Stability constants: comparative study of fitting methods. Determination of second‐order complexation constants by<sup>23</sup>Na and<sup>7</sup>Li NMR chemical shift titration

Masiker, Marilyn C.; Mayne, Charles L.; Eyring, Edward M.

doi:10.1002/mrc.1787

“…It is common practice in the literature to report log K values for stability constants. As we pointed out in a previous study, [16] since log is not a linear function, symmetrical error bars on log K imply unsymmetrical errors in the value of K. Since we have reported values for K from other studies, we follow our previous method of reporting K as the antilog of these log K values and including the unsymmetrical error for these cases. K values from this study were reported directly along with their errors from the regression.…”

Section: Discussionmentioning

confidence: 91%

“…The notation used here follows closely that of Ref. [16]. It is common practice in the literature to report log K values for stability constants.…”

Section: Discussionmentioning

confidence: 98%

“…[16] to the observed chemical shift data for all of the solvent and anion combinations mentioned above to yield estimates of the stability constants K 1 and K 2 as well as the relative shifts for the 1 : 1 and 1 : 2 complexes for these systems. Parameter values and errors are given in Table 1.…”

Section: Discussionmentioning

confidence: 99%

“…A nonlinear regression, as described previously, [16] was performed, fitting Eqn (14) of Ref. [16] to the observed chemical shift data for all of the solvent and anion combinations mentioned above to yield estimates of the stability constants K 1 and K 2 as well as the relative shifts for the 1 : 1 and 1 : 2 complexes for these systems.…”

Section: Discussionmentioning

confidence: 99%

“…Because the 7 Li chemical shift is extremely sensitive to temperature, extreme care was taken to stabilize the sample temperature during the experiment as described previously. [16] A series of samples was prepared with the amount of lithium cation, M 0 , constant at 0.02 M. The initial amount of ligand, L 0 , was varied to produce ligand/metal ratios, as shown in Figs 1 and 2, of approximately 0.2-8, and the 7 Li chemical shifts measured.…”

Section: Methodsmentioning

confidence: 99%

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⁷Li NMR chemical shift titration and theoretical DFT calculation studies: solvent and anion effects on second‐order complexation of 12‐crown‐4 and 1‐aza‐12‐crown‐4 with Lithium cation in several aprotic solvents

Masiker

¹

,

Mayne

²

,

Boone

³

et al. 2009

Magnetic Reson in Chemistry

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(7)Li NMR titration was used to determine stepwise complexation constants for the second-order complexation of lithium cation with 12-crown-4 in acetonitrile, propylene carbonate and a binary mixture of propylene carbonate and dimethyl carbonate. The anions used were perchlorate, hexaflurophosphate and trifluromethanesulfonate. A second ligand 1-aza-12-crown-4 was similarly investigated. The exchange between the free and complexed cation in these reactions is fast on an NMR timescale resulting in a single lithium peak which is a concentration-weighted average of the free and bound species. Solvent effects show that the 1:1 complex is much more stable in acetonitrile than in propylene carbonate or in the propylene carbonate dimethyl carbonate mixture. Anion effects for a given solvent were small. Optimized geometries of the free ligands and the 1:1 and 1:2 (sandwich) metal-ligand complexes were predicted by hybrid-density functional theory using the Gaussian 03 software package. Results were compared to literature values for 1:1 stability constants found by microcalorimetry for several of these systems and are found to be in good agreement. Although microcalorimetry only considered the formation of 1:1 complexes, (7)Li NMR shows evidence that both 1:1 and 1:2 complexes should be considered.

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Protein Crystallography through Supramolecular Interactions between a Lanthanide Complex and Arginine

Pompidor

¹

,

D’Aléo

²

,

Vicat

³

et al. 2008

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The determination of the complete sequence of the human genome triggered the emergence of structural proteomics, a challenging field of research devoted to the determination of the structure of proteins at atomic resolution to understand their structure-function relationships. Among the various techniques for structure determination, [1] X-ray crystallography plays an essential role. Its bottleneck is the serendipitous and time-consuming preparation of well-diffracting crystals. Once such crystals are obtained, de novo structure determination requires the preparation of at least one heavy-atom derivative. Nowadays, methods based on anomalous diffraction are routinely used.[2] Lanthanide ions are thus very convenient for this purpose because of their large anomalous signal with either synchrotron or Cu Ka radiation. Lanthanide derivative crystals of the protein may be prepared by: 1) replacing Ca 2+ by Ln 3+ ions in calcium-binding proteins, [3] 2) covalent grafting of dysprosium complexes [4] or a terbium binding tag, [5] or 3) cocrystallization with macrocyclic gadolinium, ytterbium, or lutetium complexes.[6] The last method is very easy to carry out, but the interactions between the lanthanide complexes and the protein are difficult to predict. To shed light on this problem, we recently developed a research program devoted to the study of the solid-state and solution interactions between lanthanide complexes and biological macromolecules.Herein we describe the properties of tris(dipicolinate)-lanthanide complexes [Ln(dpa) 3 ] 3À (dpa = dipicolinate = pyridine-2,6-dicarboxylate), [7] which could be highly interesting for macromolecular crystallography, since 1) successful derivatization can easily be detected through the intrinsic luminescence of the europium and terbium complexes, 2) the new crystal form of derivatives with hen egg-white lysozyme (HEWL) evidenced strong interactions between the tris(dipicolinate)lanthanide complexes and the protein; these interactions were shown to involve guanidinium moieties of arginine residues, and 3) the occurrence of these supramolecular interactions ocurred both in aqueous solution as well as in the solid state, with the ethylguanidinium cation (EtGua + ) mimicking the behavior of accessible arginine groups of proteins.Cocrystallized derivative crystals of HEWL were obtained by the hanging-drop method. Mixing HEWL and A 3 [Ln(dpa) 3 ] (Figure 1 a, Ln = Eu, Tb; A = Li, Na, Cs, NH 4 ) led to a precipitate from which crystals grew within a few days. The shape of the resulting crystals (Figure 1 b) was very different from that of native tetragonal crystals obtained under similar conditions.[8] Irradiation with UV light (l ex =

show abstract

Protein Crystallography through Supramolecular Interactions between a Lanthanide Complex and Arginine

