Nature Of Cation Research Articles

Antimicrobial activity of different substituted meso-porphyrin derivatives

Abstract The increasing resistance against classical antibiotic treatment forces the researchers to develop novel non-toxic antimicrobial agents. The aim of this study was to determine the antimicrobial properties of seven different porphyrins having distinctive hydrophobicity/hydrophilicity: P1 meso-tetra(4-methoxy-phenyl)porphyrin, P2 Zn(II)-meso-5,10,15,20-tetrapyridylporphyrin, P3 meso-tetra(p-tolyl)porphyrin, P4 5,10,15,20-tetraphenylporphyrin; P5 (5,10,15,20-tetraphenylporphinato) dichlorophosphorus(V) chloride, P6 5,10,15,20-tetrakis-(N-methyl-4-pyridyl) porphyrin-Zn(II) tetrachloride, P7 Zn(II)-5,10,15,20-meso-tetrakis-(4-aminophenyl)porphyrin. The meso-porphyrin derivatives were screened for their antimicrobial activity against six reference strains: Streptococcus pyogenes ATCC 19615, Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, Klebsiella pneumoniae ATCC 700603, Pseudomonas aeruginosa ATCC27853 and Candida albicans ATCC 10231. The antimicrobial activity of these samples was evaluated by the agar disk diffusion method and dilution method, with the determination of the minimum inhibitory concentration (MIC), the minimum bactericidal concentration (MBC) and the minimum fungicidal concentration (MFC). The most significant result is provided by the water-soluble P5 manifesting an obvious antimicrobial activity against Streptococcus pyogenes. On the other hand, P6 is a moderately active derivative against Streptococcus pyogenes and Escherichia coli and P7 presents moderate activity against Streptococcus pyogenes and Staphylococcus aureus. All the tested porphyrin bases, presenting hydrophobic character, have no antimicrobial activity under the investigated conditions. The common characteristics of the porphyrins that act as promising antimicrobial agents in the non-irradiated methods are: the cationic nature, the increased hydrophilicity and the presence of both amino functional groups grafted on the porphyrin ring and the coordination with Zn or phosphorus in the inner core.

Sustainable Oxidation of Cyclohexane and Toluene in the Presence of Affordable Catalysts: Impact of the Tandem of Promoter/Oxidant on Process Efficiency.

The oxygenation of cyclohexane and toluene by O2 and H2O2 catalyzed by VO(acac)2 and Co(acac)2 was studied at 40–100 °C and 1–10 atm. Upon such conditions, the process can be remarkably (30× times) enhanced by the minute (6–15 mM) additives of oxalic acid (OxalH) or N-hydroxyphthalimide (NHPI). The revealed effect of OxalH on H2O2-piloted oxidation is closely associated with the nature of the catalyst cation and boosted by VO(acac)2. Whereas the effectiveness of Co(acac)2-based systems was curbed by the addition of OxalH and remained much below the one displayed with the previous system. The observed conspicuous difference in activity was attributed to the substantially higher solubility of in situ formed VO(IV)oxalate compared to that of Co(II)oxalate. The exploration of H2O2 for the NHPI-promoted process leads to the decisively lower (5–7 times) yield in comparison to the O2-driven reaction. Similarly, for the O2-operated protocol, the yield cannot be improved by addition of OxalH either to VO(acac)2 + NHPI or to Co(acac)2 + NHPI mixture. By contrast, the combination of NHPI with VO(acac)2 or Co(acac)2 and particularly with the above two mixtures in O2-piloted oxidation enhances the yield of the aimed products 3–6 times regardless of the substrate used. The revealed significant synergetic effect of the cobalt + vanadyl bicomponent catalyst was due to the participation of each of its moiety in the different stages of the process mechanism. Only benzyl alcohol and benzaldehyde were identified in VO(acac)2- or Co(acac)2-catalyzed toluene oxidation, while cyclohexane oxidation yields cyclohexylhydroperoxide in line with cyclohexanol and cyclohexanone. The putative mechanism of investigated processes is highlighted and discussed.

Continuous capture of recombinant antibodies by ZnCl 2 precipitation without polyethylene glycol.

