Peculiar temperature dependence on the binding of methyl orange and its homologs by 2-hydroxyethyl methacrylate-N-vinyl-2-pyrrolidone copolymers

2-Hydroxyethyl methacrylate (HEMA)-N-vinyl-2-pyrrolidone (VPy) copolymers of various compositions have been prepared. The copolymers obtained were examined for their ability to bind a homologous series of methyl orange derivatives, methyl orange, ethyl orange, propyl orange, and butyl orange, at 5, 15, 25, and 35°C, respectively, in an aqueous solution. The first binding constants and the thermodynamic parameters that accompanied the binding were evaluated. The binding ability of the copolymer for the small cosolute was enhanced with an increase of the HEMA content in the copolymer. Moreover, a bell-shaped curve appeared in the binding of butyl orange by the copolymers having higher HEMA residues when the first binding constant was plotted as a function of temperature, whereas no such phenomenon was detected for the copolymers with less HEMA content or for the less hydrophobic dye, methyl orange, ethyl orange, or propyl orange. This peculiar temperature dependence of the first binding constant shows that the enthalpy of the binding varies from a positive (unfavorable) value below ca. 15°C to a negative (favorable) one above this temperature. This behavior can be accounted for in terms of more hydrophobic effects involved in the binding process.     

Thermodynamics of binding methyl orange and its homologs by polyvinylpyrrolidone: The effect of hexamethylenetetramine

Hexamethylenetetramine (HMT) has been examined for its effect on the binding of methyl orange homologs, methyl orange, ethyl orange, propyl orange, and butyl orange by polyvinylpyrrolidone (PVP). In the presence of HMT the entropy changes associated with the binding tend to become more positive and the absolute magnitude in the enthalpy changes becomes smaller compared with those in the absence of HMT. These tendencies are accounted for in terms of the water-structure-promoting effect of HMT, hence the enhancement of hydrophobic interactions in the binding. PVP undergoes changes in conformation on the addition of HMT and its conformation becomes more compact. This also increases the contribution of the hydrophobic interactions to the macromolecule-small molecule interaction. Some other effects exerted by the added HMT on the binding system are also described.     

Cross-linked polyvinylpyrrolidones with increased affinity and specificity for methyl orange and its homologs

Polyvinylpyrrolidones of various degrees of cross-linkage have been prepared by radical polymerization of N-vinylpyrrolidone with methylenebisacrylamide to regulate the fraction of cross-linkage. The insoluble polymers obtained were examined for their ability to bind methyl orange and its homologs, methyl orange, ethyl orange, propyl orange, and butyl orange at 5, 15, 25, and 35°C, respectively, in an aqueous solution. The first binding constants and the thermodynamic parameters that accompanied the binding were calculated. For any particular dye the extent of binding, the absolute magnitude of ΔF°, and the value of ΔS° increased as the degree of cross-linkage increased, starting with water-soluble polyvinylpyrrolidone (zero cross-linkage) and proceeding to the polymer with high cross-linking density. This behavior can be accounted for in terms of more extensive hydrophobic domains in the cross-linked polymeric matrix that enhances hydrophobic interactions in the binding process. Moreover, the cross-linked macromolecule polymerized in the presence of methyl orange and then stripped of the bound methyl orange shows substantially stronger binding for this small molecule than the polymer cross-linked in the absence of methyl orange. In contrast, the cross-linked polymer prepared similarly in the presence of the larger molecule, butyl orange, exhibits decreased affinity toward the smaller consolute, methyl orange, than either of the other polymers described. It seems, therefore, that the polymeric matrix provides favorable binding sites or pockets that can accommodate a specific small molecule. The preparative procedure, which uses a small-molecule template, molds into the polymer some structural specificity in the binding of small molecules.     

