The Importance of Heterolepticity in Improving the Antibacterial Activity of Bismuth(III) Thiolates

Hinokitiol potentiates antimicrobial activity of bismuth drugs: a combination therapy for overcoming antimicrobial resistance

Antimicrobial resistance (AMR) poses a significant global health threat, rendering many infections untreatable. To combat AMR, repurposing approved drugs has emerged as a cost-effective strategy. Bismuth drugs, when combined with antibiotics, have been proven to be effective against Helicobacter pylori, including antibiotic-resistant strains. However, bismuth drugs alone exhibit limited antimicrobial activity against a narrow spectrum of pathogens. Therefore, a novel approach to enhance the efficacy and broaden the antimicrobial spectrum of bismuth drugs is highly desirable. Herein, we show that a naturally occurring monoterpenoid, hinokitiol, could potentiate the antimicrobial activity of bismuth drugs. We demonstrate a strong synergy between hinokitiol and colloidal bismuth subcitrate (CBS) against various Gram-positive and Gram-negative bacterial strains, including methicillin-resistant Staphylococcus aureus (MRSA). Moreover, the combination of hinokitiol and CBS exhibits anti-biofilm activity by preventing biofilm formation and eliminating S. aureus persister cells. Importantly, the combination therapy demonstrates promising antimicrobial efficacy in murine infection models including skin wound, gastrointestinal and blood infections. Mechanistic studies reveal that hinokitiol enhances bismuth ion (Bi(iii)) accumulation and reduces intracellular iron levels. By using thermal proteome profiling combined with dynamic quantitative proteomics analysis, we demonstrate that the bismuth-hinokitiol combination propagated the bismuth binding and interfered with ribosome synthesis, the glycolysis process, impaired bacterial cell wall synthesis and pathogenesis in MRSA. Our finding highlights the potential of combinatorial hinokitiol and bismuth drugs in the fight against AMR.

Facile synthesis and antifungal evaluation of hypervalent organoantimony(III) and organobismuth(III) thioates with tridentate C,N,C-coordinating ligands

In the present work, a series of organometallic thioates bearing a 5,6,7,12-tetrahydrodibenzo[c,f][1,5]azastibocine or -azabismocine framework were synthesized through the cross-coupling reactions of the corresponding halide precursors with thiols and disulfides at room temperature. The former transformation can be achieved under additive-free conditions, and mild dithiothreitol (DTT) is the only additive in the latter. Both methods feature simple operation, a broad substrate scope, and good reaction yields. Antifungal assays showed that the synthesized organobismuth(III) thioates possess significantly higher antibiotic activity against Candida albicans than clinical fluconazole, while the inhibitory effects of Sb-sulfenylated products are low to negligible. Furthermore, the antibiofilm potential of such Bi-S bond-containing compounds was discovered as well.

Fusing Bismuth and Mercaptocarboranes: Design and Biological Evaluation of Low-Toxicity Antimicrobial Thiolato Complexes

This study proposes an innovative strategy to enhance the pharmacophore model of antimicrobial bismuth thiolato complex drugs by substituting hydrocarbon ligand structures with boron clusters, particularly icosahedral closo-dicarbadodecaborane (C2B10H12, carboranes). The hetero- and homoleptic mercaptocarborane complexes BiPh2L (1) and BiL3 (2) (L=9-S-1,2-C2B10H11) were prepared from 9-mercaptocarborane (HL) and triphenylbismuth. Comprehensive characterization using NMR, IR, MS, and XRD techniques confirmed their successful synthesis. Evaluation of antimicrobial activity in a liquid broth microdilution assay demonstrated micromolar to submicromolar minimum inhibitory concentrations (MIC) suggesting high effectiveness against S. aureus and limited efficacy against E. coli. This study highlights the potential of boron-containing bismuth complexes as promising antimicrobial agents, especially targeting Gram-positive bacteria, thus contributing to the advancement of novel therapeutic approaches.

