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The bonding features in metal-carbonyls including neutral MCO (M = Ni, Pd, Pt) and MCO⁺ (M⁺ = Cu⁺, Ag⁺, Au⁺) complexes have been elucidated at the DFT level with relativistic compact effective potentials for transition metals and 6-311+G(d) basis sets for C and O by the block-localized wavefunction (BLW) method. The BLW method can decompose the intermolecular interactions in terms of Heitler–London, polarization, and charge transfer energy contributions. Since the metal–CO bonding involves two synergic interactions, namely the σ-dative bond from the carbon lone electron pair to an empty d_σ orbital on the metal, and the π back-donation from filled d_π orbitals to the empty 2π* orbital on CO, the present BLW-ED analyses quantitatively demonstrated that in neutral MCO complexes the π-bonding dominates over the σ-bonding, whereas in cationic MCO⁺ complexes, the σ-bonding plays a major role. But in both neutral and cationic species, the CO polarization induced by the metals enhances the C–O bond and increases the C–O vibrational frequencies, while the π back-donation tends to weaken the C–O bond and decrease the C–O vibrational frequencies. For neutral complexes, the latter is more prominent than the former, and consequently, there is a red-shifting of the C–O vibrational frequencies. In contrast, the π back-donation is insignificant in MCO⁺ cations, and the C–O eventually vibrates at higher frequencies than the free CO frequency.

Protein Lin28 recognizes pre-let-7 microRNAs (miRNAs) through direct interactions between its zinc-knuckle type zinc-finger (ZnF) domains and the terminal loop of pre-let-7, resulting in the inhibition of the synthesis of mature let-7 miRNAs. Despite the physiological importance, the involved conformational changes and energetic factors contributing to the binding affinity and specificity remain unclear. We conducted molecular dynamics (MD) simulations in conjunction with molecular mechanics/generalized born surface area (MM/GBSA) and energy decomposition calculations to investigate the RNA binding-induced conformational changes of the ZnFs and the residual level energetic factors that influence the binding affinity and specificity. We showed that the binding of the RNA results in the inter-domain conformational changes of the two ZnF domains, including changes of the spatial relationships of several nucleobase-binding amino acids. We also observed mutation-induced weakening of the affinity of the Lin28–pre-let-7 binding, which reveals the importance of the stacking interactions between the side-chains of Tyr140, His148, His162 and the bases of nucleic acid G2 and G5 in the specific recognition of pre-let-7 by the ZnFs of Lin28.