)s containing sugars by repetitive ROMP and their attachments to poly(ethylene glycol): synthesis, TEM analysis and their properties as amphiphilic block fragments

Various poly(macromonomer)s (PMMs) have been prepared by a repeating ring opening metathesis polymerization (ROMP) technique using the well-defined molybdenum initiators of the type, [Mo(CHCMe(2)Ph)(NAr)(OR)(2)] with OR=OCMe(3), OCMeC(CF(3))(2); Ar=2,6-iPr(2)C(6)H(3), 2,6-Me(2)C(6)H(3). The synthetic strategy is based on the polymerization of norbornene and its derivatives affording di- and triblock side chains bearing sugars (mannose, galactose, glucose etc.), linked via O- (ester), and glycosidase resistant C- (isoxazoline) glycosides. The efficient placement of norbornene units on the side chain termini and their conversion into PMMs, facilitated by the Mo alkylidenes, proceeded in a living manner with the quantitative initiation. The methodology was applied to prepare poly(macromonomer)-graft-PEG [PEG: poly(ethylene glycol)], by the attachment of a pseudo phenol terminus on the PMM main chain to PEG-Ms(2) [MsO(CH(2)CH(2)O)(n)Ms, Ms=MeSO(2)] using a "grafting to" approach. Removal of the acetal protecting groups from the sugar coating of a variety of supramolecular structures including PMMs, linear amphiphilic block copolymers (ABC) and a PMM-graft-PEGby using trifluroacetic acid/water (9:1), and suspension in water, prompted the spontaneous formation of spherical architectures by self-assembly of the amphiphilic PMMs as observed by transmission electron microscopy (TEM). The ability to uptake the hydrophobic dye (Nile Red) into the micellar cores of a variety of amphiphilic polymeric fragments is a significant step towards the production of sugar-coated nanospheres for cell-targeting biomimetic applications.

N,N’-Hexadecanoyl l-2-diaminomethyl-18-crown-6 surfactant: Synthesis and aggregation features in aqueous solution

Bolas surfactants can be inserted into bi-layers and may operate as permanent holes in such membranes. Significant synthetic work and an exhaustive characterisation of their properties in the bulk was performed. On this purpose, the phase diagram of the system composed by water and 1,16-hexadecanoyl-bis-(2-aminomethyl)-18-crown-6 (termed Bola A16) was investigated in a wide temperature and concentration range. No liquid crystalline phases were observed and a large micellar solution was present, up to about 50 surfactant wt%. Surface tension experiments defined adsorption and micelle formation. The low observed cmc value is important for pharmacological applications, in fact, considering intravenous administration, only micelles with low cmc value can exist in blood. Nuclear magnetic resonance experiments determined both water and surfactant self-diffusion. According to the aforementioned experiments, slight, if any, modifications in the structure of micelles were inferred on increasing Bola A16 content. Dynamic rheological experiments probed the solution micro-structure. The observed rheological behaviour is newtonian. The solution viscosity and the shear relaxation processes were rationalized assuming the presence of spherical aggregates, occurring up to high surfactant content. The viscometric behaviour was rationalised in terms of a former theory of flow as a cooperative phenomenon. The number of micelles coordinated each other during the viscous flow and the interaction strength between them was obtained as a function of Bola A16 concentration. Such value is close to unity and practically independent of surfactant content in the whole concentration range we investigated. This behaviour points out that little, or none, interactions among micellar aggregates occur. The absence of shear induced changes in the aggregate shape implies no change in drug delivery properties under flow, this is useful in the pharmaco-dynamics field, since drug delivery usually operates in mechanically stressed conditions. Thanks to the above properties, the material results particularly suitable for application in pharmaceutical field, may solubilize lipid membranes and selectively transport ions across them. Ancillary effects, such as the uptake of counter-ions in the crown ether, are to be considered.