Controlled synthesis of photoresponsive bismuthinite (Bi2S3) nanostructures mediated through a new 1D bismuth-pyrimidylthiolate coordination polymer as a molecular precursor

Bismuthinite (Bi2S3) nanostructures have garnered significant interest due to their appealing photoresponsivity which has positioned them as an attractive choice for energy conversion applications. However, to utilize their full potential, a simple and economically viable method of preparation is highly desirable. Herein, we present the synthesis and characterization including structural elucidation of a new air- and moisture-stable bismuth-pyrimidylthiolate complex. This complex serves as an efficient single-source molecular precursor for the facile preparation of phase-pure Bi2S3 nanostructures. Powder X-ray diffraction (PXRD), Raman spectroscopy, electron dispersive spectroscopy (EDS) and electron microscopy techniques were used to assess the crystal structure, phase purity, elemental composition and morphology of the as-prepared nanostructures. This study also revealed the profound effects of temperature and growth duration on the crystallinity, phase formation and morphology of nanostructures. The optical band gap of the nanostructures was tuned within the range of 1.9-2.3 eV, which is blue shifted with respect to the bulk bandgap and suitable for photovoltaic applications. Liquid junction photo-electrochemical cells fabricated from the as-prepared Bi2S3 nanostructure exhibit efficient photoresponsivity and good photo-stability, which project them as promising candidates for alternative low-cost photon absorber materials.

Antibacterial performance of heterocyclic organobismuth (III) complexes based on bidentate C,O‐coordinating ligands: Synergism of ligand identity and coordination number

A series of heterocyclic organobismuth (III) complexes based on bidentate C,O‐coordinating ligands were designed and synthesized as antimicrobials. Antibacterial assays showed that complexes of this type are more effective for Gram‐positive bacteria (Staphylococcus aureus, Staphylococcus epidermidis, and Enterococcus faecalis) than Gram‐negative ones (Escherichia coli and Pseudomonas aeruginosa). Their activities are especially relevant to the synergism of lipophilicity, geometry, and stability, which depends on both the identity of coordinating ligands and the coordination number at the bismuth center. By comparison, the hypervalent 14‐Bi‐6 species diarylbismuth nitrate (8) was found to exhibit the most potent inhibitory effect, together with a high degree of selectivity, which gives an IC50(LO2)/MIC(Staphylococcus aureus) ratio of up to 23.08. Time–kill analysis demonstrated that complex 8 is bacteriostatic at low concentrations while displaying significant bactericidal activity at high doses. The results of drug resistance experiments suggested that complex 8 can inhibit the formation of bacterial biofilm and consequently delay or prevent the development of drug resistance. Furthermore, complex 8 also showed high inhibition efficiency against several drug‐resistant Staphylococcus aureus, and the MIC values are within the range of 0.39–1.56 μM, thus indicating the lack of cross‐resistance between this organometallic compound and commonly used antibiotics.

Facile Process for the Development of Antiviral Cotton Fabrics with Nano-Embossed Copper Oxide

Metallic or metal oxide-based nanoparticles have the potential to inactivate viruses. Among various metals, copper has shown edge over others. One of the rapidly evolving areas is to combine nanoscience for production of self-sanitizing antiviral surfaces. In this study, we designed antiviral-coated fabrics to combat the spread of viruses. Copper oxide nanoparticles were sonochemically synthesized and subsequently deposited using the dip-coat process to modify the surface of fabric. The morphology and structure of uncoated and coated fabrics were examined by scanning electron microscopy, X-ray diffraction, FTIR, and elemental analysis. The findings show that small, agglomerated rugby ball structures made of copper oxide (CuO) nanoparticles (16 ± 1.6 nm, according to the Scherrer equation) develop on the surface of fabric, resulting in nano-embossing and a hydrophobic (contact angle > 140°) surface. The CuO-coated fabric yielded the maximum zone of inhibition for antibacterial activity. The virucidal activity (against human adenovirus-B) of CuO nanoparticle-fabricated fabric against adenovirus shows decreased 99.99% according to the ISO 18184 testing standard. With the dip and dry approach, any textile industry can use the simple coating procedure without having to change its textile operations. This fabric can be widely used in the face mask, clothing, bedding, and aprons, and the coating remains efficient over more than 25 washes.

