C h a p t e r 11
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Photodecomposition of Naturally Occurring Biocides Y. Yoke Marchant ARCO Plant Cell Research Institute, 6560 Trinity Court, Dublin, CA 94568
Light-activated biocides include a wide range o f naturally occurring compounds from plants as well as some synthetic dye molecules. These chemicals are active against microorganisms, insects and nematodes, as well as s n a i l s and f i s h in v i t r o . Many are p o t e n t i a l l y useful as commercial pesticides, a property p a r t i c u l a r l y enhanced by evidence of rapid biodegradability in the environment. The mechanisms of photodegradation and the factors which influence t h i s process w i l l be discussed in t h i s review.
Many k i n d s o f compounds have been r e p o r t e d t o be t o x i c t o b i o l o g i c a l systems i n the presence o f l i g h t under a e r o b i c and a n a e r o b i c conditions. In photodynamic r e a c t i o n s the p h o t o n - e x c i t e d s e n s i t i z e r m o l e c u l e t r a n s f e r s i t s e x c i t a t i o n energy t o oxygen, g e n e r a t i n g t h e s i n g l e t s t a t e which may s u b s e q u e n t l y r e a c t w i t h p h o s p h o l i p i d s , p r o t e i n s and s t e r o l s o f c e l l u l a r membranes. A s t r u c t u r a l l y d i v e r s e group o f p h y t o c h e m i c a l s i s o l a t e d from p l a n t s has been r e p o r t e d t o e x h i b i t b i o c i d a l a c t i v i t y towards v i r u s e s , b a c t e r i a , f u n g i , nematodes and i n s e c t s i n the presence o f s u n l i g h t o r UV-A r a d i a t i o n (320-400nm) (±zD- Such compounds i n c l u d e v a r i o u s a l k a l o i d s ( 5 . 6 ) , acetophenones ( J ) , extended a n t h r a q u i n o n e s ( 4 ) , f u r a n o c o u m a r i n s furochromones ( 1 0 ) , s t r a i g h t - c h a i n and a r o m a t i c p o l y a c e t y l enes, and t h i o p h e n e s ( e . g . 11-15). In a d d i t i o n , s y n t h e t i c xanthene dyes such a s r o s e bengal a r e w e l l known p h o t o a c t i v e p e s t i c i d e s and f i s h p o i s o n s (16-20). R e p r e s e n t a t i v e examples o f these compounds a r e shown i n F i g u r e s 1 and 2. In the s e a r c h f o r e f f e c t i v e and e n v i r o n m e n t a l l y n o n t o x i c b i o l o g i c a l c o n t r o l a g e n t s , the b i o d e g r a d a b i l i t y o f a c t i v e compounds i s an e s s e n t i a l p r a c t i c a l c o n s i d e r a t i o n . A p e s t i c i d e o r f u n g i c i d e which has performed i t s f u n c t i o n s h o u l d s u b s e q u e n t l y decompose i n t o m o i e t i e s which have no l o n g term e f f e c t s on the environment. S i n c e t h i s i s a symposium on l i g h t - a c t i v a t e d p e s t i c i d e s , t h i s d i s c u s s i o n a d d r e s s e s the i s s u e s o f l i g h t s t a b i l i t y and p h o t o d e g r a d a t i o n o f n a t u r a l l y - o c c u r r i n g b i o c i d e s , p a r t i c u l a r l y p h o t o a c t i v e ones, w i t h
0097-6156/87/0339-0168$06.00/0 © 1987 American Chemical Society
In Light-Activated Pesticides; Heitz, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
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MARCHANT
Photodecomposition of Naturally Occurring Biocides
IX
CH -CH»CH-(C«C) -(CH=CH) (CH ) 3
2
2
2
4
CH-CH
2
X
F i g u r e 1. N a t u r a l l y o c c u r r i n g p h o t o a c t i v e compounds. I . Dictamnine (Dictamnus a l b a ) I I . H y p e r i c i n (Hypericum s p p . ) , I I I . 8-Methoxypsoralen (Rutaceae, A p i a c e a e ) , IV. K h e l l i n (Ammi s p p . ) , V. Harman, V I . 6-Methoxyeuparin ( E n c e l i a s p p . ) , V I I . A l p h a - t e r t h i e n y l (Tagetes s p p . ) V I I I . P h e n y l h e p t a d i y n e ene ( B i d e n s s p p . ) , IX. P h e n y l h e p t a t r i y n e ( B i d e n s s p p . ) , X. Heptadeca t e t r a e n e d i y n e ( B i d e n s s p p . ) . t
t
In Light-Activated Pesticides; Heitz, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Downloaded by UNIV OF TENNESSEE KNOXVILLE on November 23, 2015 | http://pubs.acs.org Publication Date: May 7, 1987 | doi: 10.1021/bk-1987-0339.ch011
LIGHT-ACTIVATED PESTICIDES
B = CI Br, B = CI
A=I, A =
A=I,
A=
B=H
Br, B B
A= H,
XI XH
xm
=H
JN
= H
XV
F i g u r e 2. S y n t h e t i c xanthene dyes. X I . Rose B e n g a l , X I I . P h l o x i n B, X I I I . E r y t h r o s i n B, XIV. E o s i n Y e l l o w , XV. Fluorescein.
In Light-Activated Pesticides; Heitz, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
11.
MARCHANT
Photodecomposition of Naturally Occurring Biocides
171
r e f e r e n c e t o t h e work on t h e p h o t o d e c o m p o s i t i o n o f t h e h a l o g e n a t e d xanthene dyes.
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Degradation o f Non-photoactive Natural
Pesticides
Many h e r b i c i d e s and p e s t i c i d e s i n t h e environment a r e degraded by UV r a d i a t i o n from the s u n . The exposure o f a z a d i r a c h t i n s o l u t i o n s t o s u n l i g h t caused a r a p i d d e c r e a s e i n a n t i f e e d i n g potency a g a i n s t f i r s t i n s t a r l a r v a e o f Spodoptera f r u g i p e r d a ( J . E. Smith) and r e s u l t e d i n complete d e s t r u c t i o n o f t h e compound and i t s a c t i v i t y a f t e r 16 days. HPLC a n a l y s e s o f t h e exposed s o l u t i o n s showed no t r a c e s o f a z a d i r a c h t i n ( 2 1 ) . The a d d i t i o n o f v a r i o u s p l a n t o i l s , such as neem and c a s t o r , t o t h e t e s t s o l u t i o n s a f f o r d e d some p r o t e c t i o n (
