Light regime, riboflavin, and pH effects on 2,4-D photodegradation in water

Abstract

A laboratory study was conducted to determine the effects of light regime, riboflavin, and pH on photodegradation of 2,4-D in aqueous solution. In controlled-environment chamber experiments, riboflavin sensitized 2,4-D photolysis in a concentration-dependent manner under both attenuated UV (-UV) and enhanced UV (+UV) light regimes. The photolysis half-life of 2,4-D in solutions containing 10 mg L-1 riboflavin was 9.7 and 12.5 h when exposed to +UV and -UV, respectively, compared to no photolysis in the absence of riboflavin. In contrast, the extrapolated half-life of 2,4-D in solutions containing 2.5 mg L-1 riboflavin was 46 h under +UV and 72 h under -UV. The rate of 2,4-D photolysis in the presence of riboflavin increased under both light regimes as initial pH of the solution was decreased from 7.5 to 4.5. The half-life of 2,4-D in the presence of 10 mg L-1 riboflavin at pH 4.5 and exposed to +UV was 1.6 h. Lumichrome, a principal photoproduct of riboflavin, did not photosensitize 2,4-D. Concentrations of 2,4-dichlorophenol formed as a result of riboflavin-sensitized 2,4-D photolysis were higher under the -UV than the +UV regime. These results indicate that riboflavin concentration, solution pH, and light regime are interacting factors that may be manipulated to enhance rates of aqueous 2,4-D photolysis.

Photophysics of alloxazines on cellulose

“…6 A further point of interest is the possibility of using alloxazines to sensitise the photooxidation of substituted phenols in water. 7,8 The lumichrome-sensitised photodecomposition of substituted phenols has been found to be very efficient, with photolysis rates that may be ordered as p-methoxyphenol > pchlorophenol > phenol > p-nitrophenol. 7 The singlet oxygenproducing capacity of lumichrome in water was examined under UVA.…”

Photolytic degradation of 2,4-D onZea maysleaves

“…Levels of 3H-riboflavin on Z mays leaves decreased to 100/0 or less of the nonabsorbed 3H under both light regimes~10 h exposure. Previous work has shown that lumichrome does not photosensitize 2,4-D (Harrison and Venkatesh 1999), so it appears that another compound or other compounds continued to promote 14C_ 2,4-D photolysis after riboflavin was photodegraded. No 3H-riboflavin was detected in the absorbed 3H fraction in any of the treatments.…”

“…Riboflavin-enhanced losses of total 14C and 14C-2,4-D from the Z. mays leaf surface were attributed to riboflavinsensitized photolysis of 14C-2,4-D residues in the nonab-' sorbed fraction. Volatilization or subsequent metabolic decarboxylation of absorbed 14C ,r,hotoproducts may account for some of the loss of total 1 C. Based on previous work (Harrison and Venkatesh 1999), we hypothesized that riboflavin would photosensitize solid-phase 14C-2,4-D residues and that supplemental W would enhance this process.…”

“…Total 3H in the nonabsorbed fraction of 14C-2,4-D + 3H-riboflavin treatments exposed to light ranged from 62 to 80 0 /0 of that recovered and decreased at the same rate in the +UV and -UV light regimes (Table 2). Parent 3H-riboflavin remaining in the nonabsorbed 3H fraction following 3 h exposure to +UV was 320/0 compared to 700/0 in plants exposed to -Ã lthough a potent sensitizer, riboflavin itself is photolabile over a range of wavelengths and undergoes rapid and pHdependent photolysis in aqueous solution, yielding lumichrome as a principal photoproduct (Halwer 1951;Harrison and Venkatesh 1999). Levels of 3H-riboflavin on Z mays leaves decreased to 100/0 or less of the nonabsorbed 3H under both light regimes~10 h exposure.…”

New Insights into the Nature of Co‐components and Their Impact on Pd Structure: X‐ray Absorption Studies on Toluene Acetoxylation Catalysts

“…51 Riboflavin was suggested as a sensitizer in the photodegradation of pollutants such as pesticides, herbicides, toluene, and phenol derivatives in open basins of fresh water 2. 3, 52–55 Flavins are also used as catalysts in organic synthesis for the oxidation of amines and sulfides with significant selectivity and efficiency, applying mild oxidation conditions 56. 57 Flavin hydroperoxides, especially 4α‐hydroperoxyflavins, a simplified model structure of flavoenzyme, arouse the interest of investigators thanks to their structural features and unique reactivity.…”