Aqueous Solvent Mixtures Research Articles

Synthesis of hydrophilic conjugated porphyrin dimers for one-photon and two-photon photodynamic therapy at NIR wavelengths

We report the synthesis of a series of hydrophilic butadiyne-linked conjugated zinc porphyrin dimers, designed as photodynamic therapy (PDT) agents. These porphyrin dimers exhibit exceptionally high two-photon absorption cross sections (delta(max) approximately 8,000-17,000 GM) and red-shifted linear absorption spectra (lambda(max) approximately 700-800 nm) making them ideal candidates for one-photon and two-photon excited photodynamic therapy. Four polar triethyleneglycol substituents are positioned along the sides of each dimer, but, on their own, these TEG chains do not confer sufficient solubility in aqueous physiological media for reproducible delivery into live cells. Charged cationic (methylpyridinium and trimethylammonium) and anionic (sulfonate and carboxylate) substituents have been appended to the meso-positions of porphyrin dimers using three synthetic strategies: 1) Suzuki coupling, 2) Sonogashira coupling, and 3) nucleophilic Senge arylation. Approaches 1 and 3 both allow attachment of aromatic substituents directly to the meso-positions of porphyrins. Approach 2 provides a route to hydrophilic porphyrin dimers with an ethyne link between the porphyrin and the polar aromatic substituent. The palladium-catalysed approaches 1 and 2 allow the synthesis of a broader range of meso-capped porphyrins, as many aryl halides are available. However the synthesis of the intermediate required for these routes necessitates a statistical reaction step, which decreases the overall yield. On the other hand, Senge-arylation provides highly regioselective nucleophilic aromatic substitution, and offers higher overall yield than the other routes. All these charged dimers exhibit good solubility in polar solvents (e.g. methanol) and aqueous solvent mixtures (aqueous DMSO or DMF).

Solubility of Ethyl Maltol in Aqueous Ethanol Mixtures

With a laser monitoring observation technique, the solubility of ethyl maltol in binary aqueous ethanol solvent mixtures in the temperature range of 293.15 K to 333.15 K was measured by a synthetic method. The solubility data were correlated with the combined nearly ideal binary solvent/Redlich−Kister (CNIBS/R−K) model. For the nine group data studied, the CNIBS/R−K model was found to provide an accurate mathematical representation of the experimental data.

Expedient synthesis and solvent dependent oxidation behavior of a water-soluble IBX derivative

IBX derivative 6, synthesized in two steps from 2-aminoterephthalic acid, 8, is soluble in both DMF and water. A variety of alcohols are oxidized using 6 in DMF with ease and selectivity identical to that of parent IBX. However, oxidations carried out in water and other aqueous solvent mixtures using 6 exhibit unique selectivities toward different substrates and provide products different from reactions carried out in DMF. A mechanistic rationale is provided for this solvent dependent behavior of 6.

Solubility of Form α and Form γ of Glycine in Aqueous Solutions

The solubilities of two polymorphs of glycine (α-form and γ-form) in different aqueous solvent mixtures were measured by using the analytical gravimetric method. Based on the measured solubility data in pure water, the relative stability and the enthalpy and entropy of dissolution of the two forms were determined using van’t Hoff plots. The solubilities of forms α and γ were also investigated in aqueous solutions containing methanol or polyethylene glycol (PEG200) at 20 °C. It was shown that the solubilities of both forms decreased with increasing concentration of methanol and PEG200. The pH dependence of solubility of the γ-form was measured in the pH range of (0.35 to 13.7) at temperatures of (20 and 25) °C. The solubility profiles show a U-shape with pronounced changes at pH below 3.0 or above 10.0.

Room-temperature single-step synthesis of nanoparticle-decorated nanotubes

A simple method to synthesize silver or silver sulfide nanoparticle-decorated nanotubes without additional templating molecules or thermal treatment is reported in this study. Silver precursor ions were transferred to organic phase using phase-transfer agent from the aqueous precursor and organic solvent mixture, and then reduced to form nanoparticle-decorated nanotubes under the guidance of the self-assembled alkylthiol molecules at room temperature without additional templates. During the reduction of the precursor metal ions, the alkylthiol molecules formed cylindrical template as well as capped silver and silver sulfide nanoparticles, simultaneously. Through this multifunctional role of alkylthiol molecules, one-step preparation of nanoparticle-decorated nanotubes or nanorods was achieved. A series of control experiments were carried out in order to survey the effect of thiol amount on the nanotube formation. The concentration of alkylthiol was turned out to be a key factor determining the final morphology of the product. In addition, the nanotube formation is governed by the type of metal precursor ion used. These results will provide an advanced synthesis method on the alkylthiol-based nanotubes decorated with functional nanoparticles.

