Nitrogen loss during conversion

Schiffs base, but the spectra for the M-412 intermediate indicate that this proton is lost. The deprotonation of the Schiffs base is apparently after the K intermediate [262], and proposed to be during the L to M transition [209,263,264], Reprotonation of the nitrogen is suggested to occur during the M-412 to 0-640 conversion [265], Part of the blue-shift in the formation of M-412 is, of course, explained by the fact that, in model retinal compounds, loss of the proton leads to a 440-380 nm shift [266], but other effects must also be present. Circumstantial evidence, which includes the finding of 13-cis retinal in M-like intermediates stabilized under somewhat denaturing conditions [198,267], favors the idea that the retinal is isomerized in the M intermediate, as do the more direct resonance Raman data [268,269], In fact, the K and L intermediates seem already to contain the 13-c/i isomer of retinal, as indicated by extraction of 13-c/i retinal from the L intermediate [270] and spectroscopic data on the K and L intermediates [271-274], The resonance Raman spectroscopy of bacteriorhodopsin photointermediates has been recently reviewed [275],... 

During exposure to elevated temperatures in air, nearly all metals react to form oxides and, in some cases, nitrides. The conversion of a structural component from metal to oxide can lead initially to a loss of load-bearing capacity and ultimately to failure. Dissolution of oxygen or nitrogen into a metal in advance of the oxidation front can also occur. In metals such as Ti, Nb, or Cr this results in extensive embrittlement and, as with conversion to oxide, can culminate in failure of the component. The rate at which these processes occur is a major factor in determining the lifetime of a component. 

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