Dioxane-water Mixtures Research Articles

Insights into biomimetic system-ligand interaction of substituted isophthalic acid: A functionality induced photophysical study.

The present article attempts to interpret the modulation of photophysical properties of isophthalic acid (IPA) through its amino [5-amino isophthalic acid (5-amino IPA)] and azido [5-azido isophthalic acid (5-azido IPA)] substituted derivatives which are chemically potent organic ligands. The ground state structure-reactivity correlation of 5-amino IPA and 5-azido IPA has been deciphered through computational studies. The computed energetics show significant interaction feasibility of the substituted ligand systems with the biomimetic systems which is further validated experimentally. The binding interaction of the probes with oppositely polarized functionalization is studied to be significant with cetyltrimethylammonium bromide (CTAB) and bovine serum albumin (BSA) with the amino functionalized derivative having a comparatively stronger binding constant value. The steady-state absorption and fluorescence study establish significant modification of polarity of the heteronuclear probes. The micro polarity study in water-dioxane mixtures enables determination of polarity of 5-amino IPA in CTAB and BSA unlike 5-azido IPA. Presence of an overlapping region between the emission spectrum of BSA and the absorption spectrum of the probes as probable donor-acceptor pair are also scrutinized via the steady-state fluorescence studies. The photophysical behavior of 5-amino IPA is observed to be somewhat dissimilar to that of 5-azido IPA.

Synthesis of glycyl-(<i>S</i>)-5-hydroxynorvaline

The dipeptide glycyl-( S )-5-hydroxynorvaline was obtained from 1- tert -butyl 5-methyl N -Boc-glycyl-( S )-glutamate as a result of saponification and subsequent reduction of the activated 5-carboxyl group with sodium borohydride followed by removal of the N -Boc and OBu t protecting groups by refluxing in a dioxane-water mixture. Using the example of the synthesis of ( S )-5-hydroxynorvaline, it has been shown that the used sequence of chemical transformations is not accompanied by racemization.

Effect Of Solvents On Stability Constants of Fe(II) and Ni(II) Transition Metal Ions Chelates With Some Substituted Pyrazoles

The reaction of Fe(II) and Ni (II) metal ions with L1 : 3 (2’- chlorophenyl) - 4- benzoyl - 5 (2-hydroxy phenyl) pyrazole, L2: 3 (2’-chlorophenyl) - 4- pyridoyl -5 (2-hydroxy phenyl) pyrazole , L3: 3 (2’-aminophenyl)- 4-pyridoyl - 5 (2- hydroxyl phenyl) pyrazole and L4: 3 (4’-chlorophenyl) -4-Benzoyl -5(2-hydroxy-phyenyl) pyrazole, at 0.1M ionic strength at 28 ± 0.10C in 70% ethanol -water mixture and 70% dioxane-water mixture have been studied pH-metrically. The data obtained were used to estimate the values of proton-ligand (pK) and metal-ligand (logK) stability constants in different solvents. It is observed that the pK and logK values in 70% dioxane-water mixture are greater than in 70% ethanol -water mixture. Fe(II) and Ni(II) metal ions formed 1:1 and 1:2 complexes with all the ligands in both solvent medium.

Preparation, investigation, DFT, pH-metric and cyclic voltammetry of Cr(III), Fe(III), Co(II), Ni(II) and Cu(II) complexes derived from 2-(2-((2Z,3Z)-3-(hydroxyimino) butan-2-ylidene) hydrazineyl)-2-oxo-N-(pyridin-2-yl) acetamide (H3BYPA) and evaluation of their biological activity

