Ester linkage definition

Our current work is concentrated on the series of porphyrin-quinone molecules (V). These are very similar to I in that amide linkages have replaced the ester linkages. We chose to study these molecules not only because they provided a definite change... 

The experiments presented above definitively established the fact the Lipson s HPD-forming procedure gives dimeric and trimeric porphyrin esters as the high-molecular weight component which is eminently better localized and retained in tumor cells and is responsible for most of the photodynamic activity associated with HPD. Mechanistically, the formation of ester linkage is not only understandable but expected as well. Under the alkaline condition employed in the synthesis of HPD, the nucleophilic substitution reaction illustrated in the following scheme is very similar to the... 

If the classification of lipides were to be examined, some points would have to be made clear. In the first place, a definition of lipides should be made that excludes esters of mineral acids such as orthophosphoric acid. The phosphoric esters of alcohols and phenols are alkalino-stable—excluding those possessing a free carbonyl group moreover, they are not very soluble in organic solvents. The definition of lipides should therefore take into account the hydrolysis of ester linkage by heating with alkalies and the solubility of lipides in some organic solvents. 

Solution. Here, one might expect the ordinary polyesters to have higher A// s, particularly the PET, because of the decreased spacing between the polar ester linkages, so the explanation must lie in the AS s. Because thermotropic LCPs by definition maintain considerable order in the molten state, they randomize less upon melting and therefore have lower Sm s than non-LC polyesters. 

Auxins are defined as organic substances that promote cell elongation when applied in low concentrations to plant tissue segments in a bioassay. By this definition, there are several other native auxins that have been reported to occur in plants in addition to the most often studied auxin, IAA. These include the halogen-substituted 4-C1-IAA,23 as well as phenylacetic acid and indole-3-butyric acid.24 All native auxins are found in planta as both free acids and conjugated forms through ester or amide linkages. IAA, the auxin most extensively studied, will be the focus of this chapter. 

---