Potentiometric pH Research Articles

Synthesis, single crystal X-ray characterization, and solution studies of Zn(II)-, Cu(II)-, Ag(I)- and Ni(II)-pyridine-2,6-dipicolinate N-oxide complexes with different topologies and coordination modes

In this paper, we have synthesized two new coordination complexes and two new coordination polymers at room temperature formulated as {(Htata)2[Cu(pydco)2(tata)]·3H2O} (1), {(H9a-acr)2[Ni0.51Zn0.49(pydco)2(H2O)2]·4H2O} (2), [Cu(pydco)(H2O)2]n (3), [Ag(Hpydco)(2a-pym)]n (4) in which pydco=pyridine-2,6-dicarboxylic acid N-oxide, tata=2,4,6-triamino-1,3,5-triazine (melamine), 9a-acr=9-aminoacridine and 2a-pym=2-aminopyrimidine. The structures of these compounds and their physical and chemical properties were characterized via elemental analysis, infrared spectroscopy and single crystal X-ray diffraction methods. Complex 1has a honeycomb-like 2-D network whilst complex 2 is a mixed crystal with almost equal amounts of Ni and Zn in the metal sites and has a 4-connected {4^4.6^2}topology. Complexes 3 and 4 display coordination modes for the pydco ligand which differ from those of previous reports. Complex 3 forms a 1-D 3-connected staircase-like network with unequal footsteps and possess a {4^2.6} topology while 4 is a 2-D staircase-like 4-connected network with a {4^4.6^2} topology exhibiting rectangular grids Ag–Ag interactions. In the structures of 1–4 several supramolecular interactions like hydrogen-bonding and π⋯π and lone pair⋯π stacking interactions play important roles in the formation and stability of the crystalline materials. The complexation reactions of these systems with Cu2+ and Ag+ ions were investigated by potentiometric pH titration method (solution studies). The stoichiometry of the most abundant species in the solution was very similar to the corresponding crystalline metal ion complexes.

A novel salt of antidiabetic drug metformin resulting from a proton transfer reaction: Synthesis, characterization, crystal structure and solution studies

Reaction between N,N-dimethylebiguanidine, Met = Metformin, and 4-hydroxy-2,6-pyridinedicarboxylic acid, HO-dipicH2, results in the formation of a novel proton transfer compound, [MetH2][HO-dipicH]2·H2O, 1. The characterization was performed using FTIR, UV–Vis, 1H and 13C NMR spectroscopy and X-ray crystallography. The crystal system is triclinic with space group P1¯ and two molecules per unit cell. The protonation constants of O-dipic and Met, in all of probability protonated forms, and the equilibrium constants for the O-dipic–Met proton transfer system were investigated by the potentiometric pH titration method using the Hyperquad2008 program. The stoichiometry of the proton transfer species in solution were in agreement with the solid state result.

Acid–Base Properties of N-Doped Carbon Nanotubes: A Combined Temperature-Programmed Desorption, X-ray Photoelectron Spectroscopy, and 2-Propanol Reaction Investigation

Chemical and electronic properties of N-doped multiwalled carbon nanotubes (NCNTs) synthesized by NH3 treatment of preoxidized CNTs at 300, 500, and 700 °C have been investigated by a set of surface sensitive techniques. Temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) were applied to characterize the nature, thermal stability, and binding state of N and/or O containing surface functional groups. Acid–base properties in aqueous phase were analyzed by potentiometric pH titration, while the catalytic reaction of 2-propanol probed the acid–base behavior of the materials in the gas phase. NH3 treatment at 300 °C leads to an acid–base bifunctional surface, predominantly decorated with imide species. Contrarily, pyrrolic N is the most abundant moiety present on the sample modified at 500 °C. Here, only small fractions of lactam groups and pyridinic species are present. The incorporation of N at 700 °C leads to a carbon nanotube (CNT) surface with a well-defined basicity due to ...

