Nature Of Cation Research Articles

Phosphonium-ammonium-based di-cationic ionic liquids as antibacterial over the ESKAPE group

Emergence of antibioresistance is currently a major threat of public health worldwide. Hence there is an urge need of finding new antibacterial material. Herein, we report a simple and eco-friendly method to synthesize homo and heterodicationic ionic liquids based on quaternary phosphonium and ammonium salt. In order to investigate the structure activity relationship (SAR) we measured the MICs of a series of 16 derivatives with structural variations (nature of cations and counter-ions, size of linker and alkyl side chains as well as structural symmetry) over a range of Gram-positive and Gram-negative bacterial strains from the ESKAPE group. Some of the tested structures exhibit high antimicrobial activities (MIC = 0.5 mg/L) and are active over a wide range of bacteria from Gram-positive to Gram-negative. Overall, these results reveal the strong potential of di-cationic derivatives as antibacterial agents and the determination of activities from structural features gives decisive information for future synthesis of such di-cationic structures for biocidal purpose.

Mineral sources of aqua regia extractable base cations in Scottish soils interpreted from Cubist models trained with quantitative mineralogy data

The long-term potential capacity for soils to deliver essential elements to plants and the soil solution is often assessed using aqua regia (AR) extractions, and understanding specific mineral contributions to extracted element concentrations is central to the accurate interpretation of such data. The objective of this study was to assess whether the supplying quantitative soil mineralogy data to the Cubist machine learning algorithm could result in accurate prediction of AR extractable base cation concentrations (Naaqr, Mgaqr, Kaqr and Caaqr), and consequently facilitate the interpretation of meaningful mineral sources of these elements.Mineral concentrations were quantified in 191 soil samples collected by horizon from 96 sites across Scotland. These mineral concentrations together with pH and soil organic matter data were used to train Cubist models for the prediction of log(Naaqr), log(Mgaqr), log(Kaqr), and log(Caaqr), yielding concordance correlation coefficients of 0.77, 0.87, 0.78 and 0.71, respectively when assessed by cross validation. The dominant variables selected by Cubist for the conditions of the models contrasted substantially between the four elements, aligning with the independent nature of each base cation interpreted from compositional biplot analysis. Namely, plagioclase concentrations were predominantly selected by Cubist for log(Naaqr) prediction, chlorite concentrations for log(Mgaqr) prediction, dioctahedral mica concentrations for log(Kaqr) prediction, and pH for log(Caaqr) prediction. The selection of these variables is found to be geochemically appropriate for each element, demonstrating how data-driven methods can yield meaningful conclusions with respect to mineral sources of AR extractable elements. In validating the utility of combining quantitative soil mineralogy data with the Cubist machine learning algorithm on the relatively well characterised base cations, future work can progress towards using similar approaches to define mineral sources of more challenging trace elements in new detail.

Controlling the Thermoelectric Properties of Organometallic Coordination Polymers via Ligand Design

AbstractOrganometallic coordination polymers (OMCPs) are a promising class of thermoelectric materials with high electrical conductivities and thermal resistivities. The design criteria for these materials, however, remain elusive and so far material modifications have been focused primarily on the nature of the metal cation to tune the thermoelectric properties. Herein, an alternative approach is described by synthesizing new organic ligands for OMCPs, allowing modulation of the thermoelectric properties of the novel OMCP materials over several orders of magnitude, as well as controlling the polarity of the Seebeck coefficient. Extensive material purification combined with spectroscopy experiments and calculations furthermore reveal the charge‐neutral character of the polymer backbones. In the absence of counter‐cations, the OMCP backbones are composed of air‐stable, ligand‐centered radicals. The findings open up new synthetic possibilities for OMCPs by removing structural constraints and putting significant emphasis on the molecular structure of the organic ligands in OMCP materials to tune their thermoelectric properties.

Lignosulfonates as charge carriers and precursors forthe synthesis of nanoparticles

