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PubMed2000

Founder's Award, Society for Biomaterials. Sixth World Biomaterials Congress 2000, Kamuela, HI,May 15-20, 2000. Really smart bioconjugates of smart polymers and receptor proteins.

Over the past 18 years we have been deeply involved with the synthesis and applications of stimuli-responsive polymer systems, especially polymer-biomolecule conjugates. This article summarizes our work with one of these conjugate systems, specifically polymer-protein conjugates. We include conjugates prepared by random polymer conjugation to lysine amino groups, and also those prepared by site-specific conjugation of the polymer to specific amino acid sites that are genetically engineered into the known amino acid sequence of the protein. We describe the preparation and properties of thermally sensitive random conjugates to enzymes and several affinity recognition proteins. We have also prepared site-specific conjugates to streptavidin with temperature-sensitive polymers, pH-sensitive polymers, and light-sensitive polymers. The preparation of these conjugates and their many fascinating applications are reviewed in this article.

Acrylamides↗

PubMed1991

Zinc ion-DNA polymer interactions.

The adjacent GN7-M-GN7 cross-linking and adjacent G-M-G sandwich-complex models for DNA metal ion binding were evaluated both with native DNAs differing in GC content as well as with the synthetic polymers poly [(dGdC)]2, poly[(dAdT)]2, and poly[(dAdC)(dGdT)]. The effect of Zn2+ was studied in depth, and limited studies were also performed with Co2+ and Mg2+. The results were compared to the extensive information available on Cu2+ binding to native DNAs and poly[(dAdT)]2. At high ratios of metal/base (R), Zn2+ caused all native DNAs to denature with the same melting temperature Tm, approximately 61 degrees C. A similar pattern was reported previously for Cu2+, but the typical Tm was approximately 35 degrees C. The extent of renaturation on cooling DNAs denatured in the presence of Zn2+ increased with GC content, as reported previously for Cu2+. These results, together with previously reported similarities, strongly indicate that the DNA binding characteristics of the two cations are similar. By comparison of the Tm values and hyperchromicity changes monitored at 260 and 282 nm, it is clear that, during thermal denaturation in the presence of Zn2+, both AT and GC regions were denatured, even at high R. The Tm vs R profile for the native DNAs was typical. The rise at low R and subsequent decrease at high R were inversely and directly related, respectively, to GC content. Except for poly[(dAdT)]2, where Tm increased with R, the other synthetic polymers exhibited the increase/decrease pattern. Poly[(dAdC)(dGdT)] gave a Tm value at high R of 54 degrees C. In the absence of Zn2+, this polymer exhibited little hypochromicity on cooling of denatured polymer. However, in the presence of Zn2+, nearly complete hypochromicity was observed, although the midpoint of the cooling curve was lower than the Tm value by approximately 15 degrees C at R = 10. These characteristics were similar to those with native DNAs, although viscosity and CD studies suggested that the "renatured" polymer was not identical to the unheated polymer. Furthermore, addition of Zn2+ after denaturation nearly completely reversed the absorption increase. This finding contrasts with those for native DNAs, where the Zn2+ must be present during denaturation in order to reverse the absorption increase nearly completely on cooling. With some caveats, poly[(dAdC)(dGdT)] appears to be a good model for native DNAs since its properties, including CD and uv changes on addition of Zn2+ to premelted and melted polymer, parallel those of the native polymers.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2001

Engineering temperature-sensitive poly(N-isopropylacrylamide) polymers as carriers of therapeutic proteins.

