Study on the interaction between nucleic acids and cationic surfactants

The interactions of nucleic acids and cationic surfactants (cetylpyridine bromide (CPB) and cetyltrimethylammonium bromide (CTMAB)) in aqueous solution have been studied using the techniques of resonance light scattering (RLS) spectroscopy, the absorption spectroscopy, zeta potential assay and NMR assignment measurement. It is considered that CPB or CTMAB can assemble on the surface of nucleic acid via electrostatic and hydrophobic forces, which results in the formation of large associate of nucleic acid-cationic surfactant and RLS enhancement of nucleic acid. Besides these forces, the pi-pi stacking force between CPB and nucleic acid also exists in the associate. In comparison with CTMAB, CPB has larger enhancement on RLS of nucleic acid, which is attributed to that the enhancement of the former is only due to the absorption of the bases of nucleic acid, while the enhancement of the latter is own to the synergetic resonance caused by the absorption of both bases of nucleic acid and the pyridyl in CPB. These results have important implication for understanding the influence of surfactants on nucleic acid functionality in life science.     

A spectrophotometric flow procedure for the determination of cationic surfactants in natural waters using a solenoid micro-pump for fluid propulsion

An automatic flow-analysis procedure for spectrophotometric determination of cationic surfactants in surface water using a solenoid micro-pump for propelling solutions of reagents and sample is described. The proposed method is based on a ternary formation complex between chromazurol S, the Fe(III) ion, and the cationic surfactant. The flow network comprised four solenoid micro-pumps controlled by a microcomputer, which performed the sampling step by loading a reaction coil with sample and reagent solutions and displacing the sample zone through the analytical path. The system is simple, easy to operate, and very flexible, with sufficient sensitivity to determine cationic surfactants in water without any pre-concentration or separation step. After determining the best operational conditions, favourable features such as a linear response between 0.34 and 10.2?mg?L^?1 of surfactant (R?=?0.999), a relative standard deviation of 0.6% (n?=?11) for a sample containing 3.4?mg?L^?1 of surfactant, a detection limit of 0.035?mg?L^?1 of surfactant, and a sampling throughput of 72 determinations per hour were achieved. The system was used to determine cationic surfactant in river-water samples, and recovery values between 91 and 106% were achieved.     

Mixed micelles of series of monomeric and dimeric cationic, zwitterionic, and unequal twin-tail cationic surfactants with sugar surfactants: a fluorescence study

Steady state fluorescence measurements have been carried out for binary mixtures of a series of monomeric cationic (MC), zwitterionic (ZI), dimeric cationic (DC), and twin-tail cationic (TC) surfactants with sugar (beta-C8G and beta-C12G) over the whole mole fraction range using pyrene as fluorescence probe. The cmc values thus determined for all the binary mixtures have been further evaluated using the regular solution theory. The various micellar parameters, such as micelle mole fraction (X1), regular solution interaction parameter (beta), micropolarity, and mean micelle aggregation number (Nagg), have been determined for all these series of mixtures. Variation in all these micellar parameters demonstrates that mixed micelles of these surfactants with beta-C8G are mostly synergistic in nature and the synergism increases with the increase in hydrophobicity of the cosurfactant in each case. The mixtures of beta-C12G with various cosurfactants do not show this behavior and instead of it, they show an increase in antagonism with the increase in hydrophobicity of cosurfactants. This discrepancy has been attributed to a large difference in hydrophobicity between beta-C8G and beta-C12G, and the chain folding of the latter is considered to be the reason for the antagonism.     

Spectrophotometric study of reactions of scandium,ytrium and lanthanum ions with some triphenylmethane dyes in the presence of cationic surfactants

Optimum conditions for the formation of ternary complexes of scandium, ytrium and lanthanum ions with chrome azurol S, eriochrome cyanine R and pyrocatechol violet in the presence of cetyltrimethylammonium, cetypyridinium and tetradecyldimethylbenzyl-ammonium (zephiramine) ions are described. The spectrophotometric determination of scandium with chrome azurol S and zephiramine exhibits the greatest sensitivity (? = 1.50 × 10⁵ l mol^?1 cm^?1 at 610 nm). In the spectrophotometric determination of scandium with eriochrome cyanine R and cetylpyridinium ion (? = 9.2 × 10⁴ at 600 nm), the interference caused by yttrium is the least. In the best method for yttrium (with pyrocatechol violet and zephiramine), the molar absorptivity is 3.3 × 10⁴ at 660 nm. Lanthanum does not form ternary complexes of analytical interest in these systems. Some aspects of the formation of ternary complexes with cationic surfactants are discussed.     

