Influence of temperature and ethanol content on aggregation of rhodamine 6G molecules in aqueous ethanol solutions

The effect of temperature on absorption spectra of Rhodamine 6G at concentrations of 10⁻⁶ and 10⁻³ M in water:ethanol solutions of various ethanol content was studied. The dimeric molecular fraction of Rhodamine 6G (10⁻³ M) was found as a function of temperature and ethanol content in the aqueous solution. It was shown that the absorption spectrum of Rhodamine 6G dimers (10⁻³ M) is dependent on temperature and ethanol content in the aqueous solution. Based on the relationship between J-and H-bands in the absorption spectrum of Rhodamine 6G dimers, both the angle between planes of associated Rhodamine 6G dye molecules and the free enthalpy of association were calculated. The structure of Rhodamine 6G dimers depends essentially on the ethanol content and aqueous ethanol solution temperature while experiencing the most temperature changes at an ethanol concentration of 25%. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 640–645, September–October, 2008.     

Cooperativity effects of intramolecular OH…O interactions on pKa values of polyolalkyl sulfonic acids in the gas phase and solution: a density functional theory study

Density functional theory method and B3LYP/6‐311++G(d,p) level of theory were used to determine the acidity of alkyl sulfonic acids and polyolalkyl sulfonic acids in the gas and solution (H₂O, DMSO, and CH₃CN) phase. Polarized continuum model was applied to calculate pK_a values of alkyl sulfonic acids and polyolalkyl sulfonic acids. A comparison between acidity of alkyl sulfonic acids and polyolalkyl sulfonic acids in the gas and solution phase indicates that the acidity strength of polyolalkyl sulfonic acids enhances with the increase of the cooperativity effect of intramolecular hydrogen bonds in polyolalkyl sulfonic acids. Natural bond orbital and quantum theory of atoms in molecules analyses also confirm the role of cooperativity effect on the acidity of polyolalkyl sulfonic acids. Copyright © 2014 John Wiley & Sons, Ltd.     

Sub‐ppm determination of Hg and Cr in water: Cr speciation

A sensitive and alternative analytical procedure for the determination of chromium and mercury content in natural waters by coprecipitation with APDC and determination using an absolute thin layer EDXRF method is described. The use of ¹⁰⁹Cd and ²³⁸Pu annular radioisotope sources, the influence of the chromium oxidation states and the elemental concentration were studied. At pH 4, 100% recovery was found for mercury. The coprecipitation of Cr(VI) was not quantitative (75%) but constant for the selected concentration range (5–100 µg/l). On the other hand, Cr(III) did not precipitate at the same pH. The relative standard deviations (RSD) were lower than 9.0% for mercury (10 µg/l) and 5.0% for chromium (50 µg/l). The detection limits (DLs) for mercury and chromium were 0.4 and 0.6 µg/l when the ²³⁸Pu source was employed. Nevertheless, higher DL values were achieved using ¹⁰⁹Cd (0.6 and 3.3 µg/l). The proposed method was applied to the analysis of surface water samples. An alternative and simple chromium speciation procedure without chemical separation of Cr species is recommended. Copyright © 2007 John Wiley & Sons, Ltd.     

Genotoxic halofuranones in water: isomerization and acidity of mucohalic acids

Among the genotoxic halofuranones formed by chlorination in water are mucochloric acid (MCA, 3,4‐dichloro‐5‐hydroxyfuran‐2(5H)‐one) and mucobromic acid (MBA, 3,4‐dibromo‐5‐hydroxyfuran‐2(5H)‐one). These acids are direct genotoxins and potential carcinogens, with the capacity to alkylate the DNA bases. In recent years, they have also attracted attention in the synthesis of furanone derivatives. Mucohalic acids (MXA) exist in solution as an equilibrium between three species; a cyclic lactone‐lactol , an open‐chain aldehyde‐acid , and the dissociated form of the latter . The distribution of the three species in the equilibrium has synthetic, toxicological, and environmental implications owing to their different functionalization. The case of the neutral open‐chain form is of special interest, since it is expected to be highly reactive. We have experimentally determined the apparent dissociation constant of the cyclic species . Their values suggest that at neutral pH MXA are mostly present as the dissociated carboxylate‐aldehyde. The dissociation constant of the open‐chain neutral species and the cyclization equilibrium constant were determined in water and organic solvents, using density functional theory and ab initio methods. The results suggest that the undissociated aldehyde is a minor species at any given pH. The structure of MXA in solution and the influence of the level of theory on the calculated geometry are discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

Conformation/Tautomerization effect on the pKa values of lumazine and 6‐thienyllumazine

