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PubMed2000

Toxicity effects of compressed and supercritical solvents on thermophilic microbial metabolism.

Selection of biocompatible solvents is critical when designing bioprocessing applications for the in situ biphasic extraction of metabolic end-products. The prediction of the biocompatibility of supercritical and compressed solvents is more complicated than for liquid solvents, because their properties can change significantly with pressure and temperature. The activity of the anaerobic thermophilic bacterium, Clostridium thermocellum, was studied when the organism was incubated in the presence of compressed nitrogen, ethane, and propane at 333 K and multiple pressures. The metabolic activity of the organisms in contact with compressed solvents was analyzed using traditional indicators of solvent biocompatibility, such as log P, interfacial tension, and solvent density. The toxicity of the compressed solvents was compared with the phase and molecular toxicity effects measured in liquid alkanes at atmospheric pressure. Inactivation increased with time in the presence of the compressed solvents, but was constant in the presence of atmospheric liquid solvents. Knowledge of molecular and phase toxicity provides a framework for the interpretation of C. thermocellum metabolism in contact with atmospheric and compressed solvents.

Clostridium↗
PubMed1991

Exposure to organic solvents and adverse pregnancy outcome.

In a large case-control study (n = 1,926) of spontaneous abortion (SAB), exposure to solvents was ascertained by a telephone interview that asked about occupational use of 18 specific solvents or products, as well as an open-ended "other" solvent category. The adjusted odds ratio for use of any solvent was 1.1 (0.8, 1.5). Solvents for which at least a doubled crude risk of SAB was found included perchlorethylene (OR = 4.7, 95% CI = 1.1, 21.1), trichloroethylene (OR = 3.1, CI = 0.9, 10.4), and paint thinners (OR = 2.3, CI = 1.0, 5.1). Comparing exposure greater than 10 hours per week versus less did not show consistent dose-response effects. By solvent class, an association was seen with aliphatic solvents (adjusted OR = 1.8, 95% CI = 1.1, 3.0), but there was no dose-response effect by hours of use. Household use of solvent-containing products was generally not strongly associated with SAB, nor did it appear to confound the association seen with occupational use. From this and other studies, occupational exposure to at least some solvents appears associated with SAB. The associations of solvent exposure and fetal growth among liveborn offspring of controls was also examined.

Abortion, Spontaneous↗
PubMed1995

Comparison of neurobehavioral function in workers exposed to a mixture of organic and inorganic lead and in workers exposed to solvents.

The neurobehavioral effects of lead (organic and inorganic) and organic solvents were compared in 386 U.S. workers (52 reference, 190 lead, and 144 solvent workers). The association between neurobehavioral test performance and duration of exposure to lead or solvents was also examined and compared. The neurobehavioral test battery consisted of examiner and computer-administered neurobehavioral tests, a test of olfactory function, and questionnaires that assessed neuropsychiatric symptoms. Adjusted mean differences on the neurobehavioral test scores were estimated by comparing the exposed group to the referent group using linear regression and adjusting for premorbid intellectual ability, age, and race. Both lead and solvents were associated with diminished neurobehavioral performance in all neurobehavioral areas tested. Specifically, while lead and solvent exposure had the same magnitude of adverse effects on tests of manual dexterity, lead exposure was associated with greater adverse effects on memory and learning tests but with less adverse effects on executive/motor tests and on a test of olfaction than solvent exposure. An elevated number of neuropsychiatric symptoms was reported by 7% of the referent group, 43% of the lead group, and 15% of the solvent group. For exposure duration of < or = 10 years, more neurobehavioral decrements were found in the solvent group relative to the lead group. However, for exposure duration of > or = 18 years, the lead group showed more decrements than the solvent group. Overall, these data suggest differences in neurobehavioral functioning between the lead (organic and inorganic) and solvent exposed workers examined in this study.

Adult↗
PubMed2003

Influence of solvent on temperature and thermal peak broadening in capillary zone electrophoresis.

