Thermodynamics of the interaction between hydroxypropyl-α-cyclodextrin and alkanols in aqueous solutions

The interactions of hydroxypropyl-α-cyclodextrin (HP-α-CD) with 1-alkanols and with some α,ω-alkanediols have been studied by calorimetric titration at 298.15 K. This technique enables the determination of the enthalpy and association constant for the complex formation, from which Gibbs energy and entropy can be derived. The results are compared to those reported for the complex formation between the native α-cyclodextrin (α-CD) and 1-alkanols or α,ω-alkanediols in the literature. Thermodynamic parameters corresponding to the transfer process of the alkanol from the native to the modified α-CD are also calculated. The results clearly show that the hydrophobic interactions are important in this process, but there are other effects like the size of the alkanol that are also of some importance.     

Bentonitic earth catalyzed rearrangement of aryl 1,1-dimethylpropargyl ethers. Synthesis of 2,2-dimethyl-2H-1-benzopyrans

Mexican Bentonitic earth (Tonsil) catalyzed the Claisen rearrangement of aryl 1,1-dimethylpropargyl ethers under mild conditions to provide 2,2-dimethyl-2H-1-benzopyrans. The synthesis of encecalin 2f and desmethoxyencecalin 2i , two biologically active products among other natural products ( 2b, 2e ) was performed by this procedure.     

Stereoselective Michael addition of 6-amino-1,3-dimethyl-2,4-pyrimidinedione to the exocyclic methylene of three sesquiterpene lactones. 1H and 13C NMR evidence of a new C-C bond and lactam formation

The Stereoselective addition of the pyrimidine derivative 1 to the exocyclic methylene of the α,β unsaturated dehydrocostus lactone 2, Ivalin acetate 3 and Zaluzanin A diacetate 4, was achieved resulting in a new C-C bond formation. In the cases of compounds 3 and 4, after the addition, the lactone was cleaved followed by reclosure into a lactam ring system.     

Method development and validation for optimized separation of benzo[a]pyrene-quinone isomers using liquid chromatography-mass spectrometry and chemometric response surface methodology

The successful separation of three benzo[a]pyrene-quinone isomers, two of which were previously unresolved, using liquid chromatography-mass spectrometry (LC-MS) and response surface methodology is presented. Initial efforts centered on chromatographic separation of benzo[a]pyrene-1,6/3,6-quinone peaks evaluated for both resolution and retention time. The mergence of the two parameters was accomplished using the Derringer's desirability function with subsequent optimization by a Box-Behnken response surface design. By implementing the optimal flow rate, column temperature and eluent composition predicted by the validated model, enhanced resolution of the two isomers was achieved in less than 20 min. Calibrations were performed to quantify these isomers and the limits of detection were determined. Optimal model conditions were then used to identify three independent benzo[a]pyrene-quinone isomers produced in the irradiation of a benzo[a]pyrene standard solvated in oxygen-saturated methanol/methylene chloride. This work is not only highly significant to the field of environmental chemistry, but instructive for investigators struggling with the co-elusion of isomeric compounds in their work.     

Supramolecular electrostatic nanoassemblies for bacterial forensics

Electrostatic nanoassemblies were employed to identify bacterial growth conditions. They comprise a cationic conjugated oligoelectrolyte and fluorescein-tagged ssDNA and were optimized with a hybrid, computational neural network model. The photoluminescence spectra contained the oligomer and sensitized fluorescein emission. The spectra changed depending on the growth history of the bacteria introduced (see figure).