Aggregation behavior and interaction of an amphiphilic drug imipramine hydrochloride with cationic surfactant cetyltrimethylammonium bromide: light scattering studies

The aggregation behavior and interaction of an amphiphilic antidepressant drug imipramine (IMP) hydrochloride with the cationic surfactant cetyltrimethylammonium bromide (CTAB) have been studied using light scattering (both static and dynamic) techniques. Due to rigid tricyclic hydrophobic moiety present in the molecule, the drug shows interesting association behavior. The static light scattering measurements show that the self-association of IMP commenced above a well-defined critical micellar concentration (CMC), which decreases with increasing the mole fraction of the CTAB surfactant. Both the excess Gibbs energy (ΔG(ex)) and the Gibbs energy of micellization (ΔG(M)°) are negative, and decrease with increasing mole fraction of the surfactant. The hydrodynamic diameters (d(h)) of the micellar aggregates were also evaluated using the dynamic light scattering measurements. The data indicate formation of larger aggregates by IMP and CTAB due to mixed micellization and subsequent micellar growth. The results have been analyzed using different models (viz., Clint, Motomura, Rosen, Rubingh, etc.) for mixed micelle formation.     

Small-angle X-ray scattering and light scattering on lysozyme and sodium glycocholate micelles

Small-angle X-ray scattering (SAXS) together with static (SLS) and dynamic light scattering (DLS) measurements were carried out on aqueous solutions of lysozyme (LY) and of the ionic biological detergent sodium glycocholate (NaGC). Apparent diffusion coefficients (D app), excess Rayleigh ratio, and SAXS spectra were measured for 0.1 M NaGC solutions at different ionic strengths (0.05-0.30 M NaCl). The same data were collected for LY in sodium acetate buffer 50 mM without and with 92 mM NaCl as a function of protein concentration (10-80 g L(-1)). A correlated analysis of SLS data and SAXS spectra was first tested on the LY samples and then extended to the interpretation of the NaGC data to infer information on particle structure and interaction potential. A hard-core (HC) interaction shell of uniform thickness, a screened Coulomb potential of the electric double layer (EDL) or the complete DLVO potential were alternatively used to represent the long-range tail of the interaction potential. Whenever an essentially repulsive tail is expected, all the representations give reasonable results, but the data analysis does not allow the discrimination between the oblate and the prolate symmetries of the NaGC aggregates. The DLVO model allows the interpretation of the data even when the attractive component determines the tail character. With this model an overall fit of the micelle data at all the NaCl concentrations was successfully performed by assuming a simple spherical symmetry of the micelles and invariant values of their ionization degree and Hamaker constant, thus considering just the screening effect of the added electrolyte. Whatever model is used, the results point out that the aggregates are quite hydrated (26-38 water molecules per monomer) and very slightly grow by increasing the NaCl concentration. When spherical symmetry is assumed the aggregate radii for all the samples fall in the range 15-16 A. From the SAXS and SLS, best fitting geometrical parameters, and interparticle structure factor, a D app value was calculated for each sample. An excellent consistence is achieved for LY results. On the contrary, calculated D app values systematically lower than the experimental values are always obtained for the NaGC micelles. Micelle polydispersity and internal dynamics seem to be the most probable reasons of the bad agreement.     

Colloid stability of synthetic titania and the influence of surface roughness

The colloid stability of synthetic titania particles was studied as a function of KCl concentration at pH values of 6.3, 6.7, and 8.4, using static light scattering to obtain stability ratios. Standard DLVO theory was then used to calculate the stability ratios as a function of salt concentration. Reasonable agreement between theory and experiment could only be obtained if an effective interaction radius, corresponding to surface asperities on the titania particles, was used in the calculation. High-resolution TEM images suggest that the effective interaction radius corresponds to the size of surface crystallites formed during synthesis.     

