Electrochemical sensor for determination of butylated hydroxyanisole (BHA) in food products using poly O-cresolphthalein complexone coated multiwalledcarbon nanotubes electrode

In this study, we have reported an electrochemical sensor for the determination of butylated hydroxyanisole (BHA) by electropolymerization of O-cresolphthalein complexone (OC) over the multiwalled carbon nanotubes (MWCNTs). In order to confirm the surface morphology, oxidation states, functional groups and charge transfer property of POC/MWCNTs electrode, the resulting POC film with MWCNTs electrode was characterized by spectroscopy, microscopy, and electrochemical techniques. The fabricated electrode was evaluated for its electrochemical performance in oxidation of BHA and the study showed that at POC/MWCNTs electrodes BHA oxidation occurred at 0.27 V. POC/MWCNTs electrode has shown a linear range for the detection of BHA from 0.33 µM to 110 µM with the detection limit of 0.11 µM (S/N = 3). Amperometric determination of BHA was also done using chronoamperometric techniques and the result was found to be linear. The real time analysis of sensors is also validated by analysing the packed potato chips samples.

Structural and fluorescence properties of phenolphthalein bridged cyclotriphosphazatrienes

This study dealt with the reactions of hexachlorocyclotriphosphazatriene, N(3)P(3)Cl(6) (trimer) (1) with phenolphthalein (2) to give the phenolphthalein bridged compounds 3, 4 and 5. The phenolphthalein bridged cyclotriphosphazatriene derivatives are reported for the first time. The new compounds (3-5) are characterized by elemental analysis, mass spectrometry, UV-vis, FT-IR, (1)H, (31)P NMR and fluorescence spectroscopy. The more bridged phenolphthalein groups show the higher intensity of the absorption bands in the UV-vis spectra. Fluorescence spectrum of compound 3 shows a small band in the lower spectral range, while the spectra of compounds 4 and 5 show more intense and a band in higher spectral range.

Phosphorescent sensing of carbon dioxide based on secondary inner-filter quenching

A study of different strategies to prepare phosphorescence-based sensors for gaseous CO(2) determination has been performed. It includes the characterization of different configurations tested, a discussion of the results obtained and possibilities for the future. The optical sensor for gaseous CO(2) is based on changes in the phosphorescence intensity of the platinum octaethylporphyrin (PtOEP) complex trapped both on oxygen-insensitive poly(vinylidene chloride-co-vinyl chloride) (PVCD) membranes and PVCD microparticles, due to the displacement of the alpha-naphtholphthalein acid-base equilibrium with CO(2) concentration. A secondary inner-filter mechanism was tested for the sensor and a full range linearized calibration was obtained by plotting (I(100)-I(0))/(I-I(0)) versus the inverse of the CO(2) concentration, where I(0) and I(100) are the detected luminescence intensities from a membrane exposed to 100% nitrogen and 100% CO(2), respectively, and I at a defined CO(2) concentration. The different configurations tested included the use of membranes containing luminophore and pH-sensitive dye placed on two opposite sides of a transparent support to prevent the observed degradation of the PtOEP complex in the presence of the tetraoctylammonium hydroxide (TOAOH) phase transfer agent, which produced better results regarding stability and sensitivity. The CO(2) gas sensor based on PtOEP homogeneous membranes presented better properties in terms of response time and sensitivity than that based on PtOEP microparticles. With a detection limit of 0.02%, the response time (10-90% maximum signal) is 9 s and the recovery time (90-10%) is 115 s. The lifetime of the membranes for CO(2) sensing preserved in a 94% RH atmosphere and dark conditions is longer than at least 4 months.

Preconcentration of some trace elements via using multiwalled carbon nanotubes as solid phase extraction adsorbent

In present study preconcentration followed by solid phase extraction of heavy metal ions, Cu(II), Co(II), Ni(II) and Pb(II) using a multiwalled carbon nanotubes (MWNTs) and complexing reagent o-cresolphthalein complexone were investigated. The effects of parameters, including pH of the solutions, amounts of complexing reagent, eluent type, sample volume, flow rates of solution, and matrix ions, were examined for the optimum recoveries of the analyte ions. The preconcentration factor was 40. Detection limit (3s) obtained for the investigated metals in the optimal conditions were observed in the range of 1.64-5.68 microg l(-1). The validation of the presented method was obtained by the analysis of certified reference material HR 1 (Humber river sediment), the obtained results were agreed with certified values. The optimum experimental conditions that ensure the efficiency of the procedure have been investigated and have been successfully applied to the determination of trace elements in environmental samples with satisfactory results.

