Probe In Aqueous Solution Research Articles

Counterion Condensation and Conformational Transitions of Polyelectrolytes Characterized by EPR Spectroscopy

Counterion condensation of multivalent, charged spin probes to highly charged cationic and anionic polyelectrolytes is characterized by CW and FT EPR spectroscopy. Line broadening and deviation from Lorentzian line shape in the EPR spectra of the spin probes are observed upon addition of the polyelectrolyte. These effects are due to dynamic electrostatic attachment of the counterions with exchange between the condensed and free states on a subnanosecond time scale. The spectral changes can be separated into a contribution due to slowdown of rotational dynamics and a contribution due to enhanced spin exchange. A drastic increase of the spin-exchange contribution is observed upon increasing the concentration of two anionic spin probes in aqueous solutions of the cationic polyelectrolyte poly(diallyldimethylammonium chloride), PDADMAC. This can be traced back to a counterion-induced chain collapse which is, however, not observed in mixtures of water with organic solvents of either higher (N-methylpropionamid...

Rate Constants of the Thermal Cis → Trans Isomerization of Azo Dyes as Kinetic Probes in Aqueous Solutions of Poly(ethylene glycols) and Poly(ethylene oxide)−Poly(propylene oxide)−Poly(ethylene oxide) Block Copolymer F88

By means of microsecond flash photolysis the rate constants, kiso, of the thermal cis → trans isomerization of two azo dyes were determined in dependence on temperature in aqueous solutions of poly(ethylene glycols) (PEGs) and of a poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) block copolymer (F88, EO96PO39EO96). PEG/water mixtures are considered as a model for the PEO/water interface layer of micelles of F88. The dependence of kiso on bulk viscosity of PEG/water mixtures varying with the number of water molecules, Z, per ethylene oxide unit is stronger than that in water-free solutions, and the kinetic solvent isotope effect (kiso,H2O/kiso,D2O) is larger than the viscosity solvent isotope effect of the mixtures (ηD2O/ηH2O). Therefore we assume that beside changes of microviscosity a dynamic hydrogen bonding effect of water contributes to the sensitivity of kiso on nanostructure changes in aqueous surfactant solutions. Comparing temperature-dependent kiso,Z data from PEG/water mixtures with kiso values determined in aqueous solutions of F88, hydration numbers Z in the microenvironment of isomerizing dyes were approximately estimated. From S-shaped Arrhenius plots of kiso critical micellization temperatures were determined, and the dependence of kiso data on copolymer concentration is discussed.

Near-field optical microscopy with a vibrating probe in aqueous solution

We show that with an appropriately configured scanning quartz pipette coated with aluminum, a near-field scanning optical microscope (NSOM) can be constructed to operate in aqueous solution for applications in biology. Many of the technical limitations associated with a scanning pipette were circumvented by introducing a small modulation of the distance between the pipette and the sample. We show that this ac method allows the pipette to be positioned very close to the sample surface and is robust in obtaining reproducible NSOM images in solution. This approach is also compatible with fluorescence imaging and fluorescence resonance energy transfer, and should further facilitate the use of NSOM in various areas of cell biology where high resolution is considered to be critical.

Electron spin resonance (ESR) spectra of amphiphilic spin probes in the triblock copolymer EO13PO30EO13 (Pluronic L64): hydration, dynamics and order in the polymer aggregates

