2. 4-(p-Nitrobenzyl)pyridine as a spray reagent for the thin-layer chromatographic detection of dimethyl tetrachloroterphthalate herbicide
M T Ragab J Environ Sci Health B. 1977;12(2):155-61. doi: 10.1080/03601237709372060.
The developed thin-layer chromatogram of DCPA (Dacthal) is sprayed with 4-(p-nitrobenzyl)pyridine chromogenic reagent followed by ammonium carbonate solution. The chromatogram is then heated in an over at 130 degrees C for 20 minutes. When cool, the chromatogram is sprayed with tetraethylenepentamine reagent. DCPA spots appear blue against a white background. The sensitivity of this test is about 1 microgram. The procedure is useful to detect DCPA in water and in soil.
3. Structures of cytochrome P450 2B6 bound to 4-benzylpyridine and 4-(4-nitrobenzyl)pyridine: insight into inhibitor binding and rearrangement of active site side chains
Manish B Shah, Jaime Pascual, Qinghai Zhang, C David Stout, James R Halpert Mol Pharmacol. 2011 Dec;80(6):1047-55. doi: 10.1124/mol.111.074427. Epub 2011 Aug 29.
The biochemical, biophysical, and structural analysis of the cytochrome P450 2B subfamily of enzymes has provided a wealth of information regarding conformational plasticity and substrate recognition. The recent X-ray crystal structure of the drug-metabolizing P450 2B6 in complex with 4-(4-chlorophenyl)imidazole (4-CPI) yielded the first atomic view of this human enzyme. However, knowledge of the structural basis of P450 2B6 specificity and inhibition has remained limited. In this study, structures of P450 2B6 were determined in complex with the potent inhibitors 4-benzylpyridine (4-BP) and 4-(4-nitrobenzyl)pyridine (4-NBP). Comparison of the present structures with the previous P450 2B6-4-CPI complex showed that reorientation of side chains of the active site residue Phe206 on the F-helix and Phe297 on the I-helix was necessary to accommodate the inhibitors. However, P450 2B6 does not require any major side chain rearrangement to bind 4-NBP compared with 4-BP, and the enzyme provides no hydrogen-bonding partners for the polar nitro group of 4-NBP within the hydrophobic active site. In addition, on the basis of these new structures, substitution of residue 172 with histidine as observed in the single nucleotide polymorphism Q172H and in P450 2B4 may contribute to a hydrogen bonding network connecting the E- and I-helices, thereby stabilizing active site residues on the I-helix. These results provide insight into the role of active site side chains upon inhibitor binding and indicate that the recognition of the benzylpyridines in the closed conformation structure of P450 2B6 is based solely on hydrophobicity, size, and shape.
