Hydrogen bridges atoms

As an example, let us consider neutral boranes with composition BpHp+g. Suppose the number of hydrogen bridge atoms is denoted by s, the number of terminal BH or BH2 groups by x, the number of three-centre bonds BBB (both open and central) by t, and the number of two-centre bonds B—B by y. 

The species at the centre of tire rings is usually Si or Ge and tire bridging atom is oxygen. In one study tire peripheral hydrogens on tire phtlialocyanine molecules were replaced by alkyl groups and tire resulting polymers could be rendered soluble in ordinary organic solvents [108, 109 and 110]. Successful deposition of several of tliese materials has been achieved and different techniques were employed to study tlieir stmctural properties [109, ill, ill, ill and 1141. 

Aluminium tetrahydridoborate is a volatile liquid. It is the most volatile aluminium compound known. It is covalent and does not contain ions but has a hydrogen-bridge structure like that of diborane, i.e. each boron atom is attached to the aluminium by two hydrogen bridges ... 

Carbon-6, which bears two hydrogens, is pentacoordinate and serves as the bridging atom in the cation. 

The different behaviour of difluorophosphoric acid which is of a higher degree of association, is probably induced by the ability of the fluorine ligands to act, besides the 0-atoms, as bridging atoms in the hydrogen bridges. 

In both compounds the hydratemolecules form hydrogen bridges, in which as in the difluorophosphates, only the 0-atoms of the [POgF] ions participate in (NH4)2[P03F] H2O there are additional N—H 0 bridges (26). In the P03F ion the formal bond order po decreases from 1.83 to 1.67 (95) in comparison to... 

The same kind of layers also occur in a second modification of Al(OH)3, hydrargillite (gibbsite), but with a stacking in which adjacent O atoms of two layers are exactly one on top of the other they are joined via hydrogen bridges. 

It seems that water hydrolyzes the Si-O-Si connections between the slica tetrahedra, yielding Si-OH HO-Si. That is, strong -O- bridges are replaced by weak H H hydrogen bridges. These become associated with kinks on dislocation lines increasing the mobilities of kinks and therefore dislocations (Griggs, 1967). Since the concentration of kinks is small compared with the total number of atoms, relatively little water is needed for this catalytic mechanism. 

The IR spectrum of carbene li indicates a very strong hydrogen bridge between the carboxyl hydrogen atom and the ring carbonyl group.92 The red shift... 

Fig. 1.6. Binding domain to DNA. ERs contain two structures called zinc fingers, typical of proteins that interact with DNA. One zinc atom forms four links of coordination with four cysteine residues of the protein structure, which occupy nearby positions, thus leaving a loop of some 15 to 22 aminoacids. The zinc fingers of the receptor are capable of interacting with specific sequences of DNA, the hormone response elements, with which they establish hydrogen bridges and form stable structures...

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