The capture of recombinant antibodies from cell culture broth is the first critical step of downstream processing. We were able to develop a precipitation‐based method for the capture and purification of monoclonal antibodies based on divalent cations, namely ZnCl2. Traditional precipitation processes have to deal with high dilution factors especially for resolubilization and higher viscosity due to the use of PEG as precipitation or co‐precipitation agent. By the use of the crosslinking nature of divalent cations without the use of PEG, we kept viscosity from the supernatant and resolubilization dilution factors very low. This is especially beneficial for the solid–liquid separation for the harvest and wash of the precipitate in continuous mode. For this harvest and wash, we used tangential flow filtration that benefits a lot from low viscosity solutions, which minimizes the membrane fouling. With this precipitation based on ZnCl2, we were able to implement a very lean and efficient process. We demonstrated precipitation studies with three different antibodies, Adalimumab, Trastuzumab, and Denosumab, and a continuous capture case study using tangential flow filtration for precipitate recovery. In this study, we achieved yields of 70%.

Using conformational landscape to explain the non-classical nature of cyclobutyl and cyclopropylcarbinyl cations

Carbocations, organic chemistry corner stones, play a major role in carbonic skeletal rearrangements. A turning point in their study was the introduction of non-classical Carbocations, which establish a rapid equilibrium among their different forms to distribute their positive charge. Here a new stereospecific mechanistic pathway for cyclopropylcarbinyl and cyclobutyl cations is proposed. Carbon scrambling is plotted into a conformational landscape model, usually used for true conformers. A deeper insight into these cationic interconversions provides the underpinning principals that govern their dynamics. Future studies are expected to reveal the role of cyclopropyl structural motifs in the vast arrays of natural products and their dynamics.

Effects of Conventional Surfactants on the Activity of Designed Antimicrobial Peptide.

In this article, the interaction between a designed antimicrobial peptide (AMP) G(IIKK)3I-NH2 (G3) and four typical conventional surfactants (sodium dodecyl sulfonate (SDS), hexadecyl trimethyl ammonium bromide (C16TAB), polyoxyethylene (23) lauryl ether (C12EO23), and tetradecyldimethylamine oxide (C14DMAO)) has been studied through surface tension measurement and circular dichroism (CD) spectroscopy. The antimicrobial activities of AMP/surfactant mixtures have also been studied with Gram-negative Escherichia coli, Gram-positive Staphylococcus aureus, and the fungus Candida albicans. The cytotoxicity of the AMP/surfactant mixtures has also been assessed with NIH 3T3 and human skin fibroblast (HSF) cells. The surface tension data showed that the AMP/SDS mixture was much more surface-active than SDS alone. CD results showed that G3 conformation changed from random coil, to β-sheet, and then to α-helix with increasing SDS concentration, showing a range of structural transformation driven by the different interactions with SDS. The antimicrobial activity of G3 to Gram-negative and Gram-positive bacteria decreased in the presence of SDS due to the strong interaction of electrostatic attraction between the peptide and the surfactant. The interactions between G3 and C16TAB, C12EO23, and C14DMAO were much weaker than SDS. As a result, the surface tension of surfactants with G3 did not change much, neither did the secondary structures of G3. The antimicrobial activities of G3 were little affected in the presence of C12EO23, slightly improved by C14DMAO, and clearly enhanced by cationic surfactant C16TAB due to its strong cationic and antimicrobial nature, consistent with their surface physical activities as binary mixtures. Although AMP G3 did not show activity to fungus, the mixtures of AMP/C16TAB and AMP/C14DMAO could kill C. albicans at high surfactant concentrations. The mixtures had rather high cytotoxicity to NIH 3T3 and HSF cells although G3 is nontoxic to cells. Cationic AMPs can be formulated with nonionic, cationic, and zwitterionic surfactants during product development, but care must be taken when AMPs are formulated with anionic surfactants, as the strong electrostatic interaction may undermine their antimicrobial activity.

