Dimer ions heterodimers

Dimer ions such as (M + M + H)+ or of higher order ( M + H)+ are often observed. The proton can be replaced by another cation. Heterodimers of the general formula (M + M + H)+, or with a metal cation or of higher order, are also observed. The corresponding ions are also observed in negative ion mode. 

This review article deals primarily with addition reactions of nucleophiles, electrophiles, and neutral radicals to photochemically generated radical ions of organic compounds and some organometallic compounds. Photocyclodimerizations of electron-rich alkenes, photo-Diels-Alder reactions between alkenes and alkadienes via dimer or heterodimer radical cations, and photocycloadditions via triplexes are also included. 

Our strategy for the spontaneous dimerization of EGF was to incorporate an ot-helical oligopeptide with the ability to participate in forming a coiled-coil structure [99]. We implemented a heterodimerization system in which (KELASVK)5 (K5) and (EKLASVE)5 (E5) peptides could form stable coiled-coil heterodimers. We then synthesized two chimeric proteins that contained EGF attached to either the K5 (EGF-K5-His) or the E5 (EGF-E5-His). Both had the hexahistidine sequence added to the C-terminus for anchoring through coordination with Ni2+ ions fixed to a substrate. 

In erythrocytes and most other cells, the major structural link of plasma membranes to the cytoskeleton is mediated by interactions between ankyrin and various integral membrane proteins, including Cf/HCOj antiporters, sodium ion pumps and voltage-dependent sodium ion channels. Ankyrin also binds to the =100 nm, rod-shaped, antiparallel a(3 heterodimers of spectrin and thus secures the cytoskeleton to the plasma membrane. Spectrin dimers self-associate to form tetramers and further to form a polygonal network parallel to the plasma membrane (Fig. 2-9D). Neurons contain both spectrin I, also termed erythroid spectrin, and spectrin II, also termed fodrin. Spectrin II is found throughout neurons, including axons, and binds to microtubules, whereas spectrin I occurs only in the soma and dendrites. 

LCA toward amino acids and nucleic bases has also been measured. Wesdemiotis and Cerda measured the alkali metal ion affinities of nucleobases in the gas phase from the dissociation of metal ion-bound heterodimers [nucleobase + B]M+, in which B represents a reference base of known affinity and M is an alkali metal. By assessing the dimer decomposition for two different internal energies, entropy is deconvoluted from enthalpy and LCA values are obtained. For guanine, cytosine, adenine, thymine and uracil, the corresponding Li+-nucleobase bond energies are as follows 57.2, 55.5, 54.1,... 

Photoinduced electron transfer reactions that occur between neutral electron donor molecules and neutral electron acceptor molecules have several characteristic features (1) a radical cation and a radical anion are produced as a pair, (2) radical ion species are produced under neutral and mild conditions, and (3) the polarity inversion (umpolung) of original electron donor and electron acceptor molecules arises through their conversion into radical ion species. As a result, the radical cation D can interact with another D or a different electron donor molecule D to yield a dimer radical cation Dj or heterodimer radical... 

The dimer formation of anionic metalloporphyrins [677], cationic porphyrins [678], heterodimer formation [679-682], an aggregate between porphyrin and cytochrome c [683], and dimer formation through metal-metal interaction [684] has been reported. The 1 2 complex formation between the metal ions such as Th ° and Ce and porphyrins afforded an interesting double-decker sandwich complex [685-687] and a triple-decker one [688]. 

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