Bipyridine Research Articles

The influence of Fe2+ on the self-assembly of a bipyridine containing homopolymer: From bowl-shaped nanoparticles to vesicles

Metal ion coordination has critical influence on the self-assembly behavior of amphiphilic polymers and the morphology of the obtained assemblies. Herein, an amphiphilic homopolymer with 2,2′-bipyridine (BPy) as side chain is synthesized (noted as PBPyAA), which can self-assemble into bowl-shaped nanoparticles (BNPs) in tetrahydrofuran (THF)/water. Taking advantage of the coordination interaction between BPy and metal ions, Fe2+ is chosen to regulate the self-assembly behavior and the morphology of the assemblies of PBPyAA in two pathways. (Ⅰ) The aqueous solution of Fe2+ with various concentrations is added to the THF solution of PBPyAA during self-assembly. (Ⅱ) Fe2+ is added into the THF solution of PBPyAA before self-assembly, followed by the addition of deionized water to promote the self-assembly. The results show that the pathway Ⅰ facilitates the coordination of BPy and Fe2+. With the increase of the concentration of Fe2+ aqueous solution, the coordination efficiency of BPy increases from 0.419 % to 7.789 %, leading to the transformation of BNPs to vesicles. Though the coordination efficiency of BPy also increases with the concentration of Fe2+ in pathway Ⅱ, which is still quite low of 0.274 % to 0.366 %, and the morphology of the BNPs barely changes. In addition, ethylene diamine tetraacetic acid (EDTA), a strong chelating agent, is also added to promote the competitive complexation with BPy, resulting in the dissociation of BPy and Fe2+ and the reversible transformation from vesicles to BNPs. Overall, the effect of Fe2+ coordination on the self-assembly behavior of PBPyAA in two pathways is investigated and the reversible transformation of BNPs to vesicles is also achieved.

Synthesis and luminescent properties of five-six-membered bis(metallacyclic) platinum(II) complexes bearing polypyridine alkynes

A series of five-six-membered bis(metallacyclic) Pt(II) complexes bearing a 2,2′-bipyridine (BPY) or 2,2′:6′,2"-terpyridine (TPY) ethynyl ligand were synthesized and characterized. The structures of N^C*N-coordinated Pt(II) complexes (−)-1 and (−)-5 were confirmed by single crystal X-ray diffraction, displaying a slightly distorted square-planar coordination environment around the Pt(II) centers. Compared to N^N*C-coordinated Pt(II) derivatives ((−)-2, (−)-4 and (−)-6), N^C*N-coordinated complexes ((−)-1, (−)-3 and (−)-5) demonstrate a more significant AIE property with a sharp luminescence variation in response to water content. In addition, due to the existence of the pendent BPY or TPY unit, N^C*N-coordinated Pt(II) complexes show a luminescence response to Zn2+ ions. Cytotoxicity and cell imaging of luminescent five-six-membered bis(metallacyclic) Pt(II) complexes with polypyridine alkynes have been evaluated.

Antimicrobial blue light inactivation of Pseudomonas aeruginosa: Unraveling the multifaceted impact of wavelength, growth stage, and medium composition

Pseudomonas aeruginosa, a notable pathogen frequently associated with hospital-acquired infections, displays diverse intrinsic and acquired antibiotic resistance mechanisms, posing a significant challenge in infection management. Antimicrobial blue light (aBL) has been demonstrated as a potential alternative for treating P. aeruginosa infections. In this study, we investigated the impact of blue light wavelength, bacterial growth stage, and growth medium composition on the efficacy of aBL. First, we compared the efficacy of light wavelengths 405 nm, 415 nm, and 470 nm in killing three multidrug resistant clinical strains of P. aeruginosa. The findings indicated considerably higher antibacterial efficacy for 405 nm and 415 nm wavelength compared to 470 nm. We then evaluated the impact of the bacterial growth stage on the efficacy of 405 nm light in killing P. aeruginosa using a reference strain PAO1 in exponential, transitional, or stationary phase. We found that bacteria in the exponential phase were the most susceptible to aBL, followed by the transitional phase, while those in the stationary phase exhibited the highest tolerance. Additionally, we quantified the production of reactive oxygen species (ROS) in bacteria using the 2′,7′-dichlorofluorescein diacetate (DCFH-DA) probe and flow cytometry, and observed a positive correlation between aBL efficacy and ROS production. Finally, we determined the influence of growth medium on aBL efficacy. PAO1 was cultivated in brain heart infusion (BHI), Luria-Bertani (LB) broth or Casamino acids (CAA) medium, before being irradiated with aBL at 405 nm. The CAA-grown bacteria exhibited the highest sensitivity to aBL, followed by those grown in LB broth, and the BHI-grown bacteria demonstrated the lowest sensitivity. By incorporating FeCl3, MnCl2, ZnCl2, or the iron chelator 2,2′-bipyridine (BIP) into specific media, we discovered that aBL efficacy was affected by the iron levels in culture media.

