ABSTRACT
Between 6 0 an d 70 % o f th e h u m a n organism's weigh t i s water . I t is presen t bot h
outside th e cell s (extracellularly) , suc h as in the bloodstream , an d inside th e cell s
(intracellularly). Wate r i s a uniqu e substanc e servin g a s a solven t fo r m a n y
biologically importan t substances , a s a mean s o f controllin g bod y temperature ,
as a mean s o f removin g wast e products , an d i n man y othe r capacities . Unde r
normal circumstances , a substanc e wi t h a molecula r weigh t ( M W ) of 1 8 shoul d
be a gas (e.g. , N H 3 , MW 17, o r even propane , M W 44). Ye t water remains a l iquid
up t o 100° C becaus e i t form s intermolecula r hydrogen bonds. Thes e ar e physica l
interactions i n w h i c h a hydroge n ato m wit h a partia l positiv e charg e form s a
bond wi t h a n atom carryin g a n unshared pair o f electrons , suc h a s =0 o r - O . H
atoms attache d t o O o r N, bu t no t t o C , form hydroge n bonds . Ther e i s a partia l
positive charg e (8 +) o n suc h atom s becaus e th e bondin g electron s i n — O H , fo r
example, ar e closer t o th e O ato m (becaus e o f it s larger nucleus) tha n they ar e t o
the H atom . Subsequently , O atom s ma y carr y a partia l negativ e charg e (8~). I n
l iquid water , w e therefor e hav e th e following , wher e th e dotte d line s represen t
hydrogen bonds :