Characterization of poly( N-alkylanilines) by Raman spectroscopy

Thin films of poly( N-alkylaniline) were synthesized in acidic aqueous solution and in mixtures of aqueous and organic solvents. The polymer films (alkyl = methyl, ethyl, propyl and butyl) were characterized by Raman spectroscopy with the excitation wavelengths of 514.5, 632.8 and 780 nm. The main Raman bands have been characterized for the leucoemeraldine, emeraldine and pernigraniline oxidation states between −0.2 and 0.8 V (vs. Ag|AgCl). This fundamental study shows that the structure of the half-oxidized emeraldine form contains quinoid units, which supports the commonly accepted oxidation and reduction scheme of poly( N-alkylanilines).

2-Amino-7-nitro-fluorenes in Neat and Mixed SolventsOptical Band Shapes and Solvatochromism

Femtosecond transient absorption spectroscopy of amino-nitro-fluorenes in the UV-visible range shows that the dynamic Stokes shift of the emission band is sensitive to infrared-active modes of the solvent. Bandshapes for stationary absorption and emission are needed to quantify the observed spectral evolution. They are reported for 2-amino-7-nitro-fluorene (ANF), 2-dimethylamino-7-nitro-fluorene (dM-ANF), and 2-di(n-butyl)amino-7-nitro-9-di(n-propyl)-fluorene (dBdP-ANF) in a variety of solvents. Bands broaden systematically with increasing solvent polarity. This effect is taken into account in an improved location of band positions. The resulting solvatochromic plots differ significantly from those that use peak positions of absorption spectra and fluorescence quantum distributions. Absorption spectra were also measured in aqueous solvent mixtures, and shifts are described by binding curves for hydrogen bonding and stepwise solvent exchange.

Chiral extraction of ketoprofen enantiomers with chiral selector tartaric esters

Distribution behavior of ketoprofen enantiomers was examined in methanol aqueous and organic solvent mixture containing tartaric esters. The influence of length of alkyl chain of tartaric esters, concentration of L-tartaric esters and methanol aqueous, kind of organic solvent on partition ratio and separation factors was investigated. The results show that L-tartaric and D-tartaric esters have different chiral recognition abilities. S-ketoprofen is easily extracted by L-tartaric esters, and R-ketoprofen is easily extracted by D-tartaric esters. L-tartaric esters form more stable diastereomeric complexes with S-enantiomer than that with R-enantiomer. This distribution behavior is consistent with chiral recognition mechanism. With the increase of the concentration of tartaric ester from 0 to 0.3 mol/L, partition coefficient K and separation factor α increase. Also, the kind of organic solvent and the concentration of the methanol aqueous have significant influence on K and α.

Quenching of Singlet Molecular Oxygen (1O2) by Azide Anion in Solvent Mixtures¶

The azide ion is a strong physical quencher of singlet molecular oxygen (1O2) and is frequently employed to show involvement of 1O2 in oxidation processes. Rate constants (kq) for the quenching of 1O2 by azide are routinely used as standards to calculate kq values for quenching by other substrates. We have measured kq for azide in solvent mixtures containing deuterium oxide (D2O), acetonitrile (MeCN), 1,4-dioxane, ethanol (EtOH), propylene carbonate (PC), or ethylene carbonate (EC), mixtures commonly used for many experimental studies. The rate constants were calculated directly from 1O2 phosphorescence lifetimes observed after laser pulse excitation of rose bengal (RB), used to generate 1O2. In aqueous mixtures with MeCN and carbonates, the rate constant increased nonlinearly with increasing volume of organic solvent in the mixtures. kq was 4.78 × 108M−1 s−1 in D2O and increased to 26.7 × 108 and 27.7 × 108M−1 s−1 in 96% MeCN and 97.7% EC/PC, respectively. However, in EtOH/D2O mixtures, kq decreased with increasing alcohol concentration. This shows that a higher solvent polarity increases the quenching efficiency, which is unexpectedly decreased by the proticity of aqueous and alcohol solvent mixtures. The rate constant values increased with increasing temperature, yielding a quenching activation energy of 11.3 kJ mol−1 in D2O. Our results show that rate constants in most solvent mixtures cannot be derived reliably from kq values measured in pure solvents by using a simple additivity rule. We have measured the rate constants with high accuracy, and they may serve as a reliable reference to calculate unknown kq values.