Binuclear Cu(II), Co(II) and Ni(II) and mononuclear Fe(III) and Cr(III) complexes derived from new ligand, namely 2-(2-((2Z,3Z)-3-(hydroxyimino) butan-2-ylidene) hydrazineyl)-2-oxo-N-(pyridin-2-yl) acetamide (H3BYPA) have been prepared and identified by elemental analysis, magnetic measurements and spectral methods. The separated complexes appointed the general formula, [M2(HBYPA)(H2O)mCln].xH2O where M = Co(II) and Cu(II) and x = 0 and 3, respectively. IR data detected that the ligand behaves as monobasic NO bidentate in [Fe(H2BYPA)2Cl(H2O)].H2O complex. However, as dibasic tetradentate in [Cr(HBYPA)Cl(H2O)], [Co2(HBYPA)Cl2(H2O)2] and [Cu2(HBYPA)Cl2(H2O)2].3H2O complexes. Furthermore, H3BYPA behaves as tribasic pentadentate in the binuclear [Ni2(BYPA)Cl(H2O)4].4H2O complex,. pH-metric titration was accomplished in 50% water-dioxane mixture at 298, 318 and 328 K, respectively and the ligand's dissociation constant as well as the complexes’ stability constants were recorded. Also, the thermodynamic and kinetic parameters for the several thermal degradation phases of the complexes were calculated using the Horowitz–Metzger and Coats–Redfern approaches. The optical band gap values were compared to those produced by DFT and found to be equivalent. Moreover, antitumor and antibacterial activities of the compounds have been tested. Finally, the ligand and complexes docking study was utilized against HEPG-2 and MCF-7 by Schrödinger suite program using XP glide protocol.

The equivalent electric conductivity of hydrochloric acid in solvents of lower permittivity than water, and its interrelation with the acid’s activity coefficient: A theoretical analysis

Theory–experiment fit for electrolytes in solvents other that pure water has always been challenging. In ionic activity, solvent’s permittivity (ε) plays an important role; at ambient pressure, ε is only a function of temperature, but in different solvents, it is also influenced by the nature of the solvent used, being smaller in less polar solvents. Employing the extended Debye–Hückel ion activity theory DH–SiS, HCl in nonaqueous or mixed solvents provided, up to moderate concentration, an excellent theory–experiment agreement even at very low ε, < 10 (Fraenkel, J. Phys. Chem. B 115 (2011) 14634). A parallel analysis is now reported for the ionic electric conductance of HCl in such solvents; specifically, in pure methanol, methanol–water mixtures, and dioxane–water mixtures. The analysis is done using DHO–SiS – a recently presented refined and extended Debye–Hückel–Onsager theory (Fraenkel, Phys. Chem. Chem. Phys. 20 (2018) 29896). In conductance, theory is further complicated by the effect of solvent’s viscosity (η) that – like ε – in addition to varying with temperature, varies also with the kind of solvent. However, good-to-excellent theory–experiment fit is achieved with different η values at ε > 30; and the equivalent conductivity proves, as before, to be theoretically interrelated with the activity coefficient. At ε < 30, a fit occurs only with an adjusted ε (εadj) postulated to reflect the influence of the exerted external electric field on solvent’s molecular arrangement.

The Microscopic and Tautomeric Protonation Constants of Some α-Amino Acids in Dioxane–Water Mixtures

The Microscopic and Tautomeric Protonation Constants of Some α-Amino Acids in Dioxane–Water Mixtures

Equilibrium Studies of Binary and Ternary Complexes Involving 2-Hydroxy-1- Naphthoic Acid and Amino Acids in Dioxane–Water Mixture

Complex formation equilibria of 2-hydroxy-1-naphthoic acid with Cu2+, Ni2+, Co2+ and Mn2+ and the ternary complexes involving Cu2+, 2-hydroxy-1-naphthoic acid and some amino acids containing different functional groups are investigated. Stoichiometry and stability constants for the complexes are estimated at 25 oC and 0.1M ionic strength in 50% dioxane-water mixture. The stability of the complexes follows the trend Cu2+ > Ni2+ > Co2+ > Mn2+, which is in agreement with the Irving–Williams order of the metal ions. Ternary complexes of amino acids are formed by a simultaneous mechanism. The stabilities of ternary complexes are quantitatively compared with their corresponding binary complexes. The concentration distribution diagrams of the complexes were evaluated.

