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PubMed2003

Stereospecific radical polymerization of N-triphenylmethylmethacrylamides leading to highly isotactic helical polymers.

N-Triphenylmethylmethacrylamide (TrMAM) and N-[di(4-butylphenyl)phenylmethyl]methacrylamide (DBuTrMAM) were polymerized using radical initiators. The polymer PTrMAM obtained from TrMAM was insoluble in the common solvents, but was dissolved in sulfuric acid to quantitatively give polymethacrylamide. The 1H NMR spectrum of PTrMAM in sulfuric acid-d2 indicated that the derived polymethacrylamide was nearly 100% isotactic. On the other hand, DBuTrMAM yielded the polymer PDBuTrMAM, which was soluble in THF and chloroform and whose NMR pattern in sulfuric acid-d2 was similar to that of PTrMAM. The polymerization of TrMAM and DBuTrMAM in an optically active solvent, (-)- or (+)-menthol, afforded the optically active polymers having a prevailing one-handed helical structure. The monomers were not solvolized in a methanol-chloroform mixture. TrMAM was not polymerized by anionic initiators.

Journal Article↗
PubMed2005

Streptavidin as a macroinitiator for polymerization: in situ protein-polymer conjugate formation.

This communication reports the first example of polymerization initiated from specific domains on proteins. Streptavidin was coupled with a biotinylated initiator for atom transfer radical polymerization (ATRP) and exposed to an aqueous solution of CuBr/2,2'-bipyridine and monomer. N-Isopropylacrylamide (NIPAAm) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) were readily initiated by the modified streptavidin and polymerized from the protein at room temperature. Formation of streptavidin-polymer conjugates was confirmed by size exclusion chromatography (SEC) and gel electrophoresis. Polymer identity and biotinylation was verified using 1H NMR spectroscopy, gel permeation chromatography (GPC), and surface plasmon resonance (SPR) after dissociation of the biotin-streptavidin complex. This general approach is likely to be extended to other proteins and monomers and promises to enable easy synthesis and purification of a variety of polymer-protein conjugates.

Acrylamides↗
PubMed2005

Rhodopsin reconstituted into a planar-supported lipid bilayer retains photoactivity after cross-linking polymerization of lipid monomers.

Transmembrane proteins (TMPs), particularly ion channels and receptors, play key roles in transport and signal transduction. Many of these proteins are pharmacologically important and therefore targets for drug discovery. TMPs can be reconstituted in planar-supported lipid bilayers (PSLBs), which has led to development of TMP-based biosensors and biochips. However, PSLBs composed of natural lipids lack the high stability desired for many technological applications. One strategy is to use synthetic lipid monomers that can be polymerized to form robust bilayers. A key question is how lipid polymerization affects TMP structure and activity. In this study, we have examined the effects of UV polymerization of bis-Sorbylphosphatidylcholine (bis-SorbPC) on the photoactivation of reconstituted bovine rhodopsin (Rho), a model G-protein-coupled receptor. Plasmon-waveguide resonance spectroscopy (PWR) was used to compare the degree of Rho incorporation and activation in fluid and poly(lipid) PSLBs. The results show that reconstitution of Rho into a supported lipid bilayer composed only of bis-SorbPC, followed by photoinduced lipid cross-linking, does not measurably diminish protein function.

Biosensing Techniques↗
PubMed2005

The radical trap in atom transfer radical polymerization need not be thermodynamically stable. A study of the MoX(3)(PMe(3))(3) catalysts.

