Radiochemical Investigation of the Kinetics of the Electron Exchange Between the Oxidation States of Tin Citation Craig, Roy Phillip (1950) Radiochemical Investigation of the Kinetics of the Electron Exchange Between the Oxidation States of Tin. Master's thesis, California Institute of Technology. doi:10.7907/4e56-hq86. https://resolver.caltech.edu/CaltechTHESIS:06162025-180659877 Abstract The kinetics of the electron exchange between Sn II and Sn IV in 10.0 f HCl have been investigated by the use of a radio-active tracer. It is found that the rate of exchange is proportional to the product of the Sn II and Sn IV concentrations. In the HCl concentration range between 9.0 f and 11.0 f, the exchange rate is found to be proportional to the 0.3 power of the HCl activity, giving the empirical rate equation R = k [Sn II ] [Sn IV ] (HCl) 0.3 Radio-active exchange experiments carried out at 0° C. and at 25.2°C. show this exchange to have an activation energy of 10.7 Kcal. per mole. The exchange is found to be homogeneous. It is found that exposure of the Sn II -Sn IV solutions to illumination from a capillary Hg arc gives a marked photochemical increase in the rate of electron exchange between the two valence states. Preliminary spectrophotometric investigations of cobalt-glycine systems also have been made. Item Type: Thesis (Master's thesis) Subject Keywords: (Chemistry) Degree Grantor: California Institute of Technology Division: Chemistry and Chemical Engineering Major Option: Chemistry Thesis Availability: Public (worldwide access) Research Advisor(s): Davidson, Norman R. Thesis Committee: Unknown, Unknown Defense Date: 1949 Funders: Funding Agency Grant Number United States Navy UNSPECIFIED Record Number: CaltechTHESIS:06162025-180659877 Persistent URL: https://resolver.caltech.edu/CaltechTHESIS:06162025-180659877 DOI: 10.7907/4e56-hq86 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 17461 Collection: CaltechTHESIS Deposited By: Benjamin Perez Deposited On: 27 Jun 2025 21:02 Last Modified: 27 Jun 2025 21:26 Thesis Files PDF - Final Version See Usage Policy. 20MB Repository Staff Only: item control page

Ra.d:ioehemical lnvest1gat ion of the K inet ies of the .Electron Exohange be1nveen the Qxida.t:l,on States of Tin Thesis by ; ' Rc.y Phillip Craig In Pali"tial Fulfi11ment of the Re quireraent e For t he Degree of Maater of So lenee California lnstitu.te of Tethnology Pasadena, California Aek.now'.l. edgement f!l 'l'he author w-isbes to ex,:rass his $/in~el't a.ppreeiat!on to Drt No:rman R• Da.vi<l•an. who su,gge,st•d this wo:rk and save Anvalu.abl.·& gtli<ian,ee th~o~ghout 4t, pertol'ma.nee. l am also indebted to the United St~tes Navy for the pt1rehaee ef materl~1a an~ tquf,pm'eat-• and for finan~iai suppo:rt during the l.at.ter pa.rt of i hi• work. The kinetic• tt the ,t leet1ton exehan- between Sall an4 tn 1Y in u,.o ! Mel b1'e btcut 1nveat1gate4 by the u.ee ot a ra410•a~t1Te tracel"• lt ia teun4 tba;t tbe rate of exohange i• proportional to the product ot the so.II an4 snlV oonct&Q• tratton•• ln the HCl oonoeati-at1an :range 'bet1rcu,1n 9.0 ! an.ct 11.0 .t. th• exchaflge rate 1• to~-., to be proport 1ottal to the 0.3 power of the RC1 act4:Ylty. gtvlng the elllpirioal rate eqlf.at1Gn l!l I k (SnlIJ CsnIV] (JIQ1) 6 •l. ltadio•activa •~change experiments earr1•4 011t at o0 c. an4 at 2;.2°0. ehow thia exchange to have an activation energy et 1<>.7 Keal. per mole, Tbe exchange ie t~n4 to be homogeneoue ♦. l\ ta found that exposure ot tht Snll.-SnlV eolU;tion• to llltunination trom a oa.p111ary Hg a.re givee a rnarke4 photo• ohemica1 inor,na.ae ln the rate or eieetron- exchange betwen th• two Valene• atatee. :Pre11m1nar7 iSpeetroph.otomet:rie investiga.t iona o.f oobal tglyoine syatema alGo hav• been mdt• Table of Q.o ntent s - :Part Titl• l IC1neties ot the .Eleot:,on Exchan~e between the OXJda.t ion Sta.tea of Tin 4;. . Xnt:roduet ion B. Experiment al c:. Dt 11 Reauilts and Conc111sions S.'JlEtC~rophotome.trie lnvestiga.t ions of Gobal tGlyc 1ne System, A. lntrodu.st ion lh, l;xper i ment al 0~ Data D• lll )a.ta References Reau.lts and Conclusions Pas_! 1 2 10 13 Rad!<:H!:hemica.1 I.nvest i gat ion of the Kinet iee of t h~ Electron Ib:~h e.J1Se bet~e.ti the Ox:!dati o:n Si a't.s s sf Tin l.n.troduct ion It has pr ev;iously been reported tha.t Snll a.nd snlV ex<:hange r~dioa.~tivity moderately s l owly in 9 acid (l)~ t. hydrochle:rio Knowl e dge of the kinetics of this e:xehl:i.nge 1hou.ld lead to a log ic al explanation et the mechani sm by whi ch it takes place ., a.nd to a bet~er understanding of oxidat i on Th1s kne wl.ed.ge may al so gilre a tu.:rther 1nd4ca.. t1on of the na ture of the complex which 1,s respeneible tor the non•a.ddi ·tive al:lso:rp tion of ultra.--v i olet l.ight (2). by $olut ions 1n which both oxidat ion eta.tea or tin are present. In view of the e.xi13tence of non•ad.d i t ive 1 i ght absorp ... tion,, tt would alee be of gtee.t 1nte4test to o.etermine whether -o r net the;re is a phQtoehem.ical effect on the ra.