Codes with the Same Weight Distributions as the Goethals Codes and the Delsarte-Goethals Codes

The Goethals code is a binary nonlinear code of length 2^m+1 which has codewords and minimum Hamming distance 8 for any odd . Recently, Hammons et. al. showed that codes with the same weight distribution can be obtained via the Gray map from a linear code over Z ₄of length 2^m and Lee distance 8. The Gray map of the dual of the corresponding Z ₄ code is a Delsarte-Goethals code. We construct codes over Z ₄ such that their Gray maps lead to codes with the same weight distribution as the Goethals codes and the Delsarte-Goethals codes.     

Rapid Characterization of Wood Pulp Lignin by Fourier Transform Raman Spectroscopy

FT-Raman spectroscopy is used for the rapid measurement of wood pulp lignin. A total of 23 western softwood pulp samples with known kappa numbers (10–38) are used. Each sample is divided into three portions and scanned separately. The integrated area of the lignin band at approximately 1600 cm⁻¹is ratioed against the integrated area of the cellulose bands in the 1200–1010 cm⁻¹region and correlated to known kappa numbers. The measured ratios behave linearly with the kappa number (r= 0.99) and can be reproducibly determined with an error of approximately 2% or less. The data are presented and discussed in view of the potential for at-line analysis of lignin associated with chemical delignification of wood pulp.     

The molecular structures of gaseous cyclopentene oxide,cyclohexene oxide and cycloheptene oxide as determined by electron diffraction

The molecular structures of gaseous cyclopentene oxide, cyclohexene oxide and cycloheptene oxide are investigated by electron diffraction. The boat conformation of cyclopentene oxide is confirmed, while a half-chair conformer is determined for cyclohexene oxide. Cycloheptene oxide is found to exist in a 66(2):34(2) conformational mixture of two chair forms.     

Simple fluorescent pyrimidine analogues detect the presence of DNA abasic sites

A family of simple pyrimidine analogues has been synthesized, and their photophysical properties have been investigated. The most responsive of the family was incorporated in DNA. This isosteric fluorescent DNA analogue monitors denaturation of a DNA duplex via fluorescence and positively detects the presence of abasic sites in DNA duplexes.     

Donor/acceptor interactions in systematically modified Ru(II)-Os(II) oligonucleotides

Donor/acceptor (D/A) interactions are studied in a series of doubly modified 19-mer DNA duplexes. An ethynyl-linked Ru(II) donor nucleoside is maintained at the 5' terminus of each duplex, while an ethynyl-linked Os(II) nucleoside, placed on the complementary strands, is systematically moved toward the other terminus in three base pair increments. The steady-state Ru(II)-based luminescence quenching decreases from 90% at the shortest separation of 16 A (3 base pairs) to approximately 11% at the largest separation of 61 A (18 base pairs). Time-resolved experiments show a similar trend for the Ru(II) excited-state lifetime, and the decrease in the averaged excited-state lifetime for each duplex is linearly correlated with the fraction quenched obtained by steady-state measurements. Analysis according to the F?rster dipole-dipole energy transfer mechanism shows a reasonable agreement. Deviation from idealized behavior is primarily attributed to uncertainty in the orientation factor, kappa(2). Analyzing D/A interactions in an analogous series of doubly modified oligonucleotides, where the ethynyl-linked Ru(II) center is replaced with a saturated two-carbon linked complex, yields an excellent correlation with the F?rster mechanism. As this simple change partially relaxes the rigid geometry of the donor chromophore, these results suggest that the deviation from idealized F?rster behavior observed for the duplexes containing the rigidly held Ru(II) center originates, at least partially, from ambiguities in the orientation factor. Surprisingly, analyzing both quenching data sets according to the Dexter mechanism also shows an excellent correlation. Although this can be interpreted as strong evidence for a Dexter triplet energy transfer mechanism, it does not imply that this electron exchange mechanism is operative in these D/A duplexes. Rather, it suggests that systems that transfer energy via the F?rster mechanism can under certain circumstances exhibit Dexter-like "behavior", thus illustrating the danger of imposing a single physical model to describe D/A interactions in such complex systems. While we conclude that the F?rster dipole-dipole energy transfer mechanism is the dominant pathway for D/A interactions in these modified oligonucleotides, a minor contribution from the Dexter electron exchange mechanism at short distances is likely. This complex behavior distinguishes DNA-bridged Ru(II)/Os(II) dyads from their corresponding low molecular-weight and covalently attached counterparts.     

On the electronic structure of ethidium

The electronic structure of the common intercalating agent ethidium bromide (3,8-diamino-5-ethyl-6-phenylphenanthridinium bromide) is dominated by an interplay of electron donating and withdrawing effects mediated by its nitrogen atoms. X-ray crystallography, UV/Vis and IR absorption, fluorescence emission, and NMR spectroscopy are used to probe the electronic properties of the phenanthridinium "core" of ethidium as well as its exocyclic amines and 6-phenyl groups. Interestingly, despite its positive charge, most of ethidium's aromatic carbon and hydrogen atoms have high electron densities (compared to both 6-phenylphenanthridine and benzene). The data suggest that electron donation by ethidium's exocyclic amines dominates over the electron withdrawing effects of its endocyclic iminium in their combined influence on the electron densities of these atoms. Ethidium's nitrogen atoms are, conversely, electron deficient where the 5-position is the most electropositive, followed by the 3-amino, and lastly the 8-amino group. These results have been used to generate an empirically-based pi-electron density map of ethidium that may prove useful to understanding its nucleic acid binding specificity.     

Pyranophane transannular diels-alder approach to (+)-chatancin: a biomimetic asymmetric total synthesis

An asymmetric total synthesis of (+)-chatancin was achieved via a transannular Diels-Alder (TADA) reaction of an in situ generated macrocyclic pyranophane pseudobase. The presented route constitutes the second of two proposed biosynthetic pathways that involves a TADA reaction. It links this diterpene biogenetically to the cembranoids. A set of TADA selection rules that rationalize the formation of (+)-chatancin from a dynamic equilibrium of four 2-hydroxy-2H-pyrane bicycles and their 16 potential TADA transition states are also outlined. Beyond the TADA reaction, highlights of the synthetic work include the assembly of a chiral acyclic macrocyclization substrate from (S)-citronellol and an efficient macrocyclization via a beta-ketosulfoxyde/enone Michael addition.     

Transannular Diels-Alder studies on the asymmetric total synthesis of chatancin: the pyranophane approach

[reaction: see text] A pathway is proposed for the biosynthesis of (+)-chatancin and (+)-sarcophytin linking these tetracycles to cembranoids by a pyranophane transannular Diels-Alder reaction. Preliminary synthetic results in this direction to reach macrocyclic dienedione 28 from farnesol are reported. Major synthetic steps include a Prins reaction, two enantioselective hydrogenations, and a macrocyclization via a beta-ketosulfoxide Michael-addition on an enone.