A new chemosensing ensemble for fluorescent recognition of pyrophosphate in water at physiological pH

A novel chemosensing ensemble that exhibits sensitive and selective recognitions of pyrophosphate in 100% aqueous solution at physiological pH has been developed. The chemosensing ensemble was constructed by a dinuclear Zn(II) complex of 2,6-bis[(bis(2-benzimidazolylmethyl)amino)methyl]-p-cresol and sodium fluorescein, the receptor–indicator pair is able to highly selectively discriminate pyrophosphate from phosphate and other anions in water at physiological pH.     

Electrophoresis in one buffer at two pH values

A theory for discontinuous electrophoresis in a polyacrylamide gel is presented for one buffer at two pH values. It is shown that polyions stack between identical leading and trailing ions, and resolve in a gel of constant polyacrylamide concentration. The theory is illustrated by the separation of serum protein polyions in a Tris-glycinate buffer of pH 8.19 in the well-forming gel, and pH 9.16 in the resolving gel. The selected concentrations and electrolyte ionization degrees of Tris and glycine have values at which the serum protein polyions stack between the resolving and electrode buffers, followed by separation in the resolving gel.     

Susceptibility to hydrolysis of phenylboronic pinacol esters at physiological pH

Boronic acids and their esters are highly considered compounds for the design of new drugs and drug delivery devices, particularly as boron-carriers suitable for neutron capture therapy. However, these compounds are only marginally stable in water. Hydrolysis of some phenylboronic pinacol esters is described here. The kinetics is dependent on the substituents in the aromatic ring. Also the pH strongly influences the rate of the reaction, which is considerably accelerated at physiological pH. Therefore, care must be taken when considering these boronic pinacol esters for pharmacological purposes.      

Binuclear Cu2+ complex mediated discrimination between L-glutamate and L-aspartate in water

L-glutamate and L-aspartate selectivity is achieved by the action of two Cu2+ metal ions rightly disposed in a cyclophane-type macrocyclic framework; electrochemical sensing of glutamate has been achieved by adsorption of the copper complexes on graphite electrodes.     

A tetrameric sugar-based azobenzene that gels water at various pH values and in the presence of salts

A novel low-molecular mass tetrameric sugar derivative containing azobenzene core, 1, showed pronounced hydrogelation at micromolar concentration. Based on this observation, four related azobenzene based tetrameric sugar derivatives, 4-7, and three tetrameric sugar derivatives with a bis-terephthalamide core, 9-11, were also synthesized. However, none of these closely related analogues of the compound 1 showed effective gelation. The gel formed from 1 was characterized extensively using melting temperature analysis, UV-vis, FT-IR, circular dichroism spectroscopy, and scanning electron microscopy. The resultant gel exhibited impressive tolerance to the pH variation of the aqueous phase and gelated water in the pH range of 4-10. While UV-vis and CD spectroscopy indicated that pronounced aggregation of the azobenzene chromophores in 1 was responsible for gelation, FT-IR studies showed that hydrogen bonding is also a contributing factor in the gelation process. The melting of gel was found to depend on the pH of the aqueous medium in which gel was formed. The gel showed considerable photostability to UV irradiation, indicating tight intermolecular packing inside the gelated state that rendered azobenzene groups in the resultant aggregate refractory to photoisomerization. The electron micrographs of the aqueous gels of 1 showed the existence of spongy globular aggregates in such gelated materials. Addition of salts to the aqueous medium led to a delay in the gelation process and also caused remarkable morphological changes in the microstructure of the gel.     

Assignment of standard pH values [pH*(s)] to buffers in 50 mass % methanol + water from 288.15 to 308.15 K

The secondary dissociation constants of o-phthalic and phosphoric acids have been determined in methanol + water (50 mass %) from reversible e.m.f. measurements of the cell of the type: Pt, H(2)(1 atm)|M(2)A(m), MHA(m), MCl|AgCl; Ag at different temperatures (288.15-308.15 K) and at different ionic strengths. To minimize the unsteadiness in potential measurements palladium coated platinum electrodes have been used. The large set of such e.m.f. values has been analyzed in terms of a multi-linear regression method recommended in recent IUPAC documents. The thermodynamic values DeltaG degrees , DeltaH degrees and DeltaS degrees , for the respective equilibria, were estimated. Standard pH values [pH*(s)] have been assigned to buffers in methanol + water (50 mass %) at temperatures between 288.15 and 308.15 K.     

