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PubMed2004

Photophysics of calixarenes bearing two or four dansyl fluorophores: charge, proton and energy transfers.

The photophysical properties of calixarenes bearing two and four dansyl derivatives (Calix-DANS2 and Calix-DANS4) were investigated in a CH(3)CN/H(2)O mixture (60 : 40 v/v). The carboxydansyl (DANS1) was used as a reference compound. The pH titration of DANS1 permits determination of two pK(A) values (2.4 and 6.3). The charge-transfer character of this type of fluorophore is discussed. The protonated dansyl group LH(2)(+) undergoes photoinduced proton transfer. The photophysical characterization (absorption spectra, emission spectra, quantum yield and fluorescence decays) of Calix-DANS2 and Calix-DANS4 showed that nonradiative energy transfer occurs from a dansyl fluorophore in the basic form to another one in the neutral form. The transfer efficiencies are 0.1 and 0.5 for Calix-DANS2 and Calix-DANS4, respectively. Fluorescence data analysis allowed us to determine the fractions of dansyl fluorophores in the basic and neutral forms.

Journal Article↗
PubMed2004

Influence of the coordination geometry on the physicochemical properties of a copper(II) complex with a tailor-made calixarene-based ligand bearing dipyridyl pendants. An ESR, UV-Vis and CV study.

Dipyridyl pendants, suitably attached onto a calix[4]arene fixed in its 1,3-alternate conformation, form stable complexes with copper(ii) in acetonitrile. Both the mononuclear and the homobinuclear species ([Cu(1)](2+) and [Cu(2)(1)](4+)), previously detected through a UV-Vis investigation, have been studied by ESR, UV-Vis and cyclic voltammetry. ESR and UV-Vis data clearly indicate that in the [Cu(1)](2+) species the nitrogen atoms of dipyridyl pendants are tetrahedrally arranged around copper(II). Computer models, optimised through molecular mechanics methods, further support these spectroscopic findings. The tetrahedral arrangement, achieved thanks to the anchoring of the dipyridyl moieties onto the calixarene platform, accounts for the easy reversible reduction of this species. The aspects associated with the reduction-oxidation of the homobinuclear species are also discussed.

Journal Article↗
PubMed1985

Effect of antituberculous calixarenes on phospholipase A2 susceptibility and on fusion of phospholipid bilayers.

Some homologous calixarenes or polyoxyethylene ethers that are known to suppress or enhance experimental tuberculous infection (depending on their polyoxyethylene chain lengths) were examined for their effects on phospholipid bilayers. The effect of these solutes is seen at 0.5-50p.p.m., and their effect depends upon their structure as well as that of the phospholipid substrate. The antituberculous compound HOC-12.5 (Macrocyclon) inhibits susceptibility to pig pancreatic phospholipase A2 action and to aggregation/fusion of the ternary co-dispersions of dimyristoyl phosphatidylcholine + 1-palmitoyl lysophosphatidylcholine + palmitic acid (50:11:11 molar proportions). In contrast, the protuberculous compound HOC-60 stimulates these effects. Differential scanning calorimetry suggests that these effects are probably due to modulation of the phase equilibrium in substrate bilayers by these polyethers.

Antitubercular Agents↗
PubMed2006

The formation of endo-complexes between calixarenes and amines--a reinvestigation.

The formation of an endo-complex between p-allylcalix[4]arene and t-butylamine was described by Gutsche in 1985. However, for a comparable system, it has been shown using NOE methods that the amine does not reside inside the calix. Instead, an exo-calix complex is formed. A reevaluation suggests that the previous conclusion is an artifact due to improper NMR-data processing. DFT (RB3LYP/6-31G(d)) calculations confirm the higher stability of the exo-complex over its endo-counterpart.

Amines↗
PubMed1990

Comparison of a calixarene-based ion-selective electrode with two automated analyzers for the clinical determination of sodium in blood plasma.

Neutral-carrier ion-selective electrodes based on methyl p-t-butylcalix[4]aryl acetate have been prepared that are responsive to sodium ions. The miniaturized catheter-type electrodes were obtained by dip-coating their porcelain tips in a PVC membrane cocktail. Examination of the general performance of the electrodes revealed excellent characteristics in terms of Nernstian response, selectivity, stability, reproducibility and response time. The results from the indirect potentiometric assessment of a large number of plasma samples with the electrodes showed a good correlation with the results from two automated analyzers (Technicon Smac 3, Hitachi 704) and with flame photometric data. Although inconsistencies were observed in the measurement of some plasma samples, the variance seemed to be method-dependent, and the overall performance of the electrodes showed promise as an alternative to the sodium glass electrode. Some factors influencing the standard potential of the measuring cell are discussed as a source of error.

Autoanalysis↗
PubMedDate not supplied

New purification protocol for actinide measurement in excreta based on calixarene chemistry.

