Physicochemical characterization of the dimeric lanthanide complexes [en{Ln(DO3A)(H2O)}2] and [pi{Ln(DTTA)(H2O)}2]2-: a variable-temperature 17O NMR study

The Gd(III) complexes of the two dimeric ligands [en(DO3A)2] {N,N'-bis[1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecan-10-yl-methylcarbonyl]-N,N'-ethylenediamine} and [pi(DTTA)2]8- [bisdiethylenetriaminepentaacetic acid (trans-1,2-cyclohexanediamine)] were synthesized and characterized. The 17O NMR chemical shift of H2O induced by [en{Dy(DO3A)}2] and [pi{Dy(DTTA)}2]2- at pH 6.80 proved the presence of 2.1 and 2.2 inner-sphere water molecules, respectively. Water proton spin-lattice relaxation rates for [en{Gd(DO3A)(H2O)}2] and [pi{Gd(DTTA)(H2O)}2]2- at 37.0 +/- 0.1 degrees C and 20 MHz are 3.60 +/- 0.05 and 5.25 +/- 0.05 mM(-1) s(-1) per Gd, respectively. The EPR transverse electronic relaxation rate and 17O NMR transverse relaxation time for the exchange lifetime of the coordinated H2O molecule and the 2H NMR longitudinal relaxation rate of the deuterated diamagnetic lanthanum complex for the rotational correlation time were thoroughly investigated, and the results were compared with those reported previously for other lanthanide(III) complexes. The exchange lifetimes for [en{Gd(DO3A)(H2O)}2] (769 +/- 10 ns) and [pi{Gd(DTTA)(H2O)}2]2- (910 +/- 10 ns) are significantly higher than those of [Gd(DOTA)(H2O)]- (243 ns) and [Gd(DTPA)(H2O)]2- (303 ns) complexes. The rotational correlation times for [en{Gd(DO3A)(H2O)}2] (150 +/- 11 ps) and [pi{Gd(DTTA)(H2O)}2]2- (130 +/- 12 ps) are slightly greater than those of [Gd(DOTA)(H2O)]- (77 ps) and [Gd(DTPA)(H2O)]2- (58 ps) complexes. The marked increase in relaxivity (r1) of [en{Gd(DO3A)(H2O)}2] and [pi{Gd(DTTA)(H2O)}2]2- result mainly from their longer rotational correlation time and higher molecular weight.     

Magnetic Resonance of Paramagnetic Complexes

The line width of the ESR and NMR signals of paramagnetic transition metal complexes is determined mainly by the electron spin-lattice relaxation time τ_e. Values of τ_e greater than 10^?9 lead to ESR spectra that are readily resolved, while values smaller than 10^?11 give NMR spectra having small line widths. Since fast relaxation processes are effective in nearly all transition metal complexes with several unpaired electrons and in all complexes having an orbitally degenerate ground state, the NMR method has a wider scope. The sign and magnitude of the electron-nucleus coupling can be determined with great sensitivity from the NMR spectra, whereas only the magnitude of this interaction can be determined from the ESR spectra. Free spin densities can be found very accurately from the NMR shifts, and the method can therefore be advantageously applied to kinetic measurements, e.g. on short-lived contact complexes.     

NMR spectra of paramagnetic complexes of 1-vinylimidazole with iron group metals

The high-resolution ¹H and ¹³C NMR spectra of 1-vinylimidazole complexes with iron group metals were recorded. The contact coupling in these systems was established in the ¹H and ¹³C NMR spectra. The applicability of the NMR spectra transformed by long-range hyperfine coupling for elucidating the molecular structure of the ligand was shown. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1430–1433, June, 2005.     

Ln（Ⅲ）—Co（Ⅱ）与以水杨醛缩乙二胺Schiff碱异核配合物的合成与波谱性质

合成了双水杨醛缩乙二胺Ｓｃｈｉｆｆ碱（ＳＡＬＥＮ）与钴的配合物Ｃｏ（ＳＡＬＥＮ）（ＮＯ３）２．３Ｈ２Ｏ及镧系－钴的异核配合物ＬｎＣｏ（ＳＡＬＥＮ）２（ＮＯ３）５．２Ｈ２Ｏ（Ｌｎ＝Ｌａ,Ｎｄ,Ｓｍ,Ｇｄ,Ｙｂ,Ｙ）以紫外红外光谱,特别是ＨＮＭＲ是ＥＰＲ波谱等方法研究了它们在组成、结构和配位等方面的异同,中讨论了配合物ＥＰＲ谱在不同溶剂中峰宽的相对关系,配合物在晶体场强度及Ｇｄ＾３＋周围局部对称性等     

