Immobilization Of Chains Research Articles

Synthesis of Silyl-Terminated Polylactides for Controlled Surface Immobilization of Polylactide Macromolecular Chains

Poly(D-lactide)s (PDLA) having an end group of trimethoxysilyl (P(x)-Si-(OMe)(3)) or monoethoxydimethylsilyl (P(x)-Si-OEt) group were synthesized to immobilize macromolecular chains of polylactide onto a flat silicon surface by the "grafting onto" mechanism. Both the end-functional PDLAs were efficiently immobilized on the flat surface of silicon wafers to create different nano-ordered structures. The P(x)-Si-OEt having the monofunctional siloxyl group formed a homogeneous dot morphology consisting of homogeneously dispersed particles of 20-30 nm in diameter while the P(x)-Si-(OMe)(3) having the trifunctional siloxyl group formed a heterogeneous morphology consisting of both spots and fibrous strands. The former homogeneous morphology was attributed to the lack of the intermolecular cross-linking reaction that was evident in P(x)-Si-(OMe)(3).

Facile cathodic surfacial carboxylation of glassy carbon by means of immobilized alkanoic acids chains

The reduction of ω-bromoalkanoic acids Br(CH 2) n COOH at glassy carbon cathodes in aprotic polar solvents (acetonitrile, N, N-dimethylformamide or propylene carbonate) in the presence of tetraalkylammonium salts at E < − 1.7 V vs. Ag/AgCl results in a dense organic layer, covalently attached to carbon, which progressively covers the electrode surface. It was evidenced that the immobilization of alkyl chains occurs via the scission of C-Br bonds permitting an efficient coverage of the carbon surface with the layers built of alkyl links [CH 2 ] n (3 ≤ n ≤ 11) terminated with COOH groups. The carboxyls immobilized this way were easily transformed into electroactive esters or into amides by reacting with phenols or amines, respectively. Thus grafted π-acceptor groups allowed estimating the carboxylation level as very high, ca. (1–5) × 10 − 9 mol/cm 2 when taking into account the starting surface area. In aqueous media, the immobilized films with long alkyl linkers visibly behave as hydrophobic layers.

PH-responsive disruption of ‘liquid marbles’ prepared from water and poly(6-(acrylamido) hexanoic acid)-grafted silica particles

A chain transfer agent was immobilized onto the surface of 11-μm diameter silica particles (CPD-SiO2) for use in reversible addition-fragmentation chain transfer (RAFT)-controlled radical polymerization. pH-responsive poly(6-(acrylamido)hexanoic acid) (PAaH)-grafted silica particles (PAaH-SiO2) were prepared via RAFT-controlled radical polymerization using CPD-SiO2. Immobilization of the PAaH chains onto the surface of silica particles was confirmed by thermogravimetric analysis, attenuated total reflection-Fourier transfer infrared and scanning electron microscopy measurements. The solubility of PAaH in water is strongly dependent on the pH of the solution. PAaH-SiO2 was flocculated at pH 3 because of the hydrophobic interaction of the grafted PAaH chains with protonated carboxyl pendant groups. In contrast, PAaH-SiO2 was dispersed at pH 10 because of electrostatic repulsion between the grafted PAaH chains with pendant carboxylate ions. Millimeter-sized ‘liquid marbles’ can be prepared using the pH-responsive PAaH-SiO2 particles. The ‘liquid marble’ can be transferred intact onto the surface of a neutral or acidic water pool and exhibit long-term stability. When the pH of the water pool becomes alkaline, the ‘liquid marble’ immediately bursts on the surface of the water pool. pH-responsive poly(6-(acrylamido)hexanoic acid)-grafted silica particles (PAaH-SiO2) were prepared via reversible addition-fragmentation chain transfer (RAFT)-controlled radical polymerization using the chain transfer agent immobilized silica particles. Millimeter-sized ‘liquid marbles’ can be prepared using the pH-responsive PAaH-SiO2 particles. The ‘liquid marble’ can be transferred intact onto the surface of neutral or acidic water pool, which exhibited long-term stability. When pH of the water pool was changed to alkaline, ‘liquid marble’ burst immediately on the surface of the water pool.