Surfactants from biomass: a two-step cascade reaction for the synthesis of sorbitol fatty acid esters using solid acid catalysts

Sorbitol fatty esters have been prepared through a two-step catalytic process which involves the protection of the polyalcohol by ketalization followed by esterification with the fatty acid. Inorganic molecular sieves with different pore topologies as well as heteropolyacids (HPA) were used as acid catalysts to perform both the ketalization and the esterification step. These catalysts are found to hydrolyze the ketal function and promote the esterification between the free hydroxy groups and oleic acid in a cascade process. The results show a positive shape-selectivity effect when the process is carried out using tridirectional, and especially monodirectional (mordenite), zeolites, such that the ratio of mono- to higher esters and the hydroxy number of the final product are increased as compared to those obtained for the homogeneous-catalyzed process.

Solvent-free enzymatic synthesis of fatty alkanolamides

An environmentally benign and volume efficient process for enzymatic production of alkanolamides is described. Immobilized Candida antarctica lipase B, Novozym435, was used to catalyze the condensation of lauric acid with monoethanolamine. The reaction temperature of 90 degrees C was required to keep the reactants in a liquid state. Stepwise addition of the amine minimized problems caused by the formation of a highly viscous amine/fatty acid ion-pair. The enzyme was both very active and stable under the reaction conditions, with about half of the activity remaining after 2 weeks. The maximum amide yield obtained when using equimolar amounts of the reactants was 75%, which could be increased to 95% upon water removal. Special precautions to avoid co-distillation of the amine were required. Two different strategies to avoid the amine loss are presented.

Electrostatic Self-Assembly of Neutral and Polyelectrolyte Block Copolymers and Oppositely Charged Surfactant

We investigated the phase behavior and the microscopic structure of the colloidal complexes constituted from neutral/polyelectrolyte diblock copolymers and oppositely charged surfactant by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The neutral block is poly(N-isopropylacrylamide) (PNIPAM), and the polyelectrolyte block is negatively charged poly(acrylic acid) (PAA). In aqueous solution with neutral pH, PAA behaves as a weak polyelectrolyte, whereas PNIPAM is neutral and in good-solvent condition at ambient temperature, but in poor-solvent condition above approximately 32 degrees C. This block copolymer, PNIPAM-b-PAA with a narrow polydispersity, is studied in aqueous solution with an anionic surfactant, dodecyltrimethylammonium bromide (DTAB). For a low surfactant-to-polymer charge ratio Z lower than the critical value ZC, the colloidal complexes are single DTAB micelles dressed by a few PNIPAM-b-PAA. Above ZC, the colloidal complexes form a core-shell microstructure. The core of the complex consists of densely packed DTA+ micelles, most likely connected between them by PAA blocks. The intermicellar distance of the DTA+ micelles is approximately 39 A, which is independent of the charge ratio Z as well as the temperature. The corona of the complex is constituted from the thermosensitive PNIPAM. At lower temperature the macroscopic phase separation is hindered by the swollen PNIPAM chains. Above the critical temperature TC, the PNIPAM corona collapses leading to hydrophobic aggregates of the colloidal complexes.

Organogels from a Vitamin C-Based Surfactant

A new double chained surfactant, 2-octyl-dodecanoyl-6-O-ascorbic acid (8ASC10), with a L-ascorbic acid unit as the polar headgroup was synthesized for the first time. The behavior of the compound in the dry solid state has been characterized through DSC, XRD, and SAXS measurements. The surfactant forms stable viscous organogels in the presence of suitable organic solvents and also water-induced organogels upon addition of water to the organogel. These mixtures show shear-thinning properties and are birefringent. The behavior and properties of the organogels have been studied through rheology, DSC, and SAXS experiments. The organogels possess the same antioxidant properties of the original L-ascorbic acid ring and can be used to solubilize and protect valuable organic molecules.

