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Tramadol is a centrally acting analgesic with weak opioid agonist properties, which also has monoaminergic activity, exerted via inhibition of neuronal uptake of serotonin and norepinephrine. Tramadol is generally well tolerated and the most common adverse events are nausea, dizziness, drowsiness, sweating, vomiting and dry mouth. The effect of intraperitoneal injection of tramadol and pilocarpine were studied in rats on the flow of saliva, histological and histochemical change in the parotid salivary gland. The rats were divided into three groups, first group, rats received saline and used as control. The second group treated with 10 mg tramadol hydrochloride for three days. The third group treated with tramadol hydrochloride for three days followed with 1 mg pilocarpine. The rats were sacrificed at the fourth day after the end of experimental procedure. The administration of tramadol caused decreased in salivary flow rate by approximately 60 %. The parotid histopathological changes include vacuolation and atrophy of acini and excessive widening of the interstitial tissue area which are replaced by extensive fibrosis fibrosis mostly associated with the degenerated ducts and acini and their replaced by inflammatory cells.

In this investigation, the azo dyes; 2-(3′-phenyl-5′-pyrazolyl azo) schaffer acid (la) and 2-(3′-phenyl-5′-pyrazolyl azo) resorcinol (Ib); were prepared through diazotizing 3-phenyl-5-aminopyrazole (PAP) and coupling the resulting diazonium salt with Schäffer acid and resorcinol respectively. The prepared azo dyes are characterized using both IR spectra and the elemental analysis (C, H, N and S). The prepared azo dyes are used as chromogenic reagents for the spectrophotometric determination of copper (II), nickel (II), cobalt (II) and zinc (II) ions. The conditional acid dissociation constants of these azo dyes (la and Ib) and the stability constants of its metal ion complexes have been determined by spectro-analytical methods. The effect of pH, time, organic solvent and the foreign ions on the spectrophotometric determination of these ions and their complexes with the azo dyes under study were studied. The stoichiometric ratio (M:L) of the formed complexes was also determined. The molar absorptivity, the Sandell's sensitivity values, the obeyance of Beers law and the stability constants of the formed complexes have been also determined and discussed.

Here, we demonstrated a bio-probe based on Europium(III)-8-allyl-2-oxo-2H-chromene-3-carbaldehyde (AOCC) complex for sensing of N-acetylamino acids, nucleotides, nucleobases and CT-DNA in solution using time-resolved Luminescence method. The stoichiometry of the complex has been optimized to be 1:3 metal: ligand ratio. The limits of detection were in the range of 0.044 - 0.13 μM. The binding constants (K) and thermodynamic parameters of biomolecules under examination with Eu (III)–(AOCC)3 complex have been determined. Selectivity of Eu(III)-(AOCC)3 complex towards various biomolecules was studied utilizing ratiometric methods, where the binding affinities of these biomolecules towards Eu(III)-(AOCC)3 complex have been calculated. The binding mode between CT-DNA and Eu(III)-(AOCC)3 has been investigated using steady-state luminescence and viscosity method. The luminescence emission of this complex was found to be modulated to different degrees when interacting biomolecules under investigation and DNA. This can be considered as a model for a sensor for detecting these biologically compounds.

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol·L−1 KNO3 for the interaction of Eu–Glycylhistidine (Glyhis) with five biologically important zwitterionic buffers (Z) (HEPES, EPPS, PIPES, POPSO and HEPPSO). The formation constants for the binary Eu(III) + Glyhis or Eu(III) + Z systems and ternary Eu(III) + Glyhis + Z systems have been evaluated, and the lowest value for formation constant is assigned to the system Eu(III) + Glyhis + PIPES. The electrochemical behavior of the Eu–Glyhis complex with selected zwitterionic buffers was studied on the surface of a glassy carbon electrode using cyclic, differential pulse and square wave voltammetric techniques. The values of the standard heterogeneous rate constant (K s), diffusion coefficients of the reduction (D red) and oxidation (D ox) processes were calculated for all the studied systems. The data reveal that PIPES is the most suitable of these zwitterionic buffers for study of the biological behavior of Glycylhistidine in its europium complexes.

A time-resolved (gated) luminescence-based method for the detection of some of N-acetyl amino acids, nucleobases, nucleotides, and DNA using terbium- 8-alkyl-2-oxo-2H-chromene-3-carbaldehyde (AOCC) complex in 1:2 metal: ligand ratio in microtiterplate format has been evolved. The linear range for determination of the selected biomolecules is 0.1–1.0 µM. The detection limit was in the range of 0.0371–0.106 µM. The thermodynamic parameters, and binding constants ( K ) of N-acetyl amino acids, nucleobases, nucleotides with Tb (III) –(AOCC) 2 complex were calculated. Positive and negative values of entropy (Δ S ) and enthalpy (Δ H ) changes for Tb (III) –(AOCC) 2 – N-acetyl amino acids, nucleobases or nucleotides ternary complexes were evaluated. Selectivity of Tb (III) -complex towards different biomolecules has been studied using ratiometric methods of analysis by comparison of biomolecules binding affinities for Tb (III) -complex. Interaction of Tb (III) complex with DNA has been studied.

Potentiometric measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol·L−1 KNO3 for the interaction of guanine, thymine, uracil, aminouracil, guanosine, inosine, cytidine, guanosine 5′-monophosphate, adenosine 5′-diphosphate, adenosine 5′-triphosphate and palladium Pd(II) with the biologically important secondary ligands glycine, leucine, N,N-bis(2-hydroxyethyl) glycine, N-[tris(hydroxymethyl)methyl] glycine, d-2-t-butylglycine and Boc-N-methyl-l-leucine. The formation of various 1:1:1 ternary complexes and 1:1:2 quaternary complex species as well as the polynuclear species was inferred from the potentiometric pH-titration curves. The experimental conditions were selected such that self-association of the nucleobases, nucleosides or nucleotides and their complexes due to stacking interaction is negligibly small; that is, the normal monomeric protonated ternary complexes were studied. Formation of the ternary complexes of some systems was confirmed using cyclic voltammetry, differential pulse voltammetry and conductance measurements in solution.

