Influence of various series of additives on the clouding behavior of aqueous solutions of triblock copolymers

The cloud point (CP) studies on aqueous solutions of two ethylene oxide-propylene oxide triblock copolymers (EO)_2.5(PO)₃₁(EO)_2.5 and (EO)₁₃(PO)₃₀(EO)₁₃ with varying number of ethylene oxide (EO) units were carried out in the presence of series of additives, such as alkali, acids, ionic surfactants, alcohols, salts, and hydrotropes. The results of this study show that sodium hydroxide decreases the CP of the two copolymers. Acids increase the CP in the order hydrochloric acid > acetic acid > formic acid for both the triblock copolymers. Hydrotropes increase the CP, whereas salts decrease or increase the CP based on their salting-out/salting-in nature. Alcohols, which are polar organic additives, affect the CP of the two copolymers differently. The change in the CP of the triblock copolymers depends upon the structure and concentration of the additives and on the number of EO units of the two triblock copolymers.     

Influence of additives on the clouding phenomenon of chlorpromazine hydrochloride solutions

Herein we report the effect of various additives (viz. alcohols, cycloalcohols, amino acids, sugars, ureas) on the clouding phenomenon observed in 50mM chlorpromazine hydrochloride (CPZ) drug solutions (prepared in 10mM sodium phosphate buffer). Long chain alcohols (except octanol), cyclohexanol and allylalcohol increased the cloud point (CP) followed by a decrease with the increase in alcohol concentration but short chain alcohols affected the CP insignificantly. Effect of amino acids depended upon their nature: acidic and salts of basic amino acids increased the CP while basic amino acids depressed it; non-polar and uncharged polar amino acids caused small changes in CP. Additives of urea family decreased the CP. All sugars caused a decrease in CP, which is in consonance to their effect on the critical micellar concentration. The overall behavior is explained on the basis of additives affecting the solvent as well as micelle aggregation and/or structure.     

Role of surfactants in clouding phenomenon of imipramine hydrochloride

The clouding behavior of tricyclic antidepressant drug imipramine hydrochloride (IMP) in aqueous solution has been studied in presence of surfactants. A pH increase in the presence as well as in the absence of surfactants decreased the CP. Drug molecules become neutral at high pH and therefore head–head repulsion decreases which lead to CP decrease. Addition of non-ionic and cationic surfactants increased the CP whereas anionic surfactants showed a peaked profile. Effect of CTAB/TX-100 at different fixed drug concentrations showed that at all surfactant concentrations the CP value was higher for higher drug concentrations. However, variation of pH produced opposite effect: CP at all CTAB/TX-100 concentrations decreased with increasing pH. All results are interpreted in terms of increase in hydrophobicity or hydrophilicity of micelles on addition of surfactants.     

Influence of Electrolytes on the Micellar Growth of Amphiphilic Drug Chlorpromazine Hydrochloride

The effect of electrolytes on the micellar behavior of an amphiphilic drug, chlorpromazine (CPZ) hydrochloride, was studied using cloud point (CP) and dye solubilization techniques. In the presence of KBr, increase in pH led to decrease in the CP of 50 mmol·L_-1 drug solution (prepared in 10 mmol·L_-1 sodium phosphate (SP) buffer) because of deprotonation of drug molecules at high pH. The visible absorbance increased (due to dye solubilization) with the increase in pH from 6.5 to 6.9, which indicated micellar growth. At fixed pH (6.7), addition of inorganic salts (KF, KCl, and KBr) to drug solutions (50 mmol·L_-1) caused an increase in the CP as well as in the visible absorbance, with effectiveness being in the order: F_- < Cl_- < Br_-. The results were discussed on the basis of counter-ion binding and their effect toward micellar growth. Cations (co-ions) also led to an increase in the CP (and also the visible absorbance), with their effectiveness order being Li₊ > Na₊ > K₊, which was explained by considering cognizance of their hydrated radii. Compared with anions, their effect was small. Increase in [CPZ] caused micellar growth and hence the CP as well as the visible absorbance increased. The overall behavior was discussed in terms of electrostatic interactions and micellar growth.     