Partial least-squares regression for the simultaneous determination of aluminum and beryllium in geochemical samples using xylenol orange

A partial least-squares regression (PLS) was developed for the simultaneous spectrophotometric determination of aluminum and beryllium in geochemical samples by xylenol orange as the chromogenic reagent in water media and in micellar media. The effects of pH, xylenol orange concentration and surfactant concentration on the complexes formation reactions were studied. In the absence of surfactant the complex color development takes place at 2 h after mixing the reagents. By using CTAB as micellar media the complexes formation was improved and the rate of the complexation reactions increased. By using PLS-1 algorithm satisfactory results were obtained. The proposed procedure showed to be useful for prediction of Al and Be values from 0.1 to 1.0 mg L(-1).     

Spectrophotometric study of the formation of ternary complexes of iron(III) with some triphenylmethane dyes and cationic surfactants

The optimum conditions have been found for the formation of the ternary complexes of iron(III) with Chrome Azurol S (CAS), Eriochrome Cyanine R, and Pyrocatechol Violet in the presence of cetyltrimethylammonium (CTA), cetylpyridinium, or tetradecyldimethyl-benzylammonium ions. The pH range of the complex formation is limited mainly by the pertinent hydrolysis constants of the metal ions. The maximum absorbances were obtained for excess R and cationic surfactants, ensuring the formation of complexes with the highest R:Fe molar ratio. The method based on the Fe-CAS-CTA system (ε = 1.32 × 10⁵ liter mol⁻¹ cm⁻¹ at 628 nm) is most sensitive and is recommended for the spectrophotometric determination of iron.     

Micelle-mediated extraction for simultaneous spectrophotometric determination of aluminum and beryllium using mean centering of ratio spectra

A new micelle-mediated extraction method for preconcentration of ultra-trace quantities of beryllium and aluminum as a prior step to their simultaneous spectrophotometric determination has been developed. Chrome Azurol S (CAS), cetyltrimethylammonium bromide (CTAB) and Triton X-114 were used as chelating agent, cationic surfactant for extraction and co-extraction agent, respectively. Mean centering (MC) of ratio spectra has been used for simultaneous analysis of beryllium and aluminum. The optimal extraction and reaction conditions were studied, and the analytical characteristics of the method (e.g., limit of detection, linear range, preconcentration, and improvement factors) were obtained. Linearity was obeyed in the range of 5-40 ng mL⁻¹ of beryllium and 3-100 ng mL⁻¹ of aluminum. The detection limit of the method is 0.98 and 0.52 ng mL⁻¹ for beryllium and aluminum, respectively. The interference effect of some anions and cations was also tested. The method was applied to the simultaneous determination of beryllium in water samples.     

Amperometric determination of nitrite using natural fibers as template for titanium dioxide nanotubes with immobilized hemin as electron transfer mediator

A sensing device was constructed for the amperometric determination of nitrite. It is based on the use of titanium dioxide (TiO₂) nanotubes template with natural fibers and carrying hemin acting as the electron mediator. A glassy carbon electrode (GCE) was modified with the hemin/TNT nanocomposite. The electrochemical response to nitrite was characterized by impedance spectroscopy and cyclic voltammetry. An amperometric study, performed at a working potential of + 0.75 V (vs. Ag/AgCl), showed the sensor to enable determination of nitrite with a linear response in the 0.6 to 130 μM concentration range and with a 59 nM limit of detection. Corresponding studies by differential study voltammetry (E_p?=?0.75 V) exhibited a linear range from 0.6?×?10^?6 to 7.3?×?10^?5 M with a limit of detection of 84 nM. The sensing device was applied to the determination of nitrite in spiked tap and lake water samples.

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Graphical abstract Natural fibers templated synthesis of TNT immobilized hemin as electron transfer mediator for quantitative detection of nitrite with detection limit of 59 nM and good electrochemical sensitivity and the method can be used for quantitative determination of nitrite in water samples.

     

Trace humic and fulvic acid determination in natural water by cloud point extraction/preconcentration using non-ionic and cationic surfactants with FI-UV detection

A preconcentration and determination method for humic and fulvic acids at trace levels in natural water samples was developed. Cloud point extraction was successfully employed for the preconcentration of humic acid (HA) and fulvic acid (FA) prior to the determination by using a flow injection (FI) system coupled to a spectrophotometric UV-Vis detector. The quantitative extraction of HA and FA within the pH range 1-12 was obtained by neutralization of the anionic charge on the humic substances with a cationic surfactant, hexadecyltrimethylammonium bromide (CTAB). This generated a hydrophobic species that was subsequently incorporated (solubilized) into the micelles of a non-ionic surfactant polyethylene glycol, tert-octylphenyl ether (Triton X-114). The FI method for HA and FA determination was developed by injection of 100 microl of the extracted surfactant-rich phase using an HPLC pump with spectrophotometric detection at 350 nm. A 50 ml sample solution preconcentration allowed an enrichment factor of 167. The limit of detection (LOD) obtained under the optimal conditions was 5 microg l(-1). The precision for ten replicate determinations at 0.2 mg l(-1) HA was 3.1% relative standard deviation (RSD), calculated from the peak heights. The calibration using the preconcentration system for HA and FA was linear with a correlation coefficient (r2) of 0.9997 at levels near the detection limits up to at least 1 mg l(-1). The method was successfully applied to the determination of HA and FA in natural water samples (river water).     