Aqueous solutions of the triblock copolymer poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) EO13PO30EO13 (Pluronic L64) were investigated over a wide concentration range (20–100%, (w/w) polymer) in the micellar, liquid crystalline and reverse micellar phases, using electron spin resonance (ESR) spectroscopy of spin probes. A series of amphiphilic nitroxide spin probes based on n-doxylstearic acid (nDSA) with n, the carbon atom to which the doxyl group is attached, equal to 5 and 10 were used to measure the local polarity, dynamics and degree of order in the self-assembled system. The 14N isotropic hyperfine splitting, aN, was the polarity sensitive parameter. The probe location and the corresponding effective local hydration, Zeff, were deduced by comparing ESR spectra of the probes in L64 solutions with spectra of the probes in aqueous solutions of poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO) and a mixture of PEO and PPO containing the monomer molar ratio 26:30, as in L64. The results indicate that the probes reside in and provide evidence for the presence of hydrophobic and non-hydrated regions consisting of PO blocks and that the order in the aggregates decreases from the PO/EO interface toward the PO domains. Additional support for these conclusions was obtained from ESR spectra of the probes in the lamellar phase as a function of added cholesterol and by simulations of the ESR spectra of the probes in the lamellar phase of L64. This study of the hydrophobic part of the aggregates, together with our previous study based on ESR spectra of cationic probes that reside in the polar and hydrated EO regions, lead to a detailed description of the nature of L64 aggregates in aqueous solutions.

New Strategies for Surface-Enhanced Raman Scattering at Transition-Metal Interfaces: Thickness-Dependent Characteristics of Electrodeposited Pt-Group Films on Gold and Carbon

The surface-enhanced Raman scattering (SERS) properties of rhodium films electrodeposited onto a SERS-active gold substrate are examined as a function of overlayer thickness, using carbon monoxide and thiocyanate as chemisorbate probes in aqueous solution. Although the adsorbate Raman signals obtained for ultrathin (≤10 monolayers, ML) Rh layers emanate from the gold template, a significant or even dominant SERS component for thicker films is identified as arising instead from the transition-metal overlayer itself. The latter contribution was diagnosed and characterized from similar experiments undertaken using SERS-inactive gold and carbon substrates, and from the observation of comparable Raman enhancements obtained with green (514.5 nm) as well as red (632.8 nm) excitation. While the surface enhancement factors for these layers, of the order of 103, are markedly less than those obtained for ultrathin films on SERS-active gold, the signals even for very weak Raman scatterers (such as adsorbed hydrogen) ...

Spectroscopic Studies of the Interaction of Methyl Orange with Cationic Alkyltrimethylammonium Bromide Surfactants

The spectral signature of the azo dye methyl orange (MO) exhibits a considerable sensitivity to the polarity of the dye's environment. We have used this dependence of absorption wavelength on microenvironment to investigate the 1:1 ion pair complexes formed from electrostatic interaction of a series of cationic alkyltrimethylammonium bromide (CnTAB) detergents with the anionic organic probe in aqueous solution. At surfactant concentrations far below the critical micelle concentration, MO shifts in absorbance λmaxfrom 462 nm in aqueous solution to 367–377 nm upon complex formation. Nonlinear least-squares deconvolution of the absorbance spectra reveals a previously unreported significant blue shift in λmaxwith increasing surfactant alkyl chain length. Our time-dependent spectrophotometric studies of the MO–CnTAB complex systems reveal, also for the first time, that a subsequent spectral shift to shorter wavelengths (λmax= 348–350 nm) occurs for those alkyl chain lengths greater thann= 14. These observations are consistent with an aggregation of the surfactant–dye pair after initial complex formation. Increased hydrophobic interaction of the azo ring of the probe with additional neighboring surfactant alkyl chains to achieve a final equilibrium state is hypothesized to account for the MO absorbance spectral shift.