Ln(Ⅲ)-Co(Ⅱ)与双水杨醛缩乙二胺Schiff碱异核配合物的合成与波谱性质

合成了双水杨醛缩乙二胺Ｓｃｈｉｆ碱（ＳＡＬＥＮ）与钴的配合物Ｃｏ（ＳＡＬＥＮ）（ＮＯ３）２·３Ｈ２Ｏ及镧系－钴的异核配合物ＬｎＣｏ（ＳＡＬＥＮ）２（ＮＯ３）５·２Ｈ２Ｏ（Ｌｎ＝Ｌａ，Ｎｄ，Ｓｍ，Ｇｄ，Ｙｂ，Ｙ）．以紫外、红外光谱，特别是１ＨＮＭＲ及ＥＰＲ波谱等方法研究了它们在组成、结构和配位等方面的异同．文中讨论了配合物ＥＰＲ谱在不同溶剂中峰宽的相对关系、配合物晶体场强度及Ｇｄ３＋周围局部对称性等问题．     

Peroxidatic activity of metalloporphyrin binding to serum albumin: Enhancement effect of serum albumin on metalloporphyrin catalyzed luminol chemiluminescence reaction

The metalloporphyrin (M-P) catalyzed luminol-H₂O₂ chemiluminescence (CL) system can be significantly enhanced in the presence of serum albumins. The enhancement may be explained in terms of the formation of a molecular complex between M-P and serum albumin. The hydrophobic and coordination interactions between M-P and serum albumin were confirmed by comparing the degree of enhancement by the protein on different types of M-P catalyzed CL reactions and by comparing the catalytic activity of M-P/bovine serum albumin (BSA) and M-P/BSA/anti-BSA complexes. Only the non-ionic M-P catalyzed CL reaction was significantly enhanced, and the enhanced CL reaction was inhibited by an immunoreaction. The optimum conditions of the M-P/albumin complex catalyzed CL reaction were evaluated by using a flow-injection system, which was very similar to that using hemoglobin as the catalyst. A brief prospective on the general applicability of the enhanced CL reaction for the determination of serum albumin (2.5–500 μg/ml) is given.     

19F Paramagnetic Relaxation Enhancement: A Valuable Tool for Distance Measurements in Proteins

Fluorine NMR paramagnetic relaxation enhancement was evaluated as a versatile approach for extracting distance information in selectively F‐labeled proteins. Proof of concept and initial applications are presented for the HIV‐inactivating lectin cyanovirin‐N. Single F atoms were introduced at the 4‐, 5‐, 6‐ or 7 positions of Trp49 and the 4‐position of Phe4, Phe54, and Phe80. The paramagnetic nitroxide spin label was attached to Cys residues that were placed into the protein at positions 50 or 52. ¹⁹F‐T₂ NMR spectra with different relaxation delays were recorded and the transverse ¹⁹F‐PRE rate, ¹⁹F‐Γ₂, was used to determine the average distance between the F nucleus and the paramagnetic center. Our data show that experimental ¹⁹F PRE‐based distances correspond to 0.93 of the ¹H_N‐PRE distances, in perfect agreement with the gyromagnetic γ¹⁹F/γ¹H ratio, thereby demonstrating that ¹⁹F PREs are excellent alternative parameters for quantitative distance measurements in selectively F‐labeled proteins.     

Unraveling Complex Small‐Molecule Binding Mechanisms by Using Simple NMR Spectroscopy

Heteronuclear NMR spectroscopy provides a unique way to obtain site‐specific information about protein–ligand interactions. Usually, such studies rely on the availability of isotopically labeled proteins, thereby allowing both editing of the spectra and ligand signals to be filtered out. Herein, we report that the use of the methyl SOFAST correlation experiment enables the determination of site‐specific equilibrium binding constants by using unlabeled proteins. By using the binding of L ‐ and D ‐tryptophan to serum albumin as a test case, we determined very accurate dissociation constants for both the high‐ and low‐affinity sites present at the protein surface. The values of site‐specific dissociation constants were closer to those obtained by isothermal titration calorimetry than those obtained from ligand‐observed methods, such as saturation transfer difference. The possibility of measuring ligand binding to serum albumin at physiological concentrations with unlabeled proteins may open up new perspectives in the field of drug discovery.     

稀土与脂肪族Schiff碱多核配合物的合成及波谱

在形成多核配合物的诸条件中,认为减小空间位阻颇为重要,设计的直链脂肪族的四甘醇醛与甘氨酸缩合形成的Schiff碱(TAGL)为此提供了有利的条件,且成功地获得了它与稀土离子反应形成的三核配合物(Ln:L=3:1):[Ln~3(TAGL)(NO~3)~7]CH~3OH·nH~2O(Ln=La,Nd,Sm,n=1;Ln=Gd,Dy,Yb,Y,n=2)。以元素分析,IR,NMR等确证其组成,根据EPR谱探讨了Gd(III)配合物的晶体场强,同时见到该类脂肪族Schiff碱及其配合物中δ~H~C~=~N的质子谱向高场明显位移至～5.10。