Hesperetin–4,4′-bipyridine cocrystal: Polymorphism, crystal structures, and thermodynamic relationship

The investigation of cocrystal polymorphism remains relatively limited compared to that of single-component crystals. This study focuses on the cocrystallization of hesperetin (HES), a typical flavonoid substance, with 4,4′-bipyridine (BPY), resulting in the formation of two distinct 1:1 cocrystal phases. Single crystal X-ray diffraction analysis reveals that the O—H···N hydrogen interaction serves as the hetero-synthon of the cocrystals, driving the formation of featured 1D molecular chains in both structures. The presence of rotatable C—C bonds in both HES and BPY introduces the possibility of the molecular conformational variations, contributing to differing molecular stacking arrangements between the two structures. Thermal analysis, solvent-mediated polymorphic transformation, and theoretical calculations confirm a monotropic relationship between the two cocrystals.

Hollow porous organic framework nanotube for efficient photocatalytic H2O2 generation by promoting H2O oxidation

The hydrogen peroxide (H2O2) generation by photocatalytic O2 reduction coupling H2O oxidation is a promising alternative to the traditional anthraquinone method. However, the low mass transfer and weak water oxidation are still the major responsible for the low efficiency of photocatalytic H2O2 production. Herein, we present a porous organic framework (BPTEE-POF) with hollow nanotube structure containing 2,2′-bipyridine active center of H2O oxidation, which was synthesized by template-free Sonogashira cross-coupling reaction of 5,5′-dibromo-2,2′-bipyridine (BP) and 1,1,2,2-tetrakis(4-ethynylphenyl)ethene (TEE). The 2,2′-bipyridine moieties can effectively weaken HO bond and facilitate H2O oxidation to generate O2 and H+, which can be subsequently employed as reactants for non-sacrificial H2O2 production. Meanwhile, the throughout hollow structure of BPTEE-POF is conducive to mass transfer/diffusion of substrate and product by siphoning, which promotes O2 and H2O molecules to contact with catalytic active sites and causes the quick dissociation of H2O2 from active sites, thereby boosting the overall reaction kinetic and efficiency.

Ultrathin 2D metal-organic framework nanosheet arrays to boost the overall efficiency of water splitting

Developing cost-effective and highly efficient electrocatalysts for water splitting has posed a significant challenge in recent research. This work presents a facile approach to synthesizing a 2D nickel-based metal-organic framework (TIT-1) using 2,3,5,6-tetracarboxyphenylpyrimidine (TCPP), 4,4′-bipyridine (BPY) and nickel nitrate hexahydrate under solvothermal conditions. The detailed structure and phase purity were characterized by X-ray analysis, X-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). To enhance the water electrolysis ability, the TIT-1 nanosheet (TIT-1@NS/NF) was fabricated via ultrasonic treatment of pure TIT-1 for 30 min. The TIT-1@NS/NF electrode was synthesized via an in-situ growth method and employed as an electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at ambient temperature. The results indicate that TIT-1@NS/NF achieved a current density of 10 mA cm−2 at an overpotential of 196 mV for OER and 270 mV for HER under the same conditions, so exhibiting superior performance compared to TIT-1. The electrochemical durability of TIT-1@NS/NF showed a retention rate of 87% for OER and 90% for HER. The superior electrocatalytic performance is primarily attribute to the synergistic impact of the 2D nanosheet architecture, which significantly increased the specific surface area and facilitated enhances electronic conductivity. The presence of partially deprotonated carboxylate groups and open metal sites (OMS) in TIT-1 further boosts the enhanced activity, as they exposed a multitude of unsaturated metal sites, thereby optimizing both the OER and HER process. Additionally, an asymmetric electrolytic cell comprising TIT-1@NS/NF was designed and assembled to assess its effectiveness for overall water splitting in alkaline conditions.

From Inorganic to Organic Iodine: Stabilization of I+ Enabling High-Energy Lithium-Iodine Battery.