Effect of Geometric Constraints on the Self-Assembled Monolayer Formation of Aromatic Disulfides on Polycrystalline Gold

The self-assembled monolayer (SAM) formation tendency of two comparatively small aromatic disulfide molecules, namely naphthalene disulfide (NDS) and diphenyl disulfide (DDS), has been investigated using quartz crystal microgravimetry (QCM), cyclic voltammetric, and impedance techniques. The typical time period for monolayer formation on polycrystalline gold has been found to be about 2 h for both the molecules from the QCM data. A significant change in double-layer capacitance values (from 21 μF/cm2 for bare gold to ∼14 and ∼8 μF/cm2 for NDS and DDS, respectively) upon monolayer formation for both the cases has been observed, which correlates well with the QCM area per molecule values (∼49 and 36 Å2 for NDS and DDS, respectively). The difference in the permeability of the two monolayers to simple ionic species was also investigated using K3Fe(CN)6 as redox probes in aqueous solution. A mixed linear/radial mode of diffusion is observed at the DDS-modified electrode in contrast to a predominant linear one at the electrode derivatized with a NDS monolayer. Impedance measurements indicate apparent surface coverages of 99.6 and 99.8% and rate constants of 9.4 × 10-5 and 4.1 × 10-5 cm/s for the Fe(CN)63-/4- couple in the case of NDS and DDS, respectively. These results strongly demonstrate the effect of geometrical constraints in controlling the microscopic structure and the packing density of the SAMs and highlight the importance of intramolecular conformational changes in controlling the monolayer packing density.

水溶液中でのアクリジンオレンジ会合体の構造と解離平衡

The aggregate states of Acridine Orange bimolecular probe in aqueous solution and micelle media were strudied by absorption spectroscopy. The absorption spectra of the solutions involving Acridine Orange (AO) change with their concentrations. On the basis of Kasha's theory on the difference spectrum between the solution of the AO monomer and that of dimer, the averaged distance between molecular planes of AO's and the dihedral angle in dimer molecules were estimated as 4.4 A and 80°, respectively.It was also shown that the AO dimer dissociates by the addition of surfactant to AO aqueous solution. Dissociation equilibrium of bimolecular associates (dimer) of AO was studied thermodynamically. At the temperature of 30-60°C, absorption spectra of aqueous solutions of AO showed only monomer and dimer bands. Spectral changes with varying temperature suggested that a simple equilibrium between AO dimer and monomer. The values of dissociation constant K and dissociation enthalpy δH were estimated to be 4.24-6.45×10-5 mol dm-3 in the range from 40 to 60°C, and 4.16 kcal mol-1, respectively.

An evanescent wave biosensor. II. Fluorescent signal acquisition from tapered fiber optic probes

A biosensor was developed using antibodies, fluorescence and the evanescent wave to detect antigen binding at the surface of an optical fiber. Cladding was removed from the core along the distal end of a step-index optical fiber, and recognition antibodies were immobilized on the declad core to form the probe sensing region. Immersing the declad probe in aqueous solution creates a V-number mismatch between the immersed probe and the clad fiber. Probes created with reduced sensing region radius exhibited improved response by decreasing the V-number mismatch. Tapering the radius of this region has further improved probe response. Ray tracing analysis of the tapered probe demonstrated that the evanescent wave penetration depth increases along the length of the taper. Experiments correlating position of refraction along the taper with launch angle at the proximal end were realized in the ray tracing model. An evanescent wave immunoassay was performed with a series of the tapered fiber probes, each tapered from the fiber core radius (100 microns) to different end radii. An end radius of 29 microns was found to produce maximal signal from the tapered probe. Factors leading to the determination of the optimized probe are discussed.

Studies of the antenna effect in polymer molecules 19. Synthesis, solubilizing and photocatalytic activity of several methacrylic acid—9-vinylphenanthrene copolymers

A block copolymer of methacrylic acid (MA) and 9-vinylphenanthrene (9-VPh) was prepared by anionic polymerization, and several poly(methacrylic acid-co-9-vinylphenanthrene) (PMA—9-VPh) polymers were synthesized by free-radical polymerization. All copolymers are water soluble and display solubilizing ability towards hydrophobic probes in aqueous solution. The relative hydrophobicity of the solubilizing microdomains in aqueous solutions of PMA—9-VPh copolymers, determined using pyrene as an environment-sensitive probe, is high. The effect of the pH and ionic strength of the solution on the solubilization ability of the copolymers was studied. The PMA—9-VPh copolymers act as efficient photocatalysts in the photo-oxidation of perylene. The block copolymer is the most efficient photocatalyst. The differences between the photocatalytic efficiencies of random and block copolymers demonstrate the importance of the antenna effect in synthetic polymers.