The conductometry method was used to study the polyelectrolyte behavior of lignosulfonates in an aqueous solution. Electrical conductivity was found to be a complex function of concentration (8.5 ∙ 10–5– 9.0 ∙ 10 –2 mol/dm3), molecular weight of lignosulfonates (Mw 9250, 46,300), cation nature (Na+, Cа2+), as well as association of free counterions with polyion and temperature (288–353 K). It was shown that the molar electrical conductivity in the Kohlrausch coordinates decreases with increasing polymer concentration due to a decrease in the mobility of dissociated counterions under the action of the electrostatic potential of the macroion. In lignosulfonates solutions, an increase in temperature causes an increase in the number of particles capable of charge transfer. An inflection point was found on the temperature dependences of the electrical conductivity of high molecular weight samples, indicating structural changes in macromolecules. The reasons for this behavior of high molecular weight lignosulfonates in an aqueous solution were discussed. The activation energy of electrical conductivity was calculated, the average value of which is 14.24 kJ/mol for low molecular weight samples, and 12.17 kJ/mol for high molecular weight samples up to the inflection point and 16.49 kJ/mol after. It was found that a bimodal distribution of particles, as well as the formation of a double electric layer on their surface, is characteristic of lignosulfonates obtained. Solvent replacement (nanoprecipitation) yielded lignosulfonate nanoparticles ranging in size from 40 to 90 nm. The shape of the obtained particles is determined by the nature of organic solvent and is independent of lignosulfonates molecular weight. When using ethyl alcohol as a co-solvent, spherical nanoparticles were obtained, and pyramidal lignosulfonate nanoparticles were prepared when using acetone.

Thiophene Cation Intercalation to Improve Band-Edge Integrity in Reduced-Dimensional Perovskites.

The insertion of large organic cations in metal halide perovskites with reduced-dimensional (RD) crystal structures increases crystal formation energy and regulates the growth orientation of the inorganic domains. However, the power conversion performance is curtailed by the insulating nature of the bulky cations. Now a series of RD perovskites with 2-thiophenmethylammonium (TMA) as the intercalating cation are investigated. Compared with traditional ligands, TMA demonstrates improved electron transfer in the inorganic framework. TMA modifies the near-band-edge integrity of the RD perovskite, improving hole transport. A power conversion efficiency of 19 % is achieved, the highest to date for TMA-based RD perovskite photovoltaics; these TMA devices provide a 12 % relative increase in PCE compared to control RD perovskite devices that use PEA as the intercalating ligand, a result of the improved charge transfer from the inorganic layer to the organic ligands.

Thiophene Cation Intercalation to Improve Band‐Edge Integrity in Reduced‐Dimensional Perovskites

AbstractThe insertion of large organic cations in metal halide perovskites with reduced‐dimensional (RD) crystal structures increases crystal formation energy and regulates the growth orientation of the inorganic domains. However, the power conversion performance is curtailed by the insulating nature of the bulky cations. Now a series of RD perovskites with 2‐thiophenmethylammonium (TMA) as the intercalating cation are investigated. Compared with traditional ligands, TMA demonstrates improved electron transfer in the inorganic framework. TMA modifies the near‐band‐edge integrity of the RD perovskite, improving hole transport. A power conversion efficiency of 19 % is achieved, the highest to date for TMA‐based RD perovskite photovoltaics; these TMA devices provide a 12 % relative increase in PCE compared to control RD perovskite devices that use PEA as the intercalating ligand, a result of the improved charge transfer from the inorganic layer to the organic ligands.

Efficient and selective adsorption and separation of methylene blue (MB) from mixture of dyes in aqueous environment employing a Cu(II) based metal organic framework

In view of the increasing demand of the better adsorbents for separation of organic aromatic pollutants from waste water, we have made an attempt to design a stable polymeric material for the purpose. In this report, a copper based metal organic framework (MOF), [Cu2(Hbtc)2(H2O)2(µ2-H2O)]H2O (Cu-btc-1), where H3btc = benzene-1,2,4-tricarboxylic acid is synthesized employing one pot solvothermal method. The crystalline material, Cu-btc-1 is characterized by single crystal X-ray, XRPD, TGA and various spectroscopic techniques. X-ray data confirm that Cu(II) is present in square pyramidal environment. Topological features reveal the hxl topology of the MOF. The present MOF (Cu-btc-1) is water stable and recyclable and therefore has been employed in adsorption and separation of methylene blue with excellent efficiency from the mixture of three organic dyes, methylene blue (MB), methyl orange (MO) and rhodamine (Rh-B) in aqueous phase. MB was observed to show highest adsorption of nearly 98% at neutral pH and optimum temperature (25 °C). At equilibrium, the removal efficiency of Cu-btc-1 towards MB from the mixture of dyes was found to be 98.67%. The efficiency and highest adsorption of MB could be attributed to the cationic nature of the dye and nucleophilic aromatic moieties of carboxylates of Cu-btc-1 framework where strong electrostatic interactions take place for adoption of the MB+ molecules. Not only the cationic nature but also the linearity of the MB helps enhance its adsorption by the adsorbent by easily approaching to the sites available on MOF. H-bonding and π–π interactions are also responsible for the adsorption of the dye molecules here. Thus, mechanism of adsorption is the result of interplay of the electrostatic attraction/repulsion, π–π interactions, H-bonding and weak Van der Waals interactions. The present MOF thus represents an excellent class of adsorbent material and establishes a fine tuning between the structure-efficiency relationships for separation of the aromatic organic dyes in aqueous medium for future endeavours.

