Conformation of protonated glutamic acid at room and cryogenic temperatures

Abstract

Recognition properties of biologically relevant molecules depend on their conformation. Herein, the conformation of protonated glutamic acid (HGlu) isolated in quadruple ion traps is characterized by vibrational spectroscopy at room and cryogenic temperatures and dispersion-corrected density functional theory calculations at the B3LYP-D3/aug-cc-pVTZ level. The infrared multiple photon dissociation (IRMPD) spectrum recorded in the fingerprint range at room temperature using an IR free electron laser is attributed to the two most stable and nearly isoenergetic conformations (1-cc and 2-cc) with roughly equal population (ΔG = 0.0 kJ mol). Both have bridging C[double bond, length as m-dash]O(HNH)O[double bond, length as m-dash]C ionic H-bonds of rather different strengths but cannot be distinguished by their similar IRMPD spectra. In contrast, the higher-resolution single-photon IRPD spectrum of H-tagged HGlu recorded in the conformation-sensitive X-H stretch range in a trap held at 10 K distinguishes both conformers. At low temperature, 1-cc is roughly twice more abundant than 2-cc, in line with its slightly lower calculated energy (ΔE = 0.5 kJ mol). This example illustrates the importance of cryogenic cooling, single-photon absorption conditions, and the consideration of the X-H stretch range for the identification of biomolecular conformations involving hydrogen bonds.

A theoretical investigation of water–solute interactions: from facial parallel to guest–host structures

“…As underlined by Alonso et al [35] an inversion in the hydrogen bonding network in the water cluster leads to two similar isomers for the BPL:(H 2 O) 4 complex. Similarly, our calculations also lead to the prediction of two almost isoenergetic isomers for the BPL:(H 2 O) 5 complex, differing from one another by an inversion in the hydrogen bonding network in the water cluster.…”

“…It was found that both isomers of the BPL:(H 2 O) 4 5 isomers involve similar water-solute interactions, as demonstrated by the QTAIM analysis. The above-described structures suggest that the following features of the solvent cluster may favor an efficient facial-parallel interaction with BPL: four almost coplanar water molecules with two consecutive electron-rich regions (oxygen atoms) that may interact with the electrondeficient region of the BPL (hydrogen atoms of the -CH 2 -groups), and two consecutive electron-deficient regions (hydrogen atoms) that may interact with the electron-rich region of the BPL (ester function).…”

“…5): -a (H 2 O) 5 :BPL:(H 2 O) 5 isomer in which each water pentamer is interacting with one face of the solute, -a (H 2 O) 4 :BPL:(H 2 O) 6 isomer in which a uudd water tetramer is attached to one face of the BPL whereas a water hexamer in its book shape is interacting with the other face. (Table 7).…”

Probing chirality recognition of protonated glutamic acid dimers by gas-phase vibrational spectroscopy and first-principles simulations

“…As a consequence, only two almost isoenergetic isomers are observed in the gas phase. 47,51,52 Recently, our IRPD spectra of cryogenic GluH + revealed their relative abundance as approximately 2 : 1, showing the importance of cryogenic cooling, single-photon absorption conditions, and consideration of the XH stretch range (2600-3600 cm À1 ) for the identification of molecular conformation. 51 IR spectra and quantum chemical analysis of alkali-metalated GluM + (M = Li-Cs) revealed cation size-dependent conformational locking by HOCOÁ Á ÁM + Á Á ÁOCOH bridges.…”

“…47,51,52 Recently, our IRPD spectra of cryogenic GluH + revealed their relative abundance as approximately 2 : 1, showing the importance of cryogenic cooling, single-photon absorption conditions, and consideration of the XH stretch range (2600-3600 cm À1 ) for the identification of molecular conformation. 51 IR spectra and quantum chemical analysis of alkali-metalated GluM + (M = Li-Cs) revealed cation size-dependent conformational locking by HOCOÁ Á ÁM + Á Á ÁOCOH bridges. [52][53][54] Herein, we apply cryogenic infrared photodissociation (IRPD) and IR-IR hole burning spectroscopy and first-principles simulations to homochiral (LL) and heterochiral (LD) glutamic acid dimers (LL-/LD-Glu 2 H + ) to determine their structures, energies and eventually their chirality recognition.…”