preferred compounds are those wherein r , r 1 , r 2 and r 3 designate lower alkyl with n = 1 or 2 , m = 0 , and q = 0 or 1 . amongst other preferred compounds , are those with n = 1 or 2 , q = zero or 1 , r 1 = lower alkyl , preferably methyl , or -- ch 2 ch 2 cooalk , where alk designates lower alkyl , with r 2 = methyl and r 3 = methyl or propyl . the compounds of the present invention are tetradentate ligands which are suited for the selective extraction of a certain cation from a mixture of cations . the binders of the invention are designed in a modular fashion and fulfil the following requirements : i ) they define an ion binding cavity to fit a specific metal ion , and preferably ( ii ) create a lipophilic envelope . the cavity comprises two hydroxamate groups as binding sites . these groups are organized by the molecules &# 39 ; skeleton to form tetrahedral cavities of appropriate size . the lipophilic envelope is created by the use of lipophilic side chains to attain a solubility of the molecule and of its complex in lipid membranes . hydroxamate groups were chosen as ion binding groups in view of three major considerations : ( i ) their high binding affinity to a large range of metal ions , ( ii ) their ph dependent binding properties that allow to control metal uptake on one side of the membrane and metal release on the other side , and ( iii ) their capability to form electrically neutral complexes when binding divalent transition metal ions thereby enhancing solubility in lipids . according to this general principle , ion binders and carriers were designed and synthesized in a modular fashion . the planned modularity simplifies synthesis on one hand , and allows variability in the assembly of the modules on the other . the synthesis of these binders was performed in essentially three steps as illustrated beneath for the family of compounds with n = 2 , m = o , q = 1 . ( i ) alkylation of the parent alcohol and transformation to the corresponding acid derivative , ## str1 ## ( ii ) preparation of the amino - hydroxamate residues by condensation of the chosen amino acid with hydroxyl amine . this involves preparation of the pentachlorophenolate iv , coupling with hydroxylamine to give v and removal of the protecting group by hydrogenation to give vi . ## str2 ## where cb 2 is carbobenzoxy , ( iii ) condensation of the acid derivative with the desired amino - hydrozamate to the final products : ## str3 ## according to this procedure compounds were prepared where n = 2 , m = o , q = 1 r 1 = r 2 = r 3 = me and r = ibu , and where n = 2 , q = 0 , r 1 = r 2 = r 3 = me . in a related sequence compounds were prepared where n = 1 , m = o and q = 1 . the steps are as follows : ( i ) alkylation of the parent alcohol and transformation to the corresponding acid derivative , ## str4 ## ( ii ) preparation of the amino - hydroxamate residues by condensation of the chosen amino acid the hydroxyl amine . this involves preparation of the active ester iv , condensation with hydroxylamine to give v , and removal fo the protecting group to give vi . ## str5 ## ( iii ) condensation of the acid derivative with the desired amino - hydroxamate to the final products . ## str6 ## in this manner compounds r 1 = r 2 = r 3 = me , and r = ibu or me were prepared . ## str7 ## by sequences analogous to those shown above , compounds were prepared where n = 1 , q = 0 , r 1 = me or ch 2 ch 2 cooet , r 2 = r 3 = me or r 2 = me and r 3 = pr . ## str8 ## 3 . experimental procedure of synthesis of bishydroxamate vii ( n = 2 , m = o , q = 1 , r = ibu , r 1 = r 2 = r 3 = ch 3 9 . 36 g 1 , 1 , 1 - tris ( hydroxymethyl ) propane with 0 . 6 ml 40 % aq . naoh and then 13 . 2 ml acrylonitrile ( freshly purified by passing through neutral alumina ) are added so that the temperature does no exceed 30 ° c . then the mixture is stirred overnight at room temperature , neutralized with diluted aq . hcl , dissolved in 500 ml ethyl acetate , washed with water , dried and concentrated to give 18 . 45 g material ( tlc : toluene - ethyl acetate 85 - 15 ). the crude product is hydrolyzed by treating 2 . 40 g with 2 . 7 ml conc . hcl in an oil bath of 95 °- 100 ° c . for 6 hrs . after cooling to room temperature the residue is suspended in ethylacetate , washed with water , dried and concentrated to give 2 . 1 g diacid . 3 . 7 g ( 0 . 015 mol ) of crude diacid are dissolved in 200 ml acetonitrile ( dried over alumina ), 8 . 7 g pentachlorophenol and 400 mg dimethylaminopyridine are added , the mixture cooled in an ice bath and treated with 5 . 0 ml diisopropylcarbodiimide . then the mixture is allowed to warm up to room temperature and stirred for 1 - 2 days . concentration in vacuo and chromatography on silica gel ( toluene - ethyl aceytate 98 - 2 ) yields 2 . 