Molecular modeling of intercalation complexes of antitumor active 9-aminoacridine and a [d,e]-anellated isoquinoline derivative with base paired deoxytetranucleotides

Summary Intercalators are molecules capable of sliding between DNA base pairs without breaking up the hydrogen bonds between the DNA bases. On the basis of molecular mechanics calculations structural, models of B-DNA tetranucleotide intercalation complexes of some cytostatic active 9-aminoacridines and of a [d, e]-anellated isoquinoline derivative are presented. The drug complexes are stabilized by energetically favouredvan der Waals interactions and by selective hydrogen bonds between the side chains of the drugs and the DNA bases. Semiempirical quantum chemistry calculations revealed that the chromophoric system of the intercalators is able to form ,-charge-transfer interactions with the purine bases of the base paired deoxytetranucleotides. The theoretical findings are of interest for a more specific drug design of cytostatically active agents.

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Molecular Modeling von Interkalationskomplexen antitumoraktiver 9-Aminoacridine sowie eines [d, e]-anellierten Isochinolinderivates mit basengepaarten Desoxytetranukleotiden

Zusammenfassung Interkalatoren sind Moleküle, die in der Lage sind, sich zwischen DNA-Basenpaare einzulagern, ohne die Wasserstoffbrücken zwischen den DNA-Basen aufzubrechen. Auf der Basis von molekülmechanischen Rechnungen werden Tetranukleotid-Interkalationskomplexe von verschiedenen zytostatisch aktiven 9-Aminoacridinen und von einem [d, e]-anellierten Isochinolinderivat präsentiert. Die Komplexe werden durch energetisch günstigevan der Waals-Interaktionen sowie durch selektive Wasserstoffbrückenbindungen zwischen den Seitenketten der Wirkstoffe und den DNA-Basen stabilisiert. Semiempirische quantenchemische Rechnungen ergaben, daß der Chromophor der Interkalatoren in der Lage ist, ,-charge-transfer Wechselwirkungen mit den Purinbasen der basengepaarten Desoxytetranukleotide auszubilden. Die theoretischen Ergebnisse sind für ein spezifischeres Wirkstoffdesign zytostatisch aktiver Verbindungen von Interesse.

     

Transition from a two-dimensional superfluid to a one-dimensional Mott insulator

A two-dimensional system of atoms in an anisotropic optical lattice is studied theoretically. If the system is finite in one direction, it is shown to exhibit a transition between a two-dimensional superfluid and a one-dimensional Mott insulating chain of superfluid tubes. Monte Carlo simulations are consistent with the expectation that the phase transition is of Kosterlitz-Thouless type. The effect of the transition on experimental time-of-flight images is discussed.     

Visual spatial memory is enhanced in female rats (but inhibited in males) by dietary soy phytoestrogens

Background  

In learning and memory tasks, requiring visual spatial memory (VSM), males exhibit superior performance to females (a difference attributed to the hormonal influence of estrogen). This study examined the influence of phytoestrogens (estrogen-like plant compounds) on VSM, utilizing radial arm-maze methods to examine varying aspects of memory. Additionally, brain phytoestrogen, calbindin (CALB), and cyclooxygenase-2 (COX-2) levels were determined.     

The reaction between 3-aminocrotonates and oxindole-3-ylidene derivatives: synthesis of highly substituted pyrroles

The reaction between 3-aminocrotonates and 3-acetonylideneoxindole in refluxing toluene resulted in 2-pyrrolo-3′-yloxindoles in high yields (around 90%). At room temperature the 2-pyrrolo-3′-yloxindoles exists as keto-enol tautomers. Treatment with POCl₃ yielded the 2-chloro-3-pyrrolyl indole, which gave the pyrrolo annulated indolopyran-2-one upon basic hydrolysis of 2-chloro-3-pyrrolyl indole methyl ester.     

Combinatorial and Topological Analysis of the Ising Chain in a Field

We present an alternative solution of the Ising chain in a field under free and periodic boundary conditions, in the microcanonical, canonical, and grand canonical ensembles, from a unified combinatorial and topological perspective. In particular, the computation of the per-site entropy as a function of the energy unveils a residual value for critical values of the magnetic field, a phenomenon for which we provide a topological interpretation and a connection with the Fibonacci sequence. We also show that, in the thermodynamic limit, the per-site microcanonical entropy is equal to the logarithm of the per-site Euler characteristic. The canonical and grand canonical partition functions are identified as combinatorial generating functions of the microcanonical problem, which allows us to evaluate them. A detailed analysis of the magnetic field-dependent thermodynamics, including positive and negative temperatures, reveals interesting features. Finally, we emphasize that our combinatorial approach to the canonical ensemble allows exact computation of the thermally averaged value <????> of the Euler characteristic associated with the spin configurations of the chain, which is discontinuous at the critical fields, and whose thermal behavior is expected to determine the phase transition of the model. Indeed, our results show that the conjecture <????>?(T _C)?=?0, where T _C is the critical temperature, is valid for the Ising chain.     

Mammalian cell traces – morphology, molecular composition, artificial guidance and biotechnological relevance as a new type of “bionanotube”

During locomotion, adherently growing cells release highly ordered structures consisting of filaments and patches often dendritically organised. Such traces can be re-incorporated by the donor cell or disconnected and lost. Here, we present the results of a three-year research programme into trace formation and structural organisation including the influence of substrate surface properties. Some phenomena may, ultimately, have medical or technological applications. These include: (i) the deposition and re-incorporation of cellular material as cells move forward and backward; (ii) the ability of cells to differentiate between their own and foreign traces; (iii) the presence of receptors in the intact membrane envelope of filaments and patches; and (iv) the cytoplasmic content of patches. Trace formation is physiologically controlled and a characteristic of many types of actively migrating higher animal and human cells. Possible applications and perspectives are discussed and the importance of cell-trace elements as “bionanotubes” and biological submicron compartments of cells is explained. Received: 5 February 2001 / Accepted: 6 February 2001 / Published online: 23 May 2001