Biuret preparation

C2H4N2O3, NH2CONHCOOH. Unknown in the free state as it breaks down immediately to urea and COi- The NH4, Ba, Ca, K and Na salts are known and are prepared by treating ethyl allophanate with the appropriate hydroxide. The esters with alcohols and phenols are crystalline solids, sparingly soluble in water and alcohol. They are formed by passing cyanic acid into alcohols or a solution of an alcohol or phenol in benzene. The amide of allophanic acid is biuret. Alcohols are sometimes isolated and identified by means of their allophanates. 

Urea processes provide an aqueous solution containing 70—87% urea. This solution can be used directiy for nitrogen-fertilizer suspensions or solutions such as urea—ammonium nitrate solution, which has grown ia popularity recentiy (18). Urea solution can be concentrated by evaporation or crystallization for the preparation of granular compound fertilizers and other products. Concentrated urea is sohdified ia essentially pure form as prills, granules, flakes, or crystals. SoHd urea can be shipped, stored, distributed, and used mote economically than ia solution. Furthermore, ia the soHd form, urea is more stable and biuret formation less likely. 

Cyanuric acid can also be prepared by pyrolysis of urea derivatives. Biuret and triuret give less aminotria ines due to reduced ammonia evolution. Urea cyanurate also provides a higher assay product. 

The common method of preparation of 6-alkyl-2,4-dioxotetrahydro-triazines is the cyclization of acyl-biurets by aqueous hydroxide. Formyl biuret which should by analogy 3deld 5-azauracil had not been known until recently. Its transient formation can be expected during further synthesis of 5-azauracil. Piskala and GuP achieved... 

Final structure determination of the monomethyl derivatives was made possible only on performing straightforward syntheses of the compounds, analogous to syntheses of allantoxaidine. The 1-methyl (19) and 3-methyl (20) derivatives were prepared by cyclization of 1- and 3-methyl biuret,respectively. The 3-methyl derivative was also obtained by cyclization of A ,A -bis(methylcarbamyl)formami-dxne. The 1-methyl derivative was the same as the product obtained by Biltz on methylation of silver salt of allantoxaidine with methyl iodide. The same product is formed primarily during methylation of dioxotriazine with diazomethane. An excess of this agent produces the expected 1,3-dimethyl derivative (21). These results of alkyl-... 

From these, prepolymers are prepared where the diisocyanates may be completely reacted as in the case of the urethane oils which resemble the oil-modified alkyds but have urethane (—NHCOO—) links in place of the ester (—COO—) links of the alkyds, or where one only of the isocyanate groups is combined, leaving the other to participate in crosslinking reactions. Such a reactive prepolymer is the biuret that may be prepared from hexamethylene diisocyanate, has the following structure ... 

Both pigmented and unpigmented polyurethane paints have been prepared using a polyester resin containing hydroxyl functional groups and the biuret trlmer of hexamethylenedllsocyanate as a crosslinker. The molar ratio of hydroxyl/isocyanate has been chosen 1.0 and the pig-ment/binder ratio 0.6. 

Students will isolate intact mitochondria from beef heart and fractionate them to prepare submitochondrial particles. Each fraction will be characterized by protein estimation by the biuret method and measurement of malate dehydrogenase and monoamine oxidase activity. 

Preparation of Tubes for the Biuret Protein Assay on Mitochondrial Fractions1... 

B 9. A student group completed the biuret assay on their mitochondrial preparation. Assume that the following absorbance values were obtained as described in Table E10.2. 

Many methods are available for measuring TCA-soluble peptides. Possibly the easiest is to measure the absorbance of the solution at 280 nm, as the absorbance at this wavelength is a function of the aromatic amino acid content of the solution. This approach requires a UV spectrophotometer, and the sensitivity of the assay is likely to be lower than that of some of the colorimetric assays. There are also several colorimetric peptide assays that can be applied to this type of peptidase assay, such as the Biuret, Lowry, and Bradford dye-binding methods (for comparison see Piyachomkwan and Penner, 1995). All of these methods measure a relative value rather than an absolute amount of peptide in solution. The results should thus be reported in terms of equivalents, such as BSA equivalents when using a calibration curve prepared using a BSA standard solution. 

Notes. (1) Remove about 0.25 ml of the hydrolysate, cool it and basify it with 5 m sodium hydroxide solution. To a portion add a few drops of very dilute copper(u) sulphate solution, and note the absence of any colour change. As a control, prepare a specimen of biuret (NH2-CO-NH-CO-NH2) by heating about lOmg of urea just above its melting point for about 2 minutes. Add a little basified hydrolysate warm to dissolve, cool and add a trace of copper(u) sulphate. A deep pink colour superimposed upon the pale brown colour of the hydrolysate should be observed. If the hydrolysate gives a similar colour originally, it contains peptide material and hydrolysis should be continued until the biuret test is negative. 

In the preparation of a prepolymer, every effort is made to prevent the formation of any unplanned branching such as biuret groups. The prepolymer is essentially linear except when some cross-link sites have been introduced by using a multifunctional isocyanate or triol. 

A modified method for preparing chlorobiuret sodium salt from biuret using chlorine gas and aqueous sodium hydroxide solution is described by the author. 

Mix the contents thoroughly and transfer them to a plastic bottle. 2-6. The biuret reagent just prepared should be a deep royal blue. This solution may be stored indefinitely. If a black precipitate is observed in the storage container, however, discard the solution and prepare a fresh solution. 

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