Isomerisation of Erythro‐ and Threo‐Succinyl Units in Alternating Alkene‐Maleic Acid Copolymers: A Promising Route to New Microstructures

Summary: A first route to the isomerisation of erythro‐ and threo‐2,3‐disubstituted succinyl units in alternating alkene‐maleic acid copolymers is presented. The isomerisation reactions of the disodium salt of ethene‐maleic acid copolymer were carried out in aqueous solution at 180–240 °C in an autoclave. It is demonstrated that the erythro‐content can be changed from 17% up to 67%. The dissociation of methine C H bonds with the intermediate formation of a sp² hybridised carbon is proposed as the mechanism.

Isomerisation equilibrium between the threo‐ and erythro‐form of the 2,3‐disubstituted succinyl unit.     

Kinetic Investigations of Reactions with Maleic Anhydride Copolymers and Model Compounds

Alternating copolymers that contain maleic anhydride (MAn) as a component occur in two different stereochemical configurations which are differentiated by their reactivity. Model compounds, 2, 3-dialkylsuccinic acids and their anhydrides, were investigated and it was demonstrated that there is a distinct difference between threo and erythro configurations in their chemical and physical behavior. Both configurations also occur in the alternating copolymers. Beside the model compounds, the alternating copolymers ethylene-MAn, propylene-MAn, and styrene-MAn were investigated in their reactions with amines, alcohols, and water (hydrolysis). The cis configurations showed the higher reaction rates. Reactions of the anhydride moieties with equimolar amounts of aniline, ethanol, and water demonstrated that reactions follow second-order rate laws. With excess reactant, the reaction follows a pseudo-first-order rate law. The rate constants depend on the degree of polymerization and on the comonomer. Increasing steric hindrance and molecular weight lead to a decrease of the reaction rate. Catalysis of the hydrolysis reaction by tertiary amines results in similar rate constants for the configurations of the substituted succinic acid anhydrides. The reasons are discussed.     

Ionization equilibrium in salt‐containing aqueous solutions of synthetic polyampholytes

The peculiarities of ionic equilibrium in salt‐containing aqueous solutions of polyampholytes (acrylic acid–2‐methyl‐5‐vinylpyridine copolymers) of various compositions and molecular weights were studied. The protonation degree of base groups (β_iep), the dissociation degree of acid groups (α_iep), and the ionization constant of methylvinylpyridine groups (pK_b) for the isoelectric points of the studied polyampholytes under various ionic strength values (I) were assessed spectrophotometrically. The dependencies of α_iep and pK_b versus the copolymer composition in the absence of low molecular weight electrolyte are described by the following equations: pK_b = 6.2–0.037z and lg α_iep = 0.27–0.0215z, where z is the molar content of the acrylic acid units. The basicity of methylvinylpyridine groups increases in proportion to the content of acid groups at a constant ionic strength and is independent of the molecular weight and molecular weight distribution of the copolymer. The relationship between pK_b and the ionic strength of the solution for acrylic acid–methylvinylpyridine copolymers was established: pK_b(I) = pK + B · I^1/2, where pK is the thermodynamic ionization constant of base groups and B is 0.21 + 0.0065z. A good agreement between the experimental and theoretical (calculated from the given equation) values of the ionization constant, pK_b, of methylvinylpyridine groups for other polyampholytes (copolymers of methacrylic acid with 2‐methyl‐5‐vinylpyridine) demonstrated that the ionic state of polyampholytes is determined by the basicity of methylvinylpyridine groups, which depends on the copolymer composition and solution ionic strength. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1824–1831, 2000     

Mechanism of alternating copolymerization of 4-hydroxy-4′-vinylbiphenyl with α-chloromaleic anhydride

The copolymerization of 4-hydroxy-4′-vinylbiphenyl (HVB) with α-chloromaleic anhydride (CMAn) was investigated in THF, 1,4-dioxane, and acetonitrile. The formation of the 1:1 charge transfer complex between HVB and CMAn was confirmed spectroscopically, and the corresponding equilibrium constant (K_eq) was determined as follows: K_eq = 0.19, 0.11, and 0.058 mol/L in THF, 1,4-dioxane, and CH₃CN, respectively. The copolymer composition is affected by the solvent, i.e., the content of HVB in the copolymer obtained in THF or 1,4-dioxane is lower than 50 mol % whereas the copolymer obtained in CH₃CN has excess of HVB units. The maximum rate of copolymerization was observed at a 1:1 initial comonomer mole ratio, irrespective of the solvent polarity. Plots of R_p/[HVB] vs. [HVB] gave a straight line with a slope and an intercept for the copolymerization in THF whereas a straight line in CH₃CN has no slope. On the basis of these results and ¹³C-NMR spectra of the copolymers, the mechanism of the predominant formation of alternating copolymers is discussed.     