Rubber–Filler Interactions and Network Structure in Relation to Stress–Strain Behavior of Vulcanized, Carbon Black Filled EPDM

Immobilization of EPDM chains on the surface of carbon black and network structure in the rubber matrix of filled EPDM rubbers were studied by low-field proton NMR experiments. Advanced NMR experiments unambiguously show strong immobilization of EPDM chain fragments on the surface of carbon black. The thickness of the immobilized EPDM–carbon black interfacial layer is estimated to be ≥0.6 nm. The average number of monomer units per adsorption site is approximately nine, which suggests preferential chain adsorption at the crystal boundaries of carbon-black particles. The adsorbed chain fragments form physical (adsorption) junctions restricting chain mobility in the rubbery matrix outside of the interface. The cross-link density in filled EPDM is determined as a function of the filler type and its amount. The contribution of adsorption junctions to the total cross-link density is moderate as compared to the density of chemical cross-links and entanglement density. The mechanically effective network density in carbon-black-filled vulcanizates is determined by analysis of the stress–strain curves on the basis of the dynamic flocculation model. Comparison of the network density as measured by NMR and mechanical experiments shows significant differences which helps in better understanding of the reinforcement mechanism of filled rubbers. The study demonstrates that a relatively small amount of strongly adsorbed chains impacts the stress–strain properties of filled elastomers significantly.

Dramatic improvement of crystal quality for low-temperature-grown rabbit muscle aldolase.

Rabbit muscle aldolase (RMA) was crystallized in complex with the low-complexity domain (LC4) of sorting nexin 9. Monoclinic crystals were obtained at room temperature that displayed large mosaicity and poor X-ray diffraction. However, orthorhombic RMA-LC4 crystals grown at 277 K under similar conditions exhibited low mosaicity, allowing data collection to 2.2 A Bragg spacing and structure determination. It was concluded that the improvement of crystal quality as indicated by the higher resolution of the new RMA-LC4 complex crystals was a consequence of the introduction of new lattice contacts at lower temperature. The lattice contacts corresponded to an increased number of interactions between high-entropy side chains that mitigate the lattice strain incurred upon cryocooling and accompanying mosaic spread increases. The thermodynamically unfavorable immobilization of high-entropy side chains used in lattice formation was compensated by an entropic increase in the bulk-solvent content owing to the greater solvent content of the crystal lattice.

Kinetics and colloidal parameters of miniemulsion polymerization of butyl acrylate

AbstractBACKGROUND: The miniemulsion polymerization of butyl acrylate initiated by a macromonomeric azoinitiator (macroinimer, MIM) and stabilized by the non‐ionic emulsifier Tween 60 (TW‐60) was investigated.RESULTS: The monomer conversion and the polymerization rate increase with the amount of MIM and then decrease. The desorption rate constants were estimated using the Ugelstad/O'Toole, Gilbert and Nomura models. The Ugelstad/O'Toole and Gilbert models suggest an increase in the k′des value with increasing emulsifier concentration at the highest MIM concentration while the Nomura model proposes no variation in k′des with an increase in both TW‐60 and MIM concentrations. The polymerization rate increases in the following order with regard to initiator: MIM &lt; ammonium persulfate &lt; dibenzoyl peroxide &lt; 2, 2′‐azobisisobutyronitrile.CONCLUSION: The increase in the rate of polymerization can be discussed in terms of both increased particle concentration and the gel effect. The size of the polymer particles decreases and the number of polymer particles increases with both TW‐60 and MIM concentrations. This behaviour is attributed to the formation of a larger number of smaller monomer and/or polymer particles and higher particle nucleation rate. The observed long nucleation period for the MIM‐initiated polymerization is attributed to the creation of a crosslinked structure and the immobilization of MIM chains. Copyright © 2009 Society of Chemical Industry

High-Sensitivity Analysis of Naturally Occurring Sugar Chains, Using a Novel Fluorescent Linker Molecule

