Neutral pH In Presence Research Articles

Photo-electro-Fenton process applied to the degradation of valsartan: Effect of parameters, identification of degradation routes and mineralization in combination with a biological system

In this work, the oxidation of the antihypertensive drug valsartan by the Electro-Fenton (EF) and photo-electro-Fenton (PEF) processes was studied using a Ti/IrO2 doped with SnO2 as anode, and a carbon felt air diffusion electrode as cathode. Initially, the influence of variables such as supporting electrolyte type, current density, and pH on EF and/or PEF processes was evaluated. The processes were carried out in batch mode, in an open and undivided cell of 200 cm3. The efficiency of the systems was evaluated in terms of the removal of the initial contaminant and rate of mineralization. When NaCl was used as a supporting electrolyte at pH 3.0 and current density 3.46 mA/cm2 adding 3.6 × 10−5 mol/L of Fe2+, total valsartan (20 mg/L) degradation was observed after 45 min. After 120 min, even if total removal of valsartan was reached, only 25% of mineralization was obtained. Thus, valsartan degradation tests at near neutral pH in presence of oxalic acid (4.6 × 10−5 mol/L) lead to comparable results with those obtained at pH 3.0. Primary aromatic intermediates were identified by high resolution mass spectrometry (HRMS) using hybrid quadrupole- time-of-flight (QTOF) MS, from which an initial degradation pathway was proposed. At the end of the PEF system, several aliphatic acids were accumulated and observed, which were effectively removed in a subsequent aerobic biological system. The results demonstrate the feasibility of PEF and biological coupling process to completely mineralize emerging pharmaceutical pollutants, such as valsartan, at natural pH.

Self-assembly of water soluble perylene tetracarboxylic acid with metal cations: Selective fluorescence sensing of Cu2+ and Pb2+ ions in paper strips, zebrafish and yeast

Self-assembly of water soluble highly fluorescent perylene tetracarboxylic (PTCA, Φf = 0.67) dye via metal coordination has been leads to the selective fluorescence sensing of Cu2+ and Pb2+ ions at neutral pH and Ag+ ions sensing via nanoparticles formation at basic medium. High-resolution transmission electron microscopic (HR-TEM) analysis revealed the conversion 1-D nanostructures of PTCA to spherical aggregates with Cu2+ and hexagonal prisms with Pb2+ ions. However, Ag+ ions were reduced to silver nanoparticles (AgNPs) at higher pH. The concentration dependent studies showed detection of both metal ions up to µM concentration level. Interference studies suggested good selectivity for both Cu2+ and Pb2+ ions at neutral pH in presence of other metal cations. Importantly, application potential of PTCA for selective fluorescence sensing of Cu2+ and Pb2+ ions have been demonstrated in filter paper as well as biological environment such as zebrafish and yeast.

Target-directed Dynamic Combinatorial Chemistry: A Study on Potentials and Pitfalls as Exemplified on a Bacterial Target.

Target-directed dynamic combinatorial chemistry (DCC) is an emerging technique for the efficient identification of inhibitors of pharmacologically relevant targets. In this contribution, we present an application for a bacterial target, the lectin FimH, a crucial virulence factor of uropathogenic E. coli being the main cause of urinary tract infections. A small dynamic library of acylhydrazones was formed from aldehydes and hydrazides and equilibrated at neutral pH in presence of aniline as nucleophilic catalyst. The major success factors turned out to be an accordingly adjusted ratio of scaffolds and fragments, an adequate sample preparation prior to HPLC analysis, and the data processing. Only then did the ranking of the dynamic library constituents correlate well with affinity data. Furthermore, as a support of DCC applications especially to larger libraries, a new protocol for improved hit identification was established.

Magnesium and molecular crowding of the cosolutes stabilize the i-motif structure at physiological pH.