83 g of the biscarboxylate iii , mp 88 °- 90 ° c . 3 . 2 . preparation of hydroxamate vi ( r = ibu , r 1 = ch 3 ) 5 . 3 g ( 0 . 02 mol ) cbz - l - leucine are dissolved in 150 ml acetonitrile ( dried over basic alumina ), 5 . 8 g ( 0 . 022 mol ) pentachlorophenol are added and under cooling 3 . 9 ml ( 0 . 025 mol ) diisopropylcarbodiimide . the mixture is stirred for 1 day at room temperature , concentrated , chromatographed on silica gel and then filtered through neutral alumina to provide 10 . 41 g of pure pentachlorophenolate , mp 125 °- 126 ° c . 5 . 2 g ( 0 . 01 mol ) of phenolate are dissolved in 50 ml dry methylenechloride and treated with a solution containing 1 . 04 g ( 0 . 0125 mol ) methylhydroxyl amine hydrochloride , 1 . 21 g ( 0 . 0125 mol ) triethyl amine and 50 mg n - hydroxysuccinimide in 100 ml methylenechloride . the mixture is stirred over night , concentrated in vacuo and the residue chromatographed on silica gel ( chloroform - methanol 99 - 1 ) to provide 1 . 30 g pure z - leuhydroxamate , mp 71 °- 73 ° c . 960 mg ( 0 . 003 mol ) of the latter are dissolved in 100 ml ethanol and hydrogenated at atmospheric pressure in the presence of 500 mg pd / c , 10 %. filtration , concentration and chromathography on silicagel ( chloroformmethanol 8 - 2 ) yields 472 mg of pure hydroxamate vi . 3 . 3 . preparation of hydroxamate vii ( n = 2 , m = o , q = 1 , r = ibu ), r 1 = r 2 = r 3 = ch 3 ). 1 . 13 g biscarboxylate iii are dissolved in 50 ml dry methylene chloride and treated with a solution containing 675 mg hydroxamate vi , 50 mg n - hydroxysuccinimide and 300 mg imidazole in 50 ml methylyenechloride for 4 days . chromatography of the crude reaction product on silica gel ( chloroform , chloroformmethanol 99 - 1 as eluents ) yields 542 mg of the bishydroxamate vii ( mp . 44 °- 46 ° c .). several of the ion binders , when incorporated into bulk membranes , selectively extract and transport a specific metal ion from a plurality of cations . an example is the quantitative separation of cu 2 + from a mixture of six two - valent metal ions . this is illustrated by the quantitative removal of cu 2 + from an equimolar mixture ( 10 mm each ) of pb 2 + , cu 2 + , cd 2 + , co 2 + , zn 2 + and ni 2 + in water . using a bulk membrane consisting of 0 . 3 mm of the most lipophilic carrier ( n = 2 , m = o , q = 1 , r = ibu , r 1 = r 2 = r 3 = ch 3 ) in chcl 3 and a receiver containing 0 . 1m h 2 so 4 , cu 2 + was quantitatively removed without a trace of contamination by other metals ( as determined by ion chromatographic analysis on a dionex instrument ( see fig1 ). ( the experiments were performed in u - tubes which are the standard laboratroy method for simulating extraction procedures .) a second example is the removal of zn 2 + without any contamination of cd 2 + ( according to ion chromatography ) from an equimolar mixture of zn 2 + and cd 2 + ( 20 mm each ), when applying the same carrier ( n = 2 , m = o , q = 1 , r = ibu , r 1 = r 2 = r 3 = ch 3 ) at 3 . 0 mm concentration in chloroform . a third example is the removal of cu 2 + from an equimolar mixture of cu 2 + and fe 3 + ( 3 mm each in the presence of 6 mm citric acid titrated to ph 6 . 8 with koh ) with less than 10 % contamination of fe 3 + , by using a carrier ( n = 2 , m = o , q = 0 , r 1 = ch 3 ) 4 . 5 mm concentration in chloroform and in the receiver phase 3 mm dtpa at ph2 . ______________________________________characteristics of some of the carriers prepared : partitionn r r . sup . 1 r . sup . 2 r . sup . 3 mp coefficients______________________________________q = 01 me me me 142 - 145 2 . 251 me me pr 102 - 104 1 . 951 ch . sub . 2 ch . sub . 2 cooet me me oil 3 . 161 ch . sub . 2 ch . sub . 2 cooet me pr oil2 me me me oil 0 . 82q = 11 me me me me 32 - 35 ° c . 1 . 951 ibu me me me 28 - 30 ° c . 3 . 72 ibu me me me 44 - 46 ° c . 15 . 8______________________________________ partition coefficients relate to octanol saline ( 1 : 1 ) partition 1 . a . k . de , s . m . khopar , r . a . chalmers , ` solvent extraction of metals `, van nostrand reinhold company , london , 1970 . 2 . r . w . baker , m . e . tuttle , d . j . kelly and h . k . lonsdale , j . membr . sc ., 2 , 213 ( 1977 ). 3 . e . kimura , c . a . dalimunte , a . yamashita , r . machida , j . chem . soc ., chem comm ., 1041 ( 1985 ). 4 . k . maruyama , h . tsukube , t . araki , j . chem . soc ., dalton , 1486 ( 1981 ). 5 . k . maruyama , h . tsukube , t . araki , j . amer . chem . soc ., 102 , 3246 ( 1980 ). 6 . s . matsuno , a . ohki , m . takagi , k . ueno , chem . letters , 1543 ( 1981 ).