Bridged, also

In the case of tantalum, the treatment under H2 at 150 °C of a mixture of [(=SiO)Ta(= CHtBu)(CH2tBu)2] and [(= SiO)2Ta(= CHtBu)(CH2tBu)] is transformed into mainly one surface species [(=SiO)2Ta-H] (Scheme 13) [52]. However, when the temperature is increased step by step to 450 °C, this surface complex is gradually converted to [(=SiO)3Ta] and (Si - H) [53]. The gradual reactivity of [(= SiO)2Ta - H] with adjacent silox-ane bridges also speaks for an heterogeneity of the sihca surface. 

Two other types of specific side-chain interactions have been proposed to stabilize the a helix formed by C-peptide (Shoemaker et al., 1987b). A salt bridge between Glu-2 and Arg-10 has been detected in the crystal structure of ribonuclease A (Wlodawer and Sjolin, 1983) as well as in C-peptide in aqueous solution (Rico et al., 1986). This salt bridge also fixes the N-terminal boundary of the helix between Glu-2 and Thr-3. It is not sterically possible to make this ion pair if Glu-2 is part of the helix. Synthetic studies in which either Glu-2 or Arg-10 is replaced by Ala have provided support for the importance of this interaction in stabilizing the a-... 

Amide linkages (peptide bonds) form the backbone of the amino acid chains we call peptides and proteins. A second kind of covalent bond is possible between any cysteine residues present. Cysteine residues can form disulfide bridges (also called disulfide linkages) that can join two chains or link a single chain into a ring. 

Another analogue, with an opened C4—C7 bridge, also shows similar activity to sarcodictyin A, yet again lower than that of eleutherobin.418... 

A salt bridge also helps to minimize problems associated with liquid junction potentials (Eijp). Such potentials in combination with the ohmic potential term resulting from the presence of uncompensated resistance in the electrochemical cell (Rn) may alter the potential applied between the working and reference electrode (Eapp). so that the measured potential (Eceii) is given by (6),... 

The optimized sodium cation positions in a six-ring of FAU zeolite structure containing two A1 atoms in para-position (denoted as Na-Al-2p) ° is shown in Figure 1. This position of the cation is representative for Sn cation position in Y and X zeolites," as well as the position of Na in Na-EMT zeolite. As expected, for this and the other zeolite model structures, Na" prefers positions near to oxygen centers bonded to A1 atoms rather than those of Si-O-Si bridges. Also, tbe cation is far from oxygen centers which are connected to compensating cations, an additional proton in this case. 

The anionic octahedral complex [Ni(NCSe)g] has been reported (162,295, 647, 663), as has [Ni(NCSe)4] . Unlike its thiocyanate analog, the latter ion only exists in the polymeric octahedral from with —NCSe— bridging (295, 647). Bridging also occurs in Ni(NCSe)4Hg (714). 

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