Micellization and Clouding Phenomenon of Phenothiazine Drug Promethazine Hydrochloride: Effect of NaCl and Urea Addition

Herein we report the micellization and clouding behavior of promethazine hydrochloride (PMT) in absence and presence of NaCl/ureas. The critical micelle concentration (CMC) of PMT is measured by conductivity method and the values decrease with increasing the NaCl concentration. With increasing the temperature, the CMC first increases then decreases. At 25°C, the maximum CMC values were obtained (with or without NaCl). The thermodynamic parameters are evaluated which indicate more stability of the PMT solution in presence of NaCl. PMT shows phase separation also. The cloud point (CP) of PMT decreases with increase in pH due to deprotonation of the drug molecules. Ureas decreased the CP and the behavior is explained on the basis of removal of water from the head group region.     

电解质对两性药物分子盐酸氯丙嗪的胶团生长的影响

The effect of electrolytes on the micellar behavior of an amphiphilic drug,chlorpromazine(CPZ)hydroehloride,was studied using cloud point(CP)and dye solubilization techniques.In the presence of KBr,increase because of deprotonation of drug molecules at high pH. The visible absorbance increased(due to dye solubilization)with the increase in pH from 6.5 to 6.9,which indicated micellar growth.At fixed pH(6.7),addition of inorganic salts(KF,KC1,effecfiveness being in the order:F-Na >K ,which Was explained by considering cognizance of their hydrated radii.Compared with anions,their effect was small.Increase in[CPZ]caused micellar growth and hence the CP as well as the visible absorbance increased.The overall behavior Was discussed in terms of electrostatic interactions and micellar growth.     

Influence of additives on the clouding behavior of amphiphilic drug solutions

The present work focuses on the clouding phenomenon in an amphiphilic drug [amitriptyline (AMT), which is a tricyclic antidepressant] solution. A 50-mM AMT solution prepared in 10 mM of sodium phosphate (SP) buffer was taken where the cloud point (CP) was found to decrease with increasing pH. The same CP decreasing trend (with pH increase) followed in the presence of a fixed concentration (50 mM) of added salts [NaBr, and tetra-n-butylammonium bromide (TBuAB)]. The addition of increasing amounts of quaternary bromides (tetramethylammonium bromide, tetraethylammonium bromide, tetra-n-propylammonium bromide, TBuAB, and tetra-n-pentylammonium bromide) to 50 mM of AMT solution (prepared in 10 mM of SP buffer) caused continuous increase in CP, which was found to be dependent upon the alkyl chain length of that particular salt. The similar type of CP increase was also observed in the presence of conventional (cetyltrimethylammonium bromide and tetradecyltrimethylammonium bromide) and gemini surfactants [bis(hexadecyldimethylammonium)hexane, bis(hexadecyldimethylammonium)pentane, and bis(hexadecyldimethylammonium)butane]. The overall behavior was discussed in terms of electrostatic interactions, micellar growth, and mixed micelle formation.     

Construction of three-dimensional/one-dimensional heterostructure of flower-like Sr nanoflowers on Se microrods decorated on reduced graphene oxide: an efficient electrocatalyst for oxidation of promethazine hydrochloride

Three-dimensional (3D) strontium flowers were grown on well-defined one-dimensional (1D) selenium microrods using a simple hydrothermal technique at 180 °C. This resulted in the formation of a unique 3D/1D material which was ultrasonically treated with reduced graphene oxide to form a hybrid composite. The structural and functional analysis were performed using X-ray diffraction spectroscopy which rendered the material as pure and crystalline and Fourier transform infrared spectroscopy, respectively. X-ray photoelectron spectroscopy was performed to unravel the elemental composition and successful formation of the composite. Field emission scanning electron microscopy and transmission electron microscopy were performed to study the unique morphological features of the material. It was further used to fabricate a sensor for the detection of promethazine hydrochloride (PMZH) drug. The sensor showed a very low detection limit of 7.7 nM at a linear working range of 0.99 μM–900 μM and a sensitivity of 5.282 μA μM^?1 cm^?2. The sensor showed an excellent analyte recovery rate for real-time analysis in biological and environmental samples. The results suggested that the sensor is effective for the detection of PMZH with feasibility for future commercialization.     