To analyse the binding of sugar chains to proteins, viruses and cells, the surface plasmon resonance (SPR) technique is very convenient and effective because it is a real-time, non-destructive detection system. Key to this method is linker compounds for immobilization of the sugar chains to the gold-coated chip for SPR. Also, well-designed fluorescent labelling reagents are essential when analysing the structure of trace amounts of sugar chains derived from natural sources, such as glycoproteins on the surface of specific cells. In this report, we developed a novel linker molecule, named 'f-mono', which has both of these properties: simple immobilization chemistry and a fluorescent label. Since the molecule contains a 2,5-diaminopyridyl group and a thioctic acid group, conjugation with sugar chains can be achieved using the well-established reductive amination reaction. This conjugate of sugar chain and fluorescent linker (fluorescent ligand-conjugate, FLC) has fluorescent properties (ex. 335 nm, em. 380 nm), and as little as 1 microg of FLC can be easily purified using HPLC with a fluorescent detector. MS and MS/MS analysis of the FLC is also possible. As a +2 Da larger MS peak ([M + H + 2](+) ion) was always associated with the theoretical MS peak ([M + H](+)) (due to the reduction of the thioctic acid moiety), the MS peaks of the FLC were easily found, even using unfractionated crude samples. Immobilization of the FLC onto gold-coated chips, and their subsequent SPR analyses were successively accomplished, as had been performed previously using non-fluorescent ligand conjugates.

Growth of hydrogel nano- and microlayers covalently bounded onto PE surface

Surface modifying strategies were developed to immobilize PAA cross-linked layers (hydrogel layers) with different thicknesses by chemical binding to the surface of polyethylene (PE). Polyethylene films were functionalized by two methods, chromic acid oxidation and maleic anhydride grafting. The reaction of the functional groups placed onto the film surface with ethylenediamine promoted the formation of an amine-functionalized surface. The thickness of the hydrogel layer was correlated with the presence and the release of impregnated ethylenediamine during the immobilization of the PAA chains by thermal esterification. Ethylenediamine acts as a cross-linking agent between different PAA chains. Attenuated total reflectance (ATR) FTIR spectroscopy and scanning electron microscopy (SEM) were used to characterize the chemical composition and the morphologies of the modified film surface.

Review of the role of the interphase in the control of composite performance on micro- and nano-length scales

In fiber reinforced composites (FRCs), exhibiting heterogeneous structure at multiple length scales, the interphase phenomena at various length scales were shown to be of pivotal importance for the control of the performance and reliability of such structures. Various models based on continuum mechanics were used to describe effects of the macro- and meso-scale interphase on the mechanical response of laminates and large FRC parts, satisfactorilly. At the micro-scale, the interphase is considered a 3D continuum with ascribed average properties. Number of continuum mechanics models was derived over the last 50 years to describe the stress transfer between matrix and individual fiber with realtively good success. In these models, the interphase was characterized by some average shear strength, τa, and elastic modulus, Ea. On the other hand, models for tranforming the properties of the micro-scale interphase around individual fiber into the mechanical response of macroscopic multifiber composite have not been generally successfull. The anisotropy of these composite structures are the main reasons causing the failure of these models. The strong thickness dependence of the elastic modulus of the micro-scale interphase suggested the presence of its underlying sub-structure. On the nano-scale, the discrete molecular structure of the polymer has to be considered. The term interphase, originally introduced for continuum matter, has to be re-defined to include the discrete nature of the matter at this length scale. The segmental immobilization resulting in retarded reptation of chains caused by interactions with solid surface seems to be the primary phenomenon which can be used to re-define term interphase on the nano-scale. Thus, the Rubinstein reptation model and a simple percolation model were used to describe immobilization of chains near solid nano-particles and to explain the peculiarities in the viscoleastic response of nano-scale “interphase.” It has also been shown that below 5 nm, Bernoulli–Euler continuum elasticity becomes not valid and higher-order elasticity along with the proposed reptation dynamics approach can provide suitable means for bridging the gap in modeling the transition between the mechanics of continuum matter at the micro-scale and mechanics of discrete matter at the nano-scale.