Density functional theory [B3LYP/6‐311+G(d,p)] was used in combination with the conductor‐like polarizable continuum model (CPCM) solvation model to investigate the relative stability and site‐specific values of neutral and ionized tautomers of lumazine (LM) and 6‐thienylLM (TLM). Two types of populations should be taken into consideration when calculating the , tautomers, and conformers. The major tautomer of neutral LM in aqueous solution is 13‐LM (the 13 notation refers to the acidic protons being in positions 1 and 3 of LM) TLM has decreased acidity at N₈ relative to LM. Further, the trans conformer of TLM is more acidic than cis. Similar to the case of LM, for TLM, N₁ is more acidic than N₃ in the uracil part. However, N₈ is predicted to be a stronger acid than N₁ for TLM. This acidity enhancement is essentially because of a specific stabilization of the anion when the thienyl group replaces H. Two factors are responsible for the acidity strength of N₈: The thienyl ring upon deprotonation acts inductively as an electron‐withdrawing group, and the excess electron density is dispersed better when the system is trans and contains second‐row atoms. Accurate pK_a calculation requires that all conformers/tautomers be included into the calculation. Copyright © 2014 John Wiley & Sons, Ltd.     

NMR spectroscopy of organolithium compounds,part XXXIII: trans‐2,3‐dimethylcyclopropyllithium aggregation in diethylether: An equilibrium between three different complexes of comparable energy and the influence of LiBr on aggregate structure

The aggregate formation of trans‐2,3‐dimethylcyclopropyllithium ( 2 ) was studied in diethylether (DEE). With the help of the isotopic fingerprint method three clusters, a monomer, a dimer, and a fluxional tetramer in the ratio 1.00:0.53:0.22 were identified at 187 K. In the presence of 1 equivalent of LiBr cyclopropyllithium ( 1 ) forms in DEE at 163 K a mixed dimer and a mixed tetramer, while in THF a mixed dimer dominates. Under the same conditions 2 and 2,2,3,3‐tetramethylcyclopropyllithium ( 3 ) form in the solvent mixture DEE/THF (1:1) mixed dimers, as does 2 also in THF.     

Kinetics and product distribution of p‐nitrophenyl phosphate dianion solvolysis in ternary DMSO/alcohol/water mixtures are compatible with metaphosphate formation

The rate of solvolysis of p‐nitrophenyl phosphate (PNPP) dianion in DMSO/water strongly decreases by increasing water concentration. Addition of linear alcohols (methanol, propanol, butanol, pentanol, and hexanol) at constant DMSO/water molar ratio produced an even sharper rate decrease. Alkyl phosphate formation, resulting from PNPP solvolysis in ternary DMSO/water/alcohol mixtures, increased with alcohol concentration and was essentially temperature independent. Methanol and hexanol were the poorest nucleophiles under all conditions. Activation energies and enthalpies for solvolysis in ternary mixtures were similar and entropies varied with alcohol concentration. Taken together these results can be best interpreted in terms of a dissociative mechanism with the intervention of metaphosphate. Copyright © 2011 John Wiley & Sons, Ltd.     

Molecular organization and aggregation in Langmuir and Langmuir-Blodgett films of azo dye/liquid crystal mixtures

A study of azo dye/liquid crystal mixtures in monolayers formed at air-water (Langmuir films) and air-solid substrate (Langmuir-Blodgett films) interfaces was performed. Three azo dyes with various molecular structure and two liquid crystal materials: 4-octyl-4′-cyanobiphenyl (8CB) and trans-4-octyl(4′-cyanophenyl)-cyclohexane (8PCH) were used. The morphology of Langmuir films was monitored by means of a Brewster angle microscope (BAM). Moreover, a surface pressure and electronic absorption spectra of the monolayer spread on the water surface of dye/liquid crystal mixtures as a function of a mean molecular area were simultaneously recorded. In addition, the absorption for Langmuir-Blodgett films deposited on quartz plates was measured. Information about intermolecular interactions in the mixtures of the nonamphiphilic dye and the liquid crystal with polar terminal group was obtained. Conclusions about the formation of self-aggregates between dye molecules have been drawn. The influence of the dye molecular structure and its concentration on aggregates’ geometry was found.     

Non‐paraxial theory of self‐focusing/defocusing of Hermite cosh Gaussian laser beam in rippled density plasmas

Present research work focuses on study of self‐focusing and self‐trapping of Hermite cosh Gaussian (HchG) laser beams in rippled density plasma by considering relativistic non‐linearity. The coupled non‐linear differential equations for the beam width parameters (for modes m = 0, 1, and 2) were derived by employing higher‐order correction in comparison to paraxial ray theory by expanding dielectric function and eikonal up to r⁴ terms. It is observed that the inclusion of higher‐order terms significantly influence the off‐axial properties for m ≥ 1 mode indices. Furthermore, the effect of parameters including beam intensity, ripple factor, depth of density modulation, and decentred parameter on self‐focusing and self‐trapping is analysed and discussed both analytically and numerically.     