Spatial Charge Separation as the Origin of Anomalous Stark Effect in Fluorous 2D Hybrid Perovskites.

2D hybrid perovskites (2DP) are versatile materials, whose electronic and optical properties can be tuned through the nature of the organic cations (even when those are seemingly electronically inert). Here, it is demonstrated that fluorination of the organic ligands yields glassy 2DP materials featuring long‐lived correlated electron–hole pairs. Such states have a marked charge‐transfer character, as revealed by the persistent Stark effect in the form of a second derivative in electroabsorption. Modeling shows that electrostatic effects associated with fluorination, combined with the steric hindrance due to the bulky side groups, drive the formation of spatially dislocated charge pairs with reduced recombination rates. This work enriches and broadens the current knowledge of the photophysics of 2DP, which will hopefully guide synthesis efforts toward novel materials with improved functionalities.

Determination of Electronic Recombination Free Energy in Zeolites: Effects of the Charge Balancing Cation and Confinement.

The adsorption of DPH in M6.6 ZSM-5 (M=Na+ , K+ , Rb+ , Cs+ ), RbFER and RbMOR channel zeolites takes place without chemical or structural modification. After photoexcitation of these systems, a radical cation-electron pair is observed and has a sufficiently long lifetime to be studied by diffuse reflectance UV-visible spectroscopy. The study of the recombination of this radical cation-electron pair was carried out at different temperatures and allowed the determination of the activation energy as a function of the nature of the charge-balancing cation but also of the confinement effect. It appears that the activation energy decreases progressively from Na+ to Cs+ but also when the confinement decreases. To go further, the free enthalpies have been calculated from the Marcus theory demonstrating experimentally that these systems are located in the inverted Marcus region.

Thermal performance analysis of sugarcane bagasse pretreated by ionic liquids

This work investigated the pretreatment effect of four ionic liquids (ILs) on sugarcane bagasse (SCB) through reactivity, kinetic, and thermodynamic analysis. The ILs used in this study were 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]), 1-butyl-3-methylimidazolium methylsulfate ([Bmim][MeSO4]), Tris (2-hydroxyethyl) methylammonium methylsulfate ([MTEOA][MeSO4]), and trihexyltetradecylphosphonium chloride ([P66614] [Cl]). Pretreatment was carried out at 150 °C and 30 min, followed by thermal analysis of samples in a thermogravimetric analyzer (TGA). The activity parameters were obtained using TGA data. [P66614] [Cl] was completely absorbed in SCB, which strongly influenced the thermochemical behavior of [P66614] [Cl] treated sample. Results revealed that IL pretreatment greatly reduced ash content and increased the higher heating value (HHV) of SCB. Chemical composition analysis showed delignification of SCB by [Bmim][Cl], [Bmim][MeSO4] and [MTEOA][MeSO4]. However, [P66614] [Cl] increased lignin content indicating thermal stability. The obtained values of activation energy (Ea) for [Bmim][Cl], [Bmim][MeSO4], and [MTEOA][MeSO4] were much lower than that for untreated SCB, suggesting destruction of the lignocellulosic structure. Higher entropy change (ΔS) values after IL treatment implied higher disorder due to the breakage of SCB structure. The study demonstrated that the nature of cations and anions strongly influences the pretreatment potential of ILs for biomass undergoing thermochemical conversion processes.

Highlighting the impact of chitosan on the development of gastroretentive drug delivery systems

The development of gastroretentive systems have been growing lately due to the high demand for carriers that increase drug bioavailability and therapeutic effectiveness after oral administration. Most of systems reported up to now are based on chitosan (CS) due to its peculiar properties, such as cationic nature, biodegradability, biocompatibility and important mucoadhesiveness, which make CS a promising biopolymer to design effective gastroretentive systems. In light of this, we reported in this review the CS versatility to fabricate different types of nano- and microstructured gastroretentive systems. For a better understanding of the gastric retention mechanisms, we highlighted expandable, density-based, magnetic, mucoadhesive and superporous systems. The biological and chemical properties of CS, anatomophysiological aspects related to gastrointestinal tract (GIT) and some applications of these systems are also described here. Overall, this review may assist researchers to explore new strategies to design safe and efficient gastroretentive systems in order to popularize them in the treatment of diseases and clinical practices.

