Paul L. Dubin

Macromolecular complexes in chemistry and biology

I. Hydrophobically Associating Polymers.- 1 Synthesis and Characterization of Hydrophobically Associating Water-Soluble Polymers.- 1.1 Introduction.- 1.2 Synthesis.- 1.3 Copolymerization.- 1.4 Postpolymerization Modification.- 1.5 Characterization-Hydrophobe Incorporation.- 1.6 Summary.- 1.7 References.- 2 Analysis of Hydrophobically Associating Copolymers Utilizing Spectroscopic Probes and Labels.- 2.1 Introduction.- 2.2 Emission Probes and Labels.- 2.3 Absorption Probes.- 2.4 Concluding Remarks.- 2.5 References.- 3 Solution Properties of Hydrophobically Associating Water-Soluble Polymers.- 3.1 Introduction.- 3.2 Polymer Systems.- 3.3 Solubility Characteristics.- 3.4 Solution Stability.- 3.5 Solution Rheological Properties.- 3.6 Summary.- 3.7 References.- 4 Aggregation of Hydrophobically Modified Polyelectrolytes in Dilute Solution: Tonic Strength Effects.- 4.1 Introduction.- 4.2 Experimental.- 4.3 The Polymers.- 4.4 Dilute Solution Viscosity.- 4.5 Fluorescence Spectroscopy.- 4.6 Intrinsic Viscosity.- 4.7 Concluding Remarks.- 4.8 References.- 5 Microdomain Composition in Two-Phase Hydrogels.- 5.1 Introduction.- 5.2 Background.- 5.2.1 Microphase Separation in Polymers.- 5.2.2 Importance of Graft Polymers.- 5.3 Results.- 5.3.1 Hydrogels from Surfactant Solutions.- 5.3.2 Hydrogels from Ethanol/Water Solutions.- 5.3.3 Solute Uptake by Gels.- 5.4 Conclusions.- 5.5 References.- 6 Molecular Association and Polymerization of 1-Alkyl-4-vinylpyridinium Ions.- 6.1 Complexation in 1-Alkyl-4-vinylpyridinium Ions and Related Polymers.- 6.2 Homopolymerization of 1-Alkyl-4-vinylpyridinium Ions.- 6.3 Copolymerization of 1-Alkyl-4-vinylpyridinium Ions.- 6.4 Conclusion.- 6.5 References.- 7 Fluorocarbon-Modified Water Soluble Polymers.- 7.1 Introduction.- 7.2 Experimental.- 7.3 Results and Discussion.- 7.4 Conclusions.- 7.5 References.- II. Polyelectrolyte Complexes.- 8 Static Light Scattering of Polyelectrolyte Complex Solutions.- 8.1 Introduction.- 8.2 Survey of Static Light Scattering Studies on PEC Solutions.- 8.3 Interpretation of Light Scattering Experiments.- 8.4 Experimental.- 8.4.1 Materials.- 8.4.2 Methods of Investigation.- 8.5 Results and Discussion.- 8.6 Conclusion.- 8.7 References.- 9 Interaction Between Oppositely Charged Low Ionic Density Polyelectrolytes: Complex Formation or Simple Mixture?.- 9.1 Introduction.- 9.2 Material and Techniques.- 9.2.1 Polymer Synthesis.- 9.2.2 Polymer Characterization.- 9.2.3 Other Techniques.- 9.3 Phase Diagram.- 9.3.1 Phase Diagram Representation.- 9.3.2 Influence of the Charge Density.- 9.3.3 Influence of the Ionic Strength.- 9.3.4 Influence of the Molecular Weight of the Samples.- 9.3.5 Phase Diagram and Complex Formation.- 9.4 Polymer-Polymer Affinity and Phase Diagram.- 9.5 Conclusion.- 9.6 References.- 10 Basic Properties of Soluble Interpolyelectrolyte Complexes Applied to Bioengineering and Cell Transformations.- 10.1 Introduction.- 10.2 Kinetic and Equilibrium Properties of Interpolyelectrolyte Complexes.- 10.3 Interpolyelectrolyte Complexes as Protein Carriers.- 10.4 Complexes of DNA with Synthetic Polycations for Cell Transformation.- 10.5 Conclusion.- 10.6 References.- 11 Conformation Presumption for Polysaccharide-Polylysine Complexation.- 11.1 Introduction.- 11.2 Complex Formation.- 11.3 Pectate-Polylysine Interaction.