pH Titration Research Articles

Experimental and theoretical studies of pH-responsive iridium(III) complexes of azole and N-heterocyclic carbene ligands.

A series of nine luminescent iridium(III) complexes with pH-responsive imidazole and benzimidazole ligands have been prepared and characterized. The first series of complexes were of the form [Ir(ppy)2(N^N)]+ or [Ir(ppy)2(C^N)]+ (where ppy is 2-phenylpyridine and N^N is 2-(2-pyridyl)imidazole or 2-(2-pyridyl)benzimidazole and C^N represents a pyridyl-triazolylidene-based N-heterocyclic carbene ligand). For these complexes, the benzimidazole group was either unsubstituted or substituted with electron-withdrawing (Cl) or electron-donating (Me) groups. The second series of complexes were of the form [Ir(phbim)2(N^N)]+ or [Ir(phbim)2(C^N)]+ (where phbim is 2-phenylbenzimidazole and N^N is either 2,2'-bipyridine or 1,10-phenanthroline and C^N is either a pyridyl-imidazolylidene or pyridyl-triazolylidene N-heterocyclic carbene ligand). UV-visible and photoluminescence pH titration studies showed that changing the protonation state of these complexes results in significant changes in the photoluminescence emission properties. The pKa values of prepared complexes were estimated from the spectroscopic pH titration data and these values show that the nature of the pH-sensitive ligands (either main or ancillary ligands) resulted in a significant capacity to modulate the pKa values for these compounds with values ranging from 5.19-11.22. Theoretical investigations into the nature of the electronic transitions for the different protonation states of compounds were performed and the results were consistent with the experimental results.

Potentiometric titrations to study ligand interactions with DNA i-motifs.

i-Motifs are non-canonical secondary structures of DNA formed by mutual intercalation of hemi-protonated cytosine-cytosine base pairs, most typically in slightly acidic conditions (pH<7.0). These structures are well-studied in vitro and have recently been suggested to exist in cells. Despite nearly a decade of active research, the quest for small-molecule ligands that could selectively bind to and stabilize i-motifs continues, and no reference, bona fide i-motif ligand is currently available. This is, at least in part, due to the lack of robust methods to assess the interaction of ligands with i-motifs, since many techniques well-established for studies of other secondary structures (such as CD-, UV-, and FRET-melting) may generate artifacts when applied to i-motifs. Here, we describe an implementation of automated, potentiometric (pH) titrations as a robust isothermal method to assess the impact of ligands or cosolutes on thermodynamic stability of i-motifs. This approach is validated through the use of a cosolute previously known to stabilize i-motifs (PEG2000) and three small-molecule ligands that are able to stabilize, destabilize, or have no effect on the stability of i-motifs, respectively.

Визначення водневого показника в точці нульового поверхневого заряду для гумінової кислоти бурого вугілля

Humic acids are a complex mixture of high molecular weight aromatic oxycarboxylic acids that act as polyelectrolytes. Their structure includes aromatic nuclei, side chains, and functional groups, resulting in a variation of physicochemical properties such as solubility and stability. Carboxylic and phenolic groups impart acidic properties, while amino groups cause amphotericity, which is related to the isoelectric point (pI). The amphiphilic character contributes to the formation of micelle-like structures in neutral and acidic environments. Humic acids form supramolecular colloids connected by hydrogen bonds. It is known that the pH at the zero charge point of different humic acids varies from 0.5 to 9.3, reflecting their chemical diversity. In our experiments humic acids were obtained by alkaline extraction from lignite with a carbon content of 40.5% and an ash content of 40%. The zero charge point (the pH at which a molecule carries no net electrical charge or is electrically neutral in the statistical mean) was determined by two methods using a pH titration procedure. These methods showed quite close pH values (2.0 and 1.6) at which the surface of humic acid has a net zero surface charge. This allows us to have information about the protonation state and charge dynamics of humic acid under different pH conditions. The data obtained helps to determine the solubility of the acid depending on the pH of the medium, which is important at the stage of acid precipitation in the process of its production, because of the zero charge point value can affect the solubility of a molecule at a given pH. Keywords: lignite, humic acids, composition, extraction, zero surface charge, pH indicator, acid-base titration. Corresponding author Savchenko V.V., e-mail: korbinity@gmail.com

UV-assisted photochemical transformation of a tetranuclear copper(II) complex: a DFT supported study on β-lactamase inhibitory activity towards antibiotic resistance.