Most of the important genomic regions, especially the G,C rich gene promoters, consist of sequences with potential to form G,C-tetraplexes on both the DNA strands. In this study, we used three C-rich oligonucleotides (11Py, 21Py, and HTPy), of which 11Py and 21Py are located at various transcriptional regulatory elements of the human genome while HTPy sequence is a C-rich strand of human telomere sequence. These C-rich oligonucleotides formed i-motif structures, verified by Circular Dichroism (CD), UV absorption melting experiments, and native gel electrophoresis. The CD spectra revealed that 11Py and 21Py form i-motif structures at acidic pH values of 4.5 and 5.7 in the presence of 100 mM NaCl but remain unstructured at pH 7.0. However, 21Py can form stable i-motif structure even at neutral pH in presence of 1 mM MgCl2 . UV-thermal melting studies showed stabilization of 21Py i-motif at pH 5.7 in the presence of Na+ or K+ with increasing concentration of MgCl2 or CaCl2 from 1 to 10 mM. Significant shift in the CD peak of HTPy sequence was observed as the positive peak from 286 nm shifted to 276 nm while the negative peak from 265 to 254 nm. Further, inevitable necessity of 1 mM Mg2+ to form i-motif structure at neutral pH was observed. Under similar ionic conditions and neutral pH, all the three C-rich sequences were able to form stable i-motif structures (11Py, 21Py) or altered i-motif/homoduplex structures (HTPy) in the presence of MgCl2 and cell mimicking molecular crowding conditions of 40 wt% PEG 200. It is concluded that presence of Mg2+ ions and molecular crowding agents induce and stabilize i-motif structures at physiological solution environment.

Customized tuning of aggregation-induced emission of a napthalimide dye by surfactants and cyclodextrin

The aggregation-induced emission behaviour of an environment sensitive 2,3-substituted napthalimide dye has been investigated at neutral pH in presence of three different surfactants i.e., cationic, anionic, and neutral. The changes observed in the excitation spectrum of the dye compared to its absorption spectra in water in presence of the surfactants above their micellar concentration reveals the transformation of the H-aggregates of the dye to the monomeric form. The alteration of the dye aggregates to its monomeric form and its consequence on emission properties has been utilized to estimate the surfactant concentration parameter for pre-micellar to micellar transformation. The aggregation of the dye molecules has been made reversible by removal of the surfactant molecules from the system upon host-guest complexation with α-cyclodextrin. This switchable aggregation-deaggregation phenomenon of DMN-Bu by employing surfactants and α-cyclodextrin at neutral pH in water is utilized for determining their critical micellar concentration.

Characterization of smart auto-degradative hydrogel matrix containing alginate lyase to enhance levofloxacin delivery against bacterial biofilms

The aim of the present work is the characterization of smart auto-degradable microspheres composed of calcium alginate/high methoxylated pectin containing an alginate lyase (AL) from Sphingobacterium multivorum and levofloxacin. Microspheres were prepared by ionotropic gelation containing AL in its inactive form at pH 4.0. Incubation of microspheres in Tris–HCl and PBS buffers at pH 7.40 allowed to establish the effect of ion-chelating phosphate on matrix erodability and suggested an intrinsically activation of AL by turning the pH close to neutrality. Scanning electron and optical microscopies revealed the presence of holes and surface changes in AL containing microspheres. Furthermore, texturometric parameters, DSC profiles and swelling properties were showing strong changes in microspheres properties. Encapsulation of levofloxacin into microspheres containing AL showed 70% efficiency and 35% enhancement of antimicrobial activity against Pseudomonas aeruginosa biofilm. Levofloxacin release from microspheres was not changed at acidic pH, but was modified at neutral pH in presence of AL. Advantageously, only gel matrix debris were detectable after overnight incubation, indicating an autodegradative gel process activated by the pH. Absence of matrix cytotoxicity and a reduction of the levofloxacin toxicity after encapsulation were observed in mammalian CHO-K1 cell cultures. These properties make the system a potent and versatile tool for antibiotic oral delivery targeted to intestine, enhancing the drug bioavailability to eradicate bacterial biofilm and avoiding possible intestinal obstructions.

Degradation of nitrobenzene at near neutral pH using Fe2+–glutamate complex as a homogeneous Fenton catalyst

We examined the degradation of nitrobenzene (NB) by modified Fenton reaction at near neutral pH conditions using FeII–glutamate complex as a source of Fe2+. The reaction was conducted using 0.04mM (5mgL−1) of NB in presence of 65mM H2O2 at room temperature. Complex concentrations of 5, 10, 15 and 20mM (Fe2+=0.81, 1.62, 2.43 and 3.23mM) were assayed and showed effective rates of NB degradation with t1/2 values of 17, 6.2, 4.8 and 1.85min, respectively. In the pH range 5–7 the complex activity is pH-dependent, and the optimal pH was 6.3. The degradation was monitored by solid-phase microextraction in combination with GC analysis. The rate of degradation recorded at near neutral pH in presence of 20mM of Fe-complex was equal to that obtained in presence of Fe2+ (2.5mM) at pH 2.7. Glutamate complexes formed with Cu2+ or Co2+ did not show the improved degradation observed in case of Fe–glutamate. Furthermore, the introduction of the chelating agent as a free ion into the reaction medium containing Fe2+ did not improve the degradation of NB at neutral pH conditions.