A new luminescent europium- o -(4-methoxy benzoyl) benzoic acid [ o -(4-anisoyl)] complex in ethanol–water (5:5 v/v) solution was used for selective determination of organophosphorus pesticides. The interaction of new and selective luminescent europium complex with different pesticides was studied using electroanalytical methods and fluorescence technique. The results indicate that the pesticides azinphos ethyl, chlorfenvinphos, diazinon and isofenphos, exhibit quenching effect on the characteristics emission peak for Eu(III) at λ = 614 nm. The luminescence variations values using the probe Eu-( o -(4-anisoyl)) 2 fit Stern–Volmer equation, where the detection limits are 1.93, 2.82, 3.78 and 1.80 μmol L −1 for azinphos ethyl, chlorfenvinphos, diazinon and isofenphos, respectively. The binding constants at different temperatures were calculated. Also, it was found that the quenching mechanism is dynamic type for chlorfenvinphos, diazinon and isofenphos while static type for azinphos ethyl. Effect of some relevant interferents on the detection of pesticides has been investigated.

In this work, the interaction of new luminescent terbium-N(acetoacetyl)-3-allyl-2hydroxybenzaldehyde hydrazone complex in a metal ligand ratio 1:2 in ethanol was studied with different pesticides, using fluorescence technique. The results indicate that the pesticides chlorfenvinphos and malathion exhibit quenching effect on the characteristics emission peak for Tb(III) at λ =545 nm. The luminescence variations values using the probe Tb(III)(HBH) 2 fit Stern–Volmer equation, where the detection limits are 4.53 and 9.59 µmol/L for chlorfenvinphos and malathion, respectively. The thermodynamic parameters associated with the interaction of the complex with the two pesticides were calculated, where the reaction is spontaneous through the obtained negative values of free energy change Δ G , and the process is of exothermic nature with decrease in entropy. Hence the nature of forces acting between the complex and pesticide molecules are Vander Val's and hydrogen bond. Also, it was found that the quenching mechanism is static type. Effect of some relevant interferents on the detection of pesticides has been investigated. The new sensing complex was applied to the determination of the pesticides in different real water samples (tap, river, and waste water) with precise recovery. Also, the effect of different concentrations of pesticides on the fluorescence spectrum of DNA was studied.

The interaction of Eu-1,4,7,10-tetraazacyclododecane (Cyclen) complex by using 4,4,4 trifluoro-1-(2-naphthyl)1,3-butanedione (TNB) as antenna with some nucleosides (guanosine, adenosine, cytidine and inosine), nucleotides (AMP, GMP, CMP, ATP and IMP) and DNA is studied using fluorescence technique. Two detection modes are employed one is the time-resolved mode, and the other is the normal luminescence mode. The time-resolved mode is more sensing than the normal luminescence mode in the present study. By using Benesi–Hildebrand equation binding constants were determined at various temperatures. Thermodynamic parameters showed that the reaction is spontaneous through the obtained negative values of free energy change ΔG. The enthalpy ΔH and the entropy ΔS of reactions were all determined.

Quenching of lanthanides luminescence of a novel long live Tb(III)- Ethyl 1-allyl-1,2-dihydro-4-hydroxy-2-oxoquinoline-3-carboxylate (EADHOC) as a ligand to form a complex with molar ratio 1:3 in solution has been studiedin ethanol in presence of organophosphorus pesticides both Di-chlorvos (P1) and paraoxon-Ethyl (P2). The intensity ofluminescence of Tb(III) –(EADHOC) decrease as the concentration of pesticides increase. The quenching effect wasobserved with both pesticides. Direct methods of determination of pesticides under investigated have been developed byusing luminescence of Tb(III) –(EADHOC) probe in a solution. The linear range for determination of the selectedpesticides P1(Di-chlorovos) and P2(Paraoxon-Ethyl) is 7 and 1 μM. the detection limits were 1.9 and 9.8 μM for P1(Dichlorovos)and P2 (Paraoxon-Ethyl) respectively. The Thermodynamic parameters and binding constant (K) of OPswith Tb(III) – (EADHOC) were evaluated. Including the value of enthalpy (ΔH ) and entropy( ΔS ) changes for Probeinteraction with pesticides. As the natural water sample in this study don't contain the above mentioned OPs over thelimit detected by the methods, a recovery study was carried out after the addition of the adequate amount oforganophosphorus pesticides under investigation.

This work describes the application of time resolved fluorescence in microtiter plates for investigating the interactions of europium-allyl-3-carboxycoumarin with pesticides chlorpyrifos, endosulfan and crotoxyphos. Stern-Volmer studies at different temperatures for chlorpyrifos and crotoxyphos shows dynamic and static quenching mechanisms respectively. Direct methods for the determination of the pesticides under investigation have been developed using the luminescence variations of the probe in solution. The detection limits are 6.53, 0.004, 3.72 μmol/L for chlorpyrifos, endosulfan, and crotoxyphos, respectively. The binding constants and thermodynamic parameters of the pesticides with probe were evaluated. A thermodynamic analysis showed that the reaction is spontaneous with negative ΔG. Effect of some relevant interferents on the detection of pesticides has been investigated. The new method was applied to the determination of the pesticides in different types of water samples (tap, mineral, and waste water).

This work describes the application of fluorescence for investigating the interactions of Eu(III)-TAN-1,10 phenanthroline (where TAN=4,4,4-Trifluoro-1-(2-naphthyl)-1,3-butanedione) with pesticides Chlorpyrifos, Malathion, Endosulfan, Heptachlor. The complex was synthesized and characterized by elemental analysis, FTIR, x-ray spectroscopy, solid fluorescence and thermal analysis. The results indicated that the composition of this complex is [Eu(TAN)2(Phen)(H2O)2]Cl. The luminescence properties of the complex in different solvents and at different pH values have been investigated. The results show that the complex exhibits more efficient luminescence at pH=7.5. The interactions of Eu-complex with different pesticides (Chlorpyrifos, Malathion, Endosulfan, and Heptachlor) in aqueous medium have been investigated by fluorescence measurements. The luminescence intensity of the probe is quenched by Malathion and enhanced by (Endosulfan, Heptachlor, and Chlorpyrifos). Direct methods for the determination of the pesticides under investigation have been developed using the luminescence variations of the probe in solution. The detection limits are 0.47, 1.02, 0.66, 0.64 µmol/L for Chlorpyrifos, Endosulfan, Heptachlor, and Malathion, respectively. The binding constants and thermodynamic parameters of the pesticides with probe were evaluated. The emission quantum yield (QY=0.71) of Eu(III)-complex was determined using tris (2,2׳-bipyridyl) dichlororuthenium(II) hexahydrate. A thermodynamic analysis showed that the reaction is spontaneous with negative ΔG. Effect of some relevant interferents on the detection of pesticides has been investigated. The new method was applied to the determination of the pesticides in different types of water samples (tap, river, and waste water).