Real-Time Monitoring of Bacterial Metabolites By Scanning Electrochemical Microscopy (SECM)

Scanning Electrochemical Microscopy (SECM) is used to study the local chemical environment above live bacterial biofilms such as S. gordonii (Sg), S. mutans (Sm) etc. In this study, we report the development of a Pt decorated carbon nanotubes (CNTs) based dual SECM probe to detect low micro-molar range hydrogen peroxide (H2O2) produced by the live bacterial biofilm. This sensor showed sensitivity 2.2 ± 5 mA cm-2 mM-1 with low detection limit of 0.5 µM. Our results indicate that the Sg produced 65-70 μM H2O2 within 30 min in presence of 1 mM glucose in artificial saliva solution (pH 7.2) at 37°C. In addition, we have also developed a unique solid state carbon based potentiometric pH sensor and used as a SECM probe to map the pH change at high spatial resolution above the Sg biofilm. The sensor showed Nernstian response with slope of 58±4 and very fast response time of 5s. The pH mapping above the biofilm showed that pH above the biofilm dropped by one pH unit within 30 min only in 6 pH artificial saliva with 30 mM sucrose at 37°C. Recent developments about the real-time metabolic exchange between two bacterial species (Sg and Sm) in terms of peroxide and pH will be presented in the conference. Figure 1

A novel thiol-affinity micropipette tip method using zinc(II)-cyclen-attached agarose beads for enrichment of cysteine-containing molecules.

Cysteine-containing biomolecules are attractive targets in the study of thiol biology. Here we introduce a novel method for the selective enrichment of thiol-containing molecules using a thiol-capture zinc(II) complex of 1,4,7,10-tetraazacyclododecane (Zn(2+)-cyclen). Recognition of N-acetylcysteine amide by Zn(2+)-cyclen has been studied by potentiometric pH titration, revealing formation of a 1:1 thiolate-bound Zn(2+)-cyclen complex with a large thiolate-affinity constant of 10(6.2)M(-1) at 25°C and I=0.10M (NaCl). The Zn(2+)-bound thiolate anion is unexpectedly stable in aqueous solution at pH 7.8 under atmospheric conditions for a few days. These findings have contributed to the development of a convenient method for separation of thiol compounds by using a micropipette tip. A 200μL micropipette tip containing 10μL of hydrophilic cross-linked agarose beads attached to Zn(2+)-cyclen moieties was prepared. All steps for thiol-affinity separation (binding, washing, and eluting) are conducted using aqueous buffers at room temperature. The entire separation protocol requires less than 15min per sample. We demonstrate practical example separations of cysteine-containing molecules. This micropipette tip method would be used preferentially as an alternative to existing tools for reliable enrichment of thiol-containing molecules.

Effective cleavage of phosphodiester promoted by the zinc(II) and copper(II) inclusion complexes of β-cyclodextrin

To construct the model of metallohydrolase, two inclusion complexes [MLCl2(β-CD)] (1, M=Zn(II); 2, M=Cu(II); L=N,N′-bis(2-pyridylmethyl)amantadine; β-CD=β-cyclodextrin) were synthesized by mixing β-CDs with the pre-synthesized complexes G1, [ZnLCl2] and G2, [CuLCl2]. Structures of G1, G2, 1 and 2 were characterized by X-ray crystallography, respectively. In solution, two chloride anions of G1 and G2 underwent ligand exchange with solvent molecules according to ESI-MS analysis. The chemical equilibrium constants were determined by potentiometric pH titration. The kinetics of bis(4-nitrophenyl) phosphate (BNPP) hydrolysis catalyzed by G1, G2, 1 and 2 were examined at pHs ranging from 7.50 to 10.50 at 308±0.1K. The pH profile of rate constant of BNPP hydrolysis catalyzed by 1 exhibited an exponential increase with the second-order rate constant of 2.68×10−3M−1s−1 assigned to the di-hydroxo species, which was approximately an order of magnitude higher than those of reported mono-Zn(II)-hydroxo species. The high reactivity was presumably hydroxyl-rich microenvironment provided by β-CDs, which might effect in stabilizing either the labile zinc-hydroxo species or the catalytic transition state.

Cell Monitoring and Manipulation Systems (CMMSs) based on Glass Cell-Culture Chips (GC3s)