Organopnictogen(III) bis(arylthiolates) containing NCN-aryl pincer ligands: from synthesis and characterization to reactivity

Salt elimination reactions between organopnictogen(III) dichlorides, RPnCl₂ [R¹ = 2,6-(Me₂NCH₂)₂C₆H₃, Pn = Sb (1), Bi (2); R² = 2,6-{MeN(CH₂CH₂)₂NCH₂}₂C₆H₃, Pn = Sb (3), Bi (4); R³ = 2,6-{O(CH₂CH₂)₂NCH₂}₂C₆H₃, Pn = Sb (5), Bi (6)] and 2 equivalents of KSC₆H₃Me₂-2,6 afforded the isolation of a series of new NCN-chelated monoorganopnictogen(III) bis(arylthiolates), RPn(SC₆H₃Me₂-2,6)₂ [R¹, Pn = Sb (7), Bi (8); R², Pn = Sb (9), Bi (10); R³, Pn = Sb (11), Bi (12)]. Compounds 7 and 8 are unstable upon exposure to a dry O₂ atmosphere and their aerobic decomposition yields the monoorganopnictogen(III) oxides, cyclo-[2,6-(Me₂NCH₂)₂C₆H₃Pn(μ-O)]₂ [Pn = Sb (13), Bi (14)] with concomitant formation of the corresponding disulfide, ArS-SAr (Ar = C₆H₃Me₂-2,6). The oxidative addition of elemental sulfur or selenium to 7 undergoes a similar reaction path and gives stable heterocyclic species cyclo-[2,6-(Me₂NCH₂)₂C₆H₃Sb(μ-E)]₂ [E = S (15), Se (16)]. The reaction of 12 with I₂ (1 : 1 molar ratio) gives the diiodide [2,6-{O(CH₂CH₂)₂NCH₂}₂C₆H₃]BiI₂ (17), along with the S-S oxidative coupling by-product, ArS-SAr. The use of an excess of iodine affords the crystallization of a 2 : 1 iodine adduct of 17 (17·0.5I₂), built through halogen bonding. All new compounds were characterized by multinuclear NMR spectroscopy and ESI-MS as well as single crystal X-ray diffraction (except compounds 9 and 10).

Medicinal chemistry and biomedical applications of bismuth-based compounds and nanoparticles

Bismuth as a relatively non-toxic and inexpensive metal with exceptional properties has numerous biomedical applications. Bismuth-based compounds are used extensively as medicines for the treatment of gastrointestinal disorders including dyspepsia, gastric ulcers and H. pylori infections. Recently, its medicinal application was further extended to potential treatments of viral infection, multidrug resistant microbial infections, cancer and also imaging, drug delivery and biosensing. In this review we have highlighted the unique chemistry and biological chemistry of bismuth-209 as a prelude to sections covering the unique antibacterial activity of bismuth including a description of research undertaken to date to elucidate key molecular mechanisms of action against H. pylori, the development of novel compounds to treat infection from microbes beyond H. pylori and the significant role bismuth compounds can play as resistance breakers. Furthermore we have provided an account of the potential therapeutic application of bismuth-213 in targeted alpha therapy as well as a summary of the biomedical applications of bismuth-based nanoparticles and composites. Ultimately this review aims to provide the state of the art, highlight the untapped biomedical potential of bismuth and encourage original contributions to this exciting and important field.

A novel bimetallic (Fe/Bi)-povidone-iodine micro-flowers composite for photocatalytic and antibacterial applications

The present work describes the synthesis of polyvinylpyrrolidone (PVP) assisted Fe-BiOI based Fe/Bi-povidone‑iodine (Fe/Bi-P-I) micro-flowers based composite and its photocatalytic and antibacterial applications. The Fe/Bi-P-I micro-flowers-based composite material was synthesized using a simple co-precipitation method. The prepared Fe/Bi-P-I micro-flowers-based composite materials were characterized using various characterization techniques and tested against photocatalytic degradation of rhodamine B (RhB) dye and antibacterial analysis. The PVP or povidone‑iodine provides more exposure of reactive sites and oxygen vacancies, which leads to a high separation rate of photoinduced charge carriers, and migration, thereby 100% of photodegradation efficiency at 1 mg/L initial concentration of RhB dye towards the synthesized P-Fe-BiOI based micro-flowers composite. Interestingly, Povidone-Iodine in Fe/Bi-P-I micro-flowers-based composite might be advantageous for antimicrobial activity against both gram-negative (E. coli), and gram-positive (S. aureus) bacterial strains. Therefore, the prepared Fe/Bi-P-I micro-flowers-based composite improved both photocatalytic degradation of organic pollutants as well as high antimicrobial activity. The method of synthesizing the Bi/Fe-P-I micro flower composite in the present study is novel, facile, and economically viable.

