Aggregation behavior of polyoxyethylene (20) sorbitan monolaurate (tween 20) in imidazolium based ionic liquids

Surface tension measurements were carried out for the solutions of polyoxyethylene (20) sorbitan monolaurate (Tween 20) in 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF 4) and hexafluorophosphate (bmimPF 6) at various temperatures. Two transition points were found in the surface tension-concentration curves at each temperature. The freeze-fracture transmission electron microscopy revealed that two kinds of particles with different sizes are formed at the concentrations of each transition point. Thus, the surfactant concentrations of the two transition points are regarded as critical aggregation concentrations, CAC 1 and CAC 2. From the CAC values and their temperature dependence, we estimated the thermodynamic parameters of the aggregate formation, Delta G agg (0), Delta H agg (0), and Delta S agg (0). The thermodynamic parameters related to CAC 1 are almost independent of temperature. On the other hand, as for the aggregate formation at CAC 2, a positiveDelta S agg (0) contributes to a negative Delta G agg (0) at low temperature, while a negative Delta H agg (0) contributes to a negative Delta G agg (0) at high temperature. The behavior of the thermodynamic parameters as a function of temperature, combined with the variation of (1)H NMR chemical shifts of the bmim (+) protons as a function of the surfactant concentration, demonstrated that the aggregates formed at CAC 1 are nanodroplets of Tween 20 segregated from the solution phase, while those formed at CAC 2 are similar to the usual surfactant micelles formed in aqueous solution.     

Effect of ZnO nanoparticles doping on structural,dielectric and interfacial behavior of polyoxyethylene (20) sorbitan/ethylene glycol lyotropic phases

ABSTRACT

We are reporting on the interaction of zinc oxide (ZnO) nanoparticles (NPs) with the lyotropic phase comprises of Polyoxyethylene (20) sorbitan monolaurate and protic solvent ethylene glycol. The concentration of the NPs has been varying from 0.05 to 0.5 wt%. Multiwall lamellar and inverse phases have been observed at lower and higher concentration of ZnO NPs doping. Interestingly, the organization of ZnO NPs on the periphery and inside the periphery of ring-like structures has been observed at lower and higher concentration of the dopant, respectively. Such organization of the NPs can be explained considering interfacial interaction amid host and dopant and may also attribute to the adsorption mechanisms of surfactant. Effects of NPs doping on the dielectric dynamics has also been examined. About 32.6% decrease in the dielectric permittivity has been noticed at higher NPs doping. Such decrement in permittivity could be a result of the screening of the ZnO NPs dipole moment by the adsorption of surfactant molecules on their surface. Relaxation and optical parameters of the non-doped and doped mixtures have also been discussed.     

Properties of polyethylene glycol (23) lauryl ether with cetyltrimethylammonium bromide in mixed aqueous solutions studied by self-diffusion coefficient NMR

NMR self-diffusion coefficient measurements have been used to study the properties of polyethylene glycol (23) lauryl ether (Brij-35) with cetyltrimethylammonium bromide (CTAB) in the mixed aqueous solutions with different mole fractions of CTAB. By fitting the self-diffusion coefficients to the two-state exchange model, the critical micelle concentrations of the two solutes in the mixed solutions (cmc*1 and cmc*2) were obtained. The critical mixed micelle concentrations (cmc*) were then evaluated by the sum of cmc*1 and cmc*2, which are in good agreement with the results measured by the surface tension method. The cmc* values are lower than those of the ideal case of mixing, which indicates that the behavior of the CTAB/Brij-35 system is nonideal. Moderate interactions between CTAB and Brij-35 in their mixtures can be deduced from the interaction parameters (betaM) based on the cmc* obtained by the NMR self-diffusion method. The compositions (x1) of the mixed micelles at different total surfactant concentrations were also evaluated. By using these results, a possible mechanism of mixed micellar formation and a picture of the formation of nonsimultaneous CTAB/Brij-35 binary mixed micelle were proposed. In contrast to the case of CTAB/TX-100 system, Brij-35 molecules have a tendency to form micelles first at any mole fraction of CTAB. The mixed micellar self-diffusion coefficients (Dm) increase slightly at lower CTAB molar ratios, and then speed up with increasing CTAB mole fraction.     

