Fluorescence Spectra of Model Compounds for Light-emitting Alternating Copolymers in Heterogeneous Environments

Cao1 et al. reported that certain surfactant-like additives dissolved or dispersed in the EL polymer significantly improved electron injection from relatively high work function metals such as Al. The open question is what effect of surfactant on the photophysical properties is. Up to now, no report concerning this aspect has been documented. In our previous work2, a type of novel high-efficiency light-emitting nitrogen-containing poly (phenylene vinylene) (PPV)-related copolymers was synthe…     

Intramolecular charge transfer at reverse micelle-water pool interface: p-N,N-dimethylaminobenzoic acid in AOT/cyclohexane/water reverse micelle

Photoinduced intramolecular charge transfer (ICT) of p-N,N-dimethylaminobenzoic acid (DMABOA) in AOT/cyclohexane/H2O reverse micelle was investigated and compared with that in CTAB/1-heptanol/H2O reverse micelle. It is proposed that the DMABOA molecule exists at the AOT reverse micelle water pool interface with its carboxylic group heading toward the water pool while the dimethylaminophenyl moiety buried in the micellar phase. Dual fluorescence of DMABOA that is indicative of the ICT reaction in the excited state was observed over the investigated water pool size, W of 3-17, in the AOT reverse micelle. The ICT emission of DMABOA in the AOT reverse micelle-water pool interface was found to be much weaker than that in the CTAB reverse micelle-water pool interface, and was attributed to the parallel direction of the electric field at the AOT reverse micelle-water pool interface to the charge transfer.     

Fluorescence behavior of intramolecular charge transfer probe in anionic, cationic, and nonionic micelles

The intramolecular charge transfer (ICT) property of trans-ethyl p-(dimethylamino) cinnamate is used to probe the anionic, cationic, and nonionic micelles by steady-state and picosecond time-resolved fluorescence spectroscopy. The ICT fluorescence band intensity was found to increase with concomitant blue shift with addition of surfactants. All the experimental results suggest that the probe molecule resides in the micelle-water interface rather than going into the core. However, the penetration is more toward the micellar core in nonionic surfactants when compared with ionic micelles. The decrease in nonradiative decay constants in micellar environments indicate restricted motion of the probe toward the formation of ICT state. Critical micelle concentrations were determined from the sharp change in fluorescence intensity and effective dielectric constants of the micelle-water interface were calculated from the correlation diagram of 0,0 transition energy with polarity of the medium.     

Studies of bio-mimetic medium of ionic and non-ionic micelles by a simple charge transfer fluorescence probe N,N-dimethylaminonapthyl-(acrylo)-nitrile

In this report we have studied micellization process of anionic, cationic and non-ionic surfactants using N,N-dimethylaminonapthyl-(acrylo)-nitrile (DMANAN) as an external fluorescence probe. Micropolarity, microviscosity, critical micellar concentration of these micelles based on steady state absorption and fluorescence and time resolved emission spectroscopy of the probe DMANAN show that the molecule resides in the micelle-water interface for ionic micelles and in the core for the non-ionic micelle. The effect of variation of pH of the micellar solution as well as fluorescence quenching measurements of DMANAN provide further support for the location of the probe in the micelles.     

ESPT of 2-(2'-pyridyl)benzimidazole at the Micelle-Water interface: selective enhancement and slow dynamics with sodium dodecyl sulfate

The effect of micellar environment on the excited state proton transfer (ESPT) of 2-(2'-pyridyl)benzimidazole (2PBI) has been investigated by steady state and time resolved fluorescence spectroscopy. The ESPT, which occurs to a rather small extent at pH 7, is found to be enhanced remarkably at the interface of sodium dodecyl sulfate (SDS) micelles and water. Such an enhancement is not observed for the cationic cetyl trimethyl ammonium bromide (CTAB) or neutral Triton X-100 micelles. This selective enhancement is explained in the light of a modification of pK(a) and a more acidic local pH in the micelle-water interface. A rise time of about 890 ps is observed in the region of tautomer emission. The origin of this rise time is explored, considering three factors, namely, diffusion controlled protonation of the normal form of 2PBI, slow and possibly incomplete solvation of the transition state, leading to a slowing down of the proton transfer process and a similar slow dynamics of the tautomeric excited state.     

