Cl Complexes Research Articles

Synthesis, Characterization, and Density Functional Theory Investigation of the Solid-State [UO2Cl4(H2O)]2- Complex.

A significant number of solid-state [UO2Cl4]2- coordination compounds have been synthesized and structurally characterized. Yet, despite their purposive relative abundance in aqueous solutions, characterization of aquachlorouranium(VI) complexes remain rare. In the current study, a solid-state uranyl aqua chloro complex ((C4H12N2)2[UO2Cl4(H2O)]Cl2) was synthesized using piperazinium as a charge-balancing ligand, and the structure was determined using single-crystal X-ray diffraction. Using periodic density functional theory, the electronic structure of the [UO2Cl4(H2O)]2- complex was compared to [UO2Cl4]2- to uncover the strengthening of the U═O bond in [UO2Cl4(H2O)]2-. Changes in the strength of the U═O bond were validated further with Raman and IR spectroscopy, where uranyl symmetrical (ν1) and asymmetrical (ν3) stretches were blue-shifted compared to the reference [UO2Cl4]2- complex. Furthermore, the formation energy of the solid-state (C4H12N2)2[UO2Cl4(H2O)]Cl2 complex was calculated to be -287.60 ± 1.75 kJ mol-1 using isothermal acid calorimetry. The demonstrated higher stability relative to the related [UO2Cl4]2- complex was related to the relative stoichiometry of the counterions.

Accelerated kinetics of Pd(II) solvent extraction using functionalized 1-methyl-2-(nonylthio)-1H-imidazole and its comparison with dialkylsulfide to separate Pd(II) and Pt(IV)

Dialkylsulfide is considered as the most promising extractant for separating Pd(II) and Pt(IV) in industrial processes. However, the slow kinetics for Pd(II) extraction limits its extensive application. The development of new extractants with faster kinetics, high extraction efficiency, and exceptional Pd(II) separation selectivity has been a persisting goal over the past few decades. In this study, a new functionalized extractant, 1-methyl-2-(nonylthio)-1H-imidazole (MNI) containing both N and S atoms, was synthesized and employed to separate Pd(II) from mixed hydrochloric acid solutions with different initial Pd(II)/Pt(IV) concentration ratios. Experimental results revealed that MNI not only has a high selectivity for Pd(II) over Pt(IV) but also has faster kinetics for Pd(II) extraction than diisopentylsulfide (S201) under similar extraction conditions. In contrast to traditional dialkylsulfide extractants, MNI coordinates with Pd(II) ions via the N(5) atom in its imidazole ring to form Pd(MNI)2Cl2 complexes, instead of using the S atom as with dialkylsulfide. The extraction mechanism involving the coordination between Pd(II) and MNI was demonstrated using the slope analysis method and ultraviolet (UV), Fourier-transform infrared (FT-IR), 1H NMR, and 13C NMR spectroscopic methods. The fast extraction kinetics between MNI and Pd(II) was possibly attributed to the high charge density of the N(5) atom in the imidazole ring, whereas the outstanding separation selectivity for Pd(II) was due to the strong affinity of the N(5) atom. The facile synthesis, high saturation capacity, excellent Pd(II) selectivity, and remarkable reusability endow MNI with potential applications in Pd(II) recovery from leach solutions of waste automotive catalysts and other secondary resources.

Syntheses, characterization of Imidazo[4,5-f][1,10]phenanthroline derivative and As (III) complex, In vitro evaluation, the determine of apoptosis mechanism; theoretical and quantum studies