Micellization and mixed micellization of cationic gemini (dimeric) surfactants and cationic conventional (monomeric) surfactants: Conductometric,dye solubilization,and surface tension studies

In the present study, we have investigated the self-association, mixed micellization, and thermodynamic studies of a cationic gemini (dimeric) surfactant, hexanediyl-1,6-bis(dimethylcetylammonium bromide (16-6-16)) and a cationic conventional (monomeric) surfactant, cetyltrimethylammonium bromide (CTAB). The critical micelle concentration (CMC) of pure (16-6-16 and CTAB) and mixed (16-6-16+CTAB) surfactants was measured by electrical conductivity, dye solubilization, and surface tension measurements. The surface properties (viz., C₂₀ (the surfactant concentration required to reduce the surface tension by 20 mN/m), Π_CMC (the surface pressure at the CMC), Γ_max (maximum surface excess concentration at the air/water interface), A_min (the minimum area per surfactant molecule at the air/water interface), etc.) of micellar (16-6-16 or CTAB) and mixed micellar (16-6-16+CTAB) surfactant systems were evaluated. The thermodynamic parameters of the micellar (16-6-16 and CTAB) and mixed micellar (16-6-16+CTAB) surfactant systems were also evaluated.     

Spectrophotometric study on the quaternary complex of titanium (IV) with secondary ligands, 2,6,7-trihydroxylphenyl-fluorone derivatives and cetyltrimethylammonium bromide

The new color reactions of titanium (IV) with six 2,6,7-trihydroxyl-9-phenylsubstituted-3-fluorone derivatives (THPF) have been studied in the presence of nitrilotriacetic acid (NTA) and cetyltrimethylammonium bromide (CTMAB). The effects of secondary ligands such as NTA, ascorbic acid, hydroxylamine and mandelic acid on the ternary complex of titanium (IV) have been reported. It was found that the system of titanium (IV)-2,6,7-trihydroxyl-9-(2,4-dichlorophenyl)-3-fluorone (DCPF)-NTA-CTMAB quaternary complex is the most sensitive in these systems studied. The apparent molar absorptivity of the complex at 576 nm is 1.9 × 10⁵ 1·mol^–1·cm^–1. The stoichiometric ratio of the Ti (IV)-NTA-DCPF-CTMAB complex is estimated to be 1 1 3 3. The proposed method proves to be satisfactory for the direct determination of titanium in alloy steels, silicate minerals and aluminium alloys. The method is highly sensitive and selective.     

Platinum(II) complexes with thiourea derivatives containing oxygen,sulfur or selenium in a heterocyclic ring: computational studies and cytotoxic properties

Platinum(II) complexes with 1-(2-oxolanylmethyl)-2-thiourea, 1-(2-thiolanylmethyl)-2-thiourea and 1-(2-selenolanylmethyl)-2-thiourea were synthesized in order to compare their cytotoxic activities with those of the free thioureas. Their equilibrium geometries and bonding energies in the gas phase and in solution were calculated using density functional theory at the MPW1PW/LanL2DZ level. The IR spectra of the complexes and their free ligands were compared. Stability of the complexes in 0.9% saline aqueous solution was tested by means of HPLC. The cytotoxic activities of the species against five human cell lines were evaluated, as well as the antimicrobial activities against twelve bacterial strains.     

