Polyoxometalate Binding to Human Serum Albumin: A Thermodynamic and Spectroscopic Approach

All-Inorganic Polyoxometalates Act as Superchaotropic Membrane Carriers

Polyoxometalates (POMs) are known antitumoral, antibacterial, antiviral, and anticancer agents and considered as next-generation metallodrugs. Herein, a new biological functionality in neutral physiological media, where selected mixed-metal POMs are sufficiently stable and able to affect membrane transport of impermeable, hydrophilic, and cationic peptides (heptaarginine, heptalysine, protamine, and polyarginine) is reported. The uptake is observed in both, model membranes as well as cells, and attributed to the superchaotropic properties of the polyoxoanions. In view of the structural diversity of POMs these findings pave the way toward their biomedical application in drug delivery or for cell-biological uptake studies with biological effector molecules or staining agents.

The interaction on HSA and the antibacterial activity from four polyoxometalate hybrids based on berberine

Four organic-polyoxometalate hybrids BR4[SiW12O40] (BR-SiW), BR3[PMo12O40] (BR-PMo), BR4K[EuSiW11O40]·2H2O (BR-EuSiW) and BR6Na3[EuW10O36] (BR-EuW) were fabricated by the polyoxometalates (POMs) anions and berberine cations (BR) noted for the alkaloids in traditional Chinese herbal medicine. These hybrids have been characterized and confirmed. The interaction between hybrids and human serum albumin (HSA) was investigated in a buffer solution (pH 7.4) using ultraviolet-visible light absorption and fluorescence techniques. The classical Stern-Volmer equation was used to analyze the fluorescence quenching at three temperatures (296, 303 and 310 K), and the static quenching mechanism for interaction was proposed. The Thermodynamic parameters, enthalpy, entropy change, and Gibbs free energy of hybrids interacting on HSA were calculated by Scatchard equation. The results indicated that therewas one binding site on the protein and BR-POMs all showed stronger binding force than that of raw materials. Synchronous fluorescence results showed that the binding sites of BR-POMs and HSA were not effectively affected the surrounding microenvironment. The following antibacterial experiments implied that inhibitory effect of hybrids were synergistic effect from organic active ingredient and POMs but the simple combination. All these data were prepared for further research on biology.

Exploring the Reactivity of Polyoxometalates toward Proteins: From Interactions to Mechanistic Insights

The latest advances in the study of the reactivity of metal-oxo clusters toward proteins showcase how fundamental insights obtained so far open new opportunities in biotechnology and medicine. In this Perspective, these studies are discussed through the lens of the reactivity of a family of soluble anionic metal-oxo nanoclusters known as polyoxometalates (POMs). POMs act as catalysts in a wide range of reactions with several different types of biomolecules and have promising therapeutic applications due to their antiviral, antibacterial, and antitumor activities. However, the lack of a detailed understanding of the mechanisms behind biochemically relevant reactions-particularly with complex biological systems such as proteins-still hinders further developments. Hence, in this Perspective, special attention is given to reactions of POMs with peptides and proteins showcasing a molecular-level understanding of the reaction mechanism. In doing so, we aim to highlight both existing limitations and promising directions of future research on the reactivity of metal-oxo clusters toward proteins and beyond.

Mechanism of CK2 Inhibition by a Ruthenium-Based Polyoxometalate

CK2 is a Ser/Thr protein kinase involved in many cellular processes such as gene expression, cell cycle progression, cell growth and differentiation, embryogenesis, and apoptosis. Aberrantly high CK2 activity is widely documented in cancer, but the enzyme is also involved in several other pathologies, such as diabetes, inflammation, neurodegeneration, and viral infections, including COVID-19. Over the last years, a large number of small-molecules able to inhibit the CK2 activity have been reported, mostly acting with an ATP-competitive mechanism. Polyoxometalates (POMs), are metal-oxide polyanionic clusters of various structures and dimensions, with unique chemical and physical properties. POMs were identified as nanomolar CK2 inhibitors, but their mechanism of inhibition and CK2 binding site remained elusive. Here, we present the biochemical and biophysical characterizing of the interaction of CK2α with a ruthenium-based polyoxometalate, [Ru₄(μ-OH)₂(μ-O)₄(H₂O)₄ (γ-SiW₁₀O₃₆)₂]¹⁰⁻ (Ru₄POM), a potent inhibitor of CK2. Using analytical Size-Exclusion Chromatography (SEC), Isothermal Titration Calorimetry (ITC), and SAXS we were able to unravel the mechanism of inhibition of Ru₄POM. Ru₄POM binds to the positively-charged substrate binding region of the enzyme through electrostatic interactions, triggering the dimerization of the enzyme which consequently is inactivated. Ru₄POM is the first non-peptide molecule showing a substrate-competitive mechanism of inhibition for CK2. On the basis of SAXS data, a structural model of the inactivated (CK2α)₂(Ru₄POM)₂ complex is presented.