Effects of additives on the cloud points of selected nonionic linear ethoxylated alcohol surfactants

Effects of various additives including inorganic salts, nonionic and ionic surfactants, water-soluble polymers and alcohols on the cloud points of three linear nonionic surfactants, Tergitol 15-S-7, Tergitol 15-S-9 and Neodol 25-7, were investigated. These surfactants are readily biodegradable and either linear primary or secondary ethoxylated alcohols. Cloud points of these surfactants were functions of their concentrations and concentrations of additives. The cloud points of nonionic surfactant mixtures lay in between the cloud points of individual component surfactants. Presence of two ionic surfactants, sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB), increased the cloud point of 1 wt% Tergitol 15-S-7 micellar solution dramatically when concentrations of ionic surfactants approaching their critical micelle concentration. Addition of water-soluble polymers decreased the cloud point, while addition of inorganic salts can either increase or decrease the cloud points. However, the effect of an alcohol additive on cloud point was dependent on its chain length or its water solubility. Interestingly, synergistic effects between sulfate or phosphate and pentanol on depression of cloud points of Tergitol 15-S-9 were discovered. A linear model predicting cloud points of Tergitol 15-S-X (X = 7, 9 and 12) surfactants and Neodol 25-X (X = 7, 9 and 12) surfactants were proposed with a correlation to logarithm of their ethylene oxide numbers.     

Enantioseparation of various amino acid derivatives on a quinine based chiral anion-exchange selector at variable temperature conditions. Influence of structural parameters of the analytes on the apparent retention and enantioseparation characteristics

The influence of temperature on the performance of an enantioselective anion-exchange type chiral selector (SO) was systematically investigated. The resolution of the enantiomers of 23 N-acylated amino acids (selectands, SAs) on a covalently immobilized quinine tert.-butylcarbamate chiral stationary phase (CSP) was studied under linear chromatographic conditions over a temperature range of 0–85 °C with hydro–organic buffers (pH_a 6.0) as mobile phases. The apparent enantioseparation factors increased considerably at low column temperatures, indicating that enthalpic contributions are the dominating thermodynamic driving force for chiral recognition for all investigated SAs. Retention factors gave non-linear van’t Hoff plots, while the corresponding apparent enantioseparation factors showed linear van’t Hoff behavior. Correlations between magnitude and sign of the relative thermodynamic parameters of enantioselective adsorption (ΔΔG, ΔΔH and ΔΔS) and specific structural features of the analytes, i.e., steric and electronic nature of the various side chains and the N-acyl groups, are discussed with the aim to rationalize their possible contributions to the overall chiral recognition.     

Effect of hydrotropes on the solution behavior of PEO/PPO/PEO block copolymer L62 in aqueous solutions

Effect of hydrotropes viz. sodium benzene sulfonate (NaBS), sodium toluene sulfonate (NaTS) and sodium xylene sulfonate (NaXS) on the micellization, phase behavior and structure of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer L62 in aqueous solution was studied by surface tension, dye spectral, cloud point and small angle neutron scattering measurements. The addition of hydrotropes increased the critical micelle concentration (CMC) of L62 which appears to be logistic as the added hydrotrope enhances the solubility of PPO moiety (and PEO) making it behave like a more hydrophilic block copolymer that would micellize at high copolymer concentration. Partial phase diagram of L62 in water shows two cloud point (CP) in the concentration range (0-10 wt.%). Addition of hydrotropes shifts the L62 concentration range showing double cloud points at lower side of concentration; sodium xylene sulfonate (NaXS) being more effective. SANS data for L62 in the presence of 0.4 and 0.8 M NaXS at temperatures <30 °C showed unimers which are fully dissolved Gaussian chains. The unimer-to-micelle transition takes place when temperature is increased. It is found that SANS data for L62 in the presence of 0.4 M NaXS (40 and 50 °C) and 0.8 M NaXS (45 and 50 °C) correspond to ellipsoidal structure of micelles.     

Comparison of the chiral resolution on cis-trans isomeric chiral stationary phases derived from (S)-1-(1-naphthyl)ethylamine