In the present work, a novel ligand, (4-amino-3-methoxybenzaldehyde)-1H-imidazo[4,5-f][1,10] phenanthroline (AMIP) based on the formation of an imidazole ring and [As(AMIP)](Cl)]Cl2 was synthesized and characterized through Fourier-transform infrared (FT-IR) spectroscopy. In addition, the anticancer activity of [As(AMIP)](Cl)]Cl2 complex was tested against human acute promyelocytic leukemia cells (HL-60) and granulocytic differentiation of human promyelocytic leukemia cells (NB4). The MTT results showed IC50 values of 7.31 ± 15 and 8.4 ± 62 μM for As (III) complex against NB4 and HL-60, respectively. In a study on both cell lines, As (III) reduced gene expression Bcl-2 and Bcl-xl, increased Bax and Bad, and activated caspase-3, resulting in apoptosis. The dye Hoechst 33342 showed increased apoptosis induction in the NB4 cell line than in the HL-60 cell line. BrdU test exhibited an inhibitory effect on DNA synthesis. The protein levels of caspase-3 were enhanced in a dose-dependent manner in both HL-60 and NB-4 cell lines. Based on the Annexin V-FITC/PI assay, apoptosis was the primary mechanism of cell death. The real-time polymerase chain reaction (real-time PCR) results demonstrated that the expression level of Atg 12, Atg 7, Lc 3, and Beclin-1 genes, antiapoptotic genes including Bcl-2 and Bcl-xl, and apoptotic genes containing BAD and BAX was improved. Furthermore, the hemolysis assay showed the anti-hemolytic activity of the complex. Moreover, quantum chemical calculations were utilized to optimize all structures, and the output results were employed to study molecular docking of compounds with caspase-3 tethered to irreversible inhibitor (PDB ID: 1NMS) and DNA with sequence d(CCGTCGACGG) (PDB ID:423D). The results showed that As (III) complex had the lowest-energy conformation, suggesting the optimal interaction.

Molecular studies regarding colon cancer cell line (HCT116) treated by new ruthenium and palladium complexes

Ru(H2dtpa) (H2O) and Pd (DME)Cl2 were prepared, and their structures were confirmed by different structural tools. [Ru(H4dtpa) (cysteine)] Cl was separated as a model for the interaction of Ru (III) complex containing DTPA ligand with its corresponding most active amino acid and the geometrical parameters for the ternary complex and their constituent ligands are evaluated. Cytotoxicity was examined for both complexes against different cancer cell lines (HCT116, A549 and Mcf7). They were tested against a normal human lung cell line (W138). In addition, both complexes ensured cytocidal, not cytostatic effect. Several molecular tools were utilized in order to figure out the mechanism of action that two complexes followed to inhibit human colon cancer (HCT116) cell line. Gene expression analysis, cell cycle assay, genomic DNA analysis, and apoptosis were a molecular techniques that proved both Ru(H2dtpa) (H2O) and Pd (DME)Cl2 complexes were promising and effective chemotherapeutic agents against colon carcinoma in this current study. So, authors recommended more in vivo future studies should be done to make sure of complexes bioactivity and safety before they would be used commercially.

How generic is iodide-tagging photoelectron spectroscopy: An extended investigation on the Gly·X- (Gly = glycine, X = Cl or Br) complexes.

We report a joint negative ion photoelectron spectroscopy (NIPES) and quantum chemical computational study on glycine-chloride/bromide complexes (denoted Gly·X-, X = Cl/Br) in close comparison to the previously studied Gly·I- cluster ion. Combining experimental NIPE spectra and theoretical calculations, various Gly·X- complexes were found to adopt the same types of low-lying isomers, albeit with different relative energies. Despite more congested spectral profiles for Gly·Cl- and Gly·Br-, spectral assignments were accomplished with the guidance of the knowledge learned from Gly·I-, where a larger spin-orbit splitting of iodine afforded well-resolved, recognizable spectral peaks. Three canonical plus one zwitterionic isomer for Gly·Cl- and four canonical conformers for Gly·Br- were experimentally identified and characterized in contrast to the five canonical ones observed for Gly·I- under similar experimental conditions. Taken together, this study investigates both genericity and variations in binding patterns for the complexes composed of glycine and various halides, demonstrating that iodide-tagging is an effective spectroscopic means to unravel diverse ion-molecule binding motifs for cluster anions with congested spectral bands by substituting the respective ion with iodide.

