Vladimir A. Izumrudov

Abstract: We summarize existing knowledge and present some new results on the relationship between polyelectrolyte multilayer (PEM) growth and phase behavior of polyelectrolyte complexes (PECs) in solution. Detailed understanding of competition between surface and solution as applied to PEMs requires selective labeling of polymers and/or the application of techniques that allow chemically specific monitoring of film components, such as in-situ ATR−FTIR spectroscopy. The trends observed with multilayers directly follow from the properties of PECs in solution. Effects of a number of parameters, such as the type of interacting polyelectrolyte chains, the ratio of their lengths, and ionic strength and pH of deposition solutions, on the likelihood of the multilayer stability or erosion are considered. Polycations with high density of primary amino groups and polyanions with SO3- or SO4- groups show the strongest interpolyelectrolyte binding, resulting in inhibited chain exchange within PECs and/or PEMs. With weakly boun...

Abstract: Transfer of relatively short polycation chains (guest polyelectrolyte, GPE) from their poly-electrolyte complex (PEC) with a relatively long polyanion (host polyelectrolyte, HPE) to another polyanion of the same chemical structure and chain length but tagged with a fluorescent group has been investigated by the luminescence quenching technique. It has been shown that if only one polycation chain, on average, is transferred, the reaction follows irreversible second-order kinetics. The irreversibility of the reaction is due to additional selective nonelectrostatic interaction between the polycations and polynion chains, carrying pyrenyl groups

Abstract: The electrostatic binding of polycations with DNA·EB complex results in displacement of intercalated cationic dye ethidium bromide (EB) from DNA double helix to the solution which is accompanied by...

Abstract: Thin films obtained from a layer-by-layer deposition of a weak polycarboxylic acid and a positively charged globular protein were studied by in situ ATR-FTIR. The system was chicken egg lysozyme (Lys), bovine pancrease ribonuclease A (RNase), or bovine γ-globulin (IgG) self-assembled with polycarboxylic acids. When the pH value was lowered below a critical point, the growth of films and their tolerance to decomposition by added sodium chloride improved dramatically. Stabilization of protein/polyacid films in salt solutions at lower pH values occurred due to the onset of nonelectrostatic interactions to intermolecular binding within protein/polyacid multilayers and was controlled by polyacid ionization within the film rather than the pH of the external solution. A fractional ionization of polyacid in the pH-stabilization region was lower with protein-containing films than for polyacid/linear polycation films, reflecting hindrance of the inter-association of protonated carboxylic groups by protein globules....

Abstract: Complexation of plasmid DNA with polycations is a popular method by which to transfer therapeutic nucleic acid sequences to cells. One caveat of the approach is that the positive zeta potential of the complexes facilitates interaction with blood constituents, leading to serum protein adsorption and complement activation. As a countermeasure, investigators have developed polycations combined with polyethylene glycol (PEG) to create complexes with reduced protein adsorption potential. We have designed and synthesized PEG-polyhistidine conjugates to evaluate the material class as potential gene delivery vehicles. Two conjugate architectures (comb-shaped and linear A-B block copolymers) were synthesized and formulated with plasmid DNA. The complexes were characterized with respect to DNA complexation capacity, hydrodynamic diameter, zeta potential, in vitro cytotoxicity and transfection capacity in a model cell line. PEG content of the conjugate significantly influenced the hydrodynamic diameter of the DNA:conjugate composite in aqueous solution. For comb-shaped conjugates steric hindrance attributed to PEG led to a direct relationship between the PEG content and the complex size. Both architectures could condensed plasmid DNA into complexes with hydrodynamic diameters <150 nm. Complexation of DNA with the polyhistidine-PEG conjugates resulted in nanocomposites with negative zeta potentials that retarded DNase I-mediated hydrolysis, and all conjugates showed low cytotoxicity to macrophages cultured in vitro. The transfection efficiency was approximately equivalent to DNA:polylysine complexes. The formulation characteristics and low cytotoxicity suggest that polyhistidine-PEG conjugates may be useful for gene delivery.