-t e et exchange between snl I Qnd snlV, eapee ia.lly by wave lengths. wh ieh a.re fiot absorbed by either. v al e nee at ate alone, b"t are a.bsor'bed The pos ai'bi lity of $U e h an etfedt was suggested by Dr. 1:forma.n Da.v;tdso~ at the Brookhaven ConferenQe of Dec .. 1~3, 948 ( 3) - The ex.i etence of $UC h a. phote- chemteal effect would shew that in the optically exeited state ef the complex that is ilesponsibl e fo~ inte~act i Qn absorpt ien eleetron ex.c hange e an take place with II fairly h i gh probability., The :f o110wing :report indicates the resu.l te of invest iga... . - tions e,f t he kinetics of the r a.dioae t ive exchange !n 10.0 f c., tn which the eoncentra.tions of snIV and Snll were Ya:tied from o.ooa ! to o.oJ2 ! a£id 0.009 ! to 0.077 !► Prel at 2, 0 re,a pectively,; whtl e .the eoneent:ration ratios ot snl.l to SnlV ••r.4.ed tr~m 6.,'5,- to O, !o/', R~u;iu.l. tt ar• al so gf.ven tot exfhange ,-,,aet i one bi 9•0 !,. 'ICl and 11.0 !. Rel♦,. tne•e r ·e act ions having b.'41tn ea.rrle4 o.~t t o determine the •tteet of' va.rla.tions tn the a•ld eono.e ntra t ien on the re,a ctton rate eonstant ill thit o.one•ntta.tion :range, bchangee we:re also ca.t'ried 011t at e0 c., an, the aet1vation energy tor 'the exehange compatea. The h9mog e:neit1 of the :r,eae.tioa wae tested by the addition of g1~e$ beads te th~ re a ction vease1 in specified :r11ns. The i-eeul ts cf Ql'1 1nvestig at ion ot the photoehemical •tte~t of light tre:m a eap111a.ry merctU'Y arei upon t :hi :rate of radio•aetiv& exchange 1a al so 1nc1u,ded: in this report. :a. !D~.~t,ment,$;': ,Radi~ac t ive tin was obtaine,4 from Oak Ridge t hr ou gh !J'a~uu· I,ab., lne.1\ lloo,ton., ~ss • ., and. was ~ece 1ved as c.P. Sn.Gl4•'J l!aO• An ~u.mtn\Un abao.Jlpt ion e,uT• wae: mad.a on the s«taplt a& recei'f'ed ( Fig-. 1)-,, and i ~• ,a peot.t i.c &At ~:v1t7 wat 4eiel"ID.ine4 \>Qth when the S$?1p1e wa• reQ:e-ive4 and 90 dqa lat er, 1.)be:o ke OA t ~ pu.1it7 tlf thf a.Otiv1 ty,. Th• aett•·• isotepe '-'• S'n11.i,, ,rbiOh hae a half•life c>f lof days, at11d de"a,e by u Isomeric 'tl"'a.tisition of the •••tted: . In *ll) to the ground stat.• ( half• li.:fe ot l.Gj mtn.) prod:tu,uus Oid9 M1llV gamma rays• and it is the interrta1 .. co11verelq)n elect~on& f~om this 0 •.39 MEY radia.ti on tha.t a.re aa~d 1.n co~n:t ing. the aetlvity waa introduced in the sta.nnie state in all ex• p·tu~itne·n ts. , Stock Sn,;V $slut !t>ns were preJHtred by cU.ssolvisg Sn<:1·• • tt..., Ra~ !!" ·in -...... t .tve ... . .a e1d of au.eh. C"oncentration t1i> m~e the ;final sG'iatione· 1~/. o l 111: Rt?l., Except when h1gb eoneentl"&tiEnts of ac• ttvity were delllil'fJ·'1t ; pot"t4.ona ot these solutiorie were milted with selutiana 11mi1a.r11 prepare<l tri,m Merek :reagent g:rad~ Sn.Q1 4 •: ; tfae•• S\lfflcient a.oti'V"e saX'f wa$ tUJed to give a Qtt.u 1ting Yate• of 1100 to 2000 co11Ats pel! minute t:rom tbe initial pJ"ecipitate$.,, Sto-c k sn 1'l soluttont were p~epa:te4 b;y 411.s.s olv1ili weighed amo~n.t e ef Baker and Adamson :reagent grade tin m•e tal in !Wl of su.$h coneent:rationt) a.s ea.lotllate·d to keep th• fi.f-1 so1u.ttone 10 ♦,t . !. in RSl. !rh-eae $Oll1t lon• we>re handl$,<l ~d kept in -. tion gener$.11y takes plaee 111 the snll selai$.ons even when they ~e handled under ; ao2 , the snil ecneentrat 1on a.Ad th.e snXV 0-oneentrati(l)n were de .. erratned by ana1y$i,$ d~riraij ea.$h e:1tohange e~e~im&nt. a.s d-esoribed .'below. SeJa.l1'atJ. on of the two o:d.dation eta.tea of t1n was aceo:m- pllahetl l)y th:e method deveioped by )r.owne. that is., by pre~i;p• ' ' ltat tog the anltV a..a e.•2 sn01', leaving the snlJ tn toluti(u1. The gftnetal prtoecht.re f~r an •~$ha.Gge •ltperuie1at wat to b~-ing both th.e -s nII and snlV ee1ations to eo.-n stal\t tempeJ-ature tn a bath thetmo•t•ttt a\ a,.a :J: 0.1 °c,, ihe· snll aolu.t1oa being ln th:e reaetion flaslt, which was a 12~ mi. Erlemneyer fla.sk t1tt•4 with a eide liU'lll th:ro~h whieh CO2 eoald be patlrted whe!lever the tlaak was opf>ned. the s.n IV $011..lt ion, containing the :rad1o•active tracer, was then ptpetted into the reaet1on vessel. 'ln some expel"iments, inactive snIV was previou.sly mbced with the ·snll solution, so that only part or the SnIV, containing all .ef the act iv tty• was pipetted. inte the mi~tttre • fhe Ye$ eel -.aa shaken d.11~ ing th• mixing, and. the time ef ini.:d,ng wa.s taken ae the t 1m.e that one~halt t:>f the snlV . . . •o1iat ion had 'been ad.4.,11-. 11 sec.ond.a+ The mix.1~ generally required ab~u,t Sam,le • •re l'emo•fttl ttom the reaet 1Qn mlxtt;.re at r ,o u~hly •q~a'.'t. 't itne interTtd.s.. ,uh that gentuta11f tive samples • were obta.1 n,d tn which the eqected o.egr•e ot extha.nst " ' l,e1ween 8 •n.d 8o pe" #ltnt• !he$e •~mp:l,er, were pl.petted t1ato welgbe4 eent:ritue;t eon e•, $»,4 the 1nlV p:reot,p :itated by adding a •·0 lutioa ot \hl;'O ! CeiCl 1n l.G , RC1. The,ee st•J:113 n:r• ► of o~use, carried ou.t 1n an atmo .eph e:,e ot eo.1 t .o 1n:·evt·n t oxi~a.. tl•n of sialX 'by atmoa.phe.ric o+ya;en. The t !nl.e ot pre-eipitati on of t•aSntte na taken .a.e ~he time of •ntU.Qg •t l'&.dio-.a.ctive •~ehangt,, The eent;rltu.g, oor1ee were atopp..e red a.