Herein, we present a dark-green crystalline tetranuclear Cu(II) Schiff base complex {C1 = [Cu4L4](ClO4)4(DMF)4(H2O)} using a N,N,O donor ligand (HL), namely 2-(((2-hydroxypropyl)imino)methyl)-6-methoxyphenol. Spectro-photometrical investigation on the β-lactamase-like activity of this coordinately saturated system revealed its catalytic inefficiency towards hydrolysis of nitrocefin as a model substrate. This complex has attracted significant interest as a promising photo-catalyst owing to its narrow band gap (2.40 eV) as predicted from DFT calculations and its higher responsivity towards UV light. Therefore, C1 is effectively involved in the photocatalytic reduction of perchlorate to Cl- in the presence of a hole scavenger (H2O-MeOH) under prolonged UV irradiation and itself becomes photo-cleaved to yield a new dark-brown colored chlorobridged dinuclear crystalline complex C2 {[CuL(H2O)2Cl3]H2O}. Furthermore, C2 was deployed as a functional β-lactamase model and was found to show a remarkable catalytic proficiency towards the hydrolysis of nitrocefin in 70 : 30 (V/V) MeOH-H2O medium. This pro-catalyst C2 has been speculated to generate an aqua bridged active catalyst that plays a crucial factor in hydrolysis. This phenomenon was again experimentally established by potentiometric pH titration where C2 displays only one pKa value (7.11) in the basic pH range, indicating the deprotonation of the bridged water molecule. Based on several other kinetic studies, it may be postulated that the hydrolysis of nitrocefin is initiated by the nucleophilic attack of a bridging hydroxide, followed by very fast protonation of the intermediate to furnish the hydrolyzed product. It is noteworthy that the rate of nitrocefin hydrolysis is greatly inhibited in the presence of external chloride concentration. To the best of our knowledge, this is the first report on the photochemical behavior of such a tetranuclear copper(II) Schiff base complex. Our current interest is focused on inventing a potent β-lactamase inhibitory therapeutic as well as elucidating its mechanism through comprehensive chemical analysis.

Development of comprehensive approaches to characterizing CuII complexes: structures in solution and solid‐state, dynamic behavior, and bioactivity

AbstractCuII ternary systems with aromatic N‐donors (1,10‐phenanthroline, dipyrido‐[3,2‐f:2’,3’‐h]‐quinoxaline, and 2‐methyldipyrido‐[3,2‐f:2’,3’‐h]‐quinoxaline) and amino acids have been extensively studied in water solution under closely physiological conditions using several techniques, including potentiometric pH titration, mathematical modeling, nuclear magnetic relaxation, EPR, and DFT calculations. Based on the distribution diagrams of the complex species, single crystal syntheses of the ternary systems CuII‐aromatic N‐donor‐L‐amino acid were carried out. As a result, several crystal structures of the complexes with the desired copper‐to‐ligand ratio were established by X‐ray diffraction analysis. The most successful synthetic attempts were with L‐proline and L‐serine, resulting in the crystals with the desired copper(II) to ligand ratio. The developed approach made it possible to thoroughly describe systems with major proteinogenic amino acids in the L‐configuration. Numerous non‐covalent interactions such as H‐bonds, π‐π stacking, d‐π interactions, lone electron pair‐π interactions between CuII atom, conjugated aromatic ligand system, counterions, and water molecules were found to affect the stability and structure of the resulting complex particles. It has been found that in the CuII–N‐donor–amino acid systems there is an acceleration of ligand exchange by a factor of 2–25 compared to CuII‐amino acid systems, which is explained by taking into account steric effects, d‐π interactions, and the pseudo Jahn‐Teller effect. The investigated systems were tested for antitumor activity against MCF‐7, PC‐3, OVCAR‐4, SNB‐19, and M‐14 cell lines, and most samples, in particular, CuII–Phen–L‐His, CuII–MeDPQ−L‐Val and CuII–MeDPQ−L‐Ser, showed a therapeutic activity index greater than 2 for all selected cell types, which opens up prospects for their medical application.

