SPECTRA OF CRYSTALLINE AND COLLOIDAL PIGMENTS 



1825 



sional crystals (mesophases) of isocyanin and similar dyes (chapter 32, 

 section 5, c/. fig. 32.7), where an electronic excitation, polarized in the 

 direction of the thread, is practically uncoupled from molecular vibrations, 

 and rapidly sweeps through the whole thread; the absorption band is in 

 this case extremely narrow, and exhibits intense resonance fluorescence. 



Krasnovsky and Brin (1948) measured the absorption spectra of a 

 number of colloidal preparations and adsorbates of chlorophyll (a + 6?) 

 and also observed their fluorescence and photochemical activity, the latter 

 "mostly" by determination of chlorophyll-sensitized autoxidation of 

 ascorbic acid ("Krasnovsky reaction," cf. chapter 35). The results did not 



Table 37C.IIIB 

 Transmission Minima, Fluorescence and Photochemical Activity of Chloro- 

 phyll (a -f- 6?) Colloids and Adsorbates (after Krasnovsky and Brin 1948) 



State ^m&x • '"'' Fluorescence "Activity" 



/. True solutions, in: 



(a) Low-molecular org. solvents 660-670 -\- + + Active 



(b) Fatty acids, oils, lecithin, aq. 



emulsions of lipoids 668-670 -f 4- + 



2. Colloidal solutions, obtained by : 



(a) Dilution of ale. with water 670 — Inactive 



(b) Dilution of ale. with aq. deter- 

 gents 668-670 + + + Active 



(c) As (a), but coagulated by elec- 

 trolytes 670-690" - Inactive 



3. Adsorbates on: 



(a) Paraffin, palmitic acid, MgO 668-670 -|--1- Not measured 



(b) Al.,03, Ti02, ZnO, Si02 668-670 



(c) Ale. -sol. proteins (zein, glia- 

 din); obtained in colloidal 

 solution, by diluting ale. solns. 

 of chlorophyll and protein bv 



water \ 668-670 - Inactive 



(d) Other proteins (egg albumen, 



keratin, fibroin, edestin). 670 - Not measured 



(e) As (c), but obtained by dilu- 

 tion with aq. detergents 668-670 -|- + + Active 



4. Films left, after evaporation on 



glass or filter paper 670 — Not measured 



5. Leaves 



(a) Living leaves, chloroplasts, 



grana 677-678 + Low sensitizing 



activity 



(b) Leaves killed by boihng 670 -|- '' 



(c) Leaves killed by freezing in 



liquid air 678 + 



(d) Chloroplasts and grana in aq. 



detergents 668-670 + + + Active 



" Depending on degree of coagulation; shift may be due, at least in part, to scatter- 

 ing. 