Organic materials have been considered a class of promising cathodes for metal-ion batteries because of their sustainability in preparation and source. However, organic batteries with high energy density and application potential require high discharge voltage, multielectron transfer, and long cycling performance. Here, we report an exceptional lithium-iodine (Li//I2) battery, in which the organic iodine (BPD-HI) cathode formed by the Lewis acid-base coordination between hydroiodic acid (HI) and 4,4'-bipyridine (BPD) allows 2e- transfer via the I-/I0 and I0/I+ redox couples. The I+ stabilized by BPD exhibits a high discharge voltage plateau at ∼3.4 V. Remarkably, from inorganic to organic iodine, it realizes a 2-fold increase in the achieved capacity, up to ∼400 mA h gI-1 (Theor. 422 mA h gI-1 and 245.6 mA h g-1 based on the mass of BPD-HI), and an over 2-fold energy density, reaching 1160 W h kgI-1 (Theor. 1324 W h kgI-1). More importantly, a capacity retention rate of 85% over 850 cycles is attained for the Li//BPD-HI battery at a current density of 2 A gI-1. This facile strategy enables positively charged I+ to be electrochemically active in a rechargeable lithium battery. The new redox chemistry discovered provides new insights for developing organic batteries with high energy density.

Guest-Regulated Generation of Reactive Oxygen Species from Porphyrin-Based Multicomponent Metallacages for Selective Photocatalysis.

The development of novel materials for highly efficient and selective photocatalysis is crucial for their practical applications. Herein, we employ the host-guest chemistry of porphyrin-based metallacages to regulate the generation of reactive oxygen species and further use them for the selective photocatalytic oxidation of benzyl alcohols. Upon irradiation, the sole metallacage (6) can generate singlet oxygen (1O2) effectively via excited energy transfer, while its complex with C70 (6⊃C70) opens a pathway for electron transfer to promote the formation of superoxide anion (O2⋅-), producing both 1O2 and O2⋅-. The addition of 4,4'-bipyridine (BPY) to complex 6⊃C70 forms a more stable complex (6⊃BPY) via the coordination of the Zn-porphyrin faces of 6 and BPY, which drives fullerenes out of the cavities and restores the ability of 1O2 generation. Therefore, benzyl alcohols are oxidized into benzyl aldehydes upon irradiation in the presence of 6 or 6⊃BPY, while they are oxidized into benzoic acids when 6⊃C70 is employed as the photosensitizing agent. This study demonstrates a highly efficient strategy that utilizes the host-guest chemistry of metallacages to regulate the generation of reactive oxygen species for selective photooxidation reactions, which could promote the utilization of metallacages and their related host-guest complexes for photocatalytic applications.

Guest‐Regulated Generation of Reactive Oxygen Species from Porphyrin‐Based Multicomponent Metallacages for Selective Photocatalysis

AbstractThe development of novel materials for highly efficient and selective photocatalysis is crucial for their practical applications. Herein, we employ the host‐guest chemistry of porphyrin‐based metallacages to regulate the generation of reactive oxygen species and further use them for the selective photocatalytic oxidation of benzyl alcohols. Upon irradiation, the sole metallacage (6) can generate singlet oxygen (1O2) effectively via excited energy transfer, while its complex with C70 (6⊃C70) opens a pathway for electron transfer to promote the formation of superoxide anion (O2⋅−), producing both 1O2 and O2⋅−. The addition of 4,4′‐bipyridine (BPY) to complex 6⊃C70 forms a more stable complex (6⊃BPY) via the coordination of the Zn‐porphyrin faces of 6 and BPY, which drives fullerenes out of the cavities and restores the ability of 1O2 generation. Therefore, benzyl alcohols are oxidized into benzyl aldehydes upon irradiation in the presence of 6 or 6⊃BPY, while they are oxidized into benzoic acids when 6⊃C70 is employed as the photosensitizing agent. This study demonstrates a highly efficient strategy that utilizes the host‐guest chemistry of metallacages to regulate the generation of reactive oxygen species for selective photooxidation reactions, which could promote the utilization of metallacages and their related host‐guest complexes for photocatalytic applications.

The curious case of proton migration under pressure in the malonic acid and 4,4'-bipyridine cocrystal.

