Hydroxyisobutyrate complex

A practical application of the spectral intensity of hypersensitive transitions in lanthanide ions is the determination of stability constants. Bukietynska et al. (1977, 1981a,b) have evaluated the stability constants of lanthanide complexes from the changes of the oscillator strength of hypersensitive transitions as a function of the ligand concentration. The method was applied to acetate, propionate, glycolate, lactate and a-hydroxyisobutyrate complexes of Nd ", Ho and Er +. Bukiet5mska et al. claim that this spectrophotometric method is superior to the potentiometric method, since the best results for the latter method can be obtained only for the first complexation steps. The stability constants evaluated at several temperatures have been used also to calculate the thermodynamic quantities AG, AH and AS. 

Hydroxycarbonic adds, such as dtric, tartaric, malic, and hydroxyisobutyric acid, but also gluconate or glucoheptonate, are assumed to form the same kind of complex as the polyols do [23,28,29]. 

Several methods have been used to separate the lanthanides chemically solvent extraction, ion exchange chromatography, HPLC using Q-hydroxyisobutyric acid and, in limited cases, selective reduction of a particular metal cation.40-43 The use of di(2-ethylhexyl)orthophosphoric acid (HDEHP) for the separation of various rare-earth elements via solvent extraction has also been reported.44 16 This separation method is based on the strong tendency of Ln3+ ions to form complexes with various anions (i.e., Cl- or N03 ) and their wide range of affinities for com-plexation to dialkyl orthophosphoric acid. When the HDEHP is attached to a solid phase resin, the lanthanides can be selected with various concentrations of acid in order of size, with the smallest ion being the most highly retained. 

The need to achieve high yield in one-pot synthesis, coupled to the relative kinetic inertness of rhenium complex (e.g. compared to technetium) and the mild conditions required has led to the development of useful versatile rhenium(V) intermediates that can be quickly prepared in quantitative yield, and are metastable, i.e. kinetically labile enough to react rapidly with the final chelator, again in high yield. The most widely used ligands suitable for this purpose are polydentate hydroxycarboxylic acids such as glucoheptonate [116a], citrate (47), tartrate (48), and 2-hydroxyisobutyric acid (49) [159]. Examples are discussed elsewhere in this chapter. They are typically used in the presence of Sn(II) to reduce Re(VII) to Re(V), at moderately elevated temperature (50-100 °C) at pH 2-3 (acid pH promotes reduction of perrhenate, presumably by facilitat-... 

The enthalpies and entropies of formation of mono-mandelato-complexes have been determined and, in comparison with other hydroxycarboxylic acid complexes, the enthalpy order of stabilization is lactate > a-hydroxyiso-butyrate mandelate > glycolate, whereas the entropy order of stabilization is glycolate > a-hydroxyisobutyrate > mandelate > lactate. The stability constants and enthalpy of formation of mono- and di-malonate complexes have also been measured.The mono-1,1-cyclopentanedicarboxylato-complexes are less stable than the corresponding malonate species. 

A number of frans-[0s(0)2(py)2L] complexes (H2L = glycolic, 2-hydroxyisobutyric, (S)-(+)-mandelic, or 2-salicylic acid) have been prepared from [0s(0)2(0Me)4]2 and py with the ligand. They have been characterized by IR, mass, and NMR ( H and 13C) spectroscopies (408) and X-ray structures for L = glycolate(2-) and salicylate (401, 402). The Os(V) complex, (PPh4)[0s(0)(ehba)2] has been prepared from the reaction of the ligand with (PPh4)[0s04] and has been characterized by IR spectroscopy (23a). 

The first report demonstrating the feasibility of indirect detection in CE was published in 1987 by Hjerten et al.45 who employed indirect UV absorbance detection for the analysis of both inorganic ions and organic acids. The UV-background-providing electrolyte was 25 mM sodium veronal, pH 8.6, and detection was monitored on-column at 225 nm. In 1990, the first separation of alkali, alkaline earth, and lanthanide metals was reported by Foret et al46 Indirect UV detection at 220 nm was employed to detect 14 metals in 5 min, with baseline resolution achieved between all but two of the components. The baseline showed a reproducible upward drift between 1 and 3 min. The UV-absorbing component of the electrolyte was creatinine, with a-hydroxyisobutyric acid introduced to complex with the lanthanides and improve resolution. 

Another series of experiments with Db used its complexation with the a-hydroxyisobutyrate (a-HiB), (CH3)2COH COO", that had been used in the first liquid-phase rutherfordium experiment [15]. Chelating by a-HiB depends strongly on the charge of the metal ion [41]. Elutions from cation exchange columns in ARCA II with unbuffered dilute a-HiB show that Nb, Ta, and Pa are eluted promptly while tetravalent and divalent metal ions are... 

In addition to tartrate, a-hydroxyisobutyrate can be utilized as the complexing anion. It was employed by Cassidy et al. [144] for the separation of lanthanides. In comparison to tartrate, no particular advantages are revealed in the separation of divalent metal ions. Fig. 3-150 shows a separation of the seven heaviest lanthanides with an eluent mixture of ethylenediamine and a-hydroxybutyric acid. The pronounced tailing effects observed under isocratic conditions for late eluting ions are unsatisfactory. 

Hydroxycarboxylates and several of their complexes formed with vanadate in aqueous solution. Abbreviations lac = L-lactate hba = L-a-hydroxyisobutyric acid. The structures for the binary dinuclear complexes are based on X-ray structure determinations of mono-crystals isolated from the solutions.Note that the solid-state structure does not necessarily reflect the solution structure. 

Addition of a weak complexing anion (L), such as tartrate or a-hydroxyisobutyrate (HIBA), will convert part of a metal ion to a complexed form that is uncharged or has a lower positive charge than the free metal ion. This will cause the metal ion to elute more rapidly. Referring to Eq. 5.20, the metal ion in solution (Is,in) will be partially complexed ... 

Our ability to separate free metal cations by CE is limited because many of the metal ions have similar electrophoretic mobilities. An excellent way to enhance the separation of metal ions is to add a relatively weak complexing ligand (L ) such as tartrate, lactate or a-hydroxyisobutyric acid (HIBA) to the BGE. Now part of each metal ion will remain as the free ion (M, for example) and part will be converted to a complexed form (ML , ML2, ML3, for example). The total mobility (p) will be the sum of the mole fraction of each species (a) multiplied by its mobility. 

In these studies, the manganese complex was generated in situ from added manganese and ligand. In 1991, Saadeh et al. reported the preparation and isolation of complexes with a-hydroxy acids, for example lactic acid, 2-hydroxyisobutyric acid (HIB) and 2-hydroxy-2-ethylbutyric acid (HEB) (425). The latter two ligands led to Mn1 complexes with 06 first coordination spheres, whereas Mnin complexes were prepared and characterized with lactic acid. The crystal structure of the complex with HIB shows it to be two MnIVL2 units that are... 

---