Solution Chemistry of Alkaline Formaldehyde-Containing Electroless Copper Plating Systems and Kinetics of Electroless Copper Deposition

Electroless copper plating process using solutions containing formaldehyde as reducing agent is known from the middle of this century and are widespread in the practice up to now. However, the investigation of this system remains actual because of its complexity, e. g. alkaline medium, hydrated form of formaldehyde (methanediol), Cu(II) complex compounds with different ligands, additives which improve the properties of the coatings obtained and/or protect from the reduction of copper(II) in the solution bulk. Moreover, various equilibria are possible including deprotonation of methanediol, Cu(II) complex formation, additional interactions between components of the solution.The aims and tasksof this work were to investigate or define more precisely equilibria in conventional alkaline solutions of electroless copper deposition as well as influence of the nature of Cu(II) ligands on the copper deposition process. This research report deals with the results obtained by means of dc-polarography, vis-spectrophotometry, voltammetry, potentiometry, pH-metry, 1H and 13C NMR spectroscopy, scanning electron microscopy, X-ray diffractometry and gravimetry.The composition, stability and the values of the diffusion coefficient of Cu(II) complex compounds with ligands (EDTA, DTPA, pyridine-2,6-dicarboxylic acid and 4-hydroxypyridine-2,6-dicarboxylic acid, Quadrol, L(+)-, D(–)- and DL(-/+)-tartrate, glycerol, saccharose and OH- ions) which are used or usable in alkaline electroless copper deposition solutions were established. Formation of mixed complex compounds between Cu(II) complexonates andK4Fe(CN)6, as well as between Cu(II) tartrate complexes and methanediol was investigated. The interaction of methanediol with L(+)-tartrate alongside with the influence of the ionic strength and cation nature on the deprotonation of methanediol in alkaline solutions were studied.The kinetic data on electroless copper deposition from solutions containing above-mentioned ligands are presented and the influence of the ligand nature on the process of electroless copper deposition is discussed.

Novel 1:1 stoichiometric rare-earth HoX (X $$=$$ Pd, Ag and Cd) intermetallic compounds: DFT-based study

A systematic investigation on structural, electronic, elastic, mechanical and optical properties of novel 1:1 stoichiometric rare-earth $$\mathrm{HoX}\ (\mathrm{X}=\text {Pd, Ag and Cd})$$ intermetallic compounds has been made via ab-initio density functional theory-based linearized augmented plane wave method as coded in wien2k. An outline of local density approximation and generalized gradient approximation have been employed. Structural optimization established the stable CsCl-type cubic structure of $$\mathrm{HoX}\ (\mathrm{X}=\mathrm{Pd, Ag and Cd})$$ compounds. The determined crystal structure stability, compressibility and fracture strength of compounds are enhanced with X in the order $$\mathrm{HoPd}>\mathrm{HoAg}>\mathrm{HoCd}$$ . The interlacing electron dispersion curves at Fermi-level in band structure and density of states substantiate the metallic nature of compounds. The splitting gap between the lower and upper valence bands monotonously becomes narrower with the substitution of heavier core-element $$(\hbox {Pd}\rightarrow \hbox {Ag}\rightarrow \hbox {Cd})$$ . The mechanical constants i.e., bulk modulus (B), Young’s modulus (E), shear modulus ( $${G}_{\mathrm{H}}$$ ), Pugh’s ratio $$(B/G_{\mathrm{H}})$$ , Poisson’s ratio (v) and anisotropic factor (A) have been calculated to corroborate the mechanical properties of compounds. The cationic nature of Ho-atoms and anionic nature of X-atoms has been evaluated through the effective charge $$(\textit{Q}^{*}$$ ) computations. The observed peaks in the low energy region of optical conductivity spectra attribute the intra-band, while the high energy structures are associated with inter-band transitions in $$\mathrm{HoX}\ (\mathrm{X}=\text {Pd, Ag and Cd})$$ compounds. The bond order calculations demonstrate the highest strength of HoCd compound among the herein studied compounds.