We developed different types of glass cell-culture chips (GC3s) for culturing cells for microscopic observation in open media-containing troughs or in microfluidic structures. Platinum sensor and manipulation structures were used to monitor physiological parameters and to allocate and permeabilize cells. Electro-thermal micro pumps distributed chemical compounds in the microfluidic systems. The integrated temperature sensors showed a linear, Pt1000-like behavior. Cell adhesion and proliferation were monitored using interdigitated electrode structures (IDESs). The cell-doubling times of primary murine embryonic neuronal cells (PNCs) were determined based on the IDES capacitance-peak shifts. The electrical activity of PNC networks was detected using multi-electrode arrays (MEAs). During seeding, the cells were dielectrophoretically allocated to individual MEAs to improve network structures. MEA pads with diameters of 15, 20, 25, and 35 µm were tested. After 3 weeks, the magnitudes of the determined action potentials were highest for pads of 25 µm in diameter and did not differ when the inter-pad distances were 100 or 170 µm. Using 25-µm diameter circular oxygen electrodes, the signal currents in the cell-culture media were found to range from approximately −0.08 nA (0% O2) to −2.35 nA (21% O2). It was observed that 60-nm thick silicon nitride-sensor layers were stable potentiometric pH sensors under cell-culture conditions for periods of days. Their sensitivity between pH 5 and 9 was as high as 45 mV per pH step. We concluded that sensorized GC3s are potential animal replacement systems for purposes such as toxicity pre-screening. For example, the effect of mefloquine, a medication used to treat malaria, on the electrical activity of neuronal cells was determined in this study using a GC3 system.

Rapid measurement of urease activity using a potentiometric RuO2 pH sensor for detection of Helicobacter pylori

The feasibility of using a thin-film RuO2 (ruthenium oxide) pH sensor for the detection of Helicobacter pylori is investigated. In particular, we demonstrate the ability of the sensor to measure urease activity between 1.0 and 50U/mL in less than 30s. The developed sensor exhibited a super-Nernstian response of 77.74mV/pH and excellent reversibility. The pH sensor⿿s ability to detect H. pylori in real time is demonstrated, and found to be much faster than the rapid urease test.

Mechanism of Macroscopic Motion of Oleate Helical Assemblies: Cooperative Deprotonation of Carboxyl Groups Triggered by Photoisomerization of Azobenzene Derivatives.

Macroscopic and spatially ordered motions of self-assemblies composed of oleic acid and a small amount of an azobenzene derivative, induced by azobenzene photoisomerization, was previously reported. However, the mechanism of the generation of submillimeter-scale motions by the nanosized structural transition of azobenzene was not clarified. Herein, an underlying mechanism of the motions is proposed in which deprotonation of carboxyl groups in cooperation with azobenzene photoisomerization causes a morphological transition of the self-assembly, which in turn results in macroscopic forceful dynamics. The photoinduced deprotonation was investigated by potentiometric pH titration and FTIR spectroscopy. The concept of hierarchical molecular interaction generating macroscale function is expected to promote the next stage of supramolecular chemistry.

Fabrication and Use of Dual‐function Iridium Oxide Coated Gold SECM Tips. An Application to pH Monitoring above a Copper Electrode Surface during Nitrate Reduction.

AbstractThe fabrication of a gold microelectrode modified with iridium oxide film (IrOx) and its use as tip with a dual function in SECM experiments is reported. The defective structure of the coating onto the microelectrode surface was used as strategy to combine the advantages of both amperometric (for current‐distance determination) and potentiometric (for pH sensing) SECM operation modes. Approach curves, using oxygen and hexaammineruthenium(III) as redox mediators, were obtained without significant loss of the performance and reproducibility of the potentiometric pH response. This allowed the precise positioning of the proposed tip above a substrate in SECM experiments and, subsequently, to monitor pH at the substrate surface. The IrOx modified microelectrode was applied successfully in SECM experiments involving the local proton consumption during the nitrate reduction at a copper cathode surface.

Mn(II) and Zn(II) ions catalytic oxidation of o-phenylenediamine and characterization, X-ray crystal structure and solution study of the final products DAPH+Cl−·3H2O and [DAPH][Zn(dipicH)(dipic)]·4H2O

Compound DAPH+Cl−·3H2O (1), and complexes Mn(dipic)(H2O)3 (2) and [DAPH][Zn(dipicH)(dipic)]·4H2O (3), (dipicH2=2,6-pyridinedicarboxylic acid and DAP=2,3-diaminophenazine) were prepared from the reaction of MgCl2·4H2O and ZnCl2 with mixture of o-phenylenediamine (OPD) and 2,6-pyridinedicarboxylic acid in water. These compounds were characterized by elemental analysis, FTIR, 1H NMR and UV–Vis spectroscopy. The solid-state structure of [DAPH][Zn(dipicH)(dipic)]·4H2O (monoclinic, P21/c) was determined by the single crystal X-ray diffraction method. The protonation constants of dipic and DAP, in all of probability protonated forms, the equilibrium constants for the dipic–DAP proton transfer system and the stoichiometry and stability constants of binary and ternary complexes of this system with Zn2+ and Mn2+ ions in aqueous solution were investigated by the potentiometric pH titration method. The stoichiometries of the most complex species in solution were compared with corresponding crystalline complexes in the solid state.