Effect of metal ions on the determination of polymer flocculants using triphenylmethane dyes

Transition and heavy metals interfere with the spectrophotometric determination of flocculants based on the formation of their ion associates with triphenylmethane dyes (TPM). The absorption band of metal complexes with these reagents overlaps the absorption band of the associates; moreover, metal ions enhance the absorption of the associate. The increase in sensitivity is accompanied by a decrease in repeatability; therefore, the detection limits of flocculants change insignificantly. In the determination of flocculants in water at a level of 1 mg/L and above, these metals should be separated or masked in advance.     

Extraction and separation of cationic surfactants from river sediments: application to a spectrophotometric determination of cationic surfactant in an aquatic environment using membrane filters.

The quantitative extraction of cationic surfactant (CS+) in river sediments was studied. Further, the developed method was applied to the spectrophotometric determination of CS+ in urban river sediment samples by solid-phase extraction with membranes. A mixture of methanol and hydrochloric acid was proposed as an eluent. Dried sediment was digested in the eluent under ultrasonic irradiation. After elution, the eluent was evaporated to almost dryness. The residue was dissolved in a small volume of methanol and diluted to a certain volume with water. The pH of the solution was adjusted to 4-5 to separate iron and some other metals as precipitates of hydroxides. The solution was passed through two-piled membranes: first glass-fiber and then polytetrafluoroethylene (PTFE) membranes. A small volume of methanol was passed through the membranes to elute any CS+ retaining on the membranes. After passing the methanol solution through a cationic exchange resin column, the retained CS+ was eluted with methanol containing a high concentration of sodium chloride. Water, Bromophenol Blue (BPB) and hydrochloric acid were added to the solution. The solution was passed through a mixed cellulose ester membrane filter to retain an ion associate of CS+.BPB-. The retained ion associate was dissolved in a small volume of N,N-dimethylformamide together with the membrane filter, followed by the addition of triethanolamine to make the solution alkaline. The absorbance due to BPB2- was measured at 603 nm against a reagent blank. This method was applied to the determination of CS+ in river water and sediment. A cationic surfactant in sediments at 10(-5) mol kg-1 levels was detected with satisfactory precision. It was found that CS+ was about 500-fold enriched in the sediment from water at the place where domestic wastewater was discharged.     

Formation of ternary ion associates using diprotic acid dyes and its application to determination of cationic surfactants

A sensitive and selective method is described for the determination of cationic surfactants, such as benzethonium, benzalkonium, cetylpyridinium and trimethylstearylammonium, based on the formation and extraction of ternary ion associates with an acid dye (bromophenol blue or bromochlorophenol blue) and quinidine. Quinidine reacts with divalent anionic dyestuffs to form a bulky 11 complex anion, which is extractable into 1,2-dichloroethane as ternary ion associates with cationic surfactants in nearly neutral media. The ternary ion associate gives a blue product. Linearity of the calibration curve is improved and the extractability of the cationic surfactants is enhanced in the presence of quinidine. In addition, many other amines do not interfere with the determination. The blue ion associates can be used for the selective and sensitive spectrophotometric determination of cationic surfactants.     

Non-extraction batchwise and FIA determination of cationic and nonionic surfactants using Cu(II)-chromazurol S-surfactant complexes

Batchwise and FIA determinations have been developed for cationic and nonionic surfactants, based on the formation of ternary Cu(II)-chromazurol S-surfactant compounds. Optimum reaction conditions have been found (pH 8.0, lambda=590 and 630 nm, respectively). For the batchwise measurement, the molar absorption coefficient values epsilon(590)=5.1-5.7x10(4) l mol(-1) cm(-1) for cationic surfactants, epsilon(630)=0.7-1.5x10(4) l mol(-1) cm(-1) for nonionic surfactants. A factorial design has been carried out to determine the optimum flow conditions. Calibration curves were constructed and statistically evaluated for both the batchwise and FIA determination. For example, the linear concentration ranges for batch determination of the cationic surfactant cetyltrimethylammonium bromide and nonionic surfactant Marlophen NP 10 are 0-15 mug ml(-1) (R=0.9996, R.S.D.=6.62-0.64%) and 13-53 mug ml(-1) (R=0.9993, R.S.D.=4.48-1.40%), respectively; the respective detection limits are 0.02 and 4.0 mug ml(-1). For FIA determination of the same surfactants, the linear concentration ranges are 0-13 mug ml(-1) (R=0.9995, R.S.D.=4.44-0.49%) and 66-397 mug ml(-1) (R=0.9994, R.S.D.=8.92-1.12%), respectively, detection limits are 0.08 and 38 mug ml(-1), respectively.     