MMA在胶束水溶液中的光敏聚合

应用动力学方法研究了二苯甲酮/三乙胺引发MMA在胶束水溶液中的光敏聚合反应,结果表明表面活性剂的胶束对聚合反应具有催化作用,以离子型胶束的效果显著,可使反应的量子收率提高4—5倍。聚合速度和产物分子量随胶速浓度而增加,用紫外光谱和~1H—NMR测定了BP/TEA/MMA在离子型胶束中增溶位置,结果表明反应发生在胶束-水界面层。由于增溶于离子胶束中的单体分子具有一定取向性,提高了PMMA的立构有序性。     

Dioxouranium(VI)--carboxylate complexes. Interaction with dicarboxylic acids in aqueous solution: speciation and structure

In this paper we report the results of an investigation performed by potentiometric (H+-glass electrode) and visible spectrophotometric measurements on the interaction of UO2(2+) ion towards some carboxylic ligands (acetate, malonate, succinate, azelate). The measurements were carried out at T= 25 degrees C in different ionic media (KNO3 and NaCl) at different ionic strengths (0.1 < or = I/mol L(-1) < or = 1.0, NaCl; I/mol L(-1) = 0.1, KNO3). The dependence on ionic strength of formation constants was taken into account by using both a simple Debye-Hückel type equation and the SIT (Specific ion Interaction Theory) approach. Different speciation models (depending on concentration of reagents, ionic strength, pH-range) both for different carboxylates and different ionic media have been obtained. Linear combinations between formation constants, stoichiometric coefficients and length of alkyl chain of dicarboxylates have been observed and predicted formation constants at I= 0 mol L(-1) are reported for the interaction of UO2(2+) with HOOC-(CH2)n-COOH with 1 < or = n < or = 7. Finally, a visible absorption spectrum for each complex reaching a significant percentage of formation in solution (KNO3 medium) has been calculated to characterise the compounds found by pH-metric refinement.     

Rheological Behavior of Viscoelastic Wormlike Micelles in CTAB/SSS/H2O Systems

The effect of the addition of sodium 4-styrenesulfonate (SSS) and KNO3 as well as temperature and shear rate on the structural transition of aqueous micellar solutions of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) was studied by viscosity. The effect of hydrocarbons on viscoelastic CTAB solutions was also examined. Possible mechanism for formation of CTAB wormlike micelles in the presence of sodium 4-styrenesulfonate (SSS) and KNO3 was discussed. The rapid increase in the apparent viscosity of CTAB solutions on the addition of SSS and KNO3 was due to the transition in micellar shape from spheres to wormlike ones. The rheological properties of CTAB solutions fit Maxwell model at low shear frequency. AFM image indicated a structure of transient network of CTAB/SSS/KNO3/H2O solution.     

硝酸钾电解质溶液水化结构的分子动力学模拟

Molecular dynamics simulations were carried out to study the structure of ion clusters and hydration properties of KNO3 solution. The water molecule was treated as a simple-point-charge (SPC) model, and a four-site model for the nitrate ion was adopted. Both the Coulomb and Lennard-Jones interactions between all the charged sites were considered, and the long-range Coulomb electrostatic interaction was treated using Ewald summation techniques. The configuration of ionic pairs, the radial distribution function of the solution, and the effect of solution concentration on ionic hydration were studied in detail. It was found that there are ionic association phenomena in KNO3 solution and that the dimeric, triplet, solvent-separated ion pairs, and other complex clusters can be observed at high ionic concentration condition. As the concentration of solution decreases, the ionic hydration number increases, 5-7 for cation K+ and 3.5-4.7 for anion NO3-, which is in good agreement with former Monte Carlo and time-of-flight neutron diffraction results.     

Metal chelates of phosphonate-containing ligands-IV (Stability of some 1,6-hexamethylenediamine-N,N,N',N'-tetra(methylenephosphonic) acid metal chelates)

The stability constants of the complexes formed between the anion of 1,6-hexamethylenediamine-N,N,N',N'-tetra(methylenephosphonic) acid and some transition and non-transition metal ions have been measured potentiometrically at a temperature of 25 degrees and an ionic strength of 0.1M (KNO(3)). The acid dissociation constants of the ligand and stability constants of the protonated complexes are also reported. Comparisons are made with the acid dissociation constants of the analogous compounds EDTA, ENTMP and HDTA, and possible structural formulae are given.     

