Light stabilizing activity, test

Before hand testing of light stabilizing activity of DTIU while introducing it into a polymer as mechanical additive was carried out. Data of Table 24 show that DTIU possesses photostabilizing activity that gives the reason to consider the fact that its condensation with CDA will improve light fastness of the latter. 

As shown in Table I, these stable radicals showed strikingly higher light stabilization activity in polypropylene than that of the UV absorber tested. We felt that their activity was related to their radical scavenging ability. This hypothesis is supported by the observation that the coupled products (32) and (33) were obtained by the reaction of the nitroxyl radicals (2) and (27), respectively, with a C-radical derived from AIBN (10). The radical scavenging ability of the stable nitroxyl radicals is now well known to play a major role in the mechanism of light stabilization by hindered amine compounds (13). 

Synthesis and Stabilizing Activity of Hindered Amines. As mentioned previously, the hindered piperidine compounds showed excellent light-stabilizing activity in polypropylene. In order to find more efficient compounds, various derivatives of 2,2,6,6-tetramethyl-4-oxopi-peridine (42) were synthesized and tested. In this section we describe some typical examples from the great number of derivatives prepared in our laboratory. 

The light-stabilization activity of several esters was tested by an improved test method (25). This method was carried out as follows (i) Preparation of the test specimen. A mixture of 100 parts... 

Tests of the light stabilizing activity of monomeric HAS and the corresponding homo- and copolymers reveal mostly better properties of the monomers if physical persistence is not the decisive testing factor [8]. This was found e.g. in comparison of the functionalized urethane 182 and its copolymers with styrene or methyl methacrylate [303], The macromolecular architecture is expressed very distinctly. For example, a PP photografted HAS-functionalized acrylate was more efficient than the respective monomer or homopolymer. Another observation performed with A-(2,2,6,6-tetramethyl-4-piperidyl)methacry-lamide, piperidyl acrylate and methacrylate, their homopolymers and copolymers with dodecyl methacrylate and octadecyl acrylate revealed that the stabilizing effect in PP was in favour of copolymers [304]. Similar HAS-functionalized monomers were copolymerized with styrene. In this case, the copolymers were substantially less efficient in PS than the monomers. Masterbatches of PP-bound HAS prepared by reactive processing imparted a comparable effectivity as conventional HAS when tested at an equimolar basis [298]. 

Fig. 4.3.1 Effect of pH on the total light emission of phialidin (A), and the temperature stability profiles of phialidin (minute open circles) and aequorin (solid line) (B). In A, each buffer contained 0.1 M CaCl2 plus 0.1 M Tris, glycine or sodium acetate, the pH being adjusted with NaOH or HC1. In B, the photoprotein samples in 10 mM Tris-EDTA buffer solution, pH 8.0, were maintained at a test temperature for 10 min, and immediately cooled in an ice water bath. Then total luminescence activity was measured by injecting 1ml of 0.1 M CaCl2/Tris-HCl, pH 7.0, to 10 pd of the test solution. From Levine and Ward (1982), with permission from Elsevier.

Fig. 4.5.5 Effect of pH on the luminescence of coelenterazine catalyzed by Periphylla luciferases A, B and C, and on the stability of the luciferases. The effect on light intensity (solid lines) was measured in 3 ml of 50 mM phosphate buffers, pH 4.1-7.25, and 50 mM Tris-HCl buffers, pH 7.1-9.7, all containing 1 M NaCl, 0.025% BSA, and 0.3 pM coelenterazine. To measure the stability (dotted lines), a luciferase sample (5 pi) was left standing for 30 min at room temperature in 0.1 ml of a buffer solution containing 1 M NaCl and 0.025% BSA and having a pH to be tested, and then luciferase activity in 10 pi of the solution was measured in 3 ml of 20 mM Tris-HCl, pH 7.8, containing 1M NaCl, 0.05% BSA, and 0.3 pM coelenterazine at 24°C. The amounts of luciferases used for measuring each point were luciferase A, 150 LU luciferases B and C, 170 LU. One LU = 5.5 x 108 quanta/s. From Shimomura etal., 2001.

Stability. Producers must state the length of the reference material s useable life, since they can be sensitive to light, humidity, microbial activity, temperature, time, etc. Long-term testing is required to validate the stability of a material under a variety of storage and transport conditions. 

Real time stability tests based upon the identity tests for the active ingredient(s), physio-chemical and biological tests nota aggregation, degradation, modifications etc.I Stability of product after reconstitution tests under stress, e.g. heat, light, humidity. 

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