Spectrofluorimetric determination of total free thiols based on formation of complexes of Ce(III) with disulfide bonds

Albumin Retains Its Transport Function after Interaction with Cerium Dioxide Nanoparticles

The interaction of inorganic nanomaterials with biological fluids containing proteins can lead not only to the formation of a protein corona and thereby to a change in the biological activity of nanoparticles but also to a significant effect on the structural and functional properties of the biomolecules themselves. This work studied the interaction of nanoscale CeO2, the most versatile nanozyme, with human serum albumin (HSA). Fourier transform infrared spectroscopy, MALDI-TOF mass spectrometry, UV-vis spectroscopy, and fluorescence spectroscopy confirmed the formation of HSA-CeO2 nanoparticle conjugates. Changes in protein conformation, which depend on the concentration of both citrate-stabilized CeO2 nanoparticles and pristine CeO2 nanoparticles, did not affect albumin drug-binding sites and, accordingly, did not impair the HSA transport function. The results obtained shed light on the biological consequences of the CeO2 nanoparticles' entrance into the body, which should be taken into account when engineering nanobiomaterials to increase their efficiency and reduce the side effects.

Enlightening the Path to Protein Engineering: Chemoselective Turn-On Probes for High-Throughput Screening of Enzymatic Activity

Many successful stories in enzyme engineering are based on the creation of randomized diversity in large mutant libraries, containing millions to billions of enzyme variants. Methods that enabled their evaluation with high throughput are dominated by spectroscopic techniques due to their high speed and sensitivity. A large proportion of studies relies on fluorogenic substrates that mimic the chemical properties of the target or coupled enzymatic assays with an optical read-out that assesses the desired catalytic efficiency indirectly. The most reliable hits, however, are achieved by screening for conversions of the starting material to the desired product. For this purpose, functional group assays offer a general approach to achieve a fast, optical read-out. They use the chemoselectivity, differences in electronic and steric properties of various functional groups, to reduce the number of false-positive results and the analytical noise stemming from enzymatic background activities. This review summarizes the developments and use of functional group probes for chemoselective derivatizations, with a clear focus on screening for enzymatic activity in protein engineering.

Surface Properties and Environmental Transformations Controlling the Bioaccumulation and Toxicity of Cerium Oxide Nanoparticles: A Critical Review

Increasing production and utilization of cerium oxide nanoparticles (CNPs) in recent years have raised wide concerns about their toxicity. Numerous studies have been conducted to reveal the toxicity of CNPs, but the results are sometimes contradictory. In this review, the most important factors in mediating CNPs toxicity are discussed, including (1) the roles of physicochemical properties (size, morphology, agglomeration condition, surface charge, coating and surface valence state) on CNPs toxicity; (2) the phase transfer and transformation process of CNPs in various aqueous, terrestrial, and airborne environments; and (3) reductive dissolution of CNPs core and their chemical reactions with phosphate, sulfate/S^2-, and ferrous ions. The physicochemical properties play key roles in the interactions of CNPs with organisms and consequently their environmental transformations, reactivity and toxicity assessment. Also, the speciation transformations of CNPs caused by reactions with (in)organic ligands in both environmental and biological systems would further alter their fate, transport, and toxicity potential. Thus, the toxicity mechanisms are proposed based on the physical damage of direct adsorption of CNPs onto the cell membrane and chemical inhibition (including oxidative stress and interaction of CNPs with biomacromolecules). Finally, the current knowledge gaps and further research needs in identifying the toxicological risk factors of CNPs under realistic environmental conditions are highlighted, which might improve predictions about their potential environmental influences. This review aims to provide new insights into cost-effectiveness of control options and management practices to prevent environmental risks from CNPs exposure.

