Donald James nobel laureate Cram developed host-guest chemistry

Donald James Cram – co-founder of host-guest chemistry

Category : Personalities
Published by : Data Research Analyst, Worldofchemicals.com

Biography & Contributions

Donald James Cram was an American chemist and Nobel laureate born on April 22, 1919 – died on June 17, 2001. Cram amplified and expanded synthesis of the crown ethers. He was well known for development and use of molecules with structure-specific interactions of high selectivity.

Cram received many awards and medals like National Academy of Science Award in the year of 1955, ACS Cope Award in the year of 1974, ACS Southern California Tolman Award in the year of 1984, ACS Chicago Section Willard Gibbs Medal in the year of 1985, Nobel Prize in chemistry in the year of 1987, Glenn T. Seaborg Medal in the year of 1989.

Cram expanded upon Charles Pedersen's ground-breaking synthesis of crown ethers, two-dimensional organic compounds that are able to recognize and selectively combine with the ions of certain metal elements. He synthesized molecules that took this chemistry into three dimensions, creating an array of differently shaped molecules that could interact selectively with other chemicals because of their complementary three-dimensional structures.

In 1963, Charles Pedersen announced his discovery of the first crown ethers. Building on Ped-ersen's discovery, Jean-Marie Lehn in 1969 developed bycyclic compounds of crown ethers, called cryptands. Both Lehn and Cram later developed increasingly sophisticated organic compounds. The contribution of these scientists laid the foundation for the field of research called “host-guest” chemistry. The main goal of host-guest chemistry was to mimic the interaction between enzymes and their substrates in living cells by creating large molecules that would bind selectively with smaller ones. The compounds are utilized in building sensors, electrodes, and molecular traps.

Cram's work represented a large step toward the synthesis of functional laboratory-made mimics of enzymes and other natural molecules whose special chemical behavior is due to their characteristic structure. He also did work in stereochemistry and Cram's rule of asymmetric induction

Crown Ethers


Crown ethers are cyclic chemical compounds that consist of a ring containing several ether groups. Crown ethers are much broader than the oligomers of ethylene oxide. Crown ethers strongly bind certain cations, forming complexes. Crown ethers are not the only macrocyclic ligands that have affinity for the potassium cation.

Nucleophile

A nucleophile is a chemical species that donates an electron pair to an electrophile to form a chemical bond in relation to a reaction. Nucleophilic describes the affinity of a nucleophile to the nuclei. Neutral nucleophilic reactions with solvents such as alcohols and water are named solvolysis. Nucleophiles may take part in nucleophilic substitution.

Asymmetric Induction

Asymmetric induction in stereochemistry describes the preferential formation in a chemical reaction of one enantiomer or diastereoisomer over the other as a result of the influence of a chiral feature present in the substrate, reagent, catalyst or environment. Asymmetric induction is a key element in asymmetric synthesis.

The Cram's rule of asymmetric induction is

"In certain non-catalytic reactions that diastereomer will predominate, which could be formed by the approach of the entering group from the least hindered side when the rotational conformation of the C-C bond is such that the double bond is flanked by the two least bulky groups attached to the adjacent asymmetric center."

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