A pair of cis-trans isomeric chiral stationary phases (CSPs) derived from (S)-1-(1-naphtyl)ethylamine was prepared. The chromatographic behaviours on both CSPs with regard to the resolution of enantiomeric amino acids, amino alcohols, amines, and carboxylic acid were studied. According to separation factors, the trans-CSP showed better chiral recognition ability for the separation of most analytes chosen in this study. Three homologous series of the alkyl esters of racemic amino acids were resolved on both CSPs using n-hexane-2-propanol and n-hexane-dichloromethane as mobile phases. The trans-CSP also showed better enantioselectivity for the resolution of homologues. A reverse of elution order was observed for the resolution of the homologous series of phenylglycine alkyl esters on both CSPs. It was found that the relationship between the separation factor and the alkyl chain length of the ester homologous series depended upon the components of mobile phase. A higher magnitude of difference between the two CSPs in enantioselectivity for the resolution of a given homologue was obtained when n-hexane-dichloromethane was used as a mobile phase. A chiral recognition process, in which steric repulsion, face-to-face π-π interaction, face-to-edge π-π interaction and hydrogen bonding interaction were involved, was also suggested to describe the separation of enantiomeric homologues on both CSPs. This study clearly indicates that the chiral resolution is influenced by the geometry of the double bond in a CSP.     

Comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry detection: analysis of amino acid and organic acid trimethylsilyl derivatives, with application to the analysis of metabolites in rye grass samples

First, standard mixtures of trimethylsilyl (TMS) derivatives of amino acid and organic acid are analyzed by comprehensive two-dimensional (2D) gas chromatography (GC) coupled to time-of-flight mass spectrometry (GC × GC/TOFMS) in order to illustrate important issues regarding application of the technique. Specifically of interest is the extent to which the peak capacity of the 2D separation space has been utilized and the procedure by which the derivative standards are identified in the 2D separations using the mass spectral information. The resulting 2D separation is found to make extensive use of the GC × GC separation space provided by the complementary stationary phases employed.Second, in order to demonstrate GC × GC/TOFMS on two real sample types, trimethylsilyl metabolite derivatives were analyzed from extracts of common lawn grass samples (i.e., perennial rye grass), as a means to provide insight into both the pre and post harvest physiology. Various chemical components in the two rye grass extract samples were found to either emerge or disappear in relation to the trauma response. For example, a significant difference in the peak for the TMS derivative of malic acid was found. The successful analysis of various components was readily facilitated by the 2D separation, while a 1D separation would have produced too much peak overlap, thus impeding the analysis. The importance of using a GC × GC separation approach for the analysis of complex samples, such as metabolite extracts, is therefore demonstrated. The real-time analysis capability of GC × GC/TOFMS for multidimensional metabolite analysis makes this technique well suited to the high-throughput analysis of metabolomic samples, especially compared to slower, stopped-flow type separation approaches.     

Influence of alkoxyethanols on the mixed micelle formation by hexadecyltrimethylammonium bromide and tetradecyltrimethylammonium bromide surfactant mixtures

 The conductances of hexadecyltrimethylammonium bromide (HTAB) and tetradecyltrimethylammonium bromide (TTAB) mixtures over the entire mole fraction range of HTAB were measured in aqueous binary mixtures of ethylene glycol monomethyl ether, monoethyl ether, and monobutyl ether, and of diethylene glycol monomethyl ether and monoethyl ether containing 10–30 wt% additive in their respective binary mixtures at 30 °C. Each conductivity curve showed a single break over the whole mole fraction range of HTAB–TTAB mixtures. From the break in the conductivity curve, various micellar parameters were calculated and the results were discussed with respect to the alkoxyethanol's additive effect on the mixed micelle formation. The micellar parameters of HTAB, TTAB, and of their mixtures showed a strong dependence both on the amount as well as on the number of repeating units in the presence of ethylene glycol derivatives, whereas a significant dependence only on the amount of additive was observed in aqueous diethylene glycol derivatives. The results in the former case were attributed to the hydrophobic hydration of the mixed micelles by the ethylene glycol derivatives, which showed a large dependence on the increase in the alkyl chain length of the additive. The hydrophobic hydration was considerably reduced in the case of diethylene glycol derivatives owing to the presence of an extra ether oxygen. An evaluation of the nonideality in the HTAB–TTAB mixtures revealed that in spite of the strong hydrophobic hydration of the HTAB–TTAB mixtures by the alkoxyethanols, the mixed micelles remain almost free from the additive molecules. Received: 11 January 2000/Accepted: 14 April 2000     

The role of electrostatic interactions on the rejection of organic solutes in aqueous solutions with nanofiltration