Coagulation power comparison between fresh and powdered biduri (Calotropis gigantea) leaf extract in making suspesi soft cheese

Cheeses have different characteristics based on the coagulant used during their production. Making suspesi soft cheese by adding biduri (Calotropis gigantea) leaf extract is generally followed by heating. The present work focused only on the ability of biduri leaf extracts to coagulate milk protein, and not on heating of the extract. The present work aimed to analyse the coagulation power of fresh and powdered biduri leaf extracts, and to evaluate the physicochemical, chemical, and organoleptic characteristics of the produced suspesi soft cheeses. The present work used a completely randomised design with two treatments and six replications. The variables measured were physicochemical characteristics, including coagulation time, curd production, whey percentage, pH, and lactic acid titration. Physicochemical characteristic analyses of suspesi soft cheeses coagulated with fresh and powdered biduri leaf extracts showed significant differences (p &lt; 0.05) in the coagulation time and curd production. On the other hand, it did not show significant differences (p &gt; 0.05) in the percentage of whey, pH, and lactic acid titration. The chemical content of suspesi soft cheeses showed significant differences (p &lt; 0.05) in the water, protein, and crude fat contents. The organoleptic characteristics of suspesi soft cheeses showed a significant difference (p &lt; 0.05) in the colour, but did not show significant differences (p &gt; 0.05) in the smell, taste, and texture. Suspesi soft cheese produced with fresh biduri leaf extract had better coagulation power, physicochemical characteristics, chemical content, and organoleptic characteristics.

Unlocking the Molecular Behavior of Natural Amine-Targeted Carbon Quantum Dots for the Synthesis of Diverse Pharmacophore Scaffolds via an Unusual Nanoaminocatalytic Route.

Despite the fact that carbon quantum dots (CQDs) have significant catalytic potential, only emblematic applications that rely on simple acid-base or hydrogen-bonding activation pathways have been reported. In this study, natural amine-targeted CQDs (NAT-CQDs) have been successfully fabricated using a sustainable technique that harnesses a renewable green source. Based on a holistic sustainable assessment, the present approach for the synthesis of NAT-CQDs surpasses previously reported methods in terms of estimated circular and good-manufacturing-practice metrics. A set of spectroscopic and analytical techniques, including FTIR, XPS, conductometric assay, pH titration, 19FNMR, and 13CNMR confirms the presence of the assessable amino-rich groups (0.0083N) at the surface of NAT-CQDs. The occurrence of surface amine groups unlocked the molecular behavior of as-prepared NAT-CQDs and makes them an unprecedented nanoaminocatalytic platform for the synthesis of diverse pharmacophore scaffolds (>40 examples) via a one-pot Knoevenagel/(aza) Michael addition reaction in water at room temperature. The assessable amine group can covalently activate carbonyl groups through nucleophilic iminium activation modes in water and facilitate the ability to build valuable and therapeutic scaffolds on a gram scale. By transferring significant molecular primacy at the frontier of nanoscale materials, NAT-CQDs can thus bridge the gap between the nanoscale and molecular domains. This protocol can also be applied for the preparation of therapeutic anticoagulant drugs, warfarin, and coumachlor. All the reactions exhibited a high atom economy, low E-factor, low process mass intensity (PMI), high reaction mass efficiency (RME), high carbon efficiency (CE), and high catalyst reusability with overall high sustainable values. NAT-CQDs show high recyclability, and the spectral data of reused catalysts indicate that the NAT-CQDs maintained their surface chemistry and electronic properties, suggesting their stability under the tested conditions. This study presents a remarkable instance of NAT-CQDs showcasing covalent catalysis. Expanding on the aforementioned design concept, the utilization of NAT-CQDs' "potential" as distinct colloidal organocatalysts in aqueous environments at the molecular level introduces valuable prospects for aminocatalytic pathways.