The molybdenum(III) coordination complexes MoX(3)(PMe(3))(3) (X = Cl, Br, and I) are capable of controlling styrene polymerization under typical atom transfer radical polymerization (ATRP) conditions, in conjunction with 2-bromoethylbenzene (BEB) as an initiator. The process is accelerated by the presence of Al(OPr(i))(3) as a cocatalyst. Electrochemical and synthetic studies aimed at identifying the nature of the spin trap have been carried out. The cyclic voltammogram of MoX(3)(PMe(3))(3) (X = Cl, Br, I) shows partial reversibility (increasing in the order Cl < Br < I) for the one-electron oxidation wave. Addition of X(-) changes the voltammogram, indicating the formation of MoX(4)(PMe(3))(3) for X = Cl and Br. On the other hand, I(-) is more easily oxidized than the MoI(3)(PMe(3))(3) complex; thus, the putative MoI(4)(PMe(3))(3) complex is redox unstable. Electrochemical studies of MoI(3)(PMe(3))(3) in the presence of X(-) (X = Cl or Br) reveal the occurrence of facile halide-exchange processes, leading to the conclusion that the MoI(3)X(PMe(3))(3) products are also redox unstable. The oxidation of MoX(3)(PMe(3))(3) with (1)/(2)Br(2) yields MoX(3)Br(PMe(3))(3) (X = Cl, Br), whose molecular nature is confirmed by single-crystal X-ray analyses. On the other hand, the oxidation of MoI(3)(PMe(3))(3) by I(2) slowly yields a tetraiodomolybdate(III) salt of iodotrimethylphosphonium, [Me(3)PI][MoI(4)(PMe(3))(3)], as confirmed by an X-ray study. This product has no controlling ability in radical polymerization. The redox instability of MoI(3)X(PMe(3))(3) can be reconciled with its involvement as a radical trapping species in the MoI(3)(PMe(3))(3)-catalyzed ATRP, given the second-order nature of its decomposition rate.

Journal Article↗
PubMed2004

Cation pool-initiated controlled/living polymerization using microsystems.

The "cation pool" of an N-acyliminium ion was found to serve as an effective initiator of cationic polymerization of vinyl ethers in a microsystem consisting of two micromixers and a microtube reactor. The polymerization led to very narrow molecular weight distribution (Mw/Mn = 1.14). The molecular weight (Mn) increased linearly with an increase in the amount of the monomer. The carbocationic polymer end was effectively trapped by allyltrimethylsilane. The present observations illustrate the potential of microsystems, in conjunction with the cation pool, to effect polymerization in a highly controlled manner without the deceleration inherent in the dynamic equilibrium between active and dormant species.

Journal Article↗
PubMed2004

An investigation on the analytical potential of polymerized liposomes bound to lanthanide ions for protein analysis.

We present a promising approach to protein sensing based on Eu3+ ions incorporated into polymerized liposomes. The sensitization of Eu3+ is accomplished with 5-aminosalicylic acid, which provides energy transfer for a stable reference signal and a wide wavelength excitation range free from protein interference. The lipophilic character of polymerized liposomes provides the appropriate platform for protein interaction with the lanthanide ion. Quantitative analysis is based on the linear relationship between the luminescence signal of Eu3+ and protein concentration. Because no spectral shift of the lanthanide luminescence is observed upon protein interaction, qualitative analysis is based on the luminescence lifetime of polymerized liposomes. This parameter, which changes significantly upon protein-liposome interaction, follows a well-behaved single-exponential decay that might be useful for protein identification.

Cations↗
PubMed2004

Synthesis and utilization of monodisperse hollow polymeric particles in photonic crystals.

We developed a process to fabricate 150-700 nm monodisperse polymer particles with 100-500 nm hollow cores. These hollow particles were fabricated via dispersion polymerization to synthesize a polymer shell around monodisperse SiO(2) particles. The SiO(2) cores were then removed by HF etching to produce monodisperse hollow polymeric particle shells. The hollow core size and the polymer shell thickness, can be easily varied over significant size ranges. These hollow polymeric particles are sufficiently monodisperse that upon centrifugation from ethanol they form well-ordered close-packed colloidal crystals that diffract light. After the surfaces are functionalized with sulfonates, these particles self-assemble into crystalline colloidal arrays in deionized water. This synthetic method can also be used to create monodisperse particles with complex and unusual morphologies. For example, we synthesized hollow particles containing two concentric-independent, spherical polymer shells, and hollow silica particles which contain a central spherical silica core. In addition, these hollow spheres can be used as template microreactors. For example, we were able to fabricate monodisperse polymer spheres containing high concentrations of magnetic nanospheres formed by direct precipitation within the hollow cores.