This study was carried out to engineer N-isopropylacrylamide (NiPAM) polymers that contain protein-reactive N-acryloxysuccinimide (NASI) and hydrophobic alkylmethacrylates (AMAs). These thermoreversible, protein-conjugating polymers hold potential for retention of therapeutic proteins at an application site where tissue regeneration is desired. The lower critical solution temperatures (LCST) of the polymers were effectively controlled by the AMA mole content. The AMAs with longer side-chains were more effective in lowering the LCST. Polymers without NASI exhibited a stable LCST in phosphate buffer and in serum over a 10-day study period. The LCST of polymers containing NASI was found to increase over time in phosphate buffer, but not in serum-containing medium. The LCST increase in phosphate buffer was proportional to the AMA content. The feasibility of localizing a therapeutic protein, recombinant human bone morphogenetic protein-2 (rhBMP-2), to a site of application was explored in a rat intramuscular injection model. The results indicated that polymers capable of conjugating to rhBMP-2 were most effective in localizing the protein irrespective of the LCST (13-25 degrees C). For polymers with no NASI groups, a lower LCST resulted in a better rhBMP-2 localization. We conclude that thermosensitive polymers can be engineered for delivery of therapeutic proteins to improve their therapeutic efficacy.

Acrylic Resins↗

PubMed1989

Plasma protein adsorbed biomedical polymers: activation of human monocytes and induction of interleukin 1.

These studies involved the evaluation of human monocyte/macrophage activation by biomedical polymers coated with human blood proteins. The biomedical polymers were polyethylene, polydimethylsiloxane, woven Dacron fabric, expanded polytetrafluoroethylene, Biomer, and tissue culture treated polystyrene as the control. They were adsorbed with human blood proteins: albumin, fibrinogen, fibronectin, hemoglobin, and gamma globulin. The protein adsorbed polymers were evaluated for their potential to activate the monocyte/macrophage cellular population in vitro as assessed by the induction of the monocyte/macrophage inflammatory mediator, Interleukin 1 (IL1). Suppression of IL1 was observed when protein adsorbed polymers were compared to the appropriate protein adsorbed control. Protein adsorbed polymers, when compared to polymers without protein adsorption, stimulated IL1 production. The data presented in this manuscript show the level of induction and secretion of IL1 was dependent on the biomedical polymer and the protein adsorbed, as well as the requirement of lipopolysaccharide. These results show differential interactions occur between the proteins, monocytes/macrophages, and biomedical polymers which alter activation and induction of IL1.

Animals↗

PubMed2005

Effect of polymer size and cosolutes on phase separation of poly(vinylpyrrolidone) (PVP) and dextran in frozen solutions.

The aim of this study was to elucidate the effect of the molecular weight of polymers on their miscibility in frozen solutions to model the physical properties of freeze-dried pharmaceutical formulations. Thermal analysis of frozen solutions containing poly(vinylpyrrolidone) (PVP) and dextran of various molecular weights was performed at polymer concentrations below the binodal curve at room temperature. Frozen solutions containing PVP 29,000 and dextran 10,200 showed two thermal transitions (glass transition temperature of maximally freeze-concentrated solution: Tg') representing two freeze-concentrated amorphous phases, each containing predominantly one of the polymers. A combination of smaller polymers (PVP 10,000 and dextran 1,060) was freeze-concentrated into an amorphous mixture phase across a wide range of concentration ratios. Combinations of intermediate size polymers separated into two freeze-concentrated phases only at certain concentration ratios. Addition of NaCl prevented the phase separation of PVP and dextran in the aqueous and frozen solutions. Higher concentrations of NaCl were required to retain the miscibility of larger polymer combinations in the freeze-concentrate. The molecular weights of the component polymers, polymer concentration ratio, and cosolute composition are the important factors that determine component miscibility in frozen solutions.

Calorimetry, Differential Scanning↗

PubMedDate not supplied

Exploring the structure of a hydrogen cyanide polymer by electron spin resonance and scanning force microscopy.