Characterization and application of a new pH sensor based on magnetron sputtered porous WO3 thin films deposited at oblique angles

In this communication we report about an outstanding solid-state pH sensor based on amorphous nanocolumnar porous thin film electrodes. Transparent WO3 thin films were deposited by reactive magnetron sputtering in an oblique angle configuration to enhance their porosity onto indium tin oxide (ITO) and screen printed electrodes (SPE). The potentiometric pH response of the nanoporous WO3-modified ITO electrode revealed a quasi-Nernstian behaviour, i.e. a linear working range from pH 1 to 12 with a slope of about ⿿57.7mV/pH. pH detection with this electrode was quite reproducible, displayed excellent anti-interference properties and a high stable response that remained unaltered over at least 3 months. Finally, a pH sensor was developed using nanoporous WO3-modified screen printed electrode (SPE) using a polypyrrole-modified Ag/AgCl electrode as internal reference electrode. This full solid state pH sensor presented a Nernstian behaviour with a slope of about ⿿59mV/pH and offered important analytical and operation advantages for decentralized pH measurements in different applications.

Environmental Soil Quality Research as Prediction for Sustainable Orchards Cultivation in Southern Serbia

<p>Soil quality is one of the main environmental conditions for successful and sustainable orchards cultivation. The main role of the soil is reflected in its production activities or productivity. Soil fertility implies content available nutrients, such as individual elements, pH and humus. The research of soil quality leads to certain conclusions about which soil is suitable for growing crops. The investigation of soil quality for Pcinja District in southern Serbia is performed, with the goal to complete environmental conditions for cultivation of the most suitable crops. The methods that were used for the analysis of the soil in the laboratory are: chemical and Al-methods and calibration and potentiometric, spectrophotometric, photometric. For potentiometric method pH meter, spectrophotometer classic which is determined by phosphorus and Flame Photometar device that determines potassium are used. The results in this paper show high quality land for sustainable growing fruit crops.</p>

Force Field for Mg(2+), Mn(2+), Zn(2+), and Cd(2+) Ions That Have Balanced Interactions with Nucleic Acids.

Divalent metal ions are of fundamental importance to the function and folding of nucleic acids. Divalent metal ion-nucleic acid interactions are complex in nature and include both territorial and site specific binding. Commonly employed nonbonded divalent ion models, however, are often parametrized against bulk ion properties and are subsequently utilized in biomolecular simulations without considering any data related to interactions at specific nucleic acid sites. Previously, we assessed the ability of 17 different nonbonded Mg(2+) ion models to reproduce different properties of Mg(2+) in aqueous solution including radial distribution functions, solvation free energies, water exchange rates, and translational diffusion coefficients. In the present work, we depart from the recently developed 12-6-4 potential models for divalent metal ions developed by Li and Merz and tune the pairwise parameters for Mg(2+), Mn(2+), Zn(2+), and Cd(2+) binding dimethyl phosphate, adenosine, and guanosine in order to reproduce experimental site specific binding free energies derived from potentiometric pH titration data. We further apply these parameters to investigate a metal ion migration previously proposed to occur during the catalytic reaction of the hammerhead ribozyme. The new parameters are shown to be accurate and balanced for nucleic acid binding in comparison with available experimental data and provide an important tool for molecular dynamics and free energy simulations of nucleic acids where these ions may exhibit different binding modes.