Chelation-enhanced fluorescence of anthrylazamacrocycle conjugate probes in aqueous solution

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTChelation-enhanced fluorescence of anthrylazamacrocycle conjugate probes in aqueous solutionEngin U. Akkaya, Michael E. Huston, and Anthony W. CzarnikCite this: J. Am. Chem. Soc. 1990, 112, 9, 3590–3593Publication Date (Print):April 1, 1990Publication History Published online1 May 2002Published inissue 1 April 1990https://doi.org/10.1021/ja00165a051RIGHTS & PERMISSIONSArticle Views1624Altmetric-Citations245LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (584 KB) Get e-Alerts Get e-Alerts

Association of hydrophobic polymers in water and water-d2: fluorescence studies with (hydroxypropyl) cellulose

The effects of substituting D{sub 2}O for H{sub 2}O on the fluorescence properties of the pyrene probe in aqueous solutions of (hydroxypropyl)cellulose (HPC) and of pyrene-labeled (hydroxypropyl)cellulose (HPC/Py) have been investigated as a function of temperature and of added surfactants. The polarity-dependence of the vibrational structure of the pyrene emission indicated (1) small differences in polarity between solutions of HPC in D{sub 2}O and H{sub 2}O below and above the lower critical solution temperature and (2) the formation of micelle like surfactant aggregates with sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium chloride (HTAC) at concentrations significantly below the critical micelle concentrations of the surfactants. The extent of pyrene excimer emission from solutions of HPC/Py in D{sub 2}O and H{sub 2}O was found to depend on temperature and on the amount of added surfactants. The excimer emission increased with increasing solution temperature from 4 to 35{degree}C and then dropped sharply before the cloud point of the polymer. Addition of SDS or HTAC to solutions of HPC/Py resulted in a decrease in excimer intensity, with a corresponding increase in monomer intensity. Significant solvent isotope effects were observed. The extent of excimer emission of HPC/Py solutions was larger in D{sub 2}O than in H{submore » 2}O for solution temperatures between 25 and 40{degree}C. The critical aggregation concentration of HTAC/HPC was lower in D{sub 2}O (4.9 {times} 10{sup {minus}4} M L{sup {minus}1}) than in H{sub 2}O (6.8 {times} 10{sup {minus}4} M L{sup {minus}1}). The results were interpreted in terms of increased hydrophobic interactions between the pyrene labels of the polymer and between HTAC and the polymer in D{sub 2}O compared to H{sub 2}O.« less

Study of complex molecular systems by probe vibrational spectroscopy method

Abstract Experimental study of benzonitril as a probe in aqueous solution of sodium lauril sulphate /SDS/ by Raman spectroscopy technique showed integral moments of √ /C X N/ line to be extremely sensitive to the structural transitions in micellar systems. The central part of the experimental contour was used to determine integral moments with the help of line shape approximant received by Mori method

Picosecond relaxation of the fluorescence probes ANS and TNS in aqueous solutions