A biomimetic "polysoap" for single-walled carbon nanotube dispersion

As-synthesized single-walled carbon nanotubes (SWNTs) are bundled mixtures of different species. The current challenge in the field of carbon nanotube research lies in the processing and separation of SWNTs, which first require efficient dispersion of individual SWNTs in solvents. We report DNA-mimicking polysoap surfactants that disperse SWNTs in aqueous solutions more effectively than DNA. The polysoaps are synthesized by functionalizing the side chain of poly(styrene-alt-maleic acid) with aminopyrene. The synthetic nature of the polysoap opens a new approach to further optimization of not only SWNT dispersion efficiency but also multi-functional SWNT dispersing surfactant.

Self-assembly of peptide-amphiphile nanofibers: the roles of hydrogen bonding and amphiphilic packing

The role of hydrogen bonding and amphiphilic packing in the self-assembly of peptide-amphiphiles (PAs) was investigated using a series of 26 PA derivatives, including 19 N-methylated variants and 7 alanine mutants. These were studied by circular dichroism spectroscopy, a variety of Fourier transform infrared spectroscopies, rheology, and vitreous ice cryo-transmission electron microscopy. From these studies, we have been able to determine which amino acids are critical for the self-assembly of PAs into nanofibers, why the nanofiber is favored over other possible nanostructures, the orientation of hydrogen bonding with respect to the nanofiber axis, and the constraints placed upon the portion of the peptide most intimately associated with the biological environment. Furthermore, by selectively eliminating key hydrogen bonds, we are able to completely change the nanostructure resulting from self-assembly in addition to modifying the macroscopic mechanical properties associated with the assembled gel. This study helps to clarify the mechanism of self-assembly for peptide amphiphiles and will thereby help in the design of future generations of PAs.

Surface chemistry and rheology of polysulfobetaine-coated silica

We have measured the viscosity of suspensions of colloidal silica particles (d = 300 nm) and the properties of silica surfaces in solutions of a polymer consisting of zwitterionic monomer groups, poly(sulfobetaine methacrylate), polySBMA. This polymer has potential use in modifying surface properties because the polymer is net uncharged and therefore does not generate double-layer forces. The solubility of the polymer can be controlled and varies from poor to good by the addition of sodium chloride salt. Ellipsometry was used to demonstrate that polySBMA adsorbs to silica and exhibits an increase in surface excess at lower salt concentration, which is consistent with a smaller area per molecule at low salt concentration. Neutron reflectivity measurements show that the adsorbed polymer has a thickness of about 3.7 nm and is highly hydrated. The polymer can be used to exercise considerable control over suspension rheology. When silica particles are not completely covered in polymer, the suspension produces a highly viscous gel. Atomic force microscopy was used to show this is caused by bridging of polymer between the particles. At higher surface coverage, the polymer can produce either a high or very low viscosity slurry depending on the sodium chloride concentration. At high salt concentration, the suspension is stable, and the viscosity is lower. This is probably because the entrainment of many small ions renders the polymer film highly hydrophilic, producing repulsive surface forces and lubricating the flow of particles. At low salt concentrations, the polymer is barely soluble and more densely adsorbed. This produces less stable and more viscous solutions, which we attribute to attractive interactions between the adsorbed polymer layers.

2-DE using hemi-fluorinated surfactants

The synthesis of hemi-fluorinated zwitterionic surfactants was realized and assessed for 2-DE, a powerful separation method for proteomic analysis. These new fluorinated amidosulfobetaine (FASB-p,m) were compared to their hydrocarbon counterparts amidosulfobetaine (ASB-n) characterized by a hydrophilic polar head, a hydrophobic and lipophilic tail, and an amido group as connector. The tail of these FASB surfactants was in part fluorinated resulting in the modulation of its lipophilicity (or oleophobicity). Their effect on the red blood cell (RBC) membrane showed a specific solubilization depending on the length of the hydrophobic part. A large number of polypeptide spots appeared in the 2-DE patterns by using FASB-p,m. The oleophobic character of these surfactants was confirmed by the fact that Band 3, a highly hydrophobic transmembrane protein, was not solubilized by these fluorinated structures. The corresponding pellet was very rich in Band 3 and could then be solubilized by using a strong detergent such as amidosulfobetaine with an alkyl tail containing 14 carbon atoms (ASB-14). Thus, these hemi-fluorinated surfactants appeared as powerful tools when used at the first step of a two-step solubilization strategy using a hydrocarbon homologous surfactant in the second step.