Iridium-Complexed Dipyridyl-Pyridazine Organosilica as a Catalyst for Water Oxidation.

The heterogenization of metal-complex catalysts to be applied in water oxidation reactions is a currently growing field of great scientific impact for the development of energy conversion devices simulating the natural photosynthesis process. The attachment of IrCp*Cl complexes to the dipyridyl-pyridazine N-chelating sites on the surface of SBA-15 promotes the formation of metal bipyridine-like complexes, which can act as catalytic sites in the oxidation of water to dioxygen, the key half-reaction of artificial photosynthetic systems. The efficiency of the heterogeneous catalyst, Ir@NdppzSBA, in cerium(IV)-driven water oxidation was thoroughly evaluated, achieving high catalytic activity even at a long reaction time. The reusability and stability were also examined after three reaction cycles, with a slight loss of activity. A comparison with an analogous homogeneous iridium catalyst revealed the enhanced durability and performance of the heterogeneous system based on the Ir@NdppzSBA catalyst due to the stability of the SBA-15 structure as well as the isolated metal active sites. Thereby, this new versatile synthesis route for the preparation of water oxidation catalysts opens a new avenue for the construction of alternative heterogeneous catalytic systems with high surface area, ease of functionalization, and facile separation to improve the efficiency in the water oxidation reaction.

Protein interactions and drug displacement studies of novel copper(II) and zinc(II) complexes of a dipyrazinylpyridine ligand

A one-pot method was employed for the preparation of zinc and copper complexes of 4-methoxyphenyl-2,6-di(pyrazine-2-yl)pyridine ligand (L). The complexes were designed to acknowledge their potential as selective binders with serum albumins. The reaction of the metal chlorides with an excess of ligand L yielded mononuclear [CuL2]Cl2 (1) and [ZnL2]Cl2 (2) complexes. 1H NMR, UV–Vis spectroscopy, ESR, HRMS, XRD, and elemental analysis were carried out to characterize the complexes. The interactions of the synthesized complexes with Human Serum Albumin (HSA) and their drug displacement properties using ibuprofen and warfarin were investigated with the help of spectroscopic as well as molecular modeling techniques. Complex 1 exhibited better binding capability, indicated by its binding constant value (31.2 × 104 M−1) towards HSA, than complex 2 (5.6 × 104 M−1), as depicted from UV–Visible and fluorescence spectroscopic studies. Moreover, the complexes showed better binding affinity towards HSA than the corresponding free ligand (0.2 × 104 M−1). The mechanism through which fluorescence quenching of HSA takes place (when metal complexes 1–2 were added to it) is static in nature. The Stern-Volmer (SV) equation was utilized to deduce the binding constants (Kb) through a fluorescence titration method. Moreover, structure optimization of the synthesized complexes and theoretical studies using density functional theory (DFT) has been carried out to determine the nature of the interaction of the complexes with the biomolecules.

Iridium(III) complexes based on cyanomethane and cyanamide ligands with luminescence quenching properties for Fe(III) sensing and biological activities