~4 t he es2 SnC1 15 wa• oer.rt:d.fag:e4 ou~. wa•e hed with l ml• ot eonc. Htl , dr:t ~d to-. &)o\lt 8 hOUl'& -.t ,aoc ♦• iU'Ui weighe(i., The weighing served ae a chtck $;galnst $.n ll oxi4a~1oll. 4.tUt#;ng the rea.t.H,ioa. anti gave a, 41reet analyslt ot the sn 11' c:o~e .e u t :ratiom i n the re·a et ion OJi.ta.110 a• i <i • ol ll t ion, &Ad it• lMt t 1vi t 7 m.ea•a.re~ l n:i &a-di at ion Co.unte~ Lab~i'at¢1rl$.lJ :la- l,._ Mo_~ el 70 Ja~ket.e.d. soluti¢i..tt counter .• The r•te tf egeh~~ W$9 .d &t e nntnetl by meaiu.:ritJ.g 't he deereaee bi aftivlt_y ot the snIV wtth time ♦, Th e :final actlvit;y ot sn1V • • ttH:1asiu•-.d tr-• a ,ample p~e.ctpita.ted attt:r ·the exchange had run to ooui;plttio•• The it1it!~ a.e tivity wa'S either nte,aau.red tl"o:rn (hs2SnCl4 pit'eoipita.ted fl'<m a por-tion of the i.ui• milted snlV tolu.tio~ ,e q;1 tv$.l.ent te the amo'Q.nt in eaeh s-.ple t-1ten tr•m the mixt~r•. o:r ealeu16'.ted :fr<»n the final. aett.vity of snlV and ·the concentrations of snll and sn IV in the mix-tu.re, Z:Jinc1;1 ·i,.r,e initial activity of snlV is equal to the finaJ. aetivi ty t~mes ·~he ratio of the total tin conccnt:tation in thi mixtux'e t,o the concent.rat ion of S:n1V • ln e:1,c hanges for ~:hie}, '• U . the i nitial a,ct i-vity of ;;;nJ-• was m.easiJ.l•Bd• t he .:aeasure d•.. a<.;t1v- the d :i.fi'erent vahie s fo~ tho ini t ial !let 1-., ity a]?:pree i ably a,ffeet. the slo:p e of the lines plotted as described be1o wJ and therefore has no effect on the determination of the exchange rate. '11:he tota,l tin concentration in the mi~ti.lre 7;a.a d.eter-- rn ined by {)Xidizing .,a measured samp le wi th chlorinB gQs and determining the tin gravimetrioal. 7 y a.s Cs 2 snc1 6 • The concentra.. t ion of snll 1n the mixture is then obtained by r;ubtract ing the (snlV) frora .t h(':) toti'll tin concentration. The S"a.ine general procedure was t'ollvvved for ra.dio .. aetiYe excheHl{,~es at ~ero degrees, the sol11tions being imme rsed in an the react ion vessel, reactions were carried out in a vessel fille d with 6 ram glass beads• increasing the su 1""face area in con-t .?,ct with the solu. t ion mo1·e t \'1 c;.n te.n fold . affect ed by ordi nary dayli ght or normal ltiboratory li g hting , exch ange re a ctions vre re carried out with two similar solutions, one of which Wcl.S exposed to normal 1 aborat ory lightin g and ·t;he othe:t kept in the dark d111•ing the exchange~ Photochemical effects on t.he exchumge rate were then investi gated by exposing the mi x ed solutions to the radi a ti on of a capillary mercury arc at t he t ype desi gned by Re idt and Daniels ( 4). '.?'his t ype of arc was us e d b ec a use of t he high light int ewaity tllat can b e thus attain ed• and the -~u•e operated at abiau. t 450 wat ·&s. In this inve stigation; the gerterai met ho d W8.$ t. he same as th at previously u.sed.., alt hough t he proeediJ.re wa.s 00n~iderii1:>ly medifie d 0 lee water •,ms circulated ovet t he me:reu~y arc and through a ema.11 bath S1.:u •r0anding the a re, in which the reaction The temperata:re wa.a kept at a.a near i~ro deg re e s a.s possible, in ordel" to mini&.i ze the t herma,l ext hange. W$l'& One"!!half ml . port i ons of rad io•act ive s n l V a0l11t ions pipetted into 10 ml. pyrex test tu.bes eonta.i.ning o.,o ml. ot anllI solution, and the ,t .o ppered tu.be plaf;led oeeide the me~oury are tor various periods of time. :Both aolu.tions were .tn 10.0 J: f?'C l, and were O(Joled t o .3ero degrees before mixing. f h.e •xchang e was stopped by precip it a tion of ca2 snc16 in the tutu.al ma.nne r. Suc h tubes were mixed. and i11 wu inated one a t a time, and the tube wae st placed again9t t h i jaeket surrounding t h$ a.re that the reaotitn mi2:ture was d1reet ly opposite and parallel with t he a:l"c, wit h its e enter a.lH.nt 1.; cm. away. l should like to me nt i<.m tha t . in e,u:-tent experiments, desi gned to dete rmine i f t he photochemical etfeot on t he eJtrHiange rate .i s dae te light absorbed by the 1nter... aetion .,em.pl.ex (2), and to estimate tre qu.antum yield of t h is photo- c:hemieai e x c h a ng e, a Corning Gl a ss 15860 lig ht tilter is iase;rted between the a re and the. reaetion tube, and the intensity of the radiati on p aesin e; the filter is estimated by the i:.\&e ot an 1.1ranyl exalat e•oxa.lie acid actinometer. The #5860 filte:r- t.ransmi t ,s wave eng t lie -b et ween 320 a nd 39 0 mil l i microns, and 10 found to have a m x tmtUn transmission of 25% at about 363 m:l.11 i mierons . Charles - lo :Sr<nm e has sho-wn ( l ) t hat SnlI solu_ .. tione in 9 f HCl do not e.hserb light of wave lengths greater • t ha.n 360 mi l l i microns, and s n I V does not absorb above 330 mi 11 1... n.l icrons, b ut sol at ions eonta ini.ng both valence states show st.rong inte:ra<tt.ion abs()rpt ion ~t .365' mi ll imierons. l!3B<n-1, J'sr t!rfis- it · i=o=:de$S.:table to t-o:olat-e at .le, mi11iu.u tel!'eftrh- For t r is r e ason, it is desirable to isela.te the 3650•63 .Ang$trom me:t.