Pyridine-2-aldehyde p-nitrophenylhydrazone as an indicator for colorimetric pH measurements

Pyridine-2-aldehyde p-nitrophenylhydrazone is suggested as an indicator for colorimetric pH measurements in the high-alkaline range. Absorption spectra and indicator constant have been determined. Color change interval and other indicator characteristics have been established. A visually distinguishable transition and a good stability of color are obtained.     

The use of McMurry coupling for the synthesis of indolophanes and cis-stilbenophanes

Treatment of 2 equiv of indole-3-aldehyde with o, m, p-xylyl, 2,5-dimethoxy-p-xylyl dibromides and 4,4′-bis(bromomethyl)-1,1′-biphenyl gave the bisalkylated products, which underwent McMurry coupling with low valent titanium to give indolophanes. Various cis-stilbenophanes with m-terphenyl building blocks were also synthesized by application of the McMurry coupling technique.     

Highly selective fluorescent chemosensor with red shift for cysteine in buffer solution and its bioimage: symmetrical naphthalimide aldehyde

A new fluorescent probe 1, N-butyl-4, 5-(p-aldehyde)phenyl-1,8-naphthalimide, was designed and synthesized for the determination of the cysteine (Cys). Upon addition of Cys, the emission of 1 was enhanced with about 25 nm red-shift in the emission maximum (from 455 to 480 nm), accompanied with the fluorescent color change from blue to cyan, which was attributed to the reaction of the aldehyde groups in 1 with cysteine to form very stable thiazolidines derivative. Compound 1 was highly selective for cysteine detection without the interference of other amino acids and can be used for bioimaging of Cys.     

Use of hexamminecobalt(III)-tricarbonatocobaltate(III) as a redox titrant for the potentiometric estimation of some organic compounds

Hexamminecobalt(III)-tricarbonatocobaltate(III) was prepared, and its bicarbonate solution was standardized against ferrous ammonium sulfate using Ferroin indicator. The Co solution was used as an oxidimetric reagent for the determination of organic systems.Hydroquinone as a reversible system undergoes fast electrochemical reactions, so it can be determined with the Co(III) complex, which acts as an irreversible titrant. Thus it can be determined with both visual and potentiometric methods. Standardized hydroquinone solutions in H₂SO₄ medium gave very similar results when determined potentiometrically against standard Co(III) solution. The acid medium is important for liberating Co(III) ions. Hydrochloric acid behaves similarly but perchloric acid interferes with the reaction. Diluting the hydroquinone solutions had no effect on the determinations. The potentiometric endpoint coincides with the discharge of the color if Ferroin has been present.p-Aminophenol, p-phenylenediamine, and Metol (p-hydroxy-N-methylaniline), which slow or hinder the electrochemical reaction, do not indicate a distinct potential change at the endpoint, so cannot be determined potentiometrically. Their chemical reactions are fast enough to be titrated visually against Co(III) complex using Ferroin indicator. Titration curves representing biamperometric measurements of these solutions fulfill these results.Hydrazine sulfate and isonicotinic acid hydrazide as irreversible systems cannot react with Co(III) and thus cannot be determined either potentiometrically or visually as both electrochemical and chemical reactions are slow to be recognized.     

Photometric titrations with indicators

Various types of photometric titration curves are discussed. If a metal M is titrated conipleximetrically using a metal indicator and the absorbance is plotted vs. the titrant consumed, the inflection point appears at a pM value defined by the equation 3 pM_infl = pM_trans + 2 pM_eqThis expression is valid when M combines in a 1 : 1 ratio with the complexing agent and the indicator and when the indicator concentration is small compared to the total metal concentration.The difference between the pM values at the inflection and equivalence points can be calculated from the equation ΔpM = pM_infl — pM_eq = $\text{1}\text{3}$(pM_trans — pM_eq) = $\text{1}\text{6}$log(C_MK²_MI/K_MY)If the inflection point is taken as the equivalence point, the error arising can be calculated from ΔpM, or more simply, read from a diagram.If transmittance, instead of absorbancc, is plotted as a function of the titrant volume, the inflection point depends on the added amount of indicator. However, at high transmittance values, i.e., at low indicator concentrations, the inflection point of a transmittance curve occurs practically at the same volume of added titrant as the inflection point of an absorbance curve. Rules are given for applying an indicator correction for the amount of metal bound to the indicator at the end-point.The derived equations and discussions can also be applied to acid-base titrations.     

