Derivatives In Aqueous Solution Research Articles

MesoDyn simulation study of phase behavior for dye–polyether derivatives in aqueous solutions

Mesoscale simulation was carried out to investigate the phase behavior of dye–polyether derivatives in aqueous solutions. The effect of the concentration of dye–polyether derivatives on the morphology of micelles and the process of formation of micelles were studied. The simulation results presented that dye–polyether derivatives can form different morphologies at different volume fractions and three aggregate types, which were spherical micelles, worm-like micelles and micellar clusters, were observed. The kinetic process of the formation of micelles can be divided into three stages. For the spherical micelles and worm-like micelles, the long flexible PEO blocks dispersed in water formed the micellar corona, while the hydrophobic portion (dye and PPO blocks) formed the micellar cores with a very few water molecules presented in it. For the micellar clusters, the dye segment and PPO blocks still form the micellar cores, while the long PEO blocks wrapped multiple micellar cores in the form of continuous phase. This simulation results are essentially consistent with the experimental results. It is concluded that the mesoscale simulation method is a valuable adjunct to experiments and can provide important mesoscopic information not easily accessible from experiments.

Ketyl Radical Formation via Proton-Coupled Electron Transfer in an Aqueous Solution versus Hydrogen Atom Transfer in Isopropanol after Photoexcitation of Aromatic Carbonyl Compounds.

The excited nπ* and ππ* triplets of two benzophenone (BP) and two anthraquinone (AQ) derivatives have been observed in acetonitrile, isopropanol, and mixed aqueous solutions using time-resolved resonance Raman spectroscopic and nanosecond transient absorption experiments. These experimental results, combined with results from density functional theory calculations, reveal the effects of solvent and substituents on the properties, relative energies, and chemical reactivities of the nπ* and ππ* triplets. The triplet nπ* configuration was found to act as the reactive species for a subsequent hydrogen atom transfer reaction to produce a ketyl radical intermediate in the isopropanol solvent, while the triplet ππ* undergoes a proton-coupled electron transfer (PCET) in aqueous solutions to produce a ketyl radical intermediate. This PCET reaction, which occurs via a concerted proton transfer (to the excited carbonyl group) and electron transfer (to the excited phenyl ring), can account for the experimental observation by several different research groups over the past 40 years of the formation of ketyl radicals after photolysis of a number of BP and AQ derivatives in aqueous solutions, although water is considered to be a relatively "inert" hydrogen-donor solvent.

Supramolecular Self-Organization of Fullerene Derivatives in Solutions Studied by Pulsed Field Gradient NMR Technique

Self-organization of a series of differently functionalized fullerene derivatives in solvents of different polarity was investigated by pulsed field gradient nuclear magnetic resonance on 1H, 19F and 31P nuclei. The hydrodynamic diameters were calculated for each fullerene derivative-solvent system on the basis of Stokes–Einstein model. It was shown that fullerene derivatives comprising no polar groups do not undergo any noticeable aggregation in carbon bisulfide, deutereted chloroform and toluene-d8. The particle diameters of 1.2–1.4 nm revealed for these solutions were very close to the van der Waals diameter of the fullerene derivative molecules. The fullerene derivatives comprising polar –COOH, –COOK and –P(O)(OH)2 groups appended to the carbon cage undergo self-assembling in solutions. The diameters of the formed clusters varied from 2.2 to 9.6 nm depending on the solvent and the temperature. The strongest tendency to self-assembling was revealed for water soluble fullerene derivatives in aqueous solutions where, presumably, water molecules are also incorporated in the structure of the clusters.

The Clusters-in-a-Liquid Approach for Solvation: New Insights from the Conformer Specific Gas Phase Spectroscopy and Vibrational Optical Activity Spectroscopy.