Two organometallic iridium(III) complexes, Ir(ppy)2Cl(NCCH3) (1) and Ir(ppy)2Cl(NCNH2) (2), were accidentally synthesized from the reaction between the chloro-bridged dimer of (ppy)2Ir(μ-Cl)2Ir(ppy)2 and 2-aminobenzothiazole (abt, C7H6N2S) ligand refluxed in dichloromethane under Ar gas. In the obtained complexes, ppy is 2-phenylpyridine, NCCH3 is cyanomethane or acetonitrile, and NCNH2 is the cyanamide ligand. Complex 1 was received instead of the expected Ir(ppy)2Cl(abt) complex, after the reaction completed for 10 h. Acetonitrile entered as a ligand to the coordination sphere of Ir(III) during the precipitation stage. The reaction was repeated, refluxing for 20 h. This time, the abt ligand fragmented into the cyanamide molecule yielding complex 2 instead of the Ir(ppy)2Cl(abt) complex. Single-crystal X-ray analysis revealed the distorted octahedral geometries of both title complexes. The N and C donors of ppy were in their typical trans- and cis- orientations, respectively. The cyanomethane and cyanamide ligands coordinated via the N-atom. Both complexes exhibited similar photo-physical properties. Complexes 1 and 2 emitted green luminescence between 520 and 525 nm when excited with 325 and 350 nm, respectively, at room temperature in dichloromethane. The respective relative quantum efficiencies were 0.06 and 0.08, compared to coumarin 6 in ethanol. The luminescent emission of both complexes was selectively turn-offtoward increasing Fe3+ concentrations. The 1:1 binding stoichiometry between the complex and Fe3+ ion was determined by Job's plot. Benesi-Hildebrand plots were applied to determine the binding constants (Kb) of 5.86 × 104 and 9.50 × 104 M−1 for complexes 1 and 2, respectively. The complex 2 displayed in vitro cytotoxicity toward HCC1937 and MDA-MB-231 human breast cancer cells with IC50 values of 13.5 and 72.8 µM, respectively. These values indicated 2–3 folds higher sensitivity than cisplatin. In addition, complex 1 showed inhibitory activity against the Gram-positive bacteria Staphylococcus aureus (SA) and methicillin-resistant Staphylococcus aureus (MRSA), with MIC/MBC values of 32/32 and 32/64 μg. mL−1, respectively.

Synthesis, characterization and antibacterial activity of ruthenium complex bearing 3,3’-dicarboxy-2,2’-bipyridine ligand

The development of bacteria has been one of the most significant advances in medical science. The need for the development of novel antibacterial is clear, but the development of new antibacterial classes is more important. In this study, the new ruthenium complex bearing the NN chelating ligand 3,3’-dicarboxy-2,2’-bipyridine (3,3’-dcbpy) and the dimethylsulphoxide (DMSO) ligand, [Ru(3,3’-dcbpy) (DMSO)2Cl2], was synthesized and characterized using FT-IR, 1H- and 13C-NMR spectroscopy, elemental analysis, and UV-Vis spectrometry. In addition, the Ru-complex was examined for its activity as an antibacterial against gram-positive and gramnegative strains. Minimum Inhibitory Concentrations (MICs) and Minimum Bactericidal Concentrations (MBCs) of the compound were assessed using sterile 96-well plates, in accordance with the Clinical and Laboratory Standards Institute. The results show that the compound shows a MIC value of 35 µg mL−1 against Staphylococcus aureus and 65 µg mL−1 against Escherichia coli with the bacteria’s mode of action. In conclusion, Ru(3,3’-dcbpy) (DMSO)2Cl2 complex can be candidate as antibacterial agent against both gram-positive and gram-negative bacteria.

Photophysics of Iridium(III) (2‐phenylpyridine)(2,2’,6,2”‐terpyridine) Chloride Encapsulated within the Zinc(II) Polyhedral MOF, USF‐2

AbstractPhotoactive metal‐organic frameworks (MOFs) provide an important class of functional porous materials for a wide range of applications including light harvesting, photocatalysis and photodynamic therapy. Two strategies have been employed in the development of photoactive MOFs, one in which the photoactive element is incorporated as an element of the framework itself and the other in which the photoactive element serves as a guest within the MOF cavities. Transition metal polyimines have now been non‐covalently incorporated within the cavities of a large number of MOFs with the RuII‐polyimine being the most widely examined guest complex. Previous studies have demonstrated that the nature of the cavity modulates the Ru‐polyimine photophysics. Here, an IrIII(terpyridine)(phenylpyridine)Cl complex has been encapsulated within the Zn‐polyhedral MOF, USF‐2. Unlike the Ru‐polyimines, the excited state photophysics associated with the encapsulated Ir polyimine shows very little change in either the steady state emission and emission lifetime. The slight decrease in emission lifetime is attributed to energy transfer between encapsulated Ir complexes. These results indicate that transition metal polyimines that exhibit excited state structural changes demonstrate the largest perturbations upon confinement.

