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Physical & Chemical properties

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Lysozyme is commonly used as hydrochloride; it is a white odourless microcrystalline powder with a somewhat sweet taste (Barbara and Pellegrini, 1976). Crystalline lysozyme hydrochloride has the form of first-order tetragonal bipyramidal plates (Jones, 1946); however at pH 9.5 in the presence of moisture, the crystals are assigned to the orthorhombic system. Depending on the pH conditions, lysozyme can polymerize (Barbara and Pellegrini, 1976).

PHYSICAL STATE

Lysozyme hydrochloride is a solid, odourless, organic white crystal at 20 °C and 1013 hPa and it is commercialized both as granular and liquid form, depending on the final application and on Customers’ preferences.

The substance decomposed when heated and the mean decomposition point was determined according to the capillary method at 208 °C; thus lysozyme hydrochloride does not melt and boil. The determination of vapour pressure of the lysozyme hydrochloride was performed by static procedure and was recorded at 147 Pa (1.1 torr).

The density determination was performed in triplicate at 20 °C, using the glass pycnometer and the estimated value resulted 0.988 g/ml.

ENZYME STABILITY CONDITIONS

Enzymes are proteins characterized by special reactions. Enzymes can be coagulated by heat, alcohol, strong acids, and alkaline reagents.

The speed of all chemical reactions is affected by temperature: the higher the temperature, the faster the rate of the reaction. This is also true for reactions involving enzymes; however, if the temperature is raised too much, the enzyme will be inactivated by denaturation and will be unable to function. The best temperature for enzyme function, i.e. the temperature at which the rate of a reaction involving an enzyme is the greatest, is called the optimum temperature for that particular enzyme. At higher temperatures, the enzyme will coagulate and will be unable to function. At temperatures below the optimum temperature, the rate of reaction will be slower than the maximum rate. Because many enzymes have an optimum temperature near 40 °C, or close to that of body temperature, they function at maximum efficiency in the body.

Another relevant parameter that may influence the enzyme activity is the pH: each enzyme has a pH range within which it can best function. This is called the optimum pH range for that particular enzyme. If the pH of a substrate is too far from the optimum pH required by the enzyme, that enzyme cannot function at all. However, since body fluids contain buffers, the pH usually does not vary too far from the optimum values.

SOLUBILITY, pH and PARTITION COEFFICIENT

The determination of the water solubility of the test item was performed by the shake flask method, according to the OPPTS 830.7840 guideline. The mean measured water solubility and standard deviation of the test item was determined to be 285 ± 5.22 g/l at 20 °C and pH 4.

Lysozyme is soluble in water (1 : 5), but insoluble in common organic solvents and concentrated salt solutions (Barbara and Pellegrini, 1976).

The pH of a 1 % (w/w) solution of the lysozyme hydrochloride was tested. The temperature for pH determination was maintained at 22 ± 1 °C and readings were taken until three consecutive values for each determination. 1 % by weight solution in ASTM Type II water yielded a mean pH of 3.64.

Furthermore, available literature data report that a 2 % hydrochloride solution has a pH of 3.3 (± 0.3) (Barbara and Pellegrini, 1976).

The determination of the n-Octanol / Water partition coefficient was performed according to the shake-flask method. Analysis of the n-octanol-saturated purified reagent water phase showed almost 96 % of the test substance remaining in the water phase. This was similar to the recovery of test substance from a sample of the prepared stock solution. Analysis of the n-octanol phase produced chromatograms with a peak that was less than the limit of quantification. With almost 96 % of the test substance in the water phase and n-octanol phase below the limit of quantification, the partition coefficient of test substance was empirically estimated to be less than 0.01. Based on these preliminary results, no further test was required.

AUTO FLAMMABILITY/FLAMMABILITY/EXPLOSIVENESS/OXIDISING PROPERTIES

In the pure form, enzymes are solids at room temperature and through a wide range of ambient temperatures, and therefore this parameter is not relevant. The flash point is only a relevant property for liquids, thus it does not need to be measured for substances that are solids or gases at room temperature.

Enzymes are proteins and do not possess the ability to ignite themselves. Furthermore, enzymes are easily soluble in water and from experience of handling together with consideration of the structure it can be concluded that enzymes are not flammable on contact with water. As they are proteins produced by fermentations or extracted for subsequent uses, i.e. usually in solution, enzymes are not pyrophoric and they are not associated with explosive properties. The minimum ignition energy (MIE, capacitive spark) of lysozyme hydrochloride lies between 300 and 1000 mJ. The maximum explosion pressure and the Kst-value (which describe the explosion behaviour of a combustible dust in a closed system) were also investigated and the result showed that Lysozyme powder is low reactive and it may generate explosions of moderate strength.

As for all other proteins the oxidising potential is not relevant for enzymes, except for oxidases that may catalyze oxidation reactions, given that the proper substrate and physic-chemical conditions are present. Since lysozyme is not an oxidase, this property does not apply.

In conclusion, the substance does not meet the criteria to be classified as auto flammable/flammable/explosive/oxidising.

REFERENCE

Barbara L. and Pellegrini R. (1975). Fleming's Lysozyme : biological significance and therapeutic applications. Torino : Minerva medica, 1976. Monograph.

Jones F.T. (1946). Optical and crystallographic properties of lysozyme. J. Am. Chem. 68, 854, 1946.