Absorption and photoluminescence properties of 4-substituted Alq3 derivatives and tris-(4-hydroxypyridinoanthrene)aluminum

A series of 4-substituted Alq₃ derivatives have been synthesized. Photophysical properties of the complexes in solution have been studied in detail. The results show that Hammett σ_p constants of the substituents have a linear correlation with the emission maximum values of the aluminum complexes. Substitution at the 4-position improves the color purity of the emission and it has also a strong influence on the quantum yields. A new type of Alq₃ derivative, tris-(4-hydroxypyridinoanthrene)aluminum, has a good quantum yield and high emission color purity.     

Rationally designed chromogenic chemosensor that detects cysteine in aqueous solution with remarkable selectivity

A sensing ensemble for cysteine was assembled conveniently by simply mixing N,N,N′,N′-tetra-(2-pyridylmethyl)-p-xylylenediamine (TPXD), cadmium perchlorate, and pyrocatechol violet in an 1:2:1 molar ratio in water of neutral pH. In the ensemble, [Cd₂(TPXD)]⁴⁺ formed from TPXD and cadmium perchlorate serves as the receptor, and pyrocatechol violet functions as the indicator in sensing the analyte. The detection can be made either spectroscopically from the decrease of the UV-visible absorbance at 665 nm or visually from the color change to yellow upon addition of an aqueous solution of the analyte to the solution of the ensemble. The association constant (K_ass) for the binding of the indicator to the receptor was determined with an isothermal titration calorimeter to be (2.77±0.98)×10⁵ M⁻¹ and that for the binding of cysteine to the receptor was obtained to have (1.62±0.97)×10⁷ M⁻¹ by the non-linear regression analysis of the titration curve obtained by titration of the solution of the ensemble with cysteine solution. The chemosensor showed excellent selectivity for cysteine over other amino acids including homocysteine.     

Application of a Schiff base derived from sulfanilamide as an acid-base indicator

The present paper firstly announces the possibility of using a Schiff base as an acid-base indicator. This surprising phenomenon can be considered as an interest due to the fact that Schiff bases are usually unstable in solutions and definitely undergo hydrolysis. It was found that such a specific observation depends merely upon the chemical structure and type of the substitute of amine that reacts with aldehyde to give the Schiff base. The latter reagent 4[(4-dimethylamino-benzylidene)-amino]-benzene sulfonamide was synthesized from the condensation of sulfanilamide with p-dimethylaminobenzaldehyde. The reagent solution shows a reproducible change in its color due to the addition of acid and base. A UV-Vis spectroscopic characterization and acid-base equilibrium study of the reagent for its possible use as an indicator were investigated. The results show that the reagent is an amphoteric which possesses four ionization constants K_a1, K_a2, K_b1 and K_b2 of weak dibasic and diacidic properties. The value of pK_a2 (9.80) is parallel to the observed transition interval pH 9.5 (yellow) and pH 10.5 (colorless), which is considered to be the indicator exponents pK_i. It was concluded that the benzyl sulfonamide group plays a key role in the stability of the reagent towards hydrolysis and also for indicator characteristics through breaking the conjugation.     

Classification of 3-3 transitions in neonlike germanium in laser-produced plasma

Classification of 3-3 transitions in neonlike germanium in laser-produced plasma has been made. The spectra have been observed in the range of 185–290 Å using a high resolving power (λ/Δλ ～ 13000) grazing-incidence spectrometer in XUV laser experiment. A total of 21 lines (including five lasing lines) have been classified as transitions between the 2s ²2p ⁵3s, 3p, 3d or 2s2p ⁶3p, 3d and sodiumlike germanium configurations. The identified transitions have been used to derive energy levels of 2s ²2p ⁵3l in neonlike germanium. The experimental results have been compared with theoretical predictions from Dirac-Fock (MCDF) calculations.     

Ab initio structure of 3p4p in Si I

Multiconfiguration calculations have been performed in order to estimate ab initio energies for the configuration 3p4p in Si I. A preliminary attempt has also been made to calculate E2 transition rates for transitions from levels of 3p ² to those of 3p4p. However, these rates show a gauge dependence, which indicates that further correlation needs to be included to obtain accurate rates and lifetimes.     

