A Contribution to the Anatomy of the Digestive Tract in Salmo Salar.
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Journal Article↗
Biomedical subjects
J K Barton
Publications and source records attributed to J K Barton.
Construction of coordinatively saturated rhodium complexes containing appended peptides.
Phenanthrenequinone diimine (phi) complexes of rhodium(III) bearing appended peptides have been prepared using two complementary solid phase synthetic strategies. The first method involves the direct coupling of the coordinatively saturated rhodium complex containing a pendant carboxylate to the N-terminus of a resin-bound peptide, in a manner analogous to the chain-elongation step in solid phase peptide synthesis. The second involves coupling a bidentate chelator containing the pendant carboxylate to the resin-bound peptide, followed by coordination of [Rh(phi)2]3+ to the bidentate chelator attached to the peptide. Peptides of length 5-30 residues have been covalently attached to rhodium complexes in 5-18% yield using both methods. Despite the low overall yields, the regioselective modification of the peptide chain afforded by these strategies is a distinct advantage over solution phase methods. With coordination complexes which are stable to peptide deprotection and cleavage conditions from the resin, the solid phase synthetic strategies are convenient to apply. Amino acid analysis, electronic spectroscopy, and circular dichroism confirm the presence of the two components in the metal-peptide chimeras; the metal-peptide complexes exhibit the combined spectral properties of the parent metal complex and the appended peptide. Significantly, plasma desorption mass spectrometry reveals a novel pattern of peptide fragmentation for the metal-peptide chimeras that is not observed in the absence of the tethered metal complex; this fragmentation facilitates the sequence analysis of the appended peptide. Thus, metal-peptide chimeras may be conveniently prepared using solid phase methodologies, and features of coordination chemistry may be exploited for new peptide design and analysis.
Amino Acid Sequence↗
Electrochemistry of methylene blue bound to a DNA-modified electrode.
Gold surfaces have been derivatized with 15-base-pair double-stranded DNA oligonucleotides containing a pendant 5' hexanethiol linker. The electrochemistry of intercalated methylene blue has been investigated at these modified electrodes. Chronocoulometry, cyclic voltammetry, ellipsometry, and quantitation via 32P labeling are all consistent with a surface coverage of > or = 75% with the DNA helices stacked at an angle from the electrode surface. Cyclic voltammetry at low methylene blue/ duplex stoichiometries yields well-behaved surface waves with E degrees = -0.25 V (vs SCE), a value 0.03 V negative of that in aqueous solution. A binding isotherm for methylene blue at an electrode derivatized with the double-stranded sequence 5' SH-(CH2)6-p-AGTACAGTCATCGCG 3' was obtained from coulometric titrations and gave an affinity constant equal to 3.8(5) x 10(6) M-1 with a saturation value of 1.4(2) methylene blue intercalators per DNA duplex. Taken together, these experiments support a model for the surface morphology in which DNA duplexes are densely packed; methylene blue therefore reversibly binds to sites in the DNA that are close to the bulk solution. Electrochemistry at DNA-derivatized electrodes provides a valuable methodology to examine DNA-bound redox reactions and may offer new insight into DNA-mediated electron transfers.
DNA↗
Synthesis of metallointercalator-DNA conjugates on a solid support.
Metallointercalator-DNA conjugates were prepared by amide bond formation between active esters on the nonintercalating ligands of transition metal complexes and primary amines presented at the 5' or the 3' termini of oligonucleotides attached to solid supports. The conjugates were liberated from the support by aminolysis and purified by HPLC on C18 or C4 stationary phases, which separates the two diastereomeric forms of the conjugates containing either the Lambda or the Delta enantiomer of the octahedral metal complex. The coupling reaction proceeds with approximately 75% conversion of the amino-terminated oligonucleotide into the conjugate; the isolated yield is approximately 200 nmol for syntheses initiated on DNA-synthesis columns with a loading of 2 micromol. The conjugates were characterized by ultraviolet-visible and circular dichorism absorption spectroscopy, electrospray ionization mass spectrometry, enzymatic digestion, and polyacrylamide gel electrophoresis (PAGE). Oligonucleotides bearing [Rh(phi)(2)(bpy')](3+) (phi = 9, 10-phenanthrene quinone diimine; bpy' = 4-butyric acid-4'-methyl bipyridyl) form 1:1 duplexes with the complementary strand, and the electrophoretic mobility under nondenaturating PAGE of duplexes containing Delta-Rh is notably different from duplexes containing Lambda-Rh. High-resolution PAGE of DNA photocleavage reactions initiated by irradiation of the tethered Rh complexes reveal intercalation of the complex only near the tethered end of the duplex. Analogous DNA-binding properties were observed with [Rh(phi)(2)(bpy')](3+) tethered to the 3' terminus. By combining the 3' and 5' modification strategies, a mixed-metal DNA conjugate containing both [Os(phen)(bpy')(Me(2)-dppz)](2+) (Me(2)-dppz = 7, 8-dimethyldipyridophenazine) on the 3' terminus and [Rh(phi)(2)(bpy')](3+) on the 5' terminus was prepared and isolated. Taken together, these strategies for preparing metallointercalator-DNA conjugates offer a useful approach to generate chemical assemblies to probe long-range DNA-mediated charge transfer where the redox initiator is confined to and intercalated in a well-defined binding site.
Base Sequence↗