Acid–base and metal ion-binding properties of diaminopropyl D-glucopyranoside and diaminopropyl D-mannopyranoside compounds in aqueous solution

Abstract

For three sugar-appended diamine compounds (1,3-diamino-2-propyl β--glucopyranoside (2-β--Glc-pn), (2S)-2,3-diaminopropyl β--glucopyranoside (1-β--Glc-pn) and 1,3-diamino-2-propyl α--mannopyranoside (2-α--Man-pn)), acidity constants and stability constants with Ni 2ϩ , Cu 2ϩ and Zn 2ϩ have been measured (I = 0.16 M NaCl, 25 ЊC). The two acidity constants of each of the three sugar-diamines differ by 10 1.65 to 10 3.09 , indicating that removal of the proton from HL ϩ species is more difficult than deprotonation from the fully protonated dication H 2 L 2ϩ . Statistical and polar effects, as well as the formation of an intramolecular hydrogen bond, may cause this increased stability of the HL ϩ species. The strength of the hydrogen bond and the degree of its formation (percentage) were estimated. The sugar ring has only a small influence on the intramolecular hydrogen bond formation. For the different metal ion-ligand systems, the predominating species in solution are quite different. In the Cu 2ϩ -1-β--Glc-pn system, the dominant species are always CuL 2ϩ and CuL 2 2ϩ in the pH range 4 to 10, where the total ligand concentration is larger than total metal ion concentration. For Ni 2ϩ , NiL 3 2ϩ is also important under these same conditions; however, for Zn 2ϩ , the hydrolysis species ZnL 2 (OH) ϩ and ZnL 2 (OH) 2 predominate in the high pH region. All possible species in the system were included during the calculations, and the corresponding stability constants were determined. The hydrolysis of the metal ions themselves is important in some cases and all possible hydrolysis species were included in the fitting calculation. The stability constant plots log K versus pK yielded straight reference lines for 1,3-diamine or 1,2-diamine ligands, reflecting the complete absence of sugar oxygen atoms in the metal ion coordination. The linkage between the metal ion and the diamine residue depends solely on the basicity of the ligand.

Synthesis and Solution Studies of the Complexes of Trivalent Lanthanides with the Tetraazamacrocycle TETA-(PO)2

“…The difference (Δp K a ) between the average of the two higher p K a values and the average of the two lower ones is 3.68 for TETA-(PO) 2 ((Δp K a = 7.76 + 8.45)/2 − (4.08 + 4.78)/2 = 3.68), 2.71 for XT (Δp K a = 9.27−6.56 = 2.71), whereas the corresponding value is 6.78 for TETA (Δp K a = (10.10 +10.82)/2 − (3.21 + 4.15)/2 = 6.78). It is known that this Δp K a value reflects the strength of the intramolecular hydrogen bond among the nitrogen atoms; , hence, the result again implies that the phosphinate groups have a large effect on intramolecular hydrogen bond formation. If one supposes that a phosphinate oxygen and a nitrogen form an intramolecular hydrogen bond, this would make the first two deprotonation steps from the nitrogen atom more difficult; i.e., higher p K a values would be expected.…”

“…The ligand to metal ion ratios used in these experiments were slightly greater than 1:1. The calculations were carried out by a previously described curve-fitting procedure . The final results are the average of at least four independent titrations for each metal ion.…”

Effects of Sequential Replacement of −NH2 by −OH in the Tripodal Tetraamine Tren on Its Acidity and Metal Ion Coordinating Properties

“…In this hydrogen bond, the donor is −NH 3 + and the acceptor is R 3 N, making the R 3 N group more acidic because the product of the deprotonation is more stable. On the other hand, in arms with only a terminal OH group, the central ammonium only experiences the polar effect, which also makes the R 3 N group more acidic; however, the OH group can also form an intramolecular hydrogen bond with R 3 NH + in which R 3 NH + is the donor and OH is the acceptor . (The fact that signal D had a larger chemical shift change in the range 3.5 ≤ pD ≤ 7.3 (0.31, Table ) than in the range 7.3 ≤ pD ≤ 13.85 (0.05, Table ) supports this suggestion.)…”

“…The titrations for determining the acidity constants of NNO 2 222 or NN 2 O222 were carried out by adding standardized NaOH solution (0.11 M) to 2.6 mM HCl (50 mL) and NaCl ( I = 0.16 M, 25 °C) in the presence of 0.4−0.6 mM H 2 (NNO 2 222) 2+ or H 3 (NN 2 O222) 3+ under N 2 . The constants were calculated using an IBM-compatible computer with a Pentium II processor by a curve-fit procedure using a Newton−Gauss nonlinear least-squares program similar to that used in other studies . For NNO 2 222, the calculation pH range was 3.3 ≤ pH ≤ 10.6, corresponding to about 2% neutralization for the equilibrium between H 2 (NNO 2 222) 2+ and H(NNO 2 222) + , and about 96% neutralization for the equilibrium between H(NNO 2 222) + and NNO 2 222.…”

Quinoline‐Based, Glucose‐Pendant Fluorescent Zinc Probes

“…The detailed analysis of pH-induced UV/VIS-spectral changes using SPECFIT software [38] (Figs. S1 -S4 1 )) revealed the protonation constants of N,N'-6-MeOBQB-GEN and the stability constant of associated Zn complex [39]. The successive protonation constants of N,N'-6-MeOBQBGEN (L), defined as the corresponding acid dissociation constants…”