Stability constants of At(I)-complexes with thiourea,iodide and mixed ligands in ethanol and water

The ion mobilities of [²¹¹At] At(I) in dependence on thiourea (tu) concentration, iodide concentration and a mixture of both ligands were measured by the electromigration method in free electrolytes. An equilibrium model was developed for the characterization of electromigration curves which permitted the calculation of stability constants and ion mobilities of the complexes [AtI], [AtI₂]^–, [Attu]⁺, [Attu₂]⁺ and [AtItu] existing in these solutions. Ethanol and water served as solvents. The temperature was 298 K and the ionic strength was about 0.05 mol/dm³.     

Synergistic effects in mixed gas chromatographic stationary phases containing hepatkis(2.3.6-tri-O-pentyl)-β-cyclodextrin and AgNO3 or TINO3 in the separation of xylene isomers

Summary The gas chromatographic separation of xylene isomers using special mixed stationary phases consisting of heptakis(2.3.6-tri-O-pentyl)-β-CD-AgNO₃, heptakis (2.3.6-tri-O-pentyl)-β-CD-TINO₃ or bentone-34-AgNO₃ is investigated. The first two have positive synergistic effects for the separation of m, and p-xylene isomers, but negative synergistic effects for the m, and oisomers. The separation effects depend on temperature, mixing ratio and how mixing is accomplished.     

Modulating the emission intensity of poly-(9,9-bis(6'-N,N,N-trimethylammonium)hexyl)-fluorene phenylene) bromide through interaction with sodium alkylsulfonate surfactants

The interaction between the cationic HTMA-PFP (Poly-(9,9-bis(6'-N,N,N-trimethylammonium)hexyl-fluorene phenylene) bromide) and oppositely charged sodium n-alkyl sulfonate surfactants of different chain lengths has been studied in DMSO-water solutions (4% v/v) by UV-visible absorption, fluorescence spectroscopy, fluorescence lifetimes, electrical conductivity, and (1)H NMR spectroscopy. Polymer-surfactant interactions lead to complex spectroscopic behaviors which depends on surfactant concentration. At low surfactant concentrations, the observed strong static fluorescence quenching of fluorescence seems to be associated with formation of aggregates between polymer chains neutralized through interaction with surfactants. This is supported by conductivity and by analysis of absorption spectra deconvoluted at each surfactant concentration using an adapted iterative method. In contrast, above the surfactant critical micelle concentration, there is a strong fluorescence enhancement, leading in some cases to higher intensities than in the absence of surfactants. This is attributed to the transformation of the initially formed aggregates into some new aggregate species involving surfactant and polymer. These changes in HTMA-PFP fluorescence as a function of n-alkyl sulfonate concentration are important for the general understanding of polymer-surfactant interactions, and the aggregates formed may be important as novel systems for applications of these conjugated polyelectrolytes.     

Synthesis, characterization and electrochemical studies of mixed ligand complexes of ruthenium(ii) with DNA

Two mixed ligand complexes of ruthenium(ii) [Ru(bzimpy)(bpy)(OH(2))](2+) (1) and [Ru(bzimpy)(phen)(OH(2))](2+) (2) have been synthesized and characterized by FAB mass, (1)H NMR, cyclic voltammetry and spectroelectrochemical measurements. Controlled potential electrolysis of these complexes results in the conversion of ruthenium(ii) to ruthenium(iii) at 0.6 V and ruthenium(iii) to ruthenium(iv) at 0.8 V vs. SCE. The binding constant of these complexes with DNA has been determined electrochemically and found to be (3.58 +/- 0.25) x 10(4) and (2.87+/- 0.2) x 10(4) M(-1). Viscosity measurements suggest that these complexes bind with DNA through intercalation. Such intercalative binding to DNA has been found to induce chirality to the two complexes. Electrochemically generated ruthenium(iv) species of these complexes have been found to bring about oxidative cleavage in DNA.     