Effect of pH changes on water release values in hydrophobic interaction chromatographic systems

The effect on pH on protein binding in HIC systems was investigated. Isocratic experiments were carried out to determine the capacity factors of various proteins as a function of temperature, pH and salt type. This paper presents a framework based on the Maxwell linkage function for estimating the number of released water molecules during the adsorption/desorption process due to a change of buffer pH. This approach also enables one to predict the effect of pH change on the water released values upon binding at any temperature condition. The results indicate that the total number of released water molecules (delta nu) for a pH change increased more on aromatic surfaces (phenyl Sepharose) than on aliphatic resins (butyl Sepharose). The results also indicate that the total number of released water molecules (deltanu) for a pH change increased with salt concentration and when changing from chaotropic to kosmotropic salts. The (deltanu) values also increased as the buffer pH approached the protein's pI, and decreased away from its pI. This work helps to establish a framework for the investigation of pH effects on protein selectivity in HIC systems.     

New boronic acid fluorescent reporter compounds. 2. A naphthalene-based on-off sensor functional at physiological pH

[structure: see text] A new boronic acid fluorescent on-off reporter compound (1) was synthesized. This fluorescent sensor shows a 41-fold emission intensity increase upon addition of 50 mM fructose in 0.1 M aqueous phosphate buffer at pH 7.4.     

Conformational changes of gossypulin in solutions at various pH values influence of salts

Work has continued on the study of the conformational transitions of gossypulin from the seeds of the cotton plant under various conditions. The denaturation of gossypulin as a function of the pH of the medium and the influence of salts (sodium chloride and sodium phytate) on the denaturation process have been studied with the aid of circular dichroism. The gossypulin from cotton plant seeds undergoes complex conformational changes in the pH interval from 2 to 13. Sodium phytate stabilizes the protein molecule at pH 2 and 3.Institute of the Chemistry of Plant Substances of the Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 255–258, March–April, 1987.     

Decomposition of ozone in water at pH 4–8

A systematic study of the ozone decomposition in water in the pH range 4–8 was carried out.     

Spectral characteristics of 2-aminodiphenylamine in different solvents and at various pH values.

The absorption and fluorescence spectra of 2-aminodiphenylamine (2ADA) have been studied as a function of solvent polarity and acid concentration. Analysis of solvatochromic and prototropic shifts of 2ADA reveals: (i) the presence of intramolecular hydrogen bonding between imino and amino groups in the ground state, (ii) dual fluorescence (360 and 430 nm) of the monocation (2ADA+) formed by the protonation of amino group; and (iii) proton-induced quenching of the monocation (2ADA+) fluorescence. In the dual fluorescence of 2ADA+, the longer wavelength emission at 430 nm is found to be from the twisted form of the monocation. The rate constants of the proton-induced quenching of 2ADA+ are determined.     

A semipermanent coating for preventing protein adsorption at physiological pH in kinetic capillary electrophoresis

Protein adsorption to the inner capillary wall hinders the use of kinetic capillary electrophoresis (KCE) when studying noncovalent protein-ligand interactions. Permanent and dynamic capillary coatings have been previously reported to alleviate much of the problems associated with protein adsorption. The characteristic limitations associated with permanent and dynamic coatings motivated us to look at a third type of coating - semipermanent. Here, we demonstrate that a semipermanent capillary coating, designed by Lucy and co-workers, comprised of dioctadecyldimethylammonium bromide (DODAB) and polyoxyethylene (POE) stearate, greatly reduces protein adsorption at physiological pH - a necessary requirement for KCE. The coating (i) does not inhibit protein-DNA complex formation, (ii) prevents the adsorption of the analytes, and (iii) supports an electoosmotic flow required for many applications of KCE. The coating was tested in three physiological buffers using a well-known DNA aptamer and four proteins that severely bind to bare silica capillaries as standards. For every protein, a condition was found under which the semipermanent coating effectively suppresses protein adhesion. While no coating can completely prevent the adsorption of all proteins, our findings suggest that the DODAB/POE stearate coating can have a broad impact on CE at large, as it prevents the absorption of several well studied, highly adhesive proteins at physiological pH.     

New indolium and quinolinium dyes sensitive to aqueous halide ions at physiological concentrations

Twelve new highly fluorescent dyes have been produced by the reaction of two heterocyclic nitrogen bases with 8-bromooctanoic acid, 11-bromoundecanoic acid and 15-bromopentadecanoic acid. The bromide counter ions of the first six dyes have been replaced with the tetraphenylborate ion. Unlike the bases themselves, the quaternary salts are water soluble and have fluorescence characteristics independent of pH in the pH range 7–11. Both the fluorescence intensity and fluorescence lifetime of dyes 1–12 are reduced in the presence of aqueous halide ions allowing halide concentrations to be determined accurately at physiological levels. All the dyes have been characterised in terms of steady state fluorescence spectra and steady-state Stern-Volmer analysis.     