In the search for new active pharmaceutical ingredients, the precise control of the chemistry of cocrystals becomes essential. One crucial step within this chemistry is proton migration between cocrystal coformers to form a salt, usually anticipated by the empirical ΔpKa rule. Due to the effective role it plays in modifying intermolecular distances and interactions, pressure adds a new dimension to the ΔpKa rule. Still, this variable has been scarcely applied to induce proton-transfer reactions within these systems. In our study, high-pressure X-ray diffraction and Raman spectroscopy experiments, supported by DFT calculations, reveal modifications to the protonation states of the 4,4'-bipyridine (BIPY) and malonic acid (MA) cocrystal (BIPYMA) that allow the conversion of the cocrystal phase into ionic salt polymorphs. On compression, neutral BIPYMA and monoprotonated (BIPYH+MA-) species coexist up to 3.1 GPa, where a phase transition to a structure of P21/c symmetry occurs, induced by a double proton-transfer reaction forming BIPYH22+MA2-. The low-pressure C2/c phase is recovered at 2.4 GPa on decompression, leading to a 0.7 GPa hysteresis pressure range. This is one of a few studies on proton transfer in multicomponent crystals that shows how susceptible the interconversion between differently charged species is to even slight pressure changes, and how the proton transfer can be a triggering factor leading to changes in the crystal symmetry. These new data, coupled with information from previous reports on proton-transfer reactions between coformers, extend the applicability of the ΔpKa rule incorporating the pressure required to induce salt formation.

Tuning energetic properties through co-crystallisation - a high-pressure experimental and computational study of nitrotriazolone: 4,4'-bipyridine.

We report the preparation of a co-crystal formed between the energetic molecule 3-nitro-1,2,4-triazol-5-one (NTO) and 4,4'-bipyridine (BIPY), that has been structurally characterised by high-pressure single crystal and neutron powder diffraction data up to 5.93 GPa. No phase transitions or proton transfer were observed up to this pressure. At higher pressures the crystal quality degraded and the X-ray diffraction patterns showed severe twinning, with the appearance of multiple crystalline domains. Computational modelling indicates that the colour changes observed on application of pressure can be attributed to compression of the unit cell that cause heightened band dispersion and band gap narrowing that coincides with a shortening of the BIPY π⋯π stacking distance. Modelling also suggests that the application of pressure induces proton migration along an N-H⋯N intermolecular hydrogen bond. Impact-sensitivity measurements show that the co-crystal is less sensitive to initiation than NTO, whereas computational modelling suggests that the impact sensitivities of NTO and the co-crystal are broadly similar.

Nanoarchitectonics of molecular self assembled monolayers by transition metal ion intercalation for enhancement of molecular junction conductivity.

This research delves into the role of metal ions in enhancing the electronic properties of 5,5'-bis(mercaptomethyl)-2,2'-bipyridine (BPD) self-assembled monolayers (SAMs). It combines experimental techniques and numerical simulations to understand the impact of these ions on the structural, electronic, and transport properties of BPD SAMs. Key findings include the varied bonding preferences of metal ions and their significant role in modifying the electronic structure of BPD molecules, leading to enhanced electron delocalization and migration. The study highlights the potential of metal ions in advancing molecular electronics, particularly in the development of high-performance electronic and energy devices.

Coupling effects in bipyridines linked to carbon nanowires

In this work, we conducted an investigation into the electronic transport properties of four distinct devices formed by bipyridines (BPY) as the central region, linked to carbon nanowires (polyyne-type carbyne) electrodes. These four devices have two symmetrical (2,2′ and 4,4′ BPY) and two asymmetrical (2,4′ and 2,6′ BPY) configurations. We employed Density Functional Theory combined with Non-Equilibrium Green's Function (DFT-NEGF) to calculate the molecular geometry and the electronic transport properties. Our analysis, using Fowler-Nordheim (F-N) and Millikan-Lauritsen (M-L) plots, reveals that electronic transport primarily occurs through direct tunneling without any inflection points, indicating the absence of nonlinear effects such as resonance or negative differential resistance (NDR). This demonstrates the importance of the study including an analysis of Transition Voltage Spectroscopy (TVS) which shows that the presence of nitrogen atoms in the electrode-molecule contacts, specifically in the cases 2,4′ and 4,4′ BPY, significantly alters the structural and electronic characteristics of the devices. This alteration leads to a strong coupling of the junction, improved structural and electronic properties. These findings are supported by the Device Density of States (DDOS) and Frontier Molecular Orbitals (FMOs). Moreover, we observed that the electronic characteristics of all four devices remain consistent even under bias voltage (Ve).

