Selective Sorption and Solvation in Dansyl-Labeled Poly(dimethylsiloxane) Networks Swollen in Binary Solvent Mixtures (original) (raw)
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Macromolecules, 2011
The use of fluorescent polymers has been reported in studies of scintillators, 1 luminescent solar concentrators, 2 laser-resistant materials, 3 fiber-optic sensors, 4 and laser dyes. 5 Such polymers usually consist of a backbone substituted with fluorophores such as the naphthyl, 6À9 pyrenyl, 7,10À14 and dansyl 8,15À19 entities. The fluorescence intensities and lifetimes of such fluorophores are sensitive to local environment such that steady-state and time-dependent fluorescence studies have provided considerable insight into polymer interactions. 6À19 As part of an exploration of substituent interactions of randomly substituted poly(acrylate)s, PAA, 20À25 we report a UVÀvis, steady-state, and time-resolved fluorescence and 2D 1 H NOESY NMR study of the variation of dansyl substituent spectroscopic response to environmental change at the molecular level in dilute aqueous solution. These observations are used to interpret macroscopic observations gained through rheological studies of variations in the viscosities in terms of network formation in more concentrated solutions. The poly(acrylate)s studied are 3% randomly substituted by N-(2-aminoethyl)-, N-(6-aminohexyl)-, and N-(12-aminododecyl)-5-dansylsulfonamide, PAADSen, PAADShn, and PAADSddn, in which the dansyl substituent tether length progressively increases (Scheme 1). This facilitates studies of the effect of tether length on dansyl substituent, aggregation and complexation by β-cyclodextrin, βCD, and the linked dimer N,N 0 -bis(6 A -deoxy-6 A -β-cyclodextrin)urea, 66βCD 2 ur, in dilute aqueous solution where interactions occur dominantly within individual substituted poly(acrylate) strands.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2014
Interesting solvatochromism in polyether dendron aggregates in mixed aqueous media. Reversal in solvatochromic behaviour depending on percentage of nonaqueous solvent. Negative-solvatochromism due to progressive disaggregation of dendron aggregates. Positive-solvatochromism is shown by the dendron monomers. Higher dendron hydrophobicity requires more of second solvent for disaggregation. g r a p h i c a l a b s t r a c t Reversal in solvatochromic behaviour of dendrons in aqueous medium on addition of a nonaqueous solvent. Negative-solvatochromism is attributed to the progressive disaggregation of dendron aggregates and the positive-solvatochromism is exhibited by the dendron monomers.
Solvatochromic characteristics of dansyl molecular probes bearing alkyl diamine chains
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2020
A series of dansyl-based fluorescent probes bearing linear alkyl-1,n-diamine chains of different length (DA 1.n , n = 2-8, 10, 12) was characterized in terms of the absorptive and emissive features in solvents of different polarity and hydrogen bond donor/hydrogen bond acceptor character. The probes show solvent-dependent absorption, a feature that is uncommon among dansyl derivatives. The dual emission of DA 1.n probes is strong in nonaqueous solvents and is influenced by the chain length and interactions with the solvent. Solvent effects on the spectral parameters were rationalized on the basis of the Kamlet-Taft and Catalán solvatochromic models, in order to quantify the degree of polarity-driven and hydrogen bonding interactions. A comparative discussion of the results predicted by the two models was made. In ground state, the DA 1.n probes act as hydrogen bond acceptors. In excited state, hydrogen bonding is less favoured, the solute-solvent interactions being governed by the increasing polarity of the solvent that results in a large bathochromic shift of the emission. A comparison was made with the spectral features previously reported for the corresponding series of bis-dansyl fluorescent probes (2DA 1.n).
Biochemistry, 1998
To understand the relationship between the chemical structure of polar molecules and their membrane location, the behavior of dansyl (dimethylaminonaphthalenesulfonyl) and related polar fluorescent probes was examined. The depth of these probes in lipid bilayers was determined by parallax analysis of fluorescence quenching [Chattopadhyay and London (1987) Biochemistry 26, 39-45; Abrams & London, Biochemistry (1993) 32, 10826-10831]. Quenching was measured for dansyl groups: (1) attached to the polar headgroup of PE, (2) linked to an alkyl chain, (3) attached to the end of a fatty acyl chain, and (4) attached to the polar headgroup of PE via a spacer group. In all cases, the dansyl probes located in the polar headgroup region, 19-21 Å from the bilayer center. This shows the dansyl group has a strong tendency to seek a shallow location in the polar headgroup region. The only exception to this pattern was in the case of a dialkylated dansyl, for which two populations were observed. One population was at the polar headgroup level, but the second was deeply buried in the acyl chain region. To see if the polar sulfonamide group of dansyl influences depth, a structurally related probe substituting a thiocarbamoyl linkage, dimethylaminonaphthalenethiocarbamoyl (dantyl)-labeled PE, was synthesized. Dantyl groups were located deeper than dansyl groups, 13-16 Å from the bilayer center. There was an even more dramatic difference in depth between dansyl and mansyl (methylanilinonaphthalenesulfonyl) derivatives. Mansyl probes, which have an extra phenyl group relative to dansyl, were found to locate deeply within the acyl chain region of the bilayer (6-7 Å from the bilayer center) when attached to the polar headgroup of PE. Thus, the membrane location of polar groups depends strongly on the details of their chemical structure, and it is possible for a polar group to locate both at shallow and deep locations. These results suggest the energy to bury a polar moiety in the hydrophobic part of the bilayer is not prohibitively high. This contrasts to the behavior of charged groups, which appear to be restricted to shallow locations in membranes. In this report, the effect of populations at two different depths on the parallax analysis is also considered.
