CHELATION OF TRACE METALS IN NUTRIENT SOLUTIONS | Zendy

Walter W. Heck | Zendy; Lowell F. Bailey | Zendy

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CHELATION OF TRACE METALS IN NUTRIENT SOLUTIONS

Author(s) -

Walter W. Heck,

Lowell F. Bailey

Publication year - 1950

Publication title -

plant physiology

Language(s) - English

Resource type - Journals

SCImago Journal Rank - 3.554

H-Index - 312

eISSN - 1532-2548

pISSN - 0032-0889

DOI - 10.1104/pp.25.4.573

Subject(s) - chelation , salicylic acid , chemistry , sodium diethyldithiocarbamate , trace metal , nutrient , metal ions in aqueous solution , nuclear chemistry , salt (chemistry) , sodium , carbamate , metal , environmental chemistry , inorganic chemistry , biochemistry , organic chemistry

n andprecipitation havebeenusedforthispurpose insomestudies. Thesehaveprovedmore difficult andlesseffective thantheadsorption technique developed by STEINBERG (11)andimproved byARNONandSTOUT(4),inwhichheavy metals arecoprecipitated withcalcium phosphate. Inrecent yearsatten- tionhasbeencalled tothereaction ofheavymetals withcertain organic molecules toformchelate complexes whichcanberemovedfromnutrient solutions byextraction (7,8,12).Thismeansofeliminating trace metals fromnutrient solutions suggested thepossibility thatsuchchelating agents mightbeusedinnutrient solutions indirect contact withtheroots ofgrow- ingplants toprovide acontinuing control oftrace metalcontamination in thenutrient media.Thepresent studywasundertaken todetermine the effect ofchelating agents addedtonutrient solutions onplants growing in these solutions. Testsreported describe theresponses ofseedlings ofsev- eralspecies andofoldertomatoplants tosixsuchchelating compounds present innutrient solutions. A chelating agent(fromtheGreekChele, meaningclaw)usually isa complex organic molecule containing twoelectron-donating groupswhich, acting similar tothetwojawsofa claw,mayremovesimplemetalions fromsolution. Thesechelating reactions areslightly reversible, thede- greeofreversibility, characterized asthe"stability constant," depending ontheagentusedandthemetalioninvolved. Themechanism ofchelation isillustrated withthefollowing example.Oxine(fig. 1,A),8-hydroxy- quinoline (HOC6H3N: CHCH:CH),isa doubleringcompoundformed bythefusion (intheorthoposition) ofapyridine ringtoabenzene ring withthehydroxyl groupontheeighth position ofthedoubleringcom- pound.Oxineionizes toformoxinate andhydrogen ions, thehydrogen comingfromthehydroxyl group.Thechelating effect ofoxineresults whentheoxygen andnitrogen, eachacting asaclaw,jointoametalion (Zn++) thusforminga ring, called a chelate ring.Theoxygen, witha freenegative valence, formsanelectrovalent linkage withthezincion whilenitrogen formsa co-ordinate covalent bond.Thusthezincionis boundsecurely totheoxine molecule. However, thezincionhastwofree valences andforthisreason twomolecules oftheoxinearerequired to 1Contribution fromtheBotanical Laboratory, TheIUniversity ofTennessee, New

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