3-Aryl-2-(thiazol-2-yl)acrylonitriles assembled with aryl/hetaryl rings: Design of the optical properties and application prospects

New fluorescent thiazoles were designed and synthesized based on a 3-aryl-2-(thiazol-2-yl)acrylonitrile core. Three synthetic approaches were developed to introduce specific combinations of substituents at the 2-, 4- and 5-thiazole positions. The obtained thiazolyl-2-acrylonitriles exhibited a wide range of fluorescent colours (from green to red), long wavelength maxima and intensity depending on the combination of the substituents located at rings A, B and C. The expanded photophysical investigation established the best substituent combinations to increase their emission. Absorption and emission were studied in solvents with different polarities, as well as in DMSO-water and dioxane-water mixtures. The thiazoles showed multifunctional properties and exhibited good emission in the solid phase and in suspension (aggregation induced enhancement emission/AIEE effect). Photophysical investigations revealed a large Stokes shift, significant positive solvatochromism, and the tunability of the colour and intensity. Sharp strengthening of the emission intensity of the thiazoles was observed upon stimulation with some acid (H2SO4 and BF3·OEt2) in solvents and in the solid phase (HCl). State-of-the-art quantum mechanical calculations were performed to interpret the experimental findings. Biological experiments revealed the good penetration of the thiazoles into living cells and the accumulation both in lysosomes and, to a lesser extent, near membranes.

Synthesis of polymer nanoparticles based highly selective membranes by mini-emulsion polymerization for dehydration of 1,4 dioxane and recovery of ethanol from water by pervaporation

Inorganic metal oxide or metal nanoparticles and organic graphene or carbon nanotube significantly improves the separation characteristics of polymer membranes. The high cost and compatibility issue of these nanoparticles may be countered by using low cost polymer nanoparticles (PNPs). Accordingly, several chitosan (CS) coated polyacrylonitrile (PAN) nanoparticles (CSPAN) were prepared by mini emulsion polymerization of acrylonitrile in the presence of chitosan as co-stabilizer. These CSPAN polymer nanoparticles were incorporated into polyvinyl alcohol (PVA). The filled PVA membrane was then crosslinked with maleic acid. The unfilled and filled PVA membranes were used for sorption and pervaporation of 1, 4-dioxane. Similarly, unfilled and CSPAN filled general purpose polystyrene (GPPS) membranes were used for recovery of ethanol from water. The structure, size, crystallinity, stability and morphologies of the PNPs and PNPs filled PVA and GPPS membranes were characterized with FTIR, NMR, SEM, TEM, EDAX and mechanical properties. The filled PVA18/GPPS3 membranes prepared with 18/3 wt% of CSPANs(of total PVA/GPPS wt.) containing 4.2/2.4 wt% of CS in CSPAN in PVA18/GPPS3 showed the best results for flux and selectivity (165.2/269.6 kg/m2h and 40.1/29.6 for PVA18/GPPS3) for azeotropic dioxane-water mixture (81.6 wt% dioxane) and 10 wt% ethanol in water. PVA18 and GPPS3 filled membranes were further used at varied feed concentrations of the organics in water. Both sorption and permeation were analyzed in terms of solvent-solvent and solvent-membrane interaction and solvent coupling. The hydrophilic filled PVA18 membranes showed high flux and water selectivity while the organophilic filled GPPS3 membranes showed high flux and ethanol selectivity.

Cordination Compound of Dimethyltin(IV) with N,N,N’N’-Tetraethylethylenediamine: Speciation and Theoretical approach

The formation equilibria of the dimethyltin(IV) complexes with of N,N,N’,N’-tetraethylethylenediamine (Et4en) in solution were investigated. The stoichiometry and stability constants of the complexes formed in solution phase were determined at different temperatures (15 oC – 35 oC) and in solutions of dioxane-water mixtures of different compositions (15% - 62.5%). The accepted model is composed of the 110, 111, 11-1 and 11-2 species. The thermodynamic parameters H and S associated with the protonation of N,N,N`,N`-tetraethylethylendiamine (Et4en) and its complex formation with the dimethyltin(IV) species were determined. The complex formation reaction is exothermic. The equilibrium constant for the displacement of N,N,N’,N’-tetraethylethylenediamine coordinated to dimethyltin(IV) by some selected DNA constituents was calculated. The Keq values clearly indicate the ability of DNA to displace the coordinated Et4en from its dimethyltin(IV) complex. The nucleotides IMP and GMP have the highest values. The DFT/B3LYP method was used for geometric optimization of the ligand and the complex using the Gaussian 09 program. Also the vibrational frequencies of the ligands and complexes were computed for the optimized geometries. The results shows that there is no imaginary frequencies as found in the calculated vibrational frequencies. The binding energies of the dimethyltin(IV) complexes were calculated. All calculated binding energy values are negative.

