The interaction of copper ions with Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli: an X-ray absorption near-edge structure (XANES) spectroscopy study

P K-Edge XANES Calculations of Mineral Standards: Exploring the Potential of Theoretical Methods in the Analysis of Phosphorus Speciation

Phosphorus K-edge X-ray absorption near-edge structure (XANES) spectroscopy is a technique routinely employed in the qualitative and quantitative analysis of phosphorus speciation in many scientific fields. The data analysis is, however, often performed in a qualitative manner, relying on linear combination fitting protocols or simple comparisons between the experimental data and the spectra of standards, and little quantitative structural and electronic information is thus retrieved. Herein, we report a thorough theoretical investigation of P K-edge XANES spectra of NaH₂PO₄·H₂O, AlPO₄, α-Ti(HPO₄)₂·H₂O, and FePO₄·2H₂O showing excellent agreement with the experimental data. We find that different coordination shells of phosphorus, up to a distance of 5-6 Å from the photoabsorber, contribute to distinct features in the XANES spectra. This high structural sensitivity enables P K-edge XANES spectroscopy to even distinguish between nearly isostructural crystal phases of the same compound. Additionally, we provide a rationalization of the pre-edge transitions observed in the spectra of α-Ti(HPO₄)₂·H₂O and FePO₄·2H₂O through density of states calculations. These pre-edge transitions are found to be enabled by the covalent mixing of phosphorus s and p orbitals and titanium or iron d orbitals, which happens even though neither metal ion is directly bound to phosphorus in the two systems.

Reaction of N-Acetylcysteine with Cu2+: Appearance of Intermediates with High Free Radical Scavenging Activity: Implications for Anti-/Pro-Oxidant Properties of Thiols

We studied the kinetics of the reaction of N-acetyl-l-cysteine (NAC or RSH) with cupric ions at an equimolar ratio of the reactants in aqueous acid solution (pH 1.4−2) using UV/Vis absorption and circular dichroism (CD) spectroscopies. Cu2+ showed a strong catalytic effect on the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) radical (ABTSr) consumption and autoxidation of NAC. Difference spectra revealed the formation of intermediates with absorption maxima at 233 and 302 nm (ε302/Cu > 8 × 103 M−1 cm−1) and two positive Cotton effects centered at 284 and 302 nm. These intermediates accumulate during the first, O2-independent, phase of the NAC autoxidation. The autocatalytic production of another chiral intermediate, characterized by two positive Cotton effects at 280 and 333 nm and an intense negative one at 305 nm, was observed in the second reaction phase. The intermediates are rapidly oxidized by added ABTSr; otherwise, they are stable for hours in the reaction solution, undergoing a slow pH- and O2-dependent photosensitive decay. The kinetic and spectral data are consistent with proposed structures of the intermediates as disulfide-bridged dicopper(I) complexes of types cis-/trans-CuI2(RS)2(RSSR) and CuI2(RSSR)2. The electronic transitions observed in the UV/Vis and CD spectra are tentatively attributed to Cu(I) → disulfide charge transfer with an interaction of the transition dipole moments (exciton coupling). The catalytic activity of the intermediates as potential O2 activators via Cu(II) peroxo-complexes is discussed. A mechanism for autocatalytic oxidation of Cu(I)−thiolates promoted by a growing electronically coupled −[CuI2(RSSR)]n− polymer is suggested. The obtained results are in line with other reported observations regarding copper-catalyzed autoxidation of thiols and provide new insight into these complicated, not yet fully understood systems. The proposed hypotheses point to the importance of the Cu(I)−disulfide interaction, which may have a profound impact on biological systems.

Antibacterial approaches in tissue engineering using metal ions and nanoparticles: From mechanisms to applications

Bacterial infection of implanted scaffolds may have fatal consequences and, in combination with the emergence of multidrug bacterial resistance, the development of advanced antibacterial biomaterials and constructs is of great interest. Since decades ago, metals and their ions had been used to minimize bacterial infection risk and, more recently, metal-based nanomaterials, with improved antimicrobial properties, have been advocated as a novel and tunable alternative. A comprehensive review is provided on how metal ions and ion nanoparticles have the potential to decrease or eliminate unwanted bacteria. Antibacterial mechanisms such as oxidative stress induction, ion release and disruption of biomolecules are currently well accepted. However, the exact antimicrobial mechanisms of the discussed metal compounds remain poorly understood. The combination of different metal ions and surface decorations of nanoparticles will lead to synergistic effects and improved microbial killing, and allow to mitigate potential side effects to the host. Starting with a general overview of antibacterial mechanisms, we subsequently focus on specific metal ions such as silver, zinc, copper, iron and gold, and outline their distinct modes of action. Finally, we discuss the use of these metal ions and nanoparticles in tissue engineering to prevent implant failure.

PDA/Cu Bioactive Hydrogel with "Hot Ions Effect" for Inhibition of Drug-Resistant Bacteria and Enhancement of Infectious Skin Wound Healing

Quick and effective sterilization of drug-resistant bacteria inevitably became an ever-growing global challenge. In this study, a multifunctional composite (PDA/Cu-CS) hydrogel mainly composed of polydopamine (PDA) and copper-doped calcium silicate ceramic (Cu-CS) was prepared. It was confirmed that PDA/copper (PDA/Cu) complexing in the composite hydrogel played a key role in enhancing the photothermal performance and antibacterial activity. Through a unique "hot ions effect", created by the heating of Cu ions through the photothermal effect of the composite hydrogel, the hydrogel showed high-efficiency, quick, and long-term inhibition of methicillin-resistant Staphylococcus aureus and Escherichia coli. In addition, the hydrogel possessed remarkable bioactivity to stimulate angiogenesis. The in vivo results confirmed that the "hot ions effect" of the composite hydrogel removed existing infection in the wound area efficiently and significantly promoted angiogenesis and collagen deposition during infectious skin wound healing. Our results suggested that the design of multifunctional hydrogels with "hot ions effect" may be an effective therapeutic approach for the treatment of infectious wounds.

