Oxoperoxo Vanadium(V) Complexes of L-Lactic Acid: Density Functional Theory Study of Structure and NMR Chemical Shifts Licı ´nia L. G. Justino,* ,†,‡ M. Luı ´sa Ramos, †,‡ Fernando Nogueira, § Abilio J. F. N. Sobral, † Carlos F. G. C. Geraldes, ‡,| Martin Kaupp, ⊥ Hugh D. Burrows, † Carlos Fiolhais, § and Victor M. S. Gil † Departamento de Quı ´mica, Faculdade de Cie ˆncias e Tecnologia, UniVersidade de Coimbra, 3004-535 Coimbra, Portugal, Departamento de Fı ´sica e Centro de Fı ´sica Computacional, Faculdade de Cie ˆncias e Tecnologia, UniVersidade de Coimbra, 3004-516 Coimbra, Portugal, Departamento de Bioquı ´mica, Faculdade de Cie ˆncias e Tecnologia, UniVersidade de Coimbra, 3001-401 Coimbra, Portugal, Centro de Neurocie ˆncias e Biologia Celular, UniVersidade de Coimbra, Portugal, and Institut fu ¨r Anorganische Chemie, UniVersita ¨t Wu ¨rzburg, Am Hubland, D-97074 Wu ¨rzburg, Germany Received March 5, 2008 Various combinations of density functionals and pseudopotentials with associated valence basis-sets are compared for reproducing the known solid-state structure of [V 2 O 2 (OO) 2 L-lact 2 ] 2- cis . Gas-phase optimizations at the B3LYP/ SBKJC level have been found to provide a structure that is close to that seen in the solid state by X-ray diffraction. Although this may result in part from error compensation, this optimized structure allowed satisfactory reproduction of solution multinuclear NMR chemical shifts of the complex in all-electron DFT-IGLO calculations (UDFT-IGLO- PW91 level), suggesting that it is probably close to that found in solution. This combination of approaches has subsequently been used to optimize the structures of the vanadium oxoperoxo complexes [V 2 O 3 (OO)L-lact 2 ] 2- cis , [V 2 O 3 (OO)L-lact 2 ] 2- trans , and [VO(OO)(L-lact)(H 2 O)] - cis . The 1 H, 13 C, 51 V, and 17 O NMR chemical shifts for these complexes have been calculated and compared with the experimental solution chemical shifts. Excellent agreement is seen with the 13 C chemical shifts, while somewhat inferior agreement is found for 1 H shifts. The 51 V and 17 O chemical shifts of the dioxo vanadium centers are well reproduced, with differences between theoretical and experimental shifts ranging from 22.9 to 35.6 ppm and from 25.1 to 43.7 ppm, respectively. Inferior agreement is found for oxoperoxo vanadium centers, with differences varying from 137.3 to 175.0 ppm for 51 V shifts and from 148.7 to 167.0 ppm for 17 O(oxo) shifts. The larger errors are likely to be due to overestimated peroxo O-O distances. The chosen methodology is able to predict and analyze a number of interesting structural features for vanadium(V) oxoperoxocomplexes of R-hydroxycarboxylic acids. Introduction Vanadium occurs in nature as a trace element. It is essential for several organisms. In particular, it is implicated in the synthesis of chlorophyll in green plants and in the normal growth of some animals 1 and may also be essential for humans. 2 In recent decades, in vivo and in vitro studies of the biological effects of this metal have revealed other important effects, both at the whole organ and cellular levels. These include the ability to inhibit certain enzymes, such as phosphatases, ATPases, phosphotransferases, nucleases, and kinases, the possibility of mimicking the effects of insulin, in addition to their capacity to reduce cholesterol biosynthesis and triglyceride levels in blood plasma and, consequently, to reduce the incidence of cardiovascular diseases. Further, * To whom correspondence should be addressed. E-mail: liciniaj@ qui.uc.pt. Tel: +351-239-854453. Fax: +351-239-827703. † Departamento de Quı ´mica, Faculdade de Cie ˆncias e Tecnologia, Universidade de Coimbra. ‡ Centro de Neurocie ˆncias e Biologia Celular, Universidade de Coimbra. § Departamento de Fı ´sica e Centro de Fı ´sica Computacional, Faculdade de Cie ˆncias e Tecnologia, Universidade de Coimbra. | Departamento de Bioquı ´mica, Faculdade de Cie ˆncias e Tecnologia, Universidade de Coimbra. ⊥ Universita ¨t Wu ¨rzburg. (1) Rehder, D. Angew. Chem., Int. Ed. Engl. 1991, 30, 148–167; and references therein. (2) Crans, D. C.; Smee, J. J.; Gaidamauskas, E.; Yang, L. Chem. ReV. 2004, 104, 849–902; and references therein. Inorg. Chem. 2008, 47, 7317-7326 10.1021/ic800405x CCC: $40.75  2008 American Chemical Society Inorganic Chemistry, Vol. 47, No. 16, 2008 7317 Published on Web 07/16/2008