Interaction between oppositely charged polyelectrolytes in aqueous solution

Oppositely charged polyelectrolytes interact in solution, forming polyelectrolyte complexes, which often appear as gel-like precipitates. This kind of complex formation was studied by means of calorimetric and rheological measurements. The enthalpy effects, though being fairly small, give some information about the binding strength of counterions to the macroion. We studied the system poly(p-styrene sulfonate)/poly(trimethylammonium-2-ethyl methacrylate) (PSS-PTMA), varying systematically the low molar mass counterions of PSS. In every case, the maximum of enthalpy was found around a 1:1 (mol:mol monomer units) composition of the complexes, with the shape of enthalpy versus composition-curve indicating a stoichiometric interaction. The maximum enthalpy decreased with increasing atomic mass of the counterion when the alkaline metal salts of PSS were used and no change was made on the side of the cationic polyelectrolyte. The salts of the alkaline earth metals gave a distinctly higher enthalpy. On the contrary, viscosity measurements showed a very broad minimum as a function of composition, indicating that the formation of non-stoichiometric complexes is also occurring. The conclusion of these observations is that the complex formation is stoichiometric with respect to the monomeric units, but not necessarily stoichiometric with respect to the entire macromolecules.     

Interaction between a partially fluorinated alkyl sulfate and gelatin in aqueous solution

The interaction of a partially fluorinated alkyl sulfate, sodium 1H,1H,2H,2H-perfluorooctyl sulfate (C6F13CH2CH2OSO3Na), with the polyampholyte gelatin has been examined in aqueous solution using surface tension and small-angle neutron scattering (SANS). The 19F chemical shift of each fluorine environment in the surfactant is unaltered by the addition of gelatin, indicating that there is no contact between the gelatin and the fluorocarbon core of the micelle. The chemical shift of the two methylene groups closest to the headgroup is altered when gelatin is present, disclosing the location of the polymer. The critical micelle concentration (cmc) of the surfactant, cmc = 17+/-1 mM, corresponds to an effective alkyl chain (CnH2n+1) length of n = 11. In the presence of gelatin, the cmc is substantially reduced as expected, cmc(1) = 4+/-1 mM, which is also consistent with an effective alkyl chain length of n = 11. In the presence of the fluorosurfactant, the monotonic decay of the SANS from the gelatin-only system is replaced by a substantial peak at an intermediate Q value mirroring the micellar interaction. At low ionic strengths, the gelatin/micelle complex can be described by an ellipsoid. At higher ionic strengths, the electrostatic interaction between the micelles is screened and the peak in the gelatin scattering disappears. The correlation length describing the network structure decreases with increasing SDS concentration as the bound micelles promote a collapse of the network.     

Interaction between ethyl(hydroxyethyl)cellulose and sodium dodecyl sulphate in aqueous solution

Using sodium activity, viscosity, and cloudpoint measurements, it has been shown that sodium dodecyl sulphate (SDS) binds to ethyl(hydroxyethyl)cellulose in a cooperative manner. In the absence of salt the binding leads to an increase in the clouding temperature, but when a small amount of salt (0.01 molal) is present first a drastic decrease and then an equally drastic increase in the cloud point temperature is observed. The binding of SDS also initially leads to an increase in viscosity followed by a decreased viscosity at higher SDS concentrations. A molecular mechanism explaining the observed behavior is given.     

Adsorption and removal of tetracycline antibiotics from aqueous solution by graphene oxide

Significant concerns have been raised over pollution of antibiotics including tetracyclines in aquatic environments in recent years. Graphene oxide (GO) is a potential effective absorbent for tetracycline antibiotics and can be used to remove them from aqueous solution. Tetracycline strongly deposited on the GO surface via π-π interaction and cation-π bonding. The adsorption isotherm fits Langmuir and Temkin models well, and the theoretical maximum of adsorption capacity calculated by Langmuir model is 313 mg g(-1), which is approximately in a close agreement with the measured data. The kinetics of adsorption fits pseudo-second-order model perfectly, and it has a better rate constant of sorption (k), 0.065 g mg(-1) h(-1), than other adsorbents. The adsorption capacities of tetracycline on GO decreased with the increase in pH or Na(+) concentration. The adsorption isotherms of oxytetracycline and doxycycline on GO were discussed and compared.     

生物炭去除水中四环素的研究进展

随着抗生素药物(如四环素)的大量使用,近几年抗生素的环境行为和毒性已经成为人们的研究焦点和热点.我国的地表水、地下水、市政污水、养殖废水等不同水体中都检测到了四环素等抗生素药物,引发的水生态问题受到了众多学者的广泛关注.生物炭因具有制备来源广泛且易得廉价、比表面积大、孔隙发达、官能团种类较多等优点被学者们重点关注,已有众多文献报道发现不同种生物炭对四环素的吸附具有优越的性能.本文综述了近年来不同生物质制备的生物炭对四环素的吸附影响以及不同水化条件对四环素对生物炭吸附特征的影响,并阐述了生物炭吸附四环素过程中所涉及的机理.对进一步探究生物炭对四环素吸附的影响具有一定的指导意义.     