The present paper deals with the role of the solvent on thermal peak broadening. One main solvent property that determines the magnitude of the temperature gradient due to the generation of Joule heat in capillary zone electrophoresis is the thermal conductivity. As organic solvents have lower thermal conductivity than water (methanol and acetonitrile, e.g., nearly by a factor of 3) it can be hypothesized that the temperature gradient inside the capillary is more pronounced in organic solvents compared to an aqueous solution. On the other hand, the temperature dependence of the ion mobility (which is responsible for the velocity profile and thus for thermal peak broadening) is smaller in organic solvents. To get insight into the thermal effect of the solvent, first the temperature of a solution in a cylindrical tube was calculated utilizing the heat balance equation. It was shown that the two theoretical models most common in the literature (based on the analytical solution or on an assumption of the parabolic temperature profile in the tube, respectively) give the same results. The latter model was chosen for the further calculations, adding a quadratic term to express the electric conductivity as a function of the temperature. The temperature at the inner capillary wall and center as function of the capillary dimensions and the electric power was computed for electrolytes with a given conductivity at 25.0 degrees C with water, methanol, and acetonitrile as solvents. Capillary cooling systems used were circulating liquid cooling, enforced air-cooling, and natural convection in still air. The mean temperature (averaged over the cross section) resulting from Joule heating was compared with experimentally determined temperatures established upon application of an electric field; the latter temperature was derived from the measurement of the electric conductance of the background electrolyte solution and its (measured) temperature dependence. All investigations were carried out with solutions of the same initial electric conductivity (about 0.5 S.m(-1) at 25.0 degrees C). Agreement is found for natural convection conditions, and the deviation between theoretical and experimental results for the forced air and circulated liquid cooling systems can be related to the poorly defined thermal conditions of the capillaries in commercial instrumentation (with a part in a thermostated cassette and a part outside). For given conditions the temperature gradients in the organic solvents exceed largely those in water, independent of the type of cooling. As a consequence, the thermal plate height is significantly larger in organic solvents, at least under conditions where the deviation from the Nernst-Einstein limiting case is not too high. However, even for the maximum applicable field strengths the thermal plate height contributions are negligible compared to longitudinal diffusion in all solvents.

Electrophoresis, Capillary↗
PubMed2004

Solvation forces on biomolecular structures: a comparison of explicit solvent and Poisson-Boltzmann models.

Continuum electrostatics methods have become increasingly popular due to their ability to provide approximate descriptions of solvation energies and forces without expensive sampling required by explicit solvent models. In particular, the Poisson-Boltzmann equation (PBE) provides electrostatic potentials, solvation energies, and forces by modeling the solvent as a featureless, dielectric material, and the mobile ions as a continuous distribution of charge. Polar solvation forces and energies obtained from the PBE are often supplemented with simple solvent-accessible surface area (SASA) models of nonpolar solvation. Given the recent development of methods that enable the use of PBE and SASA forces in molecular dynamics simulations, it is important to determine the ability of these implicit solvent models to accurately reproduce the solvation forces of more detailed explicit solvent simulations. In this article, we compare PBE and SASA solvation forces with explicit solvent forces for several snapshots from eight trajectories of static conformations of intestinal fatty acid binding protein. The results from this comparison show that current implementations of the PBE are capable of generating polar solvation forces that correlate well with explicit solvent forces but systematically overestimate the magnitude of the interaction. However, SASA-based nonpolar forces are found to have no significant correlation with nonpolar explicit solvent forces. Nevertheless, due to the small magnitude of the nonpolar forces in the current system, a good correlation is still obtained for total solvation forces. The good correlation of implicit solvent forces with more detailed explicit solvent models is encouraging and implies that the systematic errors identified in these models could be corrected by appropriate parameterization of the force fields.

Computer Simulation↗
PubMed1994

Fluorescence spectroscopy of 9-anthroyloxy fatty acids in solvents.