Interpreting steep dose-response curves in early inhibitor discovery

Many screening hits inhibit enzymes with steep dose-response curves, which are considered pathological. Three models might explain these curves: multisite binding, an inhibitor phase transition, or stoichiometric inhibition caused by a high enzyme to Kd ratio. Experiments with promiscuous aggregators, for which steep curves are common, suggest that these curves owe to stoichiometric inhibition, which predicts that IC50 should vary linearly with enzyme concentration. Most steep dose-response curves in screening may be due to this effect.

Coloured chlorhexidine cotton pads may help to identify cerebrospinal fluid during epidural or spinal anaesthesia

BACKGROUND

During complicated technical conditions in epidural or spinal anaesthesia, it may be difficult to safely identify the epidural space. The confirmation or exclusion of the presence of cerebrospinal fluid (CSF) during the procedure of regional anaesthesia is helpful to determine the position of the epidural needle in order to proceed with the anaesthetic block.

METHODS

We have examined how CSF and different anaesthetic solutions change the colour of yellowish phenol red absorbed in cotton pads.

RESULTS

Sodium chloride and local anaesthetic agents do not change the colour of yellowish phenol red. However, CSF immediately changes the colour from yellow to pink or red. Letting a drop of fluid from the epidural/spinal needle fall on to the cleaning pads filled with phenol red will enable the anaesthesiologist to immediately confirm the presence or absence of CSF. The higher pH of CSF relative to that of sodium chloride and local anaesthetic agents explains the different colour reaction.

CONCLUSION

This colour reaction quickly identifies the presence of CSF and thus the intradural space during the procedure of spinal or epidural anaesthesia.

[The reactions between acidic phenolsulfonphthaleins and human serum albumin]

The reactions between HSA and acidic phenolsulfonphthaleins, including phenol red, cresol red, chlorophenol red, bromocresol purple and m-cresol purple, have been investigated by fluorescence spectrometry. The experiments showed that all of the selected acidic phenolsulfonphthaleins strongly quenched the fluorescence produced by HSA, and this fluorescence quenching could be interpreted in terms of statistic quenching. From the calculation results of binding constants K for these dyes at various temperatures, it could be found that the increase in the functional groups numbers of dyes molecules resulted in an increase in K, while the increase in reaction temperature led to a decrease in K. The interactions between dyes and HSA were attributed to static-electricity gravitation, which was confirmed by the calculation results of enthalpy and entropy for these reactions. According to the non-radiation energy transfer theory, the distances and energy transfer efficiencies between dyes and protein at various temperatures were obtained. These results further supported the conclusion that these reactions belonged to the single static quenching caused by the energy transfer.

[Highly sensitive spectrophotometric determination of trace amounts tin in water by Sn(IV)-XO-PVA system]

A new spectrophotometric method for the determination of trace amount of tin (IV) has been developed based on the reaction of Sn (IV) with o-cresolphthalexon (XO), which forms a stable complex in the presence of polyvinyl alcohol (PVA). The complex exhibited a maximum absorbance at 544 nm. The molar absorption coefficient was 4.38 x 10(5) L.mol-1.cm-1. Recovery factor ranged from 97.4%-101.1%. Beers law was obeyed in the range of Sn 0.1-5 micrograms.(25 mL)-1. The complex was stable within 6 h. The suitable conditions for the reaction were investigated. The developed method has been applied to the determination of Sn (IV) in water samples. The result obtained is satisfactory.

Molecular structure and vibrational spectra of phenolphthalein and its dianion

Infrared (IR) and Raman spectra of phenolphthalein (PP) and its dianion form (sodium and potassium salts) were studied both in the solid state and in aqueous solution. Band assignments were carried out on the basis of the isotope shifts of the ring deuterated and 13C-substituted derivatives. Spectral analyses reveal that the PP dianion exists as mixtures of the benzenoid form (colorless) and the quinonoid form (colored) in the solid state and in aqueous solution, while the neutral PP solely takes the gamma-lactone form. This work provides the first vibrational spectroscopic evidence for the coexistence of the two species in the PP dianions.

