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Dariush Ajami

Publications and source records attributed to Dariush Ajami.

6 recordsLinked to original sources
PubMed2006

Coiled molecules in spring loaded devices.

A cylindrical capsule containing a coiled alkane incorporates spacers. The alkane lengthens and gauche strain is relieved. The spacer can be removed to reset the system to the original state. The system represents a spring-loaded device that operates reversibly in response to acids and bases.

Alkanes↗
PubMed2006

Synthesis and properties of the first Möbius annulenes.

Heilbronner in 1964 predicted that annulenes with ".. a planar perimeter of N=4r AO's, which would yield an open shell configuration when occupied by 4r electrons, can be twisted into a closed shell Möbius strip perimeter without loss in pi electron energy". We have been able to synthesize the first [4n]annulene with such a Möbius topology and now present further Möbius isomers and the details of their preparation as stable compounds. To address the question whether the twist in the pi system has an effect on the properties we systematically investigate energy, geometry and magnetic parameters of a large number isomers of [16]annulenes. The Möbius twisted annulenes are consistently more aromatic than the non-twisted isomers. This is true for the parent as well as our benzoannelated systems. Our results are in contrast to those published recently by C. Castro, W. L. Karney, P. von R. Schleyer et al.

Journal Article↗
PubMed2006

Experimental and computational probes of a self-assembled capsule.

[reaction: see text] This research was undertaken to explore the interior surface of a synthetic receptor 1.1 with arylpyridines as guests. The interior surface differentiates the guests through the recognition of their nitrogen atoms. Experimental and computational analyses revealed that there is a delicate balance of attractions and repulsions between the host and the lone pairs of guests.

Calixarenes↗
PubMed2006

Experimental and computational probes of the space in a self-assembled capsule.

Self-assembled capsules are hosts that recognize and surround smaller molecule guests of appropriate size, shape, and chemical surfaces. The space available inside is a cage of fixed solvent molecules, many of which are aromatic. These aromatics provide anisotropic shielding to guests, and a map of induced magnetic shielding for the inner space can be obtained through nucleus-independent chemical shift calculations. Experimental values of the magnetic environment can be determined by NMR spectra of the guests inside. We describe here the environment in a cylindrical capsule with tapered ends. A series of terminal acetylenes -- the narrowest of organic structures -- was synthesized and used to probe the magnetic shielding of the capsule's ends. Their NMR spectra showed that the acetylenic hydrogen experiences deshielding as it is forced deeper into the tapered end of the capsule where four benzene rings converge. Modeling and density functional theory calculations provided excellent agreement with the experimental values and established a molecular ruler to explore steric and magnetic environments inside the capsule.

Acetylene↗