Improving Electrochemical Stability of Polyelectrolyte Multilayer Films by Thermal Immobilization of Polymer Chains

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Adhesion of eukaryotic cells and Staphylococcus aureus to silicon model surfaces

Silicon wafers modified by silanisation with different functional groups are used to study the bioactivity of surfaces with varying physicochemical properties. Oxidation of the wafers created very hydrophilic surfaces, and moderately wettable surfaces were produced by coating with poly(ethylene glycol) (PEG). Immobilization of hydrocarbon chains to the wafers produced hydrophobic surfaces, and hydrophobicity was further increased by fluorocarbon coatings. The oxidized and the hydrocarbon-modified surfaces supported the adhesion of human MG-63 osteoblasts and 3T3 mouse fibroblasts as well as Staphylococcus aureus 8325-4. Adhesion of osteoblasts and fibroblasts, however, was decreased on highly hydrophobic fluorocarbon surfaces, whereas adhesion of S. aureus was supported. Coating of the fluorocarbon surface with fibronectin increased the number of attached eukaryotic cells, but the accumulation of bacteria remained unchanged. In contrast, surface coatings with PEG-groups inhibited the binding of S. aureus; however, the adhesion of the eukaryotic cells was high. The number of S. aureus on PEG-modified surfaces covered with fibronectin increased about twofold, yet it was still decreased to 25-30% related to the number of bacteria on other surfaces. These findings provide evidence that the PEG-modified surfaces showed selective bioactivity, preventing the attachment of a microbial pathogen but supporting the adhesion of eukaryotic cells.

Atomic force acoustic microscopy analysis of epoxy–silica nanocomposites

A DGEBA-based epoxy matrix was loaded with 10, 20 and 30 phr of fumed silica particles. Single edge notched bend (SENB) specimens were prepared and deformed to failure in three-point bending configuration. Their fracture surfaces were examined by atomic force acoustic microscopy (AFaM) in order to obtain information about the local elastic modulus of the surface at high spatial resolution. The collected information was correlated to the bulk thermo-mechanical properties of the composites. In particular, the decrease in thermo-mechanical properties like tensile modulus, yield strength, stress at break and glass transition temperature, observed for samples filled with 10 and 20 phr with respect to the unfilled matrix was found to correspond to highly heterogeneous fracture surfaces presenting a broad distribution of elastic modulus values. The AFaM data were interpreted as representative of different degrees of filler exposure on fracture surfaces and also of localized cavitation effects involved in crack propagation, both phenomena accounting for the effective plasticizing effect macroscopically observed at silica amounts of 10 and 20 phr. A substantial reduction in the exposure probability of silica particles on fracture surfaces was found for the sample filled with 30 phr of silica, which also displayed an improvement of the mechanical and thermal properties. This latter evidence was tentatively explained by supposing a physical immobilization of polymer chains at the polymer-matrix interface.

Segmental mobility in short-chain grafted-PDMS by homo- and heteronuclear residual dipolar couplings

Different homo- ( 1H– 1H) and heteronuclear ( 1H– 13C) multiple quantum solid-state NMR experiments were applied to a series of short poly (dimethylsiloxane) (PDMS) chains grafted onto hydrophilic silica. The existence and clear separation of a strongly dipolar coupled region which is attributed to the silica–PDMS interface and a weakly dipolar coupled region attributed to the mobile chain portions outside the interface is evident in all experiments. In a sample series with different average chain lengths the residual dipolar couplings and with that the average order parameters are constant for the interface part and correlate for the mobile part linearly with the average chain length. Temperature dependent studies using 1H double quantum experiments indicate the different stages of immobilization of the polymer chains. Solid-state NMR techniques therefore can give detailed information about the microscopic structure of this material and especially the effect of chain anchoring. It is also demonstrated that sample rotation influences the mobility of the mobile component and therefore the analysis of such materials should always be done under static conditions.

