Sheet structures parallel’ mode

For an octapeptide sequence taken from the C-terminal residues of the Alzheimer s Ap-peptide Lansbury et al. identified a large intensity enhancement for 13C-labeled modes that was sequence-dependent and assessed as largely due to interstrand dipole-coupling.1207,2351 Mendelsohn et al. found a similar effect by double labeling on alternate sites a peptide that formed a P-sheet-like structure in methanol.12501 Subsequent theoretical modeling showed this latter intensity enhancement to be a function of forming extended, flat, anti-parallel P-sheet structures,12511 and the overall effect to be highly position sensitive.12451... 

The sheet thus plays an important role in the structure of proteins. In some it is the main secondary structural component (e.g., con-canavalin A and Bence-Jones proteins) in others it is found in conjunction with a-helical segments and in many proteins it occurs as a mixed sheet of parallel and antiparallel strands. To date, normal-mode analy-... 

The crystal structure of VI viewed along the fe-axis is shown in Figure 4.7. There are two MTA cations and bromide anions and two o-iodophenol molecules in the asymmetric unit. The OH group of the o-iodophenol is hydrogen bonded with the bromide anions. The packing mode of the MTA cations and the bromide anions is nearly the same as that of the CTAB complex, crystal V. The pleated sheet is parallel to the flc-plane and the sheets are stacked along the fe-axis. 

Two structures have been proposed for (Gly) I an antiparallel-chain pleated sheet (APPS) and a similar rippled sheet (APRS) (see Section III,B,1). These structures have different symmetries the APPS, with D2 symmetry, has twofold screw axes parallel to the a axis [C (a)] and the b axis [C (b)], and a twofold rotation axis parallel to the c axis [62(0)] the APRS, with C2h symmetry, has a twofold screw axis parallel to the b axis ( 2(6)], an inversion center, i, and a glide plane parallel to the ac plane, o-Sj. Once these symmetry elements are known, together with the number of atoms in the repeat, it is possible to determine a number of characteristics of the normal modes the symmetry classes, or species, to which they belong, depending on their behavior (character) with respect to the symmetry operations the numbers of normal modes in each symmetry species, both internal and lattice vibrations their IR and Raman activity and their dichroism in the IR. These are given in Table VII for both structures. 

Raman spectroscopy of proteins runs parallel to IR spectroscopy. The same vibrational transitions associated with the same normal vibrational modes centred on atom motions within peptide links are observed (Table 4.3 Figure 4.10). The same is true for the Raman spectroscopy of nucleic acids as well. Arguably, Raman spectroscopy of a globular protein of interest gives an even more precise characterisation of vibrational transitions than IR spectroscopy, allowing for the clear discrimination and identification of random coil structure as well as a-helix, parallel jd-sheet and antiparallel jd-sheet secondary structures. 

Similarly to partially overlapping channels, microchannels with mesh contactors (Figure 7.2h) are used to create the partial contact of fluids. The advantage of these contactors is that both modes of operation, cocurrent and countercurrent, can be apphed. Besides, the flow is stabilized because of the solid support between two fluids. The solid contactors are porous membrane [9, 10] and metal sheets with sieve-like structure [11]. Similarly to parallel flow, the mass transfer in both cases is only by diffusion and the flow is under laminar flow regime dominated by capillary forces. The membrane contactor has the advantage of being flexible with respect to the ratio of two fluids. In addition to flow velocities, the mass transfer is a function of membrane porosity and thickness. In another type of microextractor, two microchaimels are separated by a sieve-like wall architecture to achieve the separation of two continuous phases. However, the hydrodynamics in both types of contactors is more complex because of interfadal support and bursting of fluid... 

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