A study of C-F...M(+) interaction: metal complexes of fluorine-containing cage compounds

The C-F...M(+) interaction was investigated by observation of the NMR spectroscopic changes and complexation studies between metal cations and the cage compounds 1 and 2 which have fluorobenzene units as donor atoms. As a result, the interaction was detected with all of the metal cations which form complexes with 1 and 2. The stability of the complexes of 1 and 2 was determined by the properties of the metal cations (ionic radii and degree of hydrolysis), not by the hard-soft nature of the cations. Crystallographic analyses of Tl(+) subset 1 and La(3+) subset 2 provided structural information (interatomic distances and bond angles), and the bond strengths, C-F...M(+), O...M(+), and N...M(+), were estimated by Brown's equation based on the structural data. Short C-F...Tl(+) (2.952-3.048 A) distances were observed in the complex Tl(+) subset 1. The C-F bond lengths in the complexes, Tl(+) subset 1 and La(3+) subset 2, are elongated compared to those of the metal-free compounds. Interestingly, no solvent molecules including water molecules were coordinated to La(3+) in the La(3+) subset 2. The stabilization energy of cation-dipole interaction was calculated on the basis of the data from X-ray crystallographic analysis, and it is roughly consistent with the (-)Delta H values estimated in solution. Thus, the C-F...M(+) interaction can be expressed by the cation-dipole interaction. This result explains the fact that compound 1 which has fluorine atom as hard donor strongly binds soft metals such as Ag(+) and Tl(+). Furthermore, it was concluded that the fluorobenzene unit has a poor electron-donating ability compared to that of ether oxygen or amine nitrogen, and thus the ratio of the coordination bond in C-F...M(+) is small. The specific and remarkable changes in the (1)H, (13)C, and (19)F NMR spectra were observed accompanied by the complexation between M(+) and the hosts 1 and 2. These spectral features are important tools for the investigation of the C-F...M(+) interaction. Furthermore, F.Tl(+) spin couplings were observed at room temperature in the Tl(+) subset 1, 2 (J(F-Tl) = 2914 Hz for Tl(+) subset 1 and 4558 Hz for Tl(+) subset 2), and these are clear and definitive evidence of the interaction.

Synthesis, electronic spectra, and crystal structural properties of fluorinated [3(3)](1,3,5)cyclophanes

[structure: see text] Trifluoro- and hexafluoro[3(3)](1,3,5)cyclophanes 3 and 4 were synthesized with TosMIC coupling as a key reaction. The pi-pi absorption bands show blue shifts as the number of fluorine atoms is increased. In the crystalline state, characteristic stacking with the fluorinated benzene rings facing each other is observed in both cases.

A study of C-F.M+ interaction: alkali metal complexes of the fluorine-containing cage compound

The C-F.M(+) interaction was investigated by employing a cage compound 1 that has four fluorobenzene units. The NMR ((1)H, (13)C, and (19)F) spectra and X-ray crystallographic analyses of 1 and its metal complexes showed clear evidence of the interaction. Short C-F.M(+) distances (C-F.K(+), 2.755 and 2.727 A; C-F.Cs(+), 2.944 and 2.954 A) were observed in the crystalline state of K(+) subset 1 and Cs(+) subset 1. Furthermore, the C-F bond lengths were elongated by the interaction with the metal cations. By calculating Brown's bond valence, it is shown that the contribution of the C-F unit to cation binding is comparable or greater than the ether oxygen in the crystalline state. Representative spectroscopic changes implying the C-F.M(+) interaction were observed in the NMR ((1)H, (13)C, and (19)F) spectra. In particular, (133)Cs-(19)F spin coupling (J = 54.9 Hz) was observed in the Cs(+) complex.