New fluorescent probe Tb(III) (7-carboxymethoxy-4-methylcoumarin)2(SCN) (C2H5OH)(H2O) was synthesized and characterized by spectroscopy and thermal analysis. The absorption and fluorescence spectra of 7-carboxymethoxy-4-methylcoumarin (CMMC) and Tb(III)–CMMC complex have been measured in different solvents. The interactions of Tb(III)–CMMC complex with calf thymus nucleic acid (CT-DNA) have been investigated using steady state fluorescence measurements. The changes in the fluorescence intensity have been used for the quantitative determination of DNA with LOD of 3.45 ng in methanol–water (9:1, v/v). The association constants of DNA with Tb(III)–CMMC complex was found to be 2.62×1010 M−1.

New bis(acridine-9-carboxylate)-nitro-europium(III) dihydrate complex was synthesized and characterized. In vivo anti-angiogenic activities of bis(acridine-9-carboxylate)-nitro-europium(III) dihydrate complex against Ehrlich ascites carcinoma (EAC) cells are described. The newly synthesized complex resulted in inhibition of proliferation of EAC cells and ascites formation. The anti-tumor effect was found to be through anti-angiogenic activity as evident by the reduction of microvessel density in EAC solid tumors. The anti-angiogenic effect is mediated through down-regulation of VEGF receptor type-2 (Flk-1). The complex was also found to significantly increase the level of caspase-3 in laboratory animals compared to the acridine ligand and to the control group. This was also consistent with the DNA fragmentation detected by capillary electrophoresis that proved the apoptotic effect of the new complex. Our complex exhibited anti-angiogenic and apoptotic activity in vivo, a thing that makes it a potential effective chemotherapeutic agent. The interaction of calf thymus DNA (ct-DNA) with bis(acridine-9-carboxylate)-nitro-europium(III) dihydrate complex has been investigated using fluorescence technique. A competitive experiment of the europium(III)-acridine complex with ethidium bromide (EB) to bind DNA revealed that interaction between the europium(III)-acridine and DNA was via intercalation. The interaction of the synthesized complex with tyrosine kinases was also studied using molecular docking simulation to further substantiate its mode of action.

An optical sensor microtiterplate for quantitative analysis of the total content of biogenic amines (TAC) in meat and cheese was developed and validated for the first time. In the plate, a chameleon dye (Py-1) is embedded in a polymeric cocktail which is deposited on the bottom of the wells in a common microtiterplate. On reaction with biogenic amines (BAs), the fluorescence of Py-1 at 620 nm rapidly delivers a precise TAC. After 10 min incubation at 25 °C the determination of the TAC in various (real) samples is possible in high-throughput with a standard microplate reader. The optimized fluorescence method was validated for linearity, sensitivity, accuracy, precision (intraday and inter day repeatability) and recovery using histamine (HIS) as a representative BA. The sensor microtiterplate was successfully applied to quantitatively analyze the TAC in 10 real samples of cheese and meat obtained from various Egyptian markets. The TAC of these real samples obtained by the sensor microtiterplate was validated against the contents of BAs obtained by GC-MS at various times of storage. The data of the sensor microtiterplate agreed well with those of GC-MS. This demonstrates that the sensor microtiterplate is a reliable screening tool for the degradation status of food samples.

The formation of binary and ternary complexes of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Ca(II), Mg(II), and Pd(II) with 4-morpholinoethane sulfonic acid (MES), 2-(cyclohexylamino)ethane sulfonic a...

New complexes with a potent DNA-binding anti-tumor agent, europium(III)- and terbium(III)-2-thioacetate benzothiazole were synthesized and characterized. These complexes showed strong binding affinity to calf thymus DNA using fluorometric and electronic absorption spectroscopy. The synthesized complexes resulted in inhibition of proliferation of EAC cells and ascites formation. Their anti-tumor effect was found to be through anti-angiogenic activity as was evident by the reduction of microvessel density and down-regulation of VEGF receptor type-2 (Flk-1). It was found that EAC cells had distinct DNA fragmentation patterns analyzed by capillary electrophoresis in the treated animals. Moreover, the synthesized complexes exhibited significant cytotoxic activity against HepG2 and MCF7 cell lines. Furthermore, complexes showed a potent anti-bacterial activity against two pathogenic bacteria Escherichia coli and Salmonella.

The luminescence arising from lanthanide cations offers several advantages over organic fluorescent molecules: sharp, distinctive emission bands allow for easy resolution between multiple lanthanide signals; long emission lifetimes (μs -ms) make them excellent candidates for time-resolved measurements; and high resistance to photo bleaching allow for long or repeated experiments. A method is presented for determination of nucleosides using the effect of enhancement of fluorescence of the easily accessible europium(III)-TNB in presence of different nucleosides. The latter coordinates to Eu(III) -TNB and enhances its luminescence intensity as a result of the displacement of water from the inner coordination sphere of the central metal. A similar method for the determination of DNA based on the quenching of Eu(III)-TNB has been established. The interaction of Eu(III)-4,4,4 trifluoro-1-(2-naphthyl)1,3-butanedione (TNB) complex with nucleosides (NS) (guanosine, adenosine, cytidine, inosine) and DNA has been studied using normal and time-resolved luminescence techniques. Binding constants were determined at 293 K, 298 K, 303 K, 308 K and 313 K by using Benesi-Hildebrand equation. A thermodynamic analysis showed that the reaction is spontaneous with ΔG being negative. The enthalpy ΔH and the entropy ΔS of reactions were all determined. The formation of binary and ternary complexes of Eu(III) with nucleosides and TNB has been studied potentiometrically at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol.dm(-3) (KNO3) . The formation of the 1:1 binary and 1:1:1 ternary complexes are inferred from the corresponding titration curves. Initial estimates of the formation constants of the resulting species and the protonation constants of the different ligands used have been refined with the HYPERQUAD computer program. Electrochemical investigations for the systems under investigations have been carried out using cyclic voltammetry (CV), differential pulse polarography (DPP), and square wave voltammetry (SWV) on a glassy carbon electrode in I = 0.1 mol/L p-toluenesulfonate as supporting electrolyte.