Aqueous solutions of potassium cyanide and ammonium hydroxide are known to yield a heterogeneous cyanide polymer, containing paramagnetic sites and biologically significant substructures including polypeptides. Here, such solutions were used to prepare various samples of polymer for study by X-band and W-band electron spin resonance (ESR), scanning electron microscopy (SEM), and scanning force microscopy (SFM). Elemental composition of a typical sample of the polymer was C-35.2%, N-38.47%, 0-14.51%, and H-4.13%, exposing the polymer to 6M HCl hydrolyzed portions of the polymer and released glycine and traces of other amino acids. The X-band ESR spectra consist of a single slightly asymmetric line centered at g = 2.003; spin concentration measurements made at X-band using a nitroxide radical standard yield approximate radical concentrations of 10(18) spins/gm. W-band ESR indicates the presence of a single rhombic paramagnetic site with g(x) = 2.0025, g(y) = 2.0030, and g(z) = 2.0048 and the possibility of small 14N hyperfine splittings. The ESR spin echo studies yield a longitudinal relaxation time, Tl of 75 microS and a short-phase memory relaxation time, Tm, of about 300 nS. Scanning electron microscopy studies of the polymer show that it is made of ellipsoidal particles about one micron in size. The particles tend to clump together when suspended in aqueous solution. The particles disperse and dissolve in dimethyl sulfoxide (DMSO); when these solutions dry on microscope slides, optical microscopy shows a branched island morphology for the polymer. This morphology is reminiscent of snowflakes and is identified as dendritic. Phase contrast SFM of the dendritic arms show a striking segregation and ordering of various components of the polymer. Paramagnetic sites are conserved in the series of steps leading to dendritic structures.

Journal Article↗

PubMed2004

FI catalysts: new olefin polymerization catalysts for the creation of value-added polymers.

This contribution reports the discovery and application of phenoxy-imine-based catalysts for olefin polymerization. Ligand-oriented catalyst design research has led to the discovery of remarkably active ethylene polymerization catalysts (FI Catalysts), which are based on electronically flexible phenoxy-imine chelate ligands combined with early transition metals. Upon activation with appropriate cocatalysts, FI Catalysts can exhibit unique polymerization catalysis (e.g., precise control of product molecular weights, highly isospecific and syndiospecific propylene polymerization, regio-irregular polymerization of higher alpha-olefins, highly controlled living polymerization of both ethylene and propylene at elevated temperatures, and precise control over polymer morphology) and thus provide extraordinary opportunities for the syntheses of value-added polymers with distinctive architectural characteristics. Many of the polymers that are available via the use of FI Catalysts were previously inaccessible through other means of polymerization. For example, FI Catalysts can form vinyl-terminated low molecular weight polyethylenes, ultra-high molecular weight amorphous ethylene-propylene copolymers and atactic polypropylenes, highly isotactic and syndiotactic polypropylenes with exceptionally high peak melting temperatures, well-defined and controlled multimodal polyethylenes, and high molecular weight regio-irregular poly(higher alpha-olefin)s. In addition, FI Catalysts combined with MgCl(2)-based compounds can produce polymers that exhibit desirable morphological features (e.g., very high bulk density polyethylenes and highly controlled particle-size polyethylenes) that are difficult to obtain with conventionally supported catalysts. In addition, FI Catalysts are capable of creating a large variety of living-polymerization-based polymers, including terminally functionalized polymers and block copolymers from ethylene, propylene, and higher alpha-olefins. Furthermore, some of the FI Catalysts can furnish living-polymerization-based polymers catalytically by combination with appropriate chain transfer agents. Therefore, the development of FI Catalysts has enabled some crucial advances in the fields of polymerization catalysis and polymer syntheses.

Journal Article↗

PubMed1998

Sorption Isotherms of Gases by Polymer Membranes in the Glassy State: An Explanation Based on the Nonequilibrium Thermodynamics.