Interference of magnetic resonance imaging contrast agents with the serum calcium measurement technique using colorimetric reagents

A possible interaction between either linear (Gd-DTPA-BMA and Gd-DTPA) or macrocyclic (Gd-DOTA) gadolinium complexes used as magnetic resonance imaging (MRI) contrast agents and colorimetric technique reagents for the measurement of serum calcium was evaluated on human serum pools, and its mechanism was investigated by means of UV spectrometry and electro-spray ionization mass spectrometry (ESI-MS). The highest concentration tested was 2.5 mM (corresponding to a putative strictly intravascular distribution of the compound) and the lowest dose was 0.2 mM (i.e. about two elimination half lives). Serum calcium was dosed in duplicate by conventional colorimetric techniques involving o-cresol-phthalein complexone (OCP) or methylthymol blue (MTB) as reagents. No interference was detected when mixing Gd DOTA with serum, whatever the concentration. Gd DTPA (2.5 mM) did not interfere with the colorimetric technique either. Conversely, the Gd DTPA-BMA solution induced a concentration-related variation in apparent calcium levels. In the UV experiments, solutions of 2.5 mM MRI contrast media were mixed with OCP or MTB and UV absorption spectra were recorded between 400 and 800 nm. For Gd-DOTA/OCP and Gd-DOTA/MTB, no significant variations in the absorbance were detected. However, in the presence of Gd DTPA BMA, the absorbance of OCP and MTB showed substantial and immediate variations over time. The ESI-MS studies showed a complete displacement of Gd3+ ion in the case of Gd-DTPA BMA. In the presence of OCP, we observed the disappearance of Gd-DTPA BMA and the formation of the free ligand DTPA BMA and a new complex Gd OCP with an original stoichiometry of 2/2. Such a phenomenon did not occur in the case of Gd DOTA and Gd DTPA. The decomplexation of Gd-DTPA BMA in the presence of OCP can probably be explained by the weaker thermodynamic stability of Gd-DTPA BMA compared to that of Gd-DOTA and Gd DTPA.

Bisphenols that stimulate cells to release alkali metal cations: a structure-activity study

The laxative action of phenolphthalein (5) is believed to result from induction of potassium and water efflux from the colon epithelium. In cultured cells, K+ efflux is promoted by 5 and by a contaminant (1) present in commercial phenol red. Six compounds with chemical structures related to those of 5 and 1 were tested for ability to induce the release of 86Rb from COS-7 cells preloaded with this isotope: 4,4'-(9-fluorenylidene)diphenol (2), 4, 4'-(9-fluorenylidene)dianiline, 4, 4'-(9-fluorenylidene)bisphenoxyethanol, 1,1'-bi-2-naphthol, 4, 4'-biphenol, and bis(4-hydroxyphenyl)methane. With one exception these compounds were all inactive at a concentration of 10 microM. However, 2 caused profound 86Rb efflux at concentrations as low as 100 nM. Concentrations of 5 1-2 orders of magnitude higher were needed to achieve similar levels of activity. The three compounds known to be active in this experimental system share a common feature that is absent in all the inactive compounds: a five-membered ring structure, one of whose carbon atoms is disubstituted with p-hydroxyphenyl residues. Because 2 and 5 are readily available, comparative studies on the mechanism of action of these biphenols at the cellular level can now be undertaken.

Phenolphthalein and 3',3"-dinitrophenolphthalein

Phenolphthalein, C20H14O4, crystallized in the noncentrosymmetric space group Pna2(1) with two crystallographically inequivalent molecules. Each of these is linked to four others of its own type by four hydrogen bonds having Odonor...Oacceptor distances ranging from 2.631 (4) to 2.787 (4) A. While chains of hydrogen bonds propagate in a number of directions in this structure, cyclic hydrogen bonding is not observed. 3',3"-Dinitrophenolphthalein, C20H12N2O8, crystallized in the centrosymmetric space group Pbcn with a single molecule in the asymmetric unit. Each molecule is linked to three others by four hydrogen bonds having Odonor...Oacceptor distances ranging from 2.572 (4) to 3.274 (3) A. Although chains of hydrogen bonds are prominent in this structure, cyclic hydrogen bonding also occurs and forms dimers. As expected on the basis of the excess of potential acceptor O atoms over donors in both structures, significant C-H...O interactions are also abundant.