Liquid‐State Cathode Enabling a High‐Voltage and Air‐Stable Fe‐Al Hybrid Battery

AbstractAluminum (Al) is an ideal anode material in low‐cost battery system for energy storage, with high theoretical capacities. However, the sluggish Al3+‐involved kinetics challenges the selection of common cathode materials (Al3+ intercalation or conversion). Herein, a redox‐active Fe–Cl complex serves as the liquid‐state cathode to couple with a low‐cost Al anode, which synergizes the advantages of redox flow batteries and Al rechargeable batteries. The interplay of Fe‐Cl coordinated formula and electrochemical properties are revealed for the first time. It is found that [Fe2Cl7]− molecule has a high voltage versus Al anode (1.3 V), and the novel Fe‐Al hybrid battery fulfills a capacity of 1.6 mAh cm−2 (20 Ah L−1) record high in a coin cell among Al‐based batteries. Furthermore, the energy efficiency, which is a vital parameter to evaluate the energy cost of the energy storage technology, reaches 85% (superior to most Al‐based batteries) and an average of 70% over ≈900 h cycling. Particularly, the unique air‐stable character enables normal operation of the battery assembled in ambient air. This work establishes a new application scenario for Al anode toward low‐cost large‐scale energy storage.

Understanding the Effect of Internal Electrostatic Fields Created by Alkaline Earth Metal Ions Poised over Secondary Coordination Sphere of Molecular Iron Complexes.

Understanding the effect of the local electrical field around the reaction center in enzymes and molecular catalysis is an important topic of research. Herein, we explored the electrostatic field exerted by the alkaline earth metal ions (M2+ = Mg2+, Ca2+, Sr2+, and Ba2+) around Fe in FeIII(Cl) complexes by experimental and computational investigations. M2+ coordinated dinuclear FeIII(Cl) complexes (12M) were synthesized and characterized by X-ray crystallography and different spectroscopic techniques. EPR and magnetic moment measurements exhibited the presence of high-spin FeIII centers in the 12M complexes. Electrochemical investigations revealed FeIII/FeII reduction potential values shifted anodically in 12M complexes compared to 1. Likewise, 2p3/2 and 2p1/2 peaks in the XPS data were found to shift positively in the 12M complexes, demonstrating that redox-inactive metal ions make FeIII more electropositive. However, nearly similar λmax values in the UV-vis spectra were observed in 1 and 12M complexes. The first-principles-based computational simulations further revealed the impact of M2+ on stabilizing 3d-orbitals of Fe. The distortion in Laplacian distribution (∇2ρ(r)) of electron density around M2+ also indicates the possibility of having Fe-M interactions in these complexes. The absence of a bond critical point between FeIII and M2+ ions in the 12M complexes indicates dominant through-space interaction between these metal centers. Experimental and computational studies collectively imply that the installation of internal electrostatic fields exerted by M2+ ions in 12M complexes alters the electronic structure of FeIII.

Inhibition of photosensitized degradation of organic contaminants by copper under conditions typical of estuarine and coastal waters

Dissolved organic matter (DOM) driven-photochemical processes play an important role in the redox cycling of trace metals and attenuation of organic contaminants in estuarine and coastal ecosystems. In this study, we evaluate the effect of Cu on 4-carboxybenzophenone (CBBP) and Suwannee River natural organic matter (SRNOM)-photosensitized degradation of seven target contaminants (TCs) including phenols and amines under pH conditions and salt concentrations typical of those encountered in estuarine and coastal waters. Our results show that trace amounts of Cu(II) (25 −500 nM) induce strong inhibition of the photosensitized degradation of all TCs in solutions containing CBBP. The influence of TCs on the photo-formation of Cu(I) and the decrease in the lifetime of transformation intermediates of contaminants (TC•+/ TC•(-H)) in the presence of Cu(I) indicated that the inhibition effect of Cu was mainly due to the reduction of TC•+/ TC•(-H) by the photo-produced Cu(I). The inhibitory effect of Cu on the photodegradation of TCs decreased with the increase in Cl− concentration since less reactive Cu(I)−Cl complexes dominate at high Cl− concentrations. The impact of Cu on the SRNOM-sensitized degradation of TCs is less pronounced compared to that observed in CBBP solution since the redox active moieties present in SRNOM competes with Cu(I) to reduce TC•+/ TC•(-H). A detailed mathematical model is developed to describe the photodegradation of contaminants and Cu redox transformations in irradiated SRNOM and CBBP solutions.