- 11.4 Polyguluronate Rich Alginate-Polylysine Interaction.- 11.5 Polymannuronate Rich Alginate-Polylysine Interaction.- 11.6 Conclusion.- 11.7 References.- 12 Interpolymer Complexes and their Ion-Conduction.- 12.1 Introduction.- 12.2 Classification of Interpolymer Complexes.- 12.3 Formation of Interpolymer Complexes from PAA with POE.- 12.4 Thermodynamics of Interpolymer Complexes from PAA (or PMMA) with POE.- 12.5 Selective and Substitution Interpolymer Complexation.- 12.6 Solid Properties of a Hydrogen-Bonding Complex.- 12.7 Ion Conduction and Solid Polymer Electrolytes.- 12.8 Ion Conduction of Hydrogen-Bonding Complexes.- 12.9 References.- 13 Fluorescence Probe Studies of Poly(acrylic acid) Interchain Complexation Induced by High Shear Flow and Influence of Cationic Surfactants on the Complexation.- 13.1 Introduction.- 13.2 Experimental.- 13.2.1 Materials.- 13.2.2 Flow Processing.- 13.2.3 Fluorescence Measurements.- 13.3 Results and Discussion.- 13.3.1 Drag Reduction (DR) and PAA Conformation.- 13.3.2 Local Chain Rigidity.- 13.3.3 Hydrophobic Association.- 13.3.4 Hydrophobe-Assisted Rigidity.- 13.4 References.- III. Biopolymer Systems.- 14 Water-Soluble Biospecific Polymers for New Affinity Purification Techniques.- 14.1 Introduction.- 14.2 Discrimination on the Basis of High Molecular Weight.- 14.2.1 Biospecific Ultrafiltration.- 14.2.2 Biospecific Gel Filtration.- 14.3 Discrimination on the Basis of High Density of Charges: Affinophoresis.- 14.4 Discrimination on the Basis of Surface Tension Properties: Affinity Partition.- 14.5 Discrimination on the Basis of Reversible Solubility: Affinity Precipitation.- 14.6 Advantages and Drawbacks of Techniques Involving Water-Soluble Biospecific Polymers.- 14.7 References.- 15 Protein-Polyelectrolyte Complexes.- 15.1 Introduction.- 15.2 Investigation Methods.- 15.3 Factors Influencing Protein-Polyelectrolyte Complexation and Structures of the Protein-Polyelectrolyte Complexes.- 15.4 Protein Separation by Polyelectrolytes.- 15.5 Enzymes in Polyelectrolyte Complexes.- 15.6 Conclusion.- 15.7 References.- 16 Precipitation of Proteins with Polyelectrolytes: Role of Polymer Molecular Weight.- 16.1 Introduction.- 16.2 Materials and Methods.- 16.3 Results and Discussion.- 16.4 Conclusions.- 16.5 References.- 17 Complex Coacervation: Micro-Capsule Formation.- 17.1 Introduction and Terminology.- 17.2 Simple Coacervation.- 17.3 Complex Coacervation.- 17.4 Theory of Complex Coacervation.- 17.5 Coacervation as a Method of Microencapsulation.- 17.6 Materials and Methods.- 17.7 Results.- 17.8 Conclusions.- 17.9 References.- 18 Complexation of Proteins with Polyelectrolytes in a Salt-Free System and Biochemical Characteristics of the Resulting Complexes.- 18.1 Introduction.- 18.2 Experimental Section.- 18.3 Results and Discussion.- 18.4 Conclusions and Topics for Future Research.- 18.5 References.- IV. Ionomers in Solution.- 19 Ionomer Solutions: Polyelectrolyte or Ionomer behavior.- 19.1 Introduction.- 19.2 Sulfonated Polystyrene Ionomer Solutions in Nonpolar Solvents.- 19.3 Sulfonated Polystyrene Ionomer Solutions in Polar Solvents.- 19.4 Perfluorinated Ionomer Solutions.- 19.5 Conclusion.- 19.6 References.- 20 Scattering Studies of Ionomer Aggregates in Nonpolar Solvents.- 20.1 Introduction.- 20.2 Experimental.- 20.3 Light Scattering Analysis.- 20.4 Results and Discussion.- 20.5 References.

