Search results for "Titration"

Thermodynamic analysis of binding between drugs and glycosaminoglycans by isothermal titration calorimetry and fluorescence spectroscopy

2007

The thermodynamics of the interaction of positively charged drug molecules with negatively charged glycosaminoglycans (GAGs) is investigated by isothermal titration calorimetry (ITC) and fluorescence spectroscopy. The drugs considered are propranolol hydrochloride, tacrine, and aminacrine, and the polymers used as model GAGs are dextran sulfate, chondroitin sulfate, and hyaluronic acid. The ITC results show that the interaction between drugs and GAGs is via direct binding and that GAGs bind to drugs at one set of sites. Large negative values of heat capacity change (DeltaC(p)) are observed upon binding of GAGs to drugs. Such negative DeltaC(p) is not expected for purely electrostatic intera…

8-Hydroxyquinoline-2-Carboxylic Acid as Possible Molybdophore: A Multi-Technique Approach to Define Its Chemical Speciation, Coordination and Sequest…

2020

8-hydroxyquinoline-2-carboxylic acid (8-HQA) has been found in high concentrations (0.5&ndash

A comparative study of the application of the method of least-squares in the potentiometric determination of protonation constants.

1982

Methods of simple and multiple linear regression applied to the potentiometric determination of protonation constants of diprotic and triprotic acids are studied critically. The best way of fitting the data, according to the order of magnitude of the constants, is established. The conclusions are checked by calculating the protonation constants of succinic and citric acids.

The acidity of calix[5]arenes and their linear analogues

1999

Abstract Five new calix[5]arenes containing a single p-nitrophenol unit as the most acidic phenolic unit have been synthesised by (3+2) fragment condensation of a trimer with a p-nitrophenol in the middle with various bishydroxymethylated alkanediyl diphenols. Their first acid constant (pKal) has been determined in 2-methoxyethanol/water (9:1) at 22°C by optical titration. The pKal values are distinctly lower (ΔpKa > 2) than for the trimer, while no difference has been found in comparison to structurally analogous calix[4]arenes. Rigidification of the calix[5]arene skeleton by introducing a single alkanediyl bridge opposite to the p-nitrophenol unit has no effect on pKal. All values are in …

Electrochemistry of copper complexes with polyaza[n]paracyclophanes. Influence of ATP as an exogen ligand on the relative stability of the Cu(II) and…

2000

Abstract Interaction of Cu 2+ with the macrocycle 2,6,9,13-tetraaza[14]paracyclophane (L) and ATP has been followed by pH-metric titration, cyclic voltammetry and differential pulse voltammetry (DPV). Mixed adduct species with various degrees of protonation were found to be stable for pH>4. In neutral and alkaline media reduction of mixed complexes occurs in a two-electron quasi-reversible step in contrast with binary Cu 2+ L complexes which display two successive one-electron couples. The potentiometric and voltammetric data suggest that in ternary adducts ATP binds to Cu 2+ ions through the phosphate chain and one N-site of the adenine ring system.

A Bis(mu-phenoxo)-Bridged Dizinc Complex with Hydrolytic Activity

2013

The dinuclear complex [Zn2(papy)2]·2CH3OH [H2papy = N- (2-hydroxybenzyl)-N-(2-picolyl)glycine] was synthesized and characterized. The crystal structure of the complex reveals that both ZnII ions are pentacoordinate with distorted pentagonal bipyramidal coordination arrangements. The phenoxyl groups of each ligand bridge the two metal atoms, whereas each carboxylate of the ligand is terminally bound to one ZnII ion. Potentiometric studies of the ZnII:H2papy system in a methanol/water mixture show the existence of a mononuclear species at lower pH; but at a pH above 5, a dimeric species starts to dominate and transforms further into a bis(μ-phenoxo) bridged dizinc complex by deprotonation of …

Gaseous sensors based on solid proton conductors

1992

Abstract he chemical sensors for different gaseous (alcohol, acetone, ammonia, water vapour) detection at room temperature are developed by using polycrystalline β-alumina and xerogel of antimonic acid hydrate (AAH). The sensitivity and selectivity of sensors depend on the ion-exchange and preparative methods. The possibility of producing different types of potentiometric, amperometric, voltammetric and resistance sensors on the basis of these ion-conducting materials is shown. More success is achieved by producing ammonia-sensitive devices on β-alumina as well as on AAH xerogel.

ChemInform Abstract: (o-Hydroxyphenyl)methylphosphonic Acids: Synthesis and Potentiometric Determinations of Their pKa Values.

2010

Metal ion complexation by tetraester derivatives of bridged calix [4] arenes

1992

A series of bridged calix [4] arenes (5–10 methylene groups in the bridge) were synthesized and transformed into their tetraester derivatives by reaction with ethyl bromoacetate. The stability constants for complexes of the tetraester derivatives with sodium, potassium and silver cations, determined in methanol by spectroscopic or potentiometric techniques, show a drastic decrease (more than 105 for Na +) for the shorter methylene chains. 1H NMR studies demonstrate a conformational rearrangement of the calixarene part to fourfold symmetry to be necessary for the complexation of a cation, which is prevented by the shorter chains. This is further confirmed by the X-ray structure of a tetraest…

In silico, spectroscopic, and biological insights on annelated pyrrolo[3,2-e]pyrimidines with antiproliferative activity

2013

The in silico COMPARE analysis was performed on 8-[3-(piperidino)propyl]-4,10-dimethyl-9-phenyl-6-(methylsulfanyl)-3,4-dihydropyrimido[1,2-c]pyrrolo[3,2-e]pyrimidin-2(8H)-one, a compound with promising antiproliferative activity, previously synthetized and screened against a panel of 60 human tumor cell lines. The results evidenced that this compound matches the biological properties of Chromomycin A3 and Actinomycin D, known drugs with high DNA binding affinity. Prompted by such results, a thorough spectroscopic investigation of its DNA aqueous solutions was performed, with the aim to verify its DNA-binding properties. DNA groove-binding interaction was assigned by UV-vis spectrophotometri…