Sorption isotherms of glassy polymers are concave to the pressure axis, and the absolute sorption levels are almost an order of magnitude higher than that of rubbery polymers on the relatively low-pressure side. There are several models to interpret this behavior, and the dual sorption model is the most widely accepted one among them. In the present work, sorption isotherms were first derived from permeation data with several gases for four polymer membranes which might be representative of the dual sorption model: two of them were in a glassy state (cellulose acetate and polyamide), the third one was a block copolymer which was composed of a glassy polymer and a rubbery polymer at the measuring temperature, and the fourth one was a Nafion membrane which was taken as a model membrane because of its channel structure with adsorption sites of charged groups supported by a rubbery polymer. These results did not necessarily support the dual sorption model. Subsequently, the validity of the underlying assumptions of two other sorption models for glassy polymers, that is, the matrix model and the deformation model, were examined and a new equation for the sorption isotherm with an ordering parameter was derived, which implied that the glassy polymer was in a nonequilibrium state and changed from the glassy to the rubbery state by absorbing the gas. Copyright 1998 Academic Press.

Journal Article↗

PubMed1999

Motion of a Colloidal Sphere Covered by a Layer of Adsorbed Polymers Normal to a Plane Surface.

A combined analytical-numerical study is presented for the slow motion of a spherical particle coated with a layer of adsorbed polymers perpendicular to an infinite plane, which can be either a solid wall or a free surface. The Reynolds number is assumed to be vanishingly small, and the thickness of the surface polymer layer is assumed to be much smaller than the particle radius and the spacing between the particle and the plane boundary. A method of matched asymptotic expansions in a small parameter lambda incorporated with a boundary collocation technique is used to solve the creeping flow equations inside and outside the adsorbed polymer layer, where lambda is the ratio of the characteristic thickness of the polymer layer to the particle radius. The results for the hydrodynamic force exerted on the particle in a resistance problem and for the particle velocity in a mobility problem are expressed in terms of the effective hydrodynamic thickness (L) of the polymer layer, which is accurate to O(lambda2). The O(lambda) term for L normalized by its value in the absence of the plane boundary is found to be independent of the polymer segment distribution and the volume fraction of the segments. The O(lambda2) term for L, however, is a sensitive function of the polymer segment distribution and the volume fraction of the segments. In general, the boundary effects on the motion of a polymer-coated particle can be quite significant. Copyright 1999 Academic Press.

Journal Article↗

PubMed2000

Temperature Dependence of Adsorption of Polymer Mixtures from Solutions.

Adsorption from binary (poly(butyl methacrylate)-CCl(4), poly-styrene-CCl(4)) and ternary (poly(butyl methacrylate)-polystyrene-CCl(4)) solutions has been studied at 10, 25, and 60 degrees C. It was found that with increasing temperature the values of adsorption grew due to worsening of the thermodynamic quality of the common solvent. Worsening of the quality of the solvent leads to a decrease in size of the macromolecular coils and to an increase in the critical concentrations of overlapping macromolecules in solution. As a result, the state of macromolecules in solution depends on temperature and determines adsorption values. From the temperature dependence of adsorption using the Clapeyron-Clausius equation, the differential enthalpy of adsorbate (polymer) DeltaH was calculated for each polymer, by adsorption both from binary solution and from the mixture. Determining DeltaH values from the temperature dependence of adsorption allows us to find this value simultaneously for each polymer in the polymer mixture. It was established that transition of a polymer from solution onto the surface leads to an increase in its enthalpy in the case of adsorption from both binary and ternary solutions. DeltaH increases with increasing coverage of the surface. By transition from solution onto the surface, the enthalpy of the adsorbed polymer increases; i.e., the polymer transits in an energetically less favorable state. This effect is more pronounced for adsorption from the mixture, which may be connected with the presence of the second polymer in the adsorption layer. Copyright 2000 Academic Press.

Journal Article↗

PubMed2006

Polymer-based paclitaxel-eluting stents are superior to nonpolymer-based paclitaxel-eluting stents in the treatment of de novo coronary lesions.