Novel insights into the multistep chlorination of silver nanoparticles in aquatic environments

Due to the increasing applications, silver nanoparticles (AgNPs) are inevitably released into the environments and are subjected to various transformations. Chloride ion (Cl−) is a common and abundant anion with a wide range of concentration in aquatic environments and exhibits a strong affinity for silver. The results indicate that AgNPs experienced multistep chlorination, which was dependent on the concentration of Cl− in a non-linear manner. The dissolution of AgNPs was accelerated at Cl/Ag ratio of 1 and the intensive etching effect of Cl− contributed to the significant morphology changes of AgNPs. The dissolved Ag+ quickly precipitated with Cl− to form an amorphous and passivating AgCl(s) layer on the surface of AgNPs, thus the dissolution rate of AgNPs decreased at higher Cl/Ag ratios (100 and 1000). As the Cl/Ag ratio further increased to 10,000, the overall transformation rate increased remarkably due to the complexation of Cl− with AgCl(s) to form soluble AgClx(x-1)− species, which was verified by the reaction of AgCl nanoparticles with Cl−. Besides, several environmental factors (electrolytes, surfactants and natural organic matter) affected AgNPs dissolution and the following chlorination. These results will expand the understanding of the environmental fate and potential risks of AgNPs in natural chloride-rich waters.

Bridging Platinum and Palladium to Bipyridine-Annulated Perylene for Light-Driven Hydrogen Evolution

In this work, we present two bipyridine-annulated perylene tetracarboxylic ester (P-L) photocatalysts with PtCl2 and PdCl2. X-ray photoelectron spectroscopy showed that their binding energies match precisely the binding energies of the respective M(bpy)Cl2 complexes. Cyclic voltammetry measurements of the complexes displayed additional reduction potentials upon metal insertion. Light-driven catalysis demonstrated that both compounds are catalytically active, with P-Pt outcompeting P-Pd with a TON of 186 over 48 h in the presence of ascorbic acid (P-Pd: 50). Mercury poisoning experiments were carried out to validate the catalytically competent component. Almost quantitative quenching of the catalytic turnover was observed for P-Pd, whereas the hydrogen production rate remained unaffected for P-Pt, making it a photocatalyst that contains the structure PtN^NCl2 and nonetheless operates without a second noble metal nucleus or a separate photosensitizer under visible light. Time-resolved (fs and ns) spectroscopy on P-L and P-Pt yields insights into the light-induced intramolecular processes. In P-Pt, we observed that both 1IL (400 nm) and 1MLCT (500 nm) excitation leads to intersystem crossing with a solvent polarity-dependent distribution between 3MLCT and 3IL, where the 3IL population increases in ACN vs DCM, indicating that in aqueous catalytic samples, the 3IL state plays a major role in the catalytic process.