Preparation of Hybrid Microgels Functionalized by Silver Nanoparticles

AbstractSummary: Hybrid microgels functionalized with silver nanoparticles (AgNP) have been prepared and their physico‐chemical properties examined. Composite particles have been obtained by formation of AgNP in presence of poly[vinylcaprolactam‐co‐(acetoacetoxyethyl methacrylate)] (VCL/AAEM) microgel particles. It has been demonstrated that hybrid particles with different AgNP amounts can be prepared. Hybrid particles are sensitive to temperature and swelling, and collapse processes are reversible. Incorporation of AgNP leads to shrinkage of microgel template due to the partial immobilization of polymer chains on the microgel surface. As a consequence, gradual loss of temperature sensitivity is observed. Hybrid microgels form highly transparent well‐organized films on solid substrates, providing homogeneous distribution of AgNP in bulk material. Presence of AgNP increases considerably the thermal stability of composite films.Schematic representation (left) and TEM image (right) of hybrid microgels containing silver nanoparticles (AgNP).magnified imageSchematic representation (left) and TEM image (right) of hybrid microgels containing silver nanoparticles (AgNP).

NMR Determination of Lysine pKa Values in the Pol λ Lyase Domain: Mechanistic Implications

The base excision repair (BER) process requires removal of an abasic deoxyribose-5-phosphate group, a catalytic activity that has been demonstrated for the N-terminal 8 kDa domain of DNA polymerase beta (Pol beta), and for the homologous domain of DNA polymerase lambda (Pol lambda). Previous studies have demonstrated that this activity results from formation of a Schiff base adduct of the abasic deoxyribose C-1' with a lysine residue (K312 in the case of Pol lambda), followed by a beta-elimination reaction. To better understand the underlying chemistry, we have determined pKa values for the lysine residues in the Pol lambda lyase domain labeled with [epsilon-13C]lysine. At neutral pH, the H(epsilon) protons on 3 of the 10 lysine residues in this domain, K287, K291, and K312, exhibit chemical shift inequivalence that results from immobilization of the lysyl side chains. For K287 and K291, this results from the K287-E261 and K291-E298 salt bridge interactions, while for K312, immobilization apparently results from steric and hydrogen-bonding interactions that constrain the position of the lysine side chain. The pKa value of K312 is depressed to 9.58, a value indicating that at physiological pH K312 will exist predominantly in the protonated form. Titration of the domain with hairpin DNA containing a 5'-tetrahydrofuran terminus to model the abasic site produced shifts of the labeled lysine resonances that were in fast exchange but appeared to be complete at a stoichiometry of approximately 1:1.3, consistent with a dissociation constant of approximately 1 microM. The epsilon-proton shifts of K273 were the most sensitive to the addition of the DNA, apparently due to changes in the relative orientation between K273 and W274 in the DNA complex. The average pKa values increased by 0.55, consistent with the formation of some DNA-lysine salt bridges and with the general pH increase expected to result from a reduction in the net positive charge of the complex. A general increase in the Hill coefficients observed in the complex is consistent with the screening of the interacting lysine residues by the DNA. The pKa of K312 residue increased to 10.58 in the complex, probably due to salt bridge formation with the 5'-phosphate group of the DNA. The pKa values obtained for the lyase domain of Pol lambda in the present study are consistent with recent crystallographic studies of Pol beta complexed with 5-phosphorylated abasic sugar analogues in nicked DNA which reveal an open site with no obvious interactions that would significantly depress the pK value for the active site lysine residue. It is suggested that due to the heterogeneity of the damaged DNA substrates with which Pol lambda as well as other related polymerases may be required to bind, the unexpectedly poor optimization of the lyase catalytic site may reflect a compromise of flexibility with catalytic efficiency.

Intramolecular Quenching of Tryptophan Phosphorescence in Short Peptides and Proteins¶

