Search results for "Titration"
showing 10 items of 312 documents
Alkaline titrations of poly(dG-dC).poly(dG-dC): microemulsion versus solution behaviour
2007
PolyGC was titrated with a strong base in the presence of increasing concentrations of NaCl (from 0.00 to 0.60M) either in water solution or with the polynucleotide solubilized in the aqueous core of reverse micelles, i.e., the cationic quaternary water-in-oil microemulsion CTAB/n-hexane/n-pentanol/water. The results for matched samples in the two media were compared. CD and UV spectroscopies and, for the solution experiments, pH measurements were used to follow the course of deprotonation. In both media the primary effect of the addition of base was denaturation of the polynucleotide, reversible by back-titration with a strong acid. In solution, the apparent pK(a) of the transition decreas…
Co2+ Translocation in a Terpyridine−Cyclam Ditopic Receptor
2001
The coordination behaviour of the ditopic receptor of 1-[p-(2,2′:6′,2′′-terpyrid-4′-yl)tolyl]-1,4,8,11-tetraazacyclotetradecane (L1) towards Co2+ in acetonitrile/water (70:30, v/v) has been investigated. At acidic pH values, the L1−H+−Co2+ system shows an oxidation wave at 150 mV vs. SCE, characteristic of Co2+ in a bis(terpyridine) environment. Upon addition of OH−, a reduction in the intensity of the wave at 150 mV is observed and a new oxidation wave appears at 1.30 V. This new wave is close to that found for [Co(cyclam)]2+ under similar working conditions. The electrochemical data thus suggest that there is a pH-controlled translocation of the Co2+ ion from the bis(terpyridine) to the c…
Pentafluorophenyl salicylamine receptors in anion–π interaction studies
2012
A crystal structure analysis confirms the appropriateness of pentafluorophenyl salicylamine (1a) as a π-acceptor for anion–π interactions. Crystals of 1a·HCl show that the OH-group fixes the anion in a η2-type binding motif above the electron-deficient arene. Attempts to find some relevance for this weak intermolecular force in solution failed. Stronger CH–, NH– and OH–anion interactions are dominant over the weak anion–π interactions. Due to the hydrogen bonding, the non-fluorinated receptor exhibits the highest binding constants within this series.
Rapid Titration With Intravenous Oxycodone for Severe Cancer Pain and Oral Conversion Ratio.
2022
to assess a dose titration with intravenous oxycodone to achieve rapid pain relief of cancer pain of severe intensity. The second objective was to provide a conversion ratio with the oral route.Cancer patients admitted for severe pain were prospectively assessed. At admission (T0) previous opioid doses were recorded. Edmonton symptom assessment scale (ESAS) was collected from T0 until the conclusion of the observation. Intravenous boluses of oxycodone were given until the initial signs of significant analgesia were detected. The effective dose was multiplied for six and given as intravenous continuous infusion. When the patient was considered stabilized the intravenous daily dose was conver…
Effect of Nitrogen Methylation on Cation and Anion Coordination by Hexa- and Heptaazamacrocycles. Catalytic Properties of These Ligands in ATP Dephos…
1996
The stability constants of the complexes formed by 1,10-dimethyl-1,4,7,10,13,16-hexaazacyclooctadecane (L) and 1,4,7-trimethyl-1,4,7,10,13,16,19-heptaazacyclohenicosane (L1) with Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Pb(2+), as well as that for the formation of PbL2(2+) (L2 = 1,4,7,13-tetramethyl-1,4,7,10,13,16-hexaazacyclooctadecane), were determined by means of potentiometric (pH-metric) titrations in 0.15 mol dm(-)(3) NaClO(4) at 298.1 +/- 0.1 K. The enthalpy changes for the formation of Cu(2+) complexes with L and L1 were measured by means of microcalorimetry. These thermodynamic data were compared with those previously reported for L2, 1,4,7,10,13,16-hexaazacyclooctadecane (L3), and 1,4,…
Alkyl-Substituted Aminobis(phosphonates)Efficient Precipitating Agents for Rare Earth Elements, Thorium, and Uranium in Aqueous Solutions