-ctary r a;d i ation, and study i ts etfee t on t h e exchange rat$. The light filter transmits 25'% o:f t his radiation and part of t he ne i ghber ing aont.inti1.ull, wh icl-1 is found to be abouit 1 ~ intense as tl"l-e ]650 A. emission. :tn estimat i ~ as ti,e :il'lt.ens ity of the ti'a.nsmi tted :U,ght 1 t he concent r at ions of snI I.,. snIV solutions and of the uo2 c2 04 :Jol.ution use d a s an a c t i nometer a.re a.dju.sted so that the extinction cceffieients of the 'two solution$ a.Fe 1'lea:rly ident·ic al at the wave lengths ·t:rfll.nsmitted by the filter. aa dete~mined by a Beokmarm Model DU Spe c trophotomete~. One ml eb of the uoac204 sol~t ion i s p ipetted into a tube simil ar to tnoee uaed for ·t he snlI ... snIV· exehange :react ion. p la¢ed in the same posit ion 'by the are . and e~posed fo r similar perio ds of time. mined by Itidn04 t it rat ion, and• &S$1'lming a q_u antwn y ie ld of .5 O (5 )., the amount of l i ght ab s orbe d is t hus obtaint::elo ~inee the tnl I .. a nlV ex"ha.nge ewi at ions have t le smne ext i rict ion coeffie i e-l:1t , t '.hey absorb a a i mil a.r qu a.nt :i.'t y of l i ght, nd t he quantum yield of the p ,.otool-ien1 i cal snlI .. fhilV exchange can l,e estimated from the mea.et1red exchange r a te mi nu.s th e thermal e,xc J.,a,nge r a t e., 'J.' he tempera.tar$ taf the ill1>.trJ.ina.ted Sn · Il~snIV soliit tons is meaaitred by means of ~ ehreniel ... eJ.Ul'!lel therm.oeov~ple. :P.~~eis i2,n Julfilyt ieal. Gravimetric de'terminat :ions of snlV concentrations a.e G$aSnGla px-oved to be reprodu.oible to 0.3,; or less. ,two d:l.ff'e~-ent knewn exeesm amo1.1.nta of CsCl use o.f eola:t ion to pree ip- itate the tin. from standard solutions of sn 1V in 10 ,! mn, p:reptt:t~d by d1tHJilv1ng weighed. qaa.ntities of .B~er a.nci. Adamson reagent g:tade t1n met&.i in RCl and ox.Jd1zing t'.he tin to snlV with ohlorine, yiel.ded. we igh t e of C•2SnCl5 whieh i.t1di<:a.ta th.at the aoli.fbility produ.et ( snlY) ( ea+ ) 4 1• 3., JC 10· 8 mele.-3 liter-3 • .S.ad1o<:/hemica1 mea.su.rement fit the % ot actlT ity,, Wld thu.s the % t.Jf $ii'1lV, left b1 aoltAtion a:f-t.er p r e@i.pitation ot marked Sri.IV - trom lo f ROl conf'i.J>m.ed ·the :C$lcu.la.ted eoncentl"at ion Qi snlV . . . ' in ~he 1u.pe;,natat&t liq1tid11 . • • • ... ·~ The va1u.e Kap z J., x 10"" 0 was Qoru1eq1umtly used in all analyses e.t sn 1V ·to compute the ameu.nt of anJ.V left in eolat ion. and the corrections thus added to the analysis vari~d from o.. o to 1.3% of the Sn 1V preclpitated. l!eaa'1rements ot total tln in solution were t11n1G a.ecu.rate to lle:eause ef the 01-ticlat ion of smai.1 and varying amou.nts of snlX to snlV d1,1.:r i?Jg '.P ipetting and. centrif'uge;t ion. indtvidu.a.l va.ltl~e for snlV coneentra.tion varied as mu.eh es 5 er 10% .i.n •el~tions of low $n1V eoneet1tra.t ion and J'ela.tiTely high sull eon,uintration, Fut of th1e T.U"1atton tnay be d.u,e to differing amounts of eo•preoipita.tion of snll w1t1r: the cs 2 snC1tJ• Titra... tloa of ea:!1,pltu, f .rora. sniZ.. anIV mi~tui-ee of eont\entra.tions •9fJjlnilar to those \tSed in the exehange reaotiona., using stand.a.rd iodine &(j)1ut ion, anl'l titre.ti on ef similar '1a.mplee after precip ... ttation of the snIV as C:12Snfla, s:howtd a redtt.~tion in SnlJ concentration of aa mu.eh as 2o, to G '$ • An ~oant ef snl.1 et1_u.al to 30 to 70 % •t thls ~•d.~et iGn ;tn t tt~i" toLtl .d l;• O:;ti.• • cllaed by iodine from $ su.$pension of the ee2&1nQle., Jroving that part of this recluct ion is d~e tf> co•preeiptta.tt<ni Gt snll~ The remainder et ihe redu.etion ts tit•n· m1.t3 be dta..e tt> txtda.tt.on ti snXl 'to snJV during ma.ni:,~latton• ~o'ilo prectpiltat ion tt snll is a ni.aJ o;r 1;1ou.r.ee of eit':rer both 4.n dete;rmlna.t l•i>nii ot the. snI.V c:one.ent:rat ion. and 1n t b.e t:J«:.i:thai;g$ r•t:a !le~• l'9.it~ent s. Cal e.a1a- t itme 4.n whl.111 $11 tht ;re4uctiell in sn 11 t -it.e r 1, ~· tomd,derecl au.e to (Hi.~ pr-~eJ.pitatt~.n,. .~ d the <;\lllOtUi t ~f IQowi1..et$.ptt.at1on is a1ewntut to be ~•uist~t- l.Ulit\et- the -tsa:me p~e~t, i t atlola: 4lt.nd1tioris, 1hew that the ma~dw.lm e.:tl\ltil' introiil,¢it4. by thi.e isi.~ vo.~ in the d.etet.mina.t ion &.t e~cha.ng,e t<atfl 1$ ge.r:1•r~ ly 1th!$ tl' &l) ; %• At l .eaft. f't:ve $1ldfttt t·tr SnlV were Qb!h i.11~,1 4:"-:r111t: eatl~ egeh$11gt reacti~n, an€! even the l0i1"ts.t va.lm~•s. 1)f sniv .etl)nC,()n:t::sition are a~~aratt to ab&w, ) %~ ·val.ttes of snll c 0:n€101rt~at ff. eta .._,re gene:,.. aliy U -(intrate to witldn 1 i. :a:t.>r ~cuaeexrt r at 1('.!ll;'.?1 Ell?'e a cu:atat• to witl'lin. 1,5' %* AJ.1 eamplii:a ~ie ttiJ.ntea t <i> • m1.n1..m:!!1m ~t let ooo lit oants. gtvtr~ 8\n •~eQted 1ta.r1tia;;>~l d.eviati.0n e,f l %. l t is interesting tQ nGite- that tl'le Zi,·f ittvU~y fit the su.pel'.. natant liq,tid.