Determination of sodium bicarbonate in compositions of smoke-type fireworks based on automatic potentiometric setting dynamic pH titration method

Determination of sodium bicarbonate in compositions of smoke-type fireworks based on automatic potentiometric setting dynamic pH titration method

A novel naphthalimide-based fluorescent probe with sulfonyl hydrazide as receptor for detection of Cu2+

A novel fluorescent probe N'-(4-(2-butyl-1,3-dioxo-2,3-dihydro-1H-benzo[de] isoquinolin-6-yl)benzylidene)-4-methylbenzenesulfonohydrazide (ENM) that could selectively response to Cu2+, was reported in this paper, which was the first fluorescent probe with sulfonyl hydrazide as the receptor to detect Cu2+. The selectivity, concentration titration, pH titration, time dependence, detection limit and recognition mechanism of ENM for Cu2+ in CH3CN/H2O solution were investigated. It was shown that ENM exhibited high selectivity, sensitivity and fast response to Cu2+, and the detection limit was as low as 0.27 μmol/L. More importantly, the sensing mechanism was that ENM underwent decomposition reaction with the addition of Cu2+. In addition, ENM could work in a wide pH range. The results of determination of Cu2+ in water samples indicated that ENM had potential practical value in environmental analysis.

(General Student Poster Award Winner - 1st Place) Six Practices to Improve Alkaline Electrolyte Preparation

Alkaline electrolytes represent a critical component of electrochemical energy devices, including alkaline electrolyzers, fuel cells, supercapacitors, and alkaline batteries. In addition, these electrolytes define essential properties of electrocatalytic reactions, such as the oxygen evolution reaction (OER), the hydrogen evolution reaction (HER), and the oxygen reduction reaction (ORR). However, alkaline electrolyte concentrations and compositions are often considered trivial, resulting in misinterpretation of different phenomena and overestimating critical performance metrics. Thus, in an expanding field full of interdisciplinary research groups, there is an urgent need for standardized protocols designed to improve and evaluate the quality of alkaline electrolytes so that electrochemical energy systems can be objectively examined and compared.In this work, we propose a protocol composed of six steps to prepare, characterize and validate the quality of common alkaline electrolytes. By adapting well-established methods in the literature and validating additional features experimentally, we standardize six general practices: (1) proper alkaline electrolyte handling and preparation, (2) removal of Fe impurities, (3) alkali molarity standardization via pH titrations, (4) electrolyte composition analysis via inductively-coupled plasma mass spectrometry (ICP-MS), (5) statistical quality control assessment and (6) electrolyte validation through electrochemical aging of Ni electrodes in alkaline media. The effects of Fe incorporation for different alkaline electrolytes were examined using Ni and NiFe foam electrodes. Furthermore, ICP-MS measurements were complemented with prolonged cyclic voltammetry tests to confirm the effectiveness of the Fe purification procedure. We believe this work illustrates the importance of standardizing protocols and reporting reliable quality metrics to improve consistency and accuracy in electrochemistry. Furthermore, adopting the practices presented in this work would greatly benefit the evaluation and comparison of electrochemical energy materials and devices operating with alkaline electrolytes. Figure 1

Quantum Computer Simulation of Protein Protonation.

In attempts to simulate the protonation of proteins, a major challenge is that the number of protonation states grows rapidly as a function (2N) of the number of protonation sites (N). Expression on the free energy of the protonation state as an N-site Ising model ─ using an empirical Generalized-Born model ─ allows a quantum computer to efficiently determine the important states at a given pH value and subsequently reconstruct the pH titration process at all sites. Compared with the exact results painstakingly obtained with classical computers, the results obtained using quantum computers show good agreement for staphylococcal nuclease and excellent agreement for α-lactalbumin. This work illustrates the effectiveness of quantum computers in sampling important physical states, which may be useful in attacking challenging biomolecular problems.

A novel pyrene‐based “off–on” fluorescent probe with high selectivity and sensitivity for Hg2+

AbstractIn this article, a novel “off–on” fluorescent probe 2‐(pyren‐1‐ylmethylene)‐1H‐indene‐1,3(2H)‐dione (PID) for Hg2+ was designed and synthesized. The selectivity, concentration titration, pH titration, time dependence, limit of detection, and recognition mechanism of PID for Hg2+ in CH3CH2OH/H2O solution were also investigated. The results indicated that PID exhibited high selectivity, sensitivity, and fast response to Hg2+, and the limit of detection was as low as 20.7 nmol/L. In addition, PID could work in a wide pH range, and the determination of Hg2+ in water samples showed that it could be used as a potential detection tool in practical application.

