Residue model

There are alternative explanations for the actual mechanism by which these ions are produced, e.g. the ion-evaporation [11] and charge-residue models [12], and these have been debated for some time. 

According to the ion-evaporation model, the droplets become smaller until a point is reached at which the surface charge is sufficiently high for direct ion evaporation into the gas phase to occur. In the case of the charge-residue model, repeated Coulombic explosions take place until droplets are formed that contain a single ion. Evaporation of the solvent continues until an ion is formed in the vapour phase. 

Fig. 23. Possible helical models for the gramicidin A ion channel. The polypeptides are represented as helical strips, one molecule being stippled for clarity. Numbers refer to the substituted terminal amino acid residues. Model (i), proposed originally by Urry, is the one now generally accepted...

The elder model of ion formation, the charged-residue model (CRM), assumes the complete desolvation of ions by successive loss of all solvent molecules from droplets that are sufficiently small to contain just one analyte molecule in the end of a cascade of Coulomb fissions. [9,42,84] The charges (protons) of this ultimate droplet are then transferred onto the molecule. This would allow that even large protein molecules can form singly charged ions, and indeed, CRM is supported by this fact. [23]... 

The mechanisms for the formation of gas phase ions from droplets are not fully understood and two therories have been proposed the ion evaporation model (lEV) and the charge residue model (CR) [28]. The lEV model proposes that the ions are directly emitted into the gas phase when, after evaporation and... 

Figure 14. Directional correlation function as in Fig. 8 for amylosic chains based on the rigid residue model (filled circles) and relaxed residue model (open circles).

Amino acid residue models such as a tyrosine residue model (p-cresol) lengthen remarkably the charge hopping distance, a phenomenon which can solve i he problem in the electrocatalysis mentioned in the above item 5) and enhance remarkably the catalytic activity. 

The electron transfer from the photoexcited Ru(bpy)32+ to MV2+ confined in a polysiloxane film showed a complete static quenching following the Perrin model,32) and the electron transfer distance rc was 1.4 nm, which is comparable to a conventional electron transfer distance in biological systems. The presence of a tryptophan residue model, 3-methyindole (IND) enhanced much the quenching efficiency (Fig. 19.6) by lengthening the electron transfer distance, and the electron transfer distance was estimated to be 2.7 nm, almost twice that without the mediator.32 ... 

Regarding item 6) above on electrocatalysis, the coexistence of tyrosine residue model, p-cresol (p-Crej, enhanced remarkably the catalytic activity of Ru-red confined in a Nafion membrane coated on an electrode (Fig. 19.3).20) This was attributed to the nearly twofold lengthening of the charge hopping distance by p-cresol from 1.28 nm to 2.25nm). 

Estimates from multiple logistic regression models adjusted for age, sex, study center, education, alcohol consumption, body mass index, physical activity, family history of colorectal cancer and energy intake, according to the residual model. b Reference category. 

Liwo A, Khalili M, Scheraga HA (2005) Ab initio simulations of protein-folding pathways by molecular dynamics with the united-residue model of polypeptide chains. Proc. Natl. Acad. Sci. 

From these coefficients, calculate the 12 predicted responses, and so die residual (modelling) error as die sum of squares of the residuals. 

Two mechanisms have been proposed to account for the formation of gas-phase ions from very small and highly charged droplets. The first mechanism, proposed by Dole et al. [10,11], depends on the formation of extremely small droplets which should contain only one ion. Solvent evaporation from such a droplet will lead to a gas-phase ion. Mass spectrometric determinations by Dole and co-workers were by and large unsuccessful, but the charge residue model (CRM) proposed by them survived. A more detailed consideration of, and support for, the mechanism was later provided by Rollgen et al. [25,26]. 

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