~ and.. its :rate li1f dee:~y. meas,1.1.:r·e~ 1nune<U.ately atte:t p:r~ciplta.t ion or Cs2SnCl5, s-h-o,wed that at l~a.st 97 % of the ln*ll) ~o-.pJ~'ecd.p!ta.ted with tb.e Sn,t 1?'t erefore, 1t is r1ot neeesaary to wait a great length of time tor the establishment of e:qu.11ibt1w.a betwteti Sn 113 · and ln~113 .. and no error 1a 1ntrod~e•4 by :measuring the att 1•1t;y o.f the prect:pi ta.tea immediately &f·t&~ drying. The ttct-.nique of dieeolving the ra<U...,act1ve p:reci.pS.tatee .$t14 measllril'ig thel:r a<rt!vity 1n a Jacketed aol\lt ien counter hat be~n f Otlad. to give soo4 rep:rodl.le1b1l tt1. a11d eliminates many ot th.ii ceuntlng e;r:ror• tncot1ntere4 w1th •<>114 eu.batanoe1s. Dissolv- l~g sim.11arly p:re:paed radio•aet ive Csasne16 pree ipitatee. •zul co,.inting each solut:Lon to a •tanda:t4 d.eviatioa of 1esa than o.,%, gave vs.111-es tor tM <iitterent eolatione that were •11 within th$ tXpeoted oouating deviation. Since the $Xu~e rate •a determined. by meast1ri•g the lnolrea,u in aetivity of sa:rv, the ertor, dt1e to the t:J."J"Or ot :tadioassay. iu the exchange rat• constant is l .east at high sn 11 , to ialV eo:nf/u?.«tta.t ion ;rat ioa ( 6) • Thia, error wa• minlmisea.. wbetl otht1· req,1;1$.rem•~t• of the eXperixnent permitted.. bf keeping t 14$ r•t io high and by taking all sample• when the exehan&e was ·bet\\<Ctn S and SO % to!Xlp1et,. e. D•ta J.-og. ot a t ypl;cal. ••e hallg• Jr'vact 1011. JIXchange Vl lJ ml• ot 0.0494 t m~:rkn4 :;nlV QQ:trrtf.on ad.d.e4 ti;) 60 ml. . ~ tt 8nlX a-o.1.at:lon• Q.o,86 ! 1n sn. (:ti, t111a ez-i:.pcl"u,eui. the t•ial ttn iuuteent:a.tir.ii\ tn @(;!.eh a tt'l'J:t itn · J'at~ de·ter-1,'.iined g1•a:vi• l'l'iet,:,teally a.11 CeaSnCle; 'be tore the •<Jl titi Oil& ~:rt, mixed.• } ~ . • 0494 17'5 - .0888 f Removed 10 ml e aliquots:, precipitated Sn 1 V with 3.0 ml. ot o. 1,0 ! CsCl solution. Initial activity a • 2.0 ml. ( 15 /7.,) of .-0494 ! sn 1V solution plus · 8 ml. 10 f H01 , precipitated with 3.0 m1o CsC1 aolutione ,Activity fr·om this precipitate (:X.0 ) • 1654 co unts :per mine - wt. o:f. sample Reaction time ·- • . ]2pt. Activity ger. .0686 jmt ·_ ' . ' .. - t •• •<- il:Jal •~0§ ( l•D~. 1 ).2 min • 06,92 gm. 1414 c /min .832 .oso a s.-8 min .0697 gm. 1244 o /mi.n $712 .147 3 12.3 min .0684 g¥rlo 990 c/min .5'32 .274 , 19:·♦.·7 ·. min .0679 . gm. 7-70 c/min. .J76 .424 27.0 min · ·0682 gln<, 612 c /min . . -265' •576 6 12 hours .0674 gm. 236 c/min 0 4 wt. Ce2snc1 6 left in . solution fKsp • 3•5 x 10- 8) • •·0007 gm. (snlV) in mixture (a.) ~ .0686 -+ . • oooz .597 X 10 fsnll) in mixture (b) : · .0 888 - : • 0116 f - .0116 :: .0772 '· -· ~f flotting -.log (l.-D) vs.- react ion time gives a. line of 19.lo.p e .oal5o· Exchange :rate constant R :;- ~.3 03 .$lope x moles liter• 1 m.in""' 1 • React i _on rate. constant k ~ Jig. l Alllminum absorption curve of sn113.1n*113 radiations. Fig• 2 Rat e of exchange , in 10.0 J. RCl at 25 °c . 1 1 (sn Y) - .0311.r.. J (Sn 11 ) .0085 ! = l11g. 3 0 Rate of exchange in 10.0 .f HCl at 2, c. J (snlV) ~ .0116 ! _; (sn 11 ) == 00772 ! - Rate of exchange in presence of g las s beads.,,, 10.0 f HCl; 25Q J (snlV) ~ .0072 ! ; (snll); .0389 ! Fig. $ Exchange rate in daylight ( A) and in dark ( Bt 10.0 f'; RCLJ ( snII) Fig. 6 Exchange rate at o0 o. - 10.0 f RCl J ( snlV) -: .0108 .! ; ( snlI) ;; .05'69 ! Fig. 7 Exchange rate in 9.0 .! RCl J 25°c. J (snIV) • .0003 1 1 (sn l l ) : .02861,. Fig. 8 Exchange rate in 11.0 ! RC1 ; 25°c. ; (SnIV)•. • .0061 -t Figo '9 • (snll) • .0288 _..t I Thermal plas photochemical exchange rate; cao 5°c.; { SnlV) ~ .05'5'6 .t J ( snil) • .0900 ! '!'able .1 .E.xehange :t;>e~j.gnat ion . . "a' "b" f snivl, ( snI!l RL~b Il .0102 .0093 .,a IIi .0103 .0292 ,48 IV .0323 .0270 .;4 V . 0311 .0085 .,1 VI .011a .0772 .55 X (light} .oos4, .0382 .,3 XI (dark) .0064; i,0382 .;3 XII . oo,, .0294 .4, XV.I .00718 Jt038<J ,56 (Varying a.•b r atio) ( Subdued light ) 4Glas s beads in vessel) Exehange •a• . ( snIV) _,. ttb" ( ~nll). !Lab .0108 ,0,69 .10, XIV' (9 1') .o063a .0286 .177 xv .ooGo 8 .0288 .123 .o,,& .0900 2.20 .l)ee.t.1nat ion """ (Je:ro degrees c.) Xlll . . . ; fE!ftct of 'HCl ~one.) - ( 11 !) ( Photochemie al plus thermal) X:Vll D, l!!u.U!...S!L.9.~~..;o ~~!.~ou• .The nlwntnu.m. absorption ou.J"ve of ·t he sn 113. ln*113 ra.dia• tit?• CF!g. l) ehowe a. sb.arp b:raak at a th4.c1'~thlS vf 101 "!Xlg/em2 , oortesp~nd!~ te> an e.le~tron energy of 0~364 UV (7)• This 1a in -.cre•ent with the energy ot internal conveJ-aien el•ot:rona from 0.390 141W ( 8) gamma :radiation p~oduced by the iaome:rio tl'a.na1:t.1o:r, et ln*11l • which wQul4 bave an ene;rgy or o.362 nv. Jo definite brealc !n the Oline ts observed. to oorreapond to the o,o&; JmV radiation of sn113. l'he;re •a• no ind.ieation ot th• px-eeene, ~t :t'Or$1gn aotiv:t.t iea 1n the sample. The e~por.umt1al -,xchange law {9, 10) fox- the snIV-snll txcha.nge, expreieed in 1ta log,u-ithmJc tor.;. 