Spectral characteristics of CdS quantum dots and their associates with dye molecules dispersed in gelatin

A sol–gel method for the production of open quantum dots of CdS measuring 2-5 nm and their associates with dye molecules [methylene blue and the pyridinium salt of 3,3′-di(γ-sulfopropyl)-9-ethyl-4,5,4′,5′-dibenzothiacarbocyaninebetaine] dispersed in gelatin is described. Their spectral characteristics are analyzed. Evidence is obtained for the formation of hybrid associates of CdS quantum dots with monomers of the first and J-aggregates of the second dye.     

Photoinduced electron transfer from the excited J-aggregate state of a thiacarbocyanine dye to TiO2 colloids

The photophysical properties of the J-aggregate of 3,3'-di(3-sulfopropyl)-4,5,4',5'-dibenzo-9-phenyl-thiacarbocyanine triethyl-ammonium salt in the absence and presence of TiO(2) colloids have been studied using UV-visible absorption spectroscopy, steady-state and time-resolved fluorescence spectroscopy, and ESR spectroscopy. The fluorescence emission of the J-aggregate decreases with increasing concentration of TiO(2) colloids. The average fluorescence lifetime of the J-aggregate in the presence of TiO(2) colloids is shorter than that in the absence of TiO(2) colloids. A strong photoinduced ESR signal has been observed during illumination by light with lambda=633 nm in the presence of TiO(2) and the ESR signal can be attributed to the J-aggregate radical cation. From the above results, it is concluded that photoinduced electron transfer from the excited singlet state of the J-aggregate to the conduction band of TiO(2) takes place and the electron transfer rate is about 1.5 x 10(8) s(-1).     

Regulation of aggregation and morphology of cyanine dyes on monolayers via gemini amphiphiles

The aggregation of dyes is of considerable importance in relating to their functions and applications. In this paper, we have investigated the regulation on the aggregation and morphology of two cyanine dyes, 3,3'-disulfopropyl-4,5,4',5'-dibenzo-9-methylthiacarbocyanine triethylammonium salt (MTC) and 3,3'-disulfopropyl-4,5,4',5'-dibenzo-9-phenylthiacarbocyanine triethylammonium salt (PTC), using a series of gemini amphiphiles (bis(2'-heptadecyl-3'-ethylimidazolium)-1,n-alkane dibromide, abbreviated as Gn, n=2, 4, 6, 8, 10). It has been found that both of the dyes could be adsorbed onto the monolayers of the gemini amphiphiles through the electrostatic and pi-pi interaction and stacked into H- or J-aggregate. The spacer of the gemini amphiphile showed good control over the aggregation of MTC: H-aggregate was favored when gemini amphiphiles with short spacer were applied, while J-aggregation was preferred in the case of longer spacer. Only J-aggregate was observed for PTC on gemini monolayer, regardless of the structure of the gemini amphiphiles. Interesting morphologies were observed for all the gemini/dye complex monolayers. Network structure and nanofibers were formed for the gemini/MTC films transferred below the plateau surface pressure and close to the collapse pressure, respectively. The ability of the complex monolayers to form nanofibers strongly depended on the component amphiphiles, G2>G4>G6, and no nanofibers were observed for G8/MTC and G10/MTC after the collapse. Only squared domains were observed for gemini/PTC monolayers. When both G2 and G10 were mixed, an individual control of the gemini amphiphiles over the aggregation of MTC in the complex monolayers was observed. The relationship among the spacer, dye structure, and aggregation was revealed.     

J-aggregation of anionic ethyl meso-thiacarbocyanine dyes induced by binding to proteins

The effects of ribonuclease A (RNase), lysozyme, trypsin, and bovine serum albumin (BSA) on the J-aggregation behavior of 3,3'-bis[sulfopropyl]-5-methoxy-4',5'-benzo-9-ethylthiacarbocyanine (1), 3,3'-bis[sulfopropyl]-4,5,4',5'-dibenzo-9-ethylthiacarbocyanine (2), and 3,3'-bis[sulfopropyl]-5,5'-dimethoxy-9-ethylthiacarbocyanine (3) were studied in aqueous solution. The formation of J-aggregates at pH 6 is induced by RNase for 1-3, by lysozyme for 1 and 2, and by trypsin for 2. The formation of J-aggregates correlates with decay of the dimers and is supported by induced circular dichroism spectra. The concentration of J-aggregates for lysozyme/1 increases with an increase in the protein/dye concentration ratio, reaches a plateau, and then gradually decreases. J-aggregates are characterized by relatively weak fluorescence; e.g., Phi(f) = 0.01 for lysozyme/1, and by a small Stokes shift of 6-8 nm, indicating almost resonance fluorescence. J-aggregation proceeds in the range of seconds to minutes with sigmoidal type kinetic curves for trypsin/2 and nonsigmoidal kinetics in the other cases. The presence of BSA, in contrast to RNase, lysozyme, and trypsin, results in deaggregation of dimers of 1-3 and formation of bound monomers and exhibits intense fluorescence from the trans-monomer; e.g., Phi(f) = 0.22 for BSA/1. Generally, the binding of 1-3 to the proteins is a cooperative process, where the number of binding sites changes from n = 15 for lysozyme/1 to n = 6 for trypsin/2 and n = 0.3 and 1 for BSA/3.     