Pompidor

¹

,

D’Aléo

²

,

Vicat

³

et al. 2008

View full text Add to dashboard Cite

The determination of the complete sequence of the human genome triggered the emergence of structural proteomics, a challenging field of research devoted to the determination of the structure of proteins at atomic resolution to understand their structure-function relationships. Among the various techniques for structure determination, [1] X-ray crystallography plays an essential role. Its bottleneck is the serendipitous and time-consuming preparation of well-diffracting crystals. Once such crystals are obtained, de novo structure determination requires the preparation of at least one heavy-atom derivative. Nowadays, methods based on anomalous diffraction are routinely used.[2] Lanthanide ions are thus very convenient for this purpose because of their large anomalous signal with either synchrotron or Cu Ka radiation. Lanthanide derivative crystals of the protein may be prepared by: 1) replacing Ca 2+ by Ln 3+ ions in calcium-binding proteins, [3] 2) covalent grafting of dysprosium complexes [4] or a terbium binding tag, [5] or 3) cocrystallization with macrocyclic gadolinium, ytterbium, or lutetium complexes.[6] The last method is very easy to carry out, but the interactions between the lanthanide complexes and the protein are difficult to predict. To shed light on this problem, we recently developed a research program devoted to the study of the solid-state and solution interactions between lanthanide complexes and biological macromolecules.Herein we describe the properties of tris(dipicolinate)-lanthanide complexes [Ln(dpa) 3 ] 3À (dpa = dipicolinate = pyridine-2,6-dicarboxylate), [7] which could be highly interesting for macromolecular crystallography, since 1) successful derivatization can easily be detected through the intrinsic luminescence of the europium and terbium complexes, 2) the new crystal form of derivatives with hen egg-white lysozyme (HEWL) evidenced strong interactions between the tris(dipicolinate)lanthanide complexes and the protein; these interactions were shown to involve guanidinium moieties of arginine residues, and 3) the occurrence of these supramolecular interactions ocurred both in aqueous solution as well as in the solid state, with the ethylguanidinium cation (EtGua + ) mimicking the behavior of accessible arginine groups of proteins.Cocrystallized derivative crystals of HEWL were obtained by the hanging-drop method. Mixing HEWL and A 3 [Ln(dpa) 3 ] (Figure 1 a, Ln = Eu, Tb; A = Li, Na, Cs, NH 4 ) led to a precipitate from which crystals grew within a few days. The shape of the resulting crystals (Figure 1 b) was very different from that of native tetragonal crystals obtained under similar conditions.[8] Irradiation with UV light (l ex =

show abstract

Stability constants: comparative study of fitting methods. Determination of second‐order complexation constants by²³Na and⁷Li NMR chemical shift titration

Cited by 13 publications

References 30 publications

⁷Li NMR chemical shift titration and theoretical DFT calculation studies: solvent and anion effects on second‐order complexation of 12‐crown‐4 and 1‐aza‐12‐crown‐4 with Lithium cation in several aprotic solvents

⁷Li NMR chemical shift titration and theoretical DFT calculation studies: solvent and anion effects on second‐order complexation of 12‐crown‐4 and 1‐aza‐12‐crown‐4 with Lithium cation in several aprotic solvents

Protein Crystallography through Supramolecular Interactions between a Lanthanide Complex and Arginine

Protein Crystallography through Supramolecular Interactions between a Lanthanide Complex and Arginine

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Stability constants: comparative study of fitting methods. Determination of second‐order complexation constants by23Na and7Li NMR chemical shift titration

Cited by 13 publications

References 30 publications

7Li NMR chemical shift titration and theoretical DFT calculation studies: solvent and anion effects on second‐order complexation of 12‐crown‐4 and 1‐aza‐12‐crown‐4 with Lithium cation in several aprotic solvents

7Li NMR chemical shift titration and theoretical DFT calculation studies: solvent and anion effects on second‐order complexation of 12‐crown‐4 and 1‐aza‐12‐crown‐4 with Lithium cation in several aprotic solvents

Protein Crystallography through Supramolecular Interactions between a Lanthanide Complex and Arginine

Protein Crystallography through Supramolecular Interactions between a Lanthanide Complex and Arginine

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Product

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Stability constants: comparative study of fitting methods. Determination of second‐order complexation constants by²³Na and⁷Li NMR chemical shift titration

⁷Li NMR chemical shift titration and theoretical DFT calculation studies: solvent and anion effects on second‐order complexation of 12‐crown‐4 and 1‐aza‐12‐crown‐4 with Lithium cation in several aprotic solvents

⁷Li NMR chemical shift titration and theoretical DFT calculation studies: solvent and anion effects on second‐order complexation of 12‐crown‐4 and 1‐aza‐12‐crown‐4 with Lithium cation in several aprotic solvents