A sensor for superoxide in aqueous and organic/aqueous media based on immobilized cytochrome c on binary self-assembled monolayers

A method for the electrochemical detection of superoxide radical was developed, based on cytochrome c (cyt c) immobilized on the binary self-assembled monolayers (SAMs) of thioctic acid (T-COOH) and thioctic amide (T-NH 2) on gold electrode. The sensor works by electrochemically detecting cyt c reduced by the superoxide radical generated by a xanthine–XOD system. The electrochemical properties of immobilized cyt c were investigated in aqueous buffer and in a mixture of aqueous and organic solvents. The interaction of superoxide radical with the modified electrode was characterized in phosphate buffer solution (PBS) and in the mixtures of both PBS and dimethyl sulfoxide (DMSO) and PBS and glycerol (Gly). The results showed that the sensors responded immediately to superoxide radical in PBS and gave a steady-state anodic current within 10 s during the generation of superoxide radical. In 40% DMSO and in 30% Gly solution, the current response reached a steady-state anodic current within 20 s. The sensor could also be used to estimate superoxide dismutase (SOD).

Specific swelling behaviors of alkali‐metal poly(styrene sulfonate) gels in aqueous solvent mixtures

AbstractCounterion‐ and solvent‐specific swelling behaviors were investigated for alkali‐metal poly(styrene sulfonate) (PSSM) gels having different degrees of sulfonation in aqueous organic solvent mixtures [water plus methanol, ethanol, 2‐propyl alcohol, t‐butyl alcohol, dimethyl sulfoxide (DMSO), acetone, acetonitrile, tetrahydrofuran, or dioxane]. With an increasing organic solvent concentration, most gel systems, except for DMSO, showed a volume phase transition. The transition abruptly occurred without significant deswelling in the lower solvent concentration region. Such swelling behavior contrasted with that of other common charged gel systems, including alkali‐metal polyacrylate (PAAM) gels, which showed gel collapse after gradual deswelling with an increasing organic solvent concentration. The dielectric constant at the critical transition point (Dcr) for most mixed solvent systems decreased in the order of PSSK ≥ PSSCs ≥ PSSNa > PSSLi; that is, larger counterion systems were favorable for the transition. The counterion specificity also contrasted with our previous results for PAAM gels: PAANa > PAAK > PAALi ∼ PAACs. On the other hand, the solvent specificity for the PSSM gels was similar to that for the PAAM gels; the higher the dielectric constant was of the organic solvent, the higher the Dcr value was at which the transition occurred. These specificities were examined on the basis of the solvation properties of the counterions and polymer charged groups and the solvent properties such as the Gutmann–Mayer donor number and acceptor number. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1166–1175, 2007

Synthesis and properties of new thermosensitive polymer systems

AbstractThe controlled thermal release of aqueous solvent mixtures from polymeric gel particles was investigated. A new type of a polymeric gel consisting of a maleic anhydride/poly(ethylene glycol) condensation product as a crosslinking macromonomer and acrylamides was synthesized by solution or inverse emulsion polymerization for the investigation. Afterward a shell of crosslinked polystyrene was coated to stabilize this new kind of “microcontainer” for the application. This concept was shown as generally useful for various mixtures of organic solvents and water. The cloud point temperature of the polymer gel strongly depended on the following parameters: the type and content of organic cosolvent, the degree of polymerization and constituents of the polyester moiety, and the type and content of the comonomers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

The role of solvents in the imbibition of ascorbic acid by zeolites

Ascorbic acid is commonly used as an antioxidant agent in form of a powder. This allows the immediate availability of the molecule but cannot avoid the rapid inactivation of the excess. Sodium zeolites have frequently been proposed as agents for the controlled release of absorbed molecules. In order to prepare controlled release antioxidant agents, we treated sodium X and Y zeolites with ascorbic acid dissolved in organic solvents in order to establish how much acid they were able to retain and understand the retention and release mechanism. We found that the acid: (i) undergoes a dissociation and H+/Na+ exchange with zeolite; (ii) is retained as sodium salt while the zeolite is protonated; (iii) is released as a function of the sodium salt solubility into the solvent used. Thus, the imbibition was function of the nature of the solvent and, in aqueous-organic solvent mixtures, it was a direct function of the water concentration in the range 0–1% and an inverse function in the range 1–11%. It follows from above that, when sodium zeolite is used as a support for ascorbic acid, water percent in the range 0–11% may control the release as the ascorbate salt into aqueous–organic solvent mixtures.

