We present an X-ray absorption spectroscopy study of the local structures of Gd(DTPA)(2)(-) and Gd(DOTA)(-) complexes in the crystalline state (at room and low temperatures) and in aqueous solutions exhibiting various pH values (0.15-7) at different temperatures (25-90 degrees C). Using X-ray absorption fine structure (XAFS) analysis procedures and ab initio multiple scattering calculations of XAFS spectra at the Gd L(3) edge, we reconstructed the Gd(3+) local environment, and compared it with existing structural models. From neutral pH to a value of 1.5, we found that the local environment and complex dynamics around the gadolinium ions were conserved up to 4.5 Å, and the structure agreed well with the known crystallographic data. In these solutions, the gadolinium ions in the complex Gd(DOTA)(-) are bonded to the four carboxylate oxygen atoms [R(Gd-O(av)) 2.38 Å, Debye-Waller (DW) factor 0.006 Å(2)], to the four nitrogen atoms [R(Gd-N(av)) 2.65 Å, DW factor 0.006 Å(2)] and to one water molecule [R(Gd-O(w)) 2.46 Å, DW factor 0.012 Å(2)]. Concerning the complex Gd(DTPA)(2)(-), the gadolinium ions are bonded to the five carbonyl oxygen atoms [R(Gd-O(av)) 2.39 Å, DW factor 0.007 Å(2)], to the three nitrogen atoms [R(Gd-N(av)) 2.64 Å, DW factor 0.006 Å(2)], and to one water molecule [R(Gd-O(w)) 2.47 Å, DW factor 0.018 Å(2)]. In the range of pH (0.15-1.5) for the Gd(DTPA)(2)(-) complexes, thanks to the pH strong dependence of the XAFS signals, we observed a progressive complex dissociation. On the other hand, the XAFS signals of Gd(DOTA)(-) complexes exhibited only a slight pH (1-1.5) dependence. Concerning both complexes, we noted just a slight temperature dependence.
Absolute line intensities in the nu(6) and nu(8) interacting bands of trans-HCOOH, observed near 1105.4 and 1033.5 cm(-1), respectively, and the dissociation constant of the formic acid dimer (HCOOH)(2) have been measured using Fourier transform spectroscopy at a resolution of 0.002 cm(-1). Eleven spectra of formic acid, at 296.0(5) K and pressures ranging from 14.28(25) to 314.0(24) Pa, have been recorded between 600 and 1900 cm(-1) with an absorption path length of 19.7(2) cm. 437 integrated absorption coefficients have been measured for 72 lines in the nu(6) band. Analysis of the pressure dependence yielded the dissociation constant of the formic acid dimer, K(p)=361(45) Pa, and the absolute intensity of the 72 lines of HCOOH. The accuracy of these results was carefully estimated. The absolute intensities of four lines of the weak nu(8) band were also measured. Using an appropriate theory, the integrated intensity of the nu(6) and nu(8) bands was determined to be 3.47 x 10(-17) and 4.68 x 10(-19) cm(-1)(molecule cm(-2)) respectively, at 296 K. Both the dissociation constant and integrated intensities were compared to earlier measurements.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.