The determination of actinides concentration level in excreta, mainly urine is currently carried out to monitor people potentially exposed to alpha emitters. To measure actinides in such samples, specific analytical protocols have been set up. The chemical purification uses different chromatographic columns to selectively separate the actinides and each fraction, after electroplating, is measured by alpha spectrometry. To reach 1 mBq l(-1) of U, Pu or Am using these protocols, 6 days equally distributed between the chemical purification and the measurement are necessary. The protocol proposed here is based on a single extractant, the 1,3,5-trimethoxy-2,4,6-tricarboxy-p-tert-butylcalix[6]arene, used to selectively separate U, Pu and Am from the urinary matrix prior to be measured. Using this analytical protocol, U and Pu are quantitatively and selectively recovered in two different acidic backextraction solutions whereas Am is quantitatively and selectively recovered in the organic phase. Furthermore, the purification stage is considerably shortened. The uranium and plutonium amounts are measured in aqueous phases using alpha spectrometry or inductively coupled plasma-mass spectrometry, whereas Am is measured in the organic phase using alpha liquid scintillation (photon/electron-rejecting alpha liquid scintillation).

Actinoid Series Elements↗
PubMed2002

Non-covalent calixarene-amino acid complexes formed by MALDI-MS.

Non-covalent inclusion complexes formed between amino acids and derivatized calix[6]arenes are observed in MALDI mass spectrometry. The methyl, ethyl, and propyl ester derivatives of calix[6]arene yielded amino acid complexes, while the smaller calix[4]arene analogs did not. Similarly the underivatized calix[6]arene and calix[4]arene did not produce complexes. Amino acid complexes were observed for nearly all 20 amino acids in time-of-flight (TOF) analysis. In Fourier transform mass spectrometry (FTMS) analysis, however, only the most basic amino acids arginine, histidine, and lysine formed stable adducts. The complexes were abundant under matrix-assisted laser desorption ionization (MALDI) conditions, which suggested favorable interactions between host and guest.

Amino Acids↗
PubMed2002

Tuning and enhancing enantioselective quenching of calixarene hosts by chiral guest amines.

The synthesis of a propranolol amide derivative of p-allylcalix[4]arene is described, which has been designed to behave as a molecular sensor capable of distinguishing chiral amines on the basis of their shape and chirality. This molecule can discriminate between the enantiomers of phenylalaninol through the quenching of the fluorescence emission in methanol in contrast to an (S)-dinaphthylprolinol calix[4]arene derivative, which can discriminate between the enantiomers of phenylglycinol, but not phenylalaninol. The separation between the naphthyl fluorophores and the hydrogen-bonding sites within the chiral cavity can be tuned to recognize guest amines with similar separation between aryl groups and hydrogen-bonding sites. The formation of metal ion complexes of the p-allylcalix[4]arene propranolol amide derivative is shown to induce a more regular and rigid cone conformation in the calix[4]arene macrocycle, which generates a significant enhancement in the observed enantiomeric discrimination.

Amines↗
PubMed2005

Anionic fullerenes, calixarenes, coronenes, and pyrenes as activators of oligo/polyarginines in model membranes and live cells.

We report that the efflux of 5(6)-carboxyfluorescein anions from neutral egg yolk phosphatidylcholine vesicles is mediated by oligo/polyarginines only in the presence of activating amphiphilic anions. Screening of anion activators reveals best synergism for amphiphilic carboxylates (fullerene > calix[4]arene approximately coronene > pyrene > calix[6]arene > alkyl), whereas amphiphilic sulfates show less satisfactory activation despite often lower effective concentrations. The analogous alcohols and one calix[4]arene diphosphate were inactive. These results are discussed in the context of a tentative anion carrier mechanism, where interactions with bilayer (interface-directed translocation) and carrier (arene-templated carboxylate-guanidinium pairing) contribute to activator efficiencies. Applied to HeLa cells, pyrenebutyrate is shown to significantly increase the uptake of a fluorescently labeled octaarginine in a concentration-dependent manner.

Anions↗
PubMed2006

Energy transfer in calixarene-based cofacial-positioned perylene bisimide arrays.

The synthesis of multichromophoric perylene bisimide-calix[4]arene arrays with up to five perylene units (containing orange, violet, and green perylene bisimide chromophores) and of monochromophoric model compounds was achieved by subsequent imidization of mono-Boc functionalized calix[4]arene linkers with three different types of perylene bisimide dye units. The optical properties of all compounds were studied with UV/vis absorption and steady state and time-resolved fluorescence spectroscopy. Upon excitation of the inner orange dye at 490 nm of array 3, strong fluorescence emission of the outer green perylene bisimide (PBI) chromophore at 744 nm is observed. The fluorescence excitation spectra of compounds 3 and 4 (lambdadet = 850 nm) show all absorption bands of the parent chromophores (e.g., all perylene units contribute to the emission from S1 state of the green PBI). Thus, the fluorescence emission and excitation spectra as well as time-resolved data of fluorescence lifetimes in the absence (tauD = 5.1 ns) and in the presence of an acceptor (tauDA = 0.8 ns) suggest efficient energy transfer processes between the perylene bisimide dye units. For the bichromophoric array 4, the energy transfer rate is calculated to a value of 1.05 x 109 s-1. These results demonstrate highly efficient energy transfer in cofacially assembled dye arrays.

Biomimetic Materials↗