Interaction of crosslinked polyvinylpyrrolidone with a homologous series of methyl orange derivatives in aqueous and nonaqueous solutions: Thermodynamics of the binding equilibria

The extent of binding of methvI orange, ethyl orange, propyl orange, and butyl orange by crosslinked polyvinylpyrrolidone was measured in all aqueous Solution. The first binding constants and the thermodynamic parameters accompanying the binding were evaluated. These values were compared with those of water-soluble polyvinylpyrrolidone. The first binding constant, the absolute magnitude of ΔF°, and the value of ΔS° of the crosslinked polyvinylpyrrolidone are substantially larger than those of the water-soluble product for any particular dye. These behaviors can be accounted for in terms of increased hydrophobic domains in the former and enhanced hydrophobic contribution in the binding process. Also the binding of the dye by the crosslinked polymer in a nonaqueous solvent, ethylene glycol, was measured to assess the contribution of hydrophobic interaction to the dye-polymer complex formation in aqueous medium. It was found that the binding of butyl orange by the crosslinked polymer is suppressed in ethylene glycol and the contribution of entropy term to the free energy change in the aqueous environment is large compared with that in ethylene glycol. The significance of the hydrophobic of the hydrophobic interaction in the dye-polymer association process is described.     

Peculiar temperature dependence of the binding of methyl orange and its homologs by 2-diethylaminoethyl methacrylate-N-vinyl-2-pyrrolidone copolymers

2-Diethylaminoethyl methacrylate (DEAEMA)–N-vinyl-2-pyrrolidone (VPy) copolymers of various compositions have been synthesized. The resultant copolymers were examined for their ability to bind methyl orange and its homologs, in particular butyl orange, at 5, 15, 25, and 35°C in aqueous solutions. The amount of binding of butyl orange is much higher with the copolymers than with polyvinylpyrrolidone or with 2-hydroxyethyl methacrylate–N-vinyl-2-pyrrolidone copolymers. Introduction of only 3% of the hydrophobic DEAEMA residue increases markedly the binding affinity toward the cosolute. Maximal binding is obtained at 15°C in the temperature range measured. This peculiar temperature dependence of the extent of binding is explicable on the basis of hydrophobic effects involved in this binding. The peculiar temperature dependence disappeared in aqueous solution of NaSCN which acts as a water-structure breaker: the extent of binding changes regularly with temperature. This is interpretable only in terms of reduction of hydrophobic contribution to the binding. With propyl orange, which is a less hydrophobic cosolute than butyl orange, the peculiarity of the binding was not detected.     

Interaction of poly(vinylpyrrolidone) with methyl orange and its homologs in aqueous solution over the temperature range 60–90°c

The binding of methyl orange, ethyl orange, propyl orange, and butyl orange by poly(vinylpyrrolidone) has been examined by a technique of equilibrium dialysis over a high temperature range (60–90°C). The first binding constants and the thermodynamic parameters in the course of the binding were evaluated. The results obtained at these temperatures were compared to those at lower ones (5–35°C) described previously in order to estimate the contribution of hydrophobic bonds to the binding. It was found that at the 60–90°C range complex formation between the dye and the macromolecule is associated with an exothermic enthalpy change and a positive entropy change. The enthalpy and entropy changes of the binding are of the order of ?4.5 kcal/mole and 6 eu, respectively, for each dye measured. Thus the binding is mainly enthalpy-controlled. Furthermore the effect of the alkyl chain length of the dye on both the ΔH° and ΔS° values is not pronounced. Also temperature dependences of the ΔH° and ΔS° terms were not observed. All these observations in the higher temperature range can be explained as a result of the disruption of water structure in the binding environment and hence a decrease in hydrophobic bond formation between the dye and the polymer.     

Binding of methyl orange and its homologs by polycations containing apolar pendant groups

The binding of methyl orange, ethyl orange, and propyl orange by polycations involving various apolar pendant groups such as methyl, ethyl, benzyl, or dodecylbenzyl groups has been examined quantitatively by an equilibrium dialysis method at 5, 15, 25, and 35°C. The first binding constants and the thermodynamic parameters in the course of the binding have been calculated. The favorable free energy of the binding is accompanied by an entropy gain and an exothermic enthalpy change. The shorter the alkyl chain of the dyes or the polymers, the more negative is the enthalpy change and hence the smaller is the entropy change. Furthermore, an increase in binding affinity can be created in the polycation upon introduction of hydrophobic groups. In particular, the binding ability of the polycation containing a dodecylbenzyl group for methyl orange is almost 300-fold that of bovine serum albumin. Therefore it is clear that hydrophobic interactions, as well as electrostatic ones, are involved in the binding.     