Catalytic Use of Pd(II) Complex Bearing 2-(thiophen-2-yl)-1H-Benzimidazole Ligand for The Reduction / Degradation of Multiple Mixtures Containing 4-NP, RhB and MB Organic Pollutants

In this study, the catalytic use of [Pd(L1)2]Cl2 complex is aimed for the reduction / degradation reactions of organic pollutants in water sources which pose a threat to the environment. For this purpose, 2-(thiophen-2-yl)-1H-benzimidazole ligand (L1) and its Pd(II) complex (C1) were synthesized and characterized by FT-IR, 1H-NMR, 13C-NMR, ESI-MS spectroscopic techniques. The catalytic efficiency of the C1 complex on the reduction of 4-nitro phenol compound (4-NP) and the degradation of rhodamine B (RhB), methylene blue (MB) dyes was investigated in the presence of NaBH4 in aqueous medium. The catalytic performance was examined with single solutions of these substrates (4-NP and RhB, MB dyes) and at the end of 5 minutes, over 92% conversion was observed for all three substrates. In the catalytic trials with 4-NP + RhB + MB triple substrate mixture, 84, 94 and 93% conversion values were obtained, respectively, after 5 minutes. C1 complex catalyst is very effective in the simultaneous reduction / degradation of these toxic organic compounds from aqueous environments without any competition or selectivity.

Synthesis of 2-Cyanomethyl Indane Derivatives via Pd-Catalyzed Alkene Difunctionalization Reactions of Alkyl Nitriles.

The synthesis of indanes bearing substituted cyanomethyl groups at C2 is achieved through Pd-catalyzed coupling reactions between 2-allylphenyl triflate derivatives and alkyl nitriles. Related partially saturated analogues were generated from analogous transformations of alkenyl triflates. The use of a preformed BrettPhosPd(allyl)(Cl) complex as a precatalyst was essential for the success of these reactions.

Convenient One-Pot Synthesis of L2Pd(0) Complexes for Cross-Coupling Catalysis

A convenient one-pot synthesis of (tBu3P)2Pd(0) was successfully carried out by using various air-stable Pd(II) salts, such as Pd(cod)Cl2, Pd(nbd)Cl2, Pd(CH3CN)2Cl2, or Pd(PhCN)2Cl2, without the use of an external reducing agent. Using Pd(cod)Cl2 as the precursor, large-scale synthesis of (tBu3P)2Pd(0) was accomplished in excellent yield and purity. Another protocol was also developed for L2Pd(0) complexes via an atom economical one-pot method by reacting in situ generated LPd(R-allyl)Cl complexes (L = tBu3P, Cy3P, (o-Tol)3P, CataXCium A, AmPhos, QPhos: R = H, Me, Ph) with 1 equivalent of L in the presence of a base with yields ranging from 74% to 92%, although the process can be further optimized. These methods are superior to those reported in the literature.

Ca2+-Dependent and -Independent Calmodulin Binding to the Cytoplasmic Loop of Gap Junction Connexins

Ca2+/calmodulin (Ca2+/CaM) interaction with connexins (Cx) is well-established; however, the mechanistic basis of regulation of gap junction function by Ca2+/CaM is not fully understood. Ca2+/CaM is predicted to bind to a domain in the C-terminal portion of the intracellular loop (CL2) in the vast majority of Cx isoforms and for a number of Cx-s this prediction has proved correct. In this study, we investigate and characterise both Ca2+/CaM and apo-CaM binding to selected representatives of each of the α, β and γ connexin family to develop a better mechanistic understanding of CaM effects on gap junction function. The affinity and kinetics Ca2+/CaM and apo-CaM interactions of CL2 peptides of β-Cx32, γ-Cx35, α-Cx43, α-Cx45 and α-Cx57 were investigated. All five Cx CL2 peptides were found to have high affinity for Ca2+/CaM with dissociation constants (Kd(+Ca)) from 20 to 150 nM. The limiting rate of binding and the rates of dissociation covered a broad range. In addition, we obtained evidence for high affinity Ca2+-independent interaction of all five peptides with CaM, consistent with CaM remaining anchored to gap junctions in resting cells. However, for the α-Cx45 and α-Cx57 CL2 peptides, Ca2+-dependent association at resting [Ca2+] of 50-100 nM is indicated in these complexes as one of the CaM Ca2+ binding sites displays high affinity with Kd of 70 and 30 nM for Ca2+, respectively. Furthermore, complex conformational changes were observed in peptide-apo-CaM complexes with the structure of CaM compacted or stretched by the peptide in a concentration dependent manner suggesting that the CL2 domain may undergo helix-to-coil transition and/or forms bundles, which may be relevant in the hexameric gap junction. We demonstrate inhibition of gap junction permeability by Ca2+/CaM in a dose dependent manner, further cementing Ca2+/CaM as a regulator of gap junction function. The motion of a stretched CaM-CL2 complex compacting upon Ca2+ binding may bring about the Ca2+/CaM block of the gap junction pore by a push and pull action on the CL2 C-terminal hydrophobic residues of transmembrane domain 3 (TM3) in and out of the membrane.