Complexation and coacervation of polyelectrolytes with oppositely charged colloids.

Polyelectrolyte-colloid coacervation could be viewed as a sub-category of complex coacervation, but is unique in (1) retaining the structure and properties of the colloid, and (2) reducing the heterogeneity and configurational complexity of polyelectrolyte-polyelectrolyte (PE-PE) systems. Interest in protein-polyelectrolyte coacervates arises from preservation of biofunctionality; in addition, the geometric and charge isotropy of micelles allows for better comparison with theory, taking into account the central role of colloid charge density. In the context of these two systems, we describe critical conditions for complex formation and for coacervation with regard to colloid and polyelectrolyte charge densities, ionic strength, PE molecular weight (MW), and stoichiometry; and effects of temperature and shear, which are unique to the PE-micelle systems. The coacervation process is discussed in terms of theoretical treatments and models, as supported by experimental findings. We point out how soluble aggregates, subject to various equilibria and disproportionation effects, can self-assemble leading to heterogeneity in macroscopically homogeneous coacervates, on multiple length scales.

Protein-polyelectrolyte interactions

The interactions of proteins and polyelectrolytes lead to diverse applications in separations, delivery and wound repair, and are thus of interest to scientists in e.g. (a) glycobiology, (b) tissue engineering, (c) biosensing, and (d) pharmacology. This breadth is accompanied by an assortment of contexts and models in which polyelectrolytes are seen as (a) protein cognates assisting in complex cellular roles, (b) surrogates for the extracellular matrix, mimicking its hydration, mechanical and sequestering properties, (c) benign hosts that gently entrap, deposit and tether protein substrate specificity, and (d) selective but non-specific agents that modify protein solubility. Unsurprisingly, this literature is somewhat segregated by objectives and paradigms. We hope this review, which emphasizes publications over the last 8 years, represents and also counterbalances that divergence. An ongoing theme is the role of electrostatics, and we show how this leads to the variety of physical forms taken by protein–polyelectrolyte complexes. We present approaches towards analysis and characterization, motivated by the goal of structure–property elucidation. Such understanding should guide in applications, our third topic. We present recent developments in modeling and simulations of protein–polyelectrolyte systems. We close with a prospective on future developments in this field.

Protein Purification by Selective Phase Separation with Polyelectrolytes

Abstract Proteins phase separate in the presence of synthetic polyelectrolytes as a consequence of electrostatic interactions. This phenomenon may form the basis of protein separations and has therefore been of technological interest. In this review, we consider previous reports of such phase separation, and attempt to describe the effects of various relevant factors, such as polymer MW, ionic strength, and macromolecular concentration. Models for protein-polyelectrolyte complexation are discussed. Current challenges and problems are noted.

Protein-Polyelectrolyte Complexes

Proteins interact strongly with both synthetic and natural polyelectrolytes. Ample evidence exists for the binding of polyanions and polycations to proteins below and above their isoelectric points, respectively. These interactions may result in soluble complexes [1,2], complex coacervation [3–6], or the formation of amorphous precipitates [7–9]. The practical consequences of these phase changes may include the use of polyelectrolytes for protein separation [10–16] and immobilization or stabilization of enzymes in polyelectrolyte complexes [17–18]. In these two applications, the optimal physical states of the system are different. In the case of enzyme immobilization, highly deaggregated states may be less active. In purification or separation processes involving settling or filtration, aggregation is desirable. For efficient settling, close-packed aggregates are preferred, whereas in filtration processes more open-textured aggregates are needed to allow adequate solvent penetration. However, in both cases the aggregation should be essentially reversible.

Measurement of the Binding of Proteins to Polyelectrolytes by Frontal Analysis Continuous Capillary Electrophoresis

We have developed a novel technique, frontal analysis continuous capillary electrophoresis (FACCE), to study the binding of proteins to polyelectrolytes. Compared with existing electrophoresis methods such as conventional frontal analysis and the Hummel-Dreyer method, FACCE offers enhanced lower detection limits and is free from effects due to slow binding kinetics, thus making it suitable for studying equilibrium systems. In addition, with a single calibration, FACCE provides for efficient quantitative analysis. Here we report results obtained with β-lactoglobulin as the ligand and sodium poly(styrenesulfonate) (NaPSS) as the ligand-binding substrate. For this model system, FACCE yields reproducible calibration curves and binding isotherms. The binding parameters so determined are compared with previous results for other protein-polyelectrolyte systems.

Electrostatic selectivity in protein-nanoparticle interactions.

