Nitrogen binding

Structurally these compounds combine a eight-coordinate tetracarboxylate chelating site with stilbene chromophores. Of the six dyes proposed in Ref. 121 only Indo-1 leads to a short-wavelength fluorescence shift when bound to Ca2+. It is also the probe with the smallest D-A interactions as revealed by the shortest wavelength of fluorescence of the free ligand. As a consequence, the decrease of the electron density of the nitrogen binding site is not sufficient to break completely the interaction with Ca2+ in the excited state and the spectrum is considerably blueshifted. 

G. K.-L. Chan, M. Ka llay, and J. Gauss, State-of-the-art density matrix renormalization group and coupled cluster theory studies of the nitrogen binding curve. J. Chem. Phys. 121, 6110 (2004). 

The basic structure of Chls is the tetrapyrrolic porphyrin macrocycle with an attached isocyclic ring (Fig. 1). This structure has been termed phytoporphyrin by the lUPAC commission (2). The four nitrogens bind a magnesium ion (Mg +) as central... 

Figure 24.5. Nitrogen-Reduction Site. The FeMo cofactor contains an open center that is the likely site of nitrogen binding and reduction.

Nitrogen is absorbed as nitrate dissolved in water, through the root. The nitrogen-binding bacteria, which live symbiotically in the roots of Leguminosae plants, are able to absorb nitrogen direcdy from the air. Nitrogen is then transformed to ammonia in the plant and incorporated into the amino acids, and biosynthesised to peptides and alkaloids. 

All our attempts to observe Pt NMR signals from either PtCli " or cis-Pt( NH3)aCl2 bound to reduced cytochrome c or ribo-nuclease A (RNase) have so far failed. These platinum complexes are known to bind to the sulphur atoms of exposed methionines (residues 65 and 29 of Cyt c and RNase respectively) as shown by our previous H NMR studies on RNase (28) and those of Boswell et al on Cyt c (29) and x-ray crystallography. We assume therefore that the resonances are broadened beyond detection via chemical shift anisotropy relaxation. The restriction of Pt mobility on the protein will lead to a large increase in (see CSA equation above). The anisotropy term would also be expected to increase. Scalar coupling to N will also contribute to the increase in linewidths if nitrogen binding sites are involved. 

The reactions of alkynes at these nitrogen-binding sites are complicated since a variety of pathways can be followed, including polymerisation, and although the work I shall now briefly describe was initiated while the UNF chemistry that concerns us here was being developed, the range of chemistry which flowed from it took many years to mature. Suffice to say that Scheme 3 shows one aspect of the chemistry of alkynes which relates closely to that shown by N2 and RNC at these sites the field has been reviewed. ... 

Figure 6.15 Co-crystal structure of PF-04691502 bound to PI3K-y. The ring nitrogen of the pyridopyrimidinone forms the common H-bond hinge region interaction with the backbone NH of Val-882, while the exocyclic amine forms an additional interaction with the Val-882 backbone carbonyl. The pyridine nitrogen binds to Tyr-867 and Asp-841 through a conserved water molecule.

Table 21 Silver 3d ani Nitrogen Binding Energies (eV) for Silver(I) Complexes of bipy and phen ...

---