Interaction of polyvinylpyrrolidone with methyl orange and its homologs in aqueous solution: Thermodynamics of the binding equilibria and their temperature dependences

The interaction of polyvinylpyrrolidone with methyl orange, ethyl orange, propyl orange, and butyl orange has been studied by an equilibrium dialysis method at 5, 15, 25, and 35°C. The first binding constants and the thermodynamic parameters in the course of the binding have been calculated. It was found that the free energy and the enthalpy changes are all negative and the entropy change is largely positive. The longer the alkyl chain of the dyes, the more positive is the enthalpy change (though it is always in the negative direction) and hence the larger is the entropy change. The favorable free energy of the binding of butyl orange observed for the formation of the dye–polymer complex seems to be a result of a favorable entropy change rather than any favorable enthalpy change. Temperature dependences of the thermodynamic functions were apparently observed. That is, ΔF and ΔH become larger in absolute magnitude as the temperature increases. The positive quantity of ΔS tends to decrease with increasing temperture. All these facts obtained can be interpreted satisfactorily by the hydrophobic interaction between hydrocarbon portions of the dyes and nonpolar parts of the macromolecule.     

Interaction of crosslinked polyethylenimine with a homologous series of methyl orange derivatives in aqueous solution

Polyethylenimine (PEI) was crosslinked with dichloroethane, glyoxal, or glutaraldehyde and polymers of various degrees of crosslinkage were made. The insoluble polymers obtained were examined for their ability to bind methyl orange and its homologs, methyl, ethyl, propyl, and butyl orange at 5, 15, 25, and 35°C, respectively, in an aqueous solution. PEI crosslinked with glutaraldehyde showed markedly increased binding affinity toward these cosolutes compared with the polymers crosslinked with dichloroethane or glyoxal. The extent of the binding increased with an increase in the degree of crosslinkage. These results suggest that the enhancement of the binding by the crosslinking is due mainly to a dual effect, introduction of hydrophobic moieties and proximity of neighboring polymer chains. The first binding constants and the thermodynamic parameters that accompanied the binding were calculated. The thermodynamic data show that the binding process is athermal and is stabilized entirely by the entropy term. Water-soluble PEI exhibited stronger cooperative interactions than the crosslinked polymer because the mobilities of the chains of the former are greater than those of the latter.     

Binding of methyl orange and its homologs by polyion complexes in aqueous solution

Polyion complexes of sodium poly(methacrylate) and piperidinium cationic polymers [I], which are insoluble in water and have an equal number of positive and negative charges, bind organic anions (methyl orange, ethyl orange, propyl orange, butyl orange, and pentyl orange) in aqueous solution. The strength of the binding is enhanced by an increase in the hydrophobicity of the polyion complex and the small cosolute. Moreover, strong cooperative interactions appear with increased uptake of the small molecule. Urea and an inorganic electrolyte (KCl) were examined for their effect on the binding, the amount of which is strongly suppressed by these additives. The significance of hydrophobic and electrostatic interactions which accompany the binding is described.     

Enantioseparation of Tropic Acid and Its Esters by CEKC Using Sulfated β-Cyclodextrin as a Chiral Selector

Capillary electrokinetic chromatography was successfully applied to the enantioseparation of tropic acid and its four alkyl esters (methyl, ethyl, propyl and butyl), with the same chiral center, Separation was with sulfated β-cyclodextrin (4%, m/v) containing 20 mM phosphate buffer at pH 3.0 as background electrolyte at 20 °C. The results showed that, besides hydrogen-bonding interactions between these compounds with sulfated β-CD, for tropic acid and its methyl ester the steric hindrance effect was also an important factor. However, for the other esters (ethyl, propyl and butyl), the hydrophobicity effect was higher.     

Enantioseparation of Tropic Acid and Its Esters by CEKC Using Sulfated β-Cyclodextrin as a Chiral Selector

Capillary electrokinetic chromatography was successfully applied to the enantioseparation of tropic acid and its four alkyl esters (methyl, ethyl, propyl and butyl), with the same chiral center, Separation was with sulfated β-cyclodextrin (4%, m/v) containing 20 mM phosphate buffer at pH 3.0 as background electrolyte at 20 °C. The results showed that, besides hydrogen-bonding interactions between these compounds with sulfated β-CD, for tropic acid and its methyl ester the steric hindrance effect was also an important factor. However, for the other esters (ethyl, propyl and butyl), the hydrophobicity effect was higher.