Influence of linker structure on the anion binding affinity of biscyclopeptides

A systematic analysis is presented on the influence of the linking unit between two cyclopeptide rings on the affinity of such biscyclopeptide-based anion receptors in aqueous solvent mixtures. Although the differences in the affinity and selectivity of these receptors towards a given anion are not very pronounced, there are profound differences in the thermodynamics of anion complexation. Enthalpic and entropic contributions both (1) play a role in determining the binding affinity and (2) show significant variation as the linking structure is changed. A decrease in conformational rigidity of the linker improves the entropic advantage for complex formation, but not necessarily the overall complex stability. This effect may be due, in part, to the fact that structural constraints within more rigid linkers might prevent efficient interactions between the host and guest. The optimal linker, which exhibits both favourable enthalpic and entropic contributions, was identified using de novo structure-based design methods as implemented in the HostDesigner software.

Solvatochromic behavior of non-activated indolinobenzospiropyran 6-carboxylates in aqueous binary solvent mixtures. Part II

The solvatochromic behavior of non-activated indolinobenzospiropyran 6-carboxylates SP-1– 2 in aqueous binary solvent mixtures was investigated. Marked negative solvatochromism was exhibited by SP-1– 2 in the whole region of solvent polarity examined. Excellent linear relationships were observed between λ max and the solvent polarity parameter, E T(BM), for the aqueous binary solvent mixtures. The sensitivity of the binary solvent system toward the transition energies of the MC form was highest in the water–methanol solvents in all SP molecules examined. As of other merocyanine dyes in neat solvents, the MC form of spiropyran 6-carboxylates in the aqueous binary solvents showed a negative solvatochromism. The aqueous solvent was found to affect the solvatochromic behavior of the merocyanine dyes by increasing the sensitivity of the chromophore to the effects of solvation via H-bonding.

Electropolymerization and characterization of poly( N-methylaniline) and poly( N-butylaniline) in mixtures of aqueous and organic solvents

Electropolymerization of N-methylaniline (NMA) and N-butylaniline (NBA) was studied on glassy carbon and optically transparent tin oxide electrodes in mixtures of aqueous and organic solvents. Five different organic solvents, dimethyl formamide, dimethyl sulfoxide, tetrahydrofuran (THF), propylene carbonate (PC) and acetonitrile (ACN) were mixed with aqueous 1.0 M HClO 4 solutions. Our results show that NMA and NBA can be electropolymerized in aqueous–organic solvent mixtures with maximum 30 and 50% (v/v) organic solvents, respectively. The choice of organic solvent strongly influences the film formation. With addition of 10–20% THF, ACN and PC to the aqueous polymerization solution, the film formation was highly improved. The poly( N-methylaniline) and poly( N-butylaniline) films were characterized with cyclic voltammetry, in situ UV–vis spectroscopy, size exclusion chromatography and with electrical conductivity measurements.

Unusual Reverse Photochromic Behavior of Indolinobenzospiropyran 6-Carboxylates in Aqueous Binary Solvents