The binding of bovine serum albumin (BSA) and β-lactoglobulin (BLG) to TTMA (a cationic gold nanoparticle coupled to 3,6,9,12-tetraoxatricosan-1-aminium, 23-mercapto-N,N,N-trimethyl) was studied by high-resolution turbidimetry (to observe a critical pH for binding), dynamic light scattering (to monitor particle growth), and isothermal titration calorimetry (to measure binding energetics), all as a function of pH and ionic strength. Distinctively higher affinities observed for BLG versus BSA, despite the lower pI of the latter, were explained in terms of their different charge anisotropies, namely, the negative charge patch of BLG. To confirm this effect, we studied two isoforms of BLG that differ in only two amino acids. Significantly stronger binding to BLGA could be attributed to the presence of the additional aspartates in the negative charge domain for the BLG dimer, best portrayed in DelPhi. This selectivity decreases at low ionic strength, at which both isoforms bind well below pI. Selectivity increases with ionic strength for BLG versus BSA, which binds above pI. This result points to the diminished role of long-range repulsions for binding above pI. Dynamic light scattering reveals a tendency for higher-order aggregation for TTMA-BSA at pH above the pI of BSA, due to its ability to bridge nanoparticles. In contrast, soluble BLG-TTMA complexes were stable over a range of pH because the charge anisotropy of this protein at makes it unable to bridge nanoparticles. Finally, isothermal titration calorimetry shows endoenthalpic binding for all proteins: the higher affinity of TTMA for BLGA versus BLGB comes from a difference in the dominant entropy term.

Entering and Exiting the Protein-Polyelectrolyte Coacervate Phase via Nonmonotonic Salt Dependence of Critical Conditions

Critical conditions for coacervation of poly(dimethyldiallylammonium chloride) (PDADMAC) with bovine serum albumin were determined as a function of ionic strength, pH, and protein/polyelectrolyte stoichiometry. The resultant phase boundaries, clearly defined with this narrow molecular weight distribution PDADMAC sample, showed nonmonotonic ionic strength dependence, with the pH-induced onset of coacervation (at pH(phi)) occurring most readily at 20 mM NaCl. The corresponding onset of soluble complex formation, pH(c), determined using high-precision turbidimetry sensitive to changes of less than 0.1% transmittance units, mirrored the ionic strength dependence of pH(phi). This nonmonotonic binding behavior is attributable to simultaneous screening of short-range attraction and long-range repulsion. The similarity of pH(c) and pH(phi) was explained by the effect of salt on protein binding, and consequently on the number of bound proteins relative to that required for charge neutralization of the complex, a requirement for phase separation. Expansion of the coacervation regime with chitosan, a polycation with charge spacing similar to that of PDADMAC, could be due to either the charge mobility or chain stiffness of the former. The pH(phi) versus I phase boundary for PDADMAC correctly predicted entrance into and egress from the coacervation region by addition of either salt or water. The ability to induce or suppress coacervation via protein/polyelectrolyte stoichiometry r was found to be consistent with the proposed model. The results indicate that the conjoint effects of I, r, and pH on coacervation could be represented by a three-dimensional phase boundary.

Selective Interaction Between Proteins and the Outermost Surface of Polyelectrolyte Multilayers: Influence of the Polyanion Type, pH and Salt

Protein adsorption was studied by in-situ ATR-FT-IR spectroscopy of consecutively deposited polyelectrolyte multilayer systems terminated either with poly(ethyleneimine) (PEI) or polyanions, such as poly-(acrylic acid) (PAC), poly(maleic acid-co-propylene) (PMA-P) or poly(vinyl sulfate) (PVS). The influence of the polyanion type, pH and ionic strength was investigated. Negatively charged human serum albumin (HSA) was strongly repelled by multilayers terminated with weak polyanions (PAC, PMA-P), whereas moderate attraction was observed for those terminated with the strong polyanion PVS. Changing the pH from 7.4 to 5 resulted in enhanced HSA adsorption onto PAC-terminated multilayers. An increase in ionic strength diminished the attractive HSA adsorption onto PEI-terminated multilayers. For the PEI/PAC system, the biomedically relevant adsorption of human fibrinogen (FGN) is determined via its isoelectric point in accordance with three other proteins.

The effect of cations on the interaction between dodecylsulfate micelles and poly(ethyleneoxide)

Abstract The effect of the micelle counterion on the interaction of poly (ethyleneoxide) with dodecylsulfate micelles has been studied, using dye solubilization to determine the critical micelle concentration and dynamic light scattering to measure the relative amount of uncomplexed micelles. In the presence of 0.10- M Na + , Li + , and NH 4 + , the CMC-lowering effect of the polymer is strongly dependent on the nature of the cation. A parallel influence of the cation is seen in the distribution of scattering intensities between well-defined modes corresponding to free micelle and complex. These results are taken as evidence for a direct role of the cation in the stabilization of the complex, in which the cation interacts simultaneously with the micelle (through electrostatic forces) and with the polymer (via coordination complexation). This type of association may occur simultaneously with other interaction forces.