50 research outputs found
Meta -Bridged calix[4]arenes with the methylene moiety possessing in/out stereochemistry of substituents
meta-Substituted organomercury calix[4]arenes and their corresponding iodo derivatives have been used for lithiation followed by a reaction with various aldehydes or ketones. The resulting diastereomers were in some cases separable using simple column chromatography. Subsequent intramolecular Friedel-Crafts alkylation led to calix[4]arenes with an additional methylene bridge bearing two different substituents with in/out (relative to the cavity) stereochemistry. Our results indicate that the stereochemistry of the final cyclised product does not depend on the structure/stereochemistry of the starting compound, but rather it is influenced by the stability of the products. The relationship between the positions of these substituents and the complexation properties was demonstrated by 1H NMR titration experiments with N-methylpyridinium iodide
Evaluating Design Tradeoffs in Numeric Static Analysis for Java
Numeric static analysis for Java has a broad range of potentially useful
applications, including array bounds checking and resource usage estimation.
However, designing a scalable numeric static analysis for real-world Java
programs presents a multitude of design choices, each of which may interact
with others. For example, an analysis could handle method calls via either a
top-down or bottom-up interprocedural analysis. Moreover, this choice could
interact with how we choose to represent aliasing in the heap and/or whether we
use a relational numeric domain, e.g., convex polyhedra. In this paper, we
present a family of abstract interpretation-based numeric static analyses for
Java and systematically evaluate the impact of 162 analysis configurations on
the DaCapo benchmark suite. Our experiment considered the precision and
performance of the analyses for discharging array bounds checks. We found that
top-down analysis is generally a better choice than bottom-up analysis, and
that using access paths to describe heap objects is better than using summary
objects corresponding to points-to analysis locations. Moreover, these two
choices are the most significant, while choices about the numeric domain,
representation of abstract objects, and context-sensitivity make much less
difference to the precision/performance tradeoff
New calix[4]arene-based amides - Their synthesis, conformation, complexation
New chiral calix[4]arene-based diol-diamides 1a, 1b, tetraamides 2a, 2b and 7 as well as achiral diamide 3 and tetraamides 4-6 were prepared. The conformation of 1 has been studied in solution by NMR and in solid state by X-ray crystallography. The pinched-cone conformation of the calix[4]arene skeleton in 1 was found to be stabilized by a circular array of hydrogen bonds formed by two phenolic O-H and two amidic N-H bonds at lower rim. Whereas no significant complexation of Na+ was observed in solution for diamides 1 and 3, tetraamides 2, 4, 5, and 6 give strong complexes with Na+ as confirmed by NMR titrations of 2 and 4. The influence of anions and the solvents used on complexation ability of 2 towards Na+ is negligible