Curing reaction of unsaturated (epoxy) polyesters based on different aliphatic glycols

The influence of the structure of succinic or glutaric anhydride modified linear unsaturated (epoxy) polyesters on the course of the cure reaction with styrene initiated by benzoyl peroxide (BPO) or the mixture of benzoyl peroxide/tetrahydrophthalic anhydride (BPO/THPA) or benzoyl peroxide/maleic anhydride, as well as viscoelastic properties and thermal behavior of their styrene copolymers have been studied by DSC, DMA, and TGA analyses. Additionally, mechanical properties: flexural properties using three-point bending test and Brinell’s hardness for studied copolymers were evaluated. It was confirmed that the structure of used polyesters had a considerable influence on the course of the cure reaction with styrene, viscoelastic, thermal, and mechanical properties of prepared styrene copolymers. Generally, one or two asymmetrical peaks for the cure reaction of succinic or glutaric anhydride modified linear unsaturated epoxy polyesters with styrene were observed. They were connected with various cure reaction, e.g., copolymerization of carbon–carbon double bonds of polyester with styrene, thermal curing of epoxy groups, polyaddition reaction of epoxy to anhydride groups in dependence of used curing system. In addition, only one asymmetrical, exothermic peak attributed to the copolymerization process of succinic or glutaric anhydride modified linear unsaturated polyesters with styrene was visible. Moreover, the obtained styrene copolymers based on succinic or glutaric anhydride modified linear unsaturated epoxy polyesters were characterized by higher values of E_{20 ^°\textC}^￠ E_{{20\,^{\circ}{\text{C}}}}^{\prime} , T _g, E″, ν _e, E _mod, F _max, hardness, IDT, FDT but lower ε − F _max compared to those values observed for styrene copolymers prepared in the presence of succinic or glutaric anhydride modified linear unsaturated polyesters. This supported to the production of stiffer and more thermally stable polymeric structure of copolymers based on unsaturated epoxy polyesters. Moreover, the copolymers prepared in the use of glutaric anhydride modified linear unsaturated (epoxy) polyesters were described by lower values of E_{20 ^°\textC}^￠ E_{{20\,^{\circ}{\text{C}}}}^{\prime} , T _g, E″, ν _e, E _mod, F _max, hardness, IDT, FDT but higher ε − F _max than those based on succinic anhydride modified linear unsaturated (epoxy) polyesters. The presence of longer aliphatic chain length in polyester’s structure leads to produce more flexible network structure of styrene copolymers based on glutaric anhydride modified linear unsaturated (epoxy) polyesters than those based on succinic anhydride modified linear unsaturated (epoxy) polyesters.     

Fluoroimines from the reaction of fluoro amino acids or fluoroketo acids with the aldehyde or amine form of vitamin B6: 2—Stereochemical aspects of their formation from β-fluoroaspartates or β-fluorooxaloacetate,using 19F NMR

The fluorine NMR spectra of systems initially containing 0.05–0.1 M of pyridoxal 5′-phosphate and erythro-β-fluoroaspartate (or threo-β-fluoroaspartate) in D₂O solution were examined over the pD range 1–12. The formation of the aldimine Schiff base gave only one stereoisomer, whcih was trapped with sodium borohydride. Reactions of pyriodoxamine 5′-phosphate and fluorooxaloacetate were examined under the same conditions. A mixture of two products was given, identified as two ketimine Schiff bases (E and Z isomers) with well characterized fluorine chemical shifts and ²J(DF) values. This mixture, trapped with sodium borohydride, gives the two reduced erythro and threo aldimines. The configurations and conformations of all reaction products were determined using the ³J(HF) values and their correlation with the fluorine chemical shift. The role of the 3-phenolate oxygen of the pyridine ring, of the conjugate acid of the iminium nitrogen and of the carboxylate oxygen in ionic or hydrogen bond interactions in the determination of the stereochemistry is discussed.     

