Search results for " rate constant"

Rate constants for ion-pair dissociation and association in the anionic two-state polymerization of styrene in THF

1965

Harnessing Fluorescence versus Phosphorescence Branching Ratio in (Phenyl)n-Bridged (n = 0–5) Bimetallic Au(I) Complexes

2013

We have designed and synthesized a series of Au(I) complexes bearing either an alkynyl–(phenylene)n–diphosphine (A-0–A-3) or a (phenylene)n–diphosphine (B-1–B-5) bridge, among which the effective distance between Au(I) and the center of the emitting ππ* chromophore can be fine-tuned via the insertion of various numbers of phenylene spacers. We then demonstrated for the first time in a systematic manner the decrease of rate constant for S1 → T1 intersystem crossing (ISC) kisc as the increase of the effective distance. The results also unambiguously showed that the phosphorescence could be harvested via higher S0 → Sn (n > 1) electronic excitation, followed by fast Sn → Tm ISC and then the po…

Calcium efflux from human erythrocyte ghosts

1970

The passive Ca efflux from human red cell ghosts was studied in media of differing ion compositions and compared to the ATP-dependent Ca efflux. Cells were loaded with(45)Ca during reversible hemolysis, and the loss of radioactivity into the non-radioactive incubation medium was measured, usually for 3 hr at 37°C. Analysis of the efflux curves revealed that(45)Ca efflux followed the kinetics of a simple two-compartment system. In the concentration range between 0 and 1MM Ca in the external solution ([Ca(++)] o ), the rate constant of passive Ca efflux (k min(-1), fraction of(45)Ca lost per minute into the medium) increased from 0.00732 to 0.0150 min(-1). There was no further increase at hig…

A synergic nanoantioxidant based on covalently modified halloysite–trolox nanotubes with intra-lumen loaded quercetin

2016

We describe the preparation and properties of the first example of a synergic nanoantioxidant, obtained by different functionalizations of the external surface and the inner lumen of halloysite nanotubes (HNTs). Trolox, a mimic of natural α-tocopherol, was selectively grafted on the HNT external surface; while quercetin, a natural polyphenolic antioxidant, was loaded into the inner lumen to afford a bi-functional nanoantioxidant, HNT–Trolox/Que, which was investigated for its reactivity with transient peroxyl radicals and a persistent 1,1-diphenyl-2-picrylhydrazyl (DPPH˙) radical in comparison with the corresponding mono-functional analogues HNT–Trolox and HNT/Que. Both HNT–Trolox and HNT/Q…

Photocatalytic degradation of nitrophenols in aqueous titanium dioxide dispersion

1991

Abstract The results are reported of an investigation into the photodegradation of nitrophenol isomers carried out in aqueous titania (anatase) dispersions under various experimental conditions. We investigated the influence of various parameters on the photodegradation rate, such as the concentrations of the catalyst, dissolved oxygen and organic compound, and the presence of various anions in the dispersion. A plausible explanation is proposed for the influence of these parameters, both mechanistic and kinetic factors being accounted for. Gas chromatography and mass spectrometry were used as analytical methods in order to determine intermediate products. Spectroscopic methods (UV-vis and …

Heterogeneous fenton oxidation using magnesium ferrite nanoparticles for ibuprofen removal from wastewater: optimization and kinetics studies

2020

In this study, the catalytic properties of Fenton-like catalyst based on magnesium ferrite nanoparticles for IBP degradation were examined. Structural and morphological studies showed the low crystallinity and mesoporous structure for the catalyst obtained via a glycine-nitrate method. The influences of catalyst dosage, oxidant concentration, and solution pH on the pollutant degradation were investigated. The pseudo-first-order model describes kinetic data, and under optimal condition (catalyst dose of 0.5 g L-1, H2O2 concentration of 20.0 mM, and pH of 8.0), apparent rate constant reached 0.091 min-1. It was shown that Fenton reaction was mainly induced by iron atoms on the catalyst surfac…

On the characterization of some [bmim][X]/co-solvent binary mixtures: a multidisciplinary approach by using kinetic, spectrophotometric and conductom…

2008

Abstract In order to study the intrinsic characteristics and to evaluate the structural variations determined by the addition of a co-solvent to 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF 4 ]) we examined the behaviour of some probes in [bmim][BF 4 ]/co-solvent binary mixtures. The rate constants of the piperidino-catalyzed rearrangement of the Z -phenylhydrazone of the 3-benzoyl-5-phenyl-1,2,4-oxadiazole into the relevant 4-benzoylamino-2,5-diphenyl-1,2,3-triazole as well as the spectrometric properties of pyrene and Nile Red were evaluated. With the same purpose also 1 H NMR and conductivity measurements were carried out. By comparison the behaviour of 1-butyl-3-methylimidaz…

Second harmonic ac polarography of strongly adsorbed electroactive species

1981

Abstract The second harmonic ac current is calculated for the case of a quasi-reversible surface redox system: both species are strongly adsorbed according to a Langmuir isotherm and the kinetics of the process are controlled by the electron transfer. The current is measured with a phase-sensitive detector and the variation of the in-phase and quadrature components vs. the frequency leads to the surface rate constant ks. The experimental results obtained for benzo-(c)cinnoline are in good agreement with the theoretical predictions and with the results of impedance measurements. The advantages of the two methods are compared.

Multimetallic Oxynitrides Nanoparticles for a New Generation of Photocatalysts

2019

A versatile synthetic strategy for the preparation of multimetallic oxynitrides has been designed and here exemplarily discussed considering the preparation of nanoscaled zinc-gallium oxynitrides and zinc-gallium-indium oxynitrides, two important photocatalysts of new generation, which proved to be active in key energy related processes from pollutant decomposition to overall water splitting. The synthesis presented here allows the preparation of small nanoparticles (less than 20 nm in average diameter), well-defined in size and shape, yet highly crystalline and with the highest surface area reported so far (up to 80 m2  g-1 ). X-ray diffraction studies show that the final material is not a…

Kinetic evidence for the incorporation of the [(pentamethylcyclopentadienyl) (2,2′-bipyridyl)(aquo)rhodium(III)] complex into DPPC vesicles

2008

Abstract The binding of the [(pentamethylcyclopentadienyl) (2,2′-bipyridyl)(aquo)rhodium(III)] complex [Cp*RhIII(bpy)H2O]2+, to l -α-dipalmitoylphosphatidyl choline (DPPC) vesicles has been estimated by studying the kinetics of the electron transfer reaction between the rhodium(III) complex and formiate ions. Kinetic measurements carried out under anaerobic conditions in absence and presence of DPPC show that the total reaction is composed of two steps. The rate of the first reaction increases with the phospholipid concentration, while that of the second process is independent of the concentration of DPPC. This is consistent with a reaction, where the two reacting species are partitioned be…