Search results for "Potentiometry"

Coordination abilities of N-methyl alkylaminomethane-1,1-diphosphonic acids towards zinc(II), magnesium(II) and calcium(II) metal ions. Equilibrium s…

2017

Abstract Complex-formation abilities of a series of N-methyl alkylaminomethane-1,1-diphosphonic acids (1–7) with a common tertiary nitrogen atom (CH3−N−R) bearing linear or branched alkyl, cycloheptyl or phenylalkyl R substituents towards zinc(II), magnesium(II) and calcium(II) in aqueous solution have been studied by means of pH-potentiometry, ESI-MS spectrometry, 1H NMR and 31P NMR methods. The obtained results indicate that in the all presented systems mononuclear protonated equimolar and bis complexes are formed. In acidic and neutral solution, the formation of the protonated dinuclear species has been confirmed. The comparative analysis of the potentiometric and NMR data reveal that th…

Coordination properties of adenosine-5'-monophosphate and related ligands towards Me2Sn(IV)2+ in aqueous solution.

2002

Abstract The coordination of Me 2 Sn(IV) 2+ to adenosine-5′-monophosphate (AMP) and the related compounds d -ribose-5-phosphate (R5P), d -glucose-1-phosphate (G1P) and d -glucose-6-phosphate (G6P) in aqueous solution was investigated by means of potentiometric titration, and 1 H-, 31 P-NMR and Mossbauer spectroscopic methods in the pH range 2–11 ( I =0.1 M NaClO 4 , 298 K). The complex of AMP and Me 2 Sn(IV) 2+ precipitated at low pH was characterised by elemental analysis, FT-IR and Mossbauer spectroscopic methods. From a comparison of the p K values obtained in the presence and absence of metal ion and the stability constants for the different systems, the coordination of {N} is excluded,…

The effect of cathartic agents on transmucosal electrical potential difference in the human rectum.

1980

Active ion transport in the colon is generating a transmucosal electrical potential difference (PD) of about 40 mV. Cathartic agents inhibit electrolyte and water net-absorption or cause net-secretion which should be reflected in a change of PD. In 83 normal subjects the effect of an isotonic eletrolyte solution (control) and different cathartic agents on rectal PD was tested: Laxatives (bisacodyl, rhein), bile acids (cholic and deoxycholic acid), fatty acids (oleic and ricinoleic acid) and cardiac glycosides (meproscillarin, digitoxin, digoxin). Bisacodyl, deoxycholic acid in high concentration, meproscillarin and digitoxin significantly decreased PD, while the other substances did not. Ca…

Esophageal transmural potential difference in patients with symptomatic gastroesophageal reflux.

1980

Esophageal electrical potential difference (PD) was studied in 9 patients with symptomatic gastroesophageal reflux and in 9 healthy control subjects. None of the patients revealed gross mucosal damage by radiography or endoscopy, but all of them showed positive acid perfusion studies. In the stomach and across the lower esophageal sphincter PD profiles were remarkably similar in patients and controls. Throughout the lower esophagus however, PD values were slightly higher in patients with symptomatic reflux than in healthy volunteers. These data are in contrast to a previous investigation, in which patients with reflux-induced gross mucosal damage revealed a decreased PD in the lower esophag…

Polyfunctional recognition of pyridinedicarboxylate anions with macrocyclic polyamine receptors containing heteroaromatic groups.

2008

The interaction of the biologically relevant anions deriving from the six pyridinedicarboxylic acids (H2PDC) with two macrocyclic receptors containing a pentamine chain and a bipyridine (1) or a phenanthroline (2) moiety, as well as with the aliphatic analogue [21]aneN7 (3), was studied by means of spectroscopic methods (UV-vis, NMR) and potentiometric titrations affording the stability constants of the adducts formed. All three receptors form stable complexes with the substrates thanks to the formation of several salt bridges and hydrogen bond contacts, as observed in the crystal structure of the H8[3(2,6-PDC)4] x H2O x 0.5 EtOH solid compound. Additional pi-stacking interactions between t…

A highly enantioselective abiotic receptor for malate dianion in aqueous solution

2006

The highly enantioselective molecular recognition of the malate dianion by a synthetic receptor in aqueous solution has been studied by potentiometric titrations, mass spectrometry (ESI-MS), diffusion measurements (PGSE NMR) and molecular modeling. Garcia-España Monsonis, Enrique, Enrique.Garcia-Es@uv.es

Cu2+and AMP complexation of enlarged tripodal polyamines

2006

The synthesis, characterization, Cu2+ coordination and interaction with AMP of three tripodal polyamines are reported. The polyamines are based on the structure of the tetraamine (tren) which has been enlarged with three propylamino functionalities (TAL), with a further anthrylmethyl fragment at one of its terminal primary nitrogens (ATAL) or with naphthylmethyl fragments at its three ends (N3TAL). The protonation constants of all three polyamines show that at pH 6, all six primary and secondary nitrogen atoms in the arms are protonated. The interaction with Cu2+ and AMP (adenosine-5′-monophosphate) has been studied by potentiometric, UV-Vis, ESI-MS spectroscopy and NMR techniques. pH-Metri…

Specific Zn(II)-binding site in the C-terminus of Aspf2, a zincophore from Aspergillus fumigatus

2022

Abstract Aspergillus fumigatus, one of the most widespread opportunistic human fungal pathogens, adapts to zinc limitation by secreting a 310 amino acid Aspf2 zincophore, able to specifically bind Zn(II) and deliver it to a transmembrane zinc transporter, ZrfC. In this work, we focus on the thermodynamics of Zn(II) complexes with unstructured regions of Aspf2; basing on a variety of spectrometric and potentiometric data, we show that the C-terminal part has the highest Zn(II)-binding affinity among the potential binding sites, and Ni(II) does not compete with Zn(II) binding to this region. The 14 amino acid Aspf2 C-terminus coordinates Zn(II) via two Cys thiolates and two His imidazoles and…

Relationship between the caudate nucleus and the dorsal hippocampus, in the cat.

1972

How copper ions and membrane environment influence the structure of the human and chicken tandem repeats domain?

2019

Abstract Prion proteins (PrPs) from different species have the enormous ability to anchor copper ions. The N-terminal domain of human prion protein (hPrP) contains four tandem repeats of the –PHGGGWGQ– octapeptide sequence. This octarepeat domain can bind up to four Cu2+ ions. Similarly to hPrP, chicken prion protein (chPrP) is able to interact with Cu2+ through the tandem hexapeptide -HNPGYP- region (residues 53–94). In this work, we focused on the human octapeptide repeat (human Octa4, hPrP60–91) (Ac-PHGGGWGQPHGGGWGQPHGGGWGQPHGGGWGQ-NH2) and chicken hexapeptide repeat (chicken Hexa4, chPrP54–77) (Ac-HNPGYPHNPGYPHNPGYPHNPGYP-NH2) prion protein fragments. Due to the fact that PrP is a membr…