A SOLID Fe2O3-GRAPHITE COMPOSITE ELECTRODE FOR pH MEASUREMENT

A solid Fe2O3-graphite composite electrode was prepared and investigated for use as a potentiometric pH sensor. The electrode was constructed by mixing iron (III) oxide, oxidized graphite and wax that was put over silver disc onto a polypropylene rod. The response of the electrode was investigated by measuring electrode potential as a function of pH.The effect of composition of the electrode material (Fe2O3 and oxidized graphite ration) on the electrode response was investigated. The electrode with 40% Fe2O3, 30% graphite and 30% wax by mass was found to give the best potentiometric response. This electrode behaves in Nernstian manner with a potentiometric gradient of 56.6±0.4 mV per unit change in pH at 25?C within the working range of pH 2-9.The electrode was also used for the end-point detection in potentiometric acid-base titrations and found to be an excellent electrode for pH-metric titration. The effect of oxidation of electrode on pH response was investigated by dipping electrode in 0.1N KMnO4, 1:1HNO3 and 0.1N Ce4+ solutions for different interval of time. This treatment of the electrode with oxidizing agents increased the standard electrode potential of the electrode however potential gradient per unit change in pH remains unaltered. Low cost, quick response and easy to prepare are the advantages of the iron oxide - graphite composite electrode as a pH sensor. However some metal ions and oxidising agents interfered in the determination of pH using this electrode which is the limitation of using these electrodes.Scientific World, Vol. 12, No. 12, September 2014, page 44-47

Potentiometric RuO2–Ta2O5 pH sensors fabricated using thick film and LTCC technologies

The paper reports on the preparation, properties and application of potentiometric pH sensors with thick film RuO2–Ta2O5 sensing electrode and Ag/AgCl/KCl reference electrode screen printed on an alumina substrate. Furthermore, it presents fabrication procedure and characterization of a new miniaturized pH sensor on LTCC (low temperature cofired ceramics) substrate, destined for wireless monitoring. The crystal structure, phase and elemental composition, and microstructure of the films were investigated by X-ray diffractometry, Raman spectroscopy, scanning electron microscopy and energy dispersive spectroscopy. Potentiometric characterization was performed in a wide pH range of 2–12 for different storage conditions and pH loops. The advantages of the proposed thick film pH sensors are: (a) low cost and easy fabrication, (b) excellent sensitivity close to the Nernstian response (56mV/pH) in the wide pH range, (c) fast response, (d) long lifetime, (e) good reproducibility, (f) low hysteresis and drift effects, and (g) low cross-sensitivity towards Li+, Na+ and K+ as interfering ions. The applicability of the sensors for pH measurement of river, tap and distilled water, and some drinks was also tested.

Geochemical characterization and heavy metal migration in a coastal polluted aquifer incorporating tidal effects: field investigation in Chongming Island, China.

The occurrence and migration of heavy metal in coastal aquifer incorporating tidal effects were investigated in detail by the field geological survey and observation. The continuous groundwater sampling, field observation (for groundwater potentiometric surface elevation, pH, dissolved oxygen, temperature, and salinity), and laboratory analysis (for Cr, Ni, Cu, Zn, Cd, and Pb concentration) were conducted through eight monitoring wells located around the landfill in the northern part of Chongming Island, China. The results showed that the unconfined aquifer medium was estuary-littoral facies deposit of Holocene, mainly gray clayey silt and grey sandy silt, and the groundwater flow was mainly controlled by topography condition of the aquifer formation strike. The background values of Cr, Ni, Cu, Zn, Cd, and Pb in Chongming Island were 3.10 ± 3.09, 0.81 ± 0.25, 1.48 ± 1.09, 43.32 ± 33.06, 0.08 ± 0.16, and 0.88 ± 1.74 μg/L, respectively. Compared with the groundwater samples around the study area, the drinking water was qualified and was free from the seawater intrusion/estuarine facies contaminant encroachment. Pollutant discharge was reflected in water quality parameters, the Cr and Cu concentrations elevated to the peak of 50.07 and 46.00 μg/L, respectively, and meanwhile specific migration regularity was embodied in observation time series as well as other elements. This migration regularity was not fully identical according to correlations between these analyzed elements. Ambient watery environment, anthropogenic disturbance, regional hydrogeological condition, and biogeochemical reactivity on heavy metals reduced/altered the significance of elements correlation in the migration pathway in coastal aquifer.

