Genetic Manipulation of the Fusarium fujikuroi Fusarin Gene Cluster Yields Insight into the Complex Regulation and Fusarin Biosynthetic Pathway

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Triterpenoids

This review covers the isolation and structure determination of triterpenoids including squalene derivatives, lanostanes, cycloartanes, dammaranes, euphanes, tirucallanes, tetranortriterpenoids, quassinoids, lupanes, oleananes, friedelanes, ursanes, hopanes, isomalabicanes and saponins. The literature from January to December 2000 is reviewed and 277 references are cited.     

Electronic structure of excimer molecular lasers

The electronic structure, potential energy curves, and radiative transition probabilities of excimer systems have been examined using quantum mechanical methods. These molecules are characterized by repulsive or weakly bound ground state potential curves and by bound, strongly ionic, or Rydberg, excited states. They constitute a very interesting class of molecules which offer the possibility for high power, high efficiency UV laser operation. Calculations have been carried out using the density functional SCF -X_α method, modified extensively to correct for well known errors arising from approximations to the potential and exchange terms. A limited number of ab initio calculations were also carried out for comparison purposes. For the ArF system we find that the lowest excited ionic state has symmetry ²∑${}_{\text{½}}^{\text{+}}$ , and that the dominant laser transition observed at 1933 Å should be assigned to B ²∑${}_{\text{½}}^{\text{+}}$ → X ²∑${}_{\text{½}}^{\text{+}}$ . The C ²Π_3/2 → X ²∑${}_{\text{½}}^{\text{+}}$ transition is calculated to be two orders of magnitude smaller in emission intensity than the dominant transition, thus ruling out this assignment for the observed laser line in ArF. Preliminary calculations carried out for Ar₂F indicate that the bound upper ionic state has ²B₂ symmetry and that the most probable ground state also has ²B₂ symmetry. This polyatomic system is predicted to exhibit a broadband emission spectrum with a relatively long radiative lifetime.     

Triterpenoids

This review covers the isolation and structure determination of triterpenoids including squalene derivatives, lanostanes, cycloartanes, dammaranes, euphanes, tirucallanes, tetranortriterpenoids, quassinoids, lupanes, oleananes, friedelanes, ursanes, hopanes, fernanes, sipholanes, isomalabaricanes, serratanes and saponins The literature from January to December 2001 is reviewed and 242 references are cited.     

Magnetic resonance imaging of nasopharyngeal and paranasal sinus melanoma

Malignant melanoma of the nasopharynx and paranasal sinuses is relatively rare. We retrospectively reviewed the magnetic resonance appearance of five cases and correlated this with the histopathological appearance. In all cases, the magnetic resonance (MR) images clearly demonstrated the precise anatomic extent of the tumor and were sensitive in assessing intracranial extension and invasion into surrounding structures, including the skull base. Three cases were reviewed for histopathological evidence of melanin, hemosiderin, and acute hemorrhage. One case was reviewed for melanin and hemorrhage only. The findings in this series suggest that melanoma of the nasopharynx and paranasal sinuses have extremely variable amounts of paramagnetic substances, both melanin and products of hemorrhage. T1 shortening appears to be more often a reflection of the paramagnetic effects associated with products of hemorrhage rather than the presence of melanin.     

Micro-bore titanium housed polymer monoliths for reversed-phase liquid chromatography of small molecules

A new method for the fixation of polymethacrylate monoliths within titanium tubing of up to 0.8 mm I.D. for use as a chromatographic column under elevated temperatures and pressures is described. The preparation of butyl methacrylate–ethylene dimethacrylate-based monolithic stationary phases with desired porous structures was achieved within titanium tubing with pre-oxidised internal walls. The oxidised titanium surface was subsequently silanised with 3-trimethoxysilylpropyl methacrylate resulting in tight bonding of butyl methacrylate porous monolith to the internal walls, providing stationary phase stability at column temperatures up to 110 °C and at operating column pressure drops of >28 MPa. The titanium housed monoliths exhibited a uniform and dense porous structure, which provided peak efficiencies of up to 59,000 theoretical plates per meter when evaluated for the separation of small molecules in reversed-phase mode, under optimal conditions (achieved at 15 μL/min and temperature of 110 °C for naphthalene with a retention factor, k = 0.58). The developed column was applied to the reversed-phase isocratic separation of a text mixture of pesticides.     

On braid groups and right-angled Artin groups

In this article we prove a special case of a conjecture of A. Abrams and R. Ghrist about fundamental groups of certain aspherical spaces. Specifically, we show that the \(n\) -point braid group of a linear tree is a right-angled Artin group for each \(n\) .     

Overview of the perspectives devoted to tautomerism in molecular design

This communication summarizes the important points made in each contribution. They show that there remain issues in the cheminformatic handling of tautomers and predicting the relative energies of various tautomers.     

Enzymatic Method for the Synthesis of Long DNA Sequences with Multiple Repeat Units

A polymerase chain reaction (PCR) derived method for preparing long DNA, consisting of multiple repeat units of one to ten base pairs, is described. Two seeding oligodeoxynucleotides, so‐called oligoseeds, which encode the repeat unit and produce a duplex with 5′‐overhangs, are extended using a thermostable archaeal DNA polymerase. Multiple rounds of heat–cool extension cycles, akin to PCR, rapidly elongate the oligoseed. Twenty cycles produced long DNA with uniformly repeating sequences to over 20 kilobases (kb) in length. The polynucleotides prepared include [A]_n/[T]_n, [AG]_n/[TC]_n, [A₂G]_n/[T₂C]_n, [A₃G]_n/[T₃C]_n, [A₄G]_n/[T₄C]_n, [A₉G]_n/[T₉C]_n, [GATC]_n/[CTAG]_n, and [ACTGATCAGC]_n/[TGACTAGTCG]_n, indicating that the method is extremely flexible with regard to the repeat length and base sequence of the initial oligoseeds. DNA of this length (20 kb≈7 μm) with strictly defined base reiterations should find use in nanomaterial applications.