Complexation of Fluorofenidone by Cucurbit[7]uril and β-Cyclodextrin: Keto-Enol Tautomerization to Enhance the Solubility.

This study is designed to compare drug encapsulation by cucurbit[7]uril and β-cyclodextrin, using fluorofenidone as a model drug. Single-crystal X-ray diffraction analysis was employed to successfully determine the crystal structures of fluorofenidone·H+@cucurbit[7]uril Form, fluorofenidone@cucurbit[7]uril Form, and fluorofenidone@β-cyclodextrin Form. Keto-enol tautomerization of fluorofenidone mediated by cucurbit[7]uril in acid solution is confirmed by crystal structures, pH titration, and nuclear magnetic resonance experiments. However, β-cyclodextrin cannot cause the keto-enol tautomerization of fluorofenidone under similar conditions. The phase solubility study demonstrates that cucurbit[7]uril has a much higher solubilization capacity for fluorofenidone than β-cyclodextrin in 0.1 M HCl since the Kc values of fluorofenidone with cucurbit[7]uril and β-cyclodextrin were 1223.97 ± 452.68 and 78.49 ± 10.56 M-1, respectively. Excellent solubility can be attributed to the keto-enol tautomerization of fluorofenidone under the conditions of cucurbit[7]uril in acid solution. The enol form of fluorofenidone is encapsulated by cucurbit[7]uril by hydrogen bonding interaction and hydrophobic interaction to increase binding affinity. Rat pharmacokinetic studies demonstrate that the area under the plasma concentration-time curve from time 0 to 7 h value of fluorofenidone@cucurbit[7]uril complex is 1.70-fold greater than that of free fluorofenidone, and the mean residence time from time 0 to 7 h is slightly prolonged from 1.29 to 1.76 h (P < 0.01) after oral administration. However, no significant difference is found between fluorofenidone and fluorofenidone@β-cyclodextrin complex. This work indicates that the induction of keto-enol tautomerization of drugs using macrocyclic molecules has the potential to be an effective method to improve their solubility and bioavailability, providing valuable insights for the application of macrocyclic molecules in the biomedical field.

Histidine Protonation and Conformational Switching in Diphtheria Toxin Translocation Domain.

Protonation of key histidine residues has been long implicated in the acid-mediated cellular action of the diphtheria toxin translocation (T-) domain, responsible for the delivery of the catalytic domain into the cell. Here, we use a combination of computational (constant-pH Molecular Dynamics simulations) and experimental (NMR, circular dichroism, and fluorescence spectroscopy along with the X-ray crystallography) approaches to characterize the initial stages of conformational change happening in solution in the wild-type T-domain and in the H223Q/H257Q double mutant. This replacement suppresses the acid-induced transition, resulting in the retention of a more stable protein structure in solutions at pH 5.5 and, consequently, in reduced membrane-disrupting activity. Here, for the first time, we report the pKa values of the histidine residues of the T-domain, measured by NMR-monitored pH titrations. Most peaks in the histidine side chain spectral region are titrated with pKas ranging from 6.2 to 6.8. However, the two most up-field peaks display little change down to pH 6, which is a limiting pH for this protein in solution at concentrations required for NMR. These peaks are absent in the double mutant, suggesting they belong to H223 and H257. The constant-pH simulations indicate that for the T-domain in solution, the pKa values for histidine residues range from 3.0 to 6.5, with those most difficult to protonate being H251 and H257. Taken together, our experimental and computational data demonstrate that previously suggested cooperative protonation of all six histidines in the T-domain does not occur.

Eu(III) and Cm(III) Complexation by the Aminocarboxylates NTA, EDTA, and EGTA Studied with NMR, TRLFS, and ITC-An Improved Approach to More Robust Thermodynamics.