Polyoxometalate-Based Metal-Organic Frameworks as the Solid Support to Immobilize MP-11 Enzyme for Enhancing Thermal and Recyclable Stability

The immobilization of enzymes has received much attention. Metal-organic framework (MOF) as the adsorbent for enzyme encapsulation provides an effective strategy. However, the encapsulation efficacy is not dependent solely on the specific surface area. Though leading into appropriate substrate with negative charge would enhance the encapsulation efficacy. Polyoxometalates (POMs) as the electron sponge would donate electrons without any structural change. In this study, Keggin-type phosphotungstic acid (PW₁₂) was encapsulated in Zirconium metal-organic framework (PW₁₂@UiO-67) as a heterogeneous adsorbent for the encapsulation of enzyme. Our following data proved that this composite cluster could enhance the adsorption of enzyme and the stability of MP-11 was then significantly improved after immobilization.

Stability in solution and chemoprotection by octadecavanadates(IV/V) in E. coli cultures

Two mixed-valence octadecavanadates, (NH₄)₂(Me₄N)₅[V^IV₁₂V^V₆O₄₂I]·Me₄NI·5H₂O (V₁₈I) and [{K₆(OH₂)₁₂V^IV₁₁V^V₇O₄₁(PO₄)·4H₂O}_n] (V₁₈P), were synthesized and characterized by single-crystal X-ray diffraction analysis and FTIR, Raman, ⁵¹V NMR, EPR and UV/Vis/NIR spectroscopies. The chemoprotective activity of V₁₈I and V₁₈P towards the alkylating agent diethyl sulfate was assessed in E. coli cultures. The complex V₁₈I was nontoxic in concentrations up to 5.0 mmol L^-1, while V₁₈P presented moderate toxicity in the concentration range 0.10 - 10 mmol L^-1. Conversely, a ca. 35% enhancement in culture growth as compared to cells treated only with diethyl sulfate was observed upon addition of V₁₈I (0.10 to 2.5 mmol L^-1), while the combination of diethyl sulfate with V₁₈P increased the cytotoxicity presented by diethyl sulfate alone. ⁵¹V NMR and EPR speciation studies showed that V₁₈I is stable in solution, while V₁₈P suffers partial breakage to give low nuclearity oxidometalates of vanadium(V) and (IV). According to the results, the chemoprotective effect depends strongly on the direct reactivity of the polyoxidovanadates (POV) towards the alkylating agent. The reaction of diethyl sulfate with V₁₈I apparently produces a new, rearranged POV instead of poorly-reactive breakage products, while V₁₈P shows the formation and subsequent consumption of low-nuclearity species. The correlation of this chemistry with that of other mixed-valence polyoxidovanadates, [H₆V^IV₂V^V₁₂O₃₈PO₄]^5- (V₁₄) and [V^IV₈V^V₇O₃₆Cl]^6- (V₁₅), suggests a relationship between stability in solution and chemoprotective performance.

Prefilled dual chamber devices (DCDs) - Promising high-quality and convenient drug delivery system

Prefilled dual chamber devices (DCDs) are combination products containing freeze-dried drug and diluent in two separate chambers of the device. DCDs provide high stability and convenience to patients and doctors, thus significantly improving product quality, patient compliance and market competitiveness. DCDs should also provide seal integrity, sterility and compatibility with biopharmaceuticals and avoid leachability and needle stick injuries. DCDs are promising alternatives to traditional containers or devices for biopharmaceuticals. The regulatory and medical practice to choose plastic DCDs as better alternatives over well-established glass syringes will be addressed here. The impact and major issues during processing, manufacturing, and storage of DCDs are also highlighted. Further discussion clears its business potential, composition, stability testing, and quality standard requirements to deal with market competition. It also covers major role of extractables and leachables in storage stability of the product.

Hofmeister effect in the Keggin-type polyoxotungstate series

The chaotropic character of Keggin-type polyoxotungstate anions was evaluated with respect to their ability to bind to γ-cyclodextrin (γ-CD) by varying the global charge density of the nanometer-sized polyanion.

