Topics in calixarene chemistry

Several facets of calixarene chemistry have been investigated including the mechanism of their formation by the base-induced condensation of phenols and formaldehyde, procedures for introducing functional groups onto the upper rim and lower rim of calixarenes, the conformational behavior of calixarene oxyanions, the formation of complexes in aqueous and nonaqueous systems, and the application of calixarenes as catalysts.     

3-Benzoyl-1,2,4,5-tetraphenylpentane-1.5-dione. A molecular paddlewheel

Racemic (2R,4R)-, (2S,4S)-3-benzoyl-1,2,4,5-tetraphenylpentane-1,5-dione results from the alkali-induced condensation of acetophenone with desoxybenzoin in the presence of air. The structure which resembles that of an irregular five-bladed paddlewheel is confirmed by X-ray crystallography.     

The adsorption of the HgEDTA complex at mercury electrodes

While free EDTA has no tendency to adsorption on mercury surfaces, its complex with Hg(II) is adsorbed strongly. The coverage is very small in alkaline solutions where HgYOH^3? is present, reaches 60% at moderate pH, and is high at pH = 2, where the predominant species in solution is HgYH^?. Dependence of peak potential on pH for cathodic stripping voltammetry indicated that for pH > 3, HgY^2? is adsorbed at the surface, while at pH 2 the adsorbed complex is protonated. Cyclic chronopotentiometric experiments suggest formation of a coherent film of adsorbed material at pH 2. At pH = 2 adsorption of HgEDTA can be described by a Frumkin isotherm, and at pH = 4.8 by either a virial or HFL isotherm.     

Mechanism of thermolysis of 2-hydrazono-Δ3-1,3,4-oxadiazolines to diazetidinium hydroxide inner salts : Evidence for an N-isocyanatoimine intermediate and its novel reaction with phenylisocyanate

Thermolysis of 5,5-dimethyl-2-diphenylmethylenehydrazone-Δ³-1,3,4-oxadiazoline (1a) in chlorobenzene at 130° leads to 1-diphenylmethyleneimino-4,4-dimethyl-3-oxo-1,2-diazetidinium hydroxide, inner salts (2). Evidence for initial fragmentation of 1a to 2-diazopropane (4) and N-isocyanatodiphenylmethylene imine (3), which subsequently recombine with loss of N₂ to form 2, includes trapping of both intermediates with phenylisocyanate and trapping of 3 with methanol. Intermediate 3, which is the first N-isocyanatoimine intermediate to be reported, undergoes a novel 1,3-cycloaddition reaction with phenylisocyanate.Examples of similar chemistry involving reactions of analogs of 1a in the presence of arylisocyanates are also included.     

Analysis of classes of compound of environmental concern: I. Nitroaromatic compounds

Thirty five nitroaromatic compounds (currently listed in EPA Method 8091) and 1,4-naphthoquinone have been separated on DB-5–DB-1701 and SPB-5–SPB-1701 column pairs, which were in each case connected to an inlet splitter and separate electron capture detectors. Retention times are included for 21 additional compounds evaluated for their suitability as internal standards and/or surrogate compounds for incorporation into Method 8091. Method reproducibility and linearity are discussed, and results are presented for extracts of two real samples spiked with the 35 nitroaromatic compounds and 1,4-naphthoquinone and analyzed using the dual-column-dual-detector arrangement.     

The synthesis and structure of 10,11-bistrifluoromethyl-i,o-bicyclo[7.2.2]trideca-10,12-diene. A highly strained inside-outside bicycloalkane derivative.

10,11-Bistrifluoromethyl-i,o-bicyclo[7.2.2]trideca-10,12-diene has been prepared by the Diels-Alder addition of hexafluoro-2-butyne to cis, trans-cycloundeca-1,3-diene. Purification was accomplished via formation of an iron tricarbonyl complex whose structure was established via X-ray crystallography.     

Substrate specificity for catalysis of phosphodiester cleavage by a dinuclear Zn(II) complex

The 2.4 kcal mol(-1) greater stabilization of the transition state for cleavage of the minimal substrate HpPNP compared to the nucleoside substrate UpPNP by the efficient dinuclear metal ion catalyst Zn2(L2O) provides evidence that access to the cationic core of Zn2(L2O) is sterically blocked for the bulkier nucleoside substrates, a flaw that will need to be dealt with in later generations of metal ion catalysts of RNA cleavage.     

The electrochemical reduction and determination of reduced nicotinamide adenine dinucleotide in acidic media

The apparent reduction of reduced nicotinamide adenine dinucleotide (NADH) in acidic media at a static mercury drop electrode was investigated. A simple, quick pretreatment procedure was developed to convert the NADH to its acid-hydrated form. This adsorbs on the mercury surface during a film deposition time and the film is then reduced. The adsorption is diffusion-controlled and hence the peak currents for square-wave and linear-scan voltammetry are proportional to Ct^1/2_pAf and Ct^1/2_pAv, respectively, where t_p is the effective film deposition time, C the concentration of NADH, A the electrode area, f the square-wave frequency, and ν the linear scan rate. Several electrochemical techniques were compared for the determination of NADH; the method of choice is square-wave voltammetry, although staircase or linear scan voltammetry can also be used. The detection limit is less than 7 nM, and the range of linear response covers 2–3 orders of magnitude of NADH concentration.     

Ceramic-based nanoparticles entrapping water-insoluble photosensitizing anticancer drugs: a novel drug-carrier system for photodynamic therapy

A novel nanoparticle-based drug carrier for photodynamic therapy is reported which can provide stable aqueous dispersion of hydrophobic photosensitizers, yet preserve the key step of photogeneration of singlet oxygen, necessary for photodynamic action. A multidisciplinary approach is utilized which involves (i) nanochemistry in micellar cavity to produce these carriers, (ii) spectroscopy to confirm singlet oxygen production, and (iii) in vitro studies using tumor cells to investigate drug-carrier uptake and destruction of cancer cells by photodynamic action. Ultrafine organically modified silica-based nanoparticles (diameter approximately 30 nm), entrapping water-insoluble photosensitizing anticancer drug 2-devinyl-2-(1-hexyloxyethyl) pyropheophorbide, have been synthesized in the nonpolar core of micelles by hydrolysis of triethoxyvinylsilane. The resulting drug-doped nanoparticles are spherical, highly monodispersed, and stable in aqueous system. The entrapped drug is more fluorescent in aqueous medium than the free drug, permitting use of fluorescence bioimaging studies. Irradiation of the photosensitizing drug entrapped in nanoparticles with light of suitable wavelength results in efficient generation of singlet oxygen, which is made possible by the inherent porosity of the nanoparticles. In vitro studies have demonstrated the active uptake of drug-doped nanoparticles into the cytosol of tumor cells. Significant damage to such impregnated tumor cells was observed upon irradiation with light of wavelength 650 nm. Thus, the potential of using ceramic-based nanoparticles as drug carriers for photodynamic therapy has been demonstrated.     

A pulse polarographic investigation of parathion and some other nitro-containing pesticides

The polarographic behaviour of parathion, its major metabolites (paraoxon and p-nitrophenol), and of methylparathion, EPN and pentachloronitrobenzene has been studied over a wide pH range. Differential pulse polarography is used to differentiate between parathion, p-nitrophenol and pentachloronitrobenzene. An indirect determination of parathion in the presence of paraoxon can be based on their respective rates of hydrolysis in 0.5 M sodium hydroxide solution. The electrochemical behaviour of these compounds has also been investigated in solutions containing tetraalkylammonium salts as the supporting electrolyte.