A series of anthroyloxy fatty acid (AF) fluorescent probes, with the anthroyloxy group covalently linked at various positions along the alkyl chain, were studied in solvents exhibiting a wide range of polarity and hydrogen-bond donor (Hd) and acceptor (Ha) ability. These probes were sensitive to the solvent polarity as reflected by the Stokes' shift observed in steady state fluorescence. As determined by multi-linear regression analysis of the observed Stokes' shift and solvent parameters, such as orientation polarizability (delta f), Hd and Ha of the solvents, all the probes were sensitive to the Hd of solvents but were not affected by the Ha of solvents except the 2-AF. Due to the proximity of the polar headgroup to the fluorophore, it appears that some intramolecular hydrogen-bonding is present in 2-AF, an interaction that is sensitive to the pH of the solvent, but is less sensitive to the Hd and Ha of the solvents. Fluorescence lifetimes measured by the multi-frequency phase-modulation technique in mixtures of hexane and ethanol reflect a modified Stern-Volmer behavior suggesting the second solvent, ethanol, specifically interacts with the probe, in part through collisional quenching. Also, the lifetime data were sensitive to very low concentrations of the second solvent (0-0.1%, by vol.). The results from this study provide insight into the intrinsic differences between the different AF positions that must be taken into consideration while investigating the dynamics of lipid bilayer systems. Moreover, this study illustrates the utility and resolving power of lifetime based measurements needed for the interpretation of heterogeneous biophysical environments.

Anthracenes↗
PubMed1985

In vitro dissolution of cholesterol gallstones. A study of factors influencing rate and a comparison of solvents.

Models of the common bile duct and gallbladder were constructed to study conditions that affect the rate of cholesterol gallstone dissolution by monooctanoin and other potential solvents. In the bile duct model, the rate of monooctanoin infusion was not an important factor in accelerating dissolution time. In contrast, the exclusion of bile from interfering with solvent-stone contact or the enhancement of solvent-stone contact by stirring significantly accelerated stone dissolution. The combination of both bile exclusion and stirring increased the dissolution rate of gallstones by monooctanoin 15-fold. When compared with two other ethers and with monooctanoin, methyl tert-butyl ether was found to be the most potent gallstone solvent. Methyl tert-butyl ether completely dissolved 219-mg cholesterol stones within 60 min. In the gallbladder model, in the absence of stirring both methyl tert-butyl ether and monooctanoin floated on bile, whereas the gallstones sank resulting in minimal stone-solvent contact. To increase the stone-solvent contact, we used a pump to create sufficient turbulence to mix the solvent with bile. Pump stirring of monooctanoin in the presence of bile achieved rates of stone dissolution approaching that of stirred monooctanoin without bile. Stirring of methyl tert-butyl ether and bile, however, did not achieve sufficient solvent-stone contact to appreciably accelerate dissolution in the presence of 50% bile. Stone-solvent contact was a critical factor in determining the rate of gallstone dissolution in both gallbladder and common bile duct models. Efforts to enhance contact include bile exclusion and intraluminal stirring--both of which are clinically applicable. Methyl tert-butyl ether is a potent new cholesterol gallstone solvent with excellent potential for use in humans. Even with this potent agent, however, rapid gallstone dissolution is likely to require removal of most of the bile from the dissolution medium.

Bile↗
PubMed1993

Solvent effect on testosterone-antitestosterone interaction.

The inhibition of the binding between testosterone and antitestosterone antiserum caused by organic solvents was studied at pH 7.4, 298 K. Inhibition curves were obtained at variable ranges of molar fractions for the following solvents: methanol (range 0-0.4), ethanol (0-0.317), 1-propanol (0-0.082), 2-propan-ol (0-0.260), t-butanol (0-0.223), ethylenglycol (0-0.189), 2-methoxyethanol (0.036), 2-butoxyethanol (0-0.063), 1,4-dioxan (0-0.124), tetrahydrofuran (0-0.238) and acetonitrile (0-0.392). Steroid-antibody binding decreases with increasing molar fraction of solvent in the reaction mixture for all but tetrahydrofuran and acetonitrile, which enhance binding at low molar fraction then cause a sharp inhibition. Molar fraction of solvent that causes a 50% binding inhibition is uncorrelated to some solvent properties (i.e. dielectric constant, polarity index, dipole moment) but is inversely correlated to the molecular mass of the solvent. The correlation becomes better by taking into account the length of the solvent molecule, or the Randic molecular connectivity index, suggesting that binding inhibition could be related to the length of the solvent molecules that displace water around the steroid molecule. However, the increase of binding observed at low molar fraction with tetrahydrofuran and acetonitrile, together with very different shapes of inhibition curves suggest that a molecular mechanism based on the differential solvation of the steroid by solvent and water molecules must be taken into account to explain adequately the solvent effect on testosterone-antitestosterone interaction.