Redox Reactivity of Cerium Oxide Nanoparticles Induces the Formation of Disulfide Bridges in Thiol-Containing Biomolecules

The redox state of disulfide bonds is implicated in many redox control systems, such as the cysteine-cystine couple. Among proteins, ubiquitous cysteine-rich metallothioneins possess thiolate metal binding groups susceptible to metal exchange in detoxification processes. CeO2 NPs are commonly used in various industrial applications due to their redox properties. These redox properties that enable dual oxidation states (Ce(IV)/Ce(III)) to exist at their surface may act as oxidants for biomolecules. The interaction among metallothioneins, cysteine, and CeO2 NPs was investigated through various biophysical approaches to shed light on the potential effects of the Ce(4+)/Ce(3+) redox system on the thiol groups of these biomolecules. The possible reaction mechanisms include the formation of a disulfide bridge/Ce(III) complex resulting from the interaction between Ce(IV) and the thiol groups, leading to metal unloading from the MTs, depending on their metal content and cluster type. The formation of stable Ce(3+) disulfide complexes has been demonstrated via their fluorescence properties. This work provides the first evidence of thiol concentration-dependent catalytic oxidation mechanisms between pristine CeO2 NPs and thiol-containing biomolecules.

Transfer, transformation, and impacts of ceria nanomaterials in aquatic mesocosms simulating a pond ecosystem

Mesocosms are an invaluable tool for addressing the complex issue of exposure during nanoecotoxicological testing. This experimental strategy was used to take into account parameters as the interactions between the NPs and naturally occurring (in)organic colloids (heteroaggregation), or the flux between compartments of the ecosystems (aqueous phase, sediments, biota) when assessing the impacts of CeO2 NPs in aquatic ecosystems. In this study, we determine the transfer, redox transformation, and impacts of 1 mg L(-1) of bare and citrate coated CeO2-NPs toward an ecologically relevant organism (snail, Planorbarius corneus) exposed 4 weeks in a complex experimental system mimicking a pond ecosystem. Over time, CeO2-NPs tend to homo- and heteroaggregate and to accumulate on the surficial sediment. The kinetic of settling down was coating-dependent and related to the coating degradation. After 4 weeks, Ce was observed in the digestive gland of benthic organisms and associated with 65-80% of Ce(IV) reduction into Ce(III) for both bare and coated CeO2 NPs. A transitory oxidative stress was observed for bare CeO2-NPs. Coated-NPs exposed snails did not undergo any lipid peroxidation nor change in the antioxidant contents, while Ce content and reduction in the digestive gland were identical to bare CeO2-NPs. We hypothesized that the presence of citrate coating enhanced the defense capacity of the cells toward the oxidative stress induced by the CeO2 core.

A reversible competition colorimetric assay for the detection of biothiols based on ruthenium-containing complex

A novel reversible colorimetric sensor, which based on a competitive ligation of Hg(2+) by thiols, cysteine (Cys) or glutathione (GSH), and thiocyanate (SCN) on the N3 dye (bis(4,4'-dicarboxy-2,2'-bipyridine) dithiocyanato ruthenium (II)), was developed for the detection of biothiols. First, Hg(2+) ions coordinate to the sulfur atom of the dyes' SCN groups, and this interaction induces a change in color from red to yellow, owing to the formation of a complex of Hg(2+)-N3. Then, in the presence of biothiols, the red color of N3 is recovered concomitantly with the dissociation of the Hg(2+)-N3 complex, due to the extraction of Hg(2+) by biothiols. Thus the corresponding color variation in the process of the dissociation of the Hg(2+)-N3 complex can be employed for the quantitative detection of thiols using UV-vis spectroscopy. In particular, the transformation can be readily viewed with the naked eye. A good linear relationship between the change in absorbance (ΔAbs) of Hg(2+)-N3 at 461 nm and the thiol concentration was obtained in the range of 0.5-25 μM, and the detection limits are then calculated to be 57 and 52 nM for Cys and GSH, respectively. The proposed colorimetric assay displays a high selectivity for Cys over various other amino acids and GSSG (oxidized glutathione).