Although polymer coating of coronary stents enables sufficient loading and release of incorporated drugs, it has also been associated with potentially negative effects. This study compared the clinical, angiographic, and intravascular ultrasound (IVUS) outcomes of patients treated with polymer- versus nonpolymer-based paclitaxel-eluting stents (PESs). Sixty-five consecutive patients (70 de novo lesions) treated with polymer-based PESs (TAXUS, 1 microg/mm2 of paclitaxel; Boston Scientific Corp.) and 65 consecutive patients (65 de novo lesions) treated with nonpolymer-based PESs (V-Flex Plus, 2.7 microg/mm2 of paclitaxel; Cook, Inc.) were enrolled in the study. Six-month angiographic follow-up was performed on 54 lesions of the polymer-based PES group and 51 lesions of the nonpolymer-based PES group. IVUS at angiographic follow-up was performed in 61 of the first 70 included lesions. At 6-month IVUS follow-up, mean intimal hyperplasia cross-sectional area was 2.36 +/- 1.60 mm2 in the nonpolymer-based PES group versus 0.62 +/- 0.41 mm2 in the polymer-based PES group (p = 0.003). Implantation of polymer-based PESs resulted in significantly lower in-stent late lumen loss (0.22 +/- 0.27 vs 0.74 +/- 0.61 mm, respectively, p <0.001). In-stent binary restenosis rate was 5% versus 20%, respectively (p <0.001). Target lesion revascularization rate was 9% after implantation of polymer-based PES versus 18% (p = 0.128) after implantation of nonpolymer-based PES, and the major adverse cardiac event rate was 9% versus 23%, respectively (p = 0.032). In conclusion, polymer-based PESs result in superior angiographic and IVUS follow-up findings compared with nonpolymer-based PESs.

Coronary Angiography↗

PubMed2006

Chemical and biological properties of supramolecular polymer systems based on oligocaprolactones.

We show that materials with a diverse range of mechanical and biological properties can be obtained using a modular approach by simply mixing different ratios of oligocaprolactones that are either end-functionalized or chain-extended with quadruple hydrogen bonding ureido-pyrimidinone (UPy) moieties. The use of two UPy-synthons allows for easy synthesis of UPy-modified polymers resulting in high yields. Comparison of end-functionalized UPy-polymers with chain-extended UPy-polymers shows that these polymers behave distinctively different regarding their material and biological properties. The end-modified UPy-polymer is rather stiff and brittle due to its high crystallinity. Disks made of this material fractures after subcutaneous implantation. The material shows a low inflammatory response which is accompanied by the formation of a fibrous capsule, reflecting the inertness of the material. The chain-extended UPy-material on the contrary is practically free of crystalline domains and shows clear flexible properties. This material deforms after in-vivo implantation, accompanied with cellular infiltration. By mixing both polymers, materials with intermediate properties concerning their mechanical and biological behaviour can be obtained. Surprisingly, a 20:80 mixture of both polymers with the chain-extended UPy-polymer in excess shows flexible properties without visible deformation upon implantation for 42 days. This mixture, a blend formed by intimate mixing through UPy-UPy interaction, also shows a mild tissue response accompanied with the formation of a thin capsule. The material does not become more crystalline upon implantation. Hence, this mixture might be an ideal scaffold material for soft tissue engineering due to its flexibility and diminished fibrous tissue formation, and illustrates the strength of the modular approach.

Animals↗

PubMed2004

Clay-catalyzed reactions of coagulant polymers during water chlorination.

The influence of suspended clay/solid particles on organic-coagulant reactions during water chlorination was investigated by analyses of total product formation potential (TPFP) and disinfection by-product (DBP) distribution as a function of exchanged clay cation, coagulant organic polymer, and reaction time. Montmorillonite clays appeared to act as a catalytic center where the reaction between adsorbed polymer and disinfectant (chlorine) was mediated closely by the exchanged clay cation. The transition-metal cations in clays catalyzed more effectively than other cations the reactions between a coagulant polymer and chlorine, forming a large number of volatile DBPs. The relative catalytic effects of clays/solids followed the order Ti-Mont > Fe-Mont > Cu-Mont > Mn-Mont > Ca-Mont > Na-Mont > quartz > talc. The effects of coagulant polymers on TPFP follow the order nonionic polymer > anionic polymer > cationic polymer. The catalytic role of the clay cation was further confirmed by the observed inhibition in DBP formation when strong chelating agents (o-phenanthroline and ethylenediamine) were added to the clay suspension. Moreover, in the presence of clays, total DBPs increased appreciably when either the reaction time or the amount of the added clay or coagulant polymer increased. For volatile DBPs, the formation of halogenated methanes was usually time-dependent, with chloroform and dichloromethane showing the greatest dependence.