Convenient Entry to α‐Amino‐β‐hydroxy‐γ‐methyl Carboxylic Acids. Diastereoselective Formation and Directed Homogeneous Hydrogenation of 3‐(3‐Aryl‐1‐hydroxy‐2‐methylprop‐2‐enyl)‐1,4‐benzodiazepin‐2‐ones

Aldol reaction of 7‐chloro‐1,3‐dihydro‐1‐methyl‐5‐phenyl‐2H‐1,4‐benzodiazepin‐2‐one ( 1 ) with 4‐substituted α‐methylcinnamaldehydes 2 – 5 afforded a mixture of threo‐ and erythro‐3‐(3‐aryl‐1‐hydroxy‐2‐methylprop‐2‐enyl)‐7‐chloro‐1,3‐dihydro‐1‐methyl‐5‐phenyl‐2H‐1,4‐benzodiazepin‐2‐ones 6 – 13 . The chromatographically separated threo diastereoisomers 6, 8, 10 , and 12 and erythro diastereoisomers 7, 9, 11 , and 13 were submitted to ‘directed' homogeneous hydrogenation catalyzed by [Rh^I(cod)(diphos‐4)]ClO₄ (cod=cycloocta‐1,5‐diene, diphos‐4=butane‐1,4‐diylbis[diphenylphosphine]. From the erythro‐racemates 9, 11 , and 13 , the erythro,erythro/erythro,threo‐diastereoisomer mixtures 16 / 17, 20 / 21 , and 24 / 25 were obtained in ratios of 20 : 80 to 28 : 72 (HPLC), which were separated by chromatography. From the threo racemates 8, 10 , and 12 , the threo,threo/threo,erythro‐diastereoisomer mixtures were obtained in a ratio of ca. 25 : 75 (¹H‐NMR). The relative configurations were assigned by means of ¹H‐NMR data and X‐ray crystal‐structure determination of 21 . Hydrolysis of 21 afforded the diastereoisomerically pure N‐(benzyloxy)carbonyl derivative 27 of α‐amino‐β‐hydroxy‐γ‐methylpentanoic acid 26 , representative of the novel group of polysubstituted α‐amino‐β‐hydroxycarboxylic acids.     

Determination of acid dissociation constants of histidine-containing peptides by proton magnetic resonance spectroscopy

The acid dissociation constant of the imidazolium ring of the decapeptide luliberin has been determined by ¹H NMR-followed titration in D₂O. The normal procedure for the analysis of the titration curve, i.e. direct use of the Henderson-Haselbalch equation, is still applicable in this case, but for more complex peptides a modified calculation procedure is proposed. Results obtained when both methods were applied to luliberin are compared. The influence of D₂O when used as the solvent in this type of determination has been studied using N^α-acetyl-L -histidine methyl ester as a model compound. The difference between the acid dissociation constant of this molecule determined in H₂O and in D₂O implies that a correction of ?.25 unit is needed for those pK_a values calculated by plotting the chemical shifts in D₂O vs the apparent pH meter readings. The pK_a found for N^α-acetyl-L-histidine methyl ester, 6.30 ± 0.04, can be taken as a standard value for histidine-containing peptides.     

Preparation of polymer nanoparticles from renewable biobased furfuryl alcohol and maleic anhydride by stabilizer‐free dispersion polymerization

The spherical polymer nanoparticles of biobased renewable monomers, furfuryl alcohol (FA) and maleic anhydride (MAn), with diameters (D_n) in the range of 120 to 500 nm have been prepared by stabilizer‐free dispersion copolymerization. In acetate or its mixture, the conversion of the monomers greatly depended on the concentration of AIBN. When the molar ratio of AIBN/monomers was 3.6% (wt), the monomer conversion could be as high as 80%. The aggregations of the solvated polymer chains formed the nuclei of the polymer particles. After the nucleation stage, both the monomer conversions and particle sizes increased steadily, while the coefficient of variation of the particle size decreased. The almost linear relationship between the D_n³ and the weight of polymer suggested that there is no significant secondary nucleation. The copolymer of FA and MAn could not dissolve in common organic solvents. Elemental analyses, FTIR and ¹³CP‐MAS spectra showed that the copolymer was close to the alternative copolymer of FA and MAn irrespective to the molar ratios of FA/MAn in monomer feed. Furthermore, the two 2,5‐ and 3,4‐dihydrofuran ring configurations exist in the copolymer and the later is the major one. The reaction of copolymer particles with triethylenetetramine confirmed the reactivity of the succinic anhydride groups at the surface of copolymer particles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Tunable phase transition behaviors of pH-sensitive polyaspartamides having various cationic pendant groups