Comparative study of binding interactions between three organometallic rhodium(III) complexes with curcuminoid ligands and human serum albumin

Organometallic rhodium(III) complexes with curcuminoid ligands attracted considerable attention in biological-related fields and the variation of curcuminoid ligands may regulate the biological activity of these organometallic rhodium(III) complexes. To deeply evaluate the biological influences of these complexes, the binding interactions between three rhodium(III) complexes with curcuminoid ligands and human serum albumin (HSA) were comparably investigated by spectroscopic and electrochemical techniques. The results suggested that the intrinsic fluorescence of HSA was quenched by three complexes through static fluorescence quenching mode. Three complexes bonded with Sudlow's site I of HSA to form ground-state compounds under the binding forces of van der Waals interactions, hydrogen bonds formation, and protonation. Finally, the native conformational structure and the thermal stability of HSA were all changed. Space steric hindrance of complexes took part in the differences of the fluorescence quenching processes, and the chemical polarity of the complexes played a vital role in the variations of the structure and biological activity of HSA. These results illustrated the molecular interactions between protein and organometallic rhodium(III) complexes with curcuminoid ligands, offering new insight about the prospective applications of analogical rhodium(III) complexes in biomedicine areas.

Structure-Activity Relationships for the Affinity of Chaotropic Polyoxometalate Anions towards Proteins

The influence of the composition of chaotropic polyoxometalate (POM) anions on their affinity to biological systems was studied by means of atomistic molecular dynamics (MD) simulations. The variations in the affinity to hen egg-white lysozyme (HEWL) were analyzed along two series of POMs whereby the charge or the size and shape of the metal cluster are modified systematically. Our simulations revealed a quadratic relationship between the charge of the POM and its affinity to HEWL as a consequence of the parabolic growth of POM⋅⋅⋅water interaction with the charge. As the charge increases, POMs become less chaotropic (more kosmotropic) increasing the number and the strength of POM-water hydrogen bonds and structuring the solvation shell around the POM. This atomistic description explains the proportionally larger desolvation energies and less protein affinity for highly charged POMs, and consequently, the preference for moderate charge densities (q/M=0.33). Also, our simulations suggest that POM⋅⋅⋅protein interactions are size-specific. The cationic pockets of HEWL protein show a preference for Keggin-like structures, which display the optimal dimensions (≈1 nm). Finally, we developed a quantitative multidimensional model for protein affinity with predictive ability (r² =0.97; q² =0.88) using two molecular descriptors that account for the charge density (charge per metal atom ratio; q/M) and the size and shape (shape weighted-volume; V_S ).

Similarities and differences in d6 low-spin ruthenium, rhodium and iridium half-sandwich complexes: synthesis, structure, cytotoxicity and interaction with biological targets

In this paper, we discussed the similarities and differences in d⁶ low-spin half-sandwich ruthenium, rhodium and iridium complexes containing 2,2′-biimidazole (H₂biim). Three new complexes, {[RuCl(H₂biim)(η⁶-p-cymene)]PF₆}₂·H₂O (1), [(η⁵-Cp)RhCl(H₂biim)]PF₆ (2), and [(η⁵-Cp)IrCl(H₂biim)]PF₆ (3), were fully characterized by CHN, X-ray diffraction analysis, UV–Vis, FTIR, and ¹H, ¹³C and ¹⁵N NMR spectroscopies. The complexes exhibit a typical pseudooctahedral piano-stool geometry, in which the aromatic arene ring (p-cymene or Cp) forms the seat, while the bidentate 2,2′-biimidazole and chloride ion form the three legs of the piano stool. Moreover, the cytotoxic activities of the compounds were examined in the LoVo, HL-60, MV-4-11, MCF-7 human cancer cell lines and BALB/3T3 normal mouse fibroblasts. Notably, the investigated complexes showed no cytotoxic effects towards the normal BALB/3T3 cell line compared to cisplatin, which has an IC₅₀ value of 2.20 µg. Importantly, 1 displayed the highest activity against HL-60 (IC₅₀ 4.35 µg). To predict a binding mode, we explored the potential interactions of the metal complexes with CT-DNA and protein using UV absorption and circular dichroism. The obtained data suggest that the complexes could interact with CT-DNA via an outside binding mode. Moreover, binding of the complexes with the GSH via UV–Vis and ESI mass spectra was determined. Comparative studies have shown that the rhodium complex (2) is the most GSH reactive, which is probably responsible for its deactivation towards LoVo and MCF-7 tumour cells. The influence of the metal ion on the biological activity of isostructural Rh(III) and Ir(III) complexes was an important goal of the presented investigation.