Simultaneous determination of natural and synthetic estrogens by EKC using a novel microemulsion

A novel microemulsion based on sodium bis(2-ethylhexyl) sulfosuccinate (AOT) was developed for the simultaneous determination of natural and synthetic estrogens by microemulsion EKC (MEEKC). The microemulsion system consisted of 1.4% w/w AOT, 1.0% w/w octane, 7.0% w/w 1-butanol and 90.6% w/w 20 mM sodium salt of 3-(cyclohexylamino)-2-hydroxy-1-propanesulfonic acid (CAPSO) and 10 mM phosphate buffer at pH 12.5. A baseline resolution in the separation of estrone, 17beta-estradiol, estriol, estradiol 17-hemisuccinate, etinilestradiol, estradiol 3-benzoate, and estradiol 17-valerate was achieved in comparison to the traditional MEEKC system with SDS in less than 15 min. The optimized electrophoretic conditions included the use of an uncoated-silica capillary of 60 cm of total length and 75 microm id, an applied voltage of 25 kV, a temperature of 25 degrees C and 214 UV-detection. Parameters of validation such as specificity, linearity, accuracy, LOD, LOQ and robustness were evaluated according to international guidelines. Due to its simplicity, accuracy, and reliability, the proposed method can be an advantageous alternative to the traditional methodologies for the analysis of natural and synthetic estrogens in different pharmaceutical forms.     

Spectrophotometric determination of cationic and anionic surfactants with anionic dyes in the presence of nonionic surfactants,part I: A general aspect

The behavior of color development of anionic azo dyes, methyl orange and its analogues, was examined in aqueous media by changing the microenvironment of the dyes. The addition of alcohols, organic onium ions, anionic surfactants and nonionic surfactants brought about a decrease of the band at wavelengths near 480 nm and an increase of the band at wavelengths near 420 nm. Such a shift toward the shorter wavelengths in spectra was attributed to the change of the micro-environment around the dyes from a polar field to a less polar field; that is, the shift is caused by the change of the contribution of the following resonance forms, On the basis of the color change phenomena, the spectrophotometric methods for the determination of organic onium ions and anionic surfactants were proposed.     

Fluorescence enhancement method for the determination of nucleic acids using cationic cyanine as a fluorescence probe

A fluorescence enhancement method with a cationic cyanine as a probe was developed for the determination of nucleic acids. Under the experimental conditions, the fluorescence enhancement of cyanine (lambda(ex)/lambda(em)= 524/591.5 nm) was observed in the presence of DNA. The calibration graphs were linear over the range of 0.01-15 microg mL(-1) for both calf thymus DNA (CT DNA) and fish sperm DNA (FS DNA). The limits of detection were 0.005 and 0.007 microg mL(-1) for CT DNA and FS DNA, respectively. The method was applied to the determination of DNA in synthetic and real samples and satisfactory results were obtained. A possible fluorescence enhancement mechanism was also studied.     

Effect of cationic gemini surfactants on the hydrolysis of carboxylate and phosphate esters using hydroxamate ions

The kinetics of the hydrolysis of p-nitrophenyl acetate (PNPA) and p-nitrophenyl diphenyl phosphate (PNPDPP) by hydroxamate ions mediated by gemini surfactants with quaternary ammonium bromide (16-n-16,2Br⁻, n = 3, 4, 6, 12) and pyridinium chloride (12py-n-py12,2Cl⁻, n = 3, 4) head group have been investigated at 27 °C. The gemini surfactant with the pyridinium head group, 12-py-4-py12,2Cl⁻ (tetramethylene-1,4 bis dodecylpyridinium chloride) shows a large rate acceleration effect than that with an ammonium head group, 16-12-16,2Br⁻, relative to those in water. The apparent pK _a of the hydroxamic acids have been determined in the presence of gemini surfactants. Catalytic system N-phenylbenzohydroxamate/12py-4-py12,2Cl⁻ demonstrated over ~1,590-fold and ~255-fold rate enhancement in the hydrolysis of PNPA and PNPDPP, respectively, for the identical reaction performed in buffer aqueous media at 27 °C. The second order rate constant and binding constants for reactions were determined employing pseudophase model for micellar catalysis.