Potentiometric pKa determination of biological active phenothiazine in different aqua-organic solvents

Potentiometric titrations of phenothiazines derivatives were performed in methanolwater, ethanol-water, acetonitrile-water and dioxane-water mixtures with varying contents of organic solvent. All titrations were performed in aqua-organic medium at constant ionic strength (0.15 mol⋅dm−3) and at different temperatures (25 to 45 °C). The pKa were determined at different aqua-organic proportions. Effect of temperature and dielectric constant on dissociation constant has been compared. The pKa values were then obtained by Yasuda‐Shedlovsky extrapolation.

Entrapment in micellar assemblies switches the excimer population of potential therapeutic luminophore azapodophyllotoxin.

Azapodophyllotoxin is a new class of anti-tumor agent with brilliant therapeutic activity and understanding its physicochemical nature in bio-mimetic microenvironments may provide substantial importance in context of its intercellular localization, efficacy as well as delivery. The present work epitomizes environment-sensitive fluorescence modulation of a prodigy, 4-(2-Hydroxyethyl)-10-phenyl-3,4,6,7,8,10- hexahydro-1H-cyclopenta[g]furo[3,4-b]quinoline-1-one (HPFQ) from the class of anti-cancer agent Azapodophyllotoxin, in differently charged model bio-mimetic micellar microenvironment of cationic CTAB, anionic SDS and neutral Triton X-100 using UV-visible absorption, steady state fluorescence, time-resolved fluorescence and fluorescence anisotropy studies. As a distinct phenomenon, anticancer HPFQ exhibits prolific fluorescence in solvents of varying polarity, originating from a mixed contribution of locally excited, charge transfer and excimer emission. A dramatic modulation in the photophysics of HPFQ has been observed in two types of surfactant consortiums: pre-micellar and post-micellar at physiological and anoxic pH. On photo-excitation, anti-cancer HPFQ exists in monomer-excimer equilibrium with varying ratios in different polarity regions. The marked enhancement in fluorescence intensity of HPFQ in post-micellar region of the surfactant under study probably arises due to regeneration of the monomer from its excimer. This reoccurrence reduces the possibility of Förster resonance energy transfer (FRET) from monomer to excimer, which essentially increases the desired emission intensity. Localization of HPFQ in micellar systems highly depends on polarity gradient inside the micelle, electrostatic, hydrophobic and intermolecular hydrogen bonding interactions. Further corroboration with the polarity sensitive experiments in dioxane-water mixture indicates towards spatial localization of the probe molecule in the stern layer of cationic CTAB, sheer surface of neutral TX100 and outer Gouy-Chapman layer in anionic SDS micelles. A molecular binary logic gate correlates the dominance of micellization over the polarity factor, which enhances the fluorescence response of HPFQ. The enhancement of the emissive potential of anti-cancer HPFQ in biomimetic environments by switching its excimer population may have an immense importance to achieve the status of a dual therapeutic and imaging agent altogether in progressive biomedical research.

Features of complex formation of a fibrous complexite with nickel ions in water–dioxane mixtures

The study deals with the complex-forming properties of a fibrous complexing agent (complexite) NAG with respect to nickel(II) ions in a mixed solvent water-1,4-dioxane. Spectral tests indicate that the absorption of nickel(II) ions by the NAG fibrous complexer occurs according to the mechanism of complexation. The factors affecting the complex formation of the NAG complexite with nickel(II) ions in water-1,4-dioxane mixtures are established, and the stability constants of hydroxamic and amidoxime groups are calculated depending on the pH values of the medium and the composition of the solvent. The influence of the solvation parameter on the composition and stability of the complexes under study with nickel(II) ions has been established. The solvation characteristics of the NAG complexite and complexes with nickel(II) ions depend on the nature of the mixed solvent in which the complexation reaction takes place. The solvation effects in the water-1,4-dioxane mixture with a molar fraction of dioxane of 0.00–0.17 level the stability of the resulting complexes. It is shown that the pH range of 6.2–3.8 mixed solvent creates the conditions for the formation of a wider composition and structure of the range of coordination units with different proportions of their content in the polymer. Apart from the hydroxamic, deprotonated amidoxime groups take part in the complexation. The preferred fixation of functional groups on the surface of NAG fibres leads to a high local concentration of the reaction centres and enhances the cooperativeness of the process, facilitating easy orientation of the groups during the formation of mixed-ligand coordination nodes. The stability constants of the deprotonated amidoxime groups of the the NAG complexite with nickel(II) ions are estimated. The study has proved dependence on the composition of the solvent