The complex formation of Eu(III) and Cm(III) was studied via tetradentate, hexadentate, and octadentate coordinating ligands of the aminopolycarboxylate family, viz., nitrilotriacetate (NTA3-), ethylenediaminetetraacetate (EDTA4-), and ethylene glycol-bis(2-aminoethyl ether)-N,N,N',N'-tetraacetate (EGTA4-), respectively. Based on the complexones' pKa values obtained from 1H nuclear magnetic resonance (NMR) spectroscopic pH titration, complex formation constants were determined by means of the parallel-factor-analysis-assisted evaluation of Eu(III) and Cm(III) time-resolved laser-induced fluorescence spectroscopy (TRLFS). This was complemented by isothermal titration calorimetry (ITC), providing the enthalpy and entropy of the complex formation. This allowed us to obtain genuine species along with their molecular structures and corresponding reliable thermodynamic data. The three investigated complexones formed 1:1 complexes with both Eu(III) and Cm(III). Besides the established Eu(III)-NTA 1:1 and 1:2 complexes, we observed, for the first time, the existence of a Eu(III)-NTA 2:2 complex of millimolar metal and ligand concentrations. Demonstrated for thermodynamic studies on Eu(III) and Cm(III) interaction with complexones, the utilized approach is commonly applicable to many other metal-ligand systems, even to high-affinity ligands.

Investigation of the influence of pH on the properties and morphology of gelatin hydrogels

AbstractThe behavior of gelatin hydrogels is influenced by the charges located on the amino acid side chains throughout the gelatin molecules. The presence and distribution of ionisable side chains influences the surface activity of gelatin and ultimately determines the material properties. Herein, we report the influence of pH on mechanical properties as studied by texture analysis supported by data from polarimetry, zeta potential, pH titrations and NMR experiments. When adjusted to more extreme pH values (pH 2 and 12), softer gelatin blocks were observed. However, at pH values close to the isoelectric point (pH 5–10), the material is firmer. This behavior is related to the helical content. At pH 2 and pH 12 the surface of the gelatin carries a net charge, positive and negative, respectively, that inhibits the formation of tight helices and lowers the physical crosslink network density. Chemical shift perturbations were observed for the acidic amino acids glutamic and aspartic acid, under acidic pH, where their peaks shifted to higher ppm. Intense amide signals were observed at acidic pH but diminished with increasing pH. This was due to an increase in the rate of chemical exchange between the solvent and peptide amide protons as the pH increases.

Macadamia oil-based oleogels as cocoa butter alternatives: Physical properties, oxidative stability, lipolysis, and application

In this study, macadamia oil-based oleogels were prepared using monoglyceride stearate (MG) as a gelator with a low critical gelation concentration (3.0 wt%). The physical properties of the oleogels were evaluated by polarized light microscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray diffraction, texture and rheological analysis. And the lipid digestion and oxidative stability of the macadamia oil were determined by pH titration and accelerated oxidation test, respectively. The results showed that the hardness, oil binding capacity, and thermal stability of the oleogels increased with increasing MG concentration, which was attributed to the formation of a network of MG crystals held together by van der Waals interactions and hydrogen bonds. Rheological analysis indicated that all the oleogels exhibited a thermally reversible solid-to-liquid transition and viscoelastic behavior at ambient temperatures. Moreover, the formation of oleogels increased fatty acid release during in vitro lipid digestion and improved the oxidative stability of the macadamia oil. In addition, the potential application of these oleogels as replacements for saturated fats in foods was demonstrated by creating a chocolate product where the cocoa butter was replaced with macadamia oil-based oleogels with a high degree of unsaturation. These results can provide guidance for the preparation of macadamia oil-based oleogels, which may increase their application in foods.

Development of ratiometric fluorescent probes based on peptides for sensing Pb2+ in aquatic environments and human serum.