Interactions in binary mixed systems involving a sugar-based surfactant and different n-alkyltrimethylammonium bromides

In this paper, mixtures of sugar-based decanoyl-N-methylglucamide with three different n-alkyltrimethylammonium bromides (n=12 (DTAB), 14 (TTAB), and 16 (CTAB)) have been studied using conductance and fluorescence spectroscopic techniques. The critical micelle concentration values of pure and mixed systems were determined by both the conductance and the pyrene 1:3 ratio methods. The experimental results were interpreted using thermodynamic mixing approaches based on the pseudophase separation model. These analyses allowed us to determine the interaction parameters and the composition of the mixed micelles through the whole composition range. Since all the ionic surfactants used in this study have the same headgroup, the differences observed between the three mixed systems were attributed to the lengths of their hydrocarbon chains. It was established that, besides interactions of electrostatic character, additional short-range interactions must be considered. By using the static quenching method, the mean micellar aggregation numbers of mixed micelles were obtained. In the cases of the mixed systems with DTAB and TTAB it was observed that the aggregation number is initially reduced with the participation of the ionic component, remaining almost constant and close to the aggregation number of the pure ionic micelle. However, in the systems involving CTAB it is observed that the size of micelles initially increases and then decreases slightly for mixtures with a high content of the ionic component. The hydrophobic index pyrene 1:3 ratio was used to examine possible changes in the micellar micropolarity; however, no definitive conclusions could be derived from these experiments. In order to study the evolution of the local viscosity of the mixed micelles upon addition of the ionic surfactant, fluorescence polarization measurements were carried out with two different probes, fluorescein and coumarin 6. It was found that the participation of the ionic component in the mixed micelle induces the formation of less ordered structure than that of pure nonionic micelles. An attempt was made to correlate these effects with the interaction parameters obtained from the theoretical mixing model and, consequently, with the alkyl chain length of the ionic components.     

Optical and photophysical properties of indolocarbazole derivatives

We present a study of the optical and photophysical properties of five ladder indolo[3,2-b]carbazoles, namely, M1, M2, M3, M4, and M5. The ground-state optimized structures were obtained by B3LYP/6-31G* density functional theory (DFT) calculations, whereas the optimization (relaxation) of the first singlet excited electronic state (S1) was performed using the restricted configuration interaction (singles) (RCIS/6-31G*) approach. The excitation to the S1 state does not cause important changes in the geometrical parameters of the compounds, as corroborated by the small Stokes shifts. The excitation and emission energies have been obtained by employing the time-dependent density functional theory (TDDFT). For all the compounds, excitation to the S1 state is weakly allowed, whereas the S2 <-- S0 electronic transition of each oligomer possesses a much larger oscillator strength. The absorption and fluorescence spectra of the compounds have been recorded in chloroform. A reasonable agreement is obtained between TDDFT vertical transition energies and the (0,0) absorption and fluorescence bands. On one hand, the pattern of the aliphatic side chains does not affect the absorption and fluorescence maxima of the compounds. On the other hand, the replacement of aliphatic chains by phenyl or thiophene rings induces hypsochromic shifts in the absorption and fluorescence spectra. Finally, the fluorescence quantum yield and lifetime of the compounds in chloroform have been obtained. From these data, the radiative and nonradiative rate constants of the deactivation of the S1 state have been determined.     

The effect of ionic strength on the UV-vis spectrum of congo red in aqueous solution

The major peak near 498 nm in the ultraviolet-visible spectrum of congo red in aqueous solution shifts toward the blue while the molar absorptivity of this peak decreases predictably with increasing ionic strength. The shift was observed for solutions in which ionic strength was varied from 0.0 to 1.8M using the uni-univalent ionic compounds, NaCl, NaClO(4), KNO(3) and KBr separately. A plot of the log of the absorbance at the peak versus ionic strength was linear as well as a plot of the log of the wavelength of the major peak (shifted from 498 nm) versus the ionic strength. The slopes of each of these plots were somewhat different depending on the ionic compound.     

