A number of pseudocontact shifts (PCS) in monolanthanide-substituted Calbindin D 9k (Ca 2 Cb hereafter), a protein of 75 amino acids, were measured for Ce(III), Yb(III), and Dy(III). The assignment of the shifts was obtained through the conventional assignment procedures for the Ce(III) derivative (CaCeCb), since the line broadening is not severe, whereas in the case of Dy(III) and Yb(III) the assignment was obtained by analyzing the temperature dependence of the 1 H-15 N HSQC shifts of the lanthanide derivatives and comparing the results with the 1 H-15 N HSQC spectrum of Ca 2 Cb or CaCeCb. The NOE-based solution structures of Ca 2 Cb or CaCeCb were then refined with PCS. Since the three lanthanides span a wide range of magnetic anisotropies, the refinement was effective in shells from the metal of ∼5-15 Å for Ce(III), ∼9-25 Å for Yb(III), and ∼13-40 Å for Dy(III), as useful PCS were observed in these shells. The root-mean-square deviation of 30 conformers from the average for CaCeCb was 0.74 and 1.10 Å for the backbone and all heavy atoms, respectively, obtained from 1539 NOEs, 39 3 J values, and 6 T 1 values. With 589 pseudocontact shifts for Ce(III) (out of which 280 were larger than 0.1 ppm), 92 PCS for Yb(III), and 74 for Dy(III) the RMSD decreased to 0.54 and 0.95 Å for Ce(III), 0.60 and 0.98 Å for Yb(III), and 0.66 and 1.04 Å for Dy(III) for the backbone and all heavy atoms, respectively. While for Ce(III) resolution improvements are mainly found for the metal binding site itself, Yb(III) and Dy(III) can further constrain regions far away from the metal. These results show that constructing a lanthanide binding site may be a general and convenient tool to "enlighten" shells at variable distances from the metal itself, and may be used for various purposes including the investigation of biomolecular complexes.

The full series of lanthanide ions (except the radioactive promethium and the S-state gadolinium) has been incorporated into the C-terminal calcium binding site of the dicalcium protein calbindin D(9k). A fairly constant coordination environment is maintained throughout the series. At variance with several lanthanide complexes with small chelating ligands investigated in the past, the large protein moiety provides a large number of NMR signals whose hyperfine shifts can be exclusively ascribed to pseudocontact shifts (PCS). The chemical shifts of 1H and 15N backbone and side chain amide NH groups were accurately measured through HSQC experiments. 1097 PCS were estimated from these by subtracting the diamagnetic contributions measured on HSQC spectra of either the 4f(0) lanthanum(III) or the 4f(14) lutetium(III) derivatives and used to define a quality factor for the structure. The differences in diamagnetic chemical shifts between the two diamagnetic blanks were relatively small, although some were not negligible especially for the nuclei closest to the metal center. These differences were used as a tolerance for the PCS. The magnetic susceptibility tensor anisotropies for each paramagnetic lanthanide ion were obtained as the result of the solution structure determination performed by using the NOEs of the cerium(III) derivative and the PCS of all lanthanides simultaneously. This set of reliable magnetic data permits an experimental assessment of Bleaney's theory relative to the magnetic properties for an extended series of lanthanide complexes in solution. All of the obtained tensors show some rhombicity, as could be expected from the lack of symmetry of the protein environment. The directions of the largest magnetic susceptibility component for Ce, Pr, Nd, Sm, Tb, Dy, and Ho and of the smallest magnetic susceptibility component for Eu, Er, Tm, and Yb were found to be all within 15 degrees from their average (within 20 degrees for Sm), confirming the essential similarity of the coordination environment for all lanthanides. Bleaney's theory is in excellent qualitative agreement with the observed pattern of axial anisotropies. Its quantitative agreement is substantially better than that suggested by previous analyses performed on more limited sets of PCS data for small lanthanide complexes, the so-called crystal field parameter varying only within +/-30% from one lanthanide to another. These variations are even smaller (+/-15%) if a reasonable T(-3) correction is taken into consideration. A knowledge of magnetic susceptibility anisotropy properties of lanthanides is essential in determining the self-orienting properties of lanthanide complexes in solution when immersed in magnetic fields.

The open "molecular box" [(en)Pt(UH-N(1),N(3))](4)(NO(3))(4) (with en = 1,2-diaminoethane, UH = uracil monoanion) resembles calix[4]arenes in its structure and solution dynamics. It adopts a 1,3-alternate conformation in the solid-state (1a), but in solution and after deprotonation to [(en)Pt(U-N(1),N(3))](4), a second major species (cone conformer (1b-4H(+))) occurs. 1b-4H(+) acts as an efficient ligand for additional metal ions through the oxo-surface formed by the four O(2) exocyclic atoms of the uracil nucleobases. As shown here, 1b-4H(+) can incorporate a single metal ion only, giving rise to the formation of species of type {[(en)PtU](4)M}(X)(n)() with M = Zn(II) (2a), Be(II) (3) (not isolated in the solid state), and La(III) (4); X = NO(3), SO(4)/2; n = 2, 3. In addition, both the protonated species of the cone conformer (1b, pH 2-4) and compounds 2a (at pH 3-8) and 3 (at pH 3-5) act as hosts for organic anions in water, as deduced from (1)H NMR studies. It is proposed that the cone conformers act as anion hosts due to a combination of positive charge as well as apolarity and size of the cavity. Host-guest complexes of type {[(en)PtU](4)Zn}(X)(NO(3),SO(4)/2) with X = p-toluenesulfonate (2b) and 3-(trismethylsilyl)-1-propanesulfonate (2c) included in the cone cavity have been prepared and association constants have been determined by (1)H NMR spectroscopy. The fact that 4 does not act as a host may be due to a possible tetradentate coordination of La to 1b-4H(+) which may result in a flatter cone cavity than in compounds 2 and 3.

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Reactions of [Pt(1-MeC-N3)3Cl]NO3 (1-MeC-N3 = 1-methylcytosine, bound to Pt via N3) and the respective aqua species [Pt(1-MeC-N3)3(H2O)]2+ with the model nucleobases 9-ethylguanine (9-EtGH), 9-methyladenine (9-MeA), single-stranded 5'd(T3GT3), and double-stranded [5'd(GA-GA2GCT2CTC)]2 have been studied in solution by means of 1H NMR spectroscopy, HPLC, and electrospray ionization mass spectrometry. Reactions are generally slow, in particular with the chloro species, and guanine is the only reactive base in the oligonucleotides. However, unlike (dien)PtII, which binds randomly to the guanines in the ds dodecamer, (1-MeC-N3)3PtII binds selectively to the terminal guanine only, probably because base fraying takes place at the duplex ends. The X-ray crystal structures of [Pt(1-MeC-N3)3(9-EtG-N7)]ClO4.8H2O (1b) and of [Pt(1-MeC-N3)3(9-MeA-N7)](ClO4)2.0.5H2O as well as NMR spectroscopic studies of [Pt(1-MeC-N3)3(9-EtGH-N7)] (NO3)2.H2O (1a) are reported. The tetrakis(nucleobase) complexes adopt a head-tail-head orientation of the three 1-MeC bases and an orientation of the fourth base (purine) that permits a maximum of intracomplex H bonds between exocyclic groups. As far as the guanine adduct (1a, 1b) is concerned, relative orientations of the four bases are identical in the model and in the oligonucleotide adduct.