Tripeptide Agreement

The kinetic energy dependence of H-GGG dissociation induced by collision with Xe is studied in a guided ion beam mass spectrometer. Energy-dependent kinetic sections for six primary products: [b2], [y1 -2H], LE, [b3], loss of CO, [y2 – 2H], and [a1];; three secondary products: [a2], [a3], and [y2 – 2H – CO]; and two tertiary products: [y1 – 2H] – ET and [a2 – CO] – are observed and analysed. The threshold energies at 0 K for all these processes are determined taking into account the effects of several collisions with Xe, internal energy, life effects and competition [78-80]. In particular, this work includes the first simultaneous analysis of six product chains, with appropriate results for their threshold energies. The experimental results are compared to detailed quantum chemical calculations that have been discussed above. The first experimental measures are the thresholds for reactions 2a ([y1-2-2H]), 3 ([b3]]), 4 (loss of CO), 6 ([a3]) and 7a ([a1]) and reactions 1a ([b2]) and 5 ([y2 -2H]) have been refined to ensure more accurate thermodynamics for these two products. We find that the thresholds for all reactions (except reaction 5) are in the experimental uncertainty of at least one of the four theoretical values. This good agreement confirms the reaction mechanisms theoretically studied and also allows to identify the structures of the products formed at the threshold. The difference between the experimental and theoretical threshold energies of the primary product [y2 -2H] in reaction 5 is attributed to its more speculative data analysis. A comparison of the threshold energies of primary products with the theory shows that the four levels of the theory give MADs of 6-14 kJ/mol, where M06-2X gives the best match.

Reaction threshold energies 2b ([y1 -2H]), 8a ([a2]), 9 ([y2 -2H – CO])) and 10 ([a2 – CO])) correspond to the data previously measured in our laboratory for the same products [38, 40]. In addition, Wyttenbach, Bushnell, and Bowers [64, 65] measured experimental collision sections (CCS) of proton oligopeptides (n-1-6) of oligopeptide whose values for n-1-3 are indicated in the S2 complementary table. Their ion mobility experiments used a source laser ionization desorption matrix (MALDI) and were performed at 300 and 80 K (resolution is twice as high at colder temperature as at room temperature). Experimental CCS measurements did not identify several structures for one of the systems, which is expected for the smaller H-G and H-GG systems, but is not consistent with MRIPD studies for H-GGG. This disparity can be attributed to the use of different sources of ions for both groups of experiments. As explained in more detail in the IS, CCS can be compared to those calculated by two different programs [65, 66]. A good match between experience and theory for H-G and H-GG is found, but not for the H-GGG system, so it is not possible to clearly determine what type of compliance is available. However, the low-energy [N1] structures found here are closest to the experimental results of CCS, as they are widely discussed in IS, suggesting that the MP2 theory offers the most reliable relative energy. It is interesting to note that the presence of NCN ND did not significantly alter the conformation of the beta-leaf peptide or the individual fibrile nanostructure in the hydrogel. However, circular dichroism and thioflavin-T fluorescence showed signs of interaction between the two components at the supramolecular level, consistent with an increased concentration of thinner fibers as opposed to thick beams, with a higher surface available for thioflavin-T bonding.

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