粘度法研究胶团的球-棒转变

本文基于粘度测量求得了溴化十四烷基吡啶胶团水溶液的特性粘度随盐量(0.5—2.0 mol L~(-1)NaBr), 温度(20°—40 ℃)和活性剂浓度(3-25 g L~(-1))的变化。利用Missel等提出的热力学模型,由此求算了支配球-棒转变的平衡常数K和多分散胶团的重均聚集数, 当盐浓度为0.5和1.0 mol L~(-1)时, 由粘度法在不同温度下得到的K值以及在30 ℃下随活性剂浓度的变化, 与光散射的相应结果相当一致。此外, 在不同温度下求得的参数K在一定的胶团浓度范围内保持为常量。这符合模型的要求。盐量增至2 mol L~(-1)时, K明显地具有浓度依赖性,并且两法给出的K和值都相差较大。上述模型不再适用。对于符合球-棒转变的胶团体系, 从特性粘度具有浓度依赖性出发的粘度方法是研究胶团长大的简单而可靠的方法, 能够提供很多重要的信息。     

Amphiphilic drug persuaded collapse of polyvinylpyrrolidone and poly(ethylene glycol) chains: A dynamic light scattering study

Light scattering has proved to be useful in characterizing colloidal systems. We have studied the interaction between an amphiphilic drug, amitriptyline hydrochloride (AMT), and neutral polymers, polyvinylpyrrolidone (PVP) and poly(ethylene glycol) (PEG), using the dynamic light scattering (DLS) technique. AMT was found to interact with PVP more strongly than PEG. A large decrease of the size of aggregates upon increase of AMT concentration indicates a successive collapse of the polymer conformation. The partial negatively charged oxygen atoms, present in the amide group of PVP, were believed to be responsible for the collapse while interacting with the cationic head group of AMT. Presence of NaBr in the solution enhanced the effect markedly and made the AMT–PVP aggregates more compact. The PEG aggregates also showed a similar behavior, although less pronounced than the PVP. The results obtained in the present investigations may be helpful to design the drug delivery systems for the antidepressant drugs as the higher concentration of these drugs is harmful for the human body. Likewise, as the results have shown that on increasing the temperature there is a decrease in the extent of interaction; this may be helpful for the controlled release formulations.     

Sensitive determination of nitrogenous hydrochloride drugs via their reaction with ammonium molybdate

In a hydrochloric acid medium, benzhexol hydrochloride, cyproheptadine hydrochloride, and maprotiline hydrochloride, can react with ammonium molybdate to form ion-association complexes by virtue of electrostatic attraction and hydrophobic interaction which result in a significant enhancement of the resonance light scattering intensity. The maximum scattering wavelengths were found at 364 nm, 364 nm, and 381 nm for benzhexol hydrochloride, cyproheptadine hydrochloride, and maprotiline hydrochloride systems, respectively. Spectral characteristics of the three systems, influencing factors, and optimum conditions were investigated. The reason of resonance light-scattering enhancement and the mechanism of interactions between the drugs and ammonium molybdate were also discussed. Based on the linear relationship between the enhanced intensity of resonance light scattering and the concentration of drugs, a highly sensitive method for the determination of the three drugs was developed, the detection limits being 0.0110 μmol L⁻¹, 0.0038 μmol L⁻¹, and 0.0155 μmol L⁻¹ for benzhexol hydrochloride, cyproheptadine hydrochloride, and maprotiline hydrochloride, respectively. The method was successfully applied to the determination of the investigated drugs in pharmaceutical, serum, and urine samples.     

Control of gold nanoparticle aggregates by manipulation of interparticle interaction

The size of gold nanoparticle aggregates was controlled by manipulating the interparticle interaction. To manipulate the interparticle interaction of gold nanoparticles prepared by citrate reduction, we applied the substitutive adsorption of benzyl mercaptan on the particle surface in the absence of the cross-linking effect. Various experimental techniques such as UV-vis absorption spectroscopy, surface-enhanced Raman scattering, quasi-elastic light scattering, and zeta-potential measurement were used to characterize the nanoparticle aggregates. Our results suggest that the replacement of the trivalent citrate ions adsorbed on the nanoparticle surface with monovalent benzyl mercaptan ions should destabilize the particles, causing aggregation and hence the increase in the size of nanoparticle aggregates. These experimental results were successfully rationalized by the classical DLVO (Derjaguin-Landau-Vervey-Overbeek) theory that describes the interparticle interaction and colloidal stability in solution. Our findings suggest that the control of surface potential is crucial in the design of stable gold nanoparticle aggregates.     

