Mg complexes

RI 1.4092 at 25°. Sol in aq NaOH- Prepn is by reacting at 0° with stirring an ethereal soln of 2-nitroprop-l-ene with ethylmagnesium bromide, which is added v slowly. An additional hr of stirring at 20° is reqd to complete the reaction. Subsequent decompn of the Mg complex is obtd by cautious addn of aq acet acid. The... 

Greater adsorption of trace metals is found at higher pH and C02(g) concentrations. Sites available for Zn2+ sorption are less than 10% of the Ca2+ sites on the calcite surface, and Zn adsorption is independent of surface charge. This indicates a surface complex with a covalent character (Zachara et al., 1991). Furthermore, the surface complex remains hydrated and labile because Zn2+ is rapidly exchangeable with Ca2+, Zn2+ and ZnOH. At the dolomite-solution interface, the carbonate(C03)-metal (Ca/Mg) complex dominates surface speciation at pH > 8, but at pH 4-8, hydroxide (OH) -metal (Ca/Mg) dominates surface speciation (Pokrovsky et al., 1999). Calcite has an observed selectivity sequence Cd > Zn > Mn > Co > Ni > Ba = Sr, but their sorption reversibility is correlated with the hydration energies of the metal sorbates. Cadmium and Mn dehydrate soon after adsorption to calcite and form a precipitate, while Zn, Co and Ni form surface complexes, remaining hydrated until the ions are incorporated into the structure by recystallization (Zachara et al., 1991). 

Antibiotic Mg complex induced alteration in the ultrastructural changes in the native and HI depleted chromatin were monitored by thermal melting analysis, polyacrylamide gel mobility assay, dynamic light scattering experiments and transmission electron microscopic studies. Micrococcal nuclease digestion is the biochemical probe to assess the accessibility of the antibiotic Mg + complexes to nucleosomal DNA. 

Quantitative characterization of the binding of antibiotic Mg + complexes with different levels of chromatin... 

Depletion of histone HI after covalent modification from chromatin is a key step in eukaryotic transcription (Lee et al, 1993 Juan et al, 1994 Rice and Allis, 2001). A comparison of the association of the antibiotic Mg + complexes with the normal and HI depleted chromatin suggests that smaller ligands, like anticancer drugs, have better accessibility for HI depleted chromatin compared to native chromatin. HI depleted chromatin is also more prone to aggregation upon association with the complex I of the antibiotic Mg + complexes. It is also less accessible to micrococcal nuclease. We propose that HI depleted chromatin is a better target of these antibiotics compared to native chromatin. This observation is particularly significant in case of neoplastic cells where most of the cell nuclei are transcriptionally active, and, therefore, contain HI depleted chromatin. 

Aich P, Dasgupta D (1990) Role of Mg(ll) in the Mithramycin-DNA interaction evidence for two types of Mithramycin-Mg(II) complex. Biochem Biophys Res Commun 173 689-696 Aich P, Dasgupta D (1995) Role of magnesium ion in mithramycin-DNA interaction binding of mithramycin-Mg + complexes with DNA. Biochemistr 34 1376-1385 Aich P, Sen R, Dasgupta D (1992a) Interaction between antitumor antibiotic Chromomycin A3 and Mg(ll) 1. Evidence for the formation of two types of Chromomycin A3-Mg(ll) complexes. Chem Biol Interact 83 23-33... 

Aich P, Sen R, Dasgupta D (1992b) Role of magnesium ion in the interaction between chromomycin A3 and DNA binding of chromomycin A3 — Mg + complexes with DNA. Biochemistry 31 2988-2997 Akman SA, Doroshow JJH, Thomas G, Burke J, Dizdaroglus M (1992) DNA base modifications induced in isolated human chromatin by NADH de hydrogenase-catalyzed reduction of doxorubicin. Biochemistry, 31 3500-3506... 

The L2 loop is of particular importance for the biological activity of the Ras protein. L2 contains the amino acids 32-36, which were recognized in mutation experiments as important for the interaction with GTPase-activating proteins. Thr35 of the L2 loop also participates in H-bridge contacts to the y-phosphate and to Mg +, and thus helps to correctly position the GTP-Mg complex in the active center. 

Photodissociation of the Mg+" complex of pyridine yields two products Mg as the major product (cf equation 39) and C5H5N+ via electron transfer (cf equation 40) as the minor channel . The photodissociation spectra of Mg(NCCH3) complexes has been... 

The Mg+ complexes of cytosine, thymine and uracil are the most complex system studied via photodissociation spectroscopy to date . A complication for these systems is that these nucleobases can exist in various tautomeric forms and that complexation of a metal can change the stability order of the tautomers. DFT calculations located four tautomeric Mg(cytosine)+ complexes, and three of these (29, 30, and 31) were suggested to be responsible for the four reactive photofragment ions 32-35 observed at a wavelength of 360 nm (Scheme 4) . Related photofragmentation reactions were observed for the Mg(thymine)+" and Mg(uracil)+" complexes . ... 

In early studies of these reactions, the turnover efficiency was not always high, and stoichiometric amounts of the promoters were often necessary to obtain reasonable chemical yields (Scheme 105) (256). This problem was first solved by using chiral alkoxy Ti(IV) complexes and molecular sieves 4A for reaction between the structurally elaborated a,/3-unsaturated acid derivatives and 1,3-dienes (257). Use of alkylated benzenes as solvents might be helpiul. The A1 complex formed from tri-methylaluminum and a C2 chiral 1,2-bis-sulfonamide has proven to be an extremely efficient catalyst for this type of reaction (258). This cycloaddition is useful for preparing optically active prostaglandin intermediates. Cationic bis(oxazoline)-Fe(III) catalysts that form octahedral chelate complexes with dienophiles promote enantioselective reaction with cyclopentadiene (259). The Mg complexes are equally effective. 

Catalytic hydrogenation of porphyrazines or their Mg complexes with palladium black gives tetrahydrogenated compounds which are oxidized back to the starting materials by a stoichiometric amount of 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ).2 The royal blue products are degraded to cw-succinimide and maleimide, and considered to be the tetraaza analogues of either bacterio-chlorins or isobacteriochlorins. Photochemical reduction of monoazaporphyrins is reported to occur at the meso positions. 

With Chiral Bis(oxazoline)/Mg Complexes A chiral bis(oxazoline)/MgI2 complex has been utilized for the enantioselective Diels-Alder reaction of cyclopentadiene and ethyl 2-benzoylacrylate that acts as a two-point binding dienophile [49] (Eq. 8A.27). This reaction proceeds with virtually complete endo/exo selectivity (>99 1). 

A similar chiral bis(oxazoline)/Cu(II) catalyst is useful for the asymmetric hetero Diels-Alder reaction of Danishefsky s diene and glyoxylates [63] (Eq. 8A.39). Other bis(oxa-zoline)/M(OTf)2 (M = Sn, Mg) complexes are not effective. This method provides new routes to asymmetric aldol synthesis upon hydrolysis of the resulting adducts. 

---