The optical activity of the system cellulose acetate--mesophasogenic solvent in the formation of a lyotropic liquid-crystalline phase

Vapors of a mesophasogenic solvent (which can form an liquid-crystalline phase with the polymer) have been found to actively affect the spatial structure and optical activity of natural polysaccharides (cellulose acetates). This process is accompanied by variations of the specific optical rotation value [alpha] within wide limits, including the inversion of the sign of [alpha]. The action of vapors obeys the dosage-effect rule, with lower doses producing a stronger effect. It was supposed that this approach can be applied to study the structural peculiarities of biopolymers such as DNA.     

Molecularly imprinted polymer diffraction grating as label-free optical bio(mimetic)sensor

Micropatterned molecularly imprinted polymer (MIP) transmissive 2D diffraction gratings (DGs) are fabricated and evaluated as label-free antibiotic bio(mimetic)sensors. Polymeric gratings are prepared by using microtransfer molding based on SiO(2)/Si molds. The morphology of the MIP gratings is studied by optical and atomic force microscopes. MIP 2D-DGs exhibit 2D optical diffraction patterns, and measurement of changes in diffraction efficiency is used as sensor response. The refractive index of the micropatterned MIP material was estimated, via solvent index matching experiments, to be 1.486. Immersion of a MIP 2D-DG in different solutions of target-antibiotic enrofloxacin leads to significant variations in diffraction efficiency, demonstrating target-molecule detection. On the other hand, no significant response is observed for both control experiments: MIP grating exposed to a non-retained analyte and an equivalent non-imprinted polymer grating exposed to the target analyte, showing highly specific antibiotic label-free optical recognition.     

Optical rotation of some α-1,4-linked glucopyranosides in the system H2O–DMSO and solution conformation of amylose

The specific rotation of starch components, corrected for refractive index variation, exhibits a discontinuity in the region of the water–dimethyl sulfoxide (H₂O–DMSO) system that corresponds to the composition of the complex 2H₂O–DMSO. This discontinuity is a property dependent upon the presence of a number of consecutively linked α-1,4 glucose units and, therefore, must reflect a change in symmetry of a segment, of polymer chain. The optical rotation of amylose between 26.5 and 92.5°C. does not change in DMSO and is only slightly lowered in water at the higher temperature. The behavior of amylose in both DMSO and H₂O is like that of a random coil, as indicated by viscosity and sedimentation measurements. These results may be interpreted either as being compatible with models of amylose in solution in which the polymer backbone has helical twist, or as indicating removal of strong interactions between polymer chain segments by a good solvent.     

Improvement of the biocatalytic properties of one phenylacetone monooxygenase mutant in hydrophilic organic solvents

The presence of different hydrophilic organic solvents or a water soluble polymer such as PEG 4000 led to an enhancement in the enzymatic activity of the M446G mutant of phenylacetone monooxygenase when it is employed in enantioselective sulfoxidations and Baeyer-Villiger reactions. By solvent engineering new substrates were found to be effectively converted by this Baeyer-Villiger monooxygenase. The use of 5% methanol together with the weak anion exchange resin Lewatit MP62 also allows the dynamic kinetic resolution of a set of racemic benzylketones. By this approach (S)-benzylesters could be obtained with high yields and optical purities.     

Molecularly imprinted polymer sensors for detection in the gas, liquid, and vapor phase

Fast, reliable, and inexpensive analytical techniques for detection of airborne chemical warfare agents are desperately needed. Recent advances in the field of molecularly imprinted polymers have created synthetic nanomaterials that can sensitively and selectively detect these materials in aqueous environments, but thus far, they have not been demonstrated to work for detection of vapors. The imprinted polymers function by mimicking the function of biological receptors. They can provide high sensitivity and selectivity but, unlike their biological counterparts, maintain excellent thermal and mechanical stability. The traditional imprinted polymer approach is further enhanced in this work by the addition of a luminescent europium that has been introduced into the polymers to provide enhanced chemical affinity as well as a method for signal transduction to indicate the binding event. The europium in these polymers is so sensitive to the bound target; it can distinguish between species differing by a single methyl group. The imprinted polymer technology is fiber optic-based making it inexpensive and easily integratable with commercially available miniature fiber optic spectrometer technologies to provide a shoebox size device. In this work, we will describe efforts to apply these sensors for detection of airborne materials and vapors. Successful application of this technology will provide accurate low level vapor detection of chemical agents or pesticides with little to no false positives.     