Proton/Metal–Ligand Stability Constants of Complexes of Sr(II), Cr(II), and Al(III) with N-Phthaloyl Aminoacid and Benzimidazole Derivatives in Dioxane–Water Mixture

Formation of complexes Sr(II), Cr(II), and Al(III) with ligands (1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)acetic acid (L1), 2-(1-(2-(4-nitrophenyl)-1H-benzo[d]imidazol-1-yl)-1-oxobutan-2-yl)-2,3-dihydroinden-1-one(L2) and 2-(2-(2-(4-chlorophenyl)-1H-benzo [d] imidazol-1-yl)-2-oxoethyl)isoindoline-1,3-dione (L3) investigated using pH metric technique in 70% dioxane-water mixture. Proton ligand formation number and metal-ligand formation number determined. Proton-ligand stability constants pK values and metal – ligand stability constants log k values evaluated using half integral method. It indicates that Sr(II), Cr(II), and Al(III) metal ions formed 1 : 1 and 1 : 2 complexes with the ligands L1, L2, and L3. These can be of interest for specialists in the field of coordination chemistry.

Stability Constants of Complexes of Cr(II) and Sr(II) with Quinazoline and Dihydropyridine in Dioxane–Water Mixture on Spectrophotometric Data

The interaction of Cr(II) and Sr(II) with a series of four novel N-heterocycles viz. 2-(1,3-dioxisoindoline-2-yl)-N-(4-oxo-2-phenylquinozolin3(4H)-yl), 1-(2-((4-oxo-2-phenylquinozolin-3(4H)-yl) carbomoyl), diethyl 1-(2-(1,3-dioxoisoindolin-2-yl)-3-methylbutanoyl)-2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate, diethyl 1-(2-(1,3-dioxoisoindolin-2-yl)butanoyl)-2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate studied by spectrophotometric technique at 0.01 M ionic strength and 28°C in 70% dioxane–water mixture. The data obtained used to estimate the stability constant of the complexes. Investigation of Cr(II) and Sr(II) complexes with these ligands shows 1 : 1 complex formation. The values of conditional stability constants of Sr(II) complexes are greater than the corresponding Cr(II) complexes. The results obtained of stability constants are in good agreement with the structure of ligand and reactivity pattern of metal ion. These can be of interest for specialists in the field of coordination chemistry.

Thermodynamic and kinetic studies on interaction of some transition metal ions with tryptophan

Amino acid of tryptophan (Trp) was chosen as a drug. A systematic approach was made to study its interaction with some transition metal ions, and qualitatively and quantitatively examine the thermodynamic and kinetic phenomena on this model drug. To accomplish these tasks, the stability constants of Trp complexes with Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Pb(II) at temperatures of 25, 30, 35, and 40 °C were determined potentiometrically, utilizing modified Bjerrum’s method. Potentiometric titrations were carried out in water, and water:dioxane mixture (50:50, v : v ). Our findings showed that the stability constants of the complexes increased as the dioxane content was raised or temperature was elevated. The negative values of Δ G ° are indication of spontaneity of the processes. Δ H ° values are positive, conveying the complex formation is an endothermic process and Δ S ° values are positive contributing more to spontaneity, causing reaction favoring and disordering. The variations of natural logarithm of the stability constants versus 1/T are linear leading to evaluation of the stability constant of the complexes at any temperature. Moreover, kinetic study gave rise to estimation of rate constant and activation energy for each complex formation process. It was concluded that the order of increasing stability of the complexes is: k f Co(II) -Trp » k f Zn(II)- Trp < k f Pb(II) -Trp < k f Ni(II) -Trp < k f Cu(II) -Trp < k f Fe (III) - Trp . Furthermore the activation energy values for the aforementioned complexes in water-dioxane mixture obeyed the following trend E a Zn(II)-trp < E a Fe(III)-Trp < E a Ni(II)-trp < E a Co(II)-trp < E a Cu(II)-trp < E a Pb(II)-trp .