Vibrational optical activity spectroscopies, namely vibrational circular dichroism (VCD) and Raman optical activity (ROA), have been emerged in the past decade as powerful spectroscopic tools for stereochemical information of a wide range of chiral compounds in solution directly. More recently, their applications in unveiling solvent effects, especially those associated with water solvent, have been explored. In this review article, we first select a few examples to demonstrate the unique sensitivity of VCD spectral signatures to both bulk solvent effects and explicit hydrogen-bonding interactions in solution. Second, we discuss the induced solvent chirality, or chiral transfer, VCD spectral features observed in the water bending band region in detail. From these chirality transfer spectral data, the related conformer specific gas phase spectroscopic studies of small chiral hydration clusters, and the associated matrix isolation VCD experiments of hydrogen-bonded complexes in cold rare gas matrices, a general picture of solvation in aqueous solution emerges. In such an aqueous solution, some small chiral hydration clusters, rather than the chiral solutes themselves, are the dominant species and are the ones that contribute mainly to the experimentally observed VCD features. We then review a series of VCD studies of amino acids and their derivatives in aqueous solution under different pHs to emphasize the importance of the inclusion of the bulk solvent effects. These experimental data and the associated theoretical analyses are the foundation for the proposed “clusters-in-a-liquid” approach to account for solvent effects effectively. We present several approaches to identify and build such representative chiral hydration clusters. Recent studies which applied molecular dynamics simulations and the subsequent snapshot averaging approach to generate the ROA, VCD, electronic CD, and optical rotatory dispersion spectra are also reviewed. Challenges associated with the molecular dynamics snapshot approach are discussed and the successes of the seemingly random “ad hoc explicit solvation” reported before are also explained. To further test and improve the “clusters-in-a-liquid” model in practice, future work in terms of conformer specific gas phase spectroscopy of sequential solvation of a chiral solute, matrix isolation VCD measurements of small chiral hydration clusters, and more sophisticated models for the bulk solvent effects would be highly valuable.

Supramolecular pathway selection of perylenediimides mediated by chemical fuels.

We demonstrate supramolecular pathway selection of a perylenediimide derivative in aqueous solution using chemically fueled redox reactions to control assembly/disassembly cycles. The number and frequency of cycles affect the nucleation and growth process, providing control over the size and internal order of the resulting self-assembled structures.

Chemical and photochemical properties of chloroharmine derivatives in aqueous solutions.

Thermal and photochemical stability (Φ(R)), room temperature UV-vis absorption and fluorescence spectra, fluorescence quantum yields (Φ(F)) and lifetimes (τ(F)), quantum yields of hydrogen peroxide (Φ(H2O2)) and singlet oxygen (Φ(Δ)) production, and triplet lifetimes (τ(T)) have been obtained for the neutral and protonated forms of 6-chloroharmine, 8-chloroharmine and 6,8-dichloroharmine, in aqueous media. When it was possible, the effect of pH and oxygen concentration was evaluated. The nature of electronic transitions of protonated and neutral species of the three investigated chloroharmines was established using Time-Dependent Density Functional Theory (TD-DFT) calculations. The impact of all the foregoing observations on the biological role of the studied compounds is discussed.

Modeling of equilibrium isotherms and kinetic studies of Cr (VI) adsorption into natural and acid-activated clays

Smectite clay has great potential for the removal of heavy metal ions from aqueous solution. This work aims to develop inexpensive, highly available, effective metal ion adsorbents from clay minerals as alternatives to existing commercial adsorbents. In particular, natural clay was modified with sulfuric acid to yield excellent adsorbent material. The adsorptive interactions of Cr (VI) ions with natural clay and their acid-activated derivative in aqueous solution are investigated in this study. The adsorption experiments were carried out under batch process with Cr (VI) concentration, pH, time, and temperature as the variables. The adsorption was strongly dependent on pH of the solution. Adsorption was very fast at low coverage, and equilibrium was approached within 35 min. The kinetic data were analyzed using different kinetic models. It was shown that the adsorption of Cr (VI) ions could be described by a pseudo-second-order equation and Elovich model. The experimental data were also analyzed using two- and three-parameter isotherm models of adsorption. Thermodynamic parameters such as ΔG0, ΔH0, and ΔS0 have been evaluated, and it has been found that the sorption process was spontaneous and exothermic. From all our data, we conclude that the treated clay by sulfuric acid investigated in this study showed good potential for Cr (VI) ions removal from aqueous solutions.