瑞利光散射技术用于药物中盐酸米多君的测定

建立快速、准确、灵敏的检测药物中盐酸米多君的瑞利光散射(RLS)新方法。在pH 4.55 Tris-盐酸溶液和十六烷基溴化吡啶鎓溶液中,盐酸米多君与坚绿FCF 反应生成三元离子缔合物,使体系的RLS信号显著增强并产生具有2 个强散射峰的新RLS 光谱。在最大RLS 峰364 nm 处,盐酸米多君的质量浓度在0.004~0.35 mg·L^-1范围内与缔合物的RLS 增强强度(ΔIRLS)呈线性关系,检出限(3Sb/S)为0.0031 mg·L^-1。加标回收率和相对标准偏差(RSD)(n=5)分别为98.3%~102% 和1.0%~1.3%。该法用于药物中盐酸米多君含量的测定,结果满意。     

Study of the colloidal stability of an amphoteric latex

We have studied the colloidal stability of an amphoteric latex (–COOH and NH ₂ surface groups) with a low-angle light scattering technique (nephelometry). Measurements were carried out at different pH values and electrolyte concentrations (NaCl or CaCl ₂). The results show a behaviour in agreement with DLVO theory when the pH of the medium is below the isoelectric point (i.e.p.) of the latex: at low ionic strengths the latex is stable, but it becomes completely unstable and coagulates when electrolyte concentration goes over a particular value (the critical coagulation concentration). However, when pH is raised above the isoelectric point, the latex is completely stable even at high electrolyte concentrations, showing a behaviour clearly opposite to the theory. This could be explained by means of an additional short-range repulsive "hydration force" due to the structure of water molecules that accompany hydrated cations around the hydrophilic latex surface. The morphology and electrical properties of the latex surface have been studied by different methods: dynamic light scattering, electrophoretic mobility, potentiometric and conductometric titrations.     

Characterization of aggregate structures of phospholipid in the process of vesicle solubilization with sodium cholate using laser light scattering method

The aggregate structures formed during vesicle solubilization by sodium cholate, and their properties, were characterized by static laser light scattering (SLS) and electrophoretic light scattering (ELS) methods. The change in dissymmetry value Z₄₅ was observed by examining the regions of vesicles and micelles. The angular light scattering intensity data could be fitted with a modified shell model for the vesicles and a hollow cylinder model for the mixed micelles. In the case of the vesicles, the scattering curves were fitted with a spherical shell model by introducing the interparticle scattering factor S(q) and taking into account the intervesicle positional correlations, which is a function of the fractal dimension (D) and the interparticle correlation length (L). On the basis of the physical meanings of the fractal dimension and interparticle correlation length, the molecular packings of the membrane and the repulsive interaction between the vesicles were analyzed. Furthermore, using electrophoretic light scattering (ELS) the zeta potentials on the mixed vesicles were found to increase with the molar ratio (Re) of sodium cholate to egg yolk phosphatidylcholine (EggPC) in the membrane. It is suggested that the electrostatic properties of the vesicles result in repulsive interaction which is responsible for no fusion of the mixed vesicles. In addition, in the transition from vesicles to micelles, a cylinder-like micelle appeared as an intermediate structure.     

Absolute aggregation rate constants in aggregation of kaolinite measured by simultaneous static and dynamic light scattering

The aggregation rate was determined for the < 0.2 microm size fraction of kaolinite (KGa-2) using simultaneous static and dynamic light scattering at pH 9.5. It was found that method suggested by Holthoff et al. [Langmuir 1996, 12, 5541] is suitable for determination of the absolute aggregation rate constant of a clay dispersion without using the particle optical factors. The determined fast aggregation rate constant is k11,fast = (3.7 +/- 0.2) x 10(-18) m3 s(-1). Stability behavior of kaolinite colloids was studied as a function of concentration of sodium chloride by simultaneous static and dynamic scattering. The critical aggregation concentration was found to be 0.085 +/- 0.005 mol dm(-3). When calculating the relationship between the stability ratio and the electrolyte concentration using the DLVO theory, the best fit to the experimental data was achieved with a Hamaker constant of A = (4.7 +/- 0.2) x 10(-20) J.     

Small-angle static light scattering of concentrated silica suspensions during in situ destabilization