Structure and biological evaluation of pyridine-2-carboxamidine copper(II) complex resulting from N′-(4-nitrophenylsulfonyloxy)2-pyridine-carboxamidoxime

The interaction of Cu(NO3)2·3H2O with the sulfonyl o-pyridine carboxamidoxime N′-(4-nitrophenylsulfonyloxy)picolinimidamide (L) resulted in the mononuclear complex [Cu(L1)2](L2)2 (1), where L1 = pyridine-2-carboxamidine ligand and (L2)− = 4-nitrobenzenesulfonate anion derived from the homolytic cleavage of the NO bond of L. The complex was characterized by diverse techniques including single-crystal X-ray crystallography. From the antimicrobial tests performed, complex 1 seems to be active against gram-negative bacterial strains. The complex binds tightly and reversibly to serum albumins and tightly to calf-thymus DNA via an intercalative mode and also via electrostatic interactions (as expected due to its cationic nature). Additionally, it interacts with (pBluescriptSK(+)) plasmid DNA in a concentration-dependent manner. The results from the present in silico molecular modeling simulations provide useful complementary insights for the elucidation of the mechanism of action of the studied complex at a molecular level. Molecular modeling calculations provide a molecular basis for the understanding of both the impairment of DNA by its binding with the studied complex and the ability of this compound to act as an antibacterial agent, most probably by its activity against DNA-gyrase, as well as for transportation through serum albumins and possible interaction with other protein targets involved in various diseases.

Electrodeposition of Rh/Mg/Al hydroxides with different Mg-contents on metallic foams as catalyst precursors

This work investigated the electrodeposition of Rh/Mg/Al mixed hydroxides with different Mg-contents on open-cell foams through the electro-base generation method using nitrate electrolytes. The influence of Mg2+ on both the electrodeposition process and properties of the coating (after electrodeposition, calcination, and catalytic partial oxidation (CPO) of CH4 tests) was studied. The nature of cations being precipitated (Mg2+ or Al3+) influenced significantly the production of OH– through reduction of nitrate and water, which in turn determined the quality of the coating in terms of composition and adhesion. In reference samples, an absence of either Mg2+ (Rh5Al95) or Al3+ (Rh5Mg95) declined the coating quality, namely, more cracks developed due to the prominent reduction of H2O (in case of Rh5Al95) or reduction of Rh3+ to Rh0 occurred (Rh5Mg95 ). On the other hand, the presence of both Mg2+ and Al3+ in Rh/Mg/Al hydrotalcite-type (HT) samples improved significantly the coating loading and its adhesion, even after thermal treatment at 900 °C, as well as the dispersion of Rh in the reduced catalyst. Moreover, increasing the amount of Mg2+ to a given Mg/Al ratio at which a pure Rh/Mg/Al HT precursor was formed (e.g. Rh5Mg70Al25) resulted in significant increment of Rh dispersion compared to those with lower Mg content (i.e. Rh5Mg50Al45). Such modifications on the properties of the coating (loading, adhesion, and Rh dispersion) subsequently influenced the performance in the CPO of CH4. Finally, temperature profiles along the catalytic bed were reported in correlation with CH4 conversion and syngas selectivity.

Effect of cation nature on vacuum tribo-degradation and lubrication performances of two tetrafluoroborate ionic liquids

Vacuum lubrication and tribo-degradation performance investigations of two imidazolium tetrafluoroborate ionic liquids (ILs, LAB103 and LB104), were systematically conducted by the VFBT-4000 vacuum four-ball tribometer equipped with a quadrupole mass spectrometer. They both have quite wide liquid range with high thermostability and good fluidity at low temperature. Results of vacuum tribological tests show that LAB103 present better lubricity and lower corrosivity as compared with that of LB104, due to its strong adsorption layers and robust tribofilms on worn surfaces. Tribo-degradation test results exhibit that the decomposition of ILs is mainly caused by frictional stimulus. The decomposition products partially diffuse to vacuum chamber, being captured by mass spectrometer detector and others participate in the tribochemical reactions.

Compressibility of hingganite-(Y): high-pressure single crystal X-ray diffraction study

Behaviour of hingganite-(Y), Y2□Be2Si2O8(OH)2, on compression to 47 GPa has been studied by synchrotron-based in situ high-pressure single-crystal X-ray diffraction at room temperature in a diamond anvil cell. In the studied pressure range no obvious phase transitions have been observed. The compression of hingganite-(Y) crystal structure is anisotropic, with b axis showing the maximal compressibility. A fit of the experimental pressure–volume data by the Birch-Murnaghan third-order equation of state yielded the bulk modulus of 131(2) GPa and its pressure first derivative of 3.5(2). The difference between high-pressure behaviour of hingganite-(Y) and structurally related datolite is governed by the different chemical nature of interlayer cations.

