PubMed · 13675351
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M FILOMENI. 1959-05-15. [Chelation processes in therapy].. https://pubmed.ncbi.nlm.nih.gov/13675351/
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The complex formation of vanadium(IV) with 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (taci) and 1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol (tdci) was studied in aqueous solution and in the solid state. The formation constants of [V(IV)O(taci)](2+), [V(IV)O(tdci)](2+), and [V(IV)(tdci)(2)](4+) and of the deprotonation product [V(IV)(tdci)(2)H(-)(1)](3+) were determined (25 degrees C, 0.1 M KNO(3)). Cyclic voltammetry measurements established a reversible one-electron transfer for the [V(IV)(tdci)(2)H(-)(m)]((4)(-)(m))/[V(III)(tdci)(2)H(-)(n)]((3)(-)(n)) couple (0 <or= n, m <or= 6) with a strongly pH-dependent E(1/2)(obs) (+0.15 V at pH 5, -0.57 V at pH 13.5). Slightly more negative potentials were measured for the taci complexes. An additional quasi-reversible electron transfer at strongly positive potentials (1.2-0.5 V) was assigned to the [V(V)(taci)(2)H(-)(m)]((5)(-)(m))/[V(IV)(taci)(2)H(-)(n)]((4)(-)(n)) couple. The structures of [V(IV)(taci)(2)](SO(4))(2).12H(2)O (1), [V(IV)(tdci)(2)][V(4)(V)O(12)].14.5H(2)O (2), and [V(IV)(tdci)(2)H(-)(1)]Cl(3).15H(2)O (3) were determined by single-crystal X-ray analysis. The cations of 1-3 exhibit a structure of approximate D(3)(d) symmetry. The vanadium centers have an almost regular octahedral geometry. The coordinated oxygen donors are deprotonated, and their protons are transferred to the amino groups which act as internal bases. For both ligands, EPR measurements support the formation of non-oxo V(IV) complexes, with a d(z)2 ground state, in aqueous solution above pH 7. The spectral features are indicative of hexacoordinated complexes with a geometry distorted toward a trigonal prism. Finally, a mechanism is proposed for the decomposition of [V(IV)L(2)H(-)(x)]((4)(-)(x)) (L = taci and tdci) in strongly alkaline media (pH approximately 13).
Addition of a benzyl substituent to the macrocyclic ring of DOTA has a substantial impact on the conformational ring flipping motion of the macrocycle in the resulting LnDOTA complexes. The p-NO2-benzyl substituent in the Ln(p-NO2-Bn-DOTA)- complexes lies in an equatorial position and effectively "locks" the conformation of the ring into the deltadeltadeltadelta configuration. The presence of the p-NO2-benzyl group also increases the population of the square antiprismatic (SAP) coordination isomer for all Ln(p-NO2-Bn-DOTA)- complexes relative to that seen for the respective LnDOTA- complexes. Despite this increase in SAP isomer population, the rate of water exchange in these complexes remains comparatively fast. The kinetic and thermodynamic stabilities of the Ln(p-NO2-Bn-DOTA)- complexes are also slightly lower than the corresponding LnDOTA- complexes but appear to be sufficiently high for in vivo use.
A unique peptide sequence of HGGHHG screening from a combinatorial synthetic peptide library showed a good chelating ability to bind a transition metal on a chip better than hexa-His peptide. It was directly conjugated with a His-Tagged proteins onto a chip in a mild aqueous solution and can be used this chip as a high throughput technique for protein array in order to detect and purify the His-Tagged proteins.