Water tetrahedral geometry

In summary, pure liquid water consists of HgO molecules held in a random, three-dimensional network that has a local preference for tetrahedral geometry but contains a large number of strained or broken hydrogen bonds. The presence of strain creates a kinetic situation in which HgO molecules can switch H-bond allegiances fluidity ensues. 

Start with water, which is essential for life as we know it. If the water molecule were linear rather than bent, it would lack the properties that life-forms require. Linear water would not be polar and would be a gas like carbon dioxide. Why is water bent Its four electron pairs adopt tetrahedral geometry, putting lone pairs at two vertices of a tetrahedron and hydrogen atoms at the other two vertices. 

The zinc nitrate complexes of pyridyl functionalized 12[ane]N3 ligands l-(2-pyridylmethyl) -1,5,9-triazacyclododecane and l-(2-pyridyl-2 -ethyl)-l,5,9-triazacyclododecane were formed. 13C NMR studies were used to determine conformation in solution suggesting the former gave a trigonal bipyramidal isomer in solution with a water bound and the latter gave a 2 1 mixture of tetrahedral and asymmetric trigonal bipyramidal isomers. The crystal structure of the zinc complex of l-(2-pyridyl-2 -ethyl)-1,5,9-triazacyclododecane reveals a tetrahedral geometry in the solid state.679... 

The tetrahedral geometry resultant from these sp -hybridized nitrogen and oxygen atoms is found to exist in both ammonia and water. Bond angles in... 

The structure and mechanism of catalysis of FTase were well defined in the late 1990s from several X-ray crystallography and elegant biochemical studies [24,26-30]. The enzyme is a heterodimer of a and P subunits [31,32]. The P subunit contains binding sites for both the farnesyl pyrophosphate and the CAAX protein substrates. A catalytic zinc (Zn " ) identified in the active site of the P subunit participates in the binding and activation of the CAAX protein substrates [28]. The Zn " is coordinated to the enzyme in a distorted tetrahedral geometry and surrounded by hydrophobic pockets [24,27]. Upon binding of the CAAX peptide, the thiol of the cysteine displaces water and is activated for a nucleophilic attack via thiolate on the C-1 carbon atom of farnesyl pyrophosphate [30]. 

Another zinc-utilizing enzyme is carbonate/dehydratase C (Kannan et al., 1972). Here, the zinc is firmly bound by three histidyl side chains and a water molecule or a hydroxyl ion (Fig. 27). The coordination is that of a distorted tetrahedron. Metals such as Cu(II), Co(Il), and Mn(ll) bind at the same site as zinc. Hg(II) also binds near, but not precisely at, this site (Kannan et al., 1972). Horse liver alcohol dehydrogenase (Schneider et al., 1983) contains two zinc sites, one catalytic and one noncatalytic. X-Ray studies showed that the catalytic Zn(II), bound tetrahedrally to two cysteines, one histidine, and water (or hydroxyl), can be replaced by Co(II) and that the tetrahedral geometry is maintained. This is also true with Ni(Il). Insulin also binds zinc (Adams etai, 1969 Bordas etal., 1983) and forms rhombohedral 2Zn insulin crystals. The coordination of the zinc consists of three symmetry-related histidines (from BIO) and three symmetry-related water molecules. These give an octahedral complex... 

Kimura (225) studied a potentially attractive model Zn-complex of [12]aneN3. It confirms to a tetrahedral geometry with a H20 at the fourth coordination site [LZnnOH2] and pKa of Zn-bound water is... 

The white crystalline solids are readily soluble in organic solvents (even alkanes) but are insoluble in water and the lower alcohols. They are inert to water but are hydrolyzed by dilute acid. In solution they are monomeric and non-ionized. An X-ray crystallographic study of Be40(0Ac)6 shows the O to be centrally coordinated to four Be atoms in a tetrahedral geometry each of the Be atoms is tetrahedrally surrounded by four O donors from bridging acetates and the central oxygen (62).322... 

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