Initial Ligand Concentration Research Articles

Optimization of cerium-based metal–organic framework synthesis for maximal sonophotocatalytic tetracycline degradation

Wastewater treatment is inevitably required to alleviate the pollution of water resources by various contaminants such as antibiotics. MOFs are novel materials with photocatalytic activities. In this study, sonophotocatalytic degradation of tetracycline (TC) by the Cerium-based MOF (Ce-MOF) is optimized by modification of its synthesis route. Ce-MOF synthesis by room temperature (RT), hydrothermal (HT), and sonochemical synthesis (SC) are studied. TC degradation experiments revealed the superiority of SC synthesis. The interplay of main synthesis parameters, namely, initial ligand concentration, ultrasound (US) power and time on sonophotocatalytic activity of Ce-MOF, were investigated by response surface methodology model (RSM) utilizing the central composite experimental design (CCD). The optimum SC synthesis conditions are an initial ligand concentration of 8.4 mmol/L, a sonication power of 50 amplitude, and a US time of 60 min. The optimally synthesized Ce-MOF was characterized by infrared spectroscopy, FTIR, XRD, FE-SEM, TEM, zeta potential analysis, diffuse reflectance spectroscopy, particle size analysis, Mott-Schottky analysis, photocurrent analysis, electrochemical impedance spectra, and photoluminescence spectroscopy. The findings indicate that the removal efficiency of TC can reach up to 81.75% within 120 min in an aqueous solution containing an initial TC concentration of 120 ppm and 1 g/L Ce-MOF at pH of 7. Mineralization efficiency of the process is 71% according to COD measurements. The Ce-MOF catalyst retained its chemical stability and remained active upon TC degradation which makes it a promising candidate for wastewater treatment.

Effect of ligand concentration and ultrasonic treatment on inclusion complexes of high amylose corn starch with chia seed oil fatty acids

Chia seed oil is rich in α-linolenic and linoleic fatty acids, which have multiple health benefits but are prone to oxidation due to their high degree of unsaturation. The linear component of starch, amylose, can interact with hydrophobic molecules (ligand) forming amylose inclusion complexes, which may potentially act as delivery systems of polyunsaturated fatty acids. Their physicochemical and functional properties are influenced by the conditions of formation. In the present study, it was investigated the effect of ultrasonic treatment and different ligand/starch ratios (10, 20, and 30% w/w) on the physicochemical properties of inclusion complexes formed between high amylose corn starch and enzymatically hydrolyzed chia seed oil. The increase in ligand/starch ratio, especially from 10 to 20%, yielded complexes with a higher content of α-linolenic acid. The effect of ultrasonic treatment on the acidic composition of complexes depended on the initial ligand concentration. All samples displayed a V-type X-ray diffraction pattern, indicating an effective complexation. Ultrasonically treated complexes showed a higher crystallinity than the untreated ones, suggesting that sonication promoted the fatty acid complexation. All samples displayed the same thermal behavior (Tp > 90 °C, ΔH = 7 J/g) and similar structural properties at the microscopic level. Thermogravimetric analysis showed that the untreated complexes formed with a 10% ligand/starch ratio effectively protected hydrolyzed chia seed oil from oxidative deterioration, suggesting an appropriate behavior as potential carrier agents of fatty acids from chia seed oil in food.

The effects of ligand decomposition on the pseudo first-order profile of a ligand substitution reaction: a “silent killer” in the background

The effect of ligand decomposition on the apparent rate constant for a ligand substitution reaction where the reverse reaction is negligible is examined. When the ligand concentration remains in excess for the entirety of the reaction, the data can be fitted to a modified form of the familiar pseudo first-order rate expression. However rapid ligand decomposition may result in the ligand concentration not remaining in excess for the duration of the reaction. Data simulations show that in this latter case the data still fit remarkably well to a first-order rate equation. Plots of the apparent rate constant versus the initial ligand concentration are also linear. However the reaction will not proceed to completion despite the reverse reaction being insignificant. Furthermore intercepts in the plots of apparent rate constant versus the initial ligand concentration are obtained, in addition to misleading values of the second-order rate constants for the ligand substitution reaction. We show that kinetic coupling between the decomposition of the ligand and its complex formation reaction may easily lead to falsified conclusions. Thus, the first-order appearance of a kinetic trace does not guarantee real first-order behavior.