Interfacial assemblies of cyanine dyes and gemini amphiphiles with rigid spacers: regulation and interconversion of the aggregates

A series of gemini amphiphiles with a pyridinium headgroup and rigid spacers were designed, and their interfacial assemblies with cyanine dyes, 3,3-disulfopropyl-9-methyl-selenacarbocyanine (SeCy) and 3,3-disulfopropyl-4,5,4',5'-dibenzo-9-methyl-thiocarbocyanine (MTC), through the air/water interface were investigated. Although the dyes have intrinsic tendencies to form J- or H-aggregates in aqueous solutions, their aggregation could be regulated in the complex films. Depending on the spacer, both J- and H-aggregates were formed for SeCy, whereas an H-aggregate with different absorption bands was obtained for MTC. Furthermore, the formed aggregates in the films could be reversibly switched by treating the complex films with HCl, NH3 gas, or water vapor. The J-aggregates of SeCy could be changed into H-aggregates and recovered through an alternative HCl/NH3 exposure in the films. The H-aggregate of the MTC film could be changed into J-aggregate upon exposure to HCl gas and subsequently put into air or NH 3 gas, and the thus-formed J-aggregate could be changed into H-aggregate under hot water vapor. In addition, such a reversible switch between different aggregates of MTC was only observed when the gemini amphiphiles with rigid spacers were applied. A possible explanation related to the protonation of the dye and the reorganizations in the film during the interconversion between different aggregates was proposed.     

Kinetics of J-aggregation of cyanine dyes in the presence of gelatin

The kinetics of formation of J-aggregates for 3,3'-bis[sulfopropyl]-R-4',5'-dibenzo-9-ethylthiacarbocyanines (R=5-methoxy; R=4,5-dibenzo) and 3,3'-bis[sulfopropyl]-5,5'-diphenyl-9-ethyloxacarbocyanine were studied in aqueous solution in the presence of gelatin at different pH values and at room and elevated temperatures. Addition of gelatin at concentrations of 0.0005-0.05 wt % to solutions of dyes results in the production of J-aggregates in the tens of seconds to tens of minutes range. The rate of J-aggregate formation increases with increasing concentrations of dye and gelatin, correlates with the rate of decay of dimers, and is also dependent on the dye structure, temperature, and pH. The rate of J-aggregation is increased for and decreased for with an increase in temperature. For and, the rate increases with increasing [H+] and reaches the maximum value at pH 3.3-4.3 for 3. The interaction of with gelatin is considered to be a cooperative binding process, and J-aggregation is characterized by the time-dependent rate constant. Sigmoidal- and nonsigmoidal-type kinetic curves of both formation of J-aggregates and decay of the dimers are best fitted with a stretched exponential function.     

Spectral and fluorescent study of the interaction of anionic cyanine dyes with serum albumins

The noncovalent interaction of two anionic cyanine dyes with human and bovine serum albumins was studied by spectral and fluorescent methods. Upon the interaction with albumins, a growth of fluorescence and, in most cases, a long-wavelength shift of the dye absorption band are observed. For the meso-substituted cyanine dye 3,3′-di-(γ-sulfopropyl)-9-methylthiacarbocyanine betaine (K1), a mobile cis-trans equilibrium is observed: the dye in the free state occurs mainly as the cis-isomer, whereas in the complex with albumins the equilibrium is shifted toward the trans-isomer (this shift is greater for human albumin). Dye K1 is recommended as a spectral and fluorescent probe for serum albumins.     