New pH-sensitive graft copolymers based on poly(2-hydroxyethyl aspartamide) (PHEA) were prepared by attaching various cationic monomers, such as 4-(aminomethyl)pyridine (PY), 1-(3-aminopropyl)imidazole (IM), and N-(3-aminopropyl)dibuthylamine (BU), as pH-sensitive units and octadecylamine (C₁₈) as a hydrophobic segment on poly(succinimide). Phase transition of each copolymer solution occurred at a vicinity of the pK _a value of the cationic groups, and their insoluble pH ranges were broadened as the feed amount of pH-sensitive moieties was increased. Depending on the cationic grafts having different pK _a values, the pH ranges where the copolymer became insoluble could be tuned. Copolymers PHEA-g-C₁₈-PY, PHEA-g-C₁₈-IM, and PHEA-g-C₁₈-BU exhibited phase separations in solutions at pH ranges of 4∼6, 6∼8, and 9∼12, respectively. These polymers have the unique feature of their pH sensitivity profiles being identified to three regimes. Under low pH conditions (below pK _a ), the polymer solution is transparent. At medium pH (around pK _a ), polymer precipitation occurred in solution. At pH > pK _a , the polymer solution is gradually dissolved again.     

Synthesis and metal complexation of dihydroxyphosphino‐functionalized crosslinked styrene/maleic anhydride copolymers

Crosslinked styrene (St)/maleic anhydride (MA) copolymers were synthesized, hydrolyzed with dicarboxylic acid, and converted to bear dihydroxyphosphino functionalities. The St–MA copolymers were prepared by azobisisobutyronitrile‐initiated polymerization in toluene at 90 °C in the presence of 2, 10, or 20% divinylbenzene crosslinker. The MA moiety was hydrolyzed into dicarboxylic acid to improve the hydrophilicity of the copolymers. The phenyl ring of St was phosphorylated with phosphorus trichloride in the presence of aluminum chloride and then hydrolyzed and oxidized with nitric acid at room temperature. The structures of the hydrolyzed and dihydroxyphosphino‐functionalized copolymers were confirmed by Fourier transform infrared spectroscopy and elemental analysis. The complexation behavior of these functionalized copolymers toward metal ions in 25 ppm aqueous solutions was observed over time periods of up to 7 h. The adsorption toward Pb(+2) was highest, followed by those of Cu(+2), Cr(+3), and Ni(+2). On the dihydroxyphosphino‐functionalized St–MA (20% divinylbenzene) copolymer, the adsorption of Pb(+2) showed a linear relationship with the concentrations and fit the Langmuir isotherm. The kinetics of Pb(+2) adsorption on this dihydroxyphosphino‐functionalized copolymer also fit the rate equation of the moving boundary model, t = [1 ? 3(1 ? X)^2/3 + 2(1 ? X)], where X is the fractional conversion. The metal‐ion adsorption kinetics of this copolymer appeared to be particle diffusion control, in which the moving boundary advanced from the surface toward the center. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 92–101, 2004     

Synthesis and micellization of amphiphilic poly(sebacic anhydride)–poly(ethylene glycol)–poly(sebacic anhydride) block copolymers

Amphiphilic biodegradable block copolymers [poly(sebacic anhydride)–poly(ethylene glycol)–poly(sebacic anhydride)] were synthesized by the melt polycondensation of poly(ethylene glycol) and sebacic anhydride prepolymers. The chemical structure, crystalline nature, and phase behavior of the resulting copolymers were characterized with ¹H NMR, Fourier transform infrared, gel permeation chromatography, and differential scanning calorimetry. Microphase separation of the copolymers occurred, and the crystallinity of the poly(sebacic anhydride) (PSA) blocks diminished when the sebacic anhydride unit content in the copolymer was only 21.6%. ¹H NMR spectra carried out in CDCl₃ and D₂O were used to demonstrate the existence of hydrophobic PSA domains as the core of the micelle. In aqueous media, the copolymers formed micelles after precipitation from water‐miscible solvents. The effects on the micelle sizes due to the micelle preparation conditions, such as the organic phase, dropping rate of the polymer organic solution into the aqueous phase, and copolymer concentrations in the organic phase, were studied. There was an increase in the micelle size as the molecular weight of the PSA block was increased. The diameters of the copolymer micelles were also found to increase as the concentration of the copolymer dissolved in the organic phase was increased, and the dependence of the micelle diameters on the concentration of the copolymer varied with the copolymer composition. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1271–1278, 2006     