     

Binding of anthraquinone dyes by polyion complexes consisting of a piperidinium cationic polymer and various polyanions in aqueous solution

The extent of binding of 1-amino-4-alkylaminoanthraquinone-2-sulfonates (alkyl?methyl, ethyl, propyl, and butyl), which have different chemical structures from methyl orange derivatives, by polyion complexes consisting of a piperidinium cationic polymer and various polyanions such as sodium poly acrylate, poly methacrylate, poly styrenesulfonate, carboxymethylcellulose, and dextran sulfate, was measured in an aqueous solution. The effect of alkyl group of the anthraquinone dye on the binding behavior was investigated. Also, the resultant binding characteristics were compared with those previously observed with methyl orange and its homologs. These polyion complexes exhibited very strong binding affinity toward the anthraquinone dye. The polyion complex of the polycation and sodium poly styrenesulfonate bound the dye noncooperatively and the binding process was athermal. The first binding constant accompanying the binding is of the order of 10⁵–10⁶. In contrast, the polyion complexes composed of the polycation and the other polyanions exhibited strong cooperative binding and the binding process was exothermic. The possible mode of binding is discussed.     

Temperature dependence on the binding of butyl orange by bovine serum albumin

The binding of 4′-dibutylaminoazobenzene-4-sulfonate anion (butyl orange) by bovine serum albumin has been examined quantitatively by an equilibrium dialysis method at 5, 10, 15, 20, 25, and 35°C. The first binding constants and the thermodynamic parameters for the formation of the first dye anion-protein complex have been calculated. The peculiar temperature dependence of the first binding constant could be observed. That is, the value of the first binding constant increases with increasing temperature until it reaches a maximum value at approximately 18°C and then decreases with raising temperature. Accordingly, this binding process is exothermic above 18°C and is endothermic below 18°C. Near 18°C the process exhibits athermal reaction. From the thermodynamic data obtained, it is evident that the favorable free energy of the binding is accompanied by an entropy gain and that the enthalpies of the binding vary from a positive (unfavorable) value below 18°C to a negative (favorable) one above 18°C. Furthermore an apparent temperature dependence of the thermodynamic functions was observed. That is, ΔF° becomes larger in absolute magnitude as the temperature increases. The positive quantity of ΔS° tends to decrease with increasing temperature. All these facts can be interpreted satisfactorily in terms of hydrophobic interactions between hydrophobic portions of the dye and nonpolar parts of the albumin.     

Synthesis and characterization of poly(4‐alkyl‐4‐methyl‐2‐azetidinone)s

Poly‐β‐amides (nylons 3) were synthesized via the anionic polymerization of a series of 4‐alkyl‐4‐methyl‐2‐azetidinones where the alkyl group is a methyl, ethyl, propyl, butyl, or pentyl. The “non‐assisted” polymerization was conducted under vacuum, in the bulk, at 160°C, using potassium 2‐pyrrolidonate as catalyst, whereas the “assisted” polymerization was carried in dimethylsulfoxide, at room temperature, using N‐acetylpyrrolidinone‐2 as activator but it gave no polymer with a propyl or bulkier side group. Side reactions occur in all cases. X‐ray spectra showed that poly(4‐alkyl‐4‐methyl‐2‐azetidinone)s are amorphous with propyl, butyl, and pentyl groups, and semi‐crystalline with methyl or ethyl substituents. Both semi‐crystalline polyamides exhibit an extended planar zigzag conformation, with a fiber identity period along the c axis of 4.9 Å. Glass transition temperatures, melting temperatures, and/or decomposition temperatures are also reported. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 761–769, 1999     

Thermodynamics of binding of methyl orange and its homologs by poly(vinylpyrrolidone): The effect of inorganic electrolytes

The extent of binding of methyl orange, ethyl orange, propyl orange, and butyl orange by poly(vinylpyrrolidone) has been measured in aqueous solutions of inorganic electrolytes such as NaCl, LiCl, NaSCN, and NaClO₄ by an equilibrium dialysis method. The effect of the salts on the first binding constants and the thermodynamic functions which are accompanied by the dye—polymer association process was investigated relative to the corresponding values in the absence of such salts. It was found that in aqueous solutions of NaCl and LiCl the enthalpy change accompanying the binding is small and the largest contribution to the free energy of binding is from the positive entropy gain. For NaSCN and NaClO₄, the values of ΔF° and ΔH° were both large and negative and the value of ΔS° was small and negative. Thus, the favorable free energy for the complex formation was due entirely to the negative enthalpy term. These characteristics of the thermodynamic quantities are discussed in terms of changes in structural properties of water in the vicinity of the binding entities and conformational changes of the polymer to which the dye is bound due to the added foreign electrolytes.     

