Lanthanum stability constant

Compared to later elements in their respective transition series, scandium, yttrium and lanthanum have rather poorly developed coordination chemistries and form weaker coordinate bonds, lanthanum generally being even less inclined to form strong coordinate bonds than scandium. This is reflected in the stability constants of a number of relevant 1 1 metal-edta complexes ... 

Fig. 7.27. Dependence of the isotopic exchange rate constants (k) and the stability constants (K) of the complexes R(EDTA) on the atomic number of the rare earths. The vertical bars shown in the figure represent the probable error in the k values. The dotted line describing the behavior of the elements lanthanum, neodymium and europium is from the comparison of exchange reactivity attempted by Fomin.

Selected stability constants for scandium, yttrium, lanthanum, and lutetium are shown in (Table 3) They show a preference for hard donor atoms, as might be expected for the trivalent metals, but complexes with softer donor atoms like nitrogen can be isolated by operating in nonaqueous solvents. 

Due to the anionic nature of rhamnolipids, they are able to remove metals from soil and ions such as cadmium, copper, lanthanum, lead and zinc due to their complexation ability [57-59], More information is required to establish the nature of the biosurfactant-metal complexes. Stability constants were established by an ion exchange resin technique [60], Cations of lowest to highest affinity for rhamnolipid were K+ < Mg + < Mn + < Ni " " < Co " < Ca2+ < Hg2+ < Fe + < Zn2+ < Cd2+ < Pb2+ < Cu2+ < M +. These affinities were approximately the same or higher than those with the organic acids, acetic, citric, fulvic and oxalic acids. This indicated the potential of the rhamnolipid for metal remediation. Molar ratios of the rhamnolipid to metal for selected metals were 2.31 for copper, 2.37 for lead, 1.91 for cadmium, 1.58 for zinc and 0.93 for nickel. Common soil cations, magnesium and potassium, had low molar ratios, 0.84 and 0.57, respectively. 

The lanthanum-nitrate interaction was studied in anhydrous methanol by La NMR (Bunzli et al. 1987), but the absolute stability constants could not be evaluated. The interaction with neodymium, europium and erbium was investigated by UV-VIS spectroscopy in aqueous methanol by Silber et al. (1990) and Silber and Strozier (1987). Stability constants, as well as thermodynamic parameters were calculated. Table 7 lists the stability constants available for solutions with a low water content. 

Dimethylacetamide. The stability constants and enthalpy values for lanthanide-nitrate interactions in anhydrous DMA (R=La, Nd) have been determined by means of calorimetric titration (Airoldi et al. 1982). The experimental results support the existence of the iimer-sphere mono- and dinitrato complexes with the following formation constants A i = 17,. 2= 16 for lanthanum and K =25, K2 = 92 for neodymium (cf. table 7). The enthalpies of formation 1 (La 48.2, Nd l.OkJmol" ) and AH2 (La 23.1, Nd 8.3kJmor ) are all endothermic, although rather small. Finally, mononitrate complexes appear to be less stable for both La(III) and Nd(III) ions compared to the corresponding chloro- and bromo complexes (cf. tables 6, 7). 

Table 8.21 Data for the stability constants of polymeric species of lanthanum(l... 

Tphe excellent catalytic activity of lanthanum exchanged faujasite zeo-A lites in reactions involving carbonium ions has been reported previously (1—10). Studies deal with isomerization (o-xylene (1), 1-methy 1-2-ethylbenzene (2)), alkylation (ethylene-benzene (3) propylene-benzene (4), propylene-toluene (5)), and cracking reactions (n-butane (5), n-hexane, n-heptane, ethylbenzene (6), cumene (7, 8, 10)). The catalytic activity of LaY zeolites is equivalent to that of HY zeolites (5 7). The stability of activity for LaY was studied after thermal treatment up to 750° C. However, discrepancies arise in the determination of the optimal temperatures of pretreatment. For the same kind of reaction (alkylation), the activity increases (4), remains constant (5), or decreases (3) with increasing temperatures. These results may be attributed to experimental conditions (5) and to differences in the nature of the active sites involved. Other factors, such as the introduction of cations (11) and rehydration treatments (6), may influence the catalytic activity. Water vapor effects are easily... 

Similarly, for the change in cationic size with constant charge, as in the lanthanides (where the lanthanide contraction means that the elements with higher atomic numbers give the smallest 3+ ions) where only the metal ion changes, we generally find the stability of a series of coordination compounds to increase from lanthanum (atomic number 57) to lutetium (atomic number 71). 

The effect of the non-ionic surfactant Ci2E6 on the stability of polystyrene latex as a function of electrolyte concentration and pH is shown in Fig. 9.12. At a constant surfactant concentration at pH 4.6 the value of log decreases gradually with increasing concentration of lanthanum nitrate until a concentration is reached where the curve becomes parallel to the concentration axis. This corresponds to the region of rapid flocculation. The portion below the critical concentration for rapid flocculation is the region of slow flocculation. The plots in Fig. 9.12 have been normalized to show more clearly the effect of increasing... 

Urinary bladder. Kreft and coworkers (Kreft, Romih et al. 2002) established an in vitro culture model that closely resembles whole mouse urothelial tissue. When examined at the ultrastructural level, the cultured urothelium was polarized and organized as a multilayered epithelium, and epithelial organization was stabilized by well developed cell junctions. Desquamation of urinary bladder epithelial cells can be induced by constant illumination for 96 hours or by application of endotoxin lipopolysaccharide. Cell detachment involves interruption of TJ between neighbouring cells (Jezemik 1996). Urothelium permeability was studied in an experimental ischemic model of mouse urinary bladder by means of lanthanum nitrate tracer (Korosec and Jezemik 2000). Ischemia induces breakdown of the blood-urine permeability barrier by dismption of the TJ. 

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