Radiation-induced reduction of quinoxalin-2-one derivatives in aqueous solutions

Quinoxaline-2-one derivatives have been proposed as potential drugs in treatments of various diseases since some of them showed a variety of pharmacological properties. The kinetics and spectral characteristics of the transients formed in the reactions of hydrated electrons (eaq−) with quinoxalin-2-(1H)-one (Q) and its methyl derivative, 3-methyl quinoxalin-2-(1H)-one (3-MeQ) were studied by pulse radiolysis in aqueous solutions at pH ranging from 5 to 14. The transient absorption spectra recorded in the reactions of (eaq−) with Q and 3-MeQ at pH 7 consisted of a broad, almost flat band in the range 390–450nm and were assigned to the respective protonated radical anions (QH∙/3-MeQH∙) at N4 atom in a pyrazin-2-one ring. On the other hand, the transient absorption spectra recorded in the reactions of (eaq−) with Q and 3-MeQ at pH 13 are characterized by a broad band with a much better pronounced maximum at λmax=390nm and higher intensity (in comparison to that at pH 7) and were assigned to the respective radical anions (Q∙−/3-MeQ∙−). Both forms are involved in the prototropic equilibrium with the pKa located at pH≥13.5. The rate constants of the reactions of (eaq−) with Q and 3-MeQ were found to be at pH 7 (2.6±0.1)×1010M−1s−1 and (2.1±0.1)×1010M−1s−1 and at pH 13 (1.6±0.1)×1010M−1s−1 and (1.3±0.1)×1010M−1s−1, respectively. Semi-empirical quantum mechanical calculations reproduce fairly well the spectral features of the experimental absorption spectra and show that protonated radical anions at nitrogen atom (N4) in both molecules are the most stable hydrogenated radicals.

Electrochemical lithiation/delithiation kinetics and capacity of phosphate tungsten bronze and its chemically pre-lithiated derivatives in aqueous solutions

Monophosphate bronze (PW8O26, WPB) was synthesized by low-temperature (650 °C) heating of 12-tungstophosphoric acid (WPA). Its lithiated derivative with a low lithium content (Li3-WPB) was synthesized by heating lithium salt of WPA at 650 °C. Its lithiated derivative with a high lithium content was synthesized by mechanochemical lithiation of Li3WPB (Lin-WPB) (n > 3), followed by heat treatment at 650 °C. X-ray powder diffraction analysis confirmed that the bronze structure changed with the increase of the incorporated lithium content. These bronzes were investigated from the aspect of lithiation/delithiation kinetics in an aqueous saturated LiNO3 electrolyte solution. By cyclic voltammetry, both the kinetics of intercalation/deintercalation and the coulombic capacity were found to decrease with the increase of initial lithium content, in agreement with literature data for electrochemically lithiated tungstophosphate bronzes. Monoclinic lithium-free bronze PW8O26, as the most promising material, was subjected to a further detailed galvanostatic investigation coupled with the LiFe0.95V0.05PO4/C composite as a cathode material in an aqueous battery. In comparison to its behavior in an organic electrolyte, a considerably lower initial capacity of the bronze electrode was measured. However, its cyclic stability was much better in an aqueous than in an organic electrolyte.

Selective fluorescent sensor for Al3+ using a novel quinoline derivative in aqueous solution

In this paper, a novel fluorescent Al3+-sensor (8-Hydroxyquinoline-7-aldehyde-(2′-methylquinoline-4′-formyl hydrazone, L1) based on quinoline derivative has been designed and synthesized. Compared with L1 without Al3+, the sensor L1 shows significant fluorescence enhancement in the presence of Al3+ in ethanol–water (v/v, 9:1). We hypothesize that the reason might be attributed to the formation of 1:2 ligand–metal complexes inhibiting photoinduced electron transfer (PET) progress.

Preparation and in vitro antioxidant activities of 6-amino-6-deoxychitosan and its sulfonated derivatives.

The 6-amino-6-deoxychitosan (NC) and their 2, 6-di-N-sulfonated derivatives were prepared via N-phthaloylation, tosylation, azidation, hydrazinolysis, reduction of azide groups and N-sulfonation, and their structures were systematically characterized by FT-IR, 2D HSQC NMR, XRD, gel permeation chromatography (GPC), and elemental analysis. The 6-amino-6-deoxychitosan showed effect in three selected antioxidant essays, including reducing power, superoxide anion radical scavenging ability, and hydroxyl radical scavenging effect. But the factors affecting each activity were different. The reducing power and the superoxide anion radical scavenging ability of NC were strong and closely related to the amino groups in the molecular chains. Both introducing N-sulfonated groups into NC and the concentration reduction of NC and its sulfonated derivatives decreased these activities. For the superoxide anion radical, the molecular charge property was also a significant influence factor. For the hydroxyl radical, NC only showed weak scavenging activity in a special inverse concentration-dependent manner. However, the incorporation of N-sulfonated groups significantly improved the scavenging activity, and the more N-sulfonated groups, the higher the concentrations, the stronger the activity was. The results could be due to the different conformations of NC and its sulfonated derivatives in aqueous solution.

