Crystal and molecular structure of augustamine

The crystal and molecular structure of augustamine (1), C₁₇H₁₉NO₄ an amaryllidaceae alkaloid of the tazettine group has been determined by direct methods from single crystal x-ray diffractometer data and refined by full-matrix least squares. The alkaloid (1) crystallizes in the space group P2₁2₁2₁, with cell parameters: a = 7.833(8) b = 11.08(2) å, c = 16.69(6) Å, Z = 4, D_c = 1.381 g/cm^–3, R = 7.6% for 1115 observed reflections. The molecule, having a hexacyclic ring system, is very rigid with the ring B in a chair conformation. Molecular mechanics calculations have been made using MM3(2000) force field.     

On the Integration of Digital Technologies into Mathematics Classrooms

Trouche’s [Third Computer Algebra in Mathematics Education Symposiums, Reims, France, June 2003] presentation at the Third Computer Algebra in Mathematics Education Symposium focused on the notions of instrumental genesis and of orchestration: the former concerning the mutual transformation of learner and artefact in the course of constructing knowledge with technology; the latter concerning the problem of integrating technology into classroom practice. At the Symposium, there was considerable discussion of the idea of situated abstraction, which the current authors have been developing over the last decade. In this paper, we summarise the theory of instrumental genesis and attempt to link it with situated abstraction. We then seek to broaden Trouche’s discussion of orchestration to elaborate the role of artefacts in the process, and describe how the notion of situated abstraction could be used to make sense of the evolving mathematical knowledge of a community as well as an individual. We conclude by elaborating the ways in which technological artefacts can provide shared means of mathematical expression, and discuss the need to recognise the diversity of student’s emergent meanings for mathematics, and the legitimacy of mathematical expression that may be initially divergent from institutionalised mathematics.     

Intermolecular rhodium-catalyzed [3+2+2] carbocyclization of alkenylidenecyclopropanes with activated alkynes: regio- and diastereoselective construction of cis-fused bicycloheptadienes

Polycyclic structures that contain seven-membered carbocycles constitute important structural motifs that are ubiquitous in several classes of bioactive natural products. We have developed the first regio- and diastereoselective intermolecular rhodium-catalyzed [3+2+2] carbocyclization of carbon- and heteroatom-tethered alkenylidenecyclopropanes with mono- and disubstituted alkynes for the construction of cis-fused bicycloheptadienes. This study delineates some of the critical features for controlling regioselectivity in this process and demonstrates that E-alkenes can be incorporated in a stereospecific manner to afford products with up to three new stereogenic centers. The latter feature is particularly significant given that related carbocyclization reactions are often limited in this respect.     

Evidence for non-chemical, non-electrical intercellular signaling in intestinal epithelial cells

Synchrony between mechanically separated biological systems is well known. We posed the question: can cells induce synchronous behavior in neighboring cells which are mechanically separated and which cannot communicate via chemical or electrical mechanisms. Caco-2 cell cultures were divided into three groups. "Inducer" cells were exposed to H(2)O(2). "Detector" cells were placed in separate containers near the inducer cells but were not exposed to H(2)O(2). Control cells were exposed to fresh media and were kept in a distant laboratory area. Samples were measured for total protein concentration, NFkappaB activation and structural changes, 10, 30 and 60 min after exposure respectively. Exposing inducer cells to H(2)O(2) resulted in a significant reduction in total protein content (-50%), an increase in nuclear NFkappaB activation (+38%), and structural damage (56%) compared to controls. There was a similar reduction in total protein content (-48%), increase in the nuclear fraction of NFkappaB (+35%) and structural damage (25%) in detector cells. These findings provide evidence in support of a non-chemical, non-electrical communication. This signaling system possibly plays a role in synchronous, stimulus-appropriate cell responses to noxious stimuli and may explain a number of cellular behaviors that are hard to explain based only on conventional cell signaling systems.     

Spectroscopy of the A(1B2)-X(1A1) transition of jet-cooled fluorobenzene: laser-induced fluorescence, dispersed fluorescence, and pathological Fermi resonances

A detailed study of the S1((1)B2)-S0((1)A1) electronic transition of jet-cooled fluorobenzene has been carried out using laser-induced fluorescence and dispersed fluorescence (DF) spectroscopies. Analysis of over 40 single vibronic level DF spectra resulted in the assignment of 16 fundamental frequencies in the excited electronic state. Progressions in totally symmetric modes, particularly in the ring-breathing mode nu9, feature in both types of fluorescence spectrum. There is also significant activity in non-totally-symmetric modes, with activity in Franck-Condon (FC)-allowed overtones, FC-forbidden combinations induced by Duschinsky mixing, and symmetry-forbidden transitions induced by the same Herzberg-Teller vibronic coupling mechanism that induces the benzene S1-S0 transition. Fermi resonances (FRs) are extensive throughout the spectrum, especially in the important FC-active a1 modes. A consequence of these extensive FRs is that several important previous assignments are shown to be incorrect and have been reassigned here. Ab initio and density functional theory calculations have also been performed to support the experimental assignments.     

Synthesis of porphyrins bearing 1-4 hydroxymethyl groups and other one-carbon oxygenic substituents in distinct patterns

Porphyrins that bear one-carbon oxygenic substituents (hydroxymethyl, formyl, ester) directly attached to the macrocycle afford a compact architecture of utility for diverse applications. Routes to 9 porphyrins bearing such groups in distinct architectures (A₄-, trans-A₂-, trans-A₂B₂-, trans-AB-, and trans-AB₂C-porphyrins) have been explored (A=hydroxymethyl), including porphyrins bearing two one-carbon units in different oxidation states (hydroxymethyl/ester, formyl/ester). The hydroxymethyl group was introduced via TBDMS-protected dipyrromethane precursors.     

Ab initio and molecular mechanics calculations on imine derivatives: A study of the rotational barriers and the development of MM2 parameters

The application of molecular mechanics methods for the study of structures has become a standard approach to conformational analysis. The MM2 force field has been extended to include imines. In general, a diverse group of aliphatic and aromatic imine structures can now be treated. The rotational energy profiles and barriers to N-substituted imines about the C_sp2? C_sp2 single bonds adjacent to C?N functional group were calculated via ab initio MO theory. Information obtained from the quantum mechanical calculations at the 3-21G, 6-31G*, and MP4/6-31G* //6-31G* levels was used both to study the phenomena involved and to parameterize MM2. The syn-anti isomerization was also studied, and the mechanistic pathways have been evaluated. In cases where the comparison with experimental data can be made, the agreements are good.