How Does the Redox State of Polyoxovanadates Influence the Collective Behavior in Solution? A Case Study with [I@V18O42] q- ( q = 3, 5, 7, 11, and 13)

A series of stable reduction-oxidation states of the cagelike [I@V^IV _xV^V_{18- x}O₄₂]^{5- x} polyoxovanadate (POV) with x = 8, 10, 12, 16, and 18 were studied with density functional theory and molecular dynamics to gain insight into the structural and electron distribution characteristics of these metal-oxo clusters and to analyze the charge/redox-dependent assemblage processes in water and acetonitrile (MeCN) solutions. The calculations show that the interplay between the POV redox state (molecular charge) and the solvent polarity, countercation size, and hydrophilicity (or hydrophobicity) controls the POV agglomeration phenomena, which substantially differ between aqueous and MeCN media. In MeCN, agglomeration is more pronounced for intermediate-charged POVs, whereas in water, the lowest-charged POVs and organic countercations tend to agglomerate into a microphase. Tests made on wet MeCN show diminished agglomeration with respect to pure MeCN. Simulations with alkali countercations in water show that only the highest-charged POV can form agglomerates. The herein presented theoretical investigation aims to support experimental studies of POVs in the field of functional nanomaterials and surfaces, where controlled molecular deposition from the liquid phase onto solid substrates requires knowledge about the features of these metal-oxo clusters in discrete solutions.

Transition metal substituted sandwich-type polyoxometalates with a strong metal–C (imidazole) bond as anticancer agents

The metal–carbon bond plays a pivotal role in the structural stabilities and biological activities of metal-based anticancer drugs. The strong M–C_imi bond is first introduced into sandwich-type POMs [Na_0.7M_5.3(H₂O)₂(imi)₂(Himi)(SbW₉O₃₃)₂]⁶⁻, (M = Ni^II (1), Co^II (2), imi = imidazole).

Pyridine boronic acid-polyoxometalate based porous hybrid for efficient depletion of high abundant glycoproteins in plasma

A porous hybrid, namely PW₁₂@TiO₂-Si(Et)Si/Pba, is fabricated by the modification of PW₁₂@TiO₂-Si(Et)Si with pyridine boronic acid via a solvothermal method. The covalent interactions between the boronic acid group of the hybrid and the glycosylated site of proteins provide the as-prepared hybrid with favorable adsorption performance towards glycoproteins. The adsorption behaviors of glycoproteins onto the hybrid fit well with the Langmuir model, and the adsorption capacities for glycoprotein IgG and Trf are high, up to 348.5 mg g^-1 and 262.6 mg g^-1, respectively. Thus, a protocol for the depletion of high abundant glycoproteins from human plasma is proposed. The percentage contents of Trf, IgG, haptoglobinis and IgM are reduced from 7.38%, 5.5%, 3.01% and 1.02% to 0.951%, 4.7%, 0.126% and 0.76%, respectively. 85 low abundant proteins are identified from the raw plasma after the depletion of the high abundance proteins, demonstrating the potential of PW₁₂@TiO₂-Si(Et)Si/Pba hybrid in proteomic studies.

Selective Hydrolysis of Ovalbumin Promoted by Hf(IV)-Substituted Wells-Dawson-Type Polyoxometalate

The reactivity and selectivity of Wells-Dawson type polyoxometalate (POM), K₁₆[Hf(α₂-P₂W₁₇O₆₁)₂]·19H₂O (Hf1-WD2), have been examined with respect to the hydrolysis of ovalbumin (OVA), a storage protein consisting of 385 amino acids. The exact cleavage sites have been determined by Edman degradation experiments, which indicated that Hf1-WD2 POM selectively cleaved OVA at eight peptide bonds: Phe13-Asp14, Arg85-Asp86, Asn95-Asp96, Ala139-Asp140, Ser148-Trp149, Ala361-Asp362, Asp362-His363, and Pro364-Phe365. A combination of spectroscopic methods including ³¹P NMR, Circular Dichroism (CD), and Tryptophan (Trp) fluorescence spectroscopy were employed to gain better understanding of the observed selective cleavage and the underlying hydrolytic mechanism. ³¹P NMR spectra have shown that signals corresponding to Hf1-WD2 gradually broaden upon addition of OVA and completely disappear when the POM-protein molar ratio becomes 1:1, indicating formation of a large POM/protein complex. CD demonstrated that interactions of Hf1-WD2 with OVA in the solution do not result in protein unfolding or denaturation even upon adding an excess of POM. Trp fluorescence spectroscopy measurements revealed that the interaction of Hf1-WD2 with OVA (K_q = 1.1 × 10⁵ M⁻¹) is both quantitatively and qualitatively slightly weaker than the interaction of isostructural Zr-containing Wells-Dawson POM (Zr1-WD2) with human serum albumin (HAS) (K_q = 5.1 × 10⁵ M⁻¹).