Journal Article↗

PubMed2004

Effects of chemical functional groups on the polymer adsorption behavior onto titania pigment particles.

The effects of functional groups on polymer adsorption onto titania pigment particles have been investigated as a function of pH and ionic strength using polyacrylic acid and modified polyacrylamides. The polyacrylamides include the homopolymer, an anionic copolymer with hydroxyl and carboxylate group substitution, and a nonionic copolymer with hydroxyl group substitution. Adsorption isotherms and infrared spectroscopy were used to examine the polymer-pigment interactions. The adsorption of the polyacrylic acid and anionic polyacrylamide on titania pigment is greatest when electrostatic repulsion is absent or reduced. At low pH values, below the pigment isoelectric point (IEP), or at high ionic strength, the adsorption density of the anionic polymers on titania pigment is high, while at higher pH values above the pigment IEP, the adsorption density decreases. But the adsorption of nonionic polymers on titania pigment is not influenced by either ionic strength or pH. Acrylamide groups were found to hydrogen bond with the titania pigment surface, independent of pH. With the inclusion of hydroxyl functional groups into the polyacrylamide chain, the polymer adsorption density increased without increased adsorption affinity. Carboxylate functional groups in the anionic polymers strongly interact with the pigment surface, producing the highest adsorption density at low pH values. All polymers exhibit Langmuir adsorption behavior with hydrogen bonding found as the dominant mechanism of adsorption in addition to electrostatic interaction occurring for the anionic polymers.

Journal Article↗

PubMed2006

Calcium sulfate precipitation in the presence of water-soluble polymers.

The effect of four different polymers on the precipitation of calcium sulfate was investigated in the present work. The degree of inhibition was estimated from measurements of the calcium ion activity and from specific solution conductivity measurements in the supersaturated solutions during the course of the precipitation process. The effects of polyacrylic acid (PAA, three different polymers with average molecular weight 2000, 50,000, and 240,000, respectively) and of a co-polymer of PAA with polystyrene sulfonic acid (PSA, average molecular weight<20,000) were investigated with respect to their effect on the kinetics of spontaneous precipitation of calcium sulfate salts. The results of the kinetics experiments suggested that the spontaneous precipitation from supersaturated calcium sulfate solutions at 25 degrees C yielded exclusively calcium sulfate dihydrate (gypsum) both in the absence and in the presence of the polymeric additives. The induction times, preceding the formation of the solid increased in all cases in the presence of the polymeric additives. Polymer concentrations as low as 2.0 ppm increased induction time from practically zero to 10 min. The rates of precipitation were reduced according to the solutions content in the polymers added and precipitation was completely suppressed in the presence of 6.0 ppm of the polymers tested, depending on their molecular weight. The lower the molecular weight of PAA, the more efficient was the threshold inhibition and the stronger the reduction of the rates of spontaneous precipitation. PSA yielded the poorest inhibition efficiency in comparison with the PAA, possibly because of the relatively lower affinity of the sulfonate groups for the calcium ions of the surface of the solid forming. The kinetics results analysis assuming Langmuir-type adsorption of the polymeric molecules on the growing supercritical gypsum nuclei showed different affinity for the polymers tested in agreement with the respective inhibition efficiency, in the order: PAA1>PAA2>PSA>PAA3. The presence of the polymers in the supersaturated solutions resulted in modification of the precipitated gypsum crystals morphology.

Journal Article↗

PubMed1996

Effect of water-soluble polymers on the state of aggregation, vesicle size, and phase transformations in mixtures of phosphatidylcholine and sodium cholate.