Structural studies and biological activity evaluation of Pd(II), Pt(II) and Ru(II) complexes containing N‐phenyl,N`‐(3‐triazolyl)thiourea

[MCl(H₂L)(OH₂)]·1.5H₂O (M = Pd(II) ( 1 ) and Pt(II) ( 2 )) and [Ru(H₂L)₂(OH₂)₂]·3H₂O ( 3 ) (H₃L: N‐phenyl, N`‐(3‐triazolyl)thiourea) were synthesized, characterized and tested for their antibacterial activities against Staphylococcus aureus and Escherichia coli bacteria. The thiourea derivative is coordinated to Mⁿ⁺ ions as a mono‐negatively N,S‐bidentate ligand via the enolization of C = S group and triazole N center. The density functional theory calculations reveal that presence of a water molecule in a trans position to triazole ring increased the stability of d⁸ metal ions complexes via the formation of strong Cl…NH intramolecular H‐bond. The cis‐Ru(II)‐isomer with two isoenergetically H₂L^? molecules are more stable than the trans‐analog. Coordination of H₃L to Ru(II) ion did not alter the toxicity of the free ligand, while the interaction with the d⁸ metal ions gave rise to inactive compounds.     

Synthesis, spectral characterization, catalytic and antibacterial studies of new Ru(III) Schiff base complexes containing chloride/bromide and triphenylphosphine/arsine as co-ligands

A new Ru(III) Schiff base complexes of the type [RuX(EPh₃)L] (X = Cl/Br; E = P/As; L = dianion of the Schiff bases were derived by the condensation of 1,4-diformylbenzene with o-aminobenzoic acid/o-aminophenol/o-aminothiophenol in the 1:2 stoichiometric ratio) have been synthesized from the reactions of [RuX₃(EPh₃)₃] with appropriate Schiff base ligands in benzene in the 2:1 stoichiometric ratio. The new complexes have been characterized by analytical, spectral (IR, electronic, ¹H, ¹³C NMR and ESR), magnetic moment and electrochemical studies. An octahedral structure has been tentatively proposed for all these new complexes. All the new complexes have been found to be better catalyst for the oxidation of alcohols using molecular oxygen as co-oxidant at ambient temperature and aryl–aryl coupling reactions. These complexes were also subjected to antibacterial activity studies against Escherichia coli, Aeromonas hydrophilla and Salmonella typhi.     

Determination of microquantities of mercury(II) with preliminary thin-layer chromatographic separation from mercury(I), lead(II), nickel(II), and copper(II) on acid-treated silica gel layers: Recovery of mercury(II) from river waters and industrial wastewaters

Thin-layer chromatography in combination with spectrophotometry has been applied for the separation and estimation of Hg(II) using silica gel layers impregnated with 2% oxalic acid as stationary phase with an ethyl acetate:acetone:formic acid:water (8:7:4:1) solvent system. Separation of Hg(II) from Hg(I) and of Th⁴⁺ from UO₂²⁺ is not affected by the presence of common anions in the sample solution. Hg(II) has been successfully separated from Ni(II), Cu(II), and Pb(II) over a wide range of pH (0.5–7.0) of sample solution. An attempt has been made to recover Hg(II) from rivers and industrial wastewaters.     

High-performance liquid chromatographic system for the separation of dynorphin A (1-17) fragments and its application in enzymolysis studies with rat nerve terminal membranes

A high-performance liquid chromatographic method capable of separating a large number of C- and N-terminal degradation fragments of dynorphin A (1-17) (dyn 1-17) in 1 h has been developed. The system has been applied to study the metabolism profiles of various dyn 1-17-derived peptides following in vitro incubation with rat striatum and spinal cord nerve terminal membranes. In addition to the removal of the N-terminal amino acid Tyr, major sites of cleavage between the following amino acids could be established: Leu5-Arg6 in dyn 1-7 (formation of dyn 1-5); Arg6-Arg7 and Leu5-Arg6 in dyn 1-8 (formation of dyn 1-6 and dyn 1-5, respectively); Arg7-Ile8 in dyn 1-9 (formation of dyn 1-7) and Arg9-Pro10 in dyn 1-10 (formation of dyn 1-9). Studies with inhibitors of the enzymes involved show that dyn 1-5 is formed directly from dyn 1-8 via an endopeptidase insensitive to the angiotensin-converting enzyme inhibitor MK 422 acting on the scissile Leu5-Arg6 bond in dyn 1-8. The method circumvents the use of [3H]Tyr-labelled dynorphins, which have the inherent drawback that fragments lacking the N-terminal Tyr cannot be detected. Owing to the high resolution, also for the larger dynorphins dyn 1-14, dyn 1-15 and dyn 1-16, the chromatographic system should prove especially useful in the elucidation of the enzymolysis pattern of dyn 1-17. Furthermore, the method offers a way to evaluate simultaneously the selectivity of new enzyme inhibitors for several cleavage sites in the same assay.     