ABSTRACTThe phosphorescence lifetime (τ) of tryptophan (Trp) residues in proteins in aqueous solutions at ambient temperature can vary several orders of magnitude depending on the flexibility of the local structure and the rate of intramolecular quenching reactions. For a more quantitative interpretation of τ in terms of the local protein structure, knowledge of all potential quenching moieties in proteins and of their reaction rates is required. The quenching effectiveness of each amino acid (X) side chain and of the peptide backbone was investigated by monitoring their intramolecular quenching rate (kobs) in tripeptides of the form acetyl‐Trp‐Gly‐X‐CONH2 (WGX), where Trp is joined to × by a flexible Gly link. The results indicate that among the various groups present in proteins only the side chains of Cys, His, Tyr and Phe are able to quench Trp phosphorescence at a detectable rate (kobs &gt; 40 s−1), with the quenching effectiveness for rotationally unrestricted side chains ranking in the order Cys &gt;&gt; His+ &gt; Tyr &gt;&gt; Phe ∼ His. For the aromatic side chains the corresponding contact rate at 20°C is estimated to be between 3‐4 × 109 s−1 for Cys (as determined by Lapidus et al.), 0.8‐8 × 106 s−1 for His+, 0.37‐3.7 × 106 s−1 for Tyr and 0.2‐2 × 105 s−1 for Phe and His. In the cases of His and Tyr, kobs drops sharply with increasing pH, with midpoint transitions about 1 pH unit above the pKa, indicating that quenching is almost exclusive to the protonated form. From the temperature dependence of the rate, obtained in 50/50 propylene glycol/water between −20°C and 20°C, the reaction is characterized by activation energies of about 5 kcal·M−1 for His+ and Tyr and 8 kcal ·M−1 for Phe. An analysis of the groups in contact with Trp residues in proteins that exhibit long phosphorescence lifetimes at ambient temperature leads to the conclusion that the contact rate of the peptide group and of the remaining side chains is lower than 0.1 s−1, showing that these moieties are practically inert with respect to the triplet‐state lifetime. It shows further that the immobilization of the aromatic side chains within the globular fold cuts their quenching effectiveness drastically to contact rates &lt; 2 s−1, a phenomenon attributed to the low probability of forming a stacked exciplex with the indole ring. All evidence suggests that, except in the case of nearby Cys or Trp residues, whose interaction with the triplet state reaches beyond van der Waals contact, the emission of buried Trp residues is unlikely to be quenched by surrounding protein groups.

Intramolecular quenching of Trp phosphorescence in short peptides and proteins

The phosphorescence lifetime (tau) of tryptophan (Trp) residues in proteins in aqueous solutions at ambient temperature can vary several orders of magnitude depending on the flexibility of the local structure and the rate of intramolecular quenching reactions. For a more quantitative interpretation of tau in terms of the local protein structure, knowledge of all potential quenching moieties in proteins and of their reaction rates is required. The quenching effectiveness of each amino acid (X) side chain and of the peptide backbone was investigated by monitoring their intramolecular quenching rate (k(obs)) in tripeptides of the form acetyl-Trp-Gly-X-CONH2 (WGX), where Trp is joined to X by a flexible Gly link. The results indicate that among the various groups present in proteins only the side chains of Cys, His, Tyr and Phe are able to quench Trp phosphorescence at a detectable rate (k(obs) > 40 s(-1)), with the quenching effectiveness for rotationally unrestricted side chains ranking in the order Cys >> His+ > Tyr >> Phe approximately His. For the aromatic side chains the corresponding contact rate at 20 degrees C is estimated to be between 3-4 x 10(9) s(-1) for Cys (as determined by Lapidus et al.), 0.8-8 x 10(6) s(-1) for His+, 0.37-3.7 x 10(6) s(-1) for Tyr and 0.2-2 x 10(5) s(-1) for Phe and His. In the cases of His and Tyr, k(obs) drops sharply with increasing pH, with midpoint transitions about 1 pH unit above the pKa, indicating that quenching is almost exclusive to the protonated form. From the temperature dependence of the rate, obtained in 50/50 propylene glycol/water between -20 degrees C and 20 degrees C, the reaction is characterized by activation energies of about 5 kcal.M(-1) for His+ and Tyr and 8 kcal.M(-1) for Phe. An analysis of the groups in contact with Trp residues in proteins that exhibit long phosphorescence lifetimes at ambient temperature leads to the conclusion that the contact rate of the peptide group and of the remaining side chains is lower than 0.1 s(-1), showing that these moieties are practically inert with respect to the triplet-state lifetime. It shows further that the immobilization of the aromatic side chains within the globular fold cuts their quenching effectiveness drastically to contact rates < 2 s(-1), a phenomenon attributed to the low probability of forming a stacked exciplex with the indole ring. All evidence suggests that, except in the case of nearby Cys or Trp residues, whose interaction with the triplet state reaches beyond van der Waals contact, the emission of buried Trp residues is unlikely to be quenched by surrounding protein groups.