The state of aggregation and the steady-state size of mixed aggregates made of phospholipids and surfactants are both determined by the surfactant/lipid ratio in the mixed aggregates (Re). Water-soluble polymers, such as dextrans and polyethylene glycols (PEGs) of different molecular weights, induce reversible aggregation of phospholipid vesicles, mostly due to dehydration of the vesicle surface and depletion forces, and only at much higher concentrations, PEGs (but not dextran) also induce irreversible size growth of the vesicles. Here we show that the water-soluble polymers dextrans and PEGs do not affect the vesicle-micelle phase boundaries in mixtures of phosphatidylcholine and the anionic surfactant sodium cholate. By contrast, these polymers affect markedly the steady-state size of cholate-containing vesicles. As compared with pure phosphatidylcholine vesicles, the cholate-containing vesicles have a lower tendency to undergo polymer-induced aggregation, probably due to the electrostatic repulsion between the negatively charged vesicles, but a higher tendency to undergo irreversible size growth at relatively low polymer concentrations. Such irreversible size growth was observed not only for PEG but also for dextran, which in the absence of cholate is incapable of inducing vesicle size growth. These findings are consistent with the prevailing concept that the polymer-induced size growth is due to the effect of large structural fluctuations in the bilayers of deformed aggregated vesicles, the surface of which is dehydrated by the polymer. The presence of cholate in the bilayers at sufficiently high concentrations induces such fluctuations, yielding irreversible size growth within the clusters of dehydrated vesicles formed upon mixing with polymers.

Cholic Acid↗

PubMed1986

Intercalators as probes of DNA conformation: propidium binding to alternating and non-alternating polymers containing guanine.

Propidium iodide is used as a structural probe for alternating and non-alternating DNA polymers containing guanine and the results are compared to experiments with poly[d(A-T)2], poly(dA . dT) and random DNA sequences. Viscometric titrations indicate that propidium binds to all polymers and to DNA by intercalation. The binding constant and binding site size are quite similar for all alternating polymers, non-alternating polymers containing guanine and natural DNA. Poly(dA . dT) is unusual with a lower binding constant and positive cooperativity in its propidium binding isotherms. Poly(dA . dT) and poly(dG . dC) have similar salt effects but quite different temperature effects in propidium binding equilibria. Polymers and natural DNA have similar rate constants in their SDS driven dissociation reactions. The association rate constants are similar for the alternating polymers and poly(dG . dC) but are significantly reduced for poly(dA . dT). These results suggest that natural DNA, the alternating polymers, and non-alternating polymers containing guanine convert to an intercalated conformation with bound propidium in a very similar manner.

Chemical Phenomena↗

PubMed1996

Application of spherical and other polymers in capillary zone electrophoresis: separation of antiviral drugs and deoxyribonucleoside phosphates by different principles.

Soluble polymers of linear chains with limited branching and spherical polymers (limit dextrins and sucrose, such as Dextran and Ficoll (Pharmacia Chemicals), yielding lower viscosities, are examined here for the separation of different nucleotides and several anti-AIDS drugs by capillary zone electrophoresis (CZE). The linear polymer forms a network but spherical polymers appear to create a second pseudo-phase. In general, they tend to enhance the solute mobility and reduce peak width; thus, they improve the column efficiency. We observe that the beads of a spherical polymer produce a pseudo-phase even in a very low polymer concentration. The proposed method involving a spherical polymer yields the best separation for twelve deoxyribonucleoside mono-, di- and triphosphates in ca. 10 min. Common anti-AIDS drugs (ddA, ddC, ddI, d4T, AZT) and an AZT metabolite (AZT-glucuronate) are resolved by using conventional micellar electrokinetic capillary chromatography (MEKC). These results not only offer fast and highly sensitive detection techniques for the pharmacokinetics of nucleotides, drugs, and their metabolites, but they also demonstrate an application of the proposed second pseudo-phase involving spherical polymer beads in CZE separations.

Anti-HIV Agents↗