Amorphous Solid Dispersion of Epigallocatechin Gallate for Enhanced Physical Stability and Controlled Release.

Epigallocatechin gallate (EGCG) has been recognized as the most prominent green tea extract due to its healthy influences. The high instability and low bioavailability, however, strongly limit its utilization in food and drug industries. This work, for the first time, develops amorphous solid dispersion of EGCG to enhance its bioavailability and physical stability. Four commonly used polymeric excipients are found to be compatible with EGCG in water-dioxane mixtures via a stepwise mixing method aided by vigorous mechanical interference. The dispersions are successfully generated by lyophilization. The physical stability of the dispersions is significantly improved compared to pure amorphous EGCG in stress condition (elevated temperature and relative humidity) and simulated gastrointestinal tract environment. From the drug release tests, one of the dispersions, EGCG-Soluplus® 50:50 (w/w) shows a dissolution profile that only 50% EGCG is released in the first 20 min, and the remains are slowly released in 24 h. This sustained release profile may open up new possibilities to increase EGCG bioavailability via extending its elimination time in plasma.

Simple computing of the viscosity of water-dioxane mixtures, according to a fluctuating SPC/E-Ih interstitial model.

In this contribution, we propose a new simple and fast computing approach to model liquid water and water-1,4 dioxane mixture, which is intermediate between molecular dynamics calculation and lattice fluid H-bonding theory in which water molecules are arranged according to a fluctuating hexagonal Ih network. It generalizes the interstitial mixture models of Samoilov and Pauling by increasing the number of spatial configurations into the space of phases due to the addition of rotations and vibrations of the molecules around their equilibrium positions. The potential energy landscape is determined by the generalization of the Madelung's approach to the molecular water network using simple point charge model (SPC/E partial charges). This approach allows useful predictions as the possibility of incorporation of a molecule of dioxane in the water Ih -network or how some cooperative dynamic jumps (site - hole) of water molecules, contribute to lower Eyring's activation energies and thus to facilitate the viscous flow. © 2017 Wiley Periodicals, Inc.

New Insights into the Effects of Tetrahydrofuran and Dioxane on the Selectivity of Ternary Eluent Compositions in RP-HPLC Systems

The present paper discusses the tendencies in the retention changes of a diverse set of organic model compounds on HPLC C18 stationary phases in aqueous ternary eluent mixtures containing tetrahydrofuran or 1,4-dioxane, and one short chain aliphatic alcohol (ethanol, n-propanol or isopropanol). The set of compounds consisted of steroid and non-steroid molecules with different hydrogen bond donor and/or acceptor abilities. Every eluent mixture contained 75 V/V% water and 25 V/V% organic solvent(s). The composition of the mixture was changed in 5 V/V% steps, starting with the binary alcohol–water mixtures and finishing with the binary ether–water mixtures. The results show clearly the dependency of retention times on the eluent composition, the size of the molecules, and the occurence of the hydrogen bond donor/acceptor groups. The isopropanol–tetrahydrofurane–water mixtures resulted in selective changes in the retention times of the compounds with acidic groups or with other non-acidic OH or NH protons in the neighborhood of electron-withdrawing groups. Every compound has shown elevated retention times in the isopropanol–dioxane–water, n-propanol–tetrahydrofuran–water, or n-propanol–dioxane–water mixtures. Clear trends could not be observed in the eluents with ethanol. The probable reason for the retention enhancement is the adsorption of the organic components of the mobile phase on the surface of the stationary phase. The different effects of the alcohols may originate from the interaction of their varying aliphatic alkyl chains with the C18 chains. This phenomenon may result in different availability of the C18 chains for dioxane, tetrahydrofuran and the model compounds.

Thermodynamic Studies on the Interaction between Phenylalanine with Some Divalent Metal Ions in Water and Water-Dioxane Mixtures

Thermodynamic Studies on the Interaction between Phenylalanine with Some Divalent Metal Ions in Water and Water-Dioxane Mixtures