Alkanesulfonates↗
PubMed2005

Biomimetic anchor for surface-initiated polymerization from metal substrates.

In this paper, we demonstrate the first use of a catecholic initiator for surface-initiated polymerization (SIP) from metal surfaces to create antifouling polymer coatings. A new bifunctional initiator inspired by mussel adhesive proteins was synthesized, which strongly adsorbs to Ti and 316L stainless steel (SS) substrates, providing an anchor for surface immobilization of grafted polymers. Surface-initiated atom transfer radical polymerization (SI-ATRP) was performed through the adsorbed biomimetic initiator to polymerize methyl methacrylate macromonomers with oligo(ethylene glycol) (OEG) side chains. X-ray photoelectron spectroscopy, surface FT-IR, and contact angle analysis confirmed the sequential grafting of initiator and polymer, and ellipsometry indicated the formation of polymer coatings of up to 100 nm thickness. Cell adhesion experiments performed with 3T3-Swiss albino fibroblasts showed substantially reduced cell adhesion onto polymer grafted Ti and 316L SS substrates as compared to the unmodified metals. Moreover, micropatterning of grafted polymer coatings on Ti surfaces was demonstrated by combining SI-ATRP and molecular assembly patterning by lift-off (MAPL), creating cell-adhesive and cell-resistant regions for potential use as cell arrays. Due to the ability of catechols to bind to a large variety of inorganic surfaces, this biomimetic anchoring strategy is expected to be a highly versatile tool for polymer thin film surface modification for biomedical and other applications.

Animals↗
PubMed2005

Catalyst-transfer polycondensation. mechanism of Ni-catalyzed chain-growth polymerization leading to well-defined poly(3-hexylthiophene).

We studied the mechanism of the chain-growth polymerization of 2-bromo-5-chloromagnesio-3-hexylthiophene (1) with Ni(dppp)Cl2 [dppp = 1,3-bis(diphenylphosphino)propane], in which head-to-tail poly(3-hexylthiophene) (HT-P3HT) with a low polydispersity is obtained and the M(n) is controlled by the feed ratio of the monomer to the Ni catalyst. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra showed that the HT-P3HT uniformly had a hydrogen atom at one end of each molecule and a bromine atom at the other. The reaction of the polymer with aryl Grignard reagent gave HT-P3HT with aryl groups at both ends, which indicates that the H-end was derived from the propagating Ni complex. The degree of polymerization and the absolute molecular weight of the polymer could be evaluated from the 1H NMR spectra of the Ar/Ar-ended HT-P3HT, and it was found that one Ni catalyst molecule forms one polymer chain. Furthermore, by reaction of 1 with 50 mol % Ni(dppp)Cl2, the chain initiator was found to be a bithiophene-Ni complex, formed by a coupling reaction of 1 followed by insertion of the Ni(0) catalyst into the C-Br bond of the dimer. On the basis of these results, we propose that this chain-growth polymerization involves the coupling reaction of 1 with the polymer via the Ni catalyst, which is transferred intramolecularly to the terminal C-Br bond of the elongated molecule. We call this mechanism "catalyst-transfer polycondensation".

Journal Article↗
PubMed2006

Cell-permeable and biocompatible polymeric nanoparticles for apoptosis imaging.

Here, we report for the first time cell-permeable and biocompatible polymeric nanoparticles consisting of a polymer conjugated to a near-infrared (NIR) fluorescence (Cy5.5)-linked effector caspase-specific peptide. The close spatial proximity of the NIR fluorochromes in polymeric nanoparticles results in an autoquenched state, but polymer nanoparticles give rise to strong NIR fluorescence signal under apoptotic cells. Thus, the smart polymeric nanoparticle developed here is an attractive probe for real-time imaging of apoptosis in single cells.

Apoptosis↗
PubMed2006

Alkenylsilane effects on organotitanium-catalyzed ethylene polymerization. Toward simultaneous polyolefin branch and functional group introduction.