High-performance liquid chromatographic enantioseparation of (R,S)-fluoxetine using Marfey's reagent and (S)-N-(4-nitrophenoxycarbonyl) phenylalanine methoxyethyl ester as chiral derivatizing reagents along with direct thin-layer chromatographic resolution and isolation of enantiomers using L-tartaric acid as mobile phase additive

Chiral assay of enantiomers of fluoxetine was achieved in pharmaceutical formulations using direct and indirect methods. L-tartaric acid was used as a mobile phase additive in thin-layer chromatography; the enantiomers were separated and isolated and were used to determine the elution order in HPLC. (R,S)-flouxetine was derivatized with (S)-N-(4-nitrophenoxycarbonyl)phenylalanine methoxyethyl ester [(S)-NIFE], Marfey's reagent and 1-fluoro-2,4-dinitrophenyl-L-methionine amide (FDNP-L-Met-NH?. The diastereomers were separated using RP-HPLC. The effect of flow rate and TFA concentration on resolution was studied. The diastereomers obtained by derivatization with FDNP-L-Met-NH? were also separated by RP-TLC.     

Potentiometric studies on mixed complexes of Ni(II) with taurine,dl-methionine and dl-ethionine in aqueous solution

The formation and stability of the simple and mixed complexes of Ni(II) with taurine, dl-methionine and dl-ethionine have been investigated by means of potentiometric measurement of hydrogen ion concentration at 25°C and in a 0.1 M NaClO₄ medium. Mixed complexes, [Ni(Met₂)Tau] and [Ni(Eth₂)Tau], have been considered, where Met = dl-methionine, Eth = dl-ethionine and Tau = taurine.     

Potentiometric studies on mixed complexes of Ni(II) with taurine, -methionine and -ethionine in aqueous solution

The formation and stability of the simple and mixed complexes of Ni(II) with taurine, -methionine and -ethionine have been investigated by means of potentiometric measurement of hydrogen ion concentration at 25°C and in a 0.1 M NaClO₄ medium. Mixed complexes, [Ni(Met₂)Tau] and [Ni(Eth₂)Tau], have been considered, where Met = -methionine, Eth = -ethionine and Tau = taurine.     

The synthesis and photophysical studies of cyclometalated Pt(II) complexes with C,N,N-ligands containing imidazolyl donors

Two new C,N,N-type ligands (HL(2) and HL(3)), containing a C(phenyl), a N(pyridyl), and a N(imidazolyl) donor, and their cycloplatinated complexes, [Pt(L(2))Cl] (1), [Pt(L(3))Cl] (2), [Pt(L(2))(PPh(3))](+) (3) and [Pt(L(3))(PPh(3))](+) (4), have been successfully synthesized and characterized. Spectroscopic and (3)MLCT luminescent properties of these Pt(II) cyclometalated complexes were found to be pH dependent. This was attributed to the protonation/deprotonation of the acidic 1-imidazolyl-NH moieties on the ligands. All the cycloplatinated complexes (both protonated and deprotonated forms) possessed two-photon excitability with two-photon absorption cross-sections ranging from 6.0 to 30.0 GM (protonated forms) and from 16.2 to 24.9 GM (deprotonated forms).