Reza Zadmard

Calixarene Dimers as Host Molecules for Biologically Important Di‐ and Oligophosphates

A dimeric calixarene, with an aliphatic C(6)-bridge and six anilinium head groups at its upper rim, preferably complexes diphosphates and oligonucleotides with more than 10 bonds between both anionic moieties. Free binding energies correlate with the length of the aliphatic bridge in a roughly linear fashion. The binding event, which is monitored by fluorescence titrations and competition experiments, relies on Coulomb interactions, as opposed to a nonpolar variant with tert-butyl instead of ammonium groups; here, hydrophobic forces prevail, rendering the calixarene dimer selective for less polar cofactors such as FAD. The best guest for the hexaanilinium dimer is found in ssDNA, which carries multiple copies of the optimal trinucleotide for maximum attraction towards the extended cationic host. The recognition event is also observed in the environment of a lipid monolayer, and provides a means to quantify dimer diphosphate interactions by measuring p/A shifts.

Multivalent calix[4]arene-based fluorescent sensor for detecting silver ions in aqueous media and physiological environment.

A new derivative of dipodal 1,3-calix[4]arene-based chemosensor (R), which was containing several binding sites have been synthesized and characterized by NMR, IR and LC-MS spectroscopic methods. The selectivity of Rhas been investigated in aqueous methanol, resulting in fluorescence shift and selective recognition of Ag+ among 20 various alkali, alkaline earth and transition metal ions. Microstructural features of R and its complex with Ag+have been investigated by Atomic Force Microscopy (AFM). AFM images can clearly differentiate R from its complex of Ag+. Moreover; the complicated binding mode of metal-ligand complex has been explored by UV-Vis, LC-MS, FIR, Fluorescence titration, Jobs plot method and theoretical approaches. Density functional theory (DFT) method at B3LYP/LANL2DZ level of theory was employed for computational studies. Theoretical calculations revealed that selectivity and specificity of R toward Ag+ could be attributed to structural conformation of 1,3-alternate-calix[4]arene scaffold and molecular electrostatic potential of its surface. Furthermore; the competitive experiments were carried out to test sensors ability for practical uses. Finally, the efficiency of R in matrix of physiological cations was examined and showed gradual emission enhancement which makes R an ideal candidate for monitoring of Ag+ in physiological environment.

Aminopyrazole Oligomers for β-SheetStabilization of Peptides

A general concept for the stabilization of β-sheets by designed artificial ligands is introduced. The ligands have two key features: they contain acylated 3-aminopyrazoles with a DAD hydrogen bond donor and acceptor pattern, and they were synthesized as oligomers in order to multiply their hydrogen bond interactions with peptides in the β-sheet conformation. Dimeric aminopyrazoles were accessible by reaction of the N1-Boc-protected aminopyrazole derivative 1 with several acid dichlorides followed by a standard deprotection procedure with trifluoroacetic acid. For the oligomers, Nl-PMB protection of new pyrazole amino acids followed by an iterative extension protocol with peptide coupling using PyClop or Mukaiyamas reagent led to the target compounds. All protecting groups were subsequently removed in a final deprotection step with warm trifluoroacetic acid. Two dimeric key compounds 3b and 3f were examined by NMR at various temperatures, in NOESY experiments as well as by X-ray crystallography in order to elucidate their conformational preference in solution and the solid state. The emerging picture was the same for all methods: both ligands adopt a flat conformation with a high degree of pre-orientation and the correct DAD pattern for optimal interaction with peptides in their extended conformation. Aggregation assays with the Prion protein and the Alzheimers peptide Aβ (1-40) show highly promising results for some of the dimeric and oligomeric ligands at very low concentrations.