Basicity of some aliphatic amines in mixed H2O?CH3CN solvents

The values of pK_a^ms (K_a^ms represents ionization constant of conjugate acid of amine base in mixed water–acetonitrile solvent) for all amines, except for charged amine bases, show a mild decrease (ca. 0.1–0.4 pK units) with the increase in CH₃CN content from 2 to ∼60% v/v. However, the pK_a^ms values at 70% v/v CH₃CN become nearly equal or slightly larger (by ≤0.7 pK units) than the corresponding pK_a^ms at 2% v/v CH₃CN for all neutral and charged amines. The values of pK_a^ms for phenol increase from 10.17 to 13.38 with the increase in the content of CH₃CN from 2 to 70% v/v in mixed aqueous solvent. Taft reaction constants, ρ*, obtained from the plots of pK_a^ms against ∑σ* for primary and secondary amines decrease by ca. 0.8 ρ* units with the increase in the CH₃CN content from 2 to 70% v/v. The values of pK_a^ms show an empirical linear relationship with the corresponding values of pK_a^w (where pK_a^w represents the pK_a obtained in aqueous solvent containing 2% v/v CH₃CN), which allows the estimation of a pK_a in mixed H₂O CH₃CN solvents from that in water. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 146–152, 2000     

Studies on the Physical Chemistry of (2,4-Dichlorophenoxy)acetic Acid in Two-phase Systems: Organic Solvent-Water

The dissociation constants (p _s K _a ) of 2,4-D acid were determined in methanol-water mixtures of 10.9 to 38.9 wt.% methanol content. The Yasuda-Shedlovsky procedure was used to obtain the pK _a value in zero-% methanol. The distribution of 2,4-D acid in twelve two-phase organic solvent + water systems and its dimerization in the organic phase were investigated. Values of the distribution coefficient (D _HR), distribution constant (K _D ), and dimerization constant (K _dim) of 2,4-D were obtained. The influence of the structure and polarity of the investigated organic solvents, as well as that of pH of the aqueous phase, on the physical chemistry of 2,4-D in the two-phase systems are described.     

Esterolytic activity of imidazole-containing polymers. Synthesis and characterization of copoly[1-alkyl-4- or 5-vinylimidazole/4(5)-vinylimidazole] and its catalytic activity in the hydrolysis of p-nitrophenyl acetate

The water-soluble monomers, 1-methyl-4-vinylimidazole, 1-methyl-5-vinylimidazole, 1-ethyl-5-vinylimidazole, and 1-propyl-5-vinylimidazole have been synthesized, polymerized, and copolymerized with 4(5)-vinylimidazole. The copolymers were characterized by ¹⁴C-labeling, NMR, pK_a determination and viscosity measurements. The monomer reactivity ratios determined by ¹⁴C counting are r₁ = 1.04; r₂ = 0.94 [M₁ = 4(5)-vinylimidazole, M₂ = 1-methyl-4-vinylimidazole] and r₁ = 1.01; r₂ = 0.86 [M₁ = 4(5)-vinylimidazole, M₂ = 1-methyl-5-vinylimidazole]. The esterolytic activity of the copolymers for the hydrolysis of p-nitrophenyl acetate (PNPA) at pH 7–8 in 28.5% ethanol–water was higher than that of the mixtures of homopolymers. At pH 5–6 the esterolytic activities of the copolymers and the mixtures were similar. The most efficient esterolytic activity for PNPA hydrolysis at pH 7.11 in 28.5% ethanol–water occurred for copolymers containing 75 mole % 4(5)-vinylimidazole and for copolymers containing 1-methyl-4-vinylimidazole rather than 1-methyl-5-vinylimidazole.     

Conformational study of methyl esters of some aliphatic erythro- and threo-dichlorocarboxylic acids

The average conformations of methyl esters of some aliphatic erythro- and threo-dichlorocarboxylic acids in dilute carbon tetrachloride solutions have been determined from the vicinal proton–proton coupling constants and ¹H NMR shifts. The ¹³C shift differences between the erythro and threo forms are compared and discussed with regard to the differences in the average conformations.     