Location of TEMPO derivatives in micelles: subtle effect of the probe orientation

Partition coefficients for six 4-substituted derivatives of the 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) derivatives in aqueous solutions of reduced Triton X-100 (RTX-100) were determined by measurements of the probe EPR g-factor and of the fluorescence quenching of pyrene by the radical in the micelle. The partition constant attained a maximum value and then decreased with increasing probe hydrophobicity. Simulation of the probes inside the micelle showed that this trend could be rationalized by a change in the orientation of the 4-substituted TEMPO derivatives with the increasing substituent chain-length. The use of the EPR g-factor for the determination of partition constants of radicals in micellar systems was thus validated as a reliable and sensitive method, capable of describing the probe orientation in its microenvironment.

Preparation of copper complexes coordinated by N21,N22-etheno bridged porphyrin and the application to photooxidation of phenol derivatives

Copper(I) complexes coordinated with a N21,N22-etheno bridged porphyrin ligand were synthesized as a unique coordination structure. The copper porphyrin complexes promoted photooxidations of a phenol derivative in organic solution under aerobic condition with visible photoirradiation. The complexes could be immobilized on silica gel as a support and the obtained copper porphyrin composites showed high ability as photocatalysts for heterogeneous photooxidation of a phenol derivative in aqueous solution. The composites could be easily recovered and re-used after the reaction. The structural study found that the active species contributing to the photooxidation reaction was the di(μ-hydroxo)dicopper(II) complex of N21,N22-etheno bridged porphyrin generated by oxidation of corresponding copper(I) complex in the reaction system under homogeneous and heterogeneous condition.

Nanomolar fluorescent quantitative detection of formaldehyde with a 8-hydroxyquinoline derivative in aqueous solution and electrospun nanofibers

A 8-hydroxyquinoline-based derivative was designed and synthesized, which is shown to act as a highly sensitive fluorescent probe for formaldehyde in aqueous solution. Based on the photo induced electron transfer (PET) process, addition of formaldehyde greatly enhanced the fluorescence of the probe. Formaldehyde can be detected quantitatively in the concentration range from 900nM to 1.3×10−4M and the detection limit on fluorescence response of the probe can be as low as 900nM. The proposed method was successfully employed for preliminary application in several commercially available foods. Moreover, it has been successfully blended with a host polymer polyvinyl alcohol and the polymer containing the probe has been made in nanofiber form via electrospinning. The fluorescence of the nanofibers could also be enhanced after they were immersed into water solution of formaldehyde.

Molecular dynamics simulation study of the association of lidocainium docusate and its derivatives in aqueous solution.

Ionic liquid active pharmaceutical ingredients (IL APIs) are novel materials in which the ions themselves are APIs, but the pure salt is a liquid under ambient conditions. It has been found that IL APIs can have superior performance relative to their conventional salt analogues, but the mechanism for this is unclear. We have used molecular simulations to estimate the aqueous phase association constants of the IL API lidocainium docusate and their sodium and chloride counterparts. Lidocainium is the cationic form of lidocaine, a local anesthetic, while the docusate anion is an emollient. From strongest to weakest, the calculated association constants are 10.1 M(-1) (lidocainium docusate); 0.77 M(-1) (sodium chloride); 0.086 M(-1) (sodium docusate); and 0.065 M(-1) (lidocainium chloride). These results suggest that the experimentally observed enhanced efficacy of lidocainium docusate relative to the traditional drug formulation as a lidocaine hydrochloride salt could result from association of the ions in aqueous solution and at the cell membrane, leading to a synergistic activity effect.

Aggregation state of amphiphilic cationic tetraphenylporphyrin derivatives in aqueous microheterogeneous systems

The conditions for the formation of ionic associates and J- and H-aggregates from amphiphilic cationic tetraphenylporphyrin derivatives in aqueous solutions of anionic surfactants and polyelectrolytes in a wide range of concentrations and pH are considered. The aggregation behaviors of tetraphenylporphyrin and its cationic derivatives in aqueous microheterogeneous systems are compared illustrating the influence of the porphyrin molecular structure on its ability to form supramolecular aggregates of a certain structure. The mechanism of the promoting action of premicellar solutions of anionic surfactants on the formation of J-aggregates of the diprotonated form of cationic porphyrins was proposed. The acid-base properties of a number of new synthetic meso-aryl-substituted porphyrins in aqueous microheterogeneous systems were characterized.

