1.Liquid hot NAGMA cooled to 0.4 K: benchmark thermochemistry of a gas-phase peptide.
Leavitt CM1, Moore KB 3rd, Raston PL, Agarwal J, Moody GH, Shirley CC, Schaefer HF 3rd, Douberly GE. J Phys Chem A. 2014 Oct 16;118(41):9692-700. doi: 10.1021/jp5092653. Epub 2014 Oct 3.
Vibrational spectroscopy and helium nanodroplet isolation are used to determine the gas-phase thermochemistry for isomerization between conformations of the model dipeptide, N-acetylglycine methylamide (NAGMA). A two-stage oven source is implemented to produce a gas-phase equilibrium distribution of NAGMA conformers, which is preserved when individual molecules are captured and cooled to 0.4 K by He nanodroplets. With polarization spectroscopy, the IR spectrum in the NH stretch region is assigned to a mixture of two conformers having intramolecular hydrogen bonds composed of either five- or seven-membered rings, C5 and C7, respectively. The C5 to C7 interconversion enthalpy and entropy, obtained from a van't Hoff analysis, are -4.52 ± 0.12 kJ/mol and -12.4 ± 0.2 J/(mol · K), respectively. The experimental thermochemistry is compared to high-level electronic structure theory computations.
2.Comparison of the conformational behavior of amino acids and N-acetylated amino acids: a theoretical and matrix-isolation FT-IR study of N-acetylglycine.
Boeckx B1, Maes G. J Phys Chem A. 2012 Mar 1;116(8):1956-65. doi: 10.1021/jp211382u. Epub 2012 Feb 21.
Within the structure determination task for peptides, which is of large interest due to the relation between structure and functionality, infrared spectra can provide detailed information on the conformational behavior. The conformational landscape ofN-acetylgycine has been studied by a combined theoretical and matrix-isolation FT-IR study. The acetylation simulates an amino acid a peptide bond. Four stable conformations were found at the MP2/6-31++G** level of theory. Among these, only one contains an intramolecular H-bond that has a small abundance at the considered temperature. Apart from this one, three other different conformations could be detected in an Ar matrix. The experimental rotamerization constants NAG2 ⇌ NAG1 and NAG3 ⇌ NAG1 could be estimated. The values of the rotamerization constants as well as the mean frequency deviation of N-acetylglycine were combined with previously obtained data of other N-acetylated amino acids and they appeared to be similar to the data for nonsubstituted amino acids.
3.N-Acetylglycine Cation Tautomerization Enabled by the Peptide Bond.
Kocisek J1, Piekarski DG2, Delaunay R1,3, Huber BA1, Adoui L1,3, Martín F2,4,5, Alcamí M2,4, Rousseau P1,3, Domaracka A1, Kopyra J6, Díaz-Tendero S2. J Phys Chem A. 2015 Sep 17;119(37):9581-9. doi: 10.1021/acs.jpca.5b06009. Epub 2015 Sep 3.
We present a combined experimental and theoretical study of the ionization of N-acetylglycine molecules by 48 keV O(6+) ions. We focus on the single ionization channel of this interaction. In addition to the prompt fragmentation of the N-acetylglycine cation, we also observe the formation of metastable parent ions with lifetimes in the microsecond range. On the basis of density functional theory calculations, we assign these metastable ions to the diol tautomer of N-acetylglycine. In comparison with the simple amino acids, the tautomerization rate is higher because of the presence of the peptide bond. The study of a simple biologically relevant molecule containing a peptide bond allows us to demonstrate how increasing the complexity of the structure influences the behavior of the ionized molecule.
4.Effects of sodium benzoate, a widely used food preservative, on glucose homeostasis and metabolic profiles in humans.
Lennerz BS1, Vafai SB2, Delaney NF3, Clish CB4, Deik AA5, Pierce KA6, Ludwig DS7, Mootha VK8. Mol Genet Metab. 2015 Jan;114(1):73-9. doi: 10.1016/j.ymgme.2014.11.010. Epub 2014 Nov 15.
Sodium benzoate is a widely used preservative found in many foods and soft drinks. It is metabolized within mitochondria to produce hippurate, which is then cleared by the kidneys. We previously reported that ingestion of sodium benzoate at the generally regarded as safe (GRAS) dose leads to a robust excursion in the plasma hippurate level . Since previous reports demonstrated adverse effects of benzoate and hippurate on glucose homeostasis in cells and in animal models, we hypothesized that benzoate might represent a widespread and underappreciated diabetogenic dietary exposure in humans. Here, we evaluated whether acute exposure to GRAS levels of sodium benzoate alters insulin and glucose homeostasis through a randomized, controlled, cross-over study of 14 overweight subjects. Serial blood samples were collected following an oral glucose challenge, in the presence or absence of sodium benzoate. Outcome measurements included glucose, insulin, glucagon, as well as temporal mass spectrometry-based metabolic profiles.