Binding of methyl orange and its homologs by polyion complexes consisting of a piperidinium cationic polymer and various polyanions in aqueous solution

A study was made of the formation of polyion complexes between a piperidinium cationic polymer and polyanions and of the binding of azo-dye anions (methyl, ethyl, propyl, and butyl orange) by these complexes. Sodium poly(acrylate), poly(styrenesulfonate), dextran sulfate, and carboxy-methylcellulose were used as polyanions. The resultant polyion complexes (insoluble in aqueous solutions) were compared for their ability to bind the small organic molecules in aqueous solutions, for example, of urea and an inorganic electrolyte (KCI), and exhibited a strong binding affinity toward these small anions. Polyion complexes that consisted of sodium poly(acrylate), dextran sulfate, and carboxymethylcellulose as polyanions cooperated in the binding, whereas the polyion complex of sodium poly(styrenesulfonate) did not. It was suggested that small organic anions interact with the polyion complexes primarily through electrostatic and hydrophobic forces.     

Synthesis and Crystallochromy of 1,4,7,10‐Tetraalkyltetracenes: Tuning of Solid‐State Optical Properties of Tetracenes by Alkyl Side‐Chain Length

We synthesized a series of 1,4,7,10‐tetraalkyltetracenes using a new 2,6‐naphthodiyne precursor and 2,5‐dialkylfurans as starting materials (alkyl=methyl to hexyl). Surprisingly, the solid‐state color of the tetracenes ranges through yellow, orange, and red. Both yellow and red solids are obtained for the butyl derivative. Optical properties in solution show no marked differences; however, those in the solid state show characteristics that vary with alkyl side‐chain length: methyl, propyl, and pentyl derivatives are orange; ethyl and butyl derivatives are yellow; and another butyl and hexyl derivative are red. X‐ray analyses reveal that the molecular structures are planar, semi‐chair, or chair forms; the chair form takes a herringbone‐like arrangement and the other forms take slipped parallel arrangements. The mechanism of crystallochromy is discussed in terms of molecular structure, crystal packing, and calculations that take account of exciton coupling.     

Binding of methyl orange and its homologs by powdered nylon 66

Powdered Nylon 66 was prepared as a model of amorphous polymers. The resultant powder polyamide was composed of only amorphous regions. The extent of uptake of the acid azo dyes, a homologous series of methyl orange derivatives, by the polymer was measured in an aqueous solution. The first binding constants and the thermodynamic parameters in the course of the binding were evaluated. The thermodynamic behaviors obtained are very similar to those of crosslinked polyvinylpyrrolidone. The favorable free energy of the binding is accompanied by an entropy gain and an exothermic enthalpy change. The shorter the alkyl chain of the dyes, the more negative is the enthalpy change and, hence, the smaller is the entropy change. The thermodynamic data for butyl orange showed that the binding process is athermal and is wholly an entropic effect. The binding of the dyes to the matrix is entropically favorable as a result of the operation of the hydrophobic effect. In addition, an electrostatic force is operative between the sulfonate group on the dyes and the terminal amino groups on the polyamide.     

Tricarbonylchromium complexes of styrenes in radical copolymerization

The organometallic monomers styrenetricarbonylchromium and p‐methylstyrenetricarbonylchromium were copolymerized in ethyl acetate solutions with methyl methacrylate and butyl acrylate using azobisisobutyronitrile at 50 °C and a binary system including di‐tert‐butylperoxytriphenylantimony at 30 °C as the free‐radical initiators. Comonomers are proposed to form a molecular complex based on the results of ultraviolet and electron spin resonance spectroscopy. A kinetic study shows that chromium‐containing monomers at high concentrations in the mixture reduce the rate of copolymerization. The addition of styrenetricarbonylchromium to butyl acrylate significantly slows down the autoacceleration. The reactivity ratios of the comonomer pairs, namely, styrenetricarbonylchromium–methyl methacrylate, styrenetricarbonylchromium–butyl acrylate and p‐methylstyrenetricarbonylchromium–methyl methacrylate, were determined using the method of Kelen–Tudos for low conversion polymerizations.Copyright © 2001 John Wiley & Sons, Ltd.