Ureas acidity

Alkylphenols, ammonia, asbestos, chlorinated paraffins, 4-chloroaniline, cyanide, detergents, di- -butyl phthalate, polyaromatic hydrocarbons (PAHs e.g. anthracene, benzopyrene, methylcholanthrene, /i-naphthoflavone), nitrate, nitrite, petroleum oil, phenol, pentachlorophenol, 4-nitrophenol, dinitro-o-cresol, polychlorinated biphenyls (PCBs especially coplanar), polychlorinated dioxins, polybrominated naphthalenes, /i-sitosterol, sulfide, thiourea, urea, acid water, coal dust... 

D. The Same Long-Range Structure in States Denatured by Urea, Acid,... 

The availability of different types of amino groups allows a variety of reactions typical for amines which are suitable for the derivatization of PEI. Reaction partners can be aldehydes, ketones, alkyl halides, isocyanates and thioisocyanates, epoxides, cyanamides, guanides, ureas, acids, and anhydrides. The synthesis and chemical modification reactions of PEI will be discussed in the next sections. 

Ni(II) in 74] that contribute to the polarization of the substrate molecule. Those interactions may also modulate the piCa of the urea upon coordination to avoid its premature deprotonation While O coordinated urea has almost the same piCa as the free molecule ( 14) (89, 90), N coordination was shown to dramatically increase urea acidity (down to p fa = 2-6 in aqueous solution cf. Section 111.A) (87). This result should be even more pronounced in the pi 3-N,0 mode. Even if one considers the relatively lower polarizing power of Ni(II) compared to the metals used in those studies, deprotonation is still likely to occur upon bidentate substrate under conditions optimal for urease (pH 4-8) if modulating interactions are not present. In that sense, model systems currently available are not mature yet. In view of these considerations, it may not be surprising that none of the model complexes mediates the direct hydrolytic degradation of parent urea. 

Serum albumin and ovalbumin A-Spectra with urea, acid A-spec-tral rate studies with urea de-naturation Glazer et al. (1957)... 

No.C Acid Ratio urea acid Dissoc. temp. 

The effect of chemicals is more complex and depends on the denaturant (guanidinium chloride, urea, acids). In this case, we have to deal with an additional component to the protein. For example, acids break salt bridges of protein while urea contributes to break H-bonds and P-mercaptoethanol and dithiotreitol reduce S-S bonds. (For a review see reference )... 

Preparation of polyquinazolinediones by the reaction of diisocyanates with bisanthranilic acids and subsequent cyclization of the poly(urea acids) [49]. 

Amides Acyl ureas Acids/bases Active-H... 

Reversed phase Hydro-organic mixtures Organic modifiers acetonitrile, methanol, etc. Solvents, glycols, urea, acidic solutions... 

There are few reports about the modifications of the protein induced by the coupling. Sulfonamido conjugates of ovalbumin (Weber, 1952b) have a solubility at the isoelectric point similar to that of the native protein and become insoluble after denaturation by heat, urea, acid, or alkali. Fumarase conjugates of the same type (Massey, 1953b) have 80% of the original catalytic activity after introduction of 5 groups/mole, and... 

For the identification of substituted ureas acid hydrolysis is employed, and the formed amine or amines are identified by their conversion to a suitable derivative or by paper chromatography. 

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