Fluid evolution and metallogenic mechanism of the Xianghualing skarn-type Sn deposit, South China: Evidence from petrography, fluid inclusions and trace-element composition of cassiterite

The Xianghualing Sn-polymetallic deposit is a large skarn-type Sn deposit located in the Nanling polymetallic metallogenic belt, South China. The ore bodies are controlled by NE-trending faults and mainly hosted in the contact of Middle Devonian carbonate rock and granite. The Xianghualing deposit is divided into four mineralization stages, and two stages of Sn mineralization are identified. The mineralization stages from early to late include stage I (prograde stage), stage II (retrograde stage), stage III (cassiterite-magnetite-arsenopyrite-topaz-quartz stage), stage IV (sphalerite-galena-pyrite-chalcopyrite-quartz-calcite stage). Stage II is the initial stage of Sn mineralization where only minor cassiterite precipitates, and stage III is the main Sn mineralization stage where abundant cassiterite precipitates. On this basis, fluid inclusion microthermometry and Raman spectroscopy analyses were carried out for ore and/or gangue minerals at different stages. In addition, trace element composition analysis was also conducted on cassiterite. These data can contribute to reveal the fluid properties, evolution and formation mechanism of Xianghualing deposit. Three types of fluid inclusions were identified in different mineralization stages, including halite-bearing multi-phase inclusions (Type B), liquid-rich two-phase inclusions (Type L) and vapor-rich two-phase inclusions (Type V). Garnet (stage I) contains Type B inclusions and Type V inclusions, with homogenization temperatures and salinities of 511–549 °C, 37.6–48.9 wt% NaCl equiv. and 551–559 °C, 4.0–5.1 wt% NaCl equiv., respectively. Topaz (stage II) contains Type L inclusions with homogenization temperatures of 408–445 °C and salinities of 9.5–12.4 wt% NaCl equiv. Cassiterite (stage III) contains Type L inclusions with homogenization temperatures of 368–417 °C and salinities of 8.7–11.5 wt% NaCl equiv. Quartz (stage IV) contains Type L inclusions with homogenization temperatures of 162–227 °C and salinities of 2.6–5.0 wt% NaCl equiv. The temperature and salinity of the fluid from stage I to stage II decreased significantly, recording intense meteoric water mixing. The temperature of the fluid decreased from stage II to stage III, while the salinity changed little, indicating that, except for minor meteoric water mixing, cooling of fluid is predominant. The temperature and salinity of the fluid from stage III to stage IV continued to decrease, recording the further mixing of meteoric water. From stage II to stage III, the evolution temperature of the fluid is basically consistent with the temperature indicated by trace elements (Nb, Ta, Ti) of cassiterite in the two stages. Fluid mixing may be the predominant mechanism for the minor Sn mineralization occurred in stage II. Fluid cooling may be the predominant mechanism for the abundant cassiterite precipitation in stage III, which is accompanied by redox reactions of Sn (II)-Cl complexes with As (III) and/or CO2 as potential oxidants, and acid neutralization of carbonate rocks. Combined with the cassiterite composition, it is indicated that the ore forming fluid of the Xianghualing deposit mainly derived from the highly evolved granitic magma in the region, and the genesis of cassiterite is consistent with that of typical skarn-type Sn deposