A bifunctional ligand that is capable of forming Re and 99mTc complexes as complementary fluorescent and radioactive probes was developed. The tridentate bis(quinoline) amine ligand, which is referred to as the SAACQ system, was prepared in a single step from Fmoc protected lysine in high yield. Reaction of the SAACQ ligand with [Re(CO)3Br3]2- resulted in the formation of the SAACQ-(Re(CO)3)+complex which exhibits favorable fluorescence properties including a long lifetime and a large Stoke's shift. Because the SAACQ ligand is derived from an amino acid, it can readily be linked to or incorporated within peptides as a means of targeting the probe to specific receptors. To demonstrate this feature, the SAACQ ligand and the SAACQ-Re complex were incorporated into fMLFG, a peptide that binds to the formyl peptide receptor (FPR). Uptake of the fMLF[(SAACQ-Re(CO)3)+]G conjugate into human leukocytes in vitro was visualized by fluorescence microscopy, and the observed distribution of the peptide was similar to that of a well-established fluorescent FPR probe. The corresponding Tc complex, fMLF[(SAACQ-99mTc(CO)3)+]G, was prepared in excellent yield from [99mTc(CO)3(OH2)3]+, which affords the opportunity to correlate the results of the microscopy experiments with in vivo radioimaging studies because the probes are isostructural.
In most cases, kinetic unfolding reactions of proteins follow a simple one-step mechanism that does not involve any detectable intermediates. One example for a more complicated unfolding reaction is the acid-induced denaturation of holo-myoglobin (hMb). This reaction proceeds through a transient intermediate and can be described by a sequential two-step mechanism (Konermann et al. Biochemistry 1997, 36, 6448-6454). Time-resolved electrospray ionization mass spectrometry (ESI MS) is a new technique for monitoring the kinetics of protein folding and unfolding in solution. Different protein conformations can be distinguished by the different charge state distributions that they generate during ESI. At the same time this technique allows monitoring the loss or binding of noncovalent protein ligands. In this work, time-resolved ESI MS is used to study the dependence of the kinetic unfolding mechanism of hMb on the specific solvent conditions used in the experiment. It is shown that hMb unfolds through a short-lived intermediate only at acidic pH. Under basic conditions no intermediate is observed. These findings are confirmed by the results of optical stopped-flow absorption experiments. This appears to be the first time that a dependence of the kinetic mechanism for protein unfolding on external conditions such as pH has been observed.
A new method for the preparation of Re- and (99m)Tc-metallocarboranes in water under mild reaction conditions was developed. Three nido-carborane ligands were reacted with [Re(CO)(3)Br(3)](2)(-) in the presence of aqueous potassium fluoride to give the corresponding eta(5)-Re(CO)(3)-carborane complexes. The use of KF as a base afforded the desired Re-metallocarboranes in good yields while avoiding the formation of Re clusters, which are byproducts commonly observed when reactions are carried out in the presence of strong aqueous bases. The reaction was also performed at the tracer level producing the first (99m)Tc-carborane complex, which was isolated in 80% radiochemical yield following a simple Sep-Pak purification process. The resulting organometallic complex was stable to cysteine and histidine challenges for more than 24 h.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.