@entity68375 , a suspected intermediate in @entity855 -dependent carboxylases, has not been isolated nor observed directly by experiment. Consequently, little is known concerning its structure, stability, and ionization state. Recently, @entity68375 as either a monoanion or dianion has been shown computationally to adopt a novel pseudochair conformation featuring an intramolecular charge-assisted @entity3884 bond (CAHB). In this work, additive and subtractive correction schemes to the commonly employed open-closed method are used to estimate the strength of the CAHB. Truhlar's Minnesota M06-2X functional with Dunning's aug-cc-pVTZ basis set has been used for geometry optimization, energy evaluation, and frequency analysis. The CHARMM force field has been used to approximate the Pauli repulsive terms in the closed and open forms of @entity68375 . From our additive correction scheme, differential Pauli repulsion contributions between the pseudochair (closed) and open conformations of @entity68375 are found to be significant in determining the CAHB strength. The additive correction modifies the CAHB prediction (  Eclosed-open) of -14 kcal/mol for the monoanion and -12 kcal/mol for the dianion to -22.9 and -18.4 kcal/mol, respectively. Results from the subtractive technique reinforce those from our additive procedure, where the predicted CAHB strength ranges from -17.8 to -25.4 kcal/mol for the monoanion and from -15.7 to -20.9 kcal/mol for the dianion. Ultimately, we find that the CAHB in @entity68375 meets the criteria for short-strong @entity3884 bonds. However, @entity68375 has a unique energy profile that does not result in the symmetric double-well behavior of low-barrier @entity3884 bonds. These findings provide deeper insight into the pseudochair conformation of @entity68375 , and lead to an improved mechanistic understanding of this intermediate in @entity855 -dependent carboxylases.

Intramolecular Charge-Assisted XXXX Bond Strength in Pseudochair Carboxyphosphate.

@entity68375 :: ('MESH:C015732', 'Chemical') :: ['carboxyphosphate', 'Carboxyphosphate'] @entity3884 :: ('MESH:D006859', 'Chemical') :: ['hydrogen'] @entity855 :: ('MESH:D000255', 'Chemical') :: ['ATP']
@entity3884 :: (MESH:D006859,Chemical) :: ['Hydrogen']