Intramolecular Quenching of Tryptophan Phosphorescence in Short Peptides and Proteins¶

The phosphorescence lifetime (tau) of tryptophan (Trp) residues in proteins in aqueous solutions at ambient temperature can vary several orders of magnitude depending on the flexibility of the local structure and the rate of intramolecular quenching reactions. For a more quantitative interpretation of tau in terms of the local protein structure, knowledge of all potential quenching moieties in proteins and of their reaction rates is required. The quenching effectiveness of each amino acid (X) side chain and of the peptide backbone was investigated by monitoring their intramolecular quenching rate (k(obs)) in tripeptides of the form acetyl-Trp-Gly-X-CONH2 (WGX), where Trp is joined to X by a flexible Gly link. The results indicate that among the various groups present in proteins only the side chains of Cys, His, Tyr and Phe are able to quench Trp phosphorescence at a detectable rate (k(obs) > 40 s(-1)), with the quenching effectiveness for rotationally unrestricted side chains ranking in the order Cys >> His+ > Tyr >> Phe approximately His. For the aromatic side chains the corresponding contact rate at 20 degrees C is estimated to be between 3-4 x 10(9) s(-1) for Cys (as determined by Lapidus et al.), 0.8-8 x 10(6) s(-1) for His+, 0.37-3.7 x 10(6) s(-1) for Tyr and 0.2-2 x 10(5) s(-1) for Phe and His. In the cases of His and Tyr, k(obs) drops sharply with increasing pH, with midpoint transitions about 1 pH unit above the pKa, indicating that quenching is almost exclusive to the protonated form. From the temperature dependence of the rate, obtained in 50/50 propylene glycol/water between -20 degrees C and 20 degrees C, the reaction is characterized by activation energies of about 5 kcal.M(-1) for His+ and Tyr and 8 kcal.M(-1) for Phe. An analysis of the groups in contact with Trp residues in proteins that exhibit long phosphorescence lifetimes at ambient temperature leads to the conclusion that the contact rate of the peptide group and of the remaining side chains is lower than 0.1 s(-1), showing that these moieties are practically inert with respect to the triplet-state lifetime. It shows further that the immobilization of the aromatic side chains within the globular fold cuts their quenching effectiveness drastically to contact rates < 2 s(-1), a phenomenon attributed to the low probability of forming a stacked exciplex with the indole ring. All evidence suggests that, except in the case of nearby Cys or Trp residues, whose interaction with the triplet state reaches beyond van der Waals contact, the emission of buried Trp residues is unlikely to be quenched by surrounding protein groups.

原子移動ラジカル重合法による種々のビニルポリマー鎖の大孔径シリカゲルヘの固定化と表面構造制御

原子移動ラジカル重合法による種々のビニルポリマー鎖の大孔径シリカゲルヘの固定化と表面構造制御

Acrylonitrile-Based Copolymer Membranes Containing Reactive Groups: Surface Modification by the Immobilization of Poly(ethylene glycol) for Improving Antifouling Property and Biocompatibility

The antifouling property and biocompatibility of a polyacrylonitrile-based copolymer membrane were improved by the immobilization of poly(ethylene glycol) (PEG) on the membrane surface. The studied membranes were fabricated from poly(acrylonitrile-co-maleic acid), in which the carboxyl groups could be conveniently conversed into anhydride and then esterified with poly(ethylene glycol). Chemical and morphological changes on the membrane surface were characterized by Fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA), scanning electron microscopy (SEM), and sessile drop contact angle measurements (CA). It was found that the water contact angle of the membrane was reduced and the biocompatibility corresponding to platelets adhesion and protein adsorption was improved significantly with the immobilization of PEG chains on the membrane surface. Furthermore, the permeation behaviors of the base and modified membranes were investigated by bovine serum albumin (BSA) filtration experiments. Membranes containing hydrophilic carboxyl groups or PEG chains showed higher solution flux, lower BSA adsorption, and better flux recovery after cleaning than those of polyacrylonitrile membranes. Particularly, compared with polyacrylonitrile membranes, the PEG-immobilized membrane showed a 6-fold increase in BSA solution flux, 63% reduction in total fouling, and 67% reduction in BSA adsorption.