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1.
J Phys Chem B ; 126(41): 8166-8176, 2022 10 20.
Article in English | MEDLINE | ID: mdl-36198175

ABSTRACT

MS2 bacteriophage is often used as a model for evaluating pathogenic viruses' behavior in aqueous solution. However, the questions of the virus surface's hydrophilic/hydrophobic balance, the charge distribution, and the binding mechanism are open. Using the dynamic light scattering method and laser Doppler electrophoresis, the hydrodynamic diameter and the ζ-potential of the virus particles were measured at their concentration of 5 × 1011 particles per mL and ionic strength 0.03 M. The values were found to be 30 nm and -29 or -34 mV (by Smoluchowski or Ohshima approximations), respectively. The MS2 bacteriophage surface was also investigated using a series of acid-base indicator dyes of various charge type, size, and structure. Their spectral and acid-base properties (pKa) are very sensitive to the microenvironment in aqueous solution, including containing nanoparticles. The electrostatic potential of the surface Ψ was estimated using the common formula: Ψ = 59 × (pKai - pKa) in mV at 25 °C. The Ψ values were -50 and +10 mV, respectively, which indicate the "mosaic" way of the charge distribution on the surface. These data are in good agreement with the obtained ζ-potential values and provide even more information about the virus surface. It was found that the surface of the MS2 virus is hydrophilic in solution in contrast to the commonly accepted hypothesis of the hydrophobicity of virus particles. No hydrophobic interactions between various molecular probes and the capsid were observed.


Subject(s)
Molecular Probes , Nanoparticles , Static Electricity , Hydrophobic and Hydrophilic Interactions , Levivirus/chemistry , Coloring Agents , Surface Properties
2.
Spectrochim Acta A Mol Biomol Spectrosc ; 170: 138-44, 2017 Jan 05.
Article in English | MEDLINE | ID: mdl-27423469

ABSTRACT

Rhodamine dyes are widely used as molecular probes in different fields of science. The aim of this paper was to ascertain to what extent the structural peculiarities of the compounds influence their absorption, emission, and acid-base properties under unified conditions. The acid-base dissociation (HR(+)⇄R+H(+)) of a series of rhodamine dyes was studied in sodium n-dodecylsulfate micellar solutions. In this media, the form R exists as a zwitterion R(±). The indices of apparent ionization constants of fifteen rhodamine cations HR(+) with different substituents in the xanthene moiety vary within the range of pKa(app)=5.04 to 5.53. The distinct dependence of emission of rhodamines bound to micelles on pH of bulk water opens the possibility of using them as fluorescent interfacial acid-base indicators.

3.
Methods Appl Fluoresc ; 4(3): 034002, 2016 07 20.
Article in English | MEDLINE | ID: mdl-28355149

ABSTRACT

Among the vast set of fluorescein derivatives, the double charged R2- anions of aminofluoresceins are known to exhibit only low quantum yields of fluorescence, [Formula: see text]. The [Formula: see text] value becomes as high as that of the fluorescein dianion when the lone electron pair of the amino group is involved in a covalent bond. According to Munkholm et al (1990 J. Am. Chem. Soc. 112 2608-12), a much smaller increase in the emission intensity can be observed in the presence of surfactant micelles. However, all these observations refer to aqueous or alcoholic solvents. In this paper, we show that in the non-hydrogen bond donor (or 'aprotic') solvents DMSO and acetone, the quantum yields, φ, of the 4'- (or 5')-aminofluorescein R2- species amount to 61-67% and approach that of fluorescein (φ = 87%), whereas in water φ is only 0.6-0.8%. In glycerol, a solvent with an extremely high viscosity, the φ value is only 6-10%. We report on the enhancement of the fluorescence of the aminofluorescein dianions as an indicative process, which allows us to distinguish between the micelle-like aggregates of cationic dendrimers of low generation, common spherical surfactant micelles, and surfactant bilayers. Some of these colloidal aggregates partly restore the fluorescence of aminofluoresceins in aqueous media. By contrast, other positively charged micellar-like aggregates do not enhance the quantum yield of aminofluorescein R2- species. Results for several related systems, such as CTAB-coated SiO2 particles and reverse microemulsions, are briefly described, and the possible reasons for the observed phenomena are discussed.