The use of pyridine-2-azo-p-dimethylaniline as an indicator in glacial acetic acid

Pyridine-2-azo-p-dimethylaniline is suggested as an indicator in the titration of amines (aniline, butylamine, p-phenylenediamine and ethylenediamine) with perchloric acid in glacialacetic acid medium. The precision obtainable is much better than that with crystal violet indicator. The pyridine dye can also be used satisfactorily in the titration of sodium carbonate and sodium acetate.     

Palladium(II) complexes of Schiff bases derived from 5-amino-2,4-(1H, 3H)pyrimidinedione (5-aminouracil) and 1,2-dihydro-1,5-dimethyl-2-phenyl-4-amino-3H-pyrazol-3-one

Summary New palladium(II) complexes of Schiff bases, obtained from 5-aminouracil, (AUH), and acetylacetone (AUAcAcH₂), benzaldehyde (AUBALH), furan-2-aldehyde (AUFALH), 2-hydroxynaphthaldehyde (AUNALH₂), pyridine-2-aldehyde (AUPyALH) or salicylaldehyde (AUSALH₂) and from 1,2-dihydro-1,5-dimethyl-2-phenyl-4-amino-3H-pyrazol-3-one (AAPy) and acetylacetone (AAPyAcAcH), 2-hydroxyacetophenone (AAPyAPH), furan-2-aldehyde (AAPyFAL), pytidine-2-aldehyde (AAPyPyAL), or salicylaldehyde (AAPySALH), have been prepared. The complexes, with formulae PdL₂Cl₂ (L=AUBALH, AUFALH or AUSALH₂); PdLCl₂ (L=AUAcAcH₂, AUNALH₂, AUPyALH, AAPyFAL or AAPyPyAL) and PdLCl (L=AAPyAcAc or AAPySAL) were characterized by elemental analysis, i.r. and electronic spectral studies, thermogravimetric analyses and magnetic and conductance measurements. The x-ray powder diffraction pattern of one of the complexes was also examined. The complexes were screened for their possible antitumour activityin vitro.     

A turn on ESIPT probe for rapid and ratiometric fluorogenic detection of homocysteine and cysteine in water with live cell-imaging

5(Benzothiazol-2-yl)-4-hydroxyisophthalaldehyde (BHI), an intense ESIPT containing molecule in mixed media loses its properties due to resonance-assisted H-bond (RAHB) in absolute water. Due to resonance-assisted H-bond the o-aldehyde is more reactive than the other one. With addition of cysteine/homocysteine into this solution the o-aldehyde group gets transformed into thiazolidine/thiazine ring, respectively, and the phenolic proton becomes free enough for transfer to nitrogen of the benzothiazole ring in excited state, that is, the ESIPT of BHI is turned on. Thus we can detect cysteine/homocysteine in water as well as in live cells.     

Coordination complexes of PdII with benzothiazolines

Summary Some new Pd^II complexes have been synthesized by reacting PdCl₂ with monofunctional bidentate Schiff bases (condensation product of furfuraldehyde, pyridine-2-aldehyde and thiophene-2-aldehyde witho-amino-thiophenol) in different molar ratios. The i.r. and n.m.r. spectra reveal that the nitrogen of azomethine and sulphur of thiol are coordinating sites. Electronic spectral data suggests square planar geometry for these complexes.     

Solid-supported single- and multi-enzyme amplified assays for clostridiopeptidase A

A rapid and sensitive spectrophotometric assay for Clostridium histolyticum clostridiopeptidase A (collagenase) was accomplished by measuring the activity of an alkaline phosphatase indicator enzyme released into solution from insoluble, covalently linked alkaline phosphatase indicator enzyme released into solution from activity of the alkaline phosphatase was monitored spectrophotometrically using either p-nitrophenyl phosphate as substrate or more sensitively by a signal amplification system consisting of NAD⁺, alcohol dehydrogenase, diaphorase and INT-Violet. Under the reaction conditions the amount of indicator enzyme produced is directly proportional to the concentration of collagenase. With p-nitrophenyl phosphate as substrate the magnitude of the signal was 0.003 abs. min^?1 per 100 ng ml^?1 collagenase whereas with the multienzyme amplification system it was 0.035 abs. min^?1, i.e. approximately as 12-fold increase. The method consists in first incubating the substrate with the bacterial collagenase for 20 min, then up to 96 samples of the released alkaline phosphatase can be analysed in 2 min using a microtitre plate reader run in the kinetic mode.     

