Hydrogen Tunneling above Room Temperature Evidenced by Infrared Ion Spectroscopy

Abstract

While hydrogen tunneling at elevated temperatures has, for instance, often been postulated in biochemical processes, spectroscopic proof is thus far limited to cryogenic conditions, under which thermal reactivity is negligible. We report spectroscopic evidence for H-tunneling in the gas phase at temperatures around 320-350 K observed in the isomerization reaction of a hydroxycarbene into an aldehyde. The charge-tagged carbene was generated in situ in a tandem mass spectrometer by decarboxylation of oxo[4-(trimethylammonio)phenyl]acetic acid upon collision induced dissociation. All ion structures involved are characterized by infrared ion spectroscopy and quantum chemical calculations. The charge-tagged phenylhydroxycarbene undergoes a 1,2-H-shift to the corresponding aldehyde with an half-life of about 10 s, evidenced by isomer-selective two-color (IR-IR) spectroscopy. In contrast, the deuterated (OD) carbene analogue showed much reduced 1,2-D-shift reactivity with an estimated half-life of at least 200 s under the experimental conditions, and provides clear evidence for hydrogen atom tunneling in the H-isotopologue. This is the first spectroscopic confirmation of hydrogen atom tunneling governing 1,2-H-shift reactions at noncryogenic temperatures, which is of broad significance for a range of (bio)chemical processes, including enzymatic transformations and organocatalysis.

Gas-phase complexes of Ni2+ and Ca2+ with deprotonated histidylhistidine (HisHis): A model case for polyhistidyl-metal binding motifs

“…The cc-pVTZ basis set was used throughout with the ultrafine setting for the integrals [29,30]. This computational procedure was found to give good correlation with experiment in previous work [31]. All the calculations performed on these systems were done in vacuo.…”

Unraveling the unknown areas of the human metabolome: the role of infrared ion spectroscopy

“…IR-IS has evolved in little more than a decade from an experimental technique in academic labs studying fundamental molecular physics (Lemaire et al 2002 ; Aleese et al 2006 ; Oomens et al 2006 ; Fridgen 2009 ; Polfer and Oomens 2009 ) to its current state, in which it is a demonstrated (bio)analytical technique for the identification of small molecules in complex mixtures (Martens et al 2017a , b ), though still limited to user facilities or state-of-the-art laboratories housing the most advanced tuneable infrared laser technology. In the past decade, IR-IS has been used to identify and characterize the molecular structures of many classes of chemical compounds including amino acids (Polfer et al 2005 , 2006a ; Correia et al 2008 ; Rodgers et al 2008 ; Oomens and Steill 2009 ; Scuderi et al 2011 ), nucleotides and bases (Salpin et al 2007 ; Chiavarino et al 2013 ), peptides and proteins (Balaj et al 2008 ; Polfer et al 2008 ; Yoon et al 2008 ; Fukui and Takahashi 2012 ; Martens et al 2012 , 2015 , 2016a ; Stedwell et al 2012 ; Scuderi et al 2015 ; Dunbar et al 2017 ), saccharides (Martens et al 2017b ; Polfer et al 2006b ; Cagmat et al 2010 ; Contreras et al 2012 ; Schindler et al 2014 , 2017 ), neurotransmitters (Lagutschenkov et al 2010 , 2011 ), and a variety of other mainly small organic compounds and reaction products (Martens et al 2017a ; MacAleese and Maître 2007 ; Rummel et al 2011 ; De Petris et al 2013 , 2016b ; Warnke et al 2015 ; Cismesia et al 2016 ; Seo et al 2016 ; Schäfer et al 2017 ; Gorlova et al 2017 ). Here we outline various ways IR-IS can currently be utilized by the metabolomics community.…”

TUNNEX: An easy‐to‐use wentzel‐kramers‐brillouin (WKB) implementation to compute tunneling half‐lives

“…Recent experimental findings imply that selectivity based on thermodynamic versus kinetic control is undermined by quantum mechanical tunneling (QMT) that can override this classic concept. The concept of a product that forms despite a high barrier that cannot be overcome (within finite time) at a given (low) temperature was termed “tunneling control,” and can be considered as the third paradigm of chemical reactivity next to kinetic and thermodynamic control .…”