Micropartioning and solubilization enhancement of 1,2-bis(bis(4-chlorophenyl) methyl)diselane in mixed micelles of binary and ternary cationic-nonionic surfactant mixtures

The aqueous solubilization of the organoselenium compound viz., 1,2-bis(bis(4-chlorophenyl)methyl)diselane [(ClC(6)H(4))(2)CHSe](2) has been investigated experimentally in micellar solutions of two cationic (hexadecyltrimethylammonium bromide, CTAB, hexadecyltrimethylammonium chloride, CTAC) and one nonionic (polyoxyethylene(20)mono-n-hexadecyl ether, Brij 58) surfactants possessing the same hydrocarbon "tail" length and in their single as well as equimolar binary and ternary mixed states. Solubilization capacity determined with spectrophotometry and tensiometry has been quantified in terms of molar solubilization ratio and micelle-water partition coefficient. FTIR, UV-vis, fluorescence and zeta potential measurements have been utilized to ascertain the interaction of organochalcogen compound with surfactants. Equimolar cationic-nonionic surfactant combinations show better solubilization capacity than pure cationics or nonionics, whereas equimolar cationic-cationic-nonionic ternary surfactant systems exhibit intermediate solubilization efficiency between their single and binary counterparts. Locus of solubilization of [(ClC(6)H(4))(2)CHSe](2) in different micellar solutions was probed by UV-visible spectroscopy. The investigation has presented precious information for the preference of mixed surfactants for solubilizing water-insoluble compounds. Indeed the solubilization aptitude of these surfactants is not merely related to molar capacity. The results furnish adequate support to justify comprehensive exploration of the surfactant properties that influence solubilization.     

Organization of amphiphiles: XII. Evidence in favor of formation of hydrophobic complexes in aqueous solution

The effects of nonionic surfactants OP-10 and OP-30 (polyoxyethylated octyl phenols with 10 and 30 oxyethylene groups, respectively) in surfactant mixtures with ionic surfactants hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) have been investigated by a conductometric method in conjunction with fluorescence, surface tension, zeta potential, and DLS measurements. The interactions are found to be antagonistic in nature for each of the systems; i.e., micellization of CTAB as well as SDS is hindered on addition of the nonionic surfactants. The antagonism is found to be more prominent in the presence of OP-10 compared to that of OP-30. Two types of mechanistic paths, path A operating below the critical micellar concentration and path B operating beyond the critical micellar concentration of nonionic surfactants, have been suggested. In path A, the retardation in micellization has been attributed to a decrease in monomeric concentration of the ionic surfactants from solution as a result of the formation of a hydrophobic complex between nonionic and ionic surfactants. In path B, the decrease in monomer concentration is due to the solubilization of the ionic surfactant in micelles of the nonionic surfactants in a 1:1 stoichiometric ratio. A theoretical treatment to the interaction in each ionic-nonionic pair yields a positive value of the interaction parameter supporting the concept of antagonism. The formation of the hydrophobic complex is supported by fluorescence and surface tension measurements. A schematic representation of the stabilization of these hydrophobic complexes has been suggested. The association of ionic surfactants by nonionic micelles is suggested by zeta potential and DLS studies.     

Biocatalysis in the development of functional polymer-ceramic nanocomposites

Fluorescent silica/polymer nanocomposites have been synthesized by condensing tetramethyl orthosilicate (TMOS) around fluorescent polymer strands of poly(2-naphthol). The polymer is biocatalytically synthesized via peroxidase catalyzed polymerization in micelles of the cationic surfactant, cetyltrimethylammonium bromide (CTAB). Silica condensation at the micelle-water interface results in encapsulation of the polymer. Fluorescence spectroscopy and fluorescent light microscopy provide critical evidence that the polymer luminescence properties are conferred to the composite material. The fabrication of polymer entrapped in ordered, mesoporous materials represents a viable step toward the development of functional polymer-ceramic nanocomposites.     

Coalescence of particle-laden drops with a planar oil-water interface

The coalescence mechanism of a particle-laden drop resting at an oil-water interface has been studied. Two mechanisms for drop coalescence are observed; (i) complete coalescence, in which the drop experiences total coalescence in one event, and (ii) partial coalescence, where a drop is observed to separate during coalescence, producing a smaller secondary drop that rebounds and comes to rest at the planar oil-water interface. For particle-laden drops of approximately 4mm in diameter, we show the critical condition for partial to complete coalescence to be dependent on the particle concentration, and the interparticle interaction energy. Colloidal silica spheres dispersed in 10(-4) M KNO(3) electrolyte solution are highly charged and remain dispersed in the drop. By increasing the solids concentration, we measure the transition from partial to complete coalescence at 20 wt.%. However, this critical condition can be reduced by increasing the interparticle interaction energy. In 1 M KNO(3) electrolyte solution, the particle surface charge is sufficiently screened such that particle clusters readily form in the water drop. With particle clustering, transition from partial to complete coalescence is measured at 8 wt.% solids.     