A new class of azobenzene chelators for Mg and Ca in buffer at physiological pH

A new class of azobenzene-based chelators, trans-3a and trans-3b (3a and 3b), were designed and synthesized in two steps. Both 3a and 3b were readily dissolved in a buffer solution at physiological pH. The values of the dissociation constant of 3a and 3b for Mg²⁺ and Ca²⁺ were determined by the Hills plot; K_d^Mg=1.12 mM and K_d^Ca=660 μM for 3a and K_d^Mg=158 μM and K_d^Ca=200 μM for 3b, respectively. On irradiation at 489 nm light, 3a isomerized to give cis-form, which underwent cis-to-trans thermal isomerization in darkness at room temperature. The change in the absorption spectrum of the irradiated solution of 3a in the presence of Mg²⁺, showing the cis-to-trans thermal isomerization, indicates that the affinity of cis-3a for Mg²⁺ is lower than that of 3a.     

Histograms of the size distribution of kraft lignin particles in aqueous solutions at various pH values

The size distribution of kraft lignin particles in aqueous solutions in a wide pH range (9.5−2.0) was studied by filtration through track membranes.     

Mediated bioelectrocatalytic O2 reduction to water at highly positive electrode potentials near neutral pH

Combinations of bilirubin oxidase and metal complexes: [W(CN)₈]^3−/4−, [Os(CN)₆]^3−/4− and [Mo(CN)₈]^3−/4− (the formal potentials, E^0′(M), being 0.320, 0.448, and 0.584 V vs. Ag|AgCl, respectively, at pH 7.0), allowed bioelectrocatalytic reduction of O₂ to water at their formal potentials near neutral pH. The O₂ reduction current appeared even at the standard potential of the O₂/H₂O redox couple, E^0′(O₂/H₂O), when [Mo(CN)₈]^3−/4− was used at pH 7.4, though the magnitude was small. The magnitude of the bioelectrocatalytic current systematically decreased with the decrease in the potential difference between E^0′(O₂/H₂O) and E^0′(M). A limiting current as large as 17 mA/cm² of a projected electrode surface area was obtained at 0.25 V (−0.37 V vs. E^0′(O₂/H₂O)) for the O₂ reduction at pH 7.0 with a carbon felt electrode modified with electrostatically entrapped bilirubin oxidase and [W(CN)₈]^3−/4− at the electrode rotation rate of 4000 rpm.     

Structure of the zirconium-alizarin s complex in relation to pH changes

A comparison of the absorption spectra of the zirconium-alizarin S complex with those of alizarin S at different pH values shows that the action of hydrogen ions and zirconium(IV) on alizarin S is similar. Changes caused by pH alterations are discussed. Between pH 1 and 1.8 the zirconium-alizarin S complex has the molar ratio 1:1; at higher pH, suspensions of hydroxy complexes of zirconium are formed which adsorb the above complex.     

Binding of sodium dodecyl sulfate with linear and branched polyethyleneimines in aqueous solution at different pH values

Isothermal titration microcalorimetry (ITC), conductivity, and turbidity measurements have been carried out to study the interaction of sodium dodecyl sulfate (SDS) with polyethyleneimines (PEI) including linear PEI and branched PEI at different pH values of 3, 7, and 10. In all cases, the polymers show a remarkable affinity toward SDS. At pH 3, the polymer PEI is a strong polycation, and the binding is dominated by electrostatic 1:1 charge neutralization with the anionic surfactant. At pH 7, the electrostatic attraction between SDS and PEI is weak, and the hydrophobic interaction becomes stronger. At the natural pH of 10, PEI is essentially nonionic and binds SDS in the form of polymer-bound surfactant aggregates. The charge neutralization concentration (C1) of SDS for the PEI-SDS complex can be derived from the curves of variation of the enthalpy, conductivity, and turbidity with SDS concentration. There is good agreement between the results from the three methods and all show a decrease with increasing pH. The total interaction enthalpies (deltaH(total)) of PEI with SDS are obtained from the observed enthalpy curves and the difference enthalpy (deltaH*) between the total enthalpy of branched PEI with SDS, and the total enthalpy of linear PEI with SDS can be derived from the obtained deltaH(total). The difference deltaH* increases dramatically as pH increases, which indicates that the interactions are different for linear PEI and branched PEI at high pH values. A schematic map of the different states of aggregation is presented.