A comparison of solution and solid state coordination environments for calcium(II), zirconium(IV), cadmium(II) and mercury(II) complexes with dipicolinic acid and methylimidazole derivatives

Four new supramolecular compounds, (2-mimH)[Ca(pydcH)3][Ca(pydcH2)(pydc)(H2O)2]·4H2O (1), (1-mimH)2[Zr(pydc)3] (2), (2-mimH)2[Cd(pydc)2]·8H2O (3), and (2-mimH)2[Hg(pydc)2]·8H2O (4) [where pydcH2 = pyridine-2,6-dicarboxylic acid (dipicolinic acid), 1-mim = 1-methylimidazole, and 2-mim = 2-methylimidazole], have been synthesized and characterized by elemental analyses, spectroscopic techniques (IR, UV–vis, 1H NMR, and 13C NMR), thermal (TG/DTG/DTA) analysis as well as single-crystal X-ray diffraction. All four compounds are proton-transfer salts of the methylimidazolium cations and metal complex anions that crystallized from a solution of pyridine-2,6-dicarboxylic acid, methylimidazole, metal nitrates or chlorides as starting materials. The coordinating dicarboxylic acid is deprotonated at the carboxyl group and methylimidazole is protonated to balance the charge. In the crystal structures of 1–4, hydrogen bonding and π–π stacking play important roles. Water clusters are formed in 1, 3, and 4. The equilibrium constants of dipicolinic acid (pydc) and methylimidazole derivatives (1-mim and 2-mim), pydc-2-mim, pydc-1-mim proton-transfer systems as well as those of their complexes were investigated by a potentiometric pH titration method. The stoichiometries of most of the complex species in solution were very similar to the cited crystalline metal ion complexes.

All-solid-state potentiometric sensors with a multiwalled carbon nanotube inner transducing layer for anion detection in environmental samples.

While ion to electron transducing layers for the fabrication of potentiometric membrane electrodes for the detection of cations have been well established, similar progress for the sensing of anions has not yet been realized. We report for this reason on a novel approach for the development of all-solid-state anion selective electrodes using lipophilic multiwalled carbon nanotubes (f-MWCNTs) as the inner ion to electron transducing layer. This material can be solvent cast, as it conveniently dissolves in tetrahydrofuran (THF), an important advantage to develop uniform films without the need for using surfactants that might deteriorate the performance of the electrode. Solid contact sensors for carbonate, nitrate, nitrite, and dihydrogen phosphate are fabricated and characterized, and all exhibit comparable analytical characteristics to the inner liquid electrodes. For example, the carbonate sensor exhibits a Nernstian slope of 27.2 ± 0.8 mV·dec(-1), a LOD = 2.3 μM, a response time of 1 s, a linear range of four logarithmic units, and a medium-term stability of 0.04 mV·h(-1) is obtained in a pH 8.6 buffered solution. Water layer test, reversibility, and selectivity for chloride, nitrate, and hydroxide are also reported. The excellent properties of f-MWCNTs as a transducer are contrasted to the deficient performance of poly(3-octyl-thiophene) (POT) for carbonate detection. This is evidenced both with a significant drift in the potentiometric measures as well as a pronounced sensitivity to light (either sunlight or artificial light). This latter aspect may compromise its potential for environmental in situ measurements (night/day cycles). The concentration of carbonate is determined in a river sample (Arve river, Geneva) and compared to a reference method (automatic titrator with potentiometric pH detection). The results suggest that nanostructured materials such as f-MWCNTs are an attractive platform as a general ion-to-electron transducer for anion-selective electrodes.

An experimental and theoretical study of a hydrogen-bonded complex: O-phenylenediamine with 2,6-pyridinedicarboxylic acid

The hydrogen-bonded complex, [(OPDH)+(dipicH)−.H2O], between o-phenylenediamine (OPD) and 2,6-pyridinedicarboxylic acid (dipicH2) has been characterized in water by the 1H, 13C NMR and IR spectroscopies. The crystal structure showed that the edge to face C–H⋯π and C–O⋯π stacking interactions between the dipicH2 and OPD rings play an extra significant role in the formation of the hydrogen-bonded complex and supported the H-bonding interactions. The proton transfer also investigated theoretically in gas phase and thermodynamic parameters such as ΔH‡, ΔG‡, ΔS‡ were calculated for this process. Moreover, intramolecular hydrogen-bonding interaction has been recognized by calculating the electron density ρ(r) and Laplacian ∇2ρ(r) at the bond critical point (BCP) using Atoms-In-Molecule (AIM) method and also the interaction between electron acceptor (σ*) of OH with the lone pair of the nitrogen atom as an electron donor using Natural Bond Orbital (NBO) analysis. In addition, the protonation constants of dipicH2 and OPD and the equilibrium constants for the dipic-OPD (1:1) proton transfer system were obtained by the potentiometric pH titration method using the Hyperquad 2008 program. The stoichiometry of the proton transfer species in the solution confirmed the solid state result.