Impact of structural changes in heteroleptic bismuth phosphinates on their antibacterial activity in Bi-nanocellulose composites

To study and evaluate the effect of ligand choice and distribution in bismuth phosphinates on toxicity and antibacterial activity, a series of novel diphenyl mono-phosphinato bismuth complexes, [BiPh2(O(O[double bond, length as m-dash])P(H)Ph)] 1, [BiPh2(O(O[double bond, length as m-dash])PPh2)] 2, [BiPh2(O(O[double bond, length as m-dash])PMe2)] 3 and [BiPh2(O(O[double bond, length as m-dash])P(p-MeOPh)2)] 4, were synthesised, characterised and structurally authenticated by X-ray crystallography. Evaluation of their antibacterial activity towards Staphylococcus aureus (S. aureus), methicillin-resistant S. aureus (MRSA), vancomycin-resistant Enterococci (VRE), Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) showed all four mono-phosphinato bismuth complexes to be highly active. However, unlike their less soluble bis-phosphinato analogues, they displayed an increased level of toxicity towards mammalian cells (COS-7, human and murine fibroblasts), where it was shown the complexes disrupt cellular membranes leading to cytotoxicity. The mono-phosphinato bismuth complexes were used to produce antibacterial nanocellulose composites. Leaching studies showed that complex 1 had the highest levels of leaching, at 15% of the total available bismuth when the composite was soaked in water. The aqueous leachates of 1 were bacteriostatic towards MRSA and VRE at concentrations between 4.0 and 4.6 μM, while being bactericidal towards E. coli above 2.8 μM. At similar concentrations the complex showed toxicity towards human fibroblast cells, with cell viability reduced to 2% (1, 2.4 μM). The possibility to control leaching of the bismuth complexes from cellulose composites through structural changes is evidence for their potential application in antibacterial surfaces and materials.

Bismuth(III) Flavonolates: The Impact of Structural Diversity on Antibacterial Activity, Mammalian Cell Viability and Cellular Uptake

A series of homoleptic and heteroleptic bismuth(III) flavonolate complexes derived from six flavonols of varying substitution have been synthesised and structurally characterised. The complexes were evaluated for antibacterial activity towards several problematic Gram-positive (Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant Enterococcus (VRE)) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria. The cell viability of COS-7 (monkey kidney) cells treated with the bismuth flavonolates was also studied to determine the effect of the complexes on mammalian cells. The heteroleptic complexes [BiPh(L)₂ ] (in which L=flavonolate) showed good antibacterial activity towards all of the bacteria but reduced COS-7 cell viability in a concentration-dependent manner. The homoleptic complexes [Bi(L)₃ ] exhibited activity towards the Gram-positive bacteria and showed low toxicity towards the mammalian cell line. Bismuth uptake studies in VRE and COS-7 cells treated with the bismuth flavonolate complexes indicated that Bi accumulation is influenced by both the substitution of the flavonolate ligands and the degree of substitution at the bismuth centre.

Resistance of Gram-Negative Bacteria to Current Antibacterial Agents and Approaches to Resolve It

Antimicrobial resistance represents an enormous global health crisis and one of the most serious threats humans face today. Some bacterial strains have acquired resistance to nearly all antibiotics. Therefore, new antibacterial agents are crucially needed to overcome resistant bacteria. In 2017, the World Health Organization (WHO) has published a list of antibiotic-resistant priority pathogens, pathogens which present a great threat to humans and to which new antibiotics are urgently needed the list is categorized according to the urgency of need for new antibiotics as critical, high, and medium priority, in order to guide and promote research and development of new antibiotics. The majority of the WHO list is Gram-negative bacterial pathogens. Due to their distinctive structure, Gram-negative bacteria are more resistant than Gram-positive bacteria, and cause significant morbidity and mortality worldwide. Several strategies have been reported to fight and control resistant Gram-negative bacteria, like the development of antimicrobial auxiliary agents, structural modification of existing antibiotics, and research into and the study of chemical structures with new mechanisms of action and novel targets that resistant bacteria are sensitive to. Research efforts have been made to meet the urgent need for new treatments; some have succeeded to yield activity against resistant Gram-negative bacteria by deactivating the mechanism of resistance, like the action of the β-lactamase Inhibitor antibiotic adjuvants. Another promising trend was by referring to nature to develop naturally derived agents with antibacterial activity on novel targets, agents such as bacteriophages, DCAP(2-((3-(3,6-dichloro-9H-carbazol-9-yl)-2-hydroxypropyl)amino)-2(hydroxymethyl)propane1,3-diol, Odilorhabdins (ODLs), peptidic benzimidazoles, quorum sensing (QS) inhibitors, and metal-based antibacterial agents.