Role of solvent properties of aqueous media in macromolecular crowding effects

Analysis of the macromolecular crowding effects in polymer solutions show that the excluded volume effect is not the only factor affecting the behavior of biomolecules in a crowded environment. The observed inconsistencies are commonly explained by the so-called soft interactions, such as electrostatic, hydrophobic, and van der Waals interactions, between the crowding agent and the protein, in addition to the hard nonspecific steric interactions. We suggest that the changes in the solvent properties of aqueous media induced by the crowding agents may be the root of these “soft” interactions. To check this hypothesis, the solvatochromic comparison method was used to determine the solvent dipolarity/polarizability, hydrogen-bond donor acidity, and hydrogen-bond acceptor basicity of aqueous solutions of different polymers (dextran, poly(ethylene glycol), Ficoll, Ucon, and polyvinylpyrrolidone) with the polymer concentration up to 40% typically used as crowding agents. Polymer-induced changes in these features were found to be polymer type and concentration specific, and, in case of polyethylene glycol (PEG), molecular mass specific. Similarly sized polymers PEG and Ucon producing different changes in the solvent properties of water in their solutions induced morphologically different α-synuclein aggregates. It is shown that the crowding effects of some polymers on protein refolding and stability reported in the literature can be quantitatively described in terms of the established solvent features of the media in these polymers solutions. These results indicate that the crowding agents do induce changes in solvent properties of aqueous media in crowded environment. Therefore, these changes should be taken into account for crowding effect analysis.     

Electric field effect on the helix–coil transition of poly(L-α,γ-diaminobutyric acid hydrochloride) in methanol/water mixtures

Transient electric birefringence of poly(L -α,γ-diaminobutyric acid hydrochloride) in methanol/water mixtures has been measured over a wide range of field strengths and solvent compositions and at different polymer concentrations and temperatures. The molar ellipticity at 222 nm and the specific Kerr constant underwent an abrupt change between 75 and 80 vol % methanol at 25°C, accompanied by a solvent-induced helix–coil transition. Anomalous birefringence transients were observed between 78 and 80 vol% methanol above threshold field strengths. The double logarithmic plots of the steady-state specific birefringence versus the square of field strength for different solvent compositions and polymer concentrations could be superimposed by shifting them horizontally along the abscissa and vertically along the ordinate except for the range where anomalous transients were observed. The threshold field strength could be estimated from the point at which a downward deviation occurred. It increased with increasing polymer concentration and with increasing methanol content on the verge of the transition region. The results were interpreted as indicating that a conformational change from the charged helix to the charged coil is induced by high fields in this system, as in the case of poly(L -lysine hydrobromide) in methanol/water mixtures.     

Effect of the solvent on recognition properties of molecularly imprinted polymer specific for ochratoxin A

A molecularly imprinted polymer specific for the mycotoxin ochratoxin A has been synthesised using a non-covalent approach. The polymer has shown an excellent affinity and specificity for the target template in aqueous solutions. The binding experiments, NMR study and molecular modelling have proven that the template recognition by polymer originates from the shape complementarity of binding sites. The binding mechanism is critically depended on factors that affect the polymer conformation. Thus the variation in buffer concentration, pH and presence of organic solvent, which affect the polymer swelling or shrinking, had a profound effect on the polymer recognition properties.     

The Influence of Measurement Parameters on the Specific Rotation of Amino Acids

The effects of solute and hydrochloric acid concentrations on optical rotation were studied using 20 naturally occuring amino acids.

There appeared to be no common factor among the amino acids as far as the inclination of optical rotation was concerned. Lutz-Jirgenson’s rule could be applied to few amino acids in the cationic form. Therefore, in the determination of the optical rotation, the concentration of the solute, nature of solvent and temperature must be rigorously controlled. The optical conditions of measurement and the specific rotation of 20 amino acids were recommended based on this work.     

The Effect of Electrotonus on the Olfactory Epithelium

The effect of electrotonus on the slow potential of the olfactory epithelium of the frog was studied. The "on"-slow potential induced by a general odor like amyl acetate increased its magnitude in accordance with increase of anodal current, while it decreased its magnitude with increase of cathodal current. Similar relations were also found in the case of the vapors of organic solvents like ethyl ether of low concentrations. Conversely, the on-slow potential induced by the vapors of organic solvents of high concentration decreased its magnitude in accordance with the increase of anodal current, while it increased its magnitude with the increase of cathodal current. The "off"-slow potential induced by the vapors of organic solvents of high concentration showed a potential change under the action of electrotonic currents which is similar to the change of the on-slow potential induced by general odors. It was concluded that there are two receptive processes in the olfactory cell. One is an ordinary excitatory process which produces an electronegative slow potential in response to general odors. The other is a process of a different kind which is activated only by the vapor of an organic solvent of high concentration and which shows an entirely opposite reaction from that generally found in excitable tissues when an electrotonic current is applied.     