The effect of temperature on urea–urea interactions in water: a molecular dynamics simulation

We investigate the temperature effect on the structural and dynamical properties (translation, rotation) of an urea/water system at 0.20 mole fraction of urea. We report the radial distribution functions of like and unlike molecules and conclude that, even at large distances, these molecules are spatially correlated (with respect to their centers of mass). This behavior is interpreted as an indication that urea molecules are not uniformly distributed at a microscopic level. However, the orientational distribution shows that, at long distances, the urea molecules are not orientationally correlated. A strong correlation between urea molecules is observed within the first-shells of neighboring molecules. In view of these results, it is postulated that urea behaves slightly like a nonpolar molecule. The dynamical properties were analyzed using the velocity (translation) and angular velocity (rotation) time autocorrelation functions, as well as their Fourier transforms. The results indicate a significant hydrogen bonding between urea and other molecules in the solution.     

CW measurements of resonance Raman profiles,line‐widths,and cross‐sections of fluorescent dyes: application to Nile Blue A in water and ethanol

The aim of this work is to illustrate the power of recently developed methods for measuring resonance Raman scattering (RRS) spectra of efficient fluorophores (using a standard continuous wave excitation and a charge‐coupled device (CCD)‐based Raman spectrometer), by applying them to a detailed study of a specific fluorophore: Nile Blue A. A combination of methods are used to measure the RRS properties of Nile Blue A in water (quantum yield (QY) of 4%) and ethanol (QY of 22%) at excitation wavelengths between 514 and 647 nm, thus covering both pre‐resonance and RRS conditions. Standard Raman measurements are used in situations where the fluorescence background is small enough to clearly observe the Raman peaks, while the recently introduced polarization‐difference RRS and continuously shifted Raman scattering are used closer to (or at) resonance. We show that these relatively straightforward methods allow us to determine the Raman cross‐sections of the most intense Raman peaks and provide an accurate measurement of their line‐width; even for broadenings as low as ∼ 4 cm ^{− 1}. Moreover, the obtained Raman excitation profiles agree well with those derived from the optical absorption by a simple optical transform model. This study demonstrates the possibility of routine RRS measurements using standard Raman spectrometers, as opposed to more complicated time‐resolved techniques. Copyright © 2013 John Wiley & Sons, Ltd.     

Reactions of O‐aryl S‐aryl dithiocarbonates with pyridines in aqueous ethanol: kinetics and mechanism

The reactions of O‐(4‐methylphenyl) S‐(4‐nitrophenyl) dithiocarbonate ( 1 ), O‐(4‐chlorophenyl) S‐(4‐nitrophenyl) dithiocarbonate ( 2 ), and O‐(4‐chlorophenyl) S‐phenyl) dithiocarbonate ( 3 ) with a series of pyridines were subjected to a kinetic investigation in 44 wt% ethanol–water, at 25.0 °C and an ionic strength of 0.2 M. The reactions were followed spectrophotometrically. Under amine excess, pseudo‐first‐order rate coefficients (k_obs) were determined. For the studied reactions, plots of k_obs versus free pyridine concentration at constant pH were linear, with the slope (k_N) independent of pH. The Brønsted‐type plots for ( 1 ) and ( 2 ) were biphasic, suggesting a stepwise mechanism with a change in the rate‐determining step, from breakdown to the formation of a tetrahedral intermediate (T^±), as the basicity of the pyridines increases. For the reactions of ( 3 ), at the pK_a range of the pyridines studied, only the breakdown to products of T^± was observed. Copyright © 2009 John Wiley & Sons, Ltd.     

Self‐association and hydrogen bonding of propionaldehyde in binary mixtures with water and methanol investigated by concentration‐dependent polarized Raman study and DFT calculations