Late-model Ionic Clusters of KNO3 and Their Configurations

Late-model ionic clusters of KNO3 were formed under the conditions of electrospray ionization. A series of peaks of the ionic clusters could be observed in the electrospray ionization mass spectra（ESIMS）. The general formulae of the ionic clusters were deduced to be K^ ＋ （ KNO3 ） m and NO3^-（ KNO3 ）m. By referring to the crystal structure of KNOs , the possible configurations of these new typical ionic clusters were speculated based on the calculated data by means of the Gaussian-94^x computer program.     

The Hofmeister series effect in adsorption of cationic surfactants--theoretical description and experimental results

Interfacial properties of cationic surfactants show strong dependence on the type of surfactant counterion or on the type of anion of a salt added to the surfactant solution. In the paper, the models of ionic surfactant adsorption that can take into account ionic specific effects are reviewed. Model of ionic surfactant adsorption based on the assumption that the surfactant ions and counterions undergo nonequivalent adsorption within the Stern layer was selected to describe experimental surface tension isotherms of aqueous solutions of a number of cationic surfactants. The experimental isotherms for: n-alkyl trimethylammonium cationic surfactants, namely: C(16)TABr (CTABr or CTAB), C(16)TACl, C(16)TAHSO(4), C(10)TABr and C(12)TABr as well as decyl- and dodecylpyridinium salts with and without various electrolyte anions as Cl(-), Br(-), F(-), I(-), NO(3)(-), ClO(4)(-) and CH(3)COO(-) were described in terms of the model and a good agreement between the theory and experiment was obtained for a wide range of surfactants and added electrolyte concentrations. A very pronounced Hofmeister effect in dependence of surface tension of cationic surfactants on the type of anion was found. Analysing this dependence in terms of the proposed model of ionic surfactant adsorption, strong correlation between "anion surface activity" (the model parameter accounting for ion penetration into the Stern layer), and the ion polarizability was obtained. That suggests that the mechanism related to the dispersive interaction of polarized ion with electric field at interface is responsible for Hofmeister series effects in surface activity of cationic surfactants. The same mechanism was proposed recently to explain the dependence of surface tension increase with electrolyte concentration on anion and cation type.     

Antitumor activity of 4-amino and 8-methyl-4-(3diethylamino propylamino)pyrimido[4',5':4,5]thieno (2,3-b) quinolines

The interaction of 4-aminopyrimido [4',5':4,5] thieno (2,3-b) quinoline and 8-methyl-4-(3-diethylaminopropylamino) pyrimido [4',5':4,5] thieno (2,3-b) quinoline with DNA was studied by UV-Vis and fluorescence spectrophotometry as well as by hydrodynamic methods. On binding to DNA, the absorption spectra underwent bathochromic and hypochromic shifts and the fluorescence was quenched. These compounds are able to bind to DNA with an affinity of about 10(6) M(-1) for calf thymus DNA at ionic strength 0.01 M and their intercalating characteristic (lengthening of the DNA) depends upon the length of the chain. Binding to the GC-rich DNA of Micrococcus lysodeikticus was stronger than the binding to calf thymus DNA at ionic strength 0.01 M. The cytotoxicities of these compounds on leukemia HL-60, melanoma B16F10 and neuro 2a cells are quite similar and inhibition (IC50) is in the range of 0.992-3.968 microM. The anticancer efficacy against B16 melanoma, has provided evidence of major antitumor activity for 8-methyl-4-(3diethylaminopropylamino) pyrimido [4',5':4,5] thieno(2,3-b)quinoline. Single or multiple intraperitonial (i.p) doses of drug proved high level activity against the subcutaneous (s.c) grafted B16 melanoma, significantly increasing survival (p<0.001) and inhibiting tumor growth (T/C of 4%). This study offers a new intercalation functional group to DNA-targeted drug design.