阴阳离子菁染料超快荧光动力学特性研究

采用飞秒荧光上转换技术,研究了阴阳离子菁染料及对应的阴离子和阳离子菁染料吸附在立方型和T型溴碘化银表面上形成J-聚集体的荧光衰减时间分辨特性,分析了几种菁染料增感体系的超快电子转移动力学过程及其对增感效率的影响.通过比较几种菁染料增感体系的荧光衰减特性,两种阴阳离子染料要明显快于阴离子染料、阳离子染料及二者的加合,说明阴阳离子染料聚集体到溴碘化银的电子注入速率较快,增感效果更好.对两种阴阳离子染料聚集体荧光衰减特性的比较,可以看出染料在T型颗粒溴碘化银上形成聚集体的荧光寿命更短,因而对T型颗粒的增感效果更好.染料Dye2的荧光衰减要快于染料Dye1,说明染料Dye2到溴碘化银的电子注入速率更快,增感效率更高.     

Specifics of the formation of J-aggregates of cyanine dyes in solutions of AOT/water/hexane reverse micelles

The behavior of a cyanine dye (3,3′-di-(gamma-sulfopropyl)-4,5,4′,5′-dibenzo-9-ethylthiacarbocyanine betaine pyridinium salt) was studied in AOT/water/hexane reverse micelles over a wide range of W at various concentrations of the dye, AOT, and reverse micelles. The processes occurring during the formation of the AOT/water/hexane micellar solution were studied in detail. It has been shown that, before the formation of the stable microemulsion, the dye aggregation processes occur by virtue of the interaction of the dye with the AOT anion. The amount of J-aggregates is proportional to the logarithm of the ratio of the amount of AOT molecules to the amount of dye molecules. The time behavior of J-aggregates after the formation of a micellar structure depends on the concentration of reverse micelles, thereby indicating an important role of intermicellar exchange.     

Spectral and fluorescent study of the noncovalent interaction of a meso-substituted cyanine dye with serum albumins

A comparative study of the noncovalent interaction of the cyanine dye probe 3,3′-di-(γ-sulfopropyl)-4,5,4′,5′-dibenzo-9-ethylthiacarbocyanine betaine with serum albumins of different vertebrates: rat, rabbit, bovine, and human serum albumins (RSA, TSA, BSA, and HSA, respectively) has been performed by spectral and fluorescent methods. It has been shown that, the dye forms only one product, the trans-monomer bound to HSA, by interacting with HSA, whereas other binding products are also formed with other albumins. This is probably explained by a higher interaction energy of the dye with HSA than with other serum albumins.     

Dye J-aggregate—semiconductor nanocrystal hybrid nanostructures in reverse micelles: an experimental study

Reverse micelle solutions can be used for the assembly of hybrid nanostructures of the composition dye monomer—Ag₂S nanocrystal, dye J-aggregate—CuI nanocrystal, and dye J-aggregate—PbI₂ nanocrystal. The assembly is effected by means of adsorption of the dye (3,3′-di-(γ-sulfopropyl)-4,5,4′,5′-dibenzo-9-ethylthiacarbocyanine betaine pyridinium salt) onto the nanocrystal surface. Factors responsible for the dye adsorption onto semiconductor nanocrystals in reverse micelle solutions are analyzed. It is suggested that adsorption can be the outcome of forces induced by both van der Waals and chemical interactions. The surfactants used for stabilization of reverse micelle solutions also influence the assembly of the hybrid nanostructures.     

Chiral transformation of cyanine dye aggregates induced by small peptides

Three small peptides (K4, K5, and K6) with different length were designed to induce the transformation of the assembled state and the chirality of cyanine dye supramolecule. The absorption and circular dichroism (CD) results indicated that, the peptides tend to induce cyanine dye to H-aggregation, competed with Na(+) in PBS, which would induce dye to J-aggregation. Meanwhile, all three peptides could influence the chirality of both J-aggregates induced by Na(+) and H-aggregates, among which K6 could induce chiral reversion of J-aggregates. Furthermore, molecular modeling and energy calculation results have shown that the peptides with different chain length have different conformations. This might be the reason for cyanine dye to form the different chiral assembly induced by these oligo-peptide templates.     