Development of a novel colorimetric indicator label for monitoring freshness of intermediate-moisture dessert spoilage

A colorimetric mixed pH dye-based indicator with potential for the development of intelligent packaging, as a “chemical barcode” for real-time monitoring of intermediate-moisture dessert spoilage, is described. This on-package indicator contains mixed pH-sensitive dyes, bromothymol blue and methyl red, that respond through visible color change to carbon dioxide (CO₂) as a spoilage metabolite. Both indicator solution and indicator label characteristics were studied, as well as their response to CO₂. A kinetic approach was used to correlate the response of the indicator label to the changes in intermediate-moisture dessert spoilage. Color changes, in terms of total color difference of a mixed pH dye-based indicator, correlated well with CO₂ levels of intermediate-moisture dessert. Trials on golden drop have verified that the indicator response correlates with microbial growth patterns in dessert samples, thus enabling the real-time monitoring of spoilage either at various constant temperatures or with temperature fluctuation.     

Nitration of some 2-substituted thionaphthenes

A study is made of the nitration of thionaphthene-2-aldehyde, its diacetate, and of 2-(-nitrovinyl)thionaphthene. UV and IR spectroscopy show that nitration of thionaphthene-2-aldehyde in acetic anhydride gives a mixture of 3-nitrothionaphthen-2-aldehyde diacetate, 4-nitrothionaphthene-2-aldehyde diacetate, and 6-nitrothionaphthene-2-aldehyde diacetate in the ratios 106624, while nitration of thionaphthene-2-aldehyde diacetate gives a mixture of 3-nitrothionaphthene-2-aldehyde diacetate, 4-nitrothionaphthene-2-aldehyde diacetate, and 6-nitrothionaphthene-2-aldehyde diacetate in the ratios 363826. Nitration of 2-(-nitrovinyl)thionaphthene gives 4-nitro-2-(-nitrovinyl)thionaphthene.     

M?ssbauer and other spectral studies of Fe(III) complexes of benzothiazolines

Different molar reactions of Fe(OPr¹)₃, and FeCl₃ with benzothiazolines having an NSH donor system. derived by the condensation ofo-aminothiophenol with heterocyclic aldehydes. viz. pyridine-2-aldehyde. furfuraldehyde and thiophene-2-aldehyde. lead to the formation of [Fe.Pr¹(NS)₂]₂, [Fc(NS)₃] and [Fe(NS)₂Cl| type of complexes. The resulting derivatives have been characterized by elemental analysis, conductivity measurements, molecular weight determinations and magnetic studies. IR, electronic, M?ssbauer and ESR spectral data have been used to deduce the structures of the resulting derivatives.     

p-Sulfonatocalix[7]arene: synthesis, protolysis, and binding ability

Water-soluble p-sulfonatocalix[7]arene 1 has been synthesized in good yield through standard procedures and its conformational preferences have been investigated by Monte Carlo conformational searches. The acid-base properties of 1 were investigated by means of potentiometric titration, obtaining pK_a values in agreement with those reported for other p-sulfonatocalix[n]arene homologs. The binding ability of 1 toward organic quaternary ammonium cations such as Diquat (2), Paraquat (3), and Chlormequat (4) was investigated by means of ¹H NMR titrations in D₂O at pD=7.3, DOSY NMR measurements, and 2D ROESY NMR spectroscopy. Spectrofluorimetry proved to be a useful method for the determination of trace amounts of 2 and 3 in aqueous solution by using Acridine Orange bound to 1 as a chemical indicator.     

Polyglycerol-bound phosphotriesterase enzyme model complexes for detection and hydrolysis of phosphorus species in aqueous solution

Phosphotriesterase models incorporating di(2-picolyl)amino ligands supported by m-xylylene or 2-hydroxy-m-xylylene scaffolds have been tethered to the periphery of a water-soluble hyperbranched polyglycerol (PG). In aqueous solution buffered at pH 7.4, the polymeric complexes of Zn²⁺ are useful receptors for polymeric indicator displacement assays for phosphate and pyrophosphate employing commercial complexometric indicators. Under the same conditions, the Co³⁺ effectively hydrolyze p-nitrophenylphosphate with approximately five orders of magnitude rate enhancement versus uncatalyzed hydrolysis. These systems offer promising results as mixed-metal dual detect-decontaminate materials for organophosphorus toxins under mild, neutral aqueous conditions.