Antibodies↗
PubMed2004

Evaluation of common organic solvents for gas chromatographic analysis and stability of multiclass pesticide residues.

In this study, we evaluated the suitability of six common organic solvents for gas chromatographic (GC) analysis of pesticides. Three of these, acetone, acetonitrile (MeCN) and ethyl acetate (EtAc), represent extraction solvents commonly used in multiresidue methods for determination of pesticides in produce. The other three, isooctane, hexane and toluene, often serve as exchange solvents before a GC analysis. An ideal solvent for GC analysis of multiclass pesticide residues should be compatible with: the analytes, sample preparation, and GC analysis. This study addresses each aspect with emphasis placed on stability of selected pesticides in the given solvents. In this respect, the exchange solvents proved to be superior to the more polar extraction solvents. Degradation of N-trihalomethylthio fungicides (e.g., captan, folpet, dichlofluanid) in MeCN was observed only in certain lots of the tested MeCN, but even if it occurred, the stability of these analytes as well as that of dicofol and chlorothalonil was dramatically improved by the addition of 0.1% (v/v) acetic acid. Dicofol and chlorothalonil were also unstable in acetone, and pesticides with a thioether group (e.g., fenthion, disulfoton) degraded in the tested EtAc. Formation of isomers of certain pyrethroids (deltamethrin, lambda-cyhalothrin) was recorded in the chromatograms from MeCN and acetone solutions, but this effect more likely occurred during the GC injection than in solution. For several reasons, MeCN was found to be the most suitable solvent for extraction of a wide polarity range of pesticide residues from produce. After acidification, the stability of problematic pesticides in MeCN is acceptable, and MeCN can also serve as a medium for GC injection; therefore solvent exchange is generally not required before GC analysis. If sensitivity is an issue in splitless injection, then toluene was demonstrated to be the best exchange solvent due to its miscibility with MeCN and stronger responses of relatively more polar pesticides (e.g., acephate, methamidophos) as compared to hexane and isooctane.

Organic Chemicals↗
PubMed2005

Influence of solvent properties on separation and detection performance in non-aqueous capillary electrophoresis-mass spectrometry of basic analytes.

The versatility of non-aqueous capillary electrophoresis (NACE) results mainly from the variety of physico-chemical properties of the different solvents. They provide solubility for a wide range of analytes, enable to control electrophoretic selectivity, but affect in some cases UV absorbance detection. The coupling of NACE to electrospray mass spectrometry (ESI-MS) allows to cope with the high UV cut-off of some CE relevant solvents (e.g., formamides). In this paper the pure organic solvents methanol, acetonitrile, dimethylsulfoxide, formamide, N-methylformamide and N,N-dimethylformamide are evaluated against water for the preparation of ammonium acetate electrolytes to separate the basic model substances 2-aminobenzimidazole, procaine, propranolol and quinine with NACE-MS. MS coupling is assisted with the sheath liquid water-isopropanol (1:4, v/v) with 0.1% formic acid. The goal of the paper is to assess the influence of the solvent on selectivity, separation speed, and peak efficiency for a given set of model compounds on a simple empirical basis. It should give the user an idea how the separation quality is changed when nothing but the running solvent is altered. The obtained efficiency results were discussed with respect to physico-chemical models described in literature (assuming longitudinal diffusion as the only source of band broadening), but no satisfying correlations with solvent properties could be traced. The feasibility of all six organic solvents for MS coupling was demonstrated and the influence of the separation solvent on the MS detection performance was compared. In the seven different solvents, the shortest run time was obtained with acetonitrile, the best peak resolution with the amphiprotic solvents (especially methanol) best peak efficiency with methanol and formamide, and the most sensitive ESI-MS detection with acetonitrile and methanol, but with only slight advantage to water.

