Muhammad Ashram

Synthesis of calix[4]crowns containing soft donor atoms and a study of their metal–cation binding properties: highly selective receptors for Cu2+

Two new calix[4]arenethiacrown derivatives 1 and 2 in the cone conformation were synthesized by two different pathways in good yield. Their complexation properties toward alkali, alkaline earth and transition metal cations were studied in acetonitrile at 298.15 K using a conductometric titration technique. The selectivity for Cu2+ over other cations with these novel ligands was excellent.

Supramolecular complexation of [60]fullerene with hexahomotrioxacalix[3]naphthalenes: a new class of naphthalene-based calixarenes

The hexahomotrioxacalix[3]naphthalenes 4 and 5 which are members of a new class of inherently chiral naphthalene-based calixarenes were evaluated for their supramolecular complexation properties with [60]fullerene (“C60”). The X-ray structure of a (5)2·C60 clathrate was obtained and compared with the supramolecular complexation data obtained by a 1H NMR study of 4 and 5 with C60 in benzene-d6 and toluene-d8.

Thermodynamic study of the complexes of calix[4]naphthalenes with [60]fullerene in different solvents

Calix[4]naphthalenes are a class of molecules which possess deeper cavities than those of the analogous calix[4]arenes. Preliminary data obtained for the complexation of [60]fullerene (“C60”) with the C4-symmetrical endo-calix[4]naphthalene 3 and its tert-butyl-substituted derivative 4 show that they form supramolecular 1∶1 complexes with C60 in benzene, toluene or CS2 solution with relatively high association equilibrium constants (Kassoc). Reported herein are thermodynamic parameters and additional Kassoc determined for the complexation of C60 and calix[4]naphthalenes 3 and 4 which show that both a solvophobic effect and π–π interactions are major driving forces for the complexation process.

Synthesis of novel p-tert-butylcalix[4]arene Schiff bases and their complexes with C60, potential HIV-Protease inhibitors.

Some p-tert-butylcalix[4]arene Schiff base crown ethers were synthesized, characterized using (1)H, (13)C-NMR, DEPT 135 and Mass spectrometry. Their complexes with C60 were isolated and characterized. The inhibition effect of these complexes on HIVP was studied and found that complexes of 9 and 10 have comparable Ki values to Pepstatine which is known as HIVP inhibitor and used as a control. The synthesis of the ligands, complexes and the inhibition behavior are discussed in this article.

A convenient synthesis of novel 20-, 23-, and 26-membered macrocyclic oxathiadibenzo- and oxathiadinaphthalenocrown ethers, Part 1

A series of novel oxathiadibenzo- and oxathiadinaphthalenocrown ethers 1 - 18 have been successfully synthesized in good yield and in a simple way. They were characterized by NMR, mass spectroscopy and elemental analysis.

Ester derivatives of hexahomotrioxacalix[3]naphthalenes: conformational and binding properties with alkali metal cations

The syntheses of the triesters formed between ethyl bromoacetate and hexahomotrioxacalix[3]naphthalene 8, and its tert-butyl analogue 11, are described. Depending on the conditions employed, cone or partial cone conformers are produced. The conformations appear to have some influence on their complexation in neutral medium, with alkali metal cations. The X-ray structure of the partial cone triester 10 is presented.

A Thermodynamic Study of the Charge Transfer Complexes of Iodine with Different tert-Butylcalix(4)crowns

Formation of the charge-transfer complexes between calix[4]crowns (1 - 4) and iodine in chloroform solution was studied using UV-vis spectrophotometry. The stability constants and the thermodynamic data of the resulting 1 : 1 complexes were determined and was found to decrease with increasing the size of the crown moiety of the calixcrown. All complexes formed were found to be enthalpy stabilized, and all except the complex of 2 were entropy destabilized.

Genotoxicity of different tert-butylcalix[4]crowns.

The ability of two calix[4]arene derivatives, namely 25,27-p-tert-butylcalix[4]dithiooxabenzocrown (1) and 25,27-p-tert-butylcalix[4]trithiooxabenzocrown (2), to produce chromosomal aberrations in root meristematic cells of Allium cepa and micronuclei (MN) in normochromatic erythrocytes (NCE) of Balb/c mice was investigated. NCE are normal mature red blood cells with a full complement of hemoglobin but lack ribosomes. In the first test, the root tips were treated with a series of concentrations of the two test chemicals ranging from 10 - 7 to 10 - 4 M for 24 or 48 h. Both compounds caused concentration-dependent increases in the percentage of aberrant cells and reductions in the mitotic index. These effects depended, to some extent, on the duration of the treatment. The most conspicuous chromosomal abnormalities were c-mitosis, chromosome bridges, chromosome breaks, chromosome lags as well as micronuclei and multinuclei. In the second test, acridine orange fluorescent staining was applied to evaluate the incidence of MN in NCE of mice intraperitoneally injected with varying contents of the two test chemicals (0.02 - 0.08 mg/mouse). The two chemicals induced dose-dependent MN formation as compared to the negative control. The second compound had more pronounced cytogenetic influence than the first one. Mitomycin C (MMC, 14 mg/kg body weight), employed as positive control, produced more obvious effects on the parameters investigated.

A Thermodynamic Study of The Association of K+ And Rb+ Cations with 1,3-Bis(Benzyloxy)-p-tert-butylcalix[4]crown-5 in a CHCl3–Methanol Mixture

The conductivity during the complexation reaction between K+ or Rb+ and 1,3-bis(benzyloxy)- p-tert-butylcalix[4]crown-5 in a CHCl3-methanol mixture at 288 - 303 K has been measured. The conductivity data were analyzed using a computer program based on 1 : 1 stoichiometry. The stability constants of the resulting complexes were determined, indicating that K+ is more stable than Rb+ in the solvents used. The ΔH and Δ S values for the complexation processes were determined from the temperature dependence of the complexation constants. Their significance as well as the solvent effect is discussed.

Chemical reactivity of hydroxymethylnaphthols: hetero-Diels–Alder products of o-naphthoquinomethides derived from 2- and 3-hydroxymethylnaphthols

In relation to the syntheses of exo- and endo-calixnaphthalenes, the chemical reactions of several 2- and 3-hydroxymethylnaphthols, as well as other substituted naphthols, with formaldehyde under a variety of condensation reaction conditions were evaluated. In several instances, o-naphthoquinomethides were the putative intermediates which were formed and which resulted in hetero-Diels–Alder [4+2]cyclodimerization spiro products.