Directed molecular recognition: furfurylamine appended ditopic receptor for succinic acid

A furfurylamine appended ditopic receptor (R1) for dicarboxylic acids has been designed and synthesised. The association constants (K_a) between receptors and dicarboxylic acids have been determined using UV–vis and NMR titration techniques. The binding constant (K_a) of succinic acid with R1 was observed maximum, which implies the optimum chain length selectivity for succinic acid. Theoretical calculation and molecular modelling using Gaussian 03 program also support the optimised receptor's cavity for succinic acid.     

Synthesis of periodic copolymers via ring‐opening copolymerizations of cyclic anhydrides with tetrahydrofuran using nonafluorobutanesulfonimide as an organic catalyst and subsequent transformation to aliphatic polyesters

To synthesize polyesters and periodic copolymers catalyzed by nonafluorobutanesulfonimide (Nf₂NH), we performed ring‐opening copolymerizations of cyclic anhydrides with tetrahydrofuran (THF) at 50–120 °C. At high temperature (100–120 °C), the cyclic anhydrides, such as succinic anhydride (SAn), glutaric anhydride (GAn), phthalic anhydride (PAn), maleic anhydride (MAn), and citraconic anhydride (CAn), copolymerized with THF via ring‐opening to produce polyesters (M_n = 0.8–6.8 × 10³, M_n/M_w = 2.03–3.51). Ether units were temporarily formed during this copolymerization and subsequently, the ether units were transformed into esters by chain transfer reaction, thus giving the corresponding polyester. On the other hand, at low temperature (25–50 °C), ring‐opening copolymerizations of the cyclic anhydrides with THF produced poly(ester‐ether) (M_n = 3.4–12.1 × 10³, M_w/M_n = 1.44–2.10). NMR and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectra revealed that when toluene (4 M) was used as a solvent, GAn reacted with THF (unit ratio: 1:2) to produce periodic copolymers (M_n = 5.9 × 10³, M_w/M_n = 2.10). We have also performed model reactions to delineate the mechanism by which periodic copolymers containing both ester and ether units were transformed into polyesters by raising the reaction temperature to 120 °C. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A comparative study of the stimuli‐responsive properties of DMAEA and DMAEMA containing polymers

Reversible addition‐fragmentation chain transfer copolymerization of dimethylaminoethyl acrylate (DMAEA) and methyl acrylate (MA) and their methacrylate counterparts (MMA) has been performed with good control over molecular weight and polydispersity. A screening in composition of copolymers has been performed from 0 to 75% of MA (or MMA). The behavior of these pH and temperature‐sensitive copolymers has been studied in aqueous solution by measuring the cloud point (CP) and the acid dissociation constants (pK_a). The higher incorporation of the hydrophobic monomer in the copolymer resulted in an increase in the pK_a values due to the larger distance between charges thus facilitating the protonation of adjacent nitrogens for both, the acrylate and methacrylate derivatives. The CP behavior of the copolymers has been studied in pure water and the CP values have been found to be irreproducible for the acrylate polymers, as a consequence of the self‐hydrolysis of DMAEA. Hence, kinetic studies have been performed to quantify the degree of self‐hydrolysis at different temperatures and polymer concentrations to explore the full potential and application of these versatile polymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3333–3338     

Binding of mucin to water-soluble and surface-grafted boronate-containing polymers

The binding of mucin to water-soluble copolymers of N,N-dimethylacrylamide and N-acryloyl-m-aminophenylboronic acid grafted on the surface of glass is studied. Atomic force microscopy studies show that many graft copolymer islands 20–200 nm in diameter and 50 nm in height occur on the modified surface of flat glass. Owing to the presence of phenyl boronate groups, the copolymer behaves as a weak polyelectrolyte (pK _a = 9.0) and, in the grafted state in an aqueous solution, experiences reversible transitions between states with higher and lower degrees of ionization. As evidenced by spectral correlation interferometry, this phenomenon brings about a change in the thickness of the grafted layer by approximately 0.5 nm. The ability of phenyl boronate groups to form cyclic esters with diol and polyol groups results in complexation of the soluble copolymer with mucin oligosaccharides and entails the appearance of slowly growing submicron particles formed by similarly charged polymers. The specificity of complexation is confirmed by dissolution of particles in the presence of fructose: a saccharide with a strong affinity for phenyl boronate groups. The binding of mucin to glass, which is chemically modified with the above copolymer, leads to formation of an adsorption layer with a thickness of 1.2–1.8 nm. Thus, boronate-containing copolymers are suitable for preparing carriers with controllable adsorption properties with respect to polyols, including mucinlike proteins of cellular glycocalyxes.