Electrochemical activity of phenolic calixarenes

A preliminary evaluation of the electrochemical behaviour of phenolic calix[n]arenes (n=4,6) possessing either H- or tert-butyl functionality at the para-phenol position has been undertaken by cyclic voltammetry. Electrochemical activity of these calixarenes is an inherent property, due to oxidation of the phenolic moiety in both types of calixarene. Oxidation of the p-H-substituted calixarenes leads to an electrode passivation process whereas oxidation of the p-t-butyl-substituted calixarenes does not. The former is attributed to electropolymerisation via intermolecular reaction of calixarene phenoxy radical species at the para-position to produce a non-conducting deposit on the electrode surface. This process is not possible with the p-t-butyl-substituted calixarenes.     

Inherently chiral calixarenes

Due to the nonplanarity of the basic 1 _n -metacyclophane system, calixarenes and resorcarenes can be transformed into molecules with inherent chirality. Various attempts to achieve this goal are reviewed. Special emphasis is given to derivatives withC _n -symmetry, including derivatives of spherand calixarenes and other calixarene-like macrocycles.This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

Liquid crystalline calixarenes

Bowl-shaped (bowlic) liquid crystals are reviewed and new bowlic materials containing rigid tungsten-oxo calix[4]arene based cores are discussed. Tungsten-oxo calix[4]arenes with 8 and 12 dodecyloxy sidechains have been investigated and exhibit bowlic columnar phases which are stable over approximately a 200° temperature range. The uncomplexed tetra-phenol ligands display only a transient liquid crystallinity on the first heating, and the conformational rigidity provided through tungsten-oxo complexation is necessary for well behaved mesomorphism. For the 8 sidechain analog the clearing point is at 320°C and the addition of four more sidechains results in a lower clearing point at 267°C. Polarized optical microscopy and DSC indicate that the 12 sidechain analog displays a phase with the columns packed in a hexagonal lattice which is conductive to the formation of polar phases. Both complexes exhibit a pronounced tendency to bind Lewis base guests in their cavities, and DMF forms very strong complexes which were spectroscopically characterized. The DMF guest produces large effects on the phase behavior by suppressing mesomorphism and lowering the isotropic points by 115°C and 84°C for the 8 and 12 sidechain compounds respectively. This extreme sensitivity to the DMF guest is conclusive proof that bowlic tungsten-oxo calix[4]arene liquid crystals organize in head-to-tail structures.This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

Multifunctional p-phosphonated calixarenes

p-Phosphonic acid calix[n]arenes and their O-alkylated lower rim analogues are remarkably versatile macrocycles, with applications in selective diameter uptake of single walled carbon nano-tubes, as surfactants in stabilising and protecting nano-particles and graphene sheets, as crystal growth modifiers for inorganic systems, in encapsulating molecules of anti-cancer carboplatin, self assembly into nano-arrays, including nano-fibres and molecular capsules, and for binding metal ions including biologically relevant Ca(2+). They are readily accessible via five or six high yielding steps from the parent p-Bu(t) substituted compounds.     

Deprotonation of calixarenes in acetonitrile

[Structure: see text]. The pKa values for calixarenes in MeCN have been determined by selective titration with bases using a spectroscopic method. These values are as follows: calix[4]arene pKa(1) = 19.06 +/- 0.22, pKa(2) > 33; calix[6]arene pKa(1) = 15.59 +/- 0.06, pKa(2) = 23.85 +/- 0.35, pKa(3) > 33; calix[8]arene pKa(1) = 17.20 +/- 0.20, pKa(2) = 20.32 +/- 0.31, pKa(3) > 33. The trends in acidity are rationalized using structures generated by a DFT model. For mono-deprotonation, the degree and nature of hydrogen bonding in the anion is the dominant factor; for di-deprotonation, spatial separation of the anionic charges becomes important.     

Antimicrobial activity of PVC-pyrazolone-silver nanocomposites

Poly(vinyl chloride)-pyrazolone; PVC-pz as a new modified form of PVC with high antibacterial and antifungal activities towards some Gram +ve bacteria S. Aureus, B. Subtilis and S. Faecalis) and Gram –ve bacteria (E. Coli, P. Aeruginosa and N. Gonorrhoeae) beside Candida albicans in addition to Aspragillus flavus as fungi has been synthesized in absence and in presence of silver-nanoparticles, AgNPs, in 3 and 5% by weight with respect to PVC. This was developed by a chemical reaction of PVC 1, and pyrazolone 2 in tetrahydrofuran, THF as solvent. PVC-pz derivative has been characterized by FTIR, ¹HNMR spectroscopic analyses, in addition to scanning and transmission electronic microscopy. Photostability of PVC-pz was evaluated by following the discoloration for UV- irradiated samples colorimetrically in accordance with degradation time. IR and ¹H-NMR analyses confirm that PVC-pz, 4 was formed indicating a substitution reaction of chlorine atoms of PVC chains to the hydrogen atom of active methylene and that attached to pyrazolone nitrogen at the same time. Antimicrobial activities of PVC-pz increased in the presence of AgNPs and with increasing its percentage.     

Oligodentate glycoconjugates based on calixarenes: methods for the synthesis and biological activity

The review considers principal methods for the preparation of conjugates of carbohydrates with calixarenes and resorcinarenes. The data on the biological activity of glycoconjugates are discussed taking their interaction with the carbohydrate-binding proteins, lectins as an example.     