The detection of Pb2+ ions in aquatic environments and biofluid samples is crucial for assessment of human health. Herein, we synthesized two fluorescent probes (1 and 2) consisting of the peptide receptor for Pb2+ and a benzothiazolyl-cyanovinylene fluorophore that exhibited excimer-like emission when it aggregated. The peptide-based probes sensitively detected Pb2+ in purely aqueous solution (1% DMF) through ratiometric fluorescent response with a decrease in monomer emission at 520nm and an increase in excimer emission at 570nm. Specially, probe 2 showed remarkable detection features such as high selectivity for Pb2+over 15 metal ions, high binding affinity (Kd=5.83×10-7 M) for Pb2+, significant emission intensity changes, low detection limit (3.8nM) of Pb2+, high water solubility, and visible light excitation (450nm). Probe 2 was successfully used to quantify nanomolar concentration (0∼800nM) of Pb2+ in real water samples (ground water and tap water). Specially, 2 was successfully applied for the quantification of Pb2+ in human serum by combination of microwave-assisted human serum digestion and filtration of digested serum by anion exchange cartridge. We clearly investigated the binding mode of 2 with Pb2+ using 1H NMR, IR spectroscopy, pH titration, confocal microscopy, and size analysis. The peptide-based fluorescent probe might have great application potential for sensing Pb2+ in aquatic environments and biofluid samples.

Functional characterization of xanthorhodopsin in Salinivibrio socompensis, a novel halophile isolated from modern stromatolites.

A putative xanthorhodopsin-encoding gene, XR34, was found in the genome of the moderately halophilic gammaproteobacterium Salinivibrio socompensis S34, isolated from modern stromatolites found on the shore of Laguna Socompa (3570m), Argentina Puna. XR-encoding genes were clustered together with genes encoding X-carotene, retinal (vitamin-A aldehyde), and carotenoid biosynthesis enzymes while the carotene ketolase gene critical for the salinixanthin antenna compound was absent. To identify its functional behavior, we herein overexpressed and characterized this intriguing microbial rhodopsin. Recombinant XR34 showed all the salient features of canonical microbial rhodopsin and covalently bound retinal as a functional chromophore with λmax = 561nm (εmax ca. 60,000M-1cm-1). Two canonical counterions with pK values of around 6 and 3 were identified by pH titration of the recombinant protein. With a recovery time of approximately half an hour in the dark, XR34 shows light-dark adaptation shifting the absorption maximum from 551 to 561nm. Laser-flash induced photochemistry at pH 9 (deprotonated primary counterion) identified a photocycle starting with a K-like intermediate, followed by an M-state (λmax ca. 400nm, deprotonated Schiff base), and a final long wavelength-absorbing N- or O-like intermediate before returning to the parental 561nm-state. Initiating the photocycle at pH 5 (protonated counterion) yields only bathochromic intermediates, due to the lacking capacity of the counterion to accept the Schiff base proton. Illumination of the membrane-embedded protein yielded a capacitive transport current. The presence of the M-intermediate under these conditions was demonstrated by a blue light-induced shunt process.

Hydroxyl ion release ability from mixture of Indonesian White Portland Cements - Bi2O3 - Light Cured Methacrylate Based Resin as a Potential Pulp Capping Material

ABSTRACTIntroduction: The bioactivity property of pulp capping materials is determined by the hydroxyl ion release ability, which may alter the environmental pH to become alkaline. Calcium silicate-based materials are antibacterial, able to induce reparative dentin and have a good bacteria-tight seal. The poor handling of calcium silicate-based materials can be overcome by adding resin, so the materials will be easier to handle. Therefore, the purpose of this study was to synthesize a mixture of Indonesian White Portland Cements - Bi2O3 – UDMA and analyzed its hydroxyl ion release ability. Methods: The Indonesian White Portland Cements - Bi2O3 mixture was prepared using the simple solution method and mixed with UDMA. The sample’s ability to release hydroxyl ions was measured using a pH meter and titration test. Results: This study showed that the mixture of Indonesian White Portland Cements - Bi2O3 - UDMA had an initial pH of 11.04 and increased to its peak on 168 hours mark, or on day seven, to pH 11,77 with hydroxyl ion release value of 10-2.23 Conclusion: The mixture of Indonesian White Portland Cements - Bi2O3 -UDMA had an alkaline pH, was able to release hydroxyl ion and had a potential to be used as a pulp capping material.Keywords: The mixture Indonesia White Portland Cements - Bi2O3 – UDMA, Hydroxyl ion, Release Ability