H/D exchange analysis

Dramatic advances in mass spectrometry and improvements in the various steps within the experimental hydrogen exchange procedures have resulted in the development of automated systems for high-throughput, high-resolution H/D exchange analysis [6, 8, 40-44]. 

From the simpler resonance line-shape and H/D-exchange analysis to the more complex studies of inherent dynamics, occurring on various time scale of motion, NMR remains a good choice to investigate protein flexibility and plasticity. If linebroadening due to exchange and inhomogeneity is minimized (or completely eliminated), then half-width, Aom, of a line becomes proportional to R, the transverse relaxation rate constant. 

Methylcyclohexanone, pK 20, is typical of a weak acid that undergo H/D exchange. Identify the acidic protons of 2-methylcyclohexanone, i.e., those most susceptible to attack by base, as positions for which the value of the lowest-unoccupied molecular orbital (LUMO) is large. Use a LUMO map (the value of the LUMO mapped onto the electron density surface). Does this analysis correctly anticipate which of the anions obtained by deprotonation of 2-methylcyclohexanone is actually most stable Are any of the other ions of comparable stability, or are they aU much less stable ... 

In these terms, Shatenshtein s partial rate factors (37) for the H—D exchange of monosubstituted benzenes in liquid ammonia are not anomalous (2m). The analysis of this rate data is included in Table XXVIII. Even though the data are not precise enough to meet the desired standard of precision of fits, the sequences > X and P/> p p - P/ are clearly evident in the results. Consequently, this data set (which is of the or type) may be taken as providing supporting evidence with the pyridinium ionization (which is of the gr type) for unique X blends for the positions o- and p- to ionization from the ring position as compared with the X blends for side-chain ionization. 

The ion 28 loses H2 by CID with argon to form [(PHOX)Ir(styrene)]+ (29). Compound 29 then undergoes H-D exchange with D2 gas to form the mixture of iso-topomers 29, 29-dh and 29-d2 (Scheme 13.3). When combined, these observations show that the oxidative addition of H2 to 29 is followed by alkene hydride insertion, and that both these steps occur rapidly and reversibly in the gas phase. These results thereby provide gas-phase analogues for catalytic elementary steps that are proposed to occur in solution. Support for this proposed sequence of steps was obtained from a solution-phase catalytic deuteration of styrene. Analysis showed no deuterium incorporation in the unreacted styrene at various conversions, and clean formation of dideuterio ethylbenzene as sole product. 

Since a few years, LITs belong to a rapidly expanding area of instrument development. Recently, LITs have been established to collect ions externally before injecting them in bunches into an FT-ICR [132] or TOF analyzer. [131,133] Even extensive H/D exchange in the gas phase prior to mass analysis can be accomplished this way. 

Ma, L. Fitzgerald, M.C. A new H/D exchange- and mass spectrometry-based method for thermodynamic analysis of protein-DNA interactions. Chem. Biol. 2003, 10, 1205-1213. 

Hamuro Y, Weber P.C., Griffin P.R. High throughput analysis of protein structure by H/D exchange (H/D-Ex) mass spectrometry, in Industrial Protcomics, ed. Figeys D., John Wiley Sons, New York, 2005. 

This hydride has been characterized by IR spectroscopy [v(Ta-H) = 1830cm ], gas evolution analysis, H/D exchange, chemical reactivity with water, alcohols or methane, NMR and EXAFS. For the first time, proton NMR reveals weak signals between 20 and 30 ppm, tentatively assigned to Ta-H peaks. EXAFS shows a first... 

In principle, the estimation of conformational equilibrium in a piperidine derivative by protonation is very simple. If nitrogen inversion is slow compared to deuteronation, if H+/D+ exchange does not occur in the salts, and if H+/D+ exchange is unimportant in the mixing process, then the relative proportion of the salts corresponds to that of the conformers. Thus the spectrum of pure dry cis-3,5-dimethylpiperidine in deuterotrifluoroacetic acid (unchanged after 2 days) showed a septet at 8 2.70 for the 2,6-axial protons in 112 and 113. This was interpreted as a triplet for 112 and a quartet for 113 and analysis of the multiplets gave 54% 112 and 46% 113 (AG"... 

The protolytic activation of the alkane is, however, only the apparent part of the reaction as long as the alkane or the acid is not isotopically labeled. When HF is replaced by DF and the isobutane-CO mixture is bubbled through the DF-SbF5 acid (6 1 molar ratio) at — 10°C, the apparent conversion based on ester or H2 formation is only 4% but the 1H/2H NMR analysis of the apparently unreacted isobutane (96%) shows extensive H-D exchange (18 atom% in the tertiary position and 9 atom% at each primary position).30 The most plausible rationalization of hydrogen exchange is via the formation of carbonium ions (here pentacoordinate transition states or intermediates) as described in Eq. (5.15). 

In Figure 3 (experiments) and Table 4 (results of Monte-Carlo analysis) give the selectivities in the H/D exchange of CP with the same two support materials. On the Si02 support, the... 

Most of HSQC peaks assigned to the N-terminal region disappear upon the formation of PYPm [33,34]. The loss of a-helical content is also observed by CD [35]. However the controversial conclusion was obtained by the fragmentation and H/D exchange mass spectroscopic analysis [36]. Therefore, detailed structural information about PYPm in solution is required to clarify the mechanism underlying the phototransduction. 

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