Investigating the effects of polymer chemistry on activity of biocatalytic plastic materials

The affects of polymer chemistry on the organic solvent activity of alpha-chymotrypsin-containing biocatalytic plastic materials are investigated in this study. To incorporate alpha-chymotrypsin into the polymer, the enzyme is first acryloylated, then solubilized into organic solvents via hydrophobic ion paring with surfactant molecules. Once in the organic solvent, a vinyl monomer and crosslinker are added and copolymerized with the enzyme. Due to the intimate contact between the enzyme and the resulting polymer network, the polymer chemistry plays an important role in the activity of these biocatalytic materials. The chemical composition of the monomer/polymer has the greatest effect on catalytic activity. The activity spans a range of 100-fold and appears to correlate with the hydrophilicity of the monomer, with the lowest activity exhibited for poly(methyl methacrylate) and the highest for poly(2-hydroxyethyl methacrylate). The effect of the chemical structure of the monomer/polymer appears to be an intrinsic kinetic effect, whereas other polymer chemistry conditions investigated, including crosslinker concentration and length and ratio of solvent:monomer during synthesis, appear to effect the rate of substrate diffusion, thereby affecting observed enzyme activity. Changes in the conditions of polymer synthesis can cause as much as a 20-fold change in activity for a given polymeric material. This is most likely due to an increase in the porosity of the materials, and thus a relaxation of diffusional limitations.     

Radial migration of DNA molecules in cylindrical flow. I. Theory of the free-draining model

Inward radial migration of large DNA molecules undergoing concentric-cylinder shear flow has been previously observed in this laboratory during measurements of viscoelastic retardation times. In this paper a theoretical treatment of this effect is presented in the framework of the bead-spring model of polymer molecules. Equations of motion of the diffusion type are solved for the free-draining polymer in a solvent undergoing Couette flow. The results show an inward radial motion, essentially due to the curvilinear solvent flow field.     

Aggregation of poly(γ-benzyl-L-glutamate) in mixed solvent systems

The aggregation of poly(γ-benzyl L -glutamate) has been studied by measuring the specific Kerr constants (B/c) over a tenfold range of concentration and the intrinsic viscosities of solutions of a low molecular weight sample of the polymer in four solvent mixtures, viz., benzene–dimethylformamide (DMF), benzene–ethylene dichloride (EDC), dioxane–DMF and dixoane–EDC. Sharp changes are found in the experimentally determined quantities on the addition of small amounts of polar solvent to solutions of the polymer in either benzene or dioxane; this implies that lyotropic phase changes are occuring. The aggregation in benzene produces a birefringent, viscous solution which is probably a smeetic liquid crystal. This changes on addition of polar solvent to an aggregation involving only a few molecules; the second aggregate is most likely antiparallel. Aggregation in dioxane is antiparallel; the existence of a smectic phase is ruled out by the low intrinsic viscosities.     

Intrinsic Birefringence of Poly-γ-Benzyl-l-Glutamate, A Helical Polypeptide, and the Theory of Birefringence

The intrinsic birefringence of macromolecules can be obtained directly from flow birefringence measurements in a solvent whose refractive index matches that of the solute. A small and positive value (approximately 0.01) was found for the helical polypeptide, poly-γ-benzyl-L-glutamate. The birefringence in solvents of varying index calculated from the Peterlin-Stuart theory using this value of the intrinsic birefringence did not agree with experimental values. Considerations of polydispersity and shear deformation indicated that the discrepancy could not be attributed to these effects. Also it could not be explained in terms of specific solvent effects. It is concluded that optical properties cannot be derived from the continuum model employed by Peterlin and Stuart. Much better agreement was obtained with a helical dipole necklace model.     