Morphological characterization of self-assembled peptide nucleic acid amphiphiles

Peptide nucleic acid amphiphiles (PNAA) are a promising set of materials for sequence-specific separation of nucleic acids from complex mixtures. To implement PNAA in micellar separations, the morphology and size of PNAA micelles in the presence and absence of a sodium dodecyl sulfate (SDS) cosurfactant have been studied by small-angle X-ray scattering and dynamic light scattering. We find that a 6-mer PNAA with a 12-carbon n-alkane tail forms ellipsoidal micelles (a = 5.15 nm; b = 3.20 nm) above its critical micelle concentration (CMC) of 110.9 microM. On addition of a stoichiometric amount of complementary DNA, PNAA hybridizes to DNA, suppressing the formation of PNAA micelles. At a ratio of 19:1 SDS/PNAA (total concentration = 20 mM), spherical micelles are formed with outer radius Rs = 2.67 nm, slightly larger than spherical micelles of pure SDS. Capillary electrophoresis studies show that PNAA/DNA duplexes do not comicellize with SDS micelles. No such effects are observed using noncomplementary DNA. The shape and size of the PNAA micelles is also verified by dynamic light scattering (DLS) studies. These results provide an interesting case study with competing electrostatic, hydrophobic, and hydrogen-bonding interactions in micellar systems and make possible the use of PNAA in micellar separations of DNA oligomers.

Local Delivery of Indomethacin to Arthritis-Bearing Rats through Polymeric Micelles Based on Amphiphilic Polyphosphazenes

PURPOSE

Preparation, in vitro and in vivo evaluation of indomethacin-loaded polymeric micelles based on amphiphilic polyphosphazene.

METHODS

Amphiphilic polyphosphazenes (PNIPAAm/EAB-PPPs) with poly (N-isopropylacrylamide) (PNIPAAm) and ethyl 4-aminobenzoate (EAB) as side groups were synthesized through thermal ring-opening polymerization and subsequent substitution reactions. Indomethacin (IND) loaded polymeric micelles based on PNIPAAm/EAB-PPPs were prepared by dialysis procedure. In vitro IND release kinetics was investigated in 0.1 M PBS (pH 7.4), while in vivo pharmacokinetics was performed in Sprague-Dawley rats. In vivo pharmacodynamic study was carried out based on two animal models, i.e. carrageenan-induced acute paw edema and complete Freund's adjuvant (CFA) induced ankle arthritis model.

RESULTS

Drug loading capacity of micelles based on this type of amphiphilic copolymers was mainly determined by copolymer composition and the chemical structure of drug. In addition to the compatibility between drug and micellar core, hydrogen bonding interaction between drug and hydrophilic corona may significantly influence drug loading as well. In vitro drug release in PBS suggested that there was no significant difference in release rate between micelles based on copolymers with various EAB content. Compared with the rats administered with free IND aqueous solution, IND concentration in rats' plasma showed a prolonged maintenance in experimental group treated with IND-loaded polymeric micelles. In vivo pharmacodynamic study indicated that sustained therapeutic efficacy could be achieved through topical injection of the aqueous solution of IND-loaded micelles. Local delivery of IND can avoid the severe gastrointestinal stimulation, which was frequently associated with oral administration as evidenced by ulceration evaluation.

CONCLUSIONS

The promising results of current preliminary study suggest that this type of amphiphilic copolymers could be used as injectable drug carriers for hydrophobic drugs.