Effect of inorganic and organic ligands on the sorption/desorption of arsenate on/from Al–Mg and Fe–Mg layered double hydroxides

This paper describes the sorption of arsenate on Al–Mg and Fe–Mg layered double hydroxides as affected by pH and varying concentrations of inorganic and organic ligands, and the effect of residence time on the desorption of arsenate by ligands. The capacity of ligands to inhibit the fixation of arsenate followed the sequence: nitrate < nitrite < sulphate < selenite < tartrate < oxalate ≪ phosphate on Al–Mg-LDH and nitrate < sulphate ≈ nitrite < tartrate < oxalate < selenite ≪ phosphate on Fe–Mg-LDH. The inhibition of arsenate sorption increased by increasing the initial ligand concentration and was greater on Al–Mg-LDH than on Fe–Mg-LDH. The longer the arsenate residence time on the LDH surfaces the less effective the competing ligands were in desorbing arsenate from sorbents. A greater percentage of arsenate was removed by phosphate from Al–Mg-LDH than from Fe–Mg-LDH, due to the higher affinity of arsenate for iron than aluminum.

The effect of ligand on the rate of propagation of Cu(0)‐wire catalyzed SET‐LRP of MA in DMSO at 25 °C

AbstractThe effect of initial ligand concentration on the apparent rate constant of propagation of single‐electron transfer living radical polymerization (SET‐LRP) of MA in DMSO at 25 °C was examined using various lengths of Cu(0) wire as catalyst. It was determined that unlike other parameters such as initiator concentration, solvent concentration, and deactivator concentration, no simple external rate‐order for the ligand concentration could be determined. Rather, the response of the rate of SET‐LRP to initial ligand concentration is complex and is likely determined by a competition of ligand‐dependent extent of disproportionation as well as the role of ligand concentration in the surface mediated activation process. Results suggest that a minimum concentration of ligand is needed to achieve both acceptable reaction rate and reaction control, and therefore, ligand concentration must be considered in designing experimental conditions for SET‐LRP. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5629–5638, 2009

Kinetic model of receptor-mediated adhesion of cells to a functionalized supported lipid bilayer

We present a kinetic model describing adhesion of cells to a supported lipid bilayer due to formation of bonds between cellular receptors and ligands (e.g., peptides or proteins) attached to the bilayer. The model implies a power-law dependence of the adhesion rate on the ligand concentration and takes into account ligand diffusion and association with already adhered cells. For a time interval longer than the sedimentation time, it predicts a sigmoidal dependence of the population of adhered cells on the initial ligand concentration. This feature becomes less pronounced with increasing rate of ligand association with adhered cells. The results obtained are used to interpret recent experiments with rat adult neural progenitor cells.

Interaction of nucleic acid bases and nucleosides with cobalt ions immobilized in a column system

The interactions of ligands, such as adenine, adenosine, uracil and uridine with Co(II) ions immobilized by carboxylated diaminoethyl matrix on sporopollenin were investigated as a function of temperature by the breakthrough technique. The adsorption characteristics of ligands on Co(II)-carboxylated diaminoethyl sporopollenin [Co(II)-CDAE-S] were investigated by Scatchard plot analysis under optimized conditions of flow rate and temperature. Equilibrium binding data used in Scatchard plot analysis for adenosine gave rise to a linear plot, indicating the presence of specific interaction and Langmuirean behavior. However, the adsorption of uracil on this ligand-exchange stationary phase was affected by the electrostatic or hydrophobic interaction in the whole concentration range. In the case of adenine and uridine, the adsorption performance was strongly affected by the initial ligand concentration. At high concentration, adenine and uridine were adsorbed specifically to the ligand exchanger matrix exposed on the adsorbent. At lower concentrations, the binding to the second sets of adsorbent was appeared because of nonspecific interaction such as hydrophobic and electrostatic.