Cell-transforming activity and genotoxicity of phenolphthalein in cultured Syrian hamster embryo cells

Phenolphthalein is a cathartic agent widely used in non-prescription laxatives. For the simultaneous assessment of in vitro carcinogenicity and mutagenicity of phenolphthalein, the ability of this chemical to induce cell transformation and genetic effects was examined using the Syrian hamster embryo (SHE) cell model. Cell growth was reduced by treatment with phenolphthalein at 10-40 microM in a dose-related manner. Treatment with phenolphthalein for 48 hr induced a dose-dependent increase in morphological transformation of SHE cells. Over the dose range that resulted in cell transformation ( 10-40 microM), treatment of SHE cells with phenolphthalein induced gene mutations at the hprt locus but not at the Na+/K+ ATPase locus. A statistically significant level of chromosomal aberrations was elicited in SHE cells treated with phenolphthalein at the highest dose (40 microM). Meanwhile, neither numerical chromosomal changes nor DNA adduct formation, analyzed by the nuclease P1 enhancement version of 32P-post-labeling, were induced by treatment with phenolphthalein at any concentrations examined. We thus report cell-transforming activity and mutagenicity of phenolphthalein assessed with the same mammalian cells in culture. Our results provide evidence that phenolphthalein has cell-transforming and genotoxic activity in cultured mammalian cells. The mutagenic and clastogenic activities of phenolphthalein could be a causal mechanism for carcinogenicity in rodents.

[Differences between phthaleins and sulfonphthaleins]

Differences in color and molecular structure between phthalein-pigments and sulfonphthalein-pigments were investigated using X-ray crystallography and absorption spectrophotometry of their aqueous solutions. The molecular structure of sulfonefluorescein (H2+SF-) was determined as a zwitter ion, 2-(3-hydroxonio-6-hydroxy-3H-xanthen-9-yl)benzenesulfonate. The absorption spectra of H2+SF- demonstrated the dissociation profile of a dibasic acid, while those of fluorescein (H2FL) indicated a tribasic acid and further, at pH > 10, SF2- and FL2-, while at pH < 0, H2+SF- and H3+FL to be dominant. The spectra of H2+SF- were analyzed to obtain the values of pK1 and pK2 together with the spectrum of HSF-. Similarly, from the spectra of H3+FL the values of pK1, pK2 and pK3 together with the spectra of HFL- and H2FL were obtained. Further by adding 1/5 of the H3+FL spectrum to 2/15 of HFL- spectrum, an indicated spectrum as that of H2FL was obtained. From these results, the features of dissociation of H2SF- and H3+FL were estimated. The molecular structure of phenolsulfonphtalein (H2PS-) was determined as a zwitter-ion, alpha-(4-hydroxonio-2,5-cyclohexadiene-1-ylidene)-alpha- (4-hydroxyphenyl)-2-toluenesulfonate. The absorption spectra of H2PS- demonstrated that H2PS-, HPS- and PS2- became dominant at pH << 0, pH = 4 and pH > 11, respectively. On the contrary, phenolphthalein (H2PP) displayed only one type of absorption spectrum in the visual region, the shape of which was similar to that of PS2- while the molar extinction coefficient was smaller. The spectra were analyzed to obtain the values of pK1 = 9.05 and pK2 = 9.50. The spectra also demonstrated a slow addition reaction of OH- to PP2- and pK3 = 12 was obtained by measuring the absorbance after equilibration. From these results, the features of dissociation and coloration of H2+PS- and H2PP were estimated.

High-affinity rat anti-fluorescein monoclonal antibody with unique fine specificity properties including differential recognition of dynamic ligand analogues

The ability of antibodies to specifically select and stabilize through binding one or more isomers of highly dynamic ligands remains a relatively unexplored immunochemical problem. The experimental strategy employed in this study was to elicit homogeneous antibodies to polyaromatic fluorescein which exists in one isomeric form. The binding properties of a monoclonal rat antifluorescein antibody specific to a given isomer were quantitatively studied to determine the capacity to bind dynamic analogues of fluorescein which exists in multiple isomers. To generate monoclonal anti-fluorescein antibodies that reacted with specific dynamic analogues of fluorescein possessing unconjugated aromatic ring systems, immune spleenocytes from Lou/M rats immunized with FITC(I)-KLH were fused with Balb/c SP2/0-Ag14 murine myeloma cells forming rat-mouse hybridomas. Cell line P2A12-1-C8 was selected for further characterization from the original 23 stable rat hybrids, since it produced a monoclonal antibody with a binding affinity 2.0 x 10(10)/M for fluorescein based on dissociation rate measurements. P2A12-1-C8 exhibited significant reactivity with HPF and phenol red, which are dynamic structural analogues of the homologous fluorescein ligand. No reactivity was demonstrated with phenolphthalein, which based on relative chemical structures was expected to be more reactive than phenol red. Computer-based molecular modeling and energy minimization studies of fluorescein, HPF, phenol red, and phenolphthalein showed that in terms of the most energetically favorable orientation of the three aromatic rings, phenol red more closely simulated fluorescein than phenolphthalein. The results were analyzed in terms of the mechanisms of dynamic ligand stabilization and binding involving accommodation of specific ligand isomers by energetically permissible conformational states exhibited by an antibody active site. Thus, antibody reactivity of an anti-fluorescein antibody with phenol red and phenolphthalein was dictated more by ligand dynamics and aromatic orientation than by chemical structure similarities.