Eu(III)-9-acridinecarboxylate (9-ACA) complex was synthesized and characterized by elemental analysis, conductivity measurement, IR spectroscopy, thermal analysis, mass spectroscopy, (1)H-NMR, fluorescence and ultraviolet spectra. The results indicated that the composition of this complex is [Eu(III)-(9-ACA)(2)(NCS)(C(2)H(5)OH)(2)] 2.5 H(2)O and the oxygen of the carbonyl group coordinated to Eu(III). The interaction between the complex with nucleotides guanosine 5'- monophosphate (5'-GMP), adenosine 5'-diphosphates (5'-ADP), inosine (5'-IMP) and CT-DNA was studied by fluorescence spectroscopy. The fluorescence intensity of Eu(III)-9-acridinecarboxylate complex was enhanced with the addition of CT-DNA. The effect of pH values on the fluorescence intensity of Eu(III) complex was investigated. Under experimental conditions, the linear range was 9-50 ng mL(-1) for calf thymus DNA (CT- DNA) and the corresponding detection limit was 5 ng mL(-1). The results showed that Eu(III)-(9-ACA)(2) complex binds to CT-DNA with stability constant of 2.41 × 10(4) M.

This work describes the application of time resolved fluorescence in microtiterplates and electrochemical methods on glassy carbon electrode for investigating the interactions of europium-3-carboxycoumarin with pesticides aldicarb, methomyl and prometryne. Stern-volmer studies at different temperatures indicate that static quenching dominates for methomyl, aldicarb and prometryne. By using Lineweaver-Burk equation binding constants were determined at 303 K, 308 K and 313 K. A thermodynamic analysis showed that the reaction is spontaneous with ΔG being negative. The enthalpy ΔH and the entropy ΔS of reactions were all determined. A time-resolved (gated) luminescence-based method for determination of pesticides in microtiterplate format using the long-lived europium-3-carboxycoumarin has been developed. The limit of detection is 4.80, 5.06 and 8.01 μmol L(-1) for methomyl, prometryne and aldicarb, respectively. This is the lowest limit of detection achieved so far for luminescent lanthanide-based probes for pesticides. The interaction of the probe with the pesticides has been investigated using cyclic voltammetry (CV), differential pulse polarography (DPP), square wave voltammetry (SWV) and linear sweep voltammetry (LSV) on a glassy carbon electrode in I = 0.1 mol L(-1) p-toluenesulfonate at 25 °C. The diffusion coefficients of the reduced species are calculated. The main properties of the electrode reaction occurring in a finite diffusion space are the quasireversible maximum and the splitting of the net SWV peak for Eu(III) ions in the ternary complex formed . It was observed that the increase of the cathodic peak currents using LSV is linear with the increase of pesticides concentration in the range 5 × 10(-7) to 1 × 10(-5) mol L(-1). The detection limit (DL) were about 1.01, 2.23 and 1.89 μmol L(-1) for aldicarb, methomyl and prometryne, respectively. In order to assess the analytical applicability of the method, the influence of various potentially interfering species was examined. Influence of interfering species on the recovery of 10 μmol L(-1) pesticides has been investigated.

The solid complex Tb(III)-bathophenanthroline (Bphen) was synthesized and characterized by elemental analysis, IR spectra, and thermalanalysis. The formation of binary and ternary complexes of Tb(III) with N-acetylamino acids (N-acetylaspartic acid, N-acetylhistidine, and N-acetylhistamine), and Bphen or anthracene-9-carboxylic acid (9-ANCA) has been studied potentiometrically at (25.0 ± 0.1) °C and an ionic strength of I = 0.1 mol·dm–3. The results obtained confirmed the recognition of the investigated N-acetylamino acids by the luminescent probes used at the molecular level. The formation of binary and ternary complexes of Tb(III) with nucleotides guanosine 5′-monophosphate (5′-GMP), adenosine 5′-monophosphate (5′-AMP), cytidine 5′-monophosphate (5′-CMP), or N-acetylamino acids (N-acetylaspartic acid, N-acetylhistidine, and N-acetylhistamine) has been studied potentiometrically. Confirmation of the formation of the ternary systems of the type Tb(III)-Bphen-N-acetylamino acids or Tb(III)-9-ANCA-N-acetyla...

The formation of binary and ternary model complexes of Eu(III) with the nucleobases 5-aminouracil (5-amino 2,4-dioxy pyrimidine), dihydrouracil (5,6-dihydro-2,4-dioxy pyrimidine), thymine (2,4-dihydroxy 5-methyl pyrimidine), adenine (6-aminopurine), uracil (2,4-dioxy pyrimidine), and PIPES (piperazine 1,4-bis(2-ethane sulfonic acid) dissodium salt) has been studied potentiometrically at (25.0 ± 0.1) °C and at an ionic strength of I = 0.1 mol·dm−3 (KNO3). The formation of the 1:1, 2:1 binary, and 1:1:1 and 2:1:1 ternary complexes is inferred from the corresponding titration curves. Initial estimates of the formation constants of the resulting species and the protonation constants of the different ligands used have been refined with the SUPERQUAD computer program. The experimental conditions were selected such that self-association of the nucleobases and their complexes was negligibly small; that is, the monomeric and protonated complexes were studied. Recognition of nucleobases and CT-DNA by the luminescen...

The solid complex Eu(III)−bathophenanthroline was synthesized and characterized by elemental analysis, IR spectra, and thermal analysis. The interaction of the Eu(III)−bathophenanthroline solid complex with calf-thymus DNA has been investigated by fluorescence and electrochemical methods including cyclic voltammetery and differential pulse polarography on a glassy carbon electrode. The formation of binary and ternary complexes of Eu(III) with nucleotides guanosine 5′- monophosphate (5′-GMP), adenosine 5′-monophosphate (5′-AMP), inosine 5′-monophosphate (5′-IMP), cytidine 5′-monophosphate (5′-CMP), or N-acetylamino acids (N-acetylaspartic acid, N-acetylhistidine, and N-acetylhistamine), and bathophenanthroline (BPhen) has been studied potentiometrically at (25.0 ± 0.1) °C and an ionic strength of I = 0.1 mol·dm−3 (KNO3) in 1.8 % v/v ethanol−water mixture solvent. The formation of the normal and protonated binary and ternary complexes is inferred from the corresponding titration curves. The experimental con...

