Small molecule precursors

De Gennes [41] predicted that percolation theory should hold for crosslink-ing of small molecule precursors. However, he argued that for vulcanizing polymers (high Mw), only a very narrow regime near the gel point exists for which percolation is valid, i.e. these polymers should exhibit more mean fieldlike behavior. 

Nucleotides are the building blocks for nucleic acids they are also involved in a wide variety of metabolic processes. They serve as the carriers of high-energy phosphate and as the precursors of several coenzymes and regulatory small molecules. Nucleotides can be synthesized de novo from small-molecule precursors or, through salvage pathways, from the partial breakdown products of nucleic acids. The highlights of our discussion in this chapter are as follows. 

There is continued interest in the synthesis of poly(phosphazenes) from small molecule precursors. The use of ionic sulfates as catalysts in the solution polymerization NjPjClg has been patented.The effect of N P Clg on NjPjClg polymerization is complicated, initially inducing acceleration of polymerization while at higher conversions a retardation is... 

Information on the formation of poly(phosphazenes) from small molecule precursors continues to become available. New results in ring-opening polymerization are limited in mixed ring systems. The polymerization of the cabophosphazene, CfCNPcIjNPcI, occurs at relatively mild conditions and can be... 

The small-molecule precursors of orotic acid were identified by Reichard and Lagerkvist [72]. During in vitro incubation, liver slices incorporated labelled ammonia, bicarbonate and aspartate into pyrimidine components of RNA. When the slices were incubated with the labelled precursors in the presence of extracellular orotate, isotopes were found in this extracellular fraction. In this way, orotic acid was recognized as an intermediate in pyrimidine synthesis de novo. The labelled orotate was chemically degraded and small molecules identified as the precursors of particular atoms of the orotate ring, as shown in the following scheme ... 

In the early 1950s, the small molecule precursors of the pyrimidine ring atoms were identified, principally by Lagerkvist and his group [see review (4)] ... 

The studies reviewed in Chapter 6 show that metal complexes act by both mechanisms. For indirect action the interference with either cellular biochemistry or small molecule precursors of the nucleic acids is required. In the case of direct action the binding of the molecule (drug) to the polymer is a requisite. 

Since there has been no evidence presented to support the hypothesis that free adenine can be formed de novo in biological systems from small molecule precursors, and furthermore, since purines have never been reported to have been essential dietary additions, the formation of nucleotides from free purines may be looked upon as a minor biosynthetic pathway. Undoubtedly, there is some utilization of free purines which are derived from the intestinal tract as well as from catabolic events within the cell. The term salvage pathway has been aptly applied to the reactions utilizing free bases for nucleic acid synthesis (206). 

In situations where it is desirable to preferentially form analyte ions of higher charge state—for example, to obtain more reactive precursors for tandem mass spectrometry experiments or to improve the efficiency of electron capture in either electron capture dissociation (ECD) or electron transfer dissociation (ETD) experiments—then the use of narrow diameter capillaries is recommended. Conversely, if lower charge states are desirable, such as singly charged small molecule precursor ions that present more straightforward spectral interpretation, then wider diameter capillaries are preferable. ... 

LUMO, respectively), illustrating the near-equivalence to corresponding ethylene (recc) or formaldehyde (riQ co) NBOs. Whereas the NBOs of larger molecule exhibit high transferability from small-molecule precursors, those of MOs tend to exhibit surprising variability that may challenge extrapolation even for small geometry distortions. 

McCarthy, K.E., Recent advances in the design and s3fnthesis of carbon-14 labeled pharmaceuticals from small molecule precursors, in Curr. Pharm. Design 2000, 5, 1057-1083. 

Nitration of aromatic compounds such as toluene is important for the synthesis of small-molecule precursors for further use in fine chemicals such as dyes, pharmaceuticals, perfumes, plastics, and explosives. Typically, it is the para nitration product of monosubstituted benzene compounds that is the most desirable. The traditional aromatic nitration method that is still widely used today is the homogeneous... 

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