Interactions between polyoxometalates and biological systems: from drug design to artificial enzymes

Polyoxometalates have long been studied in a variety of biological applications. Interactions between the highly charged POM molecules and biological molecules frequently occur through hydrogen-bonding and electrostatic interactions. Tellurium-centred Anderson-Evans POMs show exceptional promise as crystallization agents, while acidic and metal-substituted POMs may provide interesting alternatives to enzymes in proteomics applications. While POMs also show interesting results in a number of medicinal applications, for example as anti-amyloid agents for the treatment of Alzheimer's disease and as anti-tumoral agents, their use is often impeded by their toxicity. Many recent studies have therefore focussed on POM-functionalization to reduce toxicity and increase activity by addition of biological targeting molecules.

The Chaotropic Effect as an Assembly Motif in Chemistry

Following up on scattered reports on interactions of conventional chaotropic ions (for example, I- , SCN- , ClO4- ) with macrocyclic host molecules, biomolecules, and hydrophobic neutral surfaces in aqueous solution, the chaotropic effect has recently emerged as a generic driving force for supramolecular assembly, orthogonal to the hydrophobic effect. The chaotropic effect becomes most effective for very large ions that extend beyond the classical Hofmeister scale and that can be referred to as superchaotropic ions (for example, borate clusters and polyoxometalates). In this Minireview, we present a continuous scale of water-solute interactions that includes the solvation of kosmotropic, chaotropic, and hydrophobic solutes, as well as the creation of void space (cavitation). Recent examples for the association of chaotropic anions to hydrophobic synthetic and biological binding sites, lipid bilayers, and surfaces are discussed.

Polyoxometalates: more than a phasing tool in protein crystallography

Protein crystallography is the most widely used method for determining the molecular structure of proteins and obtaining structural information on protein–ligand complexes at the atomic level. As the structure determines the functions and properties of a protein, crystallography is of immense importance for nearly all research fields related to biochemistry. However, protein crystallography suffers from some major drawbacks, whereby the unpredictability of the crystallization process represents the main bottleneck. Crystallization is still more or less a ‘trial and error’ based procedure, and therefore, very time and resource consuming. Many strategies  have been developed in the past decades to improve or enable the crystallization of proteins, whereby the use of so-called additives, which are mostly small molecules that make proteins more amenable to crystallization, is one of the most convenient and successful methods. Most of the commonly used additives are, however, restricted to particular crystallization conditions or groups of proteins. Therefore, a more universal additive addressing a wider range of proteins and being applicable to a broad spectrum of crystallization conditions would represent a significant advance in the field of protein crystallography. In recent years, polyoxometalates (POMs) emerged as a promising group of crystallization additives due to their unique structures and properties. In this regard, the tellurium-centered Anderson–Evans polyoxotungstate [TeW₆O₂₄]⁶⁻ (TEW) showed its high potential as crystallization additive. In this lecture text, the development of POMs as tools in protein crystallography are discussed with a special focus on the so far most successful cluster TEW.

Protein-Assisted Formation and Stabilization of Catalytically Active Polyoxometalate Species

The effect of the protein environment on the formation and stabilization of an elusive catalytically active polyoxometalate (POM) species, K₆ [Hf(α₂ -P₂ W₁₇ O₆₁ )] (1), is reported. In the co-crystal of hen egg-white lysozyme (HEWL) with 1, the catalytically active monomeric species is observed, originating from the dimeric 1:2 POM form, while it is intrinsically unstable under physiological pH conditions. The protein-assisted dissociation of the dimeric POM was rationalized by means of DFT calculations. The dissociation process is unfavorable in bulk water, but becomes favorable in the protein-POM complex due to the low dielectric response at the protein surface. The crystal structure shows that the monomeric form is stabilized by electrostatic and water-mediated hydrogen bonding interactions with the protein. It interacts at three distinct sites, close to the aspartate-containing hydrolysis sites, demonstrating high selectivity towards peptide bonds containing this residue.

Polyoxometalate-Coated Magnetic Nanospheres for Highly Selective Isolation of Immunoglobulin G

Polyoxometalate [{a-PW₁₁O₃₉Zr(μ-OH)(H₂O)}₂]^8- (POM1) is first prepared by sandwiching Zr^IV among 2 mono-lacunary α-Keggin polyoxometalates, and then novel magnetic nanoparticles (NPs), Fe₃O₄@polyethyleneimine (PEI)@POM1, are fabricated by coating POM1 onto the surface of magnetic Fe₃O₄@PEI NPs under electrostatic interaction. The obtained Fe₃O₄@PEI@POM1 NPs are characterized by Fourier transform infrared, zeta potential, vibrating sample magnetometer, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. Ascribed to the hydrogen-bonding and electrostatic interactions, the NPs exhibit high adsorption selectivity toward IgG, and the adsorption capacity is high up to 304 mg g^-1 under optimal adsorption conditions. By using 0.01% cetyl trimethylammonium bromide to strip the adsorbed protein species, an elution efficiency of 95% is achieved. The feasibility of Fe₃O₄@PEI@POM1 NPs in real-world sample assay has been demonstrated by the selective isolation of IgG heavy chain and light chain from human serum, as confirmed by the sodium dodecyl sulfate polyacrylamide gel electrophoresis assay.