Electronic and structural elements that regulate the excited-state dynamics in purine nucleobase derivatives.

The excited-state dynamics of the purine free base and 9-methylpurine are investigated using experimental and theoretical methods. Femtosecond broadband transient absorption experiments reveal that excitation of these purine derivatives in aqueous solution at 266 nm results primarily in ultrafast conversion of the S2(ππ*) state to the vibrationally excited 1nπ* state. Following vibrational and conformational relaxation, the 1nπ* state acts as a doorway state in the efficient population of the triplet manifold with an intersystem crossing lifetime of hundreds of picoseconds. Experiments show an almost 2-fold increase in the intersystem crossing rate on going from polar aprotic to nonpolar solvents, suggesting that a solvent-dependent energy barrier must be surmounted to access the singlet-to-triplet crossing region. Ab initio static and surface-hopping dynamics simulations lend strong support to the proposed relaxation mechanism. Collectively, the experimental and computational results demonstrate that the accessibility of the nπ* states and the topology of the potential energy surfaces in the vicinity of conical intersections are key elements in controlling the excited-state dynamics of the purine derivatives. From a structural perspective, it is shown that the purine chromophore is not responsible for the ultrafast internal conversion in the adenine and guanine monomers. Instead, C6 functionalization plays an important role in regulating the rates of radiative and nonradiative relaxation. C6 functionalization inhibits access to the 1nπ* state while simultaneously facilitating access to the 1ππ*(La)/S0 conical intersection, such that population of the 1nπ* state cannot compete with the relaxation pathways to the ground state involving ring puckering at the C2 position.

Photochemistry of Fe(III) complexes with salicylic acid derivatives in aqueous solutions

Abstract The photochemistry of a series of 1:1 Fe(III) complexes with salicylic acid derivatives (SADs) in aqueous solution has been investigated, using the following model compounds: salicylic acid (SA), 5-sulfoSA (5SSA), 4-hydroxySA (2HSA), 6-hydroxySA (6HSA), 4-nitroSA (4NSA) and 5-nitroSA (5NSA). The results of optical spectroscopy, steady-state and nanosecond laser flash photolysis experiments show that all Fe(III)–SAD complexes exhibit good photochemical stability upon 355 nm excitation (quantum yields of photolysis do not exceed 0.01). No evidence of hydroxyl radical formation was observed in laser flash experiments. Therefore, the primary photoprocess was assumed to be an electron transfer from coordinated SAD to the Fe(III) ion in the excited complex, leading to the formation of Fe(II) and the corresponding SAD phenoxy radical. SADs containing electron-withdrawing groups (4NSA, 5NSA, 5SSA) exhibit the smallest quantum yields of photolysis of the series, whereas the highest values were observed for SA and SADs containing electron-donating groups (4HSA, 6HSA). Therefore, in contrast to Fe(III)-complexes with aliphatic carboxylates, sunlight photolysis of Fe(III)–SAD complexes cannot be an effective way for the degradation of SADs in natural water systems.

A Facile and Efficient One‐Pot Electrochemical Synthesis of Thiazole Derivatives in Aqueous Solution

AbstractIn the present work, the electrooxidation of hydroquinones 1a and 1b, and catechols 1c and 1d was studied in the presence of rhodanine (3) as nucleophile in a mixture of EtOH and phosphate buffer solution as ‘green’ media using cyclic voltammetry and controlled‐potential coulometry. The results indicated that the corresponding p‐ and o‐quinones formed from the hydroquinones and catechols, respectively, participate in Michael addition reaction to yield new thiazole derivatives. The electrochemical syntheses of these new thiazole derivatives were performed successfully at three graphite rod electrodes in undivided cells in good‐to‐excellent yields at room temperature without any catalyst.

A New Turn-Off Fluorescence Chemosensor for Hydrogen Peroxide Based on Carbazole Derivative in Aqueous Solution

A water-soluble fluorescent probe was described for detecting hydrogen peroxide with the carbazole-derived as fluorophore and boronate moiety as recognition unit. The probe was developed as a turn-off fluorescent chemosensor with fast, high selectivity and sensitivity toward H2O2over other biological reactive oxygen species. What is more, the probe was quenched linear response to H2O2concentration in the range of 1.0×10−8- 2.0×10−5M and lower detection limit down to 6 nM (S / N = 3) was obtained.