Is Bismuth Really the "Green" Metal? Exploring the Antimicrobial Activity and Cytotoxicity of Organobismuth Thiolate Complexes

Antimicrobial resistance is becoming an ever-increasing threat for human health. Metal complexes and, in particular, those that incorporate bismuth offer an attractive alternative to the typically used organic compounds to which bacteria are often able to develop resistance determinants. Herein we report the synthesis, characterization, and biological evaluation of a series of homo- and heteroleptic bismuth(III) thiolates incorporating either one (BiPh₂L), two (BiPhL₂), or three (BiL₃) sulfur-containing azole ligands where LH = tetrazolethiols or triazolethiols (thiones). Despite bismuth typically being considered a nontoxic heavy metal, we demonstrate that the environment surrounding the metal center has a clear influence on the safety of bismuth-containing complexes. In particular, heteroleptic thiolate complexes (BiPh₂L and BiPhL₂) display strong antibacterial activity yet are also nonselectively cytotoxic to mammalian cells. Interestingly, the homoleptic thiolate complexes (BiL₃) were shown to be completely inactive toward both bacterial and mammalian cells. Further biological analysis of the complexes revealed the first insights into the biological mode of action of these particular bismuth thiolates. Scanning electron microscopy images of methicillin-resistant Staphylococcus aureus (MRSA) cells have revealed that the cell membrane is the likely target site of action for bismuth thiolates against bacterial cells. This points toward a nonspecific mode of action that is likely to contribute to the poor selectivity's demonstrated by the bismuth thiolate complexes in vitro. Uptake studies suggest that reduced cellular uptake could explain the marked difference in activity between the homo- and heteroleptic complexes.

Bismuth(III) Thiophosphinates: Understanding How a Small Atomic Change Influences Antibacterial Activity and Mammalian Cell Viability

Diphenylphosphinothioic acid (HSP(=O)Ph2) and diphenylphosphinodithioic acid (HSP(=S)Ph2) have been used to synthesise four BiIII complexes: 1 [Bi(SP(=O)Ph2)3], 2 [BiPh(SP(=O)Ph2)2], 3 [BiPh2(SP(=O)Ph2)], and 4 [Bi(SP(=S)Ph2)3], using BiPh3 and [Bi(OtBu)3] as bismuth sources. The complexes have been characterised by NMR spectroscopy, mass spectrometry, infrared spectroscopy, powder X-ray diffraction, and singe crystal X-ray crystallography (2–4). Biological studies indicated that despite complexes 2 and 3 reducing mammalian cell viability, their antibacterial activity provides a good degree of selectivity towards both Gram positive and Gram negative bacterial strains. The minimum inhibitory concentrations for complexes 2 and 3 are in the range of 0.52–5.5µM towards the bacteria tested. Homoleptic complexes 1 and 4 were generally less active towards both bacterial and mammalian cells.

Bismuth Phosphinates in Bi-Nanocellulose Composites and their Efficacy towards Multi-Drug Resistant Bacteria

A series of poorly soluble phenyl bis-phosphinato bismuth(III) complexes [BiPh(OP(=O)R¹ R² )₂ ] (R¹ =R² =Ph; R¹ =R² =p-OMePh; R¹ =R² =m-NO₂ Ph; R¹ =Ph, R² =H; R¹ =R² =Me) have been synthesised and characterised, and shown to have effective antibacterial activity against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE). The bismuth complexes were incorporated into microfibrillated (nano-) cellulose generating a bismuth-cellulose composite as paper sheets. Antibacterial evaluation indicates that the Bi-cellulose materials have analogous or greater activity against Gram positive bacteria when compared with commercial silver based additives: silver sulfadiazine loaded at 0.43 wt % into nanocellulose produces a 10 mm zone of inhibition on the surface of agar plates containing S. aureus whereas [BiPh(OP(=O)Ph₂ )₂ ] loaded at 0.34 wt % produces an 18 mm zone of inhibition. These phenyl bis-phosphinato bismuth(III) complexes show potential to be applied in materials in healthcare facilities, to inhibit the growth of bacteria capable of causing serious disease.