Modification of the nanoscale structure of the J-aggregate of a sulfonate-substituted amphiphilic carbocyanine dye through incorporation of surface-active additives

The amphiphilic dye 3,3'-bis(2-sulfopropyl)-5,5',6,6'-tetrachloro-1,1'-dioctylbenzimidacarbocyanine (C8S3) self-aggregates in aqueous solution to form tubular J-aggregates with a diameter of 17.0 +/- 0.5 nm, a wall thickness of approximately 4 nm, and a length exceeding several hundred nanometers. The absorption spectrum shows the typical features expected for tubular J-aggregates with several sharp and red-shifted absorption bands. Morphological investigations using cryo-transmission electron microscopy (cryo-TEM) and spectroscopic investigations reveal a high stability of the tubular morphology but a tendency of the aggregates to assemble into ropelike bundles after several weeks of storage. It is found that aggregation in solutions containing additives such as alcohols or surfactants results in the formation of new types of aggregates. A second type of tubular aggregate with a diameter of 13.0 +/- 0.5 nm is observed when the solutions contain more than 10 wt % MeOH. On the time scale of days these tubular aggregates transform into ribbonlike structures characterized by a new absorption spectrum, and they convert after several weeks into giant tubes with diameters of up to 500 nm.     

不同取代基的噻碳菁和吲哚碳菁染料对其在溴化银微晶上吸附能力及形成J-聚集体尺寸分布的影响

本文研究了5-位不同取代基的噻碳菁和吲哚碳菁染料对其在立方型颗粒和T-颗粒溴化银微晶上吸附能力的影响,并采用ACFEM(Analytical Color Fluore scence Electron Microscopy)研究了上述结构染料对其吸附在溴化银微晶所形成的J-聚集体尺寸分布的影响。实验结果表明,对吲哚碳菁染料来说,立方体溴化银微晶表面的吸附能力较T-颗粒溴化银微晶表面的吸附能力强;但对噻碳菁染料来说则相反,它们在T-颗粒溴化银微晶表面的吸附能力较立方体溴化银微晶表面的吸附能力强。另外,对5-位不同取代基的噻碳菁染料而言,无论是在立方型颗粒或T-颗粒溴化银微晶上的吸附能力来说,含取代基(无论4-取代基是吸电子型还是推电子型)的噻碳菁染料较未取代的噻碳菁染料强;而5-位取代基是吸电子型的噻碳菁染料更有利于其吸附在T-颗粒溴化银微晶表面。此外,本文还进一步证明了溴化银微晶表面上染料J-聚集体的生长过程是符合奥斯瓦尔特成熟过程的。吲哚碳菁染料在T-颗粒溴化银微晶上形成的J-聚集体的平均尺寸明显大于在立方体溴化银微晶上形成的J-聚集体的平均尺寸。吸附在立方体溴化银微晶上的5-不同取代基的噻碳菁染料对其形成J-聚集体尺寸分布的影响的研究结果表明,含取代基(-CH₃,-Ph,-Cl)的噻碳菁染料形成的J-聚集体的尺寸分布几乎相同,但与未取代的噻碳菁染料形成的J-聚集体的尺寸分布明显不同;5-位含取代基的噻碳菁染料形成的J-聚集体平均尺寸大于未取代的噻碳菁染料的。     

Oxalic acid cross-linked sodium alginate and carboxymethyl chitosan hydrogel membrane for separation of dye/NaCl at high NaCl concentration

Dye desalination is a challenge in the treatment of textile wastewater with high salt concentration. It is imperative to develop salt resistance membrane that is from sustainable materials to effectively treat dye/salt mixtures. And most polymer membrane materials are non-renewable petrochemical resources.In this paper, a green hydrogel membrane(CMCS-OA-Na Alg) was prepared by non-metallic ions of oxalic acid(OA) cross-linking of two natural macromolecules of sodium alginate(Na Alg) and carboxym...     

Contrasting behavior of classical salts versus ionic liquids toward aqueous phase J-aggregate dissociation of a cyanine dye

The effect of addition of ionic liquids (ILs) on the aggregation behavior of a cyanine dye, 5,5',6,6'-tetrachloro-1,1'-diethyl-3,3'-di(4-sulfobutyl)-benzimidazolocarbocyanine (TDBC), was investigated. In basic aqueous buffer solutions (pH ≥ 10), TDBC preferably exists in its J-aggregated form. Addition of hydrophilic ILs > 5 wt % is observed to disrupt the TDBC J-aggregates, converting them to monomer form most likely because of the interaction between bulky IL cation and the J-aggregates in a time-dependent fashion. This is evidenced by the observed increase in monomer band absorbance at the expense of the absorbance band due to J-aggregates over time. Inorganic salts at similar molar concentrations do not cause this phenomenon but instead induce TDBC precipitation. At low concentrations (<5 wt %), the added IL acts similarly to the inorganic salts, reducing the overall absorbance of TDBC in the solution most likely due to cation exchange causing TDBC precipitation. Addition of a molecular solvent, ethanol, at 15 wt % results in an initial increase in monomer absorbance, albeit to a much lesser extent than for the corresponding molar fraction of IL, which then decreases over time with recovery of J-aggregate absorbance--quite opposite the time-dependent behavior seen for TDBC in PB at pH 12.0 with >5 wt % IL. The unique and dual behavior of ILs as an additive toward affecting cyanine dye aggregation is demonstrated.     

