Peter Huszthy

Enantiomeric recognition of chiral ammonium salts by chiral pyridino- and pyrimidino-18-crown-6 ligands: Effect of structure and solvents

Chiral pyridino- 18-crown-6 ligands interact with chiral primary organic ammonium salts by hydrogen bonding from the ammonium cation to the pyridino nitrogen and two alternate ring oxygen atoms. Enantiomeric recognition in these interactions are caused by the steric bulk of the substituents at chiral macrocycle ring positions. Recognition is best for the interaction of chiral pyridino-18-crown6 hosts with the enantiomers of a-( 1-naphthylethy1)ammonium perchlorate (NapEtHC10,) over (a-phenylethy1)ammonium perchlorate (PhEtHClO,) possibly because of a greater x-x overlap between the naphthalene ring of the guest and pyridine ring of the host. Solvents play an important role in the degree of recognition. A binary solvent composed of 7/3 &H4C12/CH,0H (v/v) gave an enhanced degree of recognition. A new chiral pyrimidino- 18-crown-6 ligand exhibited recognition for the enantiomers of NapEtHC10,.

Proton ionizable crown compounds. 18. Comparison of alkali metal transport in a H2O-CH2Cl2-H2O liquid membrane system by four proton-ionizable macrocycles containing the dialkylhydrogenphosphate moiety

The macrocycle-mediated fluxes of alkali, alkaline earth, and several transition metal cations have been determined and compared in a H2O-CH2Cl2-H2O liquid membrane system using four water-insoluble macrocycles containing a dialkylhydrogenphosphate moiety. Transport of alkali metal cations by these ligands was greatest from a source phase pH = 12 or above into an acid receiving phase (pH = 1.5). Very low fluxes were observed for the transport of the alkaline earth cations and all transition metal ions studied except Ag+ and Pb2+ which were transported reasonably well by these new macrocycles.

Proton-ionizable crown compounds. 12. Proton-Coupled selective membrane transport of Li+ using a proton-ionizable pyridono macrocycle

The macrocycle-mediated fluxes of several alkali metal cations have been determined in a H2O-CH2Cl2-H2O liquid membrane system. Water-insoluble proton-ionizable macrocycles of the pyridono type were used. The proton-ionizable feature allows the coupling of cation transport to reverse H+ transport. This feature offers promise for the effective separation and/or concentration of alkali metal ions with the metal transport being driven by a pH gradient. A counter anion in the source phase is not co-transported. The desired separation of a particular metal ion involves its selective complexation with the macrocycle, subsequent extraction from the aqueous phase to the organic phase, and exchange for H+ at the organic phase-receiving phase interface. Factors affecting transport which were studied include ring size, source phase pH, and receiving phase pH. Lithium was transported at a rate higher than that of the other alkali metals in both single and competitive systems using a 15-crown-5 pyridono carrier.

A thermodynamic study of enantiomeric recognition of organic ammonium cations by pyridino-18-crown-6 type ligands in methanol and a 1: 1 methanol-1,2-dichloroethane mixture at 25.0°C

