REACTIVE SPECIES - Oxidation of Amino Acids, Peptides, and Proteins: Kinetics and Mechanism - page 29

such as trihalomethane and haloacetic acids, are produced than in chlorine-
treated water [300]. Similar to chlorination, chloramination also produces
haloacetonitriles and haloketones, which include dichloroacetonitrile, trichlo-
roacetonitrile, and 1,1,1,-trichloro-2-propanone [300]. Other disinfectants,
ClO 2 and O 3 , are also applied as water treatments. Both disinfectants have
high reactivities with amino acids and proteins (Chapters 3 and 4). The use of
ClO 2 is beneficial in minimizing the formation of trihalomethanes, but ClO 2
itself reduces to ClO − and ClO − , which may cause hemolytic anemia and
other health effects. Ozone is an efficient disinfectant, but it may react with
Br − in water to produce the carcinogenic bromate ion. Mn(VII) and Fe(VI)
are other alternate disinfectants [306] and their reactions with amino acids,
peptides, and proteins are presented in Chapter 6.
N -Nitrosodimethylamine (NDMA) is also of considerable concern as an
environmental contaminant and has been detected in air, beverages, food
products, and water [307-309]. NDMA is classified as a “probable human
carcinogen” by the International Agency for Research on Cancer (IARC). A
number of studies have shown that both chlorination and chloramination
produce NDMA [310-312]. Ozonation has also been shown to result in the
production of NDMA [313, 314]. The formation of NDMA in water usually
occurs from the reaction of disinfectants (ClO 2 , O 3 , • OH, Mn(VII), and Fe(VI))
with nitrogen-containing precursors such as dimethylamine, tertiary amines,
amine-containing polymers, and dimethylsulfamide [315]. The destruction of
NDMA can be accomplished by oxidation, which include electrochemical,
photolytic, photocatalytic, and chemical methods [315].

1.4.3 Oxidation Processes for Purifying Water

Oxidation processes using H 2 O 2 , ozone, the Fenton reaction, electron beam
radiation, and ultrasound have been applied to degrade recalcitrant and
emerging contaminants in water [316-318]. Generally, oxidation processes
involve the formation of • OH, which reacts nonselectively with organics (see
Chapter 4) [319, 320]. The reactions of O 3 with organics are selective (see
Chapter 4). Generation of • OH to oxidize compounds can also be achieved by
applying UV/TiO 2 , UV/H 2 O 2 , TiO 2 -photocatalyzed, photoassisted Fenton, and
electro-Fenton systems [291, 321, 322]. In recent years, studies have focused
on photocatalysts under visible light to produce • OH [322-324]. Sulfate radi-
cals have also received attention in oxidation processes to destroy refractory
organic contaminants, pharmaceutical and personal care products [222, 325-
327]. More details on • OH and SO •− are presented in Chapter 4.
Among the high-valent metals, ferrate(VI) (Fe(VI), Fe O

VI 2− ) has been
shown to oxidize a number of inorganic and organic compounds in water
[328-330]. Oxidations carried out by Fe(VI) are completed in shorter time
periods than oxidations performed by Mn(VII) and Cr(VI) [331]. More details
of the chemistry of high-valent compounds of iron, manganese, and chromium
and their role in oxidizing organic compounds including amino acids and