Enhanced intra-aggregate charge separation from binary excitons in mixed J-aggregates of cyanine dyes

Well-ordered, two-dimensional, amalgamation-type J-aggregates consisting of two different kinds of structurally analogous anionic cyanine dyes were self-assembled on an amino-functionalized Au(111) electrode surface. Similar binary J-aggregates, though considerably less ordered in either one- or three-dimensional structure, could also be grown easily in a concentrated ( approximately 1.5 M) aqueous solution of NaCl. These binary J-aggregates are characterized by a singly peaked J-band associated with a unique molecular exciton shared by the two different dye components coherently. This cooperative binary excitonic state can live with substantial (more than 0.1 eV) energy gaps between the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) levels of the two dyes mixed together. These energy gaps allow the binary exciton to relax very rapidly to an intra-aggregate charge-separated state in good competition with the metal-induced quenching of the excited-state energy. The enhanced charge separation leads to a high-efficiency photocurrent generation with a simple binary J-aggregate-coated Au(111) electrode in a reversible redox solution and results in strong quenching of the fluorescence from the corresponding aggregate grown in solution free from substrate-induced quenching.     

Atomistic nature of NaCl nucleation at the solid-liquid interface

The early stage of heterogeneous nucleation of NaCl from supersaturated NaCl aqueous solution at the water-NaCl (001) interface has been investigated by molecular dynamics simulations. The critical size of the nuclei for spontaneous growth was found to be as small as two atoms (a Na(+)-Cl(-) ion pair) at high supersaturation. Due to the presence of a relatively stable water network and the effect of the hydration force at the interface, the stable nuclei formed on the NaCl (001) are found to contain more Na(+) ions than Cl(-) ions. The different deposition characteristics of the Na(+) and Cl(-) solutes lead to a positively charged substrate and thus may introduce another driving force for nucleation besides the level of solution supersaturation. The role of water was further confirmed by comparison with NaCl epitaxy growth in the vacuum.     

Kinetics of salt-induced J-aggregation of cyanine dyes

The addition of monovalent, divalent, and trivalent metal ions to three anionic ethyl meso-thiacarbocyanine dyes, an ethyl meso-oxacarbocyanine, and an imidacarbocyanine in aqueous solution at room temperature results in the production of J-aggregates within the range of tens to hundreds of seconds. The rate of formation of J-aggregates correlates with the rate of decay of dimers or monomers and is dependent on the type of metal ion, dye structure, and temperature. The rate of formation of J-aggregates increases as the temperature decreases and the dye and salt concentrations increase, and the rate is highest for trivalent ions and smallest for monovalent ions, independent of the type of anion. The time course of formation of J-aggregates is described in most cases by a sigmoidal curve, and the kinetics and mechanism are discussed within the framework of autocatalysis. Computer simulations reveal that the sigmoidal time dependence is transferred to an exponential-like curve by substantially increasing the rate constant for the noncatalytic step. The reaction pathway into J-aggregates can be switched from dimeric ion pairs as the reactant to monomeric ion pairs, when the rate constant for the catalytic step via the monomer becomes larger with respect to that via the dimer.     

Analysis of carrageenans by matrix-assisted laser desorption/ionization and electrospray ionization mass spectrometry. I. kappa-Carrageenans.

Matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) mass spectra of small kappa-carrageenans are reported and discussed. MALDI spectra can be obtained in both positive and negative ion mode. In the absence of extraneous metal ions, positive ions are formed by the attachment of one Na(+) ion to the carrageenan, whereas for negative ions one Na(+) ion is detached from the sulfate group. Multiply charged species are not observed in MALDI. Intense ESI spectra can be obtained in negative ion mode and now multiply charged species are seen. Alkali exchange experiments show that in these small carrageenan anions one, but only one, alkali metal ion is bound in a bidentate coordination with two ionic sulfate groups. G2-type ab initio calculations on model ions HO(-) [M(+)] (-)OH (M = Li, Na, K, Cs), as well as arguments based on a simple Coulombic interaction model, show that the bidentate stabilization energy drops rapidly as the size of the alkali cation increases. Exchange of Na(+) with Li(+) leads to expulsion of the Na(+) ion generating, in ESI, intense multiply charged anions. An attempt is made to rationalize this behavior in terms of hydration effects.