Fluorescent dyes whose quantum yields are particularly sensitive to their environment have been extensively used as probes in structural studies of biological species [I]. Interpretation of the emission properties is used to give information on structure and relaxation dynamics. Dyes of the N-arylaminonaphthalene sulfonate family have been widely applied as probes of the polarity of sites in proteins or as hydrophobic probes since the fluorescence of these molecules in non-polar solvents varies dramatically from that in polar solvents [2,3]. The fluorescence properties of these organic dyes covalently linked to proteins has been shown to depend upon the conformational state of the protein [4]. Generally, the most common feature of the fluorescence examined is the quantum yield. However, interest now is being directed towards understanding the kinetics of many of the processes in biological specimens following excitation with a short burst of energy. Therefore, time-resolved emission of the fluorescence is essential for an indication of the conformational changes in the specimen following excitation, solvent reorientation, complex formation or energy transfer processes, which straightforward measurement of quantum yield is incapable of providing. To understand these processes, it is first needed to examine the fluorescence decay of the fluorescence probes themselves following excitation. In the past, information of this type has been rather limited. This is due to the fact that many of the probes in aqueous solutions for example have extremely low quantum yields [5 J and ultrafast (-ps) decays, making accurate measurement difficult. However, our recently developed synchroscan streak camera used in conjunction with a low average power CW mode-locked dye laser, enables picosecond lifetimes to be examined routinely with a resolution of -3 ps. Here, we report on the measurement of the decay kinetics of the commonly used fluorescence probes, determining their radiative and non-radiative decay rates and examining these decays in various mixed solvent solutions of variable viscosity and polarity.

THE EFFECT OF ALIPHATIC ALCOHOLS ON FLUORESCENCE QUENCHING AND FLUORESCENCE POLARIZATION OF LUMINESCENCE PROBES IN HEXADECYLTRIMETHYLAMMONIUM BROMIDE MICELLES

Abstract— The fluorescence quenching of the indole chromophore by NO−2 and the fluorescence depolarization of several luminescence probes in aqueous solutions containing hexadecyltrimethylammonium bromide (HDTBr) were measured as a function of added C2–C4 aliphatic alcohol concentration. The fluorescence decay profiles of pyrene in the micellar solutions were also measured to estimate the aggregation number of the micelles. The addition of n‐butyl alcohol significantly reduces the fluorescence quenching rate and the aggregation number and increases the extent of fluorescence depolarization in HDTBr micellar systems. The addition of ethyl alcohol shows a similar but smaller effect.

The behavior of the fluorescence lifetime and polarization of oxonol potential-sensitive extrinsic probes in solution and in beef heart submitochondrial particles.

The fluorescence polarization and lifetime of the extrinsic potential-sensitive probes oxonols V and VI have been investigated both for the dyes free in aqueous and ethanol solutions and in the presence of beef heart submitochondrial particles under resting and energy-transducing conditions. The emission lifetime of the dyes appears to be inversely related to the solvent dielectric constant and increases as the solvent is changed from an aqueous medium to ethanol to the biological membrane. The fluorescence decay curve becomes biphasic in the presence of the membrane preparation and consists of a faster decaying component, the lifetime of which is the same as that of the probe in aqueous solution and of a slower decaying component. The longer lived component suffers an uncoupler-sensitive decrease in lifetime when ATP is added to the medium. The decrease in lifetime of the longer lived species is accompanied by large depolarizations of the dye fluorescence. These observations are consistent with a redistribution-type mechanism for the energy-dependent spectral changes involving the movement of probe from the aqueous phase to the membrane vesicles. The rotational relaxation time of oxonols V and VI is increased by over an order of magnitude when these dyes associate with the membrane. This observation is consistent with a previously developed model for the location of the dyes in the bilayer in which the side chains serve as anchors, preventing the rapid tumbling of the probe in the membrane.

The response of an h.f. moisture probe to soluble salts

The h.f. capacitance response of a probe in aqueous solutions of sodium chloride has been studied as a function of the conductance. The results show that there is an optimum cable length, less than the half wavelength, at which the apparent capacitance is least affected by the addition of sodium chloride, and that the effect can be further reduced by suitable cable design. The results are interpreted in terms of transmission-line theory. As a result of this work two possible ways of measuring moisture in building materials are suggested, and some results are given for gypsum plaster and a dense mortar. Maximum errors of 0·05 volume moisture fraction have been achieved for gypsum plaster and for dense mortar when the pore liquid at saturation was 0·05 M and 0·1 M respectively with respect to sodium chloride.