Self-Assembly of Polyoxometalate-Peptide Hybrids in Solution: Elucidating the Contributions of Multiple Possible Driving Forces

Incorporating the building blocks of nature (e.g., peptides and DNA) into inorganic polyoxometalate (POM) clusters is a promising approach to improve the compatibilities of POMs in biological fields. To extend their biological applications, it is necessary to understand the importance of different non‐covalent interactions during self‐organization. A series of Anderson POM–peptide hybrids have been used as a simple model to demonstrate the role of different interactions in POM–peptide (biomolecules) systems. Regardless of peptide chain length, these hybrids follow similar solution behaviors, forming hollow, spherical supramolecular structures in acetonitrile/water mixed solvents. The incorporation of peptide tails introduces interesting stimuli‐responsive properties to temperature, hybrid concentration, solvent polarity and ionic strength. Unlike the typical bilayer amphiphilic vesicles, they are found to follow the blackberry‐type assemblies of hydrophilic macroions, which are regulated by electrostatic interaction and hydrogen bonding. The formation of electrostatic assemblies before the supramolecular formation is confirmed by ion‐mobility mass spectrometry (IMS‐MS).

Heterogeneous catalysis by tungsten-based heteropoly compounds

In this review, the recent works on heterogeneous catalytic applications of polyoxotungstates in liquid-phase organic reactions are reviewed.

High-affinity binding with specific peptides endows EuW10a good luminescence probe for HPV E6 detection

EuW₁₀is applied as a sensitive biological probe, which is the first fluorescence detector of HPV E6in vitro.

Comparative investigation of binding interactions between three steroidal compounds and human serum albumin: Multispectroscopic and molecular modeling techniques

Steroidal compounds have attracted great attentions in biomedical and pharmacological areas. The investigation of structural influences during protein-compound interactions helps in understanding both the biological effects and the mechanism behind bioactivities of steroidal compounds. Herein, the structural influences of three steroidal complexes were investigated based on their binding interactions with human serum albumin (HSA) by multispectroscopic methods and molecular modeling techniques. Three steroidal compounds bonded with HSA to form three HSA-compound complexes, and van der Waals force and hydrogen bond played major roles in stabilizing these complexes. Detailed binding conformation of three steroidal compounds and HSA was further investigated by molecular modeling techniques. The changes of microenvironments and conformations of HSA were significant and the biological activity of HSA was weakened in the present of three steroidal compounds. The space steric hindrance was responsible for differences in the binding interactions between HSA and three steroidal compounds. These results provided the molecular understanding of binding interactions of protein with steroidal compounds and the strategy for research of structural influences.

Comparison of molecular interactions of Ag2 Te and CdTe quantum dots with human serum albumin by spectroscopic approaches

Ag₂ Te quantum dots (QDs) have attracted great attention in biological applications due to their superior photoluminescence qualities and good biocompatibility, but their potential biotoxicity at a molecular biology level has been rarely discussed. In order to better understand the basic behavior of Ag₂ Te QDs in biological systems and compare their biotoxicity to cadmium-containing QDs, a series of spectroscopic measurements was applied to reveal the molecular interactions of Ag₂ Te QDs and CdTe QDs with human serum albumin (HSA). Ag₂ Te QDs and CdTe QDs statically quenched the intrinsic fluorescence of HSA by electrostatic interactions, but Ag₂ Te QDs exhibited weaker quenching ability and weaker binding ability compared with CdTe QDs. Electrostatic interactions were the main binding forces and Sudlow's site I was the primary binding site during these binding interactions. Furthermore, micro-environmental and conformational variations of HSA were induced by their binding interactions with two QDs. Ag₂ Te QDs caused less secondary structural and conformational change in HSA, illustrating the lower potential biotoxicity risk of Ag₂ Te QDs. Our results systematically indicated the molecular binding mechanism of Ag₂ Te QDs with HSA, which provided important information for possible toxicity risk of these cadmium-free QDs to human health.

A survey of the different roles of polyoxometalates in their interaction with amino acids, peptides and proteins

This perspective provides a comprehensive description of the different roles of POMs in their interaction with relevant biological molecules.

