Alignment of dipoles

It has been suggested that this is due to a more favorable alignment of dipoles in the exo TS.15... 

Helixes are often amphipathic one side has hydrophobic residues that bind to h>drophobic areas in the protein the other has hydrophilic residues that interact w ith water (Figure 1.5). The alignment of dipoles of the polypeptide backbone nearly parallel to the axis of an a helix causes a net dipole moment with its positive pole at the N-terminus and negative pole at the C-terminus16 (Figure 1.6). 

Figure 3. Different mechanisms for inducing polarization through (a) redistribution of electron density, (b) bond stretching, (c) alignment of dipoles, and (d) separation of ions.

It should be apparent that the magnetic susceptibility x of a paramagnetic sample (corrected for diamagnetism) should be infinite at absolute zero (with perfect alignment of the magnetic dipoles, or 100% population of the lowest Zeeman state) and zero at infinite temperature (random alignment of dipoles, equal population of Zeeman states). An obvious expression which embodies these conditions is ... 

A further unusual characteristic of ferroelectric materials is that their properties change with time in the absence of either external mechanical or electrical stresses or temperature changes. This ageing is due to a diminution of domain wall mobility through the gradual build-up of inhibiting causes. These may be internal fields due to the alignment of dipoles formed from lattice defects... 

The arrangement of dipoles found in d(CG) and d(GC) is prototypical for B-type double helixes consisting of CG bases there will be, between consecutive base pairs, either the "near parallel" alignment of dipoles, or the "near 90 twist" between them. Thus, the segment... 

Another condition is the ability of spontaneous alignment of dipoles into domains, which occurs only with certain crystalline structures. Several are known, the most significant being the spinel structure named after the mineral spinel MgAl204., which itself is not ferromagnetic. 

Attractive interaction in solids for head-to-tail alignment of dipoles Shorter range (r ) interaction than ion-dipole or Coulomb potential (r" )... 

Figure 2. Schematic view of the alignment of dipoles in a polymer matrix by poling. First die sample is heated above the glass transition temperature. Then an external electric field is applied. When die dipoles are aUgned the temperature is lowered below the glass transition temperature. The result is a noncentrosymmetric distribution of nonlinear dipoles even in the absence of the external applied field...

An actual example of an extended application with technological potential is the organic and non-volatile memory, based on an OFET. The main advantage of a non-volatile memory is that its information is maintained during the readout procedure (non-destructive readout, NDRO). A ferroelectric polymer is introduced as a dielectric layer in the OFET. Due to the ferroelectric alignment of dipoles the threshold voltage of the transistor is affected by their dipole moments and can be used as stored information. 

These effects are present in the simple ions of standard substances such as Cs" ", Ca " ", Cl , 804 , NO3, CH3COO and (CH3)4N. They are also going to be of considerable importance in electrolyte solutions where many of the ions are large and complex, for example protein ions, phospholipid ions, nucleic acids, ions of neurotransmitters and so on. Dipoles, induced dipoles and alignment of dipoles are discussed later (see Sections 1.5, 1.7.2 and 1.7.3). 

Fig. 2.1. Response of phosphorus nuclei to an applied magnetic field, and to a radio frequency (rf) wave, (a) Nuclear magnetic dipole without applied magnetic field, (b) Applied magnetic field, with applied rf wave, (c) Alignment of dipole with (stable, low energy), (d) Alignment against B (unstable, high energy).

Figure 11.16 Domains due to the differing alignment of dipoles in adjacent regions of a crystal. The regions are separated by a domain wall, which extends over several tens of nanometres in practice...

Fig. 2 (a) Dimeric / -sheet assembly formed by cyclo[(L-Phe-D- A-Ala-L-Leu-D- A-Ala)2-]. For clarity, stick drawings were used for heavy atoms in the side chains, (b) Alignment of dipoles by stacking cyclic tripeptides built from 6-amino acids. (From Ref. [16].)... 

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