The aggregation of concentrated aqueous silica suspensions is characterized by means of static light scattering. We use an in situ destabilization mechanism based on the enzyme-catalyzed hydrolysis of urea. This method enables us to continuously and homogeneously change the interparticle potential from repulsive to attractive without disturbing the aggregation process. Moreover, our electrostatically stabilized suspensions can be destabilized by two different methods. In the first method, the pH is shifted toward the isoelectric point of the particles ( Delta pH method), thereby leading to a decrease of their surface charge. In the second method, the ionic strength is continuously increased at constant pH ( Delta I method), leading to a compression of the electrical double layer around the charged particles. A laboratory-built flat-cell light-scattering instrument is used, which allows fast data acquisition and an adjustment of the sample cell thickness. To circumvent multiple scattering effects, we use a very small sample thickness ( approximately 13 microm). In addition, the refractive index difference between the aqueous phase and the particles is reduced by adding sucrose to the liquid phase of our suspensions. We are able to characterize the structural changes at the very early stages of the destabilization process, where no significant effects are yet detected in macroscopic rheological measurements. While during the Delta pH destabilization, the scattering curve shows significant changes only after some characteristic delay time, it changes continuously during the Delta I destabilization. The latter is attributed to the formation of a weak pre-gel structure in the suspensions, as a shallow secondary minimum appears in the interparticle potential. Data are evaluated by using a HMSA square-well structure factor model. Results are in good agreement with those predicted from DLVO theory.     

Surface and bulk properties of two anionic amphiphilic penicillins in a selective solvent

The surface physicochemical properties of two anionic penicillins-cloxacillin and dicloxacillin-in mixed ethanol-water solvent were investigated by surface tension and dynamic light scattering (DLS). The data were analyzed according to the treatment of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to study the stability of the systems. The aim of the study is to obtain information about the effects of ethanol on the surface activity, bulk properties, and aggregate stability of these amphiphilic drugs, keeping in mind that both penicillins have the same counterion, and the difference in their structures is only a Cl atom in the phenyl ring that makes dicloxacillin more hydrophobic. The surface tension data show a minimum area per molecule increment with ethanol concentration that is related to the variation of the dielectric constant with the alcohol. Dicloxacillin has lower values of the standard Gibbs energies of adsorption than does cloxacillin, which gives this drug a more marked escaping tendency from the aqueous environment to the air-water monolayer. DLS data was fitted to an exponential function for cloxacillin at any drug or alcohol concentration in the range of concentrations studied that indicates that the system can be modeled as an ergodic system of dilute diffusing monodisperse particles. Dicloxacillin DLS data at an ethanol concentration of 5% (v/v) had to be fitted at a sum of an exponential and a stretched exponential function, which indicates that, besides the drug aggregates, a small population of penicillin clusters with longer relaxation times is present. The stability curves predicted by the DLVO theory, for both penicillins, indicate the predominance of electrostatic repulsion, leading to a stable system over the drug-ethanol concentration range studied, but the height of the reduced pair interaction potential energy barrier decreases with ethanol concentration, thus it is expected to undergo a transition from a stable dispersion to a coagulated one.     

Polyaniline nanoparticles prepared in rodlike micelles

The effect of aniline hydrochloride (AHC) on the size and shape of sodium dodecyl sulfate (SDS) micelles has been investigated by dynamic light scattering. A monotonic decrease in the diffusion coefficient of the micelles was observed with an increase in AHC at fixed SDS concentration. This was ascribed to prolate ellipsoidal growth of the micelles due to decrease of the effective headgroup area/molecule by adsorption of AHC on SDS micelles. The length of the micelles can be tuned by controlling the ratio of concentrations of AHC to SDS. Polymerization of aniline in micelles of different sizes leads to the formation of colloidal polyaniline with variable sizes. A direct correlation between size ofmicelles and size ofpolyaniline particles was observed. Combination of static and dynamic light scattering experiments reveal that the conformations of the polymer do not change significantly with size of the colloid.     

Probe diffusion from dilute to concentrated in polyelectrolyte solution: salt effect

The adsorption behaviors between a positively charged poly(allyamine) hydrochloride (PAH) matrix and negatively charged sulfate polystyrene (PS) particle probe were investigated using dynamic light scattering (DLS) and fluorescence photobleaching recovery (FPR) with reference to the matrix and salt concentration. The system experienced a steep decrease of diffusion (flocculation) under dilute conditions and a gradual decrease above semidilute concentrations. The fluorescence photobleaching recovery and viscometry experiments revealed that the probe behaviors in the polyelectrolyte solution were strongly affected by the coil overlap concentration (0.5 g/L poly(allyamine) hydrochloride). Near the coil overlap concentration, the hydrodynamic radius representing the entanglement dimension of the matrix was approximately 30 nm; however, at higher concentrations the radius gradually decreased, suggesting a transition toward a network structure. In this system, the salt performed two roles: (1) reinforcing the electrostatic interaction, and (2) preventing electrostatic interaction between the probe and the matrix.     