Co-assembly of polyoxometalates and peptides towards biological applications

The synergistic self-assembly of biomolecules with polyoxometalates (POMs) has recently been considered as an effective approach to construct nano-biomaterials with diverse structures and morphologies towards applications in drug delivery, controlled release, tissue engineering scaffolds, and biomineralization, due to the unique features of the clusters in addition to many well-known inorganic nanoparticles. This review presents an overview of recent work focusing on the noncovalent co-assembly of peptides and POMs as well as their biological applications. In the co-assemblies triggered by the interaction between the components significant advantages are observed that POMs or peptides alone do not possess; examples include chiral recognition of hybrid metal oxides, the quick hydrolysis of peptides, and enhanced inhibition of Aβ aggregation. Finally, we outline a brief perspective on possible unresolved issues and future opportunities in this field.

Multispectroscopic Investigation of the Interaction Between two Ruthenium(II) Arene Complexes of Curcumin Analogs and Human Serum Albumin

The interaction between two ruthenium(II) arene complexes of curcumin analogs and human serum albumin (HSA) was systematically investigated by multispectroscopic techniques. The fluorescence spectral results indicated that two complexes quenched the intrinsic fluorescence of HSA through static quenching mode. The quenching constants and the corresponding thermodynamic parameters at different temperatures were calculated. The binding interactions of two complexes with HSA resulted in the complex formation of complex-HSA, and the van der Waals interactions and hydrogen bond interactions played major roles in the complex stabilization. The distances between HSA and two complexes were obtained according to fluorescence resonance energy transfer theory. The site competitive replacement experiments illustrated that two complexes mainly bounded with HSA on site I. The results of synchronous fluorescence spectra, three-dimensional fluorescence spectra, FT-IR spectra, and circular dichroism spectra indicated that the secondary structure of HSA was changed at the present of two complexes. The results of mass spectrometry further validated the binding interaction and the binding number between two complexes and HSA.

Systematical investigation of in vitro molecular interaction between fluorescent carbon dots and human serum albumin

In vitro molecular interaction between fluorescent CDs and HSA was systematically investigated by multispectroscopic and electrochemical techniques.

Potential applications of polyoxometalates for the discrimination of human papillomavirus in different subtypes

Application of a europium decatungstate (EuW10) to discriminate between peptides from different subtypes of HPV capsid proteins.

In vitro interaction investigation between three Ru(ii) arene complexes and human serum albumin: structural influences

In vitro interactions between three Ru(ii) arene complexes and human serum albumin were systematically investigated by multi-spectroscopic techniques.

The Synthesis and Characterization of Aromatic Hybrid Anderson-Evans POMs and their Serum Albumin Interactions: The Shift from Polar to Hydrophobic Interactions

Four aromatic hybrid Anderson polyoxomolybdates with Fe³⁺ or Mn³⁺ as the central heteroatom have been synthesized by using a pre-functionalization protocol and characterized by using single-crystal X-ray diffraction, FTIR, ESI-MS, ¹H NMR spectroscopy, and elemental analysis. Structural analysis revealed the formation of (TBA)₃[FeMo₆O₁₈{(OCH₂)₃CNHCOC₆H₅}₂]⋅3.5 ACN (TBA-FeMo₆-bzn; TBA=tetrabutylammonium, ACN=acetonitrile, bzn=TRIS-benzoic acid alkanolamide, TRIS–R=(HOCH₂)₃C–R)), (TBA)₃[FeMo₆O₁₈{(OCH₂)₃CNHCOC₈H₇}₂]⋅2.5 ACN (TBA-FeMo₆-cin; cin=TRIS-cinnamic acid alkanolamide), (TBA)₃[MnMo₆O₁₈{(OCH₂)₃CNHCOC₆H₅}₂]⋅3.5 ACN (TBA-MnMo₆-bzn), and (TBA)₃[MnMo₆O₁₈{(OCH₂)₃CNHCOC₈H₇}₂]⋅2.5 ACN (TBA-MnMo₆-cin). To make these four compounds applicable in biological systems, an ion exchange was performed that gave the water-soluble (up to 80 mm) sodium salts Na₃[FeMo₆O₁₈{(OCH₂)₃CNHCOC₆H₅}₂] (Na-FeMo₆-bzn), Na₃[FeMo₆O₁₈{(OCH₂)₃CNHCOC₈H₇}₂] (Na-FeMo₆-cin), Na₃[MnMo₆O₁₈{(OCH₂)₃CNHCOC₆H₅}₂] (Na-MnMo₆-bzn), and Na₃[MnMo₆O₁₈{(OCH₂)₃CNHCOC₈H₇}₂] (Na-MnMo₆-cin). The hydrolytic stability of the sodium salts was examined by applying ESI-MS in the pH range of 4 to 9. Sodium dodecylsulfate–polyacrylamide gel electrophoresis (SDS-PAGE) showed that human and bovine serum albumin (HSA and BSA) remain intact in solutions that contain up to 100 equivalents of the sodium salts over more than 4 d at 20 °C. Tryptophan (Trp) fluorescence quenching was applied to study the interactions between the sodium salts and HSA and BSA at pH 5.5 and 7.4. The quenching constants were extracted by using Stern–Volmer analysis, which suggested the formation of a 1:1 POM–protein complex in all samples. It is suggested that the aromatic hybrid POM approaches subdomain IIA of HSA and exhibits hydrophobic interactions with its hydrophobic tails, whereas the Anderson core is stabilized through electrostatic interactions with polar amino acid side chains from, for example, subdomain IB.