Kinetic Study of Fast Complexation of Zinc(II) with 8-Quinolinol and 5-Octyloxymethyl-8-Quinolinol at 1-Butanol/Water Interface by Two-Phase Sheath Flow/Laser-Induced Fluorescence Microscopy

Abstract The kinetics of the fast complexation of zinc(II) with 8-quinolinol (Hqn) and 5-octyloxymethyl-8-quinolinol (Hocqn) at the 1-butanol/water interface was investigated with two-phase sheath flow/laser-induced fluorescence microscopy. The micrometer-sized two-phase sheath flow system was constructed in a flow cell, in which the 1-butanol phase was introduced as an inner flow and the aqueous phase as an outer flow. The fluorescence emitted from the zinc(II) complex was corrected by an objective lens, and detected with a CCD camera. It was revealed that the fluorescence intensity had a maximum value at the interfacial region, and increased with the reaction time up to 2 ms after the formation of the interface. The complexation rate increased with the increase of the initial ligand concentration in the organic phase, giving a saturation curve. The complexation rate of Hqn with zinc(II) was three times faster than that of Hocqn at equivalent conditions. A digital simulation taking into account the interfacial formation rate of 1:1 complex, the interfacial adsorption of the ligand and complex, and the diffusion of each species reproduced accurately the observed results. It was suggested that the interfacial adsorption of ligands was delayed and depressed by the preferential occupancy of 1-butanol molecules at the interface.

Formation of coordination polymeric structures on the basis of 4,4"-dipyridylethylene and Ag+ in solutions

The formation of coordination polymeric chain structures in which silver ions alternate with dipyridylethylene (DPyEt) ligands was studied. In a homogeneous ethanol solution, complex formation of DPyEt with silver cations takes place. The outcome of this reaction depends on the ligand/cation molar ratio, the initial ligand concentration, and the counter-ion type. Conditions were identified under which the coordination polymer is formed as a microdispersed solid precipitating from the solution. The precipitates formed in the DPyEt—AgNO3 and DPyEt—AgClO4 systems were investigated by various experimental techniques. The counter-ion was found to be incorporated in the polymer and to influence the structure of the precipitate particles.

The complexation of cyclic polyethers and a series of equations for determination of equilibrium constants

An outstanding and compact formalism was established to estimate the equilibrium constants Ke of essential ligands with well-known structures like crown ethers, or unknown complexing stoichiometries. The application of the general formula ⧸Ke[L0]m+n-1 = (⧸PL−1)(1-PL)m+n−1 is described by the computer-simulated plots, where m/n is the complexing ligand/cation ratio, PL is the mole fraction of the complexed ligand and [L0] is the initial ligand concentration of the complex solution.

DEFECTIVE TRANSFORMATION OF ANDROGEN-RECEPTOR COMPLEXES: A CLASS OF FAMILIAL, RECEPTOR-POSITIVE PARTIAL ANDROGEN RESISTANCE

We have analyzed the androgen (A)-receptor (R) system in genital skin fibroblasts (GSF) of 2 subjects with external genital ambiguity. Subject 1 has 5 affected maternal relatives in 3 generations. With a 2-h assay, his AR has a normal binding capacity (Bmax) (receptor-positive), but an apparent equilibrium dissociation constant (Kd) of 1.2-1.4 nM for 5α-dihydrotestosterone (DHT) or the nonmetabolizable androgen, methyltrienolone (MT) (normal: 0.1-0.3 nM). His DHT- and MT-R complexes dissociate 3 and 6 times faster than normal (0.006 and 0.012 min−1, 37°, respectively). Prolonged incubation with DHT or MT fails to augment (up-regulate) basal A-R activity. Subject 2's mother has sparse sexual hair. With DHT, his AR has a normal Bmax but an increased Kd (0.6 nM) and k (0.012 min−1), and prolonged incubation does not cause up-regulation. In contrast, with MT his AR is normal. Normal GSF yield higher Kds (0.3-1.8 nM) for either ligand after 0.5-compared to 2-h assays, and the GSF of both subjects catabolize DHT to a normal extent. Conclusions: (i) normal GSF transform initial, low-affinity A-R complexes to higher affinity states by a process that is codependent on time and initial ligand concentration; (ii) subject 1 forms DHT- and MT-complexes that remain in the initial, low-affinity state; (iii) subject 2 forms complexes that transform normally with MT but partially with DHT; and (iv) A-R complexes must attain the highest affinity state to act as the «signal» for up-regulation.