Cloud point variation of amphiphilic drug promethazine hydrochloride with added surfactants

In this paper we report clouding phenomenon occurring in an amphiphilic phenothiazine drug promethazine hydrochloride (PMT) in presence of surfactants. Cationic and nonionic surfactants increase the CP of 75 mM PMT solutions (prepared in 10 mM sodium phosphate buffer). These surfactants form mixed micelles with PMT. Anionic surfactants also form mixed micelles with the drug but the CP behavior is different by showing a peaked behavior. At low concentrations, anionic surfactants hinder micelle formation by forming ion-pairs whereas the usual CP decreasing effect at higher concentrations is due to mixed micellization. The CP behavior of 75 mM PMT+50 mM TBAB+surfactant systems is also explored which is found similar to PMT+surfactant systems with the difference only in magnitude of the clouding temperature.     

曙红Y共振光散射探针测定盐酸丙米嗪

在弱酸性介质中,盐酸丙米嗪与曙红Y依靠静电引力和疏水作用力形成离子缔合物,使曙红Y溶液的吸收光谱、荧光光谱和共振光散射光谱发生变化。其中以共振光散射法灵敏度最高。据此,建立了使用曙红Y作为共振光散射探针测定盐酸丙米嗪的新方法。研究了体系的吸收光谱、荧光光谱和共振光散射光谱特征。在最大散射峰364 nm处,测得盐酸丙米嗪的线性范围为0.025～2.5μg/mL,检测限为5.32 ng/mL,并将方法用于药物中盐酸丙米嗪含量的测定。     

Salt effect on complex formation of neutral/polyelectrolyte block copolymers and oppositely charged surfactants

The salt effect on the complex formation of poly(acrylamide)- block-poly(sodium acrylate) (PAM- b-PAA) as a neutral-anionic block copolymer and dodecyltrimethylammonium bromide (DTAB) as a cationic surfactant at different NaBr concentrations, CNaBr, was investigated by turbidimetric titration, steady-state fluorescence spectroscopy, and dynamic light scattering. At C NaBr < 0.25 M, DTAB molecules may form micelle-like aggregates on PAM- b-PAA chains to form a PAM- b-PAA/DTAB complex above the critical surfactant concentration C critical for the onset of complex formation. In the region of relatively high turbidity, a larger complex is likely to form a core-shell structure, of which the core is a dense and disordered microphase made of surfactant micelles connected by the PAA blocks. The corona was a diffuse shell of PAM chains, and it ensured steric stability. At CNaBr = 0.25 M, a higher electrostatic intermicellar repulsion and intercomplex repulsion induced by a large amount of bound DTAB micelles may lead to a redissolution of large colloidal complexes into intrapolymer complexes. Moreover, a salt-enhancing effect on the complex formation was observed in the PAM- b-PAA/DTAB system; the critical surfactant concentration decreased with increasing salt concentration at CNaBr < 0.10 M. The salt-enhancing effect is due to the larger increase of interaction in comparison to the screening of the interaction.     

反离子对胶团生长影响的研究

本文采用粘度法研究反离子对胶团生长的影响。通过粘度测量, 利用Missel等提出的热力学模型, 求算了支配球-棒转变的平衡常数K和胶团的重均聚集数n_w. 同价反离子促使溴化十四烷基吡啶胶团长大的能力为ClO_3~->NO_3~->Br~-. 在0.5 molL~(-1)的NaBr和KNO_3的介质中, 参数K在一定的胶团浓度范围内保持为常量, K值与n_W值随活性剂浓度的变化, 与光散射相应结果相当一致; 在0.5 molL~(-1)KClO_3介质中, K值明显地有浓度依赖性, 所得n_W值两法相差较大, 上述模型不再适用。     

Intermolecular interaction of actin revealed by a dynamic light scattering technique

The intermolecular interaction force of actin was studied by a dynamic light scattering technique. The mutual diffusion coefficients (D) of monomeric actin were accurately determined in a G-buffer with a low concentration of KCl from 0 to 10 mM. The translational diffusion coefficient was obtained as D(0) = (87 +/- 3) x 10(-12) m(2).s(-1) at 25 degrees C and pH 7.4, which gives a hydrodynamic radius of monomeric actin of r(H) = 2.8 +/- 0.1 nm. The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, assuming electrostatic and van der Waals potentials, failed to describe the change in interaction parameter (lambda) with KCl concentration, but the extended DLVO theory succeeded if an additional repulsive potential was assumed. The Hamaker constant of actin in the Ca(2+)-ATP bound state was determined for the first time as A(H) = 10.4 +/- 0.6 k(B)T.