G G 4 -DNA ▶ Strontium and DNA Aptamer Folding Gadolinium Takashiro Akitsu Department of Chemistry, Tokyo University of Science, Shinjuku-ku, Tokyo, Japan Definition A lanthanoid element, the seventh element of the f-elements block, with the symbol Gd, atomic number 64, and atomic weight 157.25. Electron configuration [Xe]4f 7 5d 1 6s 2 . Gadolinium is composed of stable ( 154 Gd, 2.18%; 155 Gd, 14.80%; 156 Gd, 20.47%; 157 Gd, 15.65%; 158 Gd, 24.84%) and two radioactive ( 152 Gd, 0.20%; 160 Gd, 21.86%) isotopes. Discovered by J. C. G. de Marignac in 1880. Gadolinium exhibits oxidation states III (and II); atomic radii: 180 pm, covalent radii 197 pm; redox potential (acidic solution) Gd 3+ /Gd 2.397 V; Gd 3+ /Gd 2+ 3.9 V; electronegativity (Pauling) 1.2. Ground electronic state of Gd 3+ is 8 S 7/2 with S ¼ 7/2, L ¼ 0, J ¼ 7/2 with l ¼ 0 cm 1 . Most stable technogenic radionuclide 160 Gd (half-life > 1.3  10 21 years). The most common compounds: Gd 2 O 3 , GdF 3 , and Gd(OH) 3 . Biologically, gadolinium is of high toxicity, and inhala- tional exposure to high concentrations of Gd 2 O 3 results in pneumonitis and acute inflammation in the lung (Atkins et al. 2006; Cotton et al. 1999; Huheey et al. 1997; Oki et al. 1998; Rayner-Canham and Overton 2006). Cross-References ▶ Lanthanide Ions as Luminescent Probes ▶ Lanthanide Metalloproteins ▶ Lanthanides and Cancer ▶ Lanthanides in Biological Labeling, Imaging, and Therapy ▶ Lanthanides in Nucleic Acid Analysis ▶ Lanthanides, Physical and Chemical Characteristics References Atkins P, Overton T, Rourke J, Weller M, Armstrong F (2006) Shriver and Atkins inorganic chemistry, 4th edn. Oxford University Press, Oxford/New York Cotton FA, Wilkinson G, Murillo CA, Bochmann M (1999) Advanced inorganic chemistry, 6th edn. Wiley-Interscience, New York Huheey JE, Keiter EA, Keiter RL (1997) Inorganic chemistry: principles of structure and reactivity, 4th edn. Prentice Hall, New York Oki M, Osawa T, Tanaka M, Chihara H (1998) Encyclopedic dictionary of chemistry. Tokyo Kagaku Dojin, Tokyo Rayner-Canham G, Overton T (2006) Descriptive inorganic chemistry, 4th edn. W. H. Freeman, New York Gallium ▶ Gallium(III) Complexes, Inhibition of Proteasome Activity V.N. Uversky et al. (eds.), Encyclopedia of Metalloproteins, DOI 10.1007/978-1-4614-1533-6, # Springer Science+Business Media New York 2013