Backbone tuning

Since the summation in Eq. (12) may be on any subset of atoms, it can be fine-tuned to best suit the problem at hand. The summation may be over the whole molecule, but it is very common to calculate conformational distances based only on non-hydrogen heavy atoms or, in the case of proteins, even based on only the backbone Ca atoms. Alternatively, in a study related to drug design one may consider, for example, focusing only on atoms that make up the pharmacophore region or that are otherwise known to be functionally important. 

Polymers with n-conjugated backbones are an important class of materials that have captured the imagination of the scientific community due to their remarkable properties and exciting applications [91-95]. While most of the work on n-conjugated polymers has focused on all-carbon systems, there has been considerable interest in incorporating heteroatoms into the n-conjugated backbone (i.e.,polythiophene, polypyrrole, polyaniline) to tune their properties. 

In this paragraph we complement experimental conductance data of a family of structurally well-tuned biphenyldithiols (BPDT) T1 to T8 [75, 76] with a family of biphenyl-dinitriles (BPDN) N1 to N6 [54] having the same molecular backbone,... 

The most common chiral auxiliaries are diphosphines (biphep, binap and analogues, DuPhos, ferrocenyl-based ligands, etc.) and cinchona and tartaric acid-derived compounds. It is clear that the optimal chiral auxiliary is determined not only by the chiral backbone (type or family) but also by the substituents of the coordinating groups. Therefore, modular ligands with substituents that can easily be varied and tuned to the needs of a specific transformation have an inherent advantage (principle of modularity). 

The above approaches used the idea of conjugation length control in PTs by distorting the polymer backbone with bulky substituents as side groups. Hadziioannou and coworkers [509,510] demonstrated PL and EL tuning via exciton confinement with block copolymers... 

Another successful family of ligands is the sugar-based furanoside ligands 4, 19-23 (Fig. 5) [21-23,43,50]. The modular construction of these ligands allows to fine tune (a) the different configurations of the carbohydrate backbone and (b) the steric and electronic properties of the diphosphite substituents. They show excellent enantioselectivity on both the S and R enantiomer of the product (up to 93%) and excellent regioselectivity (up to 98.8%) under mild conditions (Table 2). 

As a general rule, the addition of ethylene oxide to a resin backbone will tend to increase the water solubility of the compound. The addition of propylene oxide or butylene oxide to the resin will tend to increase the hydrocarbon solubility of the compound. Often, the dehazer or demulsifier can be made to perform selectively in oil-water systems by adding both ethylene oxide and propylene oxide to the same molecule. Performance and solubility of the alkoxylated compound can then be finely tuned by closely controlling the amount and order of epoxide addition. A random EO-PO based fuel demulsifier is shown in FIGURE 6-6. 

While the backbone of the ligand provides the stereochemical information, the two different donor groups (DJ can be introduced independently of one another in consecutive steps and therefore make a fine-tuning of the ligand s steric and electronic features possible. So with a stock of electro- and nucleophiles at hand an enormous number of ligands is accessible by employing the same synthetic procedure and workup, while the synthesis is not limited to phosphines other functionalities such as Hal, C, Si, S, O, and N can also be introduced [7b-d,i]. 

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