Asymmetric resolution in ester reduction by NaBH4 at the interface of aqueous aggregates of amino acid, peptide, and chiral-counterion-based cationic surfactants

This study provides insight into the physicochemical aspects of aqueous aggregates that comprise amino acid, peptide, and chiral-counterion-based cationic surfactants and their correlation with the proficiency of asymmetric resolution in ester reduction. The effects of the structural differences in the naturally occurring amino acid based and synthetic chiral-counterion-containing gemini surfactants on the surface properties as well as on other microstructural parameters were studied and correlated to the varied head groups of the surfactants. The supramolecular chirality induced from the head-group region of chiral amphiphiles in aqueous self-aggregates is evident from circular dichroism, scanning electron microscopy, and transmission electron microscopy studies. This large-scale chirality at the interface of self-aggregates was exploited towards asymmetric resolution in ester reduction by NaBH4. An enantiomeric excess of 53% ((R)-2-phenylpropan-1-ol) was found in the case of the n-hexyl ester of 2-phenylpropionic acid as substrate in the aqueous aggregate of N,N'-dihexadecyl-N,N,N',N'-tetramethyl-N,N'-ethanediyldiammonium diquinate. Thus, a simple and environmentally benign pathway for asymmetric resolution in ester reduction by sodium borohydride alone is reported, which utilizes the varied spatial asymmetry at the interface of aqueous aggregates of cationic chiral amphiphiles.

A facile synthesis of aliphatic thiol surfactant with tunable length as a stabilizer of gold nanoparticles in organic solvents

Three new aliphatic thiol surfactants were synthesized by reacting alkyl bromide with hexamethyldisilathiane under a mild condition. This approach provides an easy access for the direct synthesis of various different length thiol surfactants which play a crucial role in tuning the properties of gold nanoparticles. Gold nanoparticles encapsulated with one of our synthetic thiols were prepared and well characterized by H NMR, UV-vis, FT-IR, and TEM. The hybrid nanoparticles are very stable in both organic solvents and the solid state.

pH-dependent chiral vesicles from enantiomeric sodium 2,3-bis(decyloxy) succinate in aqueous solution

Enantiomeric, twin-tailed, twin-chiral, sodium (2R,3R)-(+)-bis(decyloxy)succinate and sodium (2S,3S)-(-)-bis(decyloxy)succinate have been synthesized and characterized. Surface tension, conductivity, and steady-state fluorescence spectroscopic measurements confirmed the presence of two aggregation concentrations, namely, the critical micellar concentration (CMC) and the critical vesicle concentration (CVC). The compounds behaved as true surfactants, with a CMC of 0.05 mM, and formed vesicles spontaneously in aqueous solution at a CVC of 0.14 mM. The compounds formed myelin figures in contact experiments, suggesting the formation of bilayers in aqueous solution culminating into individual vesicles. The vesicles were of 500-800 nm size and formed egg shells, porous spheres, and multivesicular vesicles, confirmed from transmission electron microscopy and optical microscopic techniques. The vesicles were found to be pH sensitive, were stable in the pH range 6-8, and formed the insoluble diacid at acidic pH due to protonation of the carboxylate head groups.

Synthesis, Critical Micelle Concentrations, and Antimycobacterial Properties of Homologous, Dendritic Amphiphiles. Probing Intrinsic Activity and the “Cutoff” Effect

Newkome-type, 1-->3 C-branched dendrons make an excellent headgroup for amphiphiles with ultralong, saturated, linear alkyl chains. Synthesis of a homologous series of five such amphiphiles from 14 to 22 carbons-RNHCONHC(CH2CH2CO2H)3, R = n-CnH2n+1, n = 14, 16, 18, 20, 22-proceeds readily. These amphiphiles are soluble in aqueous solutions of triethanolamine. Surface-tension measurements on this homologous series reveal an unusually gradual decrease in log critical micelle concentration (CMC) as the chain length increases. In fact, the tetradecyl homologue does not appear to form micelles. Further, measurements of minimal inhibitory concentration (MIC) by broth microdilution against Mycobacterium smegmatis as a function of the initial cell density provide a direct measure of the intrinsic activity (MIC0) of each homologue. The hexadecyl homologue is the most active at inhibiting growth with an MIC0 equal to 3.5 x 10-5 M, which is 100-fold below the CMC.