Tunable optical properties of bipyridine dithiol molecules self-assembled on gold substrate

Using density functional theory calculations, we study the effect of intermolecular cross-linking and metal ion inclusion on the electronic and optical properties of 5,5’-bis(mercaptomethyl)-2,2’-bipyridine (BPD) molecules self-assembled on gold substrate. The contribution of the molecules to the density of states of the system near the Fermi level becomes more pronounced after cross-linking due to the delocalization of the electronic states towards the molecules. Consequently, the absorption intensity in the infrared and visible ranges of the spectrum enhances after the cross-linking. The other optical parameters of the system (such as refractive index and reflectivity) is also affected by the cross-linking induced structural changes. Optical properties of self-assembled BPD molecules can further be improved by intercalating metal ions which get encapsulated between the pyridinic units of the molecules and create new absorption sites in the visible and UV ranges of the spectrum. These findings can be useful in tuning optical properties of different materials using molecular self-assembly approach.

CdSe nanoplatelets as photocatalyst for organic photochemistry: Synthesis of amino acid derivatives by decarboxylative alkylation of aldimines

Colloidal semiconductor two dimensional CdSe nanoplatelets (NPLs) have been widely applied in photophysics, while rarely used in photocatalytic reactions. Here we show that CdSe NPLs act as photocatalyst in visible light-driven radical alkylation of aldimines, with 2,2′-bipyridine (BPY) as an additive. The photocatalytic reaction gave amino-acid derivatives in reliably good yields with various alkyl radical precursors. Furthermore, CdSe NPLs recycled from the reactions remain active and can be reused. The structural and photoelectric properties of fresh and recycled NPLs were characterized using XRD, XPS, TEM, EDS, TRPL, DRS and electrochemical analysis, revealing that BPY can bind to the surface defects of NPLs and adjust the relative oxidation and reduction potentials. As the synthesis of CdSe NPLs is low-cost, convenient and available at industrial scales, the results suggest NPLs could serve as a practical choice of photocatalyst for organic photochemistry.

Naproxen-bipyridine cocrystallization assisted by pressurized carbon dioxide

Cocrystals of S-naproxen (S-NPX) or RS-naproxen (RS-NPX) and 4,4′bipyridine (BiPY) were prepared by the Gaseous Anti Solvent (GAS) method using CO2 as antisolvent. S-NPX and BiPY cocrystals were also produced by Cocrystallization with Supercritical Solvent (CSS) using CO2 as a solvent though leading to mixtures of cocrystals and homocrystals. Hydrogen-bond networks and stoichiometries of produced cocrystals were identical whatever the mode of preparation (evaporation, grinding and CO2-assisted processes) and matched those already described in literature: S-NPX2:BiPY1 and RS-NPX2:BiPY1. The effects of the NPX:BiPY molar ratio and of the processing conditions were investigated. By GAS, an excess of BiPY in the initial processed mixture was mandatory to produce pure S-NPX2:BiPY1 cocrystals whereas pure RS-NPX2:BiPY1 cocrystals were identically produced from mixtures of 2:2 and 2:1 NPX:BiPY initial ratio. No enrichment of the product in any of the naproxen enantiomer was reached, even when mixtures of S- + RS-NPX were coprocessed with bipyridine.

Silver Nanoparticles Anchored on Single-Walled Carbon Nanotubes via a Conjugated Polymer for Enhanced Sensing Applications.

Single-walled carbon nanotubes (SWCNTs) are candidate matrices for loading metal nanoparticles (NPs) for sensor and catalytic applications owing to their high electron conductivity and mechanical strength, larger surface area, excellent chemical stability, and ease of surface modification. The performance of the formed NP/SWCNT composites is dependent on the NP size, the physical and chemical interactions between the components, and the charge transfer capabilities. Anchoring metal complexes onto the surface of SWCNTs through noncovalent interactions is a viable strategy for achieving high-level metal dispersion and high charge transfer capacities between metal NPs and SWCNTs. However, traditional metal complexes have small molecular sizes, and their noncovalent interactions with SWCNTs are limited to provide excellent sensing and catalytic capability with restricted efficiency and durability. Here, we selected poly(9,9-di-n-dodecylfluorenyl-2,7-diyl-alt-2,2'-bipyridine-5,5') (PFBPy) to increase the noncovalent interactions between silver nanoparticles (AgNPs) and SWCNTs. A silver triflate (Ag-OTf) solution was added into a PFBPy-wrapped SWCNT solution to form Ag-PFBPy complexes on the nanotube surface, after which Ag+ was photoreduced to AgNPs to form a Ag-PFBPy/SWCNT composite in the solution. In various feeding molar ratios of Ag-OTf over the BPy unit (0.4-50), the size of the formed AgNPs may be well-controlled at sub-nm levels to provide them with an energy level comparable to that of the SWCNTs. Additionally, the 2,2'-bipyridine (BPy) unit of the polymer provided a coordinating interaction with Ag+ and the formed AgNPs as well. The 5,5'-linage of BPy with the fluorene unit in PFBPy ensured a straight main chain structure to retain strong π-π interactions with nanotubes before and after Ag+ chelation. All of these factors confirmed a tight contact between the formed AgNPs and SWCNTs, promoting the charge transfer between them and enhancing the sensing capabilities with a 5-fold increase in humidity sensing sensitivity.

