Spirodienone derivatives of a spherand-type calixarene

Oxidation of the spherand-type calixarene 4 with 1 or 2 equiv of phenyltrimethylammonium tribromide/base afforded mono- and bis(spirodienone) derivatives (8b and 9, respectively). The spirodienone groups are derived from the oxidation of two phenols connected by a common methylene group. NOESY data indicated that 9 possesses a "head to tail" arrangement of the spirodienone groups. Oxidation of 4 with 3 equiv of the oxidizing reagent afforded two tris(spirodienone) calixarene derivatives 11 and 10 with C(1) and C(3) symmetries, respectively. The same tris(spirodienone) products were obtained by oxidation of 9 with I(2)/aq KOH. Tris(spirodienone) 11 displayed NOE cross-peaks in the NOESY NMR spectrum consistent with a nonalternant disposition of carbonyl and ether groups. Upon heating 10 and 11 isomerize in the solid state and in solution. The major component in the equilibration mixtures is 11, indicating that this is the thermodynamically more stable tris(spirodienone) isomer.     

Excitations, optical absorption spectra, and optical excitonic gaps of heterofullerenes. I. C60, C59N+, and C48N12: theory and experiment

Low-energy excitations and optical absorption spectrum of C(60) are computed by using time-dependent (TD) Hartree-Fock, TD-density functional theory (TD-DFT), TD DFT-based tight-binding (TD-DFT-TB), and a semiempirical Zerner intermediate neglect of diatomic differential overlap method. A detailed comparison of experiment and theory for the excitation energies, optical gap, and absorption spectrum of C(60) is presented. It is found that electron correlations and correlation of excitations play important roles in accurately assigning the spectral features of C(60), and that the TD-DFT method with nonhybrid functionals or a local spin density approximation leads to more accurate excitation energies than with hybrid functionals. The level of agreement between theory and experiment for C(60) justifies similar calculations of the excitations and optical absorption spectrum of a monomeric azafullerene cation C(59)N(+), to serve as a spectroscopy reference for the characterization of carborane anion salts. Although it is an isoelectronic analogue to C(60), C(59)N(+) exhibits distinguishing spectral features different from C(60): (1) the first singlet is dipole-allowed and the optical gap is redshifted by 1.44 eV; (2) several weaker absorption maxima occur in the visible region; (3) the transient triplet-triplet absorption at 1.60 eV (775 nm) is much broader and the decay of the triplet state is much faster. The calculated spectra of C(59)N(+) characterize and explain well the measured ultraviolet-visible (UV-vis) and transient absorption spectra of the carborane anion salt [C(59)N][Ag(CB(11)H(6)Cl(6))(2)] [Kim et al., J. Am. Chem. Soc. 125, 4024 (2003)]. For the most stable isomer of C(48)N(12), we predict that the first singlet is dipole-allowed, the optical gap is redshifted by 1.22 eV relative to that of C(60), and optical absorption maxima occur at 585, 528, 443, 363, 340, 314, and 303 nm. We point out that the characterization of the UV-vis and transient absorption spectra of C(48)N(12) isomers is helpful in distinguishing the isomer structures required for applications in molecular electronics. For C(59)N(+) and C(48)N(12) as well as C(60), TD-DFT-TB yields reasonable agreement with TD-DFT calculations at a highly reduced cost. Our study suggests that C(60), C(59)N(+), and C(48)N(12), which differ in their optical gaps, have potential applications in polymer science, biology, and medicine as single-molecule fluorescent probes, in photovoltaics as the n-type emitter and/or p-type base of a p-n junction solar cell, and in nanoelectronics as fluorescence-based sensors and switches.     

Monomeric and polymeric anionic gemini surfactants and mixed surfactant systems in micellar electrokinetic chromatography. Part II: characterization of chemical selectivity using two linear solvation energy relationship models

Sodium di(undecenyl) tartarate monomer (SDUT), a vesicle-forming amphiphilic compound possessing two hydrophilic carboxylate headgroups and two hydrophobic undecenyl chains, was prepared and polymerized to form a polymeric vesicle (i.e., poly-SDUT). The anionic surfactants of SDUT and poly-SDUT (carboxylate head group) and sodium dodecyl sulfate, SDS (sulfate head groups) as well as mixed surfactant systems (SDS/SDUT, SDS/poly-SDUT, and SDUT/poly-SDUT) were applied as pseudostationary phases in micellar electrokinetic chromatography (MEKC). Two linear solvation energy relationship (LSER) models, i.e., solvatochromic and solvation parameter models, were successfully applied to investigate the effect of the type and composition of pseudostationary phases on the retention mechanism and selectivity in MEKC. The solvatochromic and solvation parameter models were used to help understand the fundamental nature of the solute-pseudostationary phase interactions and to characterize the properties of the pseudostationary phases (e.g., solute size and hydrogen bond-accepting ability for all pseudostationary phases). The solute types were found to have a significant effect on the LSER system coefficients and on the predicted retention factors. Although both LSER models provide the same information, the solvation parameter model is found to provide much better results both statistically and chemically than the solvatochromic model.     

Chain transfer polymerisation of poly-N-alkylacrylamides in superheated methanol and by microwave induction

The chain transfer polymerisation (telomerisation) of poly-N-isopropylacrylamide (PNIPAM), poly-N,N-dimethylacrylamide (PNDMAM) and poly-N-{3-(dimethylamino)propyl}acrylamide (PN3DMAPAM) as well as of co-polymers of PNIPAM and PNDMAM were studied. Reactions in superheated yet subcritical methanol (80-170 °C) and—under solvent free conditions—induced by microwave irradiation were compared in terms of product yield and quality to those obtained under standard reflux conditions (methanol reflux, ∼65 °C, ambient pressure). In superheated methanol the reaction time was reduced by 66%, the average molar mass and the yield (monomer conversion) remain largely unchanged. Dielectric heating reduces the reaction time even further, i.e. to the minute range. Surprisingly, the average molar mass of the polymers dropped by 30% in these experiments, an effect that is most likely caused by the higher polarity of the reaction mixture under solvent-free conditions.     

Preparative three-dimensional GC and nuclear magnetic resonance for the isolation and identification of two sesquiterpene ethers from Dictyota Dichotoma

Separation science plays a crucial role in the isolation of novel compounds contained in complex matrices. Yet their rationale employment needs preliminary structure elucidation, which usually requires sufficient aliquots of grade substances to characterize the molecule by nuclear magnetic resonance experiments. In this study, two peculiar oxa-tricycloundecane ethers were isolated by means of preparative multidimensional gas chromatography from the brown alga species Dictyota dichotoma (Huds.) Lam., aiming to assign their 3D structures. Density functional theory simulations were carried out to select the correct configurational species matching the experimental NMR data (in terms of enantiomeric couples). In this case, the theoretical approach was crucial as the protonic signal overlap and spectral overcrowding were preventing any other unambiguous structural information. Just after the identification through the density functional theory data matching of the correct relative configuration it was possible to verify an enhanced self-consistency with the experimental data, confirming the stereochemistry. The results obtained further pave the way toward structure elucidation of highly asymmetric molecules, whose configuration cannot be inferred by other means or strategies.