Influence of ring substituents on the electronic properties of 1,2,4-triazolylidenes

Methylation of 3-amino-1,2,4-triazole and 1-methyl-3-nitro-1,2,4-triazole provides access to three NHC-precursors. For the nitro compound only a monomethylation to the triazolium salt 3(OTf) is observed. The aminotriazole could be subsequently converted to mono- and dicationic carbene precursors 1I and 2(OTf)2, respectively. The nitro group on NHC 3 leads to a decrease of donor strength and a slightly enhanced acceptor character as compared to a related NHC lacking the nitro group. The cationic NHC 2 is the poorest donor within the series and shows a TEP value of 2072 cm−1. The properties of this species are dominated by its cationic nature while the influence of the NMe2 group is surprisingly small. X-ray diffraction studies suggest a guanidinium-like character for the NMe2 substituted compounds.

Experimental and computational study of crystal structure and thermal expansion of barium hollandites BaM2Ti6O16 (M = Al, Cr, Ga)

Three SYNROC-related barium hollandites BaM2Ti6O16 (M ​= ​Al, Cr, Ga) have been studied both computationally and experimentally to determine the influence of the M cation nature on hollandites crystal structure and characteristics important for their use as matrix forms for immobilizing radioactive Cs. Their crystal structures have been refined by the Rietveld method. Thermal expansion coefficients of all studied compounds have been determined by the low- and high-temperature X-ray diffraction. To gain insight into local structure of barium hollandites density functional theory calculations have been performed.

Influence of the Compensating Cation Nature on the Water Adsorption Properties of Zeolites.

The influence of the compensating cation (Na+, Li+, Mg2+) nature on the water adsorption properties of LTA and FAU-type zeolites was investigated. Cation exchanges were performed at 80 °C for 2 h using 1 M aqueous solutions of lithium chloride (LiCl) or magnesium chloride (MgCl2). XRF and ICP-OES analyses indicate that the cation exchange yields reach values between 59 to 89% depending on the number of exchange cycles and the nature of the zeolite and cation, while both zeolites structures are preserved during the process, as shown by XRD and solid state NMR analyses. Nitrogen adsorption-desorption experiments indicate a higher available microporous volume when sodium cations are replaced by smaller monovalent lithium cations or by divalent magnesium cations because twice less cations are needed compared to monovalent cations. Up to 15% of gain in the available microporous volume is obtained for FAU-type zeolites exchanged with magnesium cation. This improvement facilitates the adsorption of water with an increase in the water uptake up to 30% for the LTA and FAU type zeolites exchanged with magnesium. These exchanged zeolites are promising for uses in water decontamination because a smaller amount is needed to trap the same amount of water compared to their sodium counterparts.

Mitochondrial Dysfunctions May Be One of the Major Causative Factors Underlying Detrimental Effects of Benzalkonium Chloride.

Benzalkonium chloride (BAC) is currently the most commonly used antimicrobial preservative in ophthalmic solutions, nasal sprays, and cosmetics. However, a large number of clinical and experimental investigations showed that the topical administration of BAC-containing eye drops could cause a variety of ocular surface changes, from ocular discomfort to potential risk for future glaucoma surgery. BAC-containing albuterol may increase the risk of albuterol-related systemic adverse effects. BAC, commonly present in personal care products, in cosmetic products can induce irritation and dose-dependent changes in the cell morphology. The cationic nature of BAC (it is a quaternary ammonium) suggests that one of the major targets of BAC in the cell may be mitochondria, the only intracellular compartment charged negatively. However, the influence of BAC on mitochondria has not been clearly understood. Here, the effects of BAC on energy parameters of rat liver mitochondria as well as on yeast cells were examined. BAC, being a “weaker” uncoupler, potently inhibited respiration in state 3, diminished the mitochondrial membrane potential, caused opening of the Ca2+/Pi-dependent pore, blocked ATP synthesis, and promoted H2O2 production by mitochondria. BAC triggered oxidative stress and mitochondrial fragmentation in yeast cells. BAC-induced oxidative stress in mitochondria and yeast cells was almost totally prevented by the mitochondria-targeted antioxidant SkQ1; the protective effect of SkQ1 on mitochondrial fragmentation was only partial. Collectively, these data showed that BAC acts adversely on cell bioenergetics (especially on ATP synthesis) and mitochondrial dynamics and that its prooxidant effect can be partially prevented by the mitochondria-targeted antioxidant SkQ1.