Thermoand photochromic indolinobenzospiropyran dyes recently have become important in connection with the rapid development of information recording systems, such as high-density optical data storage, optical switching, displays and non-linear optics. These molecules are known to be in equilibrium with their metastable colored forms. The absorption of ultraviolet light shifts the equilibrium towards the merocyanine colored form (MC), while the reverse process shifting them toward the colorless form (SP) is induced by visible light, heat, or can occur spontaneously (normal photochromism). The color of the MC form as well as the rate of rearrangement back to the SP form are both dependent on the polarity of the solvent. The stabilization of the MC form in polar solvents leads to it having a larger energy of activation and a slower MC↔SP transition as compared to that in non-polar solvents. Occasionally, the merocyanine form is further stabilized by factors such as hydrogen bonding, combination with a crown ether or cyclodextrin and complexation with a metal. Thus, the initially colorless solutions of spiropyrans become deeply colored upon the spontaneous formation of the merocyanine (reverse photochromism). Continuing our previous works on the solvatokinetic and solvatochromic behaviors of spiropyran derivatives in various neat organic solvents, we examined the photochromic behaviors of spiropyran derivatives in binary aqueous solvent media. Since merocyanine dyes in solution usually exist in dipolar ionic forms, their preferential solvation in binary mixtures was expected to affect their photophysical behavior. Although many studies have been conducted on the photochromic behaviors of spiropyran derivatives in various neat organic solvents, to the best of our knowledge, no papers have previously been published on the photochromic behaviors of spiropyrans in aqueous binary solvent systems. Herein, we describe the unusual photochromic behaviors of indolinobenzospiropyran 6-carboxylates 1-2 in aqueous binary solvent media, as depicted in Scheme 1. The electronic absorption spectra of the spiropyran carboxylates 1-2 showed no absorbance in the visible region on irradiation in neat solvents, whereas, they unexpectedly showed chromotropism in aqueous binary solvent mixtures such as water/methanol, water/DMSO, water/acetonitrile, etc. The UV-Vis. spectral changes for the SP → MC conversion of SP-1 in water-methanol solvent mixtures (50/50 v/v %) are shown in Figure 1, as a representative example. Initially, the water-methanol solution of SP-1 has an absorption band only in the 300 nm region. However, the colorless solution becomes spontaneously deeply colored upon the ring-opening reaction of SP-1 to MC-1. MC-1 has a strong absorption at 522 nm in 50/50% aqueous methanol. Reproducible results for the ring-opening reaction of spiropyran to merocyanine were obtained through the development of a protocol that maximized the formation of the colored form, as indicated by the solid line in Figure 1. The colored merocyanine solutions revert to the colorless spiropyran state upon their exposure to visible light of the appropriate wavelength. In addition to its major absorption at 500-550 nm, SP-2 has an extra absorption band in the 400-450 nm region in aqueous binary solvent mixtures. This extra absorption band is probably due to the proton transferred MC form (MCHCOO−). The proton might migrate from the 6-substituent COOH to the oxygen atom of the phenoxide anion in aqueous solvents, since the COOH group is more acidic than the OH group of the phenyl ring. This was confirmed by the UV-Vis spectral behavior of spiropyran both in HCl/aqueous

Brønsted acidity of ceric ammonium nitrate in anhydrous DMF. The role of salt and solvent in sucrose cleavage

The generation of an unexpected Brønsted acidity in anhydrous DMF at 50 °C was evidenced by NMR measurements during the investigation on the course of sucrose cleavage by ceric ammonium nitrate (CAN). The formation of a nitrooxy derivative of DMF by reaction with CAN is responsible for this acidity. The reactivity of CAN at 50 °C with several solvents was evaluated by voltammetric and potentiometric measurements. The possible release of protons from these reactions, particularly when aqueous solvent mixtures are used, should always be taken into account in the mechanistic interpretation of CAN synthetic applications.

Reentrant conformation transition in poly( N, N-dimethylacrylamide) hydrogels in water–organic solvent mixtures

Conformational changes in poly( N, N-dimethylacrylamide) (PDMA) networks swollen in aqueous solutions of organic solvents are studied both experimentally and theoretically. PDMA hydrogels of various charge densities were prepared by free-radical crosslinking copolymerization. Swelling behavior of the hydrogels was investigated in aqueous organic solvent mixtures as functions of solvent species and the concentration. With increasing volume fraction ϕ of acetone, tetrahydrofuran, or 1,4-dioxane in the aqueous solution, PDMA hydrogels exhibit reentrant conformation transition. During this transition, the gel first deswells in the range of ϕ between 0.4 and 0.9, and then rapidly reswells if ϕ is monotonically increased. The reswelling of the collapsed PDMA gel occurs in a narrow of ϕ above ϕ=0.97. It was shown that the reentrant transition in PDMA gels requires moderate hydrogen bonding organic solvents, so that the hydrophobic interactions between PDMA and the organic solvent dominate the swelling process. The results were interpreted using the theory of equilibrium swelling. The interaction parameters in the gel system as well as the partition parameter of the organic solvent between the gel and the solution phases were calculated.

Solubility of Potassium Clavulanate in Aqueous 2-Propanol Mixtures

With a laser monitoring observation technique, the solubility of potassium clavulanate in binary aqueous 2-propanol solvent mixtures in temperature range from 273 K to 305 K and in the solvent comp...