Functional analysis acid hydrolysis

Vai der Waals Radii And Related Sterlc Parameters Van der Waals radii have long been considered a valid meas ure of atomic size Taft proposed the first valid set of sterlc parameters for correlation analysis defined from acid hydrolysis of esters caiarton derived equations for the calculation of Van der Waals radii, ry of symmetric top MZs groups( ) These values of the Van der Waals radii were used, together with that for H, to show that Es Is a linear function of i>y ... 

The cyclamides are small cyclic peptides that characteristically contain multiple thiazole, thiazoline, oxazole, and oxazoline rings, which are derived from cysteine, serine, and threonine residues. Some of the first examples of this class to be described were the patellamides (53-55) from the tunicate Lissoclinum patella, although it was later determined they were produced by the symbiotic cyanobacterium Prochloron sp. The structures were solved by a combination of acid hydrolysis and GC analysis, coupled with 2D NMR. Smaller cyclic peptides from this class include the hexapeptides westiellamide (56) and microcyclamide (57) from M. aeruginosa Many members of the class possess cytotoxic properties, although their biological function or mechanism of action is not fully understood. In contrast to many cyanobacterial peptides, aside from the unusual heterocyclic residues, these peptides generally contain only ribosomal amino acids. 

Each step of an isolation procedure requires confirmatory thin layer chromatographic (TLC) analysis to determine if isolation artifacts are produced (Fig. 3). Unwanted reactions include enzymatic and chemical hydrolysis during water extraction, esterification or lactonization of acidic saponins when using alcohol solvents, hydrolysis or transesterification of labile ester functions, and cyclopropane cleavage during acidic hydrolysis [10]. 

Finally, several of the amino acids listed have partial lability during acid hydrolysis and require appropriate corrections, usually derived from kinetic analyses (Smith and Stockell, 1954 Wilcox et al, 1957). One amino acid generally considered to be extremely labile to acid is tryptophan. However, its destruction is actually a function of other contaminants present in the sample (Olcott and Fraenkel-Conrat, 1947). Pure samples of this amino acid are fully stable to the standard conditions of acid hydrolysis. Nonetheless, the observed lability is encountered sufficiently often that the preferred determination of this amino acid is carried out by spectrophotometric analysis (Edelhoch, 1967) or colorimetric methods (Koshland et a/., 1964 Scoffone et al, 1968) on unhydrolyzed samples or by carefully controlled alkaline hydrolysis (Hugh and Moore, 1972) (vide infra). 

Acid hydrolysis of chitosan followed by the HPLC detection of the amount of acetic acid liberated is able to give acetyl content of chitin/chitosan. Due to the high sensitivity, availability, easiness of method and effectiveness in detection of functional groups IR spectroscopy can give usefid information about the acetyl content of chitin/chitosan as well as possible cross-contaminations. The results of Differential Thennogravimetric Analysis (DTA) show increased thermostability compared to GlcNAc. Discussed biopolymer shows its main thermal process from 275 to 280 °C respectively. 

D NMR was used to characterize native and acid hydrolyzed ethylcellulose (EC), a Hercules product widely used as a film-former in ink and coatings applications and as a binder and filler in pharmaceutical applications. An important parameter in controlling the properties of ethylcellulose is the degree of substitution (DS) of ethyl functionalities on the cellulose backbone. NMR is one technique that was used to determine both the total and positional DS (ethylation at the 2,3 and 6 positions of the anhydroglucose unit (AGU)). This analysis requires complete hydrolysis of the sample, and an improved acid hydrolysis technique was developed for this application. Two-dimensional (2-D) NMR techniques were used to confirm peak assignments related to positional DS determinations that were previously made by comparison with standards. In addition, 2-D NMR methods were used to evaluate positional DS of native ethylcellulose prior to acid hydrolysis. A comparison of the analytical results for the acid hydrolysate and native polymer will be discussed. 

Substituted DPEs have also been utilized to prepare carboxyl-functionalized polymers. The carboxyl functionality has been protected using the oxazoline group. The oxazoline-substituted DPE was not stable to the anionic chain end at room temperature, however. " It was necessary to effect this functionalization reaction in toIuene/THF mixtures (4/1, v/v) at -78 ° C to produce the carboxyl-functionalized polystyrene (Ain = 2.4 X 14.6 X lO gmoh ) in quantitative yield after acid hydrolysis as shown in eqn [42]. Quantitative formation of the oxazolyl-ftmctionalized polystyrene was determined by elemental analysis of the polymer. 

In the breakdown of the intermediate, the water bound to Ce(IV) functions as acid catalyst. With this catalysis, the alkoxide ion of 5 -OH can be promptly removed from the phosphorus atom. Otherwise, the leaving group is poor and hard to be removed. Consistently, the DNA hydrolysis by Ce(IV) is accompanied by a notable D2O solvent isotope effect ( 20/ 20 = 2.2-2.4). The proton transfer is, at least partially, rate limiting. The large coordination-number of the Ce(IV) ions in the bimetallic cluster is favorable for this acid catalysis, exactly as described above for the first step of DNA hydrolysis (formation of the pentacoordinated intermediate). This mechanism is proposed on the basis of the kinetic analysis in acidic solutions. When DNA hydrolysis is carried out at around pH 7, similar acid-base cooperation by Ce(IV)-bound water molecule and the corresponding hydroxide should occur in higher aggregates of [Ce 2(OH)4] +. 

West, K.A. and Crabb, J.W 1990 Performance evaluation automatic hydrolysis and PTC amino acid analysis. In Vallafraca, J.J., ed.. Current Research in Protein Chemistry Techniques, Structure, and Function. San Diego, Academic Press 37-48. 

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