1e .1r1 ( 1-:0,\ • R in v.h t ~ h i ia t h ii I a i- bL -ti., -u·ar deg:ree of exch ~A g e• or fl'actional. exchange. at time !; ! is the rate of exoha,r,.ge, a :r1.1neti.on t.) f .t; b, and ten1perat u.r~. ani ia eoaata.nt f' 1J¥' E. given sat ct con<U.t ions; ! and ! ar.e 't he coneent~atioru1 ot sulV and. snil, respectively, 1• gram atome pe~ liter ; ~<1 i §.s the react ion time. 1:Uuce the snff ln.1 tie,11y contained all the activity, the d.eg:ret of nonexehange; ( l•D) •• l'r!iliY be obtained. from the speoifie aotivtttea fX) of snlV at react10n tilllea ~e,o (Jo), tnti.n!.ty {X 00 ), ~• t The rate cit e;xe hange., ,!!, may 'b• e>btalned fr• plot• ot !111'1n ( l•l)) vs. 1, sinoe ,he 1lope qt the line pJ'ociu.oed is eqlilal to a (a+ b) /~,b,. an4} T'ht f>lope ts dfl't~l'Ul.ined. t%'on, the g~~pha • .! ~,-e- 4etel'm1ne4 by a\nal:,ata.. and J! oale~late4 in grma *;tom$ :p:e:, li·tet- pe:, :m!tlt1t:e., lt :l.s s a f.;n. frc;,ra ~cl1a11gea; ll: 11 l:I::t, ;t.v. v, an<l V'I• Ta.bl• 1, t-h~t e~ch.a:nge r~teH1 afte-r- varyii.,.g 'both .a and l gJ;ve Yall,es of il-U which &l"t' i:1e~rl.y ecruJta~'lt. lt ls the,eto:re ¢onelt1.ded that ihe rate '{')f rea.~ti.o.n is pl'opor·tio11a.'.l. to the f'iret powe:r of both th$ SnlV coneent:ra.t ion and the Sl'lll eoncenttat ion J 1. e. • th• - :teaeti~a in 10 f 1Tel is e.econd ;3:rder.,.. and a :t k a'bt • The average 14•vnd to bt l~~~ly d~~ ti.} $!fl.:,,'\ll v~riatlQmJ . in Eel. ()oncentra.</11 tton,. the!Je e~ncentrat ieu1.s b~ing ~Jttl~rate to r,1117 abt>t.tt 1.; %. '.t'he :rate ot oxohange ie :ro,.a.rHi to 'be .indepE,ndent of the •utt-.ce tU"ea in eonta<rt with the f>Ol~tloris (Xll -~'1d :rvI, Table l..) ,.,. ktrapola.t 1.on to t#,me t • o ~f. the f-l'~..phs ft'.t ~xchr-.ngtis in which glass beads were present iJhG-y,,\ut. ~owtrYHt. ~:tn '2i,°bn(.\rma.lly large p.otAnt of' •:tl'Miuctui• exch~.ngP.., SimJ1.e.:r $l:t?a:pcl 1.t. ion of •~her exchan~s s~wed wtdeiy va:rying and enti:r9ly nonl"ep~oduc 1~lo atnetlnt a of • induo•i" txcha.nge • va:ry#.n1 f~ om o. ~ tn aeme e~change~ to ~s high ,~ s 23 % ( Fig~ 5'). The two :reao• t tont in wiich glua bee.de we:1-e present shoived "indta.Qt:ad• f)je.Ohaages of 38 % an4 27 %. $inoe nQ • indue«a4" ~xeh~gf! ie oluie:t-ved hi several imitaJ1<:HH1, and ·the value !ltoes not ve:r1 for tlMI different p~eeipi tat es of a e lngle run. this exchange 1 s nr;t btl 1 eved tG b$ a. resa1t of the pree ipitat ie>a ~et,hod.t 4JJ m•)attonad e&;rll,er in thia report, the amtHJnt of apparent •<S.;ud,i.1;0ed" exchange is d$pendent al)on the method of d.eteMining the tnlttal activity of SnlV, b~t the large amot1..'lt r,f a.pparent lt$pid p:£trt ial e:iulhange that is $omet imss 1bserved cannot all be aecH,a.nted for on th .it4 'ba.tH. s. The sa.~e (n1ne wo~ld be ~btatne4 if • ae~ta1n amGant of e:,;~hange we:re to take pla.ce at the time of mixing tbs :,olutiona, perhaps brc~ht abou.t by aurfa.oe ef'te,ts on the veseel walls. 13?- some :reae:t j,ons tn vlhich *ind~c;ed* excmnge wee obaervetd, however, tht inttiel solation eonta4ned both snlI and SrJXV before a,4~U.tton ot the Jndke4 snlV, and ta.p1.d exthange en the vesael wal,ls at the t tme of mixing therefore the aea2,u.'eme11t e f the ratt ot •Y~hat.ge, :ls not •tt•oted by the "in4tlcecl" exchange, b.~•ver, end no err0:r is thu.s intr<>dttted in the rate meafn1rement.s,. At o0 c., R/ab QB f~nd tc be o,104, giving an. e,ettva:tion ttt•rgy ot 10,7 Keal. per mol·$ fOJ' the ex~hange reaet!on. The OQ,,>npl.ete A,rrhenJtUl eq_uat ton l .s theJa lt • l•8xlo7 t"'"l.O,/'/OO/RT , when k is expressed 1n liter mol'.. 1 m,. .... 1 ~ . lt 11 f 01,nd frQm exah~e& in 9, 10• <lJld l.1 !, RCl ( Table l, 1fi.g•• '1,8), that. 1n t 1"i .a coneentration range; the reaction rate constant, R/a.b, HC1 activity. i$ p:roportiona.l to thE 0.3 power of the This value is obtained fro rz1 the ratios of the pal"t.ia1 va:per pressures of HC1 at the three concentrations, given by the 1.c. '.r •• on the assumption that the activities of HCl are unaffected by the small amounts of tin present. The empiric al rate eqaat ion for the electron exchange react ion · is. then, ft~ k ab ( HCl) 0.3. It will 11e noted that ·the exchange &-$.te varies as appro:;;timately the third power of the HCl ~on• centrat ion. 4].th8u.gh Uie exchange rate does not vary with the fi:r s t power of tl:!e RCl activity, I should like to mention a. possible mechanism by which a ayrr.eetrieal complex of sn 1 ~snlV may be forme d, :f:rom which either nucleus may ~merge as . snlX. :aeeause of the foma.t ion of such su.b st a.ne e.s tta o eaSnCl 6 • it may be .ase~med that the snlV exists in i,olut ion mostly aa sno1 6• ions, with tdx oetahed:ral bonds formed by the sn 1V .