2021
The efficient and environmentally sustainable separation process for rare earth elements (REE), especially for adjacent lanthanoids, remains a challenge due to the chemical similarity of REEs. Tetravalent actinoids, thorium, and traces of uranium are also present in concentrates of REEs, making their separation relevant. This study reports six simple water-soluble aminobis(phosphonate) ligands, RN[CH2P(O)(OH)2]2 (1 R = CH2CH3, 2 R = (CH2)2CH3, 3 R = (CH2)3CH3, 4 R = (CH2)4CH3, 5 R = (CH2)5CH3, 6 R = CH2CH(C2H5)(CH2)3CH3) as precipitating agents for REEs, Th, and U, as well as gives insight into the coordination modes of the utilized ligands with REEs at the molecular level. Aminobis(phospho…
Tetra-CMPO-derivatives of calix[4]arenes fixed in the 1,3-alternate conformation
2010
Calix[4]arene derivatives fixed in the 1,3-alternate conformation and substituted at one side by four carbamoylmethylphosphine oxide (CMPO) residues were synthesised. Two CMPO groups are directly attached to the wide rim, while the second pair is bound to the narrow rim via a tri- or tetramethylene spacer. Similar compounds, in which two CMPO groups at the wide rim are combined with two picolinamide groups or two ionisable carboxylic groups at the narrow rim, were also prepared. Some of these calixarene derivatives were studied as extractants for lanthanides (La3+, Eu3+, Yb3+) and thorium (Th4+) from acidic solution into methylene chloride. For selected samples, stability constants in metha…
Structural investigations on diorganotin and triorganotin(IV) phosphomycin derivatives.
2008
Abstract Four new diorganotin(IV), (R = Me, Bu), and triorganotin(IV), (R = Me, Ph), derivatives of the phosphomycin disodium salt antibiotic[(1R,2S)-1,2-epoxypropylphosphonate]Na2 have been synthesized and their solid state configuration studied by X-ray crystallography, FT-IR, Mossbauer, UV–Vis spectroscopies. The X-ray diffraction investigation, performed on the bis[trimethyltin(IV)]phosphomycin, showed that the coordination geometry at all the Sn atoms is trigonal bipyramidal. The structure of the complex forms an unusual polymeric zig-zag planar network. The FT-IR and the 119Sn Mossbauer studies supported the formation of trigonal bipyramidal (Tbp) molecular structures, both in the dio…
Complex Formation of the Uranyl (UO22+) Ion with the Diethylene Triaminopentaacetate (DTPA) Ligand at 25 °C in 3 M Sodium Perchlorate
2011
The complex formation between the uranyl (UO22+) ion and the diethylene triaminopentaacetate ligand (DTPA) has been investigated at 25 °C, in a 3 M sodium perchlorate medium. The overall protonation constants βjH of the free ligand have been previously determined in this ionic medium: six protonated species (HjA), with j ranging from 1 to 6, together with the free anion A5− have been identified in the concentration range from (3·10−3 to 13·10−3) mol·kg−1. Four complex species, H2UO2A−, HUO2A2−, UO2A3−, and UO2AOH4−, have been identified in the total uranyl concentration range from (1.1·10−3 to 5.7·10−3) mol·kg−1, and their overall stability constants determined, keeping the metal to ligand …
Hydrolytically active tetranuclear [NiII2]2 complexes: synthesis, structure, spectroscopy and phosphoester hydrolysis
2015
Three tetranuclear nickel(II) complexes, [Ni4(H2chdp)2(H2O)4]Br2·4CH3OH·3H2O (1), [Ni4(H2chdp)2(H2O)4](PF6)2 (2) and [Ni4(H2chdp)2(H2O)4](ClO4)2·3.2CH3OH·0.8H2O (3) have been synthesized by exploiting the flexibility, chelating ability and bridging potential of a new symmetrical μ-bis(tetradentate) ligand, H5chdp (H5chdp = N,N′-bis[2-carboxybenzomethyl]-N,N′-bis[2-hydroxyethyl]-1,3-diaminopropan-2-ol). Complexes 1, 2 and 3 have been synthesized by carrying out reaction of the ligand H5chdp with stoichiometric amounts of NiCl2·6H2O/NaBr, NiCl2·6H2O/NH4PF6, and Ni(ClO4)2·6H2O, respectively, in methanol–water in the presence of NaOH at ambient temperature. Characterizations of the complexes ha…