Triterpenes from the resin of Boswellia neglecta

The resin of Boswellia neglecta yielded four triterpenes canaric acid, a -amyrin, a -amyrone and epi-a -amyrin. Canaric acid and epi-a -amyrin are isolated here for the first time from the family Burseraceae. The compounds were identified using 1D and 2D NMR techniques. (Received March 13, 2002; revised May 17, 2002) Bull. Chem. Soc. Ethiop. 2002, 16(1), 87-90

Dammarane triterpenes from the resins of Commiphora confusa

The resin of Commiphora confusa afforded two new dammarane triterpenes, (3R,20S)-3,20-dihydroxydammar-24-ene and (3R,20S)-3-acetoxy-20-hydroxydammar-24-ene along with the known triterpenes, cabraleadiol 3-acetate and a -amyrin. (Received March 13, 2002; revised May 17, 2002) Bull. Chem. Soc. Ethiop. 2002, 16(1), 81-86

Regioselectivity in the Thermal Rearrangement of Unsymmetrical 4-Methyl-4H-1,2,4-triazoles to 1-Methyl-1H-1,2,4-triazoles

The rearrangement of 4-methyl-3,5-diaryl-4H-1,2,4-triazoles to the corresponding 1-methyl-3,5-diaryl-1H-1,2,4-triazoles showed regioselectivity comparable to that observed for the alkylation of 3,5-diaryl-1H-1,2,4-triazoles. This lends support to a proposed mechanism for the rearrangement that involves consecutive nucleophilic displacements steps

Optical Rotation Calculations for a Set of Pyrrole Compounds

Optical rotation of 14 molecules containing the pyrrole group is calculated by employing both time-dependent density functional theory (TDDFT) with the CAM-B3LYP functional and the second-order approximate coupled-cluster singles and doubles (CC2) method. All optical rotations have been provided using the aug-cc-pVDZ basis set at \uce\ubb = 589 nm. The two methods predict similar results for both sign and magnitude for the optical rotation of all molecules. The obtained signs are consistent with experiments as well, although several conformers for four molecules needed to be studied to reproduce the experimental sign. We have also calculated excitation energies and rotatory strengths for the six lowest lying electronic transitions for several conformers of the two smallest molecules and found that each rotatory strength has various contributions for each conformer which can cause different optical rotations for different conformers of a molecule. Our results illustrate that both methods are able to reproduce the experimental optical rotations, and that the CAM-B3LYP functional, the least computationally expensive method used here, is an applicable and reliable method to predict the optical rotation for these molecules in line with previous studies

First Report of Chenodeoxycholic Acid-Substituted Dyes Improving the Dye Monolayer Quality in Dye-Sensitized Solar Cells

Chenodeoxycholic acid (CDCA) is the most used antiaggregation additive in dye-sensitized solar cells since its introduction to the field in 1993. However, effective suppression of dye aggregation comes at the cost of reduced dye loading, a lower open-circuit voltage, and limited control of dye/additive distribution when cosensitizing with free CDCA. To combat this, herein, a novel dye design concept that uses the covalent attachment of a CDCA moiety to triarylamine sensitizers is reported. The CDCA substituents do not affect the photophysical or electrochemical properties of the sensitizers but have a positive effect on the photovoltaic performance with [Cu+/2+(tmby)(2)](TFSI)(1/2) electrolyte (tmby = 4,4 ',6,6 '-tetramethyl-2,2 '-bipyridine, TFSI = bis(trifluoromethanesulfonyl)imide). By ensuring a one-to-one ratio of dye and CDCA, paired with isotropic distributions of each component, this approach results in a higher-quality dye monolayer. Compared with the reference system, the novel approach reported herein gives a higher open-circuit voltage and power conversion efficiency (PCE). The best device is fabricated with the dye C-6-CDCA, delivering a PCE of 6.84% (8 mu m TiO2, 1 mm CDCA, J(SC) = 8.64 mA cm(-2), V-OC = 1007 mV, and FF = 0.77)

Tame and wild coordinates of ℤ[x,y]

Algorithms to decide whether a polynomial is a coordinates (tame coordinate, respectively) of ℤ[x,y] are given. Moreover, if a polynomial p∈Z[x,y] is a coordinate (tame coordinate, respectively), the algorithms effectively construct a concrete automorphism of ℤ[x,y] that sends x to p. The algorithm to determine tame coordinate is applicable to R[x,y] where R is an Euclidean domain; while the algorithm to determine coordinate is applicable to D[x.y] where D is a unique factorization domain. © 2004 Published by Elsevier Inc.link_to_subscribed_fulltex