Tunneling Lifetime of the ttc/VIp Conformer of Glycine in Low-Temperature Matrices

Abstract

Conformer ttc/VIp of glycine and glycine-N,N,O-d(3) has been prepared in low-temperature Ar, Kr, Xe, and N(2) matrices by near-infrared (NIR) laser irradiation of the first OH stretching overtone of conformer ttt/Ip. Glycine (and glycine-N,N,O-d(3)) ttc/VIp was found to convert back to ttt/Ip in the dark by hydrogen-atom tunneling. The observed half-lives of ttc/VIp in Ar, Kr, and Xe matrices at 12 K were 4.4 ± 1 s (50.0 ± 1 h), 4.0 ± 1 s (48.0 ± 1 h), and 2.8 ± 1 s (99.3 ± 2 h), respectively. In correspondence with the observation for the cis-to-trans conversion of formic and acetic acid, the tunneling half-life of glycine ttc/VIp in a N(2) matrix is more than 3 orders of magnitude longer (6.69 × 10(3) and 1.38 × 10(4) s for two different sites) than in noble gas matrices due to complex formation with the host molecules. The present results are important to understand the lack of experimental observation of some computationally predicted conformers of glycine and other amino acids.

Atom Tunneling in Chemistry

“…Ring expansion as aresult of carbon tunneling, as observed in carbenes. [143,151,152] X = Cl,F Angewandte Chemie Reviews proton shifts.T unneling decay of particular conformers of glycine, [166,167] alanine, [168] cytosine, [169] and other small molecules with relevance to biology [170,171] was observed as well as the tunneling-accelerated tautomerization of tetrazole acetic acid. [172] Hydrogen peroxide is chiral if the rotation around the OÀObond is restricted at low temperature.The racemization was investigated by six-dimensional quantum dynamics [173] and shown to proceed efficiently by tunneling.…”

Tunnelling in carbonic acid

“…1B) via TS2 exhibits a 34.6 kcal mol À1 barrier at the CCSD(T)/CBS level; this compares well with the QCISD(T)/6-311++G(d,p)//MP2(full)/ 6-31++G(d,p) barrier of 34.3 kcal mol À1 reported earlier. [38][39][40][41][42][43][44] We executed a detailed kinetic analysis of this tunnelling phenomenon in different noble gases and at various temperatures (Table 1). 1).…”

High vibrational overtone excitation‐induced conformational isomerization of glycolic acid in solid argon matrix

“…This is the only case, where the isomerization back to the SSC conformer from the higher energy conformer is observed after near‐IR induced overtone excitation. The success of the SST formation in nitrogen matrix instead of the GAC and AAT is explained by the stabilization of the OCO c H dihedral angle of carboxylic acids to trans position in a nitrogen matrix . The SST conformer also observed to decay back to the SSC conformer via tunneling .…”

“…The SST conformer also observed to decay back to the SSC conformer via tunneling . The tunneling reactions are typically slower in a nitrogen matrix than in rare gas matrices . It is possible that the SST conformer can be generated upon irradiation in an argon matrix, but it might relax back to the SSC conformer in an argon matrix with the rate faster than time of detection .…”

“…The success of the SST formation in nitrogen matrix instead of the GAC and AAT is explained by the stabilization of the O¼C-O c -H dihedral angle of carboxylic acids to trans position in a nitrogen matrix. [22][23][24][25][26] The SST conformer also observed to decay back to the SSC conformer via tunneling. [13] The tunneling reactions are typically slower in a nitrogen matrix than in rare gas matrices.…”