4.
Carbohydr Res ; 345(13): 1882-90, 2010 Sep 03.
Article in English | MEDLINE | ID: mdl-20678757

ABSTRACT

The protolytic equilibrium of fluorescein in aqueous solutions was studied in the presence of cycloheptaamylose (beta-cyclodextrin, or beta-CD). The constants of stepwise ionization of the dye (H(3)R(+)left arrow over right arrowH(2)Rleft arrow over right arrow HR(-)left arrow over right arrowR(2-)), K(a0), K(a1), and K(a2) were determined using vis-spectroscopy at ionic strength 0.05 M (NaCl+buffer) and 25 degrees C. In the presence of 0.0086 M beta-CD, the indices of ionization constants are as follows: pK(a0)=1.21+/-0.12, pK(a1)=5.08+/-0.03, pK(a2)=6.35+/-0.02. The changes in these pK(a)s, as compared with the values determined without cyclodextrin, are unequal. Namely, the pK(a0) value decreases by 1.0, while the pK(a1) value increases by 0.7. Thus, the introduction of beta-CD allows to govern the ratios K(a0)/K(a1) and K(a1)/K(a2), which are equal to, respectively, 141 and 151 in water, and 7.4 x 10(3) and 18.6 with cyclodextrin added. Rationalization of the observed phenomenon is possible taking into account the detailed scheme of protolytic equilibrium. Conclusions concerning tautomerism of dye molecules were deduced from absorption spectra; the fractions of tautomers, tautomerization constants, and microscopic ionization constants were evaluated. These data allow concluding that the main reason for the aforementioned pK(a) alterations is the binding of H(2)R by the cyclodextrin cavity accompanied by turning these neutral species into the colorless lactone. The host-guest interaction of neutral species of fluorescein isothiocyanate, 2,7-dichlorofluorescein, and 3',4',5',6'-tetrachlorofluorescein also results in the cyclodextrin-assisted shift of tautomeric equilibrium. Such nature of interactions is proved by the addition of competing agents, camphor-4-carboxylic acid and sodium n-nonylsulfonate, which results in the removing of neutral dye species from the cycloheptaamylose cavity.


Subject(s)
Fluorescein/chemistry , Fluorescent Dyes/chemistry , Water/chemistry , beta-Cyclodextrins/chemistry , Absorption , Hydrogen-Ion Concentration , Isomerism , Models, Molecular , Molecular Conformation , Solutions , Spectrum Analysis
5.
J Phys Chem B ; 114(13): 4551-64, 2010 Apr 08.
Article in English | MEDLINE | ID: mdl-20232888

ABSTRACT

The stepwise ionization (H(3)R(+) <==> H(2)R <==> HR(-) <==> R(2-)) of four fluorescein fluoro derivatives was studied by visible spectroscopy. The pK(a) values were determined in water, in 50 mass % aqueous ethanol, in oil-in-water microemulsions (benzene + CTAB + pentanol-1 in water with 1.0 M KCl; CTAB = cetyltrimethylammonium bromide), and in reversed ones (water + AOT in n-octane; AOT = bis-2-ethylhexylsulphosuccinate or Aerosol OT). The medium effects, DeltapK(a), i.e., changes in pK(a) of these dyes on going from water to some other solvent systems, were rationalized by considering the tautomerism, the values of microscopic ionization constants, and the charge types of the acid-base couples. An expressed shift of the tautomeric equilibria of H(2)R toward colorless lactone was registered on going from water to both aqueous ethanol and organized solutions. While the monoanions HR(-) of 3',4',5',6'-tetrafluoro- and 2,7,3',4',5',6'-hexafluorofluorescein exist in all the systems studied as a tautomer with ionized carboxylic and nonionized hydroxy groups, in the case of 2,4,5,7-tetrafluorofluorescein, the prevalence of another tautomer was observed (COOH and O(-) groups). For 2,7-difluorofluorescein (Oregon Green 488), the partial shift of the tautomeric equilibrium of HR(-) was registered from (COO(-) and OH) in water to (COOH and O(-)) in other solvent systems. The data for the dyes located in an AOT-based pseudophase indicate that the interior of the latter exerts essential differentiation of the acid strength of the dyes, probably caused by the peculiarity of dye species location in water pools. While the state of tautomeric equilibria resembles that in nonaqueous media, the absorption maxima of R(2-) species are close to those in water. Such nonuniform influence displayed by AOT-based water droplets should be taken into account when examining them by using different molecular probes.


Subject(s)
Fluorescein/chemistry , Fluorescent Dyes/chemistry , Solutions/chemistry , Benzene/chemistry , Carboxylic Acids/chemistry , Cetrimonium , Cetrimonium Compounds/chemistry , Dioctyl Sulfosuccinic Acid/chemistry , Hydrogen-Ion Concentration , Kinetics , Octanes/chemistry , Pentanols/chemistry , Water/chemistry
6.
Langmuir ; 24(11): 5689-99, 2008 Jun 03.
Article in English | MEDLINE | ID: mdl-18452320

ABSTRACT

Aqueous solutions of four cationic poly(propylenimine) low-generation dendrimers of different architecture and hydrophobicity have been examined as media for acid-base reactions of indicator dyes. The cationic dendrimers in solution can be considered as oligomers of cationic polyelectrolytes, or surfactant-like species, able to form micelles through self-association or sometimes even as unimolecular micelles. The dendrimers influence the ionization constants, tautomeric equilibria, and absorption/emission/excitation spectra of indicator dyes. The p K a values of the majority of the indicator dyes decrease in dendrimer solutions, often by 1-2 p K a units, similar to effects registered in micellar solutions of cationic surfactants. Analogously, the shifts of absorption band maxima indicate that the microenvironments of the dyes bound to the dendrimers are less polar than in water. However, some spectral effects denote the specificity of the dendrimers. The greatest difference between the dendrimers and spherical surfactant micelles is revealed by kinetic processes, especially of bromophenol blue alkaline fading in a dendrimer solution but not in a micellar surfactant solution. Within the dendrimer series, the most significant differences were observed for substances possessing n-dodecyl tails on the one hand and those without such hydrophobic portions on the other. For the last-named, the decrease in p K a's of indicators, band shifts of their anions, and in particular displacement of tautomeric equilibria compared with aqueous solutions are much smaller than for more hydrophobic dendrimers.