Structural essentials of xenoestrogen dialkyl phthalates to bind to the estrogen receptors

Xenoestrogen dialkyl phthalates, C(6)H(4)(COOC(n)H(m))(2), lack the phenolic hydroxyl group that is an essential structural component of the steroid A ring of 17 beta-estradiol. In order to examine whether dialkyl phthalates imitate the steroid structure, we have synthesized a series of 4-hydroxyl derivatives of dialkyl phthalates. The compounds were examined for their ability to displace [(3)H]17 beta-estradiol from the recombinant human estrogen receptor, which was expressed on Sf9 cells using the vaculovirus expression system. Dialkyl 4-hydroxyl phthalates were found to exhibit several-fold higher binding affinities compared to phthalates without the 4-hydroxyl group. From the analyses of receptor binding modes of dialkyl phthalates with and without the 4-hydroxyl group, it was deduced that the phthalic benzene ring mimics the steroid A ring. A biphasic binding curve observed for dicyclohexyl phthalate was also depicted by its 4-hydroxyl derivative, but it increased binding affinity only at the high affinity binding site. These data suggest that the phthalate benzene moiety recognizes the core of the estrogen receptor binding site and the hydrophobic interaction of the dialkyl moiety substantiates the binding characteristics of the phthalates. The present data indicate that even chemicals with slight structural analogy and weak receptor affinity can perturb the endocrine system when administered in high concentrations.

The C-F...cation interaction: an ammonium complex of a hexafluoro macrocyclic cage compound

An ammonium complex of the hexafluoro cage compound 1 was isolated and its structure was elucidated by X-ray crystallographic analysis. The C-F bonds are elongated by the complexation, which is clear evidence of C-F...cation interaction. The driving force of NH4(+) inclusion is the C-F cation interaction, but the C-F...HN+ hydrogen bond does not contribute to this complexation. The crystal structure of the NH4+ complex 1 shows short C-F...HN+ contacts (2.286-2.662 A). Furthermore, it shows that closer F...H(+)(-N) distances give a larger F...H(+)-N angle. Although such structural features seem to indicate the existence of C-F...HN+ hydrogen bonds, the spectral data (1H NMR, 19F VT-NMR, and IR spectroscopy) did not support the existence of hydrogen bonds. Thermodynamic parameters, log K(s) (4.6 +/- 0.1, 298 K), deltaH (-5.3 +/- 0.1 kcal mol(-1)), and deltaS (3.2 +/- 0.3 cal mol(-1) K(-1)), of the complexation were obtained in CDCl3/CD3CN mixture.

Structural requirements of para-alkylphenols to bind to estrogen receptor

Octyl- and nonylphenols in the environment have been proposed to function as estrogens. To gain insight into their structural essentials in binding to the estrogen receptor, a series of phenols with saturated alkyl groups at the para position, HO-C6H4-CnH2n+1 (n = 0-12), were examined for their ability to displace [3H]17beta-estradiol in the recombinant human estrogen receptor, which was expressed in Sf9 cells using the vaculovirus expression system. All tested para-alkylphenols were found to bind fully to the estrogen receptors in a dose-dependent manner. The interaction of alkylphenols with the receptor became stronger with increase in the number of the alkyl carbons and the activity was maximized with n = 9 of nonylphenol. Phenol (n = 0) exhibited weak but full binding to the receptor, whereas anisole with a protected phenolic hydroxyl group was completely inactive. Also, alkanes such as n-octane, 2,2, 4-trimethylpentane corresponding to tert-octane, and n-nonane exhibited no binding. The results indicate that the binding of para-alkylphenols to the estrogen receptor is due to the effect of covalent bonding of two constituents of the phenol and alkyl groups, which correspond to the A-ring and hydrophobic moiety of the steroid structure, respectively. When alkylphenols were examined for their receptor binding conformation by 1H-NMR measurements and ab initio molecular orbital calculations, it was suggested that nonbranched alkyl groups are in an extended conformation, while branched alkyl groups are in a folded conformation. These results suggest that branched and nonbranched alkyl moieties of alkylphenols interact differently with the lipophilic ligand binding cavity of the estrogen receptor when compared to the binding of 17beta-estradiol.