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Results are presented that demonstrate the successful preparation of ultrathin (<10 nm), surface-confined, molecularly imprinted polymer (MIP) films on model gold substrates using atom transfer radical polymerization (ATRP). 2-Vinylpyridine (2Vpy) was investigated as the functional monomer, and ethylene glycol dimethacrylate (EGDMA) was the cross-linking monomer. Fluorescently labeled N,N‘-didansyl-l-cystine and N,N‘-didansyl-l-lysine were used as the template molecules to form the MIPs. Spectroscopic and ellipsometric results are presented that follow film formation and growth rates. Results are also presented from fluorescence experiments used to quantify and compare the adsorption capacities of MIP surface films and nonimprinted (NIP) control films. MIP films exhibited higher binding capacities than the control NIP films at all solution concentrations of N,N‘-didansyl-l-cystine and N,N‘-didansyl-l-lysine. Furthermore, template removal from these imprinted films appears to be 100% efficient. Selectivity studies showed that the MIPs display some cross-reactivity between these two molecules; nevertheless, MIPs prepared against one template showed selectivity for that template. A selectivity coefficient of 1.13 was achieved for MIP surfaces prepared against N,N‘-didansyl-l-lysine; a value of 1.51 was observed for MIP surfaces prepared against N,N‘-didansyl-l-cystine.

This contribution describes experimental measurements of submolecular-level interaction energies involved in the process of peptide adsorption on polymer films. The objective of this study was to use surface plasmon resonance (SPR) spectroscopy to measure the Gibbs energy change on adsorption (ΔGad) for pairs of various homopeptides on highly uniform, nanothin polymer films and to use these data, along with the principle of additivity, to predict ΔGad for homologous homopeptides, as well as for a mixed-residue peptide. By using a graft polymerization methodology, a nanothin poly(2-vinylpyridine) film was prepared and adsorption energies were measured first for a homologous series of tyrosine (Y) homopeptides on this film to determine submolecular-level interaction energies. By using SPR, adsorption isotherms were measured for YY and YYY peptides; analysis of these isotherms provided ΔGad data for a midchain tyrosine unit and a set of chain-end tyrosine units; values were −0.75 ± 0.07 kcal/mol and −2.12 ± 0.04 kcal/mol, respectively. Combining the thermodynamic contributions for adsorption of individual tyrosine units allowed a predictive estimate of −5.12 ± 0.32 kcal/mol for the adsorption energy for YYYYYY; this estimate deviated by only 2.3% from its measured value of −5.24 ± 0.06 kcal/mol. Similarly, adsorption energies were found for phenylalanine, glycine, and tyrosine−leucine peptides. Combining the thermodynamic contributions for adsorption of individual residue units allowed a predictive estimate of −3.24 ± 0.38 kcal/mol for a pentapeptide, leucine enkephalin; this estimate deviated by only 3.0% from its measured value of −3.34 ± 0.11 kcal/mol.

This paper describes a methodology for preparing uniform, nanothin polymer films for the study of biomolecule adsorption by surface plasmon resonance spectroscopy (SPR). The methodology combines molecular self-assembly of alkanethiols on gold with surface-confined atom transfer radical polymerization (ATRP). Poly(2-vinylpyridine) was chosen to demonstrate the methodology, and growth kinetics were studied by ex situ ellipsometry. Atomic force microscopy (AFM) indicated that the polymer films were uniform with RMS roughness of ~0.5 nm. Subsequent SPR measurements were done to determine thermodynamic adsorption properties (ΔG, ΔH, and ΔS) between fibronectin adhesion-promoting peptide and the surface-confined poly(2-vinylpyridine) at 15, 20, and 25 °C. The flexibility in synthesis conditions and the opportunities for manipulating film thicknesses and graft densities that ATRP provides to grow polymer films from gold surfaces holds advantages over conventional spin-coating and grafting to approaches in the design of model polymer films for biomolecule adsorption studies. These advantages are described.

Experimental data are presented for batch and fixed-bed adsorption of lactic acid from aqueous sodium lactate solutions onto the tertiary amine sorbents, Dowex MWA-1 and Amberlite IRA-35, in the presence of carbon dioxide. The effects of carbon dioxide pressure and sodium lactate concentration on lactate uptake capacity were measured. A simple complexation model, which includes chemical-equilibria and mass- and charge-balance equations, was developed to describe the system. There are no fitted parameters in the model. The model predictions compare well with batch adsorption data.

Equilibria were measured for adsorption of carboxylic acids from aqueous, binary-acid mixtures of lactic and succinic acids and acetic and formic acids onto basic polymeric sorbents. The experimentally determined adsorption isotherms compared well with model predictions, confirming that simple extensions from adsorption of individual acids apply. Fixed-bed studies were carried out that establish the efficacy of chromatographic fractionation of lactic and succinic acids using basic polymeric sorbents. Finally, sequential thermal and solvent regeneration of lactic and acetic acid-laden sorbents was investigated as a method to fractionate among coadsorbed volatile and nonvolatile acids. Essentially complete removal of the acetic acid from the acid-laden sorbent was achieved by vaporization under the conditions used; a small amount of loss of lactic acid (about 11%) was observed.

Leaching with an organic solution of a volatile base was explored as a method of regenerating tertiary amine and pyridyl sorbents. Experimental data are presented that show that regeneration efficiency correlates with the nonaqueous basicity of the regenerant as measured by the Gutmann donicity scale. Essentially complete regeneration of lactic acid-laden Dowex MWA-1 was achieved when 8−10 mol of trimethylamine were present for every mole of adsorbed acid; adequate (>70%) regeneration was obtained at a 2:1 molar ratio. The resulting trimethylamine−lactic acid complex can be thermally decomposed fully when trimethylamine is employed in an organic solvent instead of in water. A likely cause of the incomplete thermal decomposition of trimethylammonium lactate in previous, water-based systems is the aqueous environment in which the decomposition was performed.