Calix[4]arene-based crab-like molecular sensors for highly selective detection of mercury and copper ions

Abstract In this work, two novel chemosensors based on calix[4]arene bearing (thio)barbituric acid groups (BC1 and BC2) were synthesised, and their structures were characterised by HRMS, NMR and FTIR. Furthermore, their binding properties towards various biologically relevant metal ions were studied by fluorescence titrations, 1H NMR spectroscopies and Job’s plot evaluations. The chemosensor BC1 displayed excellent binding affinity and selectivity towards Cu2+, which was characterised using fluorescence spectroscopy. On the other hand, BC2 exhibited a very remarkable fluorescence enhancement as well as visible colour change from pale green to sunset yellow, in presence of Hg2+ ions. Finally, Job’s plot method revealed 1:1 binding stoichiometry for both BC1:Cu2+ complex and BC2:Hg2+ complex.

A convenient and efficient one-pot method for the synthesis of novel acridine-calix[4]arene derivatives as new DNA binding agents via multicomponent reaction

A new approach is applied for the synthesis of novel acridine-calix[4]arene derivatives via a multicomponent reaction. These compounds have been characterised by 1H NMR, 13C NMR and HR-MS. Our binding studies between acridine-functionalised calix[4]arenes and calf thymus DNA (CT-DNA) via fluorescence titration show that these compounds have a good affinity to CT-DNA. A new approach is applied for the synthesis of novel acridine-calix[4]arene derivatives via a multicomponent reaction. These compounds have been characterised by 1H NMR, 13C NMR and HR-MS. Our binding studies between acridine-functionalised calix[4]arenes and calf thymus DNA (CT-DNA) via fluorescence titration show that these compounds have a good affinity to CT-DNA.

Synthesis and protein binding properties of novel highly functionalized Calix[4]arene

A novel protein binding agent based on highly functionalized calix[4]arene 5 has been synthesized and its structure characterized by 1H and 13C NMR, FT-IR and HRMS spectral data. Protein binding studies carried out using fluorescence spectroscopic technique revealed that this compound could bind strongly to lysozyme. Furthermore, the effect of compound 5 on the conformation of lysozyme was investigated using three-dimensional fluorescence spectroscopy. Finally, the influence of various biological relevant metal ions on the binding constant of lysozyme with 5 was studied.

Palladium chloride-catalyzed reductive cleavage of benzylic acetal, ketal and ether compounds with triethylsilane

Reductive cleavage of benzylic acetal, ketal and ether compounds to the corresponding alkanes using triethylsilane and a catalytic amount of palladium(II) chloride is described. The reductive reaction took place under mild conditions, affording high yields of the corresponding alkane compounds in short reaction times.

Synthesis of a New Calix[4]Arene and Its Application in Construction of a Highly Selective Silver Ion-Selective Membrane Electrode

A PVC membrane sensor for Ag (I) ions has been prepared. The membrane has 5, 11, 17, 23-tetra-tert-butyl-25-(3-N, N-diethyldithio carbamoylpropoxy)-26,27,28-tris-propoxy calix[4]arene (CAD) as a carrier. It was found that the sensor exhibits a Nernstian response for Ag

Functionalized calix[4]arene-based receptor for saccharide recognition

A novel class of functionalized-calix[4]arene such as 1,4-dihydropyridine-calix[4]arene, acridine-calix[4]arene and pyrimidine-calix[4]arene were synthesized using multicomponent reaction. These compounds have been characterized by 1H NMR, 13C NMR and HRMS. Fluorescent and 1H NMR titration investigations reveal that these derivatives have the high binding constant towards the monosaccharide and disaccharide in aqueous solution. The formation of complex was also supported by electrospray mass spectrometry.

Synthesis, characterization and selective Cu2+ recognition of novel E– and Z–stilbenophanes

ABSTRACT We have demonstrated the synthesis and characterization of novel E- and Z-stilbenophanes via four reaction steps. X-ray structure analysis showed that the p-electrons of the double bonds and the oxygen atoms pointing towards the center of a cavity of Z-isomer. Both isomers recognize selectively Cu2+ ions over other competing metal ions as measured by UV-vis titration by the detection limit 10–12 µM. The 1:1 ratio complex formation was confirmed by HRMS analysis. Theoretical calculations based on GIAO and CMAD approaches and 1H NMR analysis confirmed the UV-vis data of Z-isomer. Graphical Abstract