The Raman spectra of neat propionaldehyde [CH₃CH₂CHO or propanal (Pr)] and its binary mixtures with hydrogen‐donor solvents, water (W) and methanol (M), [CH₃CH₂CHO + H₂O] and CH₃CH₂CHO + CH₃OH] with different mole fractions of the reference system, Pr varying from 0.1 to 0.9 at a regular interval of 0.1, were recorded in the ν(CO) stretching region, 1600–1800 cm⁻¹. The isotropic parts of the Raman spectra were analyzed for both the cases. The wavenumber positions and line widths of the component bands were determined by a rigorous line‐shape analysis, and the peaks corresponding to self‐associated and hydrogen‐bonded species were identified. Raman peak at ∼1721 cm⁻¹ in neat Pr, which has been attributed to the self‐associated species, downshifts slightly (∼1 cm⁻¹) in going from mole fraction 0.9 to 0.6 in (Pr + W) binary mixture, but on further dilution it shows a sudden downshift of ∼7 cm⁻¹. This has been attributed to the low solubility of Pr in W (∼30%), which does not permit a hydrogen‐bonded network to form at higher concentrations of Pr. A significant decrease in the intensity of this peak in the Raman spectra of Pr in a nonpolar solvent, n‐heptane, at high dilution (C = 0.05) further confirms that this peak corresponds to the self‐associated species. In case of the (Pr + M) binary mixture, however, the spectral changes with concentration show a rather regular trend and no special features were observed. Copyright © 2010 John Wiley & Sons, Ltd.     

Dimethyl sulfoxide/deep eutectic solvents mixtures as media in the reaction of 1‐fluoro‐2,4‐dinitrobenzene with piperidine: A solvent effect study

Aromatic nucleophilic substitution reaction of 1‐fluoro‐2,4‐dinitrobenzene with piperidine was kinetically investigated in ethylene glycol‐choline chloride and glycerol‐choline chloride as 2 deep eutectic solvents (DESs) mixed with dimethyl sulfoxide, in whole mole fractions, at room temperature. The investigation of the reaction in different concentrations of the piperidine shows that the reaction follows the base‐catalyzed mechanism. The measured rate coefficients of the reaction demonstrated a sharp decreasing in all mixtures with the increasing mole fraction of DESs. Linear free energy relationship investigations confirm that hydrogen bond donor ability in addition to polarity‐polarizability of the media has a major effect on the reaction rate. The decrease in the rate coefficient is attributed to not only hydrogen‐bonding donor interactions of the media with piperidine as both reactant and catalyst but also the preferential solvation of reactants by DES compared with the intermediate of the reaction.     

Enhanced self‐ordering of anodic ZrO2 nanotubes in inorganic and organic electrolytes using two‐step anodization

This work reports on the optimized growth of self‐ordered ZrO₂ nanotubes in inorganic water‐based and organic electrolyte systems containing small amounts of fluoride employing a two‐step anodization process. We show how surface pretreatments of the metallic Zr substrate can drastically improve the growth and morphology of the resulting anodic ZrO₂ nanotube arrays. Using two step anodization and employing organic electrolytes, highly regular and ordered nanotubular ZrO₂ oxide layers can be grown to significantly increased tube lengths compared with aqueous electrolytes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Solid‐phase preconcentration and determination of mercury(II) using activated carbon in drinking water by X‐ray fluorescence spectrometry

A novel and simple method was developed for the preconcentration and determination of mercury(II) from hydrochloric acid solutions through their adsorption on Aliquat 336 (tri‐octylmethylammonium chloride)‐activated carbon. The determinations were made directly on the solid by X‐ray fluorescence spectrometry, which had the advantage of eliminating the step of elution of the mercury retained. This preconcentration system enabled the determination of Hg(II) in drinking water samples at µg l^?1 levels. A 1700‐fold enrichment factor was obtained. The described methodology showed excellent reproducibility, accuracy, and detection limits improvement by eliminating the step of elution of the analyte, replacing those methods based on cold vapor generation, reducing reagent consumption, and handling of samples. Copyright © 2013 John Wiley & Sons, Ltd.     

Enhanced Physiological Stability and Long‐Term Toxicity/Biodegradation In Vitro/In Vivo of Monodispersed Glycerolphosphate‐Functionalized Bioactive Glass Nanoparticles

Monodispersed bioactive glass nanoparticles (BGNs) have received much attention in various biomedical applications such as tissue regeneration, drug/gene delivery, bioimaging, and cancer therapy. However, the poor dispersion stability of BGNs in a physiological environment has limited their wide biomedical applications. The long‐term in vitro/in vivo toxicity and biodegradation of BGNs are also not clear. Monodispersed glycerolphosphate‐functionalized BGNs (GP‐BGN) are synthesized and their stability under physiological environment in vitro, and long‐term biodegradation behavior in vitro and in vivo are investigated herein. GP‐BGN shows significantly enhanced particles stability in physiological environment, good hemocompatibility and cellular biocompatibility, as well as high cellular uptake ability. GP‐BGN also exhibits long‐term biodegradation behavior in vitro/in vivo and negligible biotoxicity (tissue and blood toxicity). This study demonstrates that monodispersed surface‐functionalized BGNs could be used as biocompatible and biodegradable nanomaterials for long‐term safe bioimaging and disease therapy.