The interaction of Eu(9-ANCA)3 (9-ANCA = anthracene-9-carboxylic acid) with DNA has been investigated by a fluorescence method. Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol·dm−3 KNO3 for the interaction of Eu(III) and 9-ANCA with adenosine 5′-diphosphate (ADP), adenosine 5′-triphosphate (ATP), N-acetyl glutamic acid (Nc-Glu), N-acetyl leucine (Nc-Leu), and N-acetyl lysine (Nc-Lys) in a 1:1:1 ratio. The formation of various mixed ligand complexes was inferred from the potentiometric titration curves. The formation constants of the binary and ternary complexes have been refined with the SUPERQUAD computer program. The interaction of Eu(III)-(9-ANCA) with Nc-Glu, Nc-Leu, and Nc-Lys has been investigated by electroanalytical methods including cyclic voltammetry (CV), differential pulse polarography (DPP), and square wave voltammetry (SWV) on a glassy carbon (GC) electrode.

Equilibrium constant measurements have been performed potentiometrically at (25±0.1) °C and an ionic strength I=0.1 mol⋅dm−3 KNO3 for the interaction of La(III), Ce(III), Pr(III) and Er(III) with the purine nucleotides adenosine 5′-mono, 5′-di, and 5′-triphosphate and with the biologically relevant secondary ligand zwitterionic buffers 3-(cyclohexyl amino)-1-propanesulfonic acid (CAPS), 3-(cyclohexylamino)-2-hydroxy-1-propane sulfonic acid (CAPSO), N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid (TAPS), 3-[N-bis(hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO), N,N-bis(2-hydroxyethyl)glycine (BICINE), and N-(2-acetamido)-2-iminodiacetic acid (ADA) in a 1:1:1 ratio. The formation of various 1:1:1 normal and protonated mixed-ligand complex species was inferred from the potentiometric pH titration curves. The experimental conditions were selected such that self-association of the purine nucleotides and their complexes was negligibly small; that is, the monomeric normal and protonated ternary complexes were studied. Initial estimates of the formation constants of the resulting species and the acid dissociation constants of adenosine 5′-mono-, 5′-di-, and 5′-triphosphate and the zwitterionic buffer secondary ligands were refined with the Superquade computer program. In some Ln(III) mixed-ligand systems, interligand interactions between the coordinating ligands, possibly involving H-bond formation, have been found to be the most important factors in deciding the stability of the mixed-ligand complexes in solutions. The thermodynamic ΔG° values of the monomeric normal and protonated ternary complexes were calculated and discussed.

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol·dm−3 KNO3 for the interaction of the biologically important ligands N-acetylhistidine, N-acetyl l-leucine, N-acetylglutamic acid, N-acetylhistamine, N-acetylaspartic acid, and La(III), Gd(III), Sm(III), Tb(III), Eu(III), and Dy(III) with the nucleotides guanosine 5′-monophosphate (5′-GMP), cytedine 5′-monophosphate (5′-CMP), inosine 5′-monophosphate (5′-IMP), adenosine 5′-monophosphate (5′-AMP), adenosine 5′-diphosphate (5′-ADP), adenosine 5′-triphosphate (5′-ATP), and cytedine 5′-triphosphate (5′-CTP) in 1:1:1 and 1:2:1 ratios. The formation constants of various mixed ligand complexes were inferred from the potentiometric titration curves. Initial estimates of the formation constants of the resulting species and the formation constants of the different N-acetyl amino acid (NAA) and nucleotide (NU) complexes in metal ligand ratios 1:1 and 2:1 have been refined with the SUPERQUAD computer program. ...

The formation of binary and ternary complexes of Eu(III) with nucleobases (NB), guanine (2-amino-6-oxypurine), thymine (2,4-dihydroxy 5-methyl pyrimidine), adenine (6-aminopurine), uracil (2,4-dioxypyrimidine), and anthracene-9-carboxylic acid (ANCA) has been studied potentiometrically at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol·dm−3 (KNO3) in 10 % ethanol−water mixture solvent. The acid−base properties of the ligands were investigated and discussed. The formation of the 1:1, 2:1 binary, and 1:1:1 and 2:1:1 ternary complexes is inferred from the corresponding titration curves. The ternary complexes formed are monoprotonated complexes. The stability constants of the binary and ternary systems were evaluated. Initial estimates of the formation constants of the resulting species and the protonation constants of the different ligands used have been refined with the SUPERQUAD computer program. The experimental conditions were selected such that self-association of the nucleobase and their complexes was n...

A generally applicable synthetic approach to dipeptide-DOTAM conjugates has been developed which is based on the peralkylation of 1,4,7,10-tetraazacyclododecane (cyclen) with protected N-iodoacetyl dipeptides. Standardized procedures were used for the alkylation, metalation, and purification of the resultant lanthanide complexes. Using this approach, we have been able to rapidly and reliably prepare and screen five different ligands each with up to six lanthanide ions. This preliminary investigation has identified several paramagnetic compounds with strong chemical exchange saturation transfer (PARACEST) properties in water at physiological temperature and pH. Extension of the synthetic approach to a wide variety of amino acids is possible.

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol·dm-3 KNO3 for the interaction of glycylglycine, glycylhistidine, glycylglycylglycine, glycylhistidylglycine, and Al(III), Ga(III), In(III), and Tl(I) with the biologically important secondary ligands bicine [N,N-bis(2-hydroxyethyl)glycine], tricine [N,N,N-tris(hydroxymethyl)methylglycine], PIPES [piperazine-1,4-bis(2-ethanesulfonic acid)], HEPES (N-[2-hydroxyethyl]piperazine-N-[2-ethanesulfonic acid]), and EPPS 4-(2-hydroxyethyl)piperazine 1-propanesulfonic acid in a 1:1:1 ratio. Ternary complexes of the type Al(III)−glycylglycine−guanosine, Al(III)−glycylglycine−guanosine 5‘-monophosphate (GMP), Al(III)−glycylglycylglycine−guanosine, Al(III)−glycylglycylglycine−GMP, Al(III)−glycylhistidine−guanosine, Al(III)−glycylhistidine−GMP, Al(III)−glycylhistidylglycine−guanosine, Al(III)−glycylhistidylglycine−GMP in a 1:1:1 ratio have been investigated. The experimental conditions were selected such that se...