Magnetosomes could be protective shields against metal stress in magnetotactic bacteria

Magnetotactic bacteria are aquatic microorganisms with the ability to biomineralise membrane-enclosed magnetic nanoparticles, called magnetosomes. These magnetosomes are arranged into a chain that behaves as a magnetic compass, allowing the bacteria to align in and navigate along the Earth’s magnetic field lines. According to the magneto-aerotactic hypothesis, the purpose of producing magnetosomes is to provide the bacteria with a more efficient movement within the stratified water column, in search of the optimal positions that satisfy their nutritional requirements. However, magnetosomes could have other physiological roles, as proposed in this work. Here we analyse the role of magnetosomes in the tolerance of Magnetospirillum gryphiswaldense MSR-1 to transition metals (Co, Mn, Ni, Zn, Cu). By exposing bacterial populations with and without magnetosomes to increasing concentrations of metals in the growth medium, we observe that the tolerance is significantly higher when bacteria have magnetosomes. The resistance mechanisms triggered in magnetosome-bearing bacteria under metal stress have been investigated by means of x-ray absorption near edge spectroscopy (XANES). XANES experiments were performed both on magnetosomes isolated from the bacteria and on the whole bacteria, aimed to assess whether bacteria use magnetosomes as metal storages, or whether they incorporate the excess metal in other cell compartments. Our findings reveal that the tolerance mechanisms are metal-specific: Mn, Zn and Cu are incorporated in both the magnetosomes and other cell compartments; Co is only incorporated in the magnetosomes, and Ni is incorporated in other cell compartments. In the case of Co, Zn and Mn, the metal is integrated in the magnetosome magnetite mineral core.

Silver, copper, and copper hydroxy salt decorated fumed silica hybrid composites as antibacterial agents

Decoration of matrices such as silicates, graphene, etc. is an efficient technique in order to develop multifunctional materials with enhanced properties, which are of use for microbial control. Consequently, it leads to an increased search for alternative matrices and synthesis methods for decoration. Herein, decoration of a fumed silica is proposed, with structures that consisted of silver (Ag@FS), copper hydroxy salt (CuHS@FS), and copper (Cu@FS), for antibacterial applications. With the simple combination of the metal precursor salt, the appropriate solvent, and the fumed silica, the composites were obtained by one-pot solvothermal (200 °C for 1 h), rapid (2 min) microwave assisted precipitation, and by ascorbic acid chemical reduction, respectively. Characterization by powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FE-SEM) proved the successful decoration of the fumed silica with layered copper hydroxy salt (90 width x 970 length nm) and round-like metallic Ag (210 nm) and Cu (370 nm) particles. Fourier transformed infrared (FTIR) and Raman spectroscopy evidenced the presence of SiOMetal interactions. The antibacterial activity was evaluated against the Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus, giving inhibition and bactericidal values between 3-12 mg/ mL and 12-24 mg/ mL, respectively, with a maximum ion liberation ratio of 1.4 %. The application of the fumed silica presented here, is an attractive alternative to existing matrices, in order to fabricate multifunctional materials, as it is ready-to-use and feasible for large-scale production. Moreover, the applied synthesis routes provide rapid approaches for decoration, creating composites useful for antibacterial applications.

A novel copper (II) PAmPiCaT complex (cPAmPiCaTc) as a biologically potent candidate: A contraption evidence against methicillin-resistant Staphylococcus aureus (MRSA) and a molecular docking proof

Increasing in the alarm against the resistant bacteria due to the failure of antibiotics, thereby the need of more efficiency/potent molecule to treat infections. In the present investigation, series of piperazine derivatives 5(a-l) compounds were synthesized and they were characterised by different spectral techniques such as ¹H NMR, ¹³C NMR, IR and LCMS. A novel copper complex (cPAmPiCaTc) was developed for the first time by using potent analog 5e and characterized by IR and LCMS. The cPAmPiCaTc evaluated for antibacterial activity and showed excellent antimicrobial effect (12 ± 0.08 mm, ZOI) at MIC 20 µg/mL against MRSA compared to standard antibiotics streptomycin and bacitracin at MIC 10 µg/mL. The results show promising anti-staphylococcal action against MRSA which confirmed by membrane damage, bioelectrochemistry, gene regulation (SarA and DHFR), and in silico molecular docking studies. Further, the cPAmPiCaTc also showed excellent blood compatibility and this result pave the way for interesting metallodrug therapeutics in future against MRSA infections.

Characterization of selenium speciation in selenium-enriched button mushrooms (Agaricus bisporus) and selenized yeasts (dietary supplement) using X-ray absorption near-edge structure (XANES) spectroscopy

Selenium is an essential trace element for which dietary intake is not sufficient in many parts of the world such as in Europe. Yeast and mushrooms may accumulate considerable amounts of selenium, but the chemical form in mushrooms has not been elucidated yet. Thus, we determined the selenium speciation of selenium-enriched button mushrooms in comparison to that of selenized yeast via Se K-edge XANES spectroscopy. Quantitative analysis of the XANES spectra revealed that the selenium in selenized yeast is mainly present as seleno-methionine but that in selenium-enriched button mushrooms, it is present predominantly as Se-methyl-l-selenocysteine. As this form is highly bioavailable and directly enters the selenium metabolic pool, selenium-enriched mushrooms may be a good food choice to improve selenium intake.