Design and synthesis of a novel peptide for selective detection of cancer cells.

Using a minimalist approach, an 11-residue peptide (Peptide 1) tagged with rhodamine fluorophore was designed and synthesized for selective detection of cancer cells. Peptide 1 contains RGD and NGR motifs to bind, respectively, integrins and aminopeptidase CD13, which are over expressed in cancer cells. Surface tension measurements revealed that peptide 1 possess surface-active property owing to the overall hydrophobicity and cationic nature of the peptide. Peptide 1 displays cancer cell-selective binding at ≤5.0µM concentrations, while peptide 2 (randomized sequence of 1) shows non-selective binding to normal and cancer cells. Fluorescence microscopy and FACS analysis demonstrated the intracellular localization of peptide 1 in three different cancer cell lines, confirming the role of RGD and NGR motifs. Cytotoxicity assay exhibited the viability of normal and cancer cells up to 100µM concentrations of peptide 1. Steady-state fluorescence measurements disclosed the preferential interactions of the peptide 1 with anionic POPC/POPG bilayers rather than with zwitterionic POPC lipid bilayers. Circular dichroism studies showed minimal changes in the secondary structure of peptide 1 upon binding with the anionic lipid bilayers. Peptide 1 is largely unordered, non-toxic, and useful for identification of cancer cells. Peptide 1 provides a template for designing drug-loaded peptides for targeted delivery into cancer cells.

Mechanistic insights into the sol-gel synthesis of complex (quaternary) Co–Mn–Zn-spinel ferrites: An annealing dependent study

Synthesis conditions, cation distribution at tetrahedral and octahedral sites and their stability play very important roles in controlling phase-purity and physicochemical properties of spinel ferrite compounds. In this work, an attempt is made to understand how the progress of phase-formation and the structural and magnetic properties are influenced by the annealing temperature and nature of cations used in the synthesis of quaternary spinel ferrite ceramics. A series of Co0.8-xMn0.2ZnxFe2O4 (x = 0, 0.2, 0.4, 0.6 and 0.8) (CMZF) spinel ferrite samples were synthesized by citric acid assisted sol-gel technique followed by annealing at 400, 600 and 800 °C. To compare the progress of phase formation/stability of the cations, simple (binary) spinel ferrite reference samples, such as CoFe2O4, MnFe2O4 and ZnFe2O4, were also synthesized by the same technique and are calcined at the same conditions. In case of CoFe2O4, all the samples have single phase spinel structure, but a transformation from an inverse spinel-type to nearly normal spinel ferrite-type cation distribution is observed with increasing annealing temperature. The as-prepared MnFe2O4 sample and that annealed at 400 °C show formation of single phase spinel ferrite, while those annealed at 600 and 800 °C decomposes completely into Mn2O3, α-Fe2O3 and amorphous-FeO phases. In contrast, for ZnFe2O4 samples, a transformation from the ZnO and α-Fe2O3 phases (present in the as-prepared and up to 600 °C annealed samples) to pure ZnFe2O4–phase occurs only at/above 800 °C. Interestingly, our results show that the progress of the phase formation behavior of the CMZF samples can be predominantly considered as a combination of the behavior and energetics typically exhibited by the individual (simple) ferrite systems. Overall, our work provides the necessary impetus for achieving the phase purity and required physicochemical properties of complex ferrite systems by choosing the cations suitably, based on their nature and annealing behavior.

Human host-defense peptide LL-37 targets stealth siderophores

A growing number of evidence shows that human-associated microbiota is an important contributor in health and disease. However, much of the complexity of host-microbiota interaction remains to be elucidated both at cellular and molecular levels. Siderophores are chemically diverse, ferric-specific chelators synthesized and secreted by microbes to secure their iron acquisition. The host defense peptide LL-37 is ubiquitously produced at epithelial surfaces modulating microbial communities and suppressing pathogenic strains. The present work demonstrates that LL-37 binds tightly siderocalin-resistant stealth siderophores which are important contributors to the virulence of several pathogens. As indicated by circular dichroism spectroscopic experiments, addition of aerobactin and rhizoferrin increases the membrane active α-helical conformation of the partially folded peptide. The cationic nature of LL-37 (+6 net charge at pH 7.4) and the multiple carboxylate groups present in siderophores refer to the dominant contribution of electrostatic interactions in the stabilization of peptide-chelator adducts. It is proposed that aside siderocalin proteins, LL-37 may be a complementary, less specific component of the siderophore scavenging repertoire of the innate immune system.