Rate constants for the coupled two-electron/halide transfer self-exchange reactions of [Cp2MX]+ with Cp2M (M = Ru, Os; X = Cl, Br) have been measured in CD3CN at 298 K by 2D NMR spectroscopic techniques. Including data for the iodo complexes, the rates vary over 6 orders of magnitude depending on the metal and the halide, with the relative orderings I > Br > Cl and Ru > Os. The relative reactant state free energies for the ruthenium complexes have been determined from halide substitution equilibria and indicate that the reactant state energy ordering is Cl < Br < I. From these data and the free energies of activation for the self-exchange reactions, the relative transition state energies have been determined. A reaction coordinate and orbital correlation is proposed which rationalizes the observed data.

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Abstract:The iohne coutent of'twcnty seven species of rnarine/fresli water fish and cral~s cc~llc.ctecl from diffc:rent arsns of Sri Lanka on different days was determined. T l~c ioclin(.: content was dctclmined usjng thc Sandell and Koltl~off reaction. M a i n e 211.4 i-1.9 k~g1100g). Most. of'the iodine in crahs is concenti.atec1 i n the gllls, t;l~us ident,iljrin:: crahs as tho sea hod richest in iodine. The iodine contcilt of marille fish was li~uncl tu he signilicantly lligher (tln-ee to five times) than t h a t oI' Li.t:sl1 wnte~. [is12 except in the cast? ol'Hisio~~7r.ororssglmrlirr.s wluch had a very low iorline lcoel. Large marinc pelagics had n s i g~c a n t l~~ lower level oliodine tllan srnnll pelagics. All species u n d t :~ stucly lost iodine 1111 l~oiling. The percentage loss (~i'ic~dinc fiom crnhs was ahuut tlle same a s from prawns. A comparison (-IS r~ei.cc!ntagc+ ic~clii~e losses fi.oru marine/ii.esl. water fish and o a h s during hoiling irlclicates t,hnt thc losscs from lagc~on crahs, large uiariile pelagics and fl-esh water fi .1 1 . dlt: . signiiicn~ltly higl~er tllan firlrn rnnriile crabs, small r n a~i n e pelngics and mnri~ic fish rt:spectively. Key words crnhs, kesh water fish, iodine, marine fish INTRODUCTIONJodine is an essenti.al, trace element in human nutrition. This element needs t,o be ingested regularly consist,e~lt with the recomlnended daily allowance. A colnplex rnech~lrlisni has evo:lved to acquire iodine from food. and water and to incorporate it i l l t o tyrosine o f t,hyrogIobuljn and eventually to synthesize thyroid hormones.Sea water fish and other marine foods are frequently regarded as a major natural source of dietary jodi~le, but little is known about their fresh water cou11terp;lrts In spite of the importance of iodine t o hulnail health, there are no publications on the iodine content of sea foods consumed in Srj Lanka apart from st,udies of th~s gr ouj> ?:L Recently, we reported1 a stud.y on iodine j.n marine prawns and its fate on boiling. However, more irlformation on iodine in sea foods will undoubtedly be of val:ue to the food ind.ustr,y, medical services (doctors/dieticians) academia and the general public.' Coi~esponding a~l ; h~l -Pleljminary work on marine crabs (Neptu,n.us pelngiczrs) was presented at the an.nual sessions of the Sli Lallka Associativn fur tl3.e Advancemellt of Science 1996.

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