The comonomer 5-hexenylsilane is introduced into organotitanium-mediated ethylene polymerizations to produce silane-terminated ethylene/5-hexenylsilane copolymers. The resulting polymers were characterized by 1H and 13C NMR, GPC, and DSC. High activities (up to 107 g polymer/(mol Ti.atm ethylene.h)) and narrow polydispersities are observed in the polymerization/chain transfer process. Ethylene/5-hexenylsilane copolymer molecular weights are found to be inversely proportional to 5-hexenylsilane concentration, supporting a silanolytic chain transfer mechanism. Control experiments indicate that chain transfer mechanism by 5-hexenylsilane is significantly more efficient than that of n-hexylsilane for organotitanium-mediated ethylene polymerization. The present study represents the first case in which a functionalized comonomer is efficiently used to effect both propagation and chain transfer chemistry during olefin polymerization.

Journal Article↗
PubMed2006

Rhodium-mediated stereoselective polymerization of "carbenes".

Unprecedented rhodium-catalyzed stereoselective polymerization of "carbenes" from ethyl diazoacetate (EDA) to give high molecular mass poly(ethyl 2-ylidene-acetate) is described. The mononuclear, neutral [(N,O-ligand)M(I)(cod)] (M = Rh, Ir) catalytic precursors for this reaction are characterized by (among others) single-crystal X-ray diffraction. These species mediate formation of a new type of polymers from EDA: carbon-chain polymers functionalized with a polar substituent at each carbon of the polymer backbone. The polymers are obtained as white powders with surprisingly sharp NMR resonances. Solution and solid state NMR data for these new polymers reveal a highly stereoregular polymer, with a high degree of crystallinity. The polymer is likely syndiotactic. Material properties are very different from those of atactic poly(diethyl fumarate) polymer obtained by radical polymerization of diethyl fumarate. Other diazoacetates are also polymerized. Further studies are underway to reveal possible applications of these new materials.

Journal Article↗
PubMed2006

Inverse miniemulsion ATRP: a new method for synthesis and functionalization of well-defined water-soluble/cross-linked polymeric particles.

A new methodology for the synthesis and functionalization of nanometer-sized colloidal particles consisting of well-defined, water-soluble, functional polymers with narrow molecular weight distribution (M(w)/M(n) < 1.3) was developed, utilizing atom transfer radical polymerization (ATRP) of water-soluble monomers in an inverse miniemulsion. The optional introduction of a disulfide-functionalized cross-linker allowed for the synthesis of cross-linked (bio)degradable nanogels. Dynamic light scattering (DLS) and atomic force microscopy (AFM) measurements indicated that these particles possessed excellent colloidal stability. ATRP in inverse miniemulsion led to materials with several desirable features. The colloidal particles preserved a high degree of halogen chain-end functionality, which enabled further functionalization. Cross-linked nanogels with a uniformly cross-linked network were prepared. They were degraded to individual polymeric chains with relatively narrow molecular weight distribution (M(w)/M(n) < 1.5) in a reducing environment. Higher colloidal stability, higher swelling ratios, and better controlled degradability indicated that the nanogels prepared by ATRP were superior to their corresponding counterparts prepared by conventional free radical polymerization (RP) in inverse miniemulsion.

Journal Article↗
PubMed2006

Synthetic, structural, mechanistic, and computational studies on single-site beta-diketiminate tin(II) initiators for the polymerization of rac-lactide.

