Laser-induced acoustic desorption (LIAD) incorporated with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR) has been utilized to investigate phenyl radical-induced damage to dipeptides in the gas phase. Based on the product branching ratios measured for the reactions of two different positively-charged phenyl radicals with seventeen different dipeptides, the overall order of susceptibility to attack of the different sites in the dipeptides was determined to be: heteroaromatic side chain ≈ S atom in SCH3 group > H atom in SH group > H atom in CH group > aromatic side chain > S atom in SH group > NH2 in side chain > N-terminal NH2 > COOH in side chain ≈ C-terminal COOH. The amino acid sequence also influences the selectivity of these reactions. As expected, the ability of a phenyl radical to damage dipeptides increases as the electrophilicity of the phenyl radical increases.

The reactivity of ten charged phenyl radicals toward several amino acids was examined in the gas phase in a dual-cell Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer. All radicals abstract a hydrogen atom from the amino acids, as expected. The most electrophilic radicals (with a greater calculated vertical electron affinity (EA) at the radical site) also react with these amino acids via NH2 abstraction (a nonradical nucleophilic addition-elimination reaction). Both the radical (hydrogen atom abstraction) and nonradical (NH2 abstraction) reaction efficiencies were found to increase with the electrophilicity (EA) of the radical. However, NH2 abstraction is more strongly influenced by EA. In contrast to an earlier report, the ionization energies of the amino acids do not appear to play a general reactivity controlling role. Studies using several partially deuterium-labeled amino acids revealed that abstraction of a hydrogen atom from the α-carbon is only preferred for glycine; for the other amino acids, a hydrogen atom is preferentially abstracted from the side chain. The electrophilicity of the radicals does not appear to have a major influence on the site from which the hydrogen atom is abstracted. Hence, the regioselectivity of hydrogen atom abstraction appears to be independent of the structure of the radical but dependent on the structure of the amino acid. Surprisingly, abstraction of two hydrogen atoms was observed for the 3-nitro-5-dehydrophenyl pyridinium radical, indicating that substituents on the radical not only influence the EA of the radical but also can be involved in the reaction. In disagreement with an earlier report, proline was found to display several unprecedented reaction pathways that likely do not proceed via a radical mechanism but rather by a nucleophilic addition-elimination mechanism. Both NH2 and 15NH2 groups were abstracted from lysine labeled with 15N on the side-chain, indicating that NH2 abstraction occurs both from the amino terminus as well as from the side-chain. Quantum chemical calculations were employed to obtain insights into some of the reaction mechanisms.

The vertical electron affinity is demonstrated to be a key factor in controlling the selectivity of charged phenyl radicals in hydrogen atom abstraction from isopropanol in the gas phase. The measurement of the total reaction efficiencies (hydrogen and/or deuterium atom abstraction) for unlabeled and partially deuterium-labeled isopropanol, and the branching ratios of hydrogen and deuterium atom abstraction, by using a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer, allowed the determination of the selectivity for each site in the unlabeled isopropanol. Examination of hydrogen atom abstraction from isopropanol by eight structurally different radicals revealed that the preferred site is the CH group. The selectivity of the charged phenyl radicals correlates with the radical's vertical electron affinity and the reaction efficiency. The smaller the vertical electron affinity of a radical, the lower its reactivity, and the greater the preference for the thermodynamically favored CH group over the CH3 group or the OH group. As the vertical electron affinity increases from 4.87 to 6.28 eV, the primary kinetic isotope effects decrease from 2.9 to 1.3 for the CD group, and the mixture of primary and alpha-secondary kinetic isotopes decreases from 6.0 to 2.4 for the CD3 group.

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Objectives According to a new report in 2020, the global functional food market size is projected to reach USD 275.77 billion by 2025 at a CAGR of 7.9%. One of the major growth drivers for this includes increasing demand for nutritional and fortifying food additives. Undenatured type II collagen (UC-II®) is a dietary ingredient derived from chicken sternum and has been shown to improve joint health. The development of undenatured type II collagen in different food and beverage (F&B) products is gaining momentum. The objective of this study was to assess the compatibility and recovery of undenatured type II collagen from different prototypes of F&B. Methods A specific ELISA test that detects the presence of native type II collagen was used to measure undenatured type II collagen content. Results Results showed the recovery of undenatured type II collagen from the F&B matrices varied depending on the pH, pressure, humidity and processing temperature. Highest recovery was seen from F&B prototype of nutritional bars (∼100%), chews (98%), gummies (96%), and dairy beverage (81%). Conclusions In summary, the results from this study shows that UC-II® is able to withstand the processing conditions used for manufacturing F&B products. The applicability of this findings will allow UC-II® to be incorporated into different functional foods thereby helping the consumers to improve their joint mobility, flexibility and comfort. Funding Sources Lonza Consumer Health Ingredients Inc.