Biomimetic and Nonbiological Dinuclear M ^{x +} Complex‐Catalyzed Alcoholysis Reactions of Phosphoryl Transfer Reactions

Cleavage of an RNA Model Catalyzed by Dinuclear Zn(II) Complexes Containing Rate-Accelerating Pendants. Comparison of the Catalytic Benefits of H-Bonding and Hydrophobic Substituents

“…The plots of k obs versus [catalyst] for the cleavage of 2 catalyzed by 3:Zn(II) 2 -6:Zn(II) 2 and 9:Zn(II) 2 are s s pHdependent, with all catalyst complexes showing both linear behavior (Figure 1A) and saturation binding (Figure 1B), indicative of a change in the strength of binding between the catalyst complex and the substrate as a function of s s pH. In all cases, a significant x-intercept was observed, similar to the behavior of most other dinuclear Zn(II) complexes in methanol we have reported, [5][6][7]11 and analyzed as being consistent with dissociation of a Zn(II) ion from the complex at low concentration that leads to an inactive or severely less active mononuclear form. Complex 8:Zn(II) 2 exhibited linear kinetics over the s s pH range studied.…”

“…Recent work from this laboratory has focused on the cleavage of simple RNA and DNA models catalyzed by dinuclear Zn(II) complexes in the light alcohols methanol and ethanol. 5 We have demonstrated that the cleavage of phosphate diesters as RNA and DNA models is accelerated by 10 [11][12][13][14][15][16][17] relative to the background reactions in the presence of the a system comprising an alcohol medium and the dinuclear complex 1:Zn(II) 2 . [6][7][8] This system far outperforms any reported synthetic nuclease models that operate in water and leads us to conclude that the large rate enhancements observed upon moving from aqueous solution 9 into alcohols of lower dielectric constant and polarity stem from an important medium effect that has, until recently, been underappreciated.…”

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The transesterification of a simple RNA model, 2-hydroxypropyl p-nitrophenyl phosphate (2, HpNPP) promoted by seven dinuclear Zn(II) catalysts (3,4,5,6,7,8,9:Zn(II) 2 :(-OCH 3 )) based on the bis[bis(2-substituted-pyridinyl-6-methyl)]amine ligand system was investigated in methanol under s s pHcontrolled conditions at 25.0 ( 0.1 °C. The two metal complexing ligands were joined together via the amino N connected to a m-xylyl linker (3,4,5,6,7) where the 2-pyridinyl substituent = H, CH 3 , (CH) 4 , NH 2 , and NH(CdO)CH 3 , respectively, and a propyl linker (8, 9) where the ring substituent = H and CH 3 .

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The transesterification of a simple RNA model, 2-hydroxypropyl p-nitrophenyl phosphate (2, HpNPP) promoted by seven dinuclear Zn(II) catalysts (3,4,5,6,7,8,9:Zn(II) 2 :(-OCH 3 )) based on the bis[bis(2-substituted-pyridinyl-6-methyl)]amine ligand system was investigated in methanol under s s pHcontrolled conditions at 25.0 ( 0.1 °C. The two metal complexing ligands were joined together via the amino N connected to a m-xylyl linker (3,4,5,6,7) where the 2-pyridinyl substituent = H, CH 3 , (CH) 4 , NH 2 , and NH(CdO)CH 3 , respectively, and a propyl linker (8, 9) where the ring substituent = H and CH 3 . All of the dinuclear complexes except 8:Zn(II) 2 exhibit saturation kinetics for the k obs versus [catalyst] plots from which one can determine catalyst:substrate binding constants (K M ), the catalytic rate constants for their decomposition (k cat ), and the second order catalytic rate constants (k 2 cat = k cat /K M ).

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