( 11). s:nIV has in no ele ctrons l'emaining/the •0 11 shell, and could use hybridized ;s5pJ5d2 orbit als (11) in fol'?Uin g these bonds. If we now assume that the snll exists mostly as anc1 4• • and, in ~ exeit•d state of this ion, the two "O" electrons effectively occupy a 5P ot,bita.1 rather tha.n the more at.a.bla 5s orbital, the 5s,:p2 5d orbitals could possibly be hy bridized to g ive a e q lU\l"e planar configu.ra t ion to the f01.1r sn--..Cl bonde. of the octahedral snc:t. 6 Coll is ion • and planar Snc1 4• collld form, together • with a single Cl ... ion fro m the :m ll solution, a. eynunetri.c::-al arrangement in which electron exchange may ooouN c1- Cl c1, I ,._..c1= Cl -----r~C 1 Cl c1, _......c1= Sn•• Cl_,,, ~Cl c1SllCh a mechanism would be in agreement with the rate equation R • K ab ( P-Cl) • A photochemical increase in the e:xc ·.n an g e rat e may be due to the absorption o:f photons by the sn 11 to form the planar snc1 4: ion, which we have already asraumed to be an excited The photon absorption also might oecu.r at the time of ,t he col. l ision, or after collisi·on, yielding. in the complex. \he exeited state necessary for the transfer of electrons. 11· a. photochemic al effect on t he exchange rate is observed for wave lengths that are absorbed by snIV_s~}I mixtures, but not b1 snII alone. the 1 atter pos sib il 1 ty would be indicated. lf a photoctie.rniea.1 effeet is observed only with wave lengt h e that ai-e absorbed. by sn 11 , • '\VOU1d a mechanism such a.a that first su ggested seem logical. Al though the rate of e xch ang e is not appreciably affected by exposure or non-exposure to daylight (Fig . 5) a marked photochemieal effect on the rate of exchange has been obse rved by ill11minat i on with a merc11ry arc ( Table J., ll"ig. 9) • Cu.rx-ent experiments indica.te that light absorbed by the lnte~•aetion complex and not absorbed by sn 11 or s nlV alone dcea incre a se t he r a te of electron exchange . These results are of a. prel i minary nature , however. and :final conclusions .c onc ern i n g t :h e exi s tence of thi a effect and the qu antum yield it produces h ave not ye t been drawn. ... 19 .. II spectrophotometric Investigations of Cobalt•Glycine Systems A.. Int rodu.ct ion _..._.._..... Numerous investigators have studied or mentioned the format ion of complexes of certain metal lie ions with aminoacids and dipeptides ( 12, 13, 14.15. 16) ai Since these metal.lie ions a.re present in many prote-olytic enzymes, and knowledge of the mechanism by which these enzymes function is of su.ch great importance in llnderstanding physiolo ical reactions. more careful physico-chemic a l investigations to determine the exact nature of the metal•amino•acid complexes are highly deairableai The following is a report of spectrophotometric investigat!ons of oobaJ.t ... glycine complexes formed in the presence and in the absence of oxygen, with determinations of the effect of ¢ha.ngea in pH• A determination of the stability constant of the complex formed in solution containing exeeaa cobalt ions, made by th~ method of Bjerrwn. is also reported. These inves• t;ga.tions are of a preliminar·y nature only, and were undertaken when a delay tn receiving a shipment of radioactive tin interru.pted the investigations that are described in the main pa.rt of this report .. ». Exper~I!!en~1 The spectrophotometric measurements vmre made with a :Beckmann Model DU Spec·trophotometer and Corex cell e of ten millimeter light path., The blank cells contained distilled water or solutions of composition similar to that of the • 0 l.ut ion being investigated, but lacking the absorbing solut,e. -20 Readings of opt ica1 density were made generally at wave length intervals of ten millimicrons. In the investigations of effect of exposure to oxygen. no effort wa.s made to control the ionic strength of the solutions. In all other investiga- tions, the ionic strength was kept at~: 1 with sodium per- chlorate, and ·the solutions i~re mixed and kept in an atmosphere of argon gas to mi.nimize o.x:lda.t ion• pH measurements were made with a Beckmann Model G glass-el eotrode pH meter. Cobaltoue soli..1.t ions we re p re:pared by diasolv ing weighed quantities of ll erck reagent grade Co(N03)2•6 HaQ in water, and dilating to the desired concentra.t ion. Glycine solutions were prepared i n a sirn ilar manner, using Merck N.F. amino•acetio acid, which was $hown to be free of ehloridee., Since these observations were meant to be of a preliminary natu.re, more accurate analyses of the solutions u.sed were net made, In determining the (CoG)+ stability eon1ta.nt, a solution initially containin g 0.10 f' co++ and o.o, f glycine was titrated ~nder argon with o.,; f NaOH, the pH being recorded from the glass-eleetrode pR meter after ea.eh addition of o.•5 cc. of base. c. :Pat a. ( Two f i gu.re s) . Figtlre 11. Effect of expoeu re to oxygen on the spectrum of cob alt-·glycine a.t :pH 9•6• I. o.116 .! glfcine ; 0.0;8 I, KOH. Il~ 0~010 f co••. r:lil. - o. 010 1 co•+ J0.• 116 ,! glye ine ; o. 05 8 .t KOR • Unoxidized. lV• Solution l l l exp o sed to air fo'1r hou.rs. V, Solution Ill ex.poeed to oxygen gas (slowly bubbling) for twenty•four hours. -21- }~ ffect of pH o n oobaJ. t-glycine solutions. 1. -! lI~ 0.010 f Co"'+; 0.10 f glyc~ne; 0.19 f HCl ( p TT : lll~ o-.010 f Co++ J o. 125 -.! ( pR :. 