Cocrystal of curcumin with 4,4′-bipyridine toward improved dissolution: Design, structure analysis, and solid-state characterization

The prime active ingredient of the herb curcuma longa, curcumin (CUR) has extensive pharmacological activities and high security. However, the low solubility severely restricts its investigation and application as a drug. In this paper, a new cocrystal, CUR–BPY, assembled by CUR and BPY (4,4′-bipyridine) has been synthesized and characterized by various analytical methods. Single-crystal X-ray diffraction reveals that CUR–BPY contains a pentameric BPY–CUR–BPY–CUR–BPY supramolecular architecture connected by OH⋯N hydrogen bonds and further extended to give a 1D loop-like chain through aromatic interactions. Powder dissolution experiment reveals that CUR–BPY exhibits obvious spring phenomenon and about 7 times higher apparent solubility than that of raw curcumin. The improved dissolution performance should be ascribed to the careful selection of BPY coformer and expected OH⋯N weak hydrogen bonding in CUR-BPY cocrystal.

Mechanical Bond-Assisted Full-Spectrum Investigation of Radical Interactions.

Molecular recognition, based on noncovalent bonding interactions, plays a central role in directing supramolecular phenomena in both chemical and biological environments. The identification and investigation of weakly associated recognition motifs, however, remains a major challenge, especially when the motifs are interlinked with and obscured by other robust binding modes in complicated systems. For example, although the host-guest recognition between the radical cations of both cyclobis(paraquat-p-phenylene) (CBPQT) and 4,4'-bipyridinium (BIPY) salts has been thoroughly investigated, the question of whether other binding modes exist between these two positively charged entities is the subject of some debate because of the complexity and dynamic nature of this supramolecular system. In order to address this conundrum, we have synthesized a [2]catenane─formed by mechanical interlocking between CBPQT and another BIPY-containing ring─which enhances the weak interactions between components and reduces significantly the complexity of the system for easier characterization. By employing this [2]catenane as a model compound, we have performed a full-spectrum investigation of radical interactions and revealed unambiguously a total of three possible binding modes between CBPQT and BIPY─to be specific, a bisradical tetracationic, a trisradical tricationic, and a bisradical dicationic association─as demonstrated by various methods of characterization including UV/vis/NIR, EPR, and NMR spectroscopies, electrochemical measurements and X-ray crystallography. The two newly discovered bisradical binding modes have potential applications in the construction of self-assembled materials and in mediating supramolecular catalysis. The mechanical bond-assisted approach used in this research is broadly applicable to investigating noncovalent bonding interactions.

Iron restriction induces the small-colony variant phenotype in Staphylococcus aureus.

Pathogens such as Staphylococcus aureus must overcome host-induced selective pressures, including limited iron availability. To cope with the harsh conditions of the host environment, S. aureus can adapt its physiology in multiple ways. One of these adaptations is the fermenting small-colony variant (SCV) phenotype, which is known to be inherently tolerant to certain classes of antibiotics and heme toxicity. We hypothesized that SCVs might also behave uniquely in response to iron starvation since one of the major cellular uses of iron is the respiration machinery. In this study, a respiring strain of S. aureus and fermenting SCV strains were treated with different concentrations of the iron chelator, 2,2' dipyridyl (DIP). Our data demonstrate that a major impact of iron starvation in S. aureus is the repression of respiration and the induction of the SCV phenotype. We demonstrate that the SCV phenotype transiently induced by iron starvation mimics the aminoglycoside recalcitrance exhibited by genetic SCVs. Furthermore, prolonged growth in iron starvation promotes increased emergence of stable aminoglycoside-resistant SCVs relative to the naturally occurring subpopulation of SCVs within an S. aureus community. These findings may have relevance to physiological and evolutionary processes occurring within bacterial populations infecting iron-limited host environments.