Histidine hydrochloride

Very recently, Nakajima and Okawa 164) investigated the hydrolysis of PNPA by Cyclo-(His-Glu-Cys-D-Phe-Gly)2. The second-order rate constant for the hydrolysis at pH 7.73 and 25 C was 19.61 M min for the cyclic decapeptide diacetate, which wt(s larger than 6.05 min for the corresponding linear pentapeptide triacetate and 1.33 M min for histidine hydrochloride, but smaller than 32.20 M min for cystein hydrochloride. The pH-rate profile for the reaction catalyzed by the cyclic decapeptide was bell-shaped with the maximum around pH 7.6, which indicates that the cyclic decapeptide is an acid—bs catalyst. On the other hand, the reaction by the cyclic decapeptide obeyed the Michaelis-Menten kinetics (i57), wdiich was found to involve a weak binding of the substrate = 2.7xlO M) prior to the unimolecular step. It is possible for imidazole, carboxyl, and thiol functions to cooperate in the cat ysis by the cyclic decapeptide, but the determination of the solution conformation would not be an easy task because of the thirty mem-bered ring. 

L-histidin-Hydrobromid XV/2, 400 -L-histidin-Hydrochlorid XV/2, 399 -L-hydroxy-prolin XV/2, 402 -insulin-B-Kette (geschiitztes) XV/1, 809... 

Rollctt. Acta Cryst. 9, 655-62 (1956). Crystal structure histidine hydrochloride monohydrate. 

Values of molar Kerr constants and dipole moments of nitrogen azoles and their complexes with phenols have been obtained. " These complexes are formed by an intermolecular hydrogen bond between the pyridine-type nitrogen of the azole and the phenolic proton. " The use of dipole moments in conformational studies has shown that A-aryl- and C-aryl- and A-furyl- and C-furyl imidazoles (and benzimidazoles) are nonplanar, but l-(a-furyl)-4,5-diphenylimidazoles do have a planar bicyclic fragment. The dipole moments and conformations of azolides (A-acylazoles) have been studied. In the 1-arylimidazoles the dipole is toward the aryl group. In 4,5-di-t-butylimidazole the molecule is essentially planar, but the C-4—C-5 bond is slightly stretched. Among other imidazole derivatives which have been studied by X-ray are histidine hydrochloride, 4-acetyl-amino - 2 - bromo - 5 - isopropyl -1 - methylimidazole, 4- acetyl - 5 - methyl - 2 -phenylimidazole, and imidazole-4-acetic acid hydrochloride. 

Studies of crystal structure have been made for imidazole the results from a low-temperature study are illustrated in Fig. 1. In 4,5-di-t-butylimidazole the ring dimensions are essentially similar, although the 4,5-bond is slightly stretched. Among derivatives of imidazole which have been examined are histidine hydrochloride, 4-acetylamino-2-bromo-5-isopropyl-l-methylimidazole, 4-acetyl-5-methyl-2-phenylimid-azole, imidazole-4-acetic acid hydrochloride, imidazole imidazolium... 

Properties Colorless crystals. DL-histidine, mp 285-286C with decomposition D(+)-histidine, mp 287-288C l(—)-histidine, mp 277C with decomposition. Soluble in water insoluble in alcohol and ether. Shows optical activity. Available commercially as L(+)-histidine hydrochloride and as the free base. 

Fig. 6-25. Analysis of Sr-90 with the aid of a radioactivity monitor. - Separator column IonPac CS2 eluent 0.03 mol/L HC1 + 0.002 mol/L histidine hydrochloride flow rate 1.5 mL/min detection scintillation measurement for Sr-90 injection volume 50 pL solute concentration 76.4 Bq Sr-90 with inactive SrCl2 as the carrier.

Fig. 23. The results of the 2H DQ OMAS experiment on a sample of deuterated l-histidine hydrochloride monohydrate.33 (a) The projection in the DQ dimension of the experiment (/j). (b) The associated scaled 2H quadrupole powder patterns arising in f2.

The amino acid histidine is used as a bulking agent for lyophilization and can additionally serve as a buffer (histidine/histidine hydrochloride) and stabilizer in the formulation (Nema et al., 2002). Histidine is a rather efficient quencher of singlet oxygen and a scavenger of hydroxyl radicals (Halliwell and Gutteridge, 1985). Thus, the presence of histidine in the parenteral formulation can be very important for the photochemical stability of the product. 

Acids were measured by conductmetric titration (21) and isotacho-phoresis analysis. An aqueous solution of 0.01M glutamic acid was used as a terminal solution and an aqueous solution containing 0.01M L-histi-dine and 0.01M L-histidine hydrochloride was used as a leading solution. 

Since l-n-dodecyl-3-(hydroxyiminomethyl)pyridinium iodide was indicated to be a more effective nucleophilic reagent for the hydrolysis of organophosphorus compounds, it was examined in addition to 2-PAM, 2-PAD, histidine hydrochloride, and succinyl choline as possible coatings (55,56). Among these, 3-PAD was found to be the best coating for compounds with the G agent structure, and histidine hydrochloride for compounds of the malathion type. Table 3. 

L-histidine hydrochloride coating. No serious interference from inorganic gases were observed with the ternary mixture coating except from so2 due to its reactivity with NaOH. 

Histidine hydrochloride (2 g.) is suspended in concentrated hydrochloric acid and slowly treated with silver nitrite (3 g.). After removal of excess nitrous acid and silver chloride, the liquid is concentrated to a sirup, which is taken up in alcohol, treated with an excess of alcoholic trimethylamine solution, and kept at 80° for 8 hours. After removal of the alcohol the product is precipitated with phosphotungstic acid. The phosphotungstate is decomposed with barium hydroxide in the usual manner, and the solution of the base thus obtained is strongly concentrated to remove trimethylamine, treated with hydrochloric acid, and the resulting chloride is taken up in alcohol and precipitated with chloroplatinic acid. It is finally converted into the chloroaurate, m.p. 183° with decomposition (14). 

In chiral systems, the racemic compound and the enantiomer usually undergo different degrees of solvation under given conditions. There are many examples of a change of the degree of solvation as a result of a change in the nature of the racemate [13], For example, enantiomeric histidine hydrochloride forms a monohydrate when crystallized from water, whereas racemic histidine hydrochloride forms a dihydrate. The racemic dihydrate transforms to the conglomerate monohydrate above 45°C [34]. 

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