Linkages, characterization

The amide linkage characterizes nylons. In the first commercial nylon, nylon-6,6, R = (CH2 )g and R = (CH2 )4. Nylon-6,6 is familiar as a textile fiber (nylon stockings) and a molded plastic (see Polyamides). 

Fig. 1. Primary stmctures of some common polysaccharides, (a) Alpha-glycoside linkages characterize amylose, amylopectin, and glycogen (b) cellulose has...

Assuming rigid monosaccharide rings, the source of flexibility in carbohydrates is the glycosidic linkage characterized by the /T torsion angles. In this approximation the complete information about the conformation of a disaccharide fragment is embodied in the conformational distribution function It has been... 

The applicability of infrared dichroism to the study of PUs has been determined by the availability of at least one weU-characterized absorption band in each type of domain. It has been shown [67, 140, 364] that the soft domains are comprised of prepolymer (polyether or polyester) segments, while the hard domains contain urethane segments. The N-H stretching which is located in the urethane linkage characterizes the orientation of the higher modulus hard domains. For the DBDI polymers, we have shown that it appears at 3 320 cm [67]. Similarly, the asymmetric C-H stretching absorption was determined. It appears at 2 940 cm and was used to describe the orientation of prepolymer segments which comprise the rubbery soft domains. 

The linkage characterizes nylons. (Both amine hydrogens can react... 

Carotenoids are natural pigments characterized by a tail to tail linkage between two C20 units and an extended conjugated system of double bonds They are the most widely dis tributed of the substances that give color to our world and occur m flowers fruits plants insects and animals It has been estimated that biosynthesis from acetate produces approximately a hundred million tons of carotenoids per year The most familiar carotenoids are lycopene and (3 carotene pigments found m numerous plants and easily isolable from npe tomatoes and carrots respectively... 

Glucuronomannans. Most glucuronomaimans occur as components of certain plant gums and are characterized by the presence of an 0-(P -D-glucurono-pyranosyl)-(1 2)-D-maimopyranosyl linkage ia the molecule (65). Less complex glucuronomaimans are found in the tissues of bracken Pteridium aquilinum) and in tobacco leaf cells where they may be part of the cultured cell wall (132) and exude into the medium in which the cells are grown (133). 

Polyamides, often also lefeiied to as nylons, are liigli polymers which contain the amide repeat linkage in the polymer backbone. They are generally characterized as tough, translucent, semicrystalline polymers that ate moderately low cost and easily manipulated commercially by melt processing. 

The ester linkage in the repeating unit characterizes polyesters. R and R represent portions of the monomer molecule that do not participate in the polymerization. They may vary widely, giving rise to many different polyesters. Poly(ethylene terephthalate) (PET), made from ethylene glycol... 

Sulfonates with ether linkages include ring-sulfonated alkylphenol ethoxylates and a disulfonated alkyldiphenyl oxide, Dowfax 2A1, and 3B2 (Dow Chemical Company). This surfactant is characterized by high solubiUty in salt solutions, strong acids, or bases. It is used in industrial and institutional cleaners. 

The amide linkage between monomer units in a protein is called a peptide bond. Peptides and polypeptides, which often exhibit biological activity (see Antibiotics, peptides Neuroregulators), are smaller than proteins. Although the differentiation between polypeptide and protein is somewhat arbitrary, the usual distinction is drawn around 100 monomer units. Proteins are also characterized by higher levels of stmcture resulting from internal interactions. 

CH2CN)4Yb[( J.-H)2BH]2, and (CgH N)4Yb[( J.-H)2BH4]2 have been stmcturally characterized by x-ray crystallography and shown to contain ytterbium to boron hydride Yb—H—B linkages. Thermal decomposition of lanthanaboranes can be used to generate lanthanide metal borides. 

Polyanilines. Initial preparations of polyaniline (PANI) led to insoluble materials that were difficult to characterize. Use of model compounds and polymers (124,125) allowed for definitive stmctural analysis. Poly( phenylene amineimine) (PPAI) was synthesized directiy to demonstrate that PANI is purely para-linked (126). The synthesis was designed so as to allow linkage through the nitrogen atoms only (eq. 9). Comparison of the properties of PPAI and PANI showed PPAI to be an excellent model both stmcturaHy and electronically. 

The report in 1968 of the first crystallographically characterized bent metal-nitrosyl linkage in [IrCl(NO)(CO)(PPh3)2]+BF4 [180],... 

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