CHMetal(II) axial interaction in planar complexes (metal = Cu, Pd) and implications for possible environmental effects of alkyl groups at biological copper sites |
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Authors: | Osamu Yamauchi Tatsuo Yajima Rie Fujii Yuichi Shimazaki Masanobu Yabusaki Masako Takani Minoru Tashiro Takeshi Motoyama Mitsuhiro Kakuto Yasuo Nakabayashi |
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Affiliation: | aUnit of Chemistry, Faculty of Engineering, Kansai University, Suita, Osaka 564-8680, Japan;bInstitute for Materials Chemistry and Engineering, Kyushu University, Higashi-ku, Fukuoka 812-8581, Japan;cFaculty of Pharmaceutical Sciences, Kanazawa University, Kanazawa 920-1192, Japan |
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Abstract: | Intramolecular M(II)H–C interactions (M(II)=Cu(II), Pd(II)) involving a side chain alkyl group of planar d8 and d9 metal complexes of the N-alkyl (R) derivatives of N,N-bis(2-pyridylmethyl)amine with an N3Cl donor set were established by structural and spectroscopic methods. The methyl group from the branched alkyl group (R = 2,2-dimethylpropyl and 2-methylbutyl) axially interacts with the metal ion with the MC and MH distances of 3.056(3)–3.352(9) and 2.317(1)–2.606(1) Å, respectively, and the M–H–C angles of 122.4–162.3°. The Cu(II) complexes showing the interaction have a higher redox potential as compared with those without it, and the 1H NMR signals of the interacting methyl group in Pd(II) complexes shifted downfield relative to the ligand signals. Dependence of the downshift values on the dielectric constants of the solvents used indicated that the M(II)H–C interaction is mainly electrostatic in nature and may be regarded as a weak hydrogen bond. Implications for possible environmental effects of the leucine alkyl group at the type 1 Cu site of fungal laccase are also discussed. |
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Keywords: | Weak interactions Planar complexes Weak hydrogen bond Laccase Metal(II)– alkane interaction |
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