一种铽配合物用于水溶液中二甲硝咪唑和四环素的检测

选用(1,1'':3'',1″-三联苯)-3,3″,4'',5,5″,6''-六羧酸(H₆L)为配体,在溶剂热条件下,与Tb³⁺离子反应得到配合物[Tb (L)_0.5(H₂O)₂]·7H₂O (1)。通过单晶X射线衍射、粉末X射线衍射、红外光谱、元素分析、热重分析对该配合物的结构和组成进行了表征,同时,对其荧光性质进行了研究。结果表明:该配合物属于正交晶系,Cmca空间群,a=2.661 61(7) nm,b=1.421 03(4) nm,c=2.109 88(6) nm。拓扑计算表明配合物1是一个新颖的(6,6)-连接的三维网络结构,符号为(4⁸.6⁶.8)(4⁹.6⁶)。该配合物具有强的荧光发射,可以快速检测水溶液中的二甲硝咪唑和四环素且灵敏度高、检出限低、可回收性好。通过实验和密度泛函理论相结合,揭示了荧光猝灭机理。     

Interaction of arsenite ions with molybdate in aqueous solution

Interaction of arsenite ions with molybdate ions in aqueous HClO₄ at pH of 3–5 were studied using spectrophotometry. A heteropoly anion (HPA) with the AsMo₄ stoichiometry was revealed. Elemental analysis, X-ray photoelectron spectroscopy, and IR spectroscopy were used to characterize the composition and structure of the cesium salt of As(III)-Mo(VI) HPA precipitated from solution. The comparison of the IR spectra of cesium salts of the synthesized HPA and dimethylarsenite HPA (CH₃)₂AsMo₄O₁₅H^2?, whose structure is known, implies that AsMo₄O ₁₅ ^3? has a similar structure, where the AsO ₂ ^? group is linked by four connected molybdenum octahedra (Mo₄O₁₂)O^2?.     

Interaction of DNA fragments with counterions in aqueous solution

Monte Carlo simulation of the hydration of metal ion—DMP⁻ and metal ion—9-methylguanine complexes was performed. A comparative analysis of the results for Na⁺ and K⁺ ions was carried out. The main stages of dissociation were revealed. The energy effects of dissociation were evaluated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2174–2177, November, 1998.     

Interaction of silver nanoparticles with ozone in aqueous solution

The interaction between ozone and silver nanoparticles stabilized with sodium polyphosphate is studied in aqueous solutions. The process of ozone decomposition is established to have a chain character. The oxidation of one silver atom initiates the decomposition of about three ozone molecules. The stability of colloidal silver decreases upon the oxidation, which leads to its partial aggregation.     

一种铽配合物用于水溶液中二甲硝咪唑和四环素的检测

选用(1,1’:3’,1"-三联苯)-3,3",4’,5,5",6’-六羧酸(H₆L)为配体,在溶剂热条件下,与Tb³⁺离子反应得到配合物[Tb(L)_0.5(H₂O)₂]·7H₂O(1)。通过单晶X射线衍射、粉末X射线衍射、红外光谱、元素分析、热重分析对该配合物的结构和组成进行了表征,同时,对其荧光性质进行了研究。结果表明:该配合物属于正交晶系,Cmca空间群,a=2.661 61(7) nm,b=1.421 03(4)nm,c=2.109 88(6) nm。拓扑计算表明配合物1是一个新颖的(6,6)-连接的三维网络结构,符号为(4⁸.6⁶.8)(4⁹.6⁶)。该配合物具有强的荧光发射,可以快速检测水溶液中的二甲硝咪唑和四环素且灵敏度高、检出限低、可回收性好。通过实验和密度泛函理论相结合,揭示了荧光猝灭机理。     

Interaction between styrene–ethylene oxide block copolymers and sodium lauryl sulfate in aqueous solution

Interactions of water-soluble AB block copolymers of polystyrene and poly(ethylene oxide) with sodium lauryl sulfate (SLS) in aqueous solution were investigated by high-resolution proton magnetic resonance (NMR). The viscosity in aqueous SLS solution was also measured. From the NMR results in D₂O, it appears that molecular motions of the polystyrene blocks of the copolymer in aqueous solution are activated by interaction between the polystyrene blocks and the added SLS. From solution viscosity, on the other hand, it is apparent that a complex is formed between the copolymer and SLS and that it exhibits typical polyelectrolyte properties. The polyelectrolyte character is attributable largely to intrachain repulsions between like charges of the SLS anions adsorbed on the poly(ethylene oxide) blocks of the copolymers since the polystyrene blocks are insoluble in water and the styrene content is less than 10%.     