Modification of halloysite nanotubes with xanthene dyes and their application in luminescent polymer nanocomposites

In this study, halloysite nanotubes (HNTs) were modified with three xanthene dyes and subsequently utilized for the fabrication of luminescent polymer nanocomposites. Two different sets of dyes (rhodamine B, rhodamine 6G, and fluorescein) were chosen because of their ability to interact differently with HNTs. Rhodamines B and 6G were adsorbed on the negatively charged external surface of HNTs due to their cationic nature, while fluorescein was infiltrated into the positively charged nano-size lumen of HNTs. The influence of the HNTs substrate on photoluminescence (PL) of the dyes in the polystyrene matrix was investigated. An enhancement in the PL intensity of fluorescein by a factor of 8 was observed upon its encapsulation into lumens of HNTs. On the other hand, the adsorption of rhodamines on HNTs led to a decrease in their PL intensity. A homogenous dispersion of the dye molecules achieved at nanoscale introduced luminescence properties in the polymer nanocomposites. The robust protocol for the modification of halloysites with organic chromophores provides a straightforward way to distribute the dye molecules in a polymer matrix and to incorporate luminescent properties into different polymer matrices.

Hydrotalcites with heterogeneous anion distributions: a first approach to producing new materials to be used as vehicles for the successive delivery of compounds

ABSTRACTHydrotalcites with heterogeneous distributions of anions between their layers were synthesized. Some synthesis parameters were studied to verify their influence on the anionic segregation properties of the hydrotalcites. The nature of the divalent cation and the crystallization method were most relevant. Zinc, in contrast to magnesium, assisted in discriminating carbonates and attracting nitrates to form hydrotalcites with heterogeneous distributions using microwave irradiation. Furthermore, the identification of this kind of hydrotalcite could be easily verified by determining the presence of a double reflection in the 003 X-ray diffraction (XRD) maximum, which definitively characterized a heterogeneous anion distribution. Finally, the reason as to why in some cases the hydrotalcite presented two reflections in the 003 XRD peak was elucidated.

Small Ion Transport Properties of the Anthrax Toxin Channels

Anthrax toxin channel, protective antigen (PA63), is known to be strongly cation selective, the property that has determined the development of positively charged inhibitors as channel blockers. Successful interpretation of small ion transport through PA63 can also contribute to the description of the translocase activity of the channel that transports the enzymatic factors of anthrax toxin, lethal factor (LF) and edema factor (EF), into the cytosol. It was recently suggested by Kalu et al (FEBS Letters, 2012) that PA63 conductance is determined by the two contributing factors: ionic strength-dependent electrical potential and access resistance, with PA63 dependence on KCl concentration showing two distinct patterns at pH 6.5 and 4.5. The model also offered an explanation for the fact that the protonation of the cavity residues does not change PA63 small ion selectivity. The authors suggested that the channel conductance is determined by the narrowest φ clamp part of the channel and the ionizable residues in proximity to it. In contrast, selectivity is governed by the concerted action of many residues in the channel lumen. To validate this, so far putative model, here we investigate PA63 small ion transport properties using different electrolyte solutions, including LiCl, NaCl, KCl, RbCl, CsCl, NH4Cl, and CaCl2. We demonstrate that PA63 conductance shows an unexpectedly strong dependence on the nature of the electrolyte solution cation, compared to the bulk conductivity change. At the same time, the channel's selectivity remains essentially unchanged for monovalent cation solutions. In CaCl2, the selectivity is reversed. We discuss the influence of PA63 lumen residues, cation hydration shells, and access resistance on small ion transport properties of the channel.

Unexpected aqueous UCST behavior of a cationic comb polymer with pentaarginine side chains

Thermoresponsive polymers, undergoing a reversible chemical or physical change using temperature as stimulus, attract increasing interest in particular as adaptable biomaterials. Except for zwitterionic polymers, fully charged polymers require the presence of specific ions to exhibit an upper critical solution temperature (UCST) in water. Herein, we report the discovery of an UCST in pure water for fully cationic comb polymers based on oligoarginine pendent grafts. These polymers were prepared using an original strategy based on solid-phase peptide synthesis of pentaarginine methacrylate-based macromonomer and its polymerization through reversible addition-fragmentation chain transfer. Despite their cationic nature, guanidinium groups from the arginine have the ability to self-associate at low temperature through hydrophobic interactions into stacked pair configuration defying the expected Coulomb interactions. These results pave the way to biomedical applications such as antimicrobial materials and drug delivery systems through the tuning of the polymer structure.