Electrophoresis, Capillary↗
PubMed2005

Comparative embryotoxicity and proteotoxicity of three carrier solvents to zebrafish (Danio rerio) embryos.

The present study examines the effects of ethanol (ETOH), dimethyl sulfoxide (DMSO), and acetone on zebrafish embryos and the implications of the observed results on the use of these solvents to zebrafish early life stage tests. The embryos were exposed to different concentrations (0.0, 0.0001, 0.001, 0.01, 0.1, 0.05, 1, 1.5, and 2.0% v/v) of the respective solvents by diluting reagent-grade solvent with reconstituted water [DIN 38415-6-Suborganismische Testverfahren (Gruppe T) Teil 6: Giftigkeit gegenüber Fischen. Deutsches Institute für Normung e.V]. The following endpoints were investigated (mortality, hatching rate, abnormalities, heart rate, and hsp 70 induction). No effect on survival was recorded for both acetone and DMSO even up to the highest concentration. On the other hand, embryos exposed to 1.5% and 2.0% ethanol showed a significant reduction in survival rate. No developmental defects occurred with any of the solvents at the 0.1% concentration. However, starting with 1.0%, weak to very pronounced abnormalities (weak pigmentation, edema, crooked bodies, eye defect, tail defect, reduced heartbeat, and abnormal hatching) were observed depending on the solvent type and the concentration used. Ethanol has been shown to be the most embryotoxic solvent while DMSO and acetone have comparably lesser effects. Heat shock protein 70 was induced by all solvents but at different concentration ranges. DMSO has been shown to be the most potent inducer of stress proteins. Based on the study, the chemicals tested here may be used as carrier solvents in the zebrafish embryo assay at levels below 1.5, 1.5, and 1% v/v for acetone, DMSO, and ethanol, respectively. For stress protein analysis of the exposed embryos, however, the solvent levels should be below 0.1%, 0.01%, and 1.5%, respectively. Additional and separate investigations utilizing other biomarkers should be carried out to further validate the suitability of using these solvents in a typical zebrafish embryo assay.

Abnormalities, Drug-Induced↗
PubMed2006

Markedly improving Novozym 435-mediated regioselective acylation of 1-beta-D-arabinofuranosylcytosine by using co-solvent mixtures as the reaction media.

A comparative study was made of Novozym 435-catalyzed regioselective acylation of 1-beta-D-arabinofuranosylcytosine with vinyl propionate for the preparation of the 5'-O-monoester in eleven co-solvent mixtures and three pure polar solvents. Novozym 435 displayed low or no acylation activity toward 1-beta-D-arabinofuranosylcytosine in pure polar solvents, although those solvents can dissolve the nucleosides well. When a hexane-pyridine co-solvent system was adopted, both the initial rate and the substrate conversion were enhanced markedly. The polarity of co-solvent mixtures had significant effect on the reaction. Among the solvent mixtures investigated, the higher the polarity of the solvent mixture, the lower the initial reaction rate and the substrate conversion. It was also found that the acylation was dependent on the hydrophobic solvent content, the water activity and the reaction temperature. The most suitable co-solvent, initial water activity, and reaction temperature were hexane-pyridine (28:72, v/v), 0.07, and 50 degrees C, respectively. Under these conditions, the initial rate, the substrate conversion and the regioselectivity were as high as 91.1 mM h(-1), >97% and >98%, respectively, after a reaction time of 6 h. Among the reaction mediums examined, the lowest apparent activation energy was achieved with hexane-pyridine (28:72, v/v), in which Novozym 435 also exhibited good thermal stability.

Acylation↗
PubMed2001

Management, disposal and recycling of waste industrial organic solvents in Hong Kong.