A family of tin(II) complexes supported by beta-diketiminate ligands has been investigated as initiators for the polymerization of rac-lactide. Kinetic studies reveal a first-order dependence on [lactide], but with a significant induction period. Linear plots of M(n) versus conversion and [M](o)/[I](o) versus conversion, along with narrow molecular weight distributions (typically 1.07-1.10), are indicative of well-controlled, "living" polymerizations. Less sterically hindered derivatives promote faster propagation than their bulky analogues, in accord with a more accessible active site. Enhanced rates of polymerization are observed for ligands bearing halogenated N-aryl substituents, a consequence of the more Lewis acidic nature of the Sn(II) centers. All of the initiators exhibit a similar bias toward heterotactic polylactide, which is attributed to a chain-end control mechanism influenced predominantly by the presence of the Sn 5s(2) lone pair of electrons rather than the steric or electronic properties of the beta-diketiminate ligand. The tin(II) isopropyl-(S)-lactate complex, ((Me)BDI(DIPP))SnOCH(Me)COO(i)Pr (14), has been synthesized as a model compound for the propagating species by treatment of ((Me)BDI(DIPP))Sn(NMe(2)) with isopropyl-(S)-lactate. An X-ray structure determination showed that the lactate ligand forms a five-membered chelate ring with a weak donor bond from the carbonyl oxygen atom to the tin center. A B3LYP density functional computational study indicates that insertion of the first lactide monomer into the tin(II) alkoxide bond is facile, with the induction period arising from a slower insertion of the second (and possibly third and fourth) monomer units.

Crystallography, X-Ray↗
PubMed2006

To patterned binary polymer brushes via capillary force lithography and surface-initiated polymerization.

An effective approach is described for the synthesis of binary patterned polymer brushes using a combination of capillary force lithography and surface-initiated polymerization. First, the approach calls for an ultrathin polystyrene (PS) mask to be deposited, in a pattern, over a surface to which a layer of polymerization initiator has already been anchored. Next, surface-initiated atom transfer radical polymerization (ATRP) is performed. This can graft the initial polymer brush onto those areas of the surface unprotected by the PS mask. After grafting is complete, the PS mask is removed and a second brush is synthesized on the newly exposed areas.

Acrylamides↗
PubMed2006

Water-soluble salicylaldiminato Ni(II)-methyl complexes: enhanced dissociative activation for ethylene polymerization with unprecedented nanoparticle formation.

Water-soluble single-component (kappa2-N,O)-salicylaldiminato nickel-methyl complexes 1-4-L (L = TPPTS, TPPDS, H2N-PEG-OMe) allow for the catalytic polymerization of ethylene under organic solvent-free aqueous conditions producing high molecular weight polyethylene with particle sizes below 10 nm. Amphiphilic TPPDS- and H2N-PEG-OMe complexes exhibit a polymerization activity in water higher than that in toluene. A solvation-favored activation of precatalysts 1-4-L by equilibrium dissociation of L in aqueous solution likely accounts for this enhanced polymerization activity. The observed generation of a given particle by a single active site is an unprecedented mechanism for formation of aqueous particle dispersions.

Journal Article↗
PubMed2006

Formation of linear polymers with pendant vinyl groups via inclusion complex mediated polymerization of divinyl monomers.

Ethylene glycol dimethacrylate (EGDMA) and ethylene glycol methacrylate 4-vinyl benzoate (EGMAVB) were shown to form 1:1 inclusion complexes with cyclodextrin and were characterized by instrumental techniques. Computational analysis showed that the bent conformation of the included divinyl monomer was more stable than its linear conformation. Complexation of the divinyl monomer with the first CD molecule offered substantial stabilization than with the second CD molecule. The vinyl group included in the CD cavity did not participate in polymerization. As a result, solvent soluble, linear polymers with pendant vinyl unsaturation per repeat unit were obtained. This was unequivocally established by the polymerization of a complex comprising CD and EGMAVB. The unreacted vinyl group can be polymerized in the subsequent step to yield cross-linked products.

Biocompatible Materials↗
PubMed2006

Synthesis of 3-miktoarm stars and 1st generation mikto dendritic copolymers by "living" radical polymerization and "click" chemistry.

The facile synthesis of 3-miktoarm star polymers and 1st generation mikto polymeric dendrimers using atom transfer radical polymerization (ATRP) and "click" chemistry is demonstrated. ATRP was used to synthesize near uniform polymers with Br chain ends, which were easily converted into azido groups. These polymer chains were then attached to a trifunctional alkyne molecule (tripropargylamine) using click reactions in a variety of ways to make the miktoarm stars and miktoarm polymeric dendrimers.

Acrylates↗

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