Metal-Ion- and Hydrogen-Bond-Mediated Interstellar Prebiotic Chemistry: The First Step in the Formose Reaction

The formose reaction, which offers a feasible chemical pathway for the prebiotic synthesis of sugars, is a well-studied reaction for over two hundred and 50 years. Yet huge knowledge gaps exist even in the very first step of the formose reaction. In this work, we provide a new and otherwise unintuitive reaction pathway for the gas-phase conversion of formaldehyde to glycolaldehyde (the first step in the formose reaction) occurring in the interstellar medium (ISM). Employing electronic structure calculations (CCSD­(T) and DFT methods), we exhaustively probe the role of various metal ions and small molecules detected in the ISM to propose a new mechanism wherein metal–oxygen interactions and hydrogen bonds cooperatively facilitate an otherwise implausible chemical reaction. The reactions involving Mg²⁺ are throughout found to be barrierless, and those featuring Al⁺ ions are noted to only have a small barrier. The proton affinities of the small molecules, metal–oxygen interactions, and the extent of C–C-bond formation are found to be the significant factors that influence the barrier heights. The mechanism is also shown to be consistent with well-known experimental details in the terrestrial formose reaction (which could, however, proceed through a different mechanism). Future experimental and theoretical scope arising out of this paper are subsequently discussed

Accurate and Computationally Efficient Prediction of Thermochemical Properties of Biomolecules Using the Generalized Connectivity-Based Hierarchy

In this study we have used the connectivity-based hierarchy (CBH) method to derive accurate heats of formation of a range of biomolecules, 18 amino acids and 10 barbituric acid/uracil derivatives. The hierarchy is based on the connectivity of the different atoms in a large molecule. It results in error-cancellation reaction schemes that are automated, general, and can be readily used for a broad range of organic molecules and biomolecules. Herein, we first locate stable conformational and tautomeric forms of these biomolecules using an accurate level of theory (viz. CCSD­(T)/6-311++G­(3df,2p)). Subsequently, the heats of formation of the amino acids are evaluated using the CBH-1 and CBH-2 schemes and routinely employed density functionals or wave function-based methods. The calculated heats of formation obtained herein using modest levels of theory and are in very good agreement with those obtained using more expensive W1-F12 and W2-F12 methods on amino acids and G3 results on barbituric acid derivatives. Overall, the present study (a) highlights the small effect of including multiple conformers in determining the heats of formation of biomolecules and (b) in concurrence with previous CBH studies, proves that use of the more effective error-cancelling isoatomic scheme (CBH-2) results in more accurate heats of formation with modestly sized basis sets along with common density functionals or wave function-based methods

Aza-PNA: Engineering E‑Rotamer Selectivity Directed by Intramolecular H‑bonding

The replacement of α(CH2) by NH in monomers of standard aeg PNA and its homologue β-ala PNA leads to respective aza-PNA monomers (1 and 2) in which the NαH can form either an 8-membered H-bonded ring with folding of the backbone (DMSO and water) or a 5-membered NαHαCO (water) to stabilize E-type rotamers. Such aza-PNA oligomers with exclusive E rotamers and intraresidue backbone H-bonding can modulate its DNA/RNA binding and assembling properties

Proton Hop Paving the Way for Hydroxyl Migration: Theoretical Elucidation of Fluxionality in Transition-Metal Oxide Clusters

The reactions of chemisorbed water on W₃O₆⁻ and Mo₃O₆⁻ clusters have been investigated to explore the phenomenon of fluxionality in transition-metal oxide clusters. The net observed phenomenon here is a hydroxyl migration. However, mechanistic studies using electronic structure theory reveal that the hydroxyl migration occurs by a synergistic pathway led by a proton hop and assisted by an interconversion between a bridging oxygen and a terminal oxygen. The proton hop provides access to two isomers, which differ in the relative position and orientation of the hydroxyl groups, thereby generating the scope for an enhanced catalytic activity in important processes such as hydrogen evolution from water

Polarized Naphthalimide CH Donors Enhance Cl^– Binding within an Aryl-Triazole Receptor

The dipolar character of 1,8-naphthalimide together with polarization of the C⁴–H and C⁵–H donors has been utilized in receptor <b>1</b> to effectively bind chloride alongside triazole and phenylene units. The Cl^– binding strength of <b>1</b> shows that the naphthalimide provides greater anion stabilization than an unactivated phenylene, and DFT calculations show that its collinear donor array can be a “urea-like” analog for CH···anion interactions