BIOORGANOMETALLIC CHEMISTRY .8. THE MOLECULAR RECOGNITION OF AROMATICAND ALIPHATIC AMINO-ACIDS AND SUBSTITUTED AROMATIC AND ALIPHATIC CARBOXYLIC-ACID GUESTS WITH SUPRAMOLECULAR 5)-PENTAMETHYLCYCLOPENTADIENYL)RHODIUM-NUCLEOBASE, NUCLEOSIDE, AND NUCLEOTIDE CYCLIC TRIMER HOSTS VIANONCOVALENT PI-PI AND HYDROPHOBIC INTERACTIONS IN WATER - STERIC, ELECTRONIC, AND CONFORMATIONAL PARAMETERS

Molecular recognition, via non-covalent processes such as hydrogen bon ding, pi-pi, and hydrophobic interactions, is an important biological phenomenon for guests, such as drugs, proteins, and other important bi ological molecules with, for example, host DNA/RNA. We have studied a novel molecular recognition process using guests that encompass aromat ic and aliphatic amino acids [L-alanine, L-glutamine (L-Gln), L-histid ine, L-isoleucine (L-Ile), L-leucine (L-Leu), L-phenylalanine (L-Phe), L-proline, L-tryptophan (L-Trp), L-valine (L-Val)], substituted aroma tic carboxylic acids [o-, m-, p-aminobenzoic acids (G1-3), benzoic aci d (G4), phenylacetic acid (G5), p-methoxyphenylacetic acid (G6), o-met hyoxybenzoic acid (G9), o-nitrobenzoic acid (G10)], and aliphatic carb oxylic acids [cyclohexylacetic acid (G7), 1-adamantanecarboxylic acid (G8)] with supramolecular, bioorganometallic hosts, (eta(5)-pentamethy lcyclopentadienyl)rhodium (CpRh)-nucleobase, nucleoside, and nudeotid e cyclic trimer complexes, [CpRh(9-methyladenine)](3)(OTf)(3) (1) (OT f = trifluoromethanesulfonate), [CpRh(adenosine)](3)(OTf)(3) (2), [Cp Rh-(2'-deoxyadenosine)](3) (OTf)3 (3), [Cp*Rh(2',3'-dideoxyadenosine) ](3)(OTf)(3) (4), and [CpRh(Me-5'-AMP)](3) (5), in aqueous solution a t pH 7, utilizing H-1 NMR, NOE, and molecular modeling techniques, and , as well, determining association constants (K-a) and free energies o f complexation (Delta G(degrees)). The host-guest complexation occurs predominantly via non-covalent pi-pi, hydrophobic, and possible subtle H-bonding interactions, with steric, electronic, and molecular confor mational parameters as important criteria. Moreover, we note that both the pi-pi and hydrophobic interactions seem to be equally important w hen competing aromatic and aliphatic carboxylic acid guests, G5 and G7 , for host 3. The solvophobic effects in H2O also control the extent o f host-guest interaction and will be discussed.