Metal hydroxides, crystal structure

The nucleophile in p-lactam hydrolysis by biomimetic Zn(II) complexes has been reported previously to be either a bridging hydroxide or a terminal water molecule. A bridging hydroxide was ruled out as nucleophile [26]. It is unlikely that this is the nucleophile in the reported complex as the two Cd(II) ions are separated by 4.162 A and thus too far away to establish a single hydroxide bridge between the two metal centers. Crystal structures with pyrazolate based ligands reported by Meyer et al. support this proposal [47, 48]. There are a number of findings that led to the proposal that the metal bound alcohol is the nucleophile (Fig. 5.22) ... 

The monosulfides of the alkaline earth metals crystallize in the rock salt (MgS, CaS, SrS, BaS) and zinc blende (BeS) structures. BaS is insoluble in water, while the other monosulfides are sparingly soluble but hydrolyzed on warming (except MgS that is completely hydrolyzed). The monoselenides are isomorphous to the sulfides. The monotellurides CaTe, SrTe, BaTe adopt the rock salt stmcture, while BeTe has the zinc blende and MgTe the wurtzite structure. Alkaline earth polysulfides may be prepared by boiling a solution or suspension of the metal hydroxide with sulfur, e.g.,... 

Before our work [39], only one catalytic mechanism for zinc dependent HDACs has been proposed in the literature, which was originated from the crystallographic study of HDLP [47], a histone-deacetylase-like protein that is widely used as a model for class-I HDACs. In the enzyme active site, the catalytic metal zinc is penta-coordinated by two asp residues, one histidine residues as well as the inhibitor [47], Based on their crystal structures, Finnin et al. [47] postulated a catalytic mechanism for HDACs in which the first reaction step is analogous to the hydroxide mechanism for zinc proteases zinc-bound water is a nucleophile and Zn2+ is five-fold coordinated during the reaction process. However, recent experimental studies by Kapustin et al. suggested that the transition state of HDACs may not be analogous to zinc-proteases [48], which cast some doubts on this mechanism. 

Hydrothermal synthesis using hard and soft acids and bases gave the metal hydroxide-based phases M3Pd2(0H)2[NC5H3(C02)2-2,4]4(H20)4 (M = Co, Ni, Zn).391 A crystal structure is shown in Figure 29. 

Phosphate ester crystal structures have been determined of zinc 1,5,9-triazacyclononane including an interesting structure containing an oligophosphate bridged zinc unit.450 The zinc complex of 1,5,9-triazacyclododecane was studied as a hydrolysis catalyst for substituted phenyl acetates.451 Kinetic analysis suggested that hydrolysis occurs by a mechanism involving hydroxide attack of a metal-bound carbonyl. 

A quite new type of antibiotic and one of the few naturally-occurring boron compounds is boromycin (86). Hydrolytic cleavage of D-valine with the M(7) hydroxides gave caesium and rubidium salts of this antibiotic, and crystal structure analysis established the formula as (XIIT). The rubidium ion is irregularly coordinated by eight oxygen atoms. Experiments with models showed that the cation site would be the natural place for the—NH3+ end of the D-valine residue, and the whole structure raises the possibility that transport of larger alkali metals is related to the N-ends of peptides and proteins. 

Hard silvery-white metal hexagonal close-packed crystal structure density 12.41 g/cm3 at 20°C melts at 2,334°C vaporizes at 4,150°C electrical resistivity 7.1 microhm-cm at 0°C hardness (annealed) 200-350 Vickers units Young s modulus 3.0x10 tons/in magnetic susceptibility 0.427 cm /g thermal neutron absorption cross section 2.6 barns insoluble in water, cold or hot acids, and aqua regia can be brought into aqueous phase by fusion of finely divided metal with alkaline hydroxides, peroxides, carbonates and cyanides. 

In the example in Figure 2.24, a clay (a layered double hydroxide [LDH]) was intercalated with a transition metal complex (NH4)2MnBr4. The EXAFS data in Figure 2.24(a) shows the Mn K-edge EXAFS of the pure complex, and we see one coordination sphere of four Br atoms at a distance of 2.49 A, corresponding well to the tetrahedral coordination found in the X-ray crystal structure. However, after intercalation, the complex reacts with the layers in the clay, and the coordination changes to distorted octahedral where Mn is now surrounded by four 0 atoms at a distance of 1.92 A and two Br atoms at a distance of 2.25 A. 

POTASSIUM. [CAS 7440-09-7]. Chemical element, symbol K, at, no. 19, at. wt. 39.098, periodic table group 1 (alkali metals i, mp 63,3cC, bp 760°C. density 0.86 g/cm3 (20°C). Elemental potassium has a body-centered cubic crystal structure. Potassium is a silver-white metal, can be readily molded, and cut by a knife, oxidizes instantly on exposure to air, and reacts violently with H2O, yielding potassium hydroxide and hydrogen gas, which burns spontaneously in air with a violet flame due to volatilized potassium element, is preserved under kerosene, burns in air at a red heat with a violet flame. Discovered by Davy in 1807. 

In 1998, Krebs and co-authors reported the crystal structures of the catechol oxidase isolated from sweet potatoes (Ipomoea batatas) in three catalytic states the native met (CunCun) state (Figure 5.2a), the reduced deoxy (Cu Cu1) form, and the complex with the inhibitor phenylthiourea (Figure 5.2b) [19]. Typically for the type 3 active site, each copper ion is coordinated by three histidine residues from the protein backbone. In the native met state, the two copper ions are 2.9 A apart and, in addition to six histidine residues, a bridging solvent molecule, most likely a hydroxide anion, has been refined in close proximity to the two metal centers... 

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