Structural Analysis of Cadmium–Glycylglycine Complexes Studied by X-Ray Diffraction and High Resolution 113Cd and 13C Solid State NMR

Abstract

Structural analysis of bis(glycylglycinato)cadmium(II) complexes prepared to adjust the pH to 6 (A) and 9 (C), were studied by X-ray diffraction and high resolution 113Cd and 13C solid state NMR. In order to compare with the structure of A, structural analysis of bis(glycylglycinato)zinc(II) complexes (B) prepared to adjust the pH to 6 was also performed by the same methods. The structure of A was six coordinate; a five-membered chelate ring was formed between the terminal amino-group and the adjacent O (peptide) and the terminal carboxygroups of the dipeptide ligands were involved in Cd binding in the complex. The structure of B was similar to A, indicating that the Cd nucleus was better suited for probing the Zn nucleus-ligand structure. The structure of C was six coordinate; the four terminal carboxygroups (O) and the two terminal aminogroups (N) of the dipeptide ligands were involved in Cd binding in the complex. High-resolution 113Cd and 13C CP/MAS NMR spectra have been measured in order to obtain detailed information about the structures. The 113Cd signal of A showed a low field chemical shift compared with the peak of C. This means that the chelate ring shows decreased shielding. From the 13C spectra of A and C, it was seen that the Cd nucleus of A is bonded to a carbonyl oxygen (peptide) and the terminal carboxyl group of the dipeptide, but that for C is not bonded to a carbonyl oxygen (peptide).

Biologically derived metal organic frameworks

“…The simplest and shortest peptide, GlyGly, has been used to construct 2-dimensional bio-MOFs with formula of [M(GlyGly)2]•2H2O (M: Zn II or Cd II ) (For Zn, Table 2, entry 1). [101] At pH 6, each GlyGly ligand, bridges two metal ions in a monodentate mode through the terminal carboxylate group and the amino group coordinates through a five membered chelation ring. Increasing the pH to 9 (and where M: Cd II ) the GlyGly ligands bind to two Cd II ions through their terminal carboxylates, and the amino group to another Cd II ion in a monodentate mode.…”

“…Increasing the pH to 9 (and where M: Cd II ) the GlyGly ligands bind to two Cd II ions through their terminal carboxylates, and the amino group to another Cd II ion in a monodentate mode. [101] Changing the peptide to GlyGlu affords a structure with two ligands coordinated through the carboxylates (O10, O11, and O13, O14) with a coordination sphere that is described as a distorted square antiprism due to the coordination angles of the carboxylates (53.27 o and 53.66 o , respectively) ( Table 2, entry 2). [102] Changing the metal to Co II affords a configuration where the Co II ions are positioned at the vertices of the Co-L-GlyGlu ladders ( Table 2, entry 3).…”

Experimental Studies on Isonicotinato Cadmium(II) Complex [Cd(C6H4NO2)2(H2O)4] and Density Functional Calculations

“…In order to form the complex of [Cd(C 6 H 4 NO 2 ) 2 (H 2 O) 4 ], two hydrogen atoms of the water molecule transfer their atomic charges to the oxygen atom; while in the isonicotinic acid ion, two oxygen atoms, four hydrogen atoms and carbon atoms of C(2), C(3) and C(6) transfer their atomic charges to the nitrogen atom and the carbon atoms of C(1), C(4) and C (5). Therefore, in [Cd(C 6 H 4 NO 2 ) 2 (H 2 O) 4 ], each water molecule donors 0.02754e to cadmium(II) ion to form Cd O bond and each isonicotinic acid ion donors 0.06850e to cadmium(II) ion to form the 93.6(4) 89.9787 C(4) N(1) C (5) 116.8 (11) 118.1093 C(4) N(1) Cd (1) 124.0(9) 120.9545 C(5) N(1) Cd (1) 119.0(9) 120.9362 O(1) C(1) O (2) 125.4 (12) 132.1479 O(1) C(1) C (2) 117.2 (12) 113.9259 O(2) C(1) C (2) 117.3 (12) 113.9262 C(6) C(2) C (3) 116.5 (11) 118.2126 C(6) C(2) C(1) 121.7 (11) 120.8942 N(1) C(4) C (3) 123.8 (12) 122.4053 N(1) C(5) C (6) 123.0 (12) 122.4059 bond of Cd N. Cadmium(II) ion (Cd 2+ ), as a d 10 element, only accepts 0.24715e during forming the title complex.…”

“…In recently, there has been an increasing interest in the coordination chemistry of cadmium due to the increased recognition of its role in biological organisms [1,2] as well as in molecular-based materials [3][4][5]. Synthesis of chelated-form antidotes for cadmium(II) ion toxicosis has also attracted more and more attentions [6].…”

“…Among numerous calculated methods, density functional theory (DFT) has long been recognized as a better alternative tool in the study of transition metal 1 New Materials and Function Coordination Chemistry Laboratory, Qingdao University of Science and Technology, Qingdao Shandong 266042, P. R. China. 2 To whom correspondence should be addressed; e-mail: zhaopusu@ 163.com chemical systems than traditional Hartree-Fock (HF) or Møller-Plesset perturbation theory at the second-order (MP2) methods [8,9], because it is computationally less demanding for inclusion of electron correlation, and gives better and more reliable descriptions of the geometries, dipole moment and vibrational frequency. Therefore, after isonicotinato cadmium(II) complex of [Cd(C 6 H 4 NO 2 ) 2 (H 2 O) 4 ] was synthesized by use of hydrothermal method, theoretical studies on the optimized structure, atomic charge distributions, electronic transition, natural population analysis and the thermodynamic properties for this compound were carried out.…”