Synthesis and in vivo biological activity of large-ringed calixarenes against Mycobacterium tuberculosis

A series of large-ringed calix[6,7,8]arene analogues have been synthesised and their affect against Mycobacterium tuberculosis in vivo established. In general, when p-phenylcalixarenes and tert-butylcalixarenes were not functionalised at the lower rim, low biological activities were observed. However on going from partially to fully lower rim pegylated calixarenes the anti-mycobacterial properties improved. The addition of cyanopropoxy groups at the lower rim gave rise to low activities, whereas the addition of acetate moieties interestingly had pro-TB effects. Two upper rim sulfonated calixarenes showed promising properties. In the course of this work, a high yielding procedure to synthesise p-phenylcalix[7]arene was also established.     

Supramolecular surfactants derived from calixarenes

Supramolecular surfactants self-aggregate via noncovalent interactions. The process is rapid and reversible which makes them potentially useful for the design of stimuli-responsive systems. Here we focus on host:guest interactions using calixarenes as molecular receptors. Calixarenes are an important family of molecular receptors because of their ease of preparation and post-modification. The calixarenes discussed here cannot self-aggregate, but when combined with an appropriate guest molecule readily self-associate. Different types of aggregates are obtained, e.g., micelles or vesicles, depending upon the structures of the calixarene and guest.     

Synthesis of siloxane analogs of calixarenes

First siloxane analogs of calixarenes were synthesized based on the stereoregular cis-tetraphenylcyclotetrasiloxanetetrol. Different methods were used to study properties of new compounds in bulk, as well as their behavior at the water–air interface.     

Inclusion of quaternary ammonium compounds by calixarenes

In weakly polar solvents, strong association occurs between calixarene anions and tetraalkylammonium cations, with the magnitude of the observed equilibrium constants depending upon the charge on the anion, the solvent, the ring size of the calixarene and the nature of the alkyl group of the cation. Large upfield shifts of the methyl resonances of the [(CH₃)₄N]⁺ cation in solutions of [(CH₃)₄N]₂[p-t-butylcalix[6]arene-2H] indicate cation inclusion in a structure which is possibly identical with that found for the solid salt by X-ray crystallography. This shows one of the cations to be included within a partial cone structure of a hinged 3-up, 3-down conformation of the calixarene. The functionalised tetramethylammonium ions, choline and acetyl choline, are also strongly included by various calixarene anions but attempts to detect significant modification of the reactivity of acetyl choline resulting from inclusion have not been successful.This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

Analytical applications of calixarenes from 2005 up-to-date

Calixarenes, as nano-baskets, are considered an important group of macrocycles as the third famous host molecules after cyclodextrins and crown ethers have been subject to extensive researches in construction of many extractants, transporters, stationary phases, electrode ionophores and optical and electrochemical sensors over the past four decades. Because of the recent rapid growth in the publications of calixarene applications, this review paper has focused on different analytical applications of calixarenes in the main fields of separation, electroanalysis, spectroscopy and chemometrics. The objectives and the results of about 300 references mainly were published in recent 6 years with emphasis on the analytical applications were reviewed.     

Recognition of amino acids by functionalized calixarenes

The calixarenic receptors exhibit remarkable host-guest properties towards biologically relevant guests. Aspects of complex formation reactions between both native and derivatized amino acids, di-and tripeptides with calixarenic (chiral or not) receptors are summarized in this critical review. Thus, the discussions emphasize the parameters that affect the molecular binding selectivity and efficiency of functionalized calix[n]arenes towards these substrates. A brief survey on their application in separation of amino acids is also considered (123 references).     

Intramolecular hydrogen bonding in calixarenes

The construction of a molecular cavity for recognition and catalysis requires either covalent synthesis or intermolecular self-assembly of complementary units. Intramolecular hydrogen bonding is another tool to control the cavity-forming process. When properly positioned within the same molecular structure, hydrogen bonding sites are responsible for the formation, preorganization, and binding ability of the host. The most typical examples from the supramolecular chemistry of calixarenes, the key cavity-containing building blocks, and derived from them receptor molecules are discussed.     

Hyperbranched molecules based on calixarenes

Synthesis of the diamide 2 derived from tris(2-aminoethyl)amine and monocarboxymethylcalix[4]arene provides a starting material useful for the preparation of a variety of hyperbranched molecules. Metal ion binding is one of the potentially useful properties of these new materials.     

Antimicrobial activity of new dumbbell-shaped phenothiazine cinnamides

Research on Chemical Intermediates - Herein, we report the synthesis and in vitro antibacterial and antifungal activities for twelve...     

Antimicrobial activity of new benzazolyl N-sulfonyl amidines

The reactions of N-(benz[d]oxazol-2-yl)- or N-(benzo[d]-thiazol-2-yl)-substituted carbothioamides with sulfonyl azides proceed as replacement of thioxo substituent by the sulfonylimino group to afford the corresponding N'-sulfonylated amidines. Acetic acid thioamides react smoothly upon boiling in ethanol, while for thioamides of trifluoroacetic and benzoic acids heating to 80–90 °C was required. Among hybrid molecules thus prepared, bacteriostatic-, bactericidal- and fungistatic-active against S. aureus and C. albicans representatives were found.