An attempt has been made to establish a mass balance of industrial organic solvents in Hong Kong. It is estimated that only a small portion, less than 4%, of all the organic solvents consumed in Hong Kong are collected as waste solvents and properly treated, while the remainder are used either in the formulation of solvent containing products, or are lost to the environment through vapour emissions, leaks and spills, or dumped illegally. It was found that solvent recycling has been a common practice in some industries but the existing level of solvent recycling in Hong Kong is difficult to estimate. About 87.4% of all the waste organic solvents disposed of at the licensed facilities are potentially recyclable although whether they can be recycled in practice depends on many factors. Examples of existing waste organic solvent management and recycling practices from selected industries in Hong Kong are presented. The economic feasibility of current and future potential recycling systems is evaluated for a few selected cases. An integrated waste organic solvent management strategy is proposed to minimize adverse impacts of organic solvents to the environment and human health.

Conservation of Natural Resources↗
PubMed1998

Ethene removal from gas by recycling a water-immiscible solvent through a packed absorber and a bioreactor.

Hydrophobic pollutants in waste gases are difficult to remove with the conventional biological treatment techniques because of the slow gas/water mass transfer rate. A two-stage system with a water-immiscible solvent as intermediate liquid was developed. This system consisted of a packed absorber for transfer of the model pollutant, ethene, from gas to solvent and a stirred-tank reactor (mixer) for solvent/water transfer and subsequent degradation by Mycobacterium parafortuitum. The solvent FC40, a perfluorocarbon, was recycled between these two compartments. The stability of the system was shown during a run of 10 days. The elimination efficiency was found to be a function of the solvent flow: 9% and 15% elimination were obtained at solvent flows of 6 x 10(-8) m3.s-1 and 11.3 x 10(-8) m3.s-1, respectively. Ethene removal remained constant at increasing solvent hold-ups up to 50% (v/v). In spite of the low elimination efficiencies caused by an inefficient use of the column, the feasibility of the system to remove ethene has been demonstrated. The system's performance was described by a steady-state mathematical model. Simulated ethene removal efficiencies agreed well with the experimental data. Based on this, the model was used to optimise the dimensions and operating conditions. Furthermore, the model was used to compare the performance of the combined system (PA/MS) with the performance of a similar system without solvent. It was found that the use of solvent as intermediate liquid can improve substantially the removal efficiency of hydrophobic gaseous pollutants compared with the system without solvent. This is dependent however, on the solubility of the pollutant in the solvent, on the dimensions of the system and on the operating conditions.

Absorption↗
PubMed2003

Solubility of drugs in aqueous solutions. Part 2: binary nonideal mixed solvent.

As in a previous paper [Int. J. Pharm. 258 (2003) 193-201], the Kirkwood-Buff theory of solutions was employed to calculate the solubility of a solid in mixed solvents. Whereas in the former paper the binary solvent was assumed ideal, in the present one it was considered nonideal. A rigorous expression for the activity coefficient of a solute at infinite dilution in a mixed solvent [Int. J. Pharm. 258 (2003) 193-201] was used to obtain an equation for the solubility of a poorly soluble solid in a nonideal mixed solvent in terms of the solubilities of the solute in the individual solvents, the molar volumes of those solvents, and the activity coefficients of the components of the mixed solvent. The Flory-Huggins and Wilson equations for the activity coefficients of the components of the mixed solvent were employed to correlate 32 experimental data sets regarding the solubility of drugs in aqueous mixed solvents. The results were compared with the models available in literature. It was found that the suggested equation can be used for an accurate and reliable correlation of the solubilities of drugs in aqueous mixed binary solvents. It provided slightly better results than the best literature models but has also the advantage of a theoretical basis.

Algorithms↗
PubMed1983

Examination of the solvent perturbation technique as a method to identify enzyme catalytic groups.