7.
Langmuir ; 21(16): 7090-6, 2005 Aug 02.
Article in English | MEDLINE | ID: mdl-16042428

ABSTRACT

In this paper, we demonstrate that the behavior of a set of eight large-sized negatively solvatochromic pyridinium N-phenolate betaine dyes reflects the principle transformations, occurring in aqueous micellar solutions of three cationic surfactants. As surfactants, cetyltrimethylammonium bromide (CTAB), n-octadecyltrimethylammonium chloride (OTAC), and N-cetylpyridinium bromide (CPB) were used. Normally, for such probes coupled with micelles, a red shift of the vis absorption band is expected as a result of a hydrophobization ("drying") of the micellar interface. However, under addition of electrolytes with anions such as tosylate, salicylate, and some n-alkanesulfonates or n-alkanecarboxylates to the micellar solutions, an unexpected effect was observed. Instead of a red shift, a blue shift of the vis absorption band of some of the dissolved betaine dyes was registered, as compared with the spectrum measured in pure aqueous micellar solutions of CTAB, OTAC, or CPB (Deltalambda(max) up to ca. 80 nm). This blue shift, indicating an increase in the polarity of the dye microenvironment, is explained by displacing the large dye dipoles from the thinned micelles toward the aqueous phase. The effect is well expressed at concentrations of C(betaine dye) approximately 10(-5) M, C(cationic surfactant) approximately 0.001 M, and C(organic anion) approximately 0.01 M. Transmission electron microscopy of dried samples confirms the distinct changes occurring in the studied micellar systems upon the addition of organic anions. The excess of inorganic salts [C(NaBr, KBr, or KCl) = 0.5-4.0 M] restored the position of the vis absorption band or even shifted it toward the red. Moreover, some of the betaine dyes studied (i.e., the more hydrophobic ones) stay in the micellar pseudophase or precipitate under the aforementioned concentration conditions. The peculiarities of the behavior of these betaine dyes are in agreement with their molecular structure.

8.
Spectrochim Acta A Mol Biomol Spectrosc ; 61(11-12): 2747-60, 2005 Sep.
Article in English | MEDLINE | ID: mdl-16043074

ABSTRACT

Stepwise dissociation and tautomerism of 2,4,5,7-tetranitrofluorescein (TNF) were studied by using vis-spectroscopy in dimethylsulfoxide (DMSO), in aqueous acetone, and in cetyl-trimethylammonium chloride (CTAC) micellar solutions at ionic strength of the bulk phase 4.00M KCl. The pK(a) values in DMSO and 90 mass% (CH3)2CO as well as the 'apparent'pK(a)(a) values of the substance in micellar media were determined spectrophotometrically. The neutral (molecular) form H2R is found to be completely converted into the colorless lactone. Moreover, the lactonic structure, yellow due to 'nitrophenolate' absorption band, predominates also in the case of TNF dianion R2-. Contrary to the unsubstituted fluorescein, and like 2,4,5,7-tetrabromofluorescein (eosin), the monoanion HR- of TNF with lambda(max) 522-525 nm and E(max) approximately (60-62)x10(3) dm(3)mol(-1)cm(-1) exists mainly as a deeply and intensively colored structure with non-ionized carboxylic and ionized hydroxylic group; its fluorescence spectra in various media are registered. In 90% acetone, the Stokes shift is 1.17x10(3)cm(-1), fluorescence lifetime equals 2.3 ns. An extremely expressed trend to dianion-lactone formation of R2- ion of TNF is confirmed in the systems studied. For TNF in DMSO, in aqueous acetone, in surfactant micelles, and in trichloromethane extracts of ionic associatiates with N(n-Bu)4+ and N(n-Hept)4+, the deeply colored 'quinon-phenolate' dianion, typical for all hydroxyxanthenes, is not registered at all. The sequence of dissociation of functional groups in solution is confirmed using IR spectroscopy in DMSO.


Subject(s)
Fluorescein/chemistry , Fluoresceins/chemistry , Nitro Compounds/chemistry , Xanthenes/chemistry , Acetone , Dimethyl Sulfoxide , Hydrogen-Ion Concentration , Ions/chemistry , Isomerism , Micelles , Molecular Structure , Solutions/chemistry , Spectrum Analysis , Thermodynamics
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