Abstract: Stimuli-responsive polymers show a sharp change in properties upon a small or modest change in environmental condition, e.g. temperature, light, salt concentration or pH. This behaviour can be utilised for the preparation of so-called 'smart' drug delivery systems, which mimic biological response behaviour to a certain extent. The possible environmental conditions to use for this purpose are limited due to the biomedical setting of drug delivery as application. Different organs, tissues and cellular compartments may have large differences in pH, which makes the pH a suitable stimulus. Therefore the majority of examples, discussed in this paper, deal with pH-responsive drug delivery system. Thermo-responsive polymer is also covered to a large extent, as well as double-responsive system. The physico-chemical behaviour underlying the phase transition will be discussed in brief. Then selected examples of applications are described.

Abstract: A review was presented to demonstrate a historical description of the synthesis of light-emitting conjugated polymers for applications in electroluminescent devices. Electroluminescence (EL) was first reported in poly(para-phenylene vinylene) (PPV) in 1990 and researchers continued to make significant efforts to develop conjugated materials as the active units in light-emitting devices (LED) to be used in display applications. Conjugated oligomers were used as luminescent materials and as models for conjugated polymers in the review. Oligomers were used to demonstrate a structure and property relationship to determine a key polymer property or to demonstrate a technique that was to be applied to polymers. The review focused on demonstrating the way polymer structures were made and the way their properties were controlled by intelligent and rational and synthetic design.

Abstract: The design of advanced, nanostructured materials at the molecular level is of tremendous interest for the scientific and engineering communities because of the broad application of these materials in the biomedical field. Among the available techniques, the layer-by-layer assembly method introduced by Decher and co-workers in 1992 has attracted extensive attention because it possesses extraordinary advantages for biomedical applications: ease of preparation, versatility, capability of incorporating high loadings of different types of biomolecules in the films, fine control over the materials’ structure, and robustness of the products under ambient and physiological conditions. In this context, a systematic review of current research on biomedical applications of layer-by-layer assembly is presented. The structure and bioactivity of biomolecules in thin films fabricated by layer-by-layer assembly are introduced. The applications of layer-bylayer assembly in biomimetics, biosensors, drug delivery, protein and cell adhesion, mediation of cellular functions, and implantable materials are addressed. Future developments in the field of biomedical applications of layer-by-layer assembly are also discussed.

Abstract: The layer-by-layer (LbL) adsorption technique offers an easy and inexpensive process for multilayer formation and allows a variety of materials to be incorporated within the film structures. Therefore, the LbL assembly method can be regarded as a versatile bottom-up nanofabrication technique. Research fields concerned with LbL assembly have developed rapidly but some important physicochemical aspects remain uninvestigated. In this review, we will introduce several examples from physicochemical investigations regarding the basics of this method to advanced research aimed at practical applications. These are selected mostly from recent reports and should stimulate many physical chemists and chemical physicists in the further development of LbL assembly. In order to further understand the mechanism of the LbL assembly process, theoretical work, including thermodynamics calculations, has been conducted. Additionally, the use of molecular dynamics simulation has been proposed. Recently, many kinds of physicochemical molecular interactions, including hydrogen bonding, charge transfer interactions, and stereo-complex formation, have been used. The combination of the LbL method with other fabrication techniques such as spin-coating, spraying, and photolithography has also been extensively researched. These improvements have enabled preparation of LbL films composed of various materials contained in well-designed nanostructures. The resulting structures can be used to investigate basic physicochemical phenomena where relative distances between interacting groups is of great importance. Similarly, LbL structures prepared by such advanced techniques are used widely for development of functional systems for physical applications from photovoltaic devices and field effect transistors to biochemical applications including nano-sized reactors and drug delivery systems.

Abstract: Chemistries that Facilitate Nanotechnology Kim E. Sapsford,† W. Russ Algar, Lorenzo Berti, Kelly Boeneman Gemmill,‡ Brendan J. Casey,† Eunkeu Oh, Michael H. Stewart, and Igor L. Medintz*,‡ †Division of Biology, Department of Chemistry and Materials Science, Office of Science and Engineering Laboratories, U.S. Food and Drug Administration, Silver Spring, Maryland 20993, United States ‡Center for Bio/Molecular Science and Engineering Code 6900 and Division of Optical Sciences Code 5611, U.S. Naval Research Laboratory, Washington, D.C. 20375, United States College of Science, George Mason University, 4400 University Drive, Fairfax, Virginia 22030, United States Department of Biochemistry and Molecular Medicine, University of California, Davis, School of Medicine, Sacramento, California 95817, United States Sotera Defense Solutions, Crofton, Maryland 21114, United States