Synthesis and spectral characterization of a long-lifetime osmium (II) metal-ligand complex: a conjugatable red dye for applications in biophysics

Inflammation-Targeted Drug Delivery Strategies via Albumin-Based Systems

Albumin, being the most abundant serum protein, has the potential to significantly enhance the physicochemical properties of therapeutic payloads, thereby improving their pharmacological effects. Apart from its passive transport via the enhanced permeability and retention effect, albumin can actively accumulate in tumor microenvironments or inflammatory tissues via receptor-mediated processes. This unique property makes albumin a promising scaffold for targeted drug delivery. This review focuses on exploring different delivery strategies that combine albumin with drug payloads to achieve targeted therapy for inflammatory diseases. Also, albumin-derived therapeutic products on the market or undergoing clinical trials in the past decade have been summarized to gain insight into the future development of albumin-based drug delivery systems. Given the involvement of inflammation in numerous diseases, drug delivery systems utilizing albumin demonstrate remarkable advantages, including enhanced properties, improved in vivo behavior and efficacy. Albumin-based drug delivery systems have been demonstrated in clinical trials, while more advanced strategies for improving the capacity of drug delivery systems with the help of albumin remain to be discovered. This could pave the way for biomedical applications in more effective and precise treatments.

Electron Transfer in Nitrogenase

Nitrogenase is the only enzyme capable of reducing N2 to NH3. This challenging reaction requires the coordinated transfer of multiple electrons from the reductase, Fe-protein, to the catalytic component, MoFe-protein, in an ATP-dependent fashion. In the last two decades, there have been significant advances in our understanding of how nitrogenase orchestrates electron transfer (ET) from the Fe-protein to the catalytic site of MoFe-protein and how energy from ATP hydrolysis transduces the ET processes. In this review, we summarize these advances, with focus on the structural and thermodynamic redox properties of nitrogenase component proteins and their complexes, as well as on new insights regarding the mechanism of ET reactions during catalysis and how they are coupled to ATP hydrolysis. We also discuss recently developed chemical, photochemical, and electrochemical methods for uncoupling substrate reduction from ATP hydrolysis, which may provide new avenues for studying the catalytic mechanism of nitrogenase.

Dynamics of bacteriophage R17 probed with a long-lifetime Ru(II) metal-ligand complex

The metal-ligand complex, [Ru(2,2'-bipyridine)(2)(4,4'-dicarboxy-2,2'-bipyridine)](2+) (RuBDc), was used as a spectroscopic probe for studying macromolecular dynamics. RuBDc is a very photostable probe that possesses favorable photophysical properties including long lifetime, high quantum yield, large Stokes' shift, and highly polarized emission. To further show the usefulness of this luminophore for probing macromolecular dynamics, we examined the intensity and anisotropy decays of RuBDc when conjugated to R17 bacteriophage using frequency-domain fluorometry with a blue light-emitting diode (LED) as the modulated light source. The intensity decays were best fit by a sum of two exponentials, and we obtained a longer mean lifetime at 4 degrees C (<tau> = 491.8 ns) as compared to that at 25 degrees C (<tau> = 435.1 ns). The anisotropy decay data showed a single rotational correlation time, which is typical for a spherical molecule, and the results showed a longer rotational correlation time at 4 degrees C (2,574.9 ns) than at 25 degrees C (2,070.1 ns). The use of RuBDc enabled us to measure the rotational correlation time up to several microseconds. These results indicate that RuBDc has significant potential for studying hydrodynamics of biological macromolecules.

[Os(bpy)2(CO)(enIA)][OTf]2: A Novel Sulfhydryl−Specific Metal−Ligand Complex

The synthesis and physical-chemical characterization of the metal-ligand complex [Os(bpy)2(CO)(enIA)][OTf]2 (where enIA = ethylenediamine iodoacetamide) with a sulfhydryl-specific functional group is described. The UV and visible absorption and luminescence emission, including lifetime and steady-state anisotropy, are reported for the free probe and the probe covalently linked to two test proteins. The spectroscopic properties of the probe are unaffected by chemical modification and subsequent covalent linkage to the proteins. The luminescence lifetime in aqueous buffer is approximately 200 ns and the limiting anisotropy is greater than 0.125, suggesting a potentially useful probe for biophysical investigations.

Spectroscopy study of 5-amino-1,10-phenanthroline

Acidity constants for the 5-amino-1,10-phenanthroline (5-Aphen) were determined in aqueous media, using SQUAD and SUPERQUAD programs. Spectrophotometry and potentiometry data were fitted to the best model to enable correlation of the following acidity equilibria: 5-AphenH = 5-Aphen + H+ (-log K = 5.78 +/= 0.03) and 5-AphenH2 = 5-AphenH2 = 5-Aphen + 2H+ (-log K = 6.89 +/= 0.07). UV absorptivity coefficients obtained suggest that the first protonation takes place on the nitrogens of the heterocycle ring and the second protonation could take place on the amino group. As expected, the electrochemical evidence of the 5-Aphen species depends on the degree of protonation.

High-molecular-weight protein hydrodynamics studied with a long-lifetime metal-ligand complex

[Ru(2,2'-bipyridine)(2)(4,4'-dicarboxy-2,2'-bipyridine)](2+) (RuBDc) is a very photostable probe that possesses favorable photophysical properties including long lifetime, high quantum yield, large Stokes' shift, and highly polarized emission. In the present study, we demonstrated the usefulness of this probe for monitoring the rotational diffusion of high-molecular-weight (MW) proteins. Using frequency-domain fluorometry with a high-intensity, blue light-emitting diode (LED) as the modulated light source, we compared the intensity and anisotropy decays of RuBDc conjugated to immunoglobulin G (IgG) and immunoglobulin M (IgM), which show a six-fold difference in MW We obtained slightly longer lifetimes for IgM (=428 ns in buffer) than IgG (=422 ns in buffer) in the absence and presence of glycerol, suggesting somewhat more efficient shielding of RuBDc from water in IgM than in IgG. The anisotropy decay data showed longer rotational correlation times for IgM (1623 and 65.7 ns in buffer) as compared to IgG (264 and 42.5 ns in buffer). Importantly, the ratio of the long rotational correlation times of IgM to IgG in buffer was 6.2, which is very close to that of MW of IgM to IgG (6.0). The shorter correlation times are most likely to be associated with domain motions within the proteins. The anisotropy decays reflect both the molecular size and shape of the immunoglobulins, as well as the viscosity. These results show that RuBDc can have numerous applications in studies of high-MW protein hydrodynamics and in fluorescence polarization immunoassays (FPI) of high-MW analytes.