Journal of Colloid and Interface Science, 2003
Solubilization environment afforded by several of the novel allyl glycidyl ether-modified methylhydrosiloxane polymers are investigated using a common polycyclic aromatic hydrocarbon fluorescence probe, pyrene. The backbone of the polymer has been modified by the addition of an alkyl chain of varying length (either C 8 , C 12 , or C 18 ) and to differing degrees of substitution. The nomenclature adopted for the purposes of these studies is as follows: "AGENT" represents the backbone polymer with no alkyl substitution, and "OAGENT," "DAGENT," and "SAGENT" are substituted with n-octyl, n-dodecyl, and n-octadecyl, respectively. The percentage of alkyl substitution is designated as 10, 15, and 20%. The pyrene polarity scale (defined as the ratio of the intensity of peak I to peak III) was used to determine the relative dipolarity of the cybotactic region provided by ∼1 w/w% aqueous polymer solutions compared to 10 mM sodium dodecylsulfate (SDS) micellar solution. Results indicate that 10-15% DAGENT afforded the most hydrophobic solubilization site, followed by 15% OAGENT and 15% SAGENT. In addition, as the degree of alkyl substitution of DAGENT increased from 10 to 20%, the cybotactic region appeared to become more hydrophobic. Furthermore, a deeper investigation into the relative size of the solubilization site revealed that all alkyl-substituted polymers promoted excimer formation at relatively low pyrene concentrations, indicating the possibility of localized concentration enhancement within the solvation pockets and/or compartmentalization of the solute molecules. The pyrene fluorescence excitation data strongly indicates ground-state heterogeneity that is most prominent in AGENT and decreases as the alkyl chain length is increased. This provides a relative sense of the size and shape of the solvation pockets afforded by each polymer solution. An overall analysis of the collected data indicated that these alkyl-substituted polymers may provide a more selective and efficient pseudostationary phase in electrokinetic chromatography with better solvation capacity for hydrophobic compounds compared to SDS. (C.P. Palmer).
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2001
Many attempts have been made to rationalize the use of detergents for membrane protein studies [J. Biol. Chem. 264 (1989) 4907]. The barrier properties of the detergent headgroup may be one parameter critically involved in protein protection. In this paper, we analyzed these properties using a model system, by comparing the accessibility of tryptophan octyl ester (TOE) to water-soluble collisional quenchers (iodide and acrylamide) in three detergent micelles. The detergents used differed only in the chemical nature of their polar headgroups, zwitterionic for dodecylphosphocholine (DPC) and nonionic for octa(ethylene glycol) dodecyl monoether (C 12 E 8 ) and dodecylmaltoside (DM). In all cases, in phosphate buffer at pH 7.5, the binding of 5 WM TOE was complete in the presence of a slight excess of detergent micelles over TOE molecules, resulting in a significant blue shift and greater intensity of TOE fluorescence emission. The resulting quantum yield of bound TOE was between 0.08 (in DPC) and 0.12 (in DM) with an emission maximum (V max ) of V335 nm whatever the detergent micelle. Time-resolved fluorescence intensity decays of TOE at V max were heterogeneous in all micelles (3^4 lifetime populations), with mean lifetimes of 1.7 ns in DPC, and 2 ns in both C 12 E 8 and DM. TOE fluorescence quenching by iodide, in detergent micelles, yielded linear Stern^Volmer plots characteristic of a dynamic quenching process. The accessibility of TOE to this ion was the greatest with C 12 E 8 , followed by DPC and finally DM (Stern^Volmer quenching constants K sv of 2 to 5.5 M 31 ). In contrast, the accessibility of TOE to acrylamide was greatest with DPC, followed by C 12 E 8 and finally DM (K sv = 2.7^7.1 M 31 ). TOE also presents less rotational mobility in DM than in the other two detergents, as shown from anisotropy decay measurements. These results, together with previous TOE quenching measurements with brominated detergents [Biophys. J. 77 (1999) 3071] provide reference data for analyzing Trp characteristics in peptide (and more indirectly protein)^detergent complexes. The main finding of this study was that TOE was less accessible (to soluble quenchers) in DM than in DPC and C 12 E 8 , the cohesion of DM headgroup region being suggested to play a role in the ability of this detergent to protect function and stability of solubilized membrane proteins. ß 2001 Elsevier Science B.V. All rights reserved. 0005-2736 / 01 / $^see front matter ß 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 5 -2 7 3 6 ( 0 1 ) 0 0 3 7 0 -4
Interaction parameters and micellisation constant of SDS and DTAB in aqueous and mixed solvents
2013
CMC values of ionic surfactants SDS and DTAB, were determined conductometrically in water, water + propanol and water + fructose systems at different concentrations of propanol and fructose at 298.15, 308.15 and 318.15 K. From CMC values micellisation constant (KM), Setchenov constant (KS N) and interaction parameters ‘P’ and ‘q’ were calculated. KM values are positive for 2-propanol + water system and negative for fructose + water system. KS N values in 2-propanol system are more as compared to fructose system. It suggests that nature of polar group of additive plays major role in solubilisation process. The high ‘P’ and ‘q’ values in presence of 2-propanol suggests that 2-propanol penetrates in the interior of micelle, while larger ‘P’ and ‘q’ values for DTAB in presence of fructose are indicative of adsorption of fructose on the micellar surface.