Application of oligonucleotide as a template for the assembly of nucleoamphiphile bearing azobenzene at the air-water interface

In order to assemble amphiphilic adenine having azobenzene, C12AzoC5Ade (AzoAde), at the air-water interface based on the molecular recognition of DNA, we prepared aqueous linear oligothymidylic acids, dTn (n = 4, 6, 8, 10, 30), subphase as templates. Surface pressure-area (pi-A) isotherms and UV-Vis reflection absorption spectra of AzoAde were measured to investigate the effect of chain length of the oligothymidylic acid on the molecular recognition by forming a complementary A-T base pair. It was showed that AzoAde did not form a stable monolayer on the dT4 subphase and remained monomeric state. While AzoAde provided expanded monolayers and formed J-aggregates of azobenzene moieties on the dTn (n > 4) subphases even at the low molecular density. We also investigated the molecular recognition of template oligonucleotides by comparing dT30 with dA30, indicating that AzoAde had not a specific interaction with dA30 at the air-water interface due to base mismatching. The AzoAde monolayer on the dA30 subphase gave H-aggregate from monomeric state by compressing it. On the other hand, it remained J-aggregated state on dT30 subphase regardless of compression. It was, therefore, suggested that the linear oligothymidylic acids, dT, (n > 4), acted as templates for assembling AzoAde at the air-water interface.

Increase of Fluorescence Anisotropy Upon Self-Assembly in Headgroup-Labeled Surfactants

The change in fluorescence anisotropy upon micellization in headgroup-labeled surfactants is investigated. After eliminating the likelihood of depolarizing RET, anisotropy is shown to increase upon self-assembly due to increased rotational correlation times of the fluorophore. This is shown using two surfactant-fluorophore systems. Anisotropy in NBD-labeled phospholipids is studied both in chloroform (unaggregated) and in water (unilamellar vesicles), while in tryptophan-containing peptide-amphiphiles, the variation of anisotropy with concentration leads to a reasonable measurement of CAC. Anisotropy increase is shown to be largely the product of increased rotational correlation times for the fluorophore, relative to its tau. These results serve as a basis for future work that measures the amount of depolarizing energy transfer, characterizing distances between similar fluorescent headgroups on mixed micelles.

Amphiphilic NO-Donor Antioxidants

Models of amphiphilic NO-donor antioxidants 24-26 were designed and synthesized. The products were obtained by linking a lipophilic tail (C(6), C(8), C(10)) with a polar head constituted by the 2,6-dimethoxyphenol antioxidant joined to the NO-donor 3-furoxancarboxamide substructure through a bridge containing a quaternary ammonium group. Compound 23, containing the shortest C(2)-alkyl chain, was also studied as a reference. The antioxidant properties (TBARS and LDL oxidation assays) and the vasodilator properties of the compounds were studied in vitro. The ability of these products to interact with phospholipid vesicles was also investigated by NMR techniques. The results indicate that both activities are modulated by the ability of the compounds to accumulate on phospholipid layers.

Self-Assembled Architectures from Biohybrid Triblock Copolymers

The synthesis and self-assembly behavior of biohybrid ABC triblock copolymers consisting of a synthetic diblock, polystyrene-b-polyethylene glycol (PSm-b-PEG113), where m is varied, and a hemeprotein, myoglobin (Mb) or horse radish peroxidase (HRP), is described. The synthetic diblock copolymer is first functionalized with the heme cofactor and subsequently reconstituted with the apoprotein or the apoenzyme to yield the protein-containing ABC triblock copolymer. The obtained amphiphilic block copolymers self-assemble in aqueous solution into a large variety of aggregate structures. Depending on the protein and the polystyrene block length, micellar rods, vesicles, toroids, figure eight structures, octopus structures, and spheres with a lamellar surface are formed.