The present study was undertaken for the purpose of evaluating the solvent perturbation technique as a method to identify enzyme catalytic residues. For establishment of expected directions and sizes of pKa perturbations for different types of acids in different classes of solvents, a study of the pKa of a series of acids in mixed solvent systems was carried out. Consistent with previous findings, the presence of organic solvents (25% v/v) increased the pKa values of neutral acids while it decreased or did not change the pKa values of cationic acids. The size of the perturbation observed was dependent on the nature of the organic solvent and on the polarity of the neutral form of the acid. The solvent perturbation studies were then extended to the catalytic aspartate residue of yeast hexokinase. The pKa of this residue was determined from the MgATP V/K profile measured in the presence and absence of organic solvents (25% v/v). While dimethylformamide and methanol induced small but perhaps significant increases in the observed pKa, dimethyl sulfoxide and propylene glycol did not. The pKa values, from the MgATP V/K profiles measured in the presence of fully saturating glucose, were not significantly increased by the organic solvents. The pKi vs. pH profile for the competitive inhibitor lyxose was also measured in the presence and absence of organic solvents. While methanol (25% v/v), dimethylformamide (25% v/v), and dioxane (17.5% v/v) induced a large increase in the pKa, propylene glycol and dimethyl sulfoxide (25% v/v) did not. The results from this investigation indicate that the solvent perturbation technique should not be relied upon indiscriminately.

Adenosine Triphosphate↗
PubMed1997

Solvent accessibility of the phycocyanobilin chromophore in the alpha subunit of C-phycocyanin: implications for a molecular mechanism for inertial protein-matrix solvation dynamics.

The solvent environment of the phycocyanobilin chromophore bound by the alpha subunit of C-phycocyanin was probed in buffered binary solvent systems consisting of water and methanol, acetonitrile, or acetone. The focus of the work was on determining whether the inertial phase of the solvent response observed previously in the alpha subunit from femtosecond transient hole-burning spectroscopy [Riter et al. (1996) J. Phys. Chem. 100, 14198-14205] involves solvent dipoles in the bulk. Continuous absorption and fluorescence spectra at room temperature show that addition of the nonaqueous solvent results in a change in the tertiary structure of the protein so that the phycocyanobilin chromophore is unclamped and allowed to assume a cyclic conformation. At low concentrations of nonaqueous solvent, we observe a conformational equilibrium characterized by a cooperative binding of nonaqueous solvent. The phycocyanobilin chromophore exhibits a nonshifted absorption and fluorescence spectrum characteristic of its native, extended conformation in the state with bound water molecules. In the state with bound solvent molecules, the phycocyanobilin chromophore exhibits an absorption spectrum that reports a cyclic configuration, and its fluorescence is essentially quenched. The absorption and fluorescence spectra exhibit a solvatochromic response in this state, indicating that the chromophore is now exposed to the bulk solvent. Far-UV circular dichroism spectra evidence an abrupt loss of 10% of the alpha-helical character in the nonaqueous solvent concentration regime that results in exposure of the chromophore to the bulk. These results show that the ultrafast solvation response previously detected in the alpha subunit in aqueous media from femtosecond transient hole-burning spectroscopy arises solely from protein-matrix solvation dynamics.

Circular Dichroism↗
PubMed2006

Molecular blending by polymerization of intercalated solvent. Poly(gamma-benzyl-L-glutamate)/benzyl methacrylate as a model system.

The aim of the present research is to obtain blending between a polymer and a (polymerized) solvent on the molecular level. Because of its rigid rod structure, poly(gamma-benzyl-L-glutamate) (PBLG) is chosen as the polymer. Benzyl methacrylate (BzMA) has been chosen as the solvent for two reasons. First, the structure of the solvent is very similar to the structure of the side chain of PBLG, favoring interactions between the two materials. Second, the solvent can be polymerized, because of the presence of a C=C bond. In cast films of PBLG and BzMA separate zones of the polymer and solvent are present. Wide-angle X-ray diffraction and Raman results show that upon heating the cast films homogenization occurs and solvent molecules intercalate between the helices of PBLG. At 150 degrees C a hexagonal packing is obtained. The dimensions of the obtained packing depend on the solvent concentration, which confirms that solvent molecules are indeed present within the crystalline lattice. DSC experiments imply that the observed changes upon heating correspond to thermodynamic processes. On cooling the homogeneous samples, disordering of the hexagonal packing occurs. Polymerization of the homogeneous samples results in a disordering of the hexagonal packing and in a contraction of the unit cell. The latter once more confirms that solvent molecules are indeed present within the crystalline lattice. The applied principle of polymerization of a solvent in a molecular homogeneous system can be favorable for many applications, for which morphology control at the molecular level is required.

Biopolymers↗