Discovery and Structure–Activity Relationships of Nociceptin Receptor Partial Agonists That Afford Symptom Ablation in Parkinson’s Disease Models

A novel series of C(3)-substituted piperdinylindoles were developed as nociceptin opioid receptor (NOP) partial agonists to explore a pharmacological hypothesis that NOP partial agonists would afford a dual pharmacological action of attenuating Parkinson's disease (PD) motor symptoms and development of levodopa-induced dyskinesias. SAR around the C-3 substituents investigated effects on NOP binding, intrinsic activity, and selectivity and showed that while the C(3)-substituted indoles are selective, high affinity NOP ligands, the steric, polar, and cationic nature of the C-3 substituents affected intrinsic activity to afford partial agonists with a range of efficacies. Compounds 4, 5, and 9 with agonist efficacies between 25% and 35% significantly attenuated motor deficits in the 6-OHDA-hemilesioned rat model of PD. Further, unlike NOP antagonists, which appear to worsen dyskinesia expression, these NOP partial agonists did not attenuate or worsen dyskinesia expression. The NOP partial agonists and their SAR reported here may be useful to develop nondopaminergic treatments for PD.

Metal-directed supramolecular architectures based on the bifunctional ligand 2,5-bis(1H-1,2,4-triazol-1-yl)terephthalic acid.

By the solvothermal reactions of 2,5-bis(1H-1,2,4-triazol-1-yl)terephthalic acid (H2L) with transition-metal ions, two novel polymeric complexes, namely, poly[diaqua[μ4-2,5-bis(1H-1,2,4-triazol-1-yl)terephthalato]cobalt(II)], [Co(C12H6N6O4)(H2O)2]n, (1), and poly[[diaqua[μ4-2,5-bis(1H-1,2,4-triazol-1-yl)terephthalato]nickel(II)] dihydrate], {[Ni(C12H6N6O4)(H2O)2]·2H2O}n, (2), were isolated. Both polymers have been characterized by FT-IR spectroscopy, elemental analysis and single-crystal X-ray diffraction analysis. The complexes have similar two-dimensional layered structures and coordination modes. Furthermore, the two-dimensional layered structures bear distinct intermolecular hydrogen-bonding interactions and π-π stacking interactions to form two different three-dimensional supramolecular networks based on 44-subnets. The structural variation depends on the nature of the metal cations. The results of variable-temperature magnetization measurements (χMT-T and χM-1-T) show that complexes (1) and (2) display antiferromagnetic behaviour.

Formation of the Structure of Aqueous Solutions of Manganese, Nickel, Copper, and Zinc Chlorides, According to X-ray Diffraction Data

The structure formation in the aqueous solutions of manganese, nickel, copper, and zinc chlorides is studied via X-ray diffraction in a broad range of concentrations. Small-angle peaks are interpreted. The change in their intensity and position is analyzed, depending on the concentration and nature of cations. The X-ray scattering intensity curves for the studied solutions are compared to the corresponding data for the solutions of lanthanide chlorides investigated earlier.