A two-step binding process of Eu-containing polyoxometalates to bovine serum albumin

Polyoxometalates (POMs) represent a type of typical polyanionic nanoclusters that can be utilized as inorganic bioactive materials; however, the detailed interactions of them with many target biomolecules such as peptides and proteins were not well clarified due to the complexity of the binding process. In the present study, the binding-induced physiochemical phenomena of a highly charged Eu-containing polyoxometalate, K13[Eu(SiW9Mo2O39)2] (EuSiWMo), with a model protein, bovine serum albumin (BSA), was identified upon the examination of luminescence of both the components during the titration. The large emission enhancement and subsequent quenching of the EuSiWMo were found in close relation to the amount of added BSA. Being different from the known binding type of less charged POMs, a distinct two-step binding process was concluded, and the possible mechanism was proposed through the analysis on the time-resolved fluorescence spectra, isothermal titration calorimetry (ITC), transmission electron microscope (TEM), and two-dimensional correlation spectroscopy (2D COS). The present results directed a new understanding for the charge numbers and existing state of POMs affecting the interaction with proteins, which is important to exploit the biological functionalities of POMs in related systems and the development of POMs as potential inorganic drugs.

The use of polyoxometalates in protein crystallography - An attempt to widen a well-known bottleneck

Polyoxometalates (POMs) are discrete polynuclear metal-oxo anions with a fascinating variety of structures and unique chemical and physical properties. Their application in various fields is well covered in the literature, however little information about their usage in protein crystallization is available. This review summarizes the impact of the vast class of POMs on the formation of protein crystals, a well-known (frustrating) bottleneck in macromolecular crystallography, with the associated structure elucidation and a particular emphasis focused on POM's potential as a powerful crystallization additive for future research. The Protein Data Bank (PDB) was scanned for protein structures with incorporated POMs which were assigned a PDB ligand ID resulting in 30 PDB entries. These structures have been analyzed with regard to (i) the structure of POM itself in the immediate protein environment, (ii) the kind of interaction and position of the POM within the protein structure and (iii) the beneficial effects of POM on protein crystallography apparent so far.

Selective hydrolysis of oxidized insulin chain B by a Zr(IV)-substituted Wells-Dawson polyoxometalate

We report for the first time on the selective hydrolysis of a polypeptide system by a metal-substituted polyoxometalate (POM). Oxidized insulin chain B, a 30 amino acid polypeptide, was selectively cleaved by the Zr(IV)-substituted Wells-Dawson POM, K15H[Zr(α2-P2W17O61)2]·25H2O, under physiological pH and temperature conditions in aqueous solution. HPLC-ESI-MS, LC-MS/MS, MALDI-TOF and MALDI-TOF MS/MS data indicate hydrolysis at the Phe1-Val2, Gln4-His5, Leu6-Cys(SO3H)7, and Gly8-Ser9 peptide bonds. The rate of oxidized insulin chain B hydrolysis (0.45 h(-1) at pH 7.0 and 60 °C) was calculated by fitting the integration values of its HPLC-UV signal to a first-order exponential decay function. (1)H NMR measurements show significant line broadening and shifting of the polypeptide resonances upon addition of the Zr(IV)-POM, indicating that interaction between the Zr(IV)-POM and the polypeptide takes place in solution. Circular dichroism (CD) measurements clearly prove that the flexible unfolded nature of the polypeptide was retained in the presence of the Zr(IV)-POM. The thermal stability of the Zr(IV)-POM in the presence of the polypeptide chain during the hydrolytic reaction was confirmed by (31)P NMR spectroscopy. Despite the highly negative charge of the Zr(IV)-POM, the mechanism of interaction appears to be dominated by a strong metal-directed binding between the positively charged Zr(IV) center and negatively charged amino acid side chains.