4.68 o~ 010 ! glyc ineJ o. 02 ! NaOH ( pH z 7•27) co++ ; o. 10 - gl ycine~ - - 2.28) - 0.010 f co+.., ; 0.10 f glycine ; o.o4 f liaoH ( pH ., 9.23) (NaCl04 :; in a11 solutions to maintain ionic strength of one .-) _______ ....__..... Result.a and Conclusions ' . One of the p1;1rpo s es of the investig ations in the absence ot oxygen wa.s to determine w:hether the , eobaltous ion itself complexes with glye 1ne• or if. the complexes whic h were prev irJ11s- 1y. ob~erved actually involve oxidation of the eobalt to the eobal tie state. lt is seen from Figure 1 t rat, at pH 9.6, the ' eobaltous ion forms a complex with glyeine whieh has an absorption maxim.um a.t 5QO xyt• Slow o:d.dation tal.tes place in the presence of oxygen, c ausing the optical density to i a cre ase at all visible wave lengt hs. The optical density incre ases most rapidly in the wc:1.ve length region between 340 and 420 n~, another maximum developing a.t 370 m_,..14 Thia increased absorption may be du.e not only to the formation of eebal·tic complexes, b\lt also to the formation of decomposition products of glycine, for addition of Ba.Cl2 solution to the oxidized mixtu.re showed appre- ciable ·quantities of c a rbonate to be present. It is probable that cob alt ions oatalyae the exidative dec-ompoai t ion of glycine, ju.et as they have been observed to catalyze t he oxidation of po1y.r1ydroxy compounds such as ma.n nitol ( 17) • A very slight decre.11se in pR was observed in the solution as ox idation progressed. ln strongly acid solution the spec.tJfa of qobal t-glycine mixtures were f0W1d to be identical with that of cobalt alone Only a sltght variation fr(?m this at the aame c oneentrat ion. line wa.e observed for a mix.tare of aqu.eoaa .c obaltoas solution $.nd glycine solation to which :neither a.eid nQX' base had been added, but some c omplex~format ioirr is indicated in this case by the decrease in p!f below that of ·e 1t11er component when the two solationa are mixed• Deoreaae in p'H upon complex fonna- tion is brought about by reactione nu.ch a.a ce++-1- G:t;;:91Cocr"' +- R,.. More st:rongly absorbing oebalt•glycine complexes a.re :f'orniud only in neatral or alkaline solutions. The speetrum of cobalt~glye1ne mixtlll'e at pl! 11.0 fFig• 2) is nearly identical with that of partially oxidized • ·. olut1ons at a iov1er pH ( Fig. 1), even though the solutions "re mixed under argon and the dete:rminat ion of the speetru.:m began immediately thereafter. oxidation takes plaee much more :tapidly in strongly alkaline sol.at ion. Exposure to oxygen dees not affect the spee t ra of s.t1~ongly acid mixtures. The detel"tnination of the stability constant of the cobalt• glycine complex formed. 1n solution containing excese cobalt was the beginning of a.n effort to establish the exact composition ' of the complex or complexes that are formed u.nder different conditions. The :pR of t h.e solution was plotted against the volume of Na.OR solution added, giving a line of nearly uniform el.ope from pH 5, 0 to pH 7.2, above which cobal tous hydroxide began to precipitate, and below wh ieh. the ine:re dse i tl pR was much more ra·pi d. " .... c.wu """""0unt • l ent •t o aboat 9Ill., • o f Na OR. equiva 1 -£ of the glyeine present was required to bring the pH up to 5' • O. Art$.'.lysis of t ris data on the aa swnption that in excess cobalt only the complex with one glycine molecule pe:r eobalt atom i i formed. that is., Co+++ G :t ~ co++o- +- H+ , leads to a con- st ant value e>f 4.83 for pK1 ., where Ki• ,.. pH range from 5' to 7• ~ {H+J Ho ' < fCt>+~P• over the lfo•• This va.J. ue 1s accurate only within about %. since the concentrations of the solutions ~sed were not knovm to much greater accuracy than this. A.t tempt a to int er• pret the data on the basle of two glycine molecules combining with ea.eh Cc,++ did not give constant valaes for pK".) {Plea = 2 pH ... 1~ ~ 2 log ___ lC~G.3) ·.. ). The eon•tant valae o:r pI,Cl indicates (Cott)½ ( G*) that co++o• is -t :re only com.plex formed und.er· these eondit iona. Further work along these lines would yield desirable inf Ol'nu1.t ion. such work may over...-lap that proposed by Mellor References Browne, c. I.• Th~s~•. Cal if• Inst. of Tech., June 1948. - - Whitney and Davidsoµ, ;r. ...... Amo Chem. Soc., 69, 3076 (1947)• llhitney, Davidson, and ·JtcConnell, Brookhaven Conference ~ •.• }!e12ort, Bl-IL•C•8, P• 196, Dec. 1 ... 3, ··t9'i8.' - Heidt and Daniels, l..• .Na• Chem. Soc., • • - 5~, 2382 (1932). Leighton and Forbes,!!.• Am • .211~• .~o,:•• 2!• 3139 (1930). - Davidson a.nd Sullivan, i• Am.• Ch~m. Soc., 71, 739 (1949)• Glendenin, ~u.s].eonies, ~• 13 ( 1948). 8. Seaborg, Rev. Mod• :Ph:[S•, l,6, 1 ( 1944) • 9• MoKa.y, Nature, 142, 997 ( 1938). 10. Duffield and Calvin, l.• ~• Chem. §,q_q,., !§1 557 ( l946). .· ''11 /i •• Pauling, Na~~.r e of the Chemical Bond, Cornell u.Press ( 1948) Borsook and Thima.nn, 1311o i• :BioJ. Ch em., 98, 671 ( 1932). Riley and Galla.fent, l• Ch~• _§a~. 1 ( 1931) 2029. :u. 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