A new technique for formation of 99mTc-labelled blood leucocytes and platelets

99 m Tc-platelets and 99 m Tc-leucocytes have been formed at neutral pH in presence of gentisic acid using 99 m Tc pretreated with concentrated hydrochloric acid and vacuum evaporation. High radiochemical purities and specific radioactivities were obtained. The complexes between 99 m Tcand the blood cells were found remarkably stable, and further studies for nuclear medicine applications are recommended.

ChemInform Abstract: HYDROGEN GENERATION BY VISIBLE LIGHT IRRADIATION OF AQUEOUS SOLUTIONS OF METAL COMPLEXES. AN APPROACH TO THE PHOTOCHEMICAL CONVERSION AND STORAGE OF SOLAR ENERGY

AbstractDie Bedingungen für eine wirkungsvolle Wasserstoffproduktion durch Wasserreduktion mittels Bestrahlung durch sichtbares oder Sonnenlicht in Lösungen, die Metall‐Bipyridyl‐Komplexe als Katalysatoren enthalten,werden diskutiert.

Hydrogen Generation by Visible Light Irradiation of Aqueous Solutions of Metal Complexes. An approach to the photochemical conversion and storage of solar energy

AbstractWe describe a photochemical system for the generation of hydrogen by water reduction under visible light or sunlight irradiation of aqueous solutions containing the following components: a photosensitizer, the Ru (bipy) complex, for visible light absorption; a relay species, the Rh (bipy) complex, which mediates water reduction by intermediate storage of electrons via a reduced state; an electron donor, triethanolamine (TEOA) which provides the electrons for the reduction process and a redox catalyst, colloïdal platinum, which facilitates hydrogen formation. The conditions for efficient hydrogen production and the influence of the concentration of the components have been investigated; the metal complexes act as catalysts with high turnover numbers; excess bipyridine facilitates the reaction. The process contains two catalytic cycles: a ruthenium cycle and a rhodium cycle. The Ru cycle involves oxidative quenching of the *Ru(bipy) excited state by Rh(bipy) forming Ru(bipy) which is converted back to Ru(bipy) by oxidation of the electron donor TEOA, which is thus consumed. The Rh cycle comprises a complicated set of transformations of the initial Rh(bipy) complex. The reduced rhodium complex formed in the quenching process undergoes a series of transformations involving the Rh(bipy) complex and hydridorhodium‐bipyridine species, from which hydrogen is generated by reaction with the protons of water. In view of the storage of two electrons in the reduced rhodium species, the process is formally a dielectronic water reduction. The properties and eventual participation of [Rh(III)(bipy)2LL′]n+(L,L′ = H2O, OH−) species are investigated. It is concluded that at neutral pH in presence of excess bipyridine, the cycle involving regeneration of the Rh(bipy) complex is predominant. A number of experiments have been performed with modified systems. Hydrogen evolution is observed with other photosensitizers (like proflavin), other relay species (like Rh(dimethylbipy) or Co(II)‐bipyridine complexes), other donor species, or in absence of the platinum catalyst. It also occurs in absence of photosensitizer by sunlight of UV. irradiation of Rh(bipy) or by visible light irradiation of iridium (III)‐bibyridine complexes. These systems deserve further investigations. The present photochemical hydrogen generating system represents the reductive component of a complete water splitting process. Its role in solar energy conversion and in photochemical fuel production is discussed.

Tonomyosin of arterial muscle.

INVESTIGATION of the protein composition of cow carotids has shown that their muscular layer contains a new protein we have called tonoactomyosin, which does not superprecipitate at low ionic strength in presence of small amounts of adenosine triphosphate and remains soluble under these conditions. When ultra-centrifuged at 0.35 and neutral pH in presence of adenosine triphosphate, it splits into two peaks, a quick one assumed so far to be F-actin and a slow one sedimenting at about the rate of skeletal myosin. Tonoactomyosin appears to be soluble in the muscle sarcoplasm and seems thus responsible for the vascular tonus1,2. A similar component can also be isolated from cow pregnant uteri3.