Interaction of metal ions with humic acids of brown coals of Kazakhstan

This paper investigates interaction processes of the Fe3+, Cu2+, Ni2+, and Co2+ cations with humic acids isolated from brown coals of Ekibastuz basin. It was demonstrated that the sorption of heavy metal ions by humic acids (HA) depends on the concentration and nature of cations and decreases in the order of Fe3+ > Cu2+ > Ni2+ > Co2+; while increase in the concentration of humic acids (HA) results in the higher yield of ions and metals. The occurrence of ion exchange and complexation reactions in metal-humic acid systems is confirmed by the appearance of new bands and the shift of the absorption bands corresponding to stretching and deformation vibrations of carboxylate ions, C = O and OH groups. The occurrence of these processes is also evidenced by spectrophotometric data, as well as a decrease in the pH of the solution due to deprotonation of humic acids during these reactions. Thus, based on the data on the degree of sorption of metal cations by humic acids, the results of infra-red spectroscopy and spectrophotometry, it can be concluded that the Fe3+, Ni2+, Co2+, Cu2+ cations interact with HA by the ionic mechanism and by the complexation mechanism with electron-donating functional groups. Electrochemical studies of the Cu2+ – humic acid system carried out by the method of cyclic voltammetry also indicate the occurrence of the interaction of humic acid with copper cations. Modification of humic acid with copper ions shows the electrochemical activity of copper immobilized on the surface of dispersed humic acid, which is important for the implementation of electrocatalytic reactions on modified glassy carbon-humic electrodes.

M4LiBe4P7O24 and M4Li(Li3P)P7O24 (M = Cs, Rb): deep-ultraviolet nonlinear-optical phosphates with a tetrahedra-substituted paracelsian-like framework.

New paracelsian-like beryllophosphates M4LiBe4P7O24 and their tetrahedra-substituted phases M4Li(Li3P)P7O24 (MLiP2O6, M = Cs, Rb) were designed and synthesized. Interestingly, two types of phases undergo a structural transformation, resulting from the radius and valence charge number of tetrahedral cations. Four crystals demonstrate potential deep-UV NLO properties such as short absorption edges (<190 nm) and phase-matching SHG response.

Изучение растворимости осадков некоторых лантаноидов в карбонатных средах

The study examines the dissolution process for the precipitates of the rare-earth carbonates and phosphates with a change in the concentration parameters of the system. The objective of the study is to determine the nature of the dissolution process at variable composition of the studied solutions. As a result of the theoretical base analysis, the qualitative and quantitative content of rare-earth metals in red sludge and phosphogypsum is presented, which governs the interest in this problem under consideration. The available techniques for extraction of rare-earth metals from red sludge and phosphogypsum have also been considered, their advantages and disadvantages are presented. A promising carbonate-alkali method for the extraction of rare-earth metals has been considered. Thermodynamic parameters of the system have been calculated to determine the possibility of the process. During the experiment the factors affecting the dissolution process have been examined: the carbonate ion concentration, the nature of the solvent cation and rare-earth metal cation. Carbonates and phosphates of europium, holmium, and neodymium have been considered as the analyzed components. Carbonates and phosphates of neodymium, europium, and holmium have been dissolved in model solutions of K2CO3 with the concentrations of 0.2–4.5 mol/L until reaching equilibrium. The obtained results show the dependence of solubility of the precipitates of rare-earth metals on the solvent nature and concentration. The explored data are presented as solubility isotherms. On the basis of experimental data the values of the extraction degree of a rare-earth metal into the solution have been calculated. For neodymium, europium, and holmium carbonates, the maximum recovery degree αmax is 72.8 %, 81.2 %, 83.0 %, respectively. During the experiment with dissolution of lanthanide phosphates, the following results have been obtained: the maximal degree of neodymium extraction is 60.59%, while for europium it equals 51.66 % and 93.01 % for holmium

Online capillary electrophoresis - mass spectrometry analysis of histatin-5 and its degradation products.

Histatin-5 (Hst-5) is a human salivary peptide with antibacterial and antifungal activities. Thorough characterization and reliable quantification of Hst-5 and its degradation products are essential for understanding the Hst-5 degradation pathway. Due to the highly basic and strong cationic nature of the Hst-5 peptide, the quantitative analysis of Hst-5 and its degradation forms by online mass spectrometry remains challenging. Here, we adopt a recently developed electrokinetically pumped sheath liquid capillary electrophoresis - mass spectrometry (CE-MS) coupling technology, and successfully apply it for the analysis of Hst-5 and its degradation products. Our CE-MS method is demonstrated to be robust and quantitative. This novel analytical platform is reproducible and free of sample carryover. The efficacy of this method is demonstrated with a kinetic study of Hst-5 degradation by Sap9, a secreted aspartic peptidase. Our work demonstrates the potential of online CE-MS as a powerful approach for characterizing highly basic peptides.