Flexible ligand docking using a genetic algorithm

Two computational techniques have been developed to explore the orientational and conformational space of a flexible ligand within an enzyme. Both methods use the Genetic Algorithm (GA) to generate conformationally flexible ligands in conjunction with algorithms from the DOCK suite of programs to characterize the receptor site. The methods are applied to three enzyme-ligand complexes: dihydrofolate reductase-methotrexate, thymidylate synthase-phenolpthalein and HIV protease-thioketal haloperidol. Conformations and orientations close to the crystallographically determined structures are obtained, as well as alternative structures with low energy. The potential for the GA method to screen a database of compounds is also examined. A collection of ligands is evaluated simultaneously, rather than docking the ligands individually into the enzyme.

Electrophoretically mediated microanalysis of calcium

Electrophoretically mediated microanalysis (EMMA) was used for the determination of calcium. The faster analyte zone containing the calcium was injected spatially behind a slower zone of o-cresolphthalein complexone in a capillary electrophoresis based system. Upon application of the electric field the calcium zone was electrophoretically mixed with the reagent and product was formed. The bulk electroosmotic flow carried the product to the detector where the absorbance of the resulting complex at 575 nm was measured. Quantitation using an internal standard yielded a linear response with an R.S.D. of 8.1%. An inter-method comparison was performed with the standard bulk method and yielded results that did not significantly differ. The advantages of EMMA with respect to traditional methods were addressed.

Structure-based discovery of inhibitors of thymidylate synthase

A molecular docking computer program (DOCK) was used to screen the Fine Chemical Directory, a database of commercially available compounds, for molecules that are complementary to thymidylate synthase (TS), a chemotherapeutic target. Besides retrieving the substrate and several known inhibitors, DOCK proposed putative inhibitors previously unknown to bind to the enzyme. Three of these compounds inhibited Lactobacillus casei TS at submillimolar concentrations. One of these inhibitors, sulisobenzone, crystallized with TS in two configurations that differed from the DOCK-favored geometry: a counterion was bound in the substrate site, which resulted in a 6 to 9 angstrom displacement of the inhibitor. The structure of the complexes suggested another binding region in the active site that could be exploited. This region was probed with molecules sterically similar to sulisobenzone, which led to the identification of a family of phenolphthalein analogs that inhibit TS in the 1 to 30 micromolar range. These inhibitors do not resemble the substrates of the enzyme. A crystal structure of phenolphthalein with TS shows that it binds in the target site in a configuration that resembles the one suggested by DOCK.

Estimation of effective diffusion coefficients of model solutes through gastric mucus: assessment of a diffusion chamber technique based on spectrophotometric analysis

A diffusion chamber technique based on spectrophotometric analysis to determine effective diffusion coefficients for solutes with various relative molecular mass (Mr) values and properties, passing through native mucus gel, is reported. For all solutes studied, a reduction in effective diffusion coefficients is observed with a retardation of solute flux by a factor of at least two. For the solutes investigated (with Mr values ranging from 126-14,400 u), no consistent effect of solutes of low Mr was evident with regard to the retarding effect of mucus; however, at high Mr values (greater than 4000 u) the retardation was greatly enhanced. A possible relationship between charged solutes of low Mr and the degree of retardation was observed, which possibly suggests the presence of ionic interactions of the solutes with the largely negatively charged mucus gel. The results provide further evidence for the suggestion that mucus is acting more than simply as a gel support for an unstirred water layer and is perhaps a more potent diffusion barrier to specific solutes.