Insights into the origins of binding and the recognition properties of molecularly imprinted polymers prepared using an amide as the hydrogen-bonding functional group

Molecularly imprinted polymers (MIPs) prepared using an amide hydrogen-bonding functional monomer (acrylamide) exhibited efficient enantiomeric recognition properties in both organic and aqueous media in the HPLC mode. The results indicate that the amide functional groups formed strong hydrogen-bonding interactions with the template molecule, and specific recognition sites were created within the polymer matrix during the imprinting process. When Boc-L-Trp was used as the template, an MIP prepared in a polar organic solvent (acetonitrile) using acrylamide as the functional monomer showed better enantiomeric recognition of Boc-Trp than the MIPs prepared in the same solvent using an acidic (methacrylic acid) or a basic (2-vinylpyridine) functional monomer or a combination of an acidic and a basic functional monomer (methacrylic acid + 2-vinylpyridine). Our results indicate that in organic media the degree of retention of the sample molecule on the imprinted polymer was controlled by hydrogen-bonding interactions between the sample molecule and the polymer, while in aqueous media it was determined to a considerable extent by hydrophobic interactions. In both media the shape, size and the nature of the hydrogen-bonding groups of the sample molecules were all important factors in determining the enantiomeric and substrate selectivity. In the aqueous media, however, the hydrophobicity of the sample molecules was also found to play an important role.     

Phase separation in the mixture of schizophyllan and poly(ethylene oxide) in aqueous solution driven by a specific interaction between the glucose side chain and poly(ethylene oxide)

We found that the mixture of schizophyllan and poly(ethylene oxide) in aqueous solution underwent phase separation at around 3-4 degrees C, and this temperature was independent of both polymer concentration and the difference in poly(ethylene oxide) molecular weight (Mw 6000 and 70,000). The phase-separation took place at the same temperature at which the optical rotation changed. Since the optical rotation change is ascribed to the difference in the nature of hydrogen bonding between the schizophyllan side chain and water, the phase separation is also considered to be due to an interaction between poly(ethylene oxide) and schizophyllan. The phase-separation temperature increased on changing H2O to D2O in accordance with a change in the optical rotation, confirming the specific interaction essential for the phase separation.     

Fluctuation of an -helix structure. Difference between the central and terminal portions

Four samples of poly-l-glutamic acid with different degrees of polymerization, 30, 60, 73 and 96, have been prepared. By optical rotatory dispersion and infrared absorption measurements, the random-coil and α-helix contents were estimated in heavy water plus dioxane solutions with various pD values. In the same solvent, the kinetics of hydrogen-deuterium exchange in each sample was followed by an infrared absorption measurement. It was found that the rate of exchange depends appreciably on the degree of polymerization; the rate is lower for the polymers with higher degrees of polymerization, so that the rate constant is considered to become lower on going from the terminals towards the inner portions of the polymer chain. An analysis of this lowering has been made by taking the random-coil content estimated by the optical rotatory dispersion measurement into account. It is suggested that the rate constant of the helix-coil fluctuation in the central portions of the chain is as low as 4 × 10⁻⁶ sec⁻¹.     

Degradation of Linseed Oil Vapors by Soil Bacteria in Trickling Biofilters

Oxidation products of linseed oil were produced by impinging a stream of air onto the surface of pure linseed oil and injecting the vapor-laden air into soil percolation columns to enrich the population of bacteria capable of degrading linseed oil vapors. As the populations of bacteria increased, the linseed oil vapors were consumed by these organisms, and the air that emerged from the columns was free of linseed oil contaminants. Five different kinds of bacteria capable of growing on the linseed oil oxidation products as sole source of carbon and energy were found and isolated in pure culture. Chromatographic analyses showed that individual organisms removed specific components of the vapor at specific rates, but none was able to remove them all within a 30-day period of time. When the five were grown together and presented the linseed oil vapor, all vapor constituents were utilized, and the rate of utilization was greater than that seen when the isolates were tested in pure culture. This indicated that the five organisms operated as a bacterial consortium in the degradation of linseed oil vapors. Trickling biofilters prepared from pregrown populations of the five organisms challenged with linseed oil vapors were able to remove all volatile constituents found in linseed oil vapor. Bioremediation of the air was complete and it was accomplished in a single pass of the air through the filter.

This work shows that bacteria found in the soil are capable of degrading linseed oil vapors and that they can be grown in the laboratory and used successfully in bench scale trickling biofilters.     

Designing enzymes for use in organic solvents.

Enzymes are routinely used in organic solvents where numerous reactions of interest to synthetic and polymer chemists can be performed with high selectivity. Recently, it has become apparent that the catalytic properties of an enzyme can be tailored to a specific catalytic requirement by the use of solvent and protein engineering. The former involves altering the polarity, hydrophobicity, water content, etc., of the organic milieu, while the later applies site-directed mutagenesis to alter the physicochemical properties of the biocatalyst. The dominant effects of organic solvents on enzyme structure and function, and the potential of solvent and protein engineering to design enzymes to function optimally in organic media, are the major foci of this review.