Interaction between anionic and cationic gemini surfactants at air/water interface and in aqueous bulk solution

The mixture of the anionic O,O′-bis(sodium 2-lauricate)-p-benzenediol (C₁₁pPHCNa) and cationic (oligoona)alkanediyl-α, ω-bis(dimethyldodecylammonium bromide) (C₁₂-2-E_x-C₁₂·2Br) gemini surfactants has been investigated by surface tension and pyrene fluorescence. The results show that the surface tension γ drops faster with total surfactant concentration C_T for α₁ = 0.1 or 0.3 than for α₁ = 0.7 or 0.9, where α₁ is the mole fraction of C₁₁pPHCNa in the bulk solution on a surfactant-only basis. The fast drop in γ for α₁ < 0.5 indicates strong adsorption at the air/water interface owing to the interaction between oppositely charged components, resulting in the formation of the adsorption double layers in the subsurface. The slow descent in γ for α₁ > 0.5 is attributed to the pre-aggregation in the solution before the critical micelle concentration cmc. A possible mechanism is proposed.     

十二烷基硫酸钠与羟乙基纤维素的相互作用

本文用表面张力(γ)和电导率(κ)方法研究了阴离子表面活性剂十二烷基硫酸钠(SDS)与天然纤维素的水溶性改性物羟乙基纤维素(HEC)的相互作用.实验结果表明,SDS-HEC溶液的γ-lgcSDS曲线和κ～CSDS曲线均呈现双拐点特征,并且γ-lgcSDS曲线上两个SDS临界浓度值(c1 )γ及(c2)γ,与κ～CSDS...     

Interaction between a stationary mercury electrode and a hydrogen bubble in an aqueous sodium dodecyl sulphate solution

The stability and rupture of thin liquid films formed from an aqueous solution of Na₂SO₄ (0.05 mol dm⁻³) in the presence of 5 × 10⁻⁵ mol dm⁻³ sodium dodecyl sulphate between a stationary mercury electrode and a hydrogen bubble has been investigated as a function of electrode potential. The electrostatic component of disjoining pressure has been calculated using the results of capacity measurement for the mercury-solution interface. Special attention has been paid to films formed on positively charged mercury surfaces. In this case, despite the positive electrode polarization, the outer Helmholtz plane potential is found to be negative due to the high surface activity of the dodecyl sulphate anion. The van der Waals component of disjoining pressure has been calculated on the basis of a double sheath model of the two interacting surfaces, taking into consideration the orientation of the adsorbed surfactant layers at the interfaces. Calculations of the total disjoining pressure can explain film stability at negative mercury potentials, but do not explain film rupture when the polarization of the mercury is positive. The existence of a hydrophobic attractive interaction is postulated in the latter case.     

Interaction of sulfophthaleine anions with cationic dyes in aqueous solution

An interaction between the singly and doubly charged anions (HAn⁻ and An²⁻) of sulfophthaleines (phenol red and its derivatives: bromophenol blue, bromocresol green, bromocresol purple, and bromothymol blue), and singly charged cations (Ct⁺) of a polymethine (pinacyanol, quinaldine red), results in formation in an aqueous solution of heteroassociate with stoichiometric composition (Ct⁺)·HAn⁻ and (Ct⁺)₂·An²⁻. On the basis of spectrophotometric data the association constants were estimated. By quantum-chemical methods AM1 and PM3 the values of formation and reaction enthalpies of the species formed were calculated and the most probable structure of the heteroassociates was determined.     

Interaction of several polymers with p-substituted phenols in aqueous solution

The interactions between several water-soluble polymers, i.e., polyethyleneimine (PEI), poly-(ethylene glycol) (PEG), polyacrylamide (PAM), and poly(methacrylic acid) (PMAA), and p-X-substituted phenols (X = CH₃O, CH₃ C₂H₅, H, Cl, Br and NO₂) in aqueous solution at 30°C were investigated by means of equilibrium dialysis. By applying the Klotz equation to the results obtained, the bonding constants between these polymers, including poly(vinylpyrrolidone) (PVP) which was reported previously, and phenol were determined; they decreased in the following order: PVP > PMAA > PEI > PAM > PEG. This order was in agreement with that reported from the solubility of naphthalene, biphenyl, and alkyl halides in aqueous solution of these polymers caused by a hydrophobic bonding interaction. In this case, therefore, a hydrophobic bonding seemed to be significant. The bonding constants of these polymers with p-substituted phenols were also determined, and they were found to be approximately correlated with Hamett σ constants of the para substituents in phenols. Therefore, it was concluded that the interactions due to electrostatic and hydrogen-bonding forces were also important.