LogK, ΔH, andTΔS values for interactions of (R) and (S) enantiomers of α-(1-naphthyl)ethylammonium perchlorate (NapEt), α-phenylethylammonium perchlorate (PhEt), and the hydrogen perchlorate salt of 2-amino-2-phenylethanol (PhEtOH) with a series of chiral and achiral pyridino-18-crown-6 type ligands and 18-crown-6 (18C6) were determined from calorimetric titration data valid in methanol and in a 1: 1 (v/v) methanol-1,2-dichloroethane (MeOH-1,2-DCE) mixture at 25.0°C. In the MeOH-1,2-DCE solvent mixture, the chiral macrocyclic ligands exhibit excellent recognition for enantiomers of the three organic ammonium cations as shown by large differences in logK values (Δ logK) which range from 0.4 to 0.6 (2.5- to 4.0-fold difference in binding constants). The Δ logK values in the solvent mixture MeOH-1,2-DCE are increased by 0.1–0.5 logK units over those in absolute methanol, indicating a favorable effect of 1,2-dichloroethane on enantiomeric recognition. In 1,2-dichloroethane, however, the interactions are too strong (logK>6) to observe the degree of recognition by a direct calorimetric method. Complexation of organic ammonium cations by these macrocyclic ligands is driven by favorable enthalpy changes. The entropy changes ure unfavorable in all cases. The thermodynamic origin of enantiomeric recognition for NapEt in 1:1 (v/v) MeOH-1,2-DCE is enthalpic, but those for PhEt and PhEtOH are entropic. Effects of the ligand structure and flexibility and of the organic cation structure on recognition and complex stability are discussed on the basis of the thermodynamic quantities. Different thermodynamic behaviors of achiral 5 and 18C6 from those of chiral macrocyclic ligands indicate a difference between chiral and achiral macrocycle interactions with the chiral organic ammonium cations. The different thermodynamic behavior of NapEt enantiomers compared to those of PhEt and PhEtOH enantiomers supports the idea that the solution complex conformation of NapEt is different from those of PhEt and PhEtOH. π-π interaction is absent for the PhEt and PhEtOH complexes with diesterpyridino-18-crown-6 ligands in solution. Therefore, the higher degree of enantiomeric recognition for NapEt than for either PhEt or PhEtOH by these chiral macrocyclic ligands is a result of the presence of π-π interaction in the NapEt system.

A structural analysis of the complexes of (S, S)-dimethylpyridino-18-crown-6 with (R) and (S)-[α-(1-naphthyl)ethyl]ammonium perchlorate by NMR techniques and molecular modeling

Significant π-π interaction is found in the complexes of (S, S)-dimethylpyridino-18-crown-6 with (R)- and (S)-[α-(1-naphthyl)ethyl]ammonium perchlorate. This finding is supported by the1H NOESY NMR spectral technique, greater chemical shift changes of aromatic protons in both host and guest molecules upon complexation, and by molecular mechanics calculations. Because of the flexibility of the ligand, the tripod hydrogen bonding causes13C relaxation times of all periphery carbons to decrease without significant selectivity. Rotational energy barrier calculations of the methyl groups of the complexed ligand also show that the (S, S)-host-(R)-guest is the more stable complex.

Various aspects of enantiomeric recognition of (S,S)-dimethylpyridino-18-crown-6 by several organic ammonium salts

Abstract Factors responsible for complex stability and enantiomeric recognition for the interactions of (S,S)-dimethylpyridino-18-crown-6 with several organic ammonium salts were examined using an 1H NMR technique. The results indicate that cation structures have a significant effect on enantiomeric recognition; solvents play a very important role in the stability of the complexes, and anions can compete with ligands for the ammonium cations.

A new method to extend dimercaptan or diamine chains with aminopropyl units using 3-bromo-N-tritylpropanamine

Abstract Dimercaptans and diamines react with 3-bromo-N-tritylpropanamine to give the corresponding N,N′-ditrityldithia and N,N′-ditritylpolyaza compounds in yields of 50–80%. The trityl protecting groups are readily removed in acid. These reactions make possible the synthesis of a number of new α-ω-diamino compounds needed for the synthesis of new dithiadiaza, di- and polyaza macrocyclic ligands.

Two new methods to form substituted oligoethylene glycols

Abstract 1-Bromo-2-trityloxyethane ( 1 ) and 1-allyloxymethyl-2-trityloxyethanol ( 2 ) react readily at room temperature with substituted oligoethylene glycols or the ditosylate derivative of an oligoethylene glycol, respectively, to form the extended, ditrityl-protected, substituted oligoethylene glycols in high yields. The trityl groups are easily removed by acidified methanol in CH 2 Cl 2 to give the extended, substituted oligoethylene glycols.