The effects of electrostatic interactions on the rejection of organic solutes with nanofiltration membranes were investigated. For two different membranes, the rejection of selected organic acids, positively and negatively charged pharmaceuticals and neutral pharmaceuticals was investigated at different feed water chemistries (different ionic strengths and pH conditions, with and without the presence of NOM and divalent cations). It was concluded that for negatively charged membranes, electrostatic repulsion leads to an increase of the rejection of negatively charged solutes and electrostatic attraction leads to a decrease of the rejection of positively charged solutes, compared to neutral solutes. Neutral and positively charged solutes engage in hydrophobic interactions with negatively charged membranes, whereas negatively charged solutes do not engage in hydrophobic interactions since they cannot approach the membrane surface. This provides proof for the theory of an increased concentration of positively charged organic solutes and a decreased concentration of negatively charged organic solutes at the membrane surface compared to the bulk fluid. This concept may be denoted as “charge concentration polarisation”. The concept was further used as a modelling tool to predict the effects of electrostatic interactions on the rejection of trace organic solutes.     

Influence of alcohols on the lower consolute behavior and thermodynamic approach of Triton X-114 aqueous two-phase systems

The addition of foreign material to surfactants shows the change in temperature at which the clouding process occurs. This work evaluates the impact of n-alcohols on Cloud Point (CP) of nonionic surfactant Triton X-114 at variable concentrations. It was found that the CP of pure Triton X-114 shows concentration-dependent variation. The presence of lower alcohols improves CP value whereas the addition of higher alcohols brings down CP with variation as concentration increases. These effects can be clarified in view of the site of the impact of molecular design of added substances on the stability of micelle organization. The foaming ability and foam stability data are also used to discuss the stability of micellar accumulation. Considering CP as a threshold temperature of the solubility, the thermodynamic parameters of the clouding process ΔG⁰_cl, ΔH⁰_cl, and ΔS⁰_cl, have been assessed, using the “Phase Separation Model”. The outcomes of the work demonstrate that the clouding phenomenon of Triton X-114 is an exothermic and non-spontaneous process.     

Influence of the structure of amphiphilic anions on the Krafft temperature of micellar solutions of anionic surfactants

The influence of the structure of surfactants on the Krafft temperature T _k was studied for aqueous solutions of anionic surfactants containing the sulfate and sulfonate head groups, the hydrophilic (H) and lipophilic (L) fragments in amphiphilic anions, and various polar and C₈—C₁₈ hydrocarbon groups. The best statistical quality was obtained for the model with separate account of the effect of the H and L structural fragments on the T _k value.     

Effects of organic modifiers on the chiral recognition by different types of silica-immobilized bovine serum albumin

We prepared three columns containing bovine serum albumin immobilized on silica by different means and the effects of organic modifiers in the eluent on chiral separation were studied using N-substituted amino acids. Adsorption on silica, covalent immobilization to diol-silica with carbonyldiimidazole (CSP-II) and covalent immobilization to amino-silica with glutaraldehyde were studied. CSP-II had the highest stereoselectivity and was the most affected by organic modifiers in the eluent. The hydrophobicity of amino acid moiety affected the chiral recognition of N-benzoylamino acids and the aromaticity of the N-substituted group was important.     

Influence of the morphology and impurities of Ni(OH)2 on the synthesis of neutral Ni(II)–amino acid complexes

Synthesis of neutral complexes of Ni²⁺ with amino acids has often been reported on a qualitative basis, with a lack of information on the parameters involved in the dissolution of the nickel-containing solid precursor. This paper reports on a systematic study of the reactivity of Ni(OH)₂ toward glycine in aqueous solution. The crystallinity and size of hydroxide particles are found to be key parameters in the rapid glycine-promoted dissolution of the hydroxide and synthesis of [Ni(glycinate)₂(H₂O)₂]. These parameters derive from the nature of the salt used to prepare the hydroxide. Ni(II) chloride leads to the most reactive solid precursor, because of the presence of defects in the Ni(OH)₂ sheets arrangements, assigned to the substitution of Cl⁻ ions to OH⁻ ions at the edges of the particles. The reaction between this hydroxide and glycine at 80 °C is quantitative after 7 min and similar rates of dissolution are obtained with other amino acids, alanine or histidine, the reaction with serine being slower. When the hydroxide contains nitrate or carbonate ions, a glycinato complex with composition similar to [Ni(glycinate)₂(H₂O)₂], but with a different crystal structure, is also formed. Spectroscopic results may suggest a structure involving bridging ligands.