The apparent dissociation constants of the nucleobases guanine, thymine, uracil, hypoxanthine, and cytosine were determined at (25.0 ± 0.1) °C and I = 0.1 mol·dm-3 (KNO3) by potentiometric pH titration in pure water and different hydroorganic solvent media. The organic solvents used were methanol and ethanol as amphiprotic hydrogen bond acceptor−donor (HBA-D) solvents, N,N-dimethylformamide (DMF), dimethyl sulfoxide, acetone, and dioxane as hydrogen bond acceptor solvents. A computer program was used to refine the initial estimates of the apparent dissociation constants of the five purine and pyrimidine nucleobases. The results obtained are discussed in terms of average macroscopic properties of the mixed solvents. The effects of organic cosolvents on the acid dissociation equilibria have been interpreted using the solvatochromic quantitative values of Kamlet−Taft hydrogen bond acidity and basicity (α, β) and dipolarity polarizability π* of the solvent. The free energy of transfer of the protons from wate...

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol·dm-3 (KNO3) for the interaction of guanine (2-amino-6-oxypurine), thymine (2,4-dihydroxy-5-methylpyrimidine), adenine (6-aminopurine), uracil (2,4-dioxypyrimidine), hypoxanthine (6-oxypurine), and Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Ca(II), and Mg(II) with the biologically important secondary ligands glycine (aminoethanoic acid), bicine [N,N-bis(2-hydroxyethyl)glycine], tricine [N,N,N-tris(hydroxymethyl)methylglycine], and ADA [N-(2-acetamido)-3-iminodiacetic acid] in a 1:1:1 ratio. The experimental conditions were selected such that self-association of the nucleobases and their complexes was negligibly small; that is, the monomeric normal and protonated complexes were studied. The formation of various 1:1:1 mixed ligand complexes was inferred from the potentiometric titration curves. Initial estimates of the formation constants of the resulting species and the acid dissociation constants of g...

The new Nd(III) and Er(III) complexes with the zwitterionic buffer ligands N-tris[hydroxymethyl]methyl-3-aminopropanesulfonic acid sodium salt (NaTAPS) and 3-[N,N-bis(2-hydroxyethyl) amino]-2-hydroxypropanesulfonic acid sodium salt (NaDIPSO) have been prepared and characterized by IR, DTA, TG, mass, elemental analyses and electrical conductivity measurements. The Nd(III) complexes may be formulated as [Nd(DIPSO)2H2O)n]NO3· mH2O, where n = 1 and m = 1 for NaDIPSO as ligand while n = 2 and m = 0 for NaTAPS as ligand, [Nd(TAPS)2(H2O)n]NO3. The Er(III) complexes may be described as [Er(DIPSO)2(H2O)n]Cl · mH2O, where n = m = 2 for NaDIPSO as ligand while n = 2 and m = 0 for NaTAPS as ligand. Thermogravemetric studies show that the Er(III) complexes are thermally more stable than the Nd(III) complexes. The electrical conductivity of DMF solutions of these complexes indicate 1:1 electrolytic behavior.

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol dm-3 KNO3 for the interaction of adenosine 5‘-monophosphate, guanosine 5‘-monophosphate, cytidine 5‘-monophosphate, and La(III), Ce(III), Pr(III), and Eu(III) with the biologically important secondary ligand zwitterionic buffers (3-[N-morpholinol])-2-hydroxypropanesulfonic acid, 2-(N-morpholino)ethanesulfonic acid, N-2-acetamido-2-aminoethanesulfonic acid, and N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid. Measurements were made in a 1:1:1 ratio. Formation constants for the monohydroxy, dihydroxy, and dimeric ligand complexes for the binary systems Ln(III) + adenosine 5‘-monophosphate, Ln(III) + guanosine 5‘-monophosphate, Ln(III) + cytidine 5‘-monophosphate, and Ln(III) + zwitterionic buffers have been evaluated. The formation of various 1:1:1 normal and protonated mixed ligand complex species was inferred from the potentiometric pH-titration curves. The experimental conditions were selected...

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol dm-3 KNO3 for the interaction of the purine nucleotides adenosine 5‘-mono, 5‘-di, and 5‘-triphosphate and Cu(II), Co(II), Ni(II), Mn(II), Zn(II), Ca(II), and Mg(II) with the biologically important secondary ligand zwitterionic buffers 3-(N-morpholino)propanesulfonic acid, 3-[(1,1-dimethyl-2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid, N-(2-hydroxyethyl)piperazine-N‘-2-hydroxypropanesulfonic acid, piperazine-N,N‘-bis(2-ethanesulfonic acid), and piperazine-N,N‘-bis(2-hydroxypropanesulfonic acid) in a 1:1:1 ratio and the formation of various 1:1:1 normal and protonated mixed-ligand complex species was inferred from the potentiometric pH titration curves. The experimental conditions were selected such that self-association of the purine nucleotides and their complexes was negligibly small; i.e., the monomeric normal and protonated ternary complexes were studied. Initial estimates of the formatio...

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol dm-3 (KNO3) for the interaction of guanosine 5‘-monophosphate, inosine 5‘-monophosphate...

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol dm-3 KNO3 for the interaction of adenosine 5‘-mono-, 5‘-di-, and 5‘-triphosphate and Cu(II), Co(II), Ni(II), Mn(II), Zn(II), Ca(II), and Mg(II) with the biologically important secondary ligand zwitterionic buffers 3-[N-bis(hydroxyethyl)amino]-2-hydroxypropanesulfonic acid, 3-[N-tris(hydroxymethyl)methylamino]-2-hydroxypropanesulfonic acid, (3-[N-morpholinol)-2-hydroxy propanesulfonic acid, N-(2-acetamido)-2-aminoethanesulfonic acid, and 2-(cyclohexylamino)ethanesulfonic acid in a 1:1:1 ratio, and the formation of various 1:1:1 normal and protonated mixed ligand complex species was inferred from the potentiometric pH titration curves. The experimental conditions were selected such that self-association of the nucleotides and their complexes was negligibly small; i.e., the monomeric normal and protonated ternary complexes were studied. Initial estimates of the formation constants of the resulting sp...

Potentiometric equilibrium measurements have been performed at (25.0 ± 0.1) °C and ionic strength I = 0.1 mol dm-3 (KNO3) for the interaction of glycine (aminoethanoic acid), serine (2-amino-3-hydroxypropanoic acid), methionine (2-amino-4-(methylthio)butanoic acid), aspartic acid (aminobutanedioic acid), glutamic acid (2-aminopropanedioic acid), and histidine (α-amino-1H-imidazole-4-propanoic acid) and Cu(II), Co(II), Ni(II), Mn(II), and Zn(II) with the biologically important secondary ligand zwitterionic buffers β-hydroxy-4-morpholinepropanesulfonic acid (MOPSO), 4-morpholinepropanesulfonic acid (MOPS), 3-[bis(2-hydroxyethyl)amino]-2-hydroxy-1-propanesulfonic acid (DIPSO), and 3-[N-tris(hydroxymethyl)methyl)amino]-2-hydroxypropanesulfonic acid (TAPSO) in 1:1:1 and 1:1:2 ratios, and the formation of various 1:1:1 ternary complexes and 1:1:2 quaternary complex species was inferred from the potentiometric pH titration curves. Initial estimates of the formation constants of the resulting species and the acid...

The apparent second stage dissociation constants of piperazine-N,N-bis[2-hydroxypropanesulfonicacid] (POPSO), N-[2-hydroxyethy1]piperazine-N‘-3-propane sulfonic acid (HEPPS), 2-[N-cyclohexylamino]ethanesulfonic acid (CHES) and mono[tris(hydroxymethyl)aminomethane] phosphate (Trizma) were determined at (25.0 ± 0.1) °C and I = 0.1 mol dm-3 (KNO3) by potentiometric pH titration in pure water and different hydroorganic solvent media. The organic solvents used were methanol and ethanol as amphiprotic hydrogen bond acceptor−donor (HBA-D) solvents, N,N-dimethylformamide (DMF), dimethy1 sulfoxide, acetone, and dioxane as hydrogen bond acceptor solvents, and acetonitrile as an HBA−HBD solvent. The ESAB2M computer program was used to refine the initial estimates of the apparent second-stage dissociation constants of the four zwitterionic buffers studied. pka2* values change with increasing organic content of the solvent mixture. The results obtained are discussed in terms of average macroscopic properties of the mi...

The apparent second-stage dissociation constants of 3-(N-morpholino)propanesulfonic acid, 3-[(1,1-dimethyl-2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid, and N-(2-hydroxyethyl)piperazine-N‘-(2-hydroxypropanesulfonic acid) were determined at (25.0 ± 0.1) °C and I = 0.1 mol dm-3 (KNO3) by potentiometric pH titration in pure water and different hydroorganic solvent media. The organic solvents used were methanol, ethanol as amphiprotic hydrogen bond acceptor−donor (HBA-D) solvents, N,N-dimethylformamide, dimethyl sulfoxide, acetone, dioxane as hydrogen bond acceptor solvents, and acetonitrile as (HBA-HBD) solvent. The ESAB2M computer program was used to refine the initial estimates of the apparent second-stage dissociation constants of the three zwitterionic buffers studied. pKa2* values change with increasing organic content of the solvent mixture. The results obtained are discussed in terms of average macroscopic properties of the mixed solvents. The implications of the results with regard to specific...

The apparent dissociation constants of 3-[N-(tris(hydroxy methyl)methyl)amino]-2-hydroxypropane sulfonic acid (TAPSO), 3-[N,N-bis(2-hydroxyethyl)amino]-2-hydroxypropane sulfonic acid (DIPSO), and 3...

The apparent dissociation constants of 3-(cyclohexylamino)-1-propanesulfonic acid (CAPS) and 3-(cyclohexylamino)-2-hydroxy-1-propanesulfonic acid (CAPSO) were determined at (25.00 ± 0.10) °C and I = 0.1 mol dm-3 KNO3 by potentiometric pH titration in pure water and different hydroorganic solvent media. The organic solvents used were methanol, ethanol, N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, acetone, and dioxane. Initial estimates of the apparent dissociation constant values of the two zwitterionic amino propanesulfonic acid buffers studied have been refined with the ESAB2M computer program. pKa2* values change with an increase in the concentration of organic solvent. The results obtained are discussed in terms of average macroscopic properties of the mixed solvents and the possible variation in microheterogenity of the solvation shells around the solute.

The apparent dissociation constants of malic acid (hydroxybutanedioic acid), tartaric acid (2,3-dihydroxybutanedioic acid), phthalic acid (1,2-benzenedicarboxylic acid), and succinic acid (butane-1,4-dioic acid) were determined at 25 °C and ionic strength I = 0.10 mol dm-3 KNO3 by potentiometric pH titration in pure water and water + methanol, water + ethanol, water + N,N-dimethylformamide, water + dimethyl sulfoxide, and water + acetonitrile. pKa values increase with an increase in the concentration of the organic solvents. These results are discussed in terms of solvent characteristics. Solvent basicity and stabilization of the conjugate acid free base by hydrogen-bonding interactions in hydroorganic solvent media relative to pure aqueous media as well as proton−solvent interaction play an important role in the acid dissociation equilibrium.

The luminescence arising from lanthanide cations offers several advantages over organic fluorescent molecules: sharp, distinctive emission bands allow for easy resolution between multiple lanthanide signals; long emission lifetimes (μs-ms) make them excellent candidates for time-resolved measurements; and high resistance to photo bleaching allow for long or repeated experiments. A time-resolved (gated) luminescence-based method for determination of pesticides methomyl, aldicarb and prometryne in microtiterplate format using the long-lived terbium-3-carboxycoumarin in 1:3 metal:ligand ratio has been developed. The limit of detection is 1.20 × 106, 5.19 × 105 and 2.74 × 106 ng L−1 for methomyl, prometryne and aldicarb, respectively. The quantum yield (QY = 0.08) of Tb(III)-3-carboxycoumarin was determined using 3-(2-benzothiazolyl)-7-diethylamino-coumarin (coumarin 6). Stern–volmer studies at different temperatures indicate that collisional quenching dominates for methomyl, aldicarb and prometryne. Binding constants were determined at 303, 308 and 313 K by using Lineweaver–Burk equation. A thermodynamic analysis showed that the reaction is spontaneous with negative ΔG. Effect of some relevant interferents on the detection of pesticides has been investigated.

Luminescence quenching of a novel long lived Eu(III)-pyridine-2,6-dicarboxylic acid probe of 1:2 stoichiometric ratio has been studied in 0.10 volume fraction ethanol-water mixture at pH 7.5 (HEPES buffer) in the presence of the organophosphorus pesticides chlorfenvinphos (P1), malathion (P2), azinphos (P3), and paraxon ethyl (P4). The luminescence intensity of Eu(III)-(PDCA)(2) probe decreases as the concentration of the pesticide increases. It was observed that the quenching due to P3 and P4 proceeds via both diffusional and static quenching processes. Direct methods for the determination of the pesticides under investigation have been developed using the luminescence quenching of Eu(III)-pyridine-2,6-dicarboxylic acid probe in solution. The linear range for determination of the selected pesticides is 1.0-35.0 μM. The detection limits were 0.24-0.55 μM for P3, P4, and P1 and 2.5 μM for P2, respectively. The binding constants (K), and thermodynamic parameters of the OPs with Eu(III)-(PDCA)(2) were evaluated. Positive and negative values of entropy (ΔS) and enthalpy (ΔH) changes for Eu(III)-(PDCA)(2)-P1 ternary complex were calculated. As the waters in this study do not contain the above mentioned OPs over the limit detectable by the method, a recovery study was carried out after the addition of the adequate amounts of the organophosphorus pesticides under investigation.

Two new ligands derived from phloroglucinol 2-{[(4-methoxy benzoyl ) oxy ] } methyl benzoic acid[L1] and 2-{[(4-methyl benzoyl )oxy] methyl} benzoic acid[L2] were synthesized. The solid complex Eu(III)-L2 has been synthesised and characterized by elemental analysis ,UV and IR spectra. The reaction of Eu(III) with the two synthesized ligands has been investigated in I = 0.1 mol dm-3 p-toluene sulfonate by cyclic voltammetry and square wave voltammetry. The reaction of Eu (III)–L1 and Eu (III)–L2 binary complexes with nucleotide 5′-AMP , 5′-ADP ,5′-ATP , 5′- GMP , 5′-IMP , and 5′-CMP has been investigated using UV, fluorescence and electrochemical methods. The experimental conditions were selected such that self-association of the nucleotides and their complexes was negligibly small, that is, the monomeric complexes were studied. The interaction of the Eu(III)–L1 or L 2 solid complexes with calf-thymus DNA has been investigated by fluorescence and electrochemical methods including cyclic voltammetery(CV) ,differential pulse polarography (DPP) and square wave voltammetry (SWV) on a glassy carbon electrode. The fluorescence intensity of Eu(III)-L2 complex was enhanced with the addition of DNA. Under optimal conditions in phosphate buffer pH 7.0 at 25 °C the linear range is 3–20 μM for calf thymus DNA (CT–DNA) and the corresponding determination limit is 1.8 μM.

We demonstrate a novel optical sensor for carbon dioxide in concentrations between 0 and 3%. The sensing scheme is based on the optical interrogation of a 12-μm polystyrene (PS) film containing upconverting nanoparticles (UCNPs; 40–100 nm in size) of the type NaYF4:Yb,Er, and the longwave absorption pH probe bromothymol blue (BTB) in its anionic (blue) form. PS is chosen as a matrix because it displays permeation selectivity for CO2 and rejects protons. The color of BTB in the PS matrix depends on the partial pressure of CO2 gas. The UCNPs are photoexcited with a 980-nm laser diode to give a green (542 nm) and a red (657 nm) emission whose intensity is screened off (depending on whether BTB is present in its blue or yellow form) due to an inner filter effect. The luminescence intensities of the UCNPs at 542 nm and 657 nm increase with increasing concentration of CO2. The pH probe BTB (a sulfonate) is used in the form of a lipophilic ion pair with the tetrabutylammonium cation (TBA). The strong base tetraoctylammonium hydroxide is added to the system and acts as a base to convert BTB in its phenoxide (blue) form, but also creates a buffer system. This is the first optical sensor for CO2 that is based on the use of UCNPs. Its response time is not, vert, similar10 s on switching from pure argon gas to 1% CO2 in argon, the recovery time of the sensing film is not, vert, similar180 s, and the detection limit is 0.11% of CO2.

Europium (III) complex with anthracene-9-carboxylic acid (9-AA) has been synthesized and characterized by elemental analysis, FT-IR, and TG-DTG techniques. The results indicated that the composition of this complex is Eu (9-AA)(3). The luminescence properties of the complex in different solvents and at different pH values have been investigated. The results show that the complex exhibits more efficient luminescence in THF and ethyl acetate. The interactions of Eu-complex with different N-acetyl amino acids and nucleotides in different solvents have been investigated by fluorescence measurements. Enhancement of the fluorescence intensities has been observed in cyclohexane, acetone, acetonitrile, and tetrahydrofuran whereas the fluorescence intensities of the investigated complex in ethanol, water, and ethyl acetate exhibit relatively low intensity.

The dissociation constant of acetic acid, benzoic acid, 3-phenylpropenoic acid, 2-methylpropionic acid, and pentanoic acid were determined at 25.0 °C (I = 0.1 mol dm -3 KNO 3 ) by potentiometric pH titration in pure water and water + methanol, water + ethanol, water + dimethylformamide, water + dimethyl sulfoxide, and water + acetonitrile. pK a values increase with an increase in the concentration of the organic compounds. These results are discussed in terms of solvent characteristics. Solvent basicity and stabilization of the conjugate acid free base by hydrogen-bonding interactions in hydroorganic solvent media relative to pure aqueous media as well as proton-solvent interaction play an important role in the acid dissociation equilibrium.

The complexes formed by the Na/sup +/, K/sup +/, Rb/sup +/, Ca/sup 2 +/, UO/sub 2//sup 2 +/, and Ag/sup +/ cations with the macrocyclic polyethers 18-crown-6, benzo-15-crown-5, and dicyclohexyl-18-crown-6 are investigated. The stability constants of these complexes have been determined potentiometrically in (90% vol.) ethanol-water solutions at 25/sup 0/C and an ionic strength ..mu.. = 0.1 (achieved with tetrabutylammonium perchlorate). The stability of the investigated complexes was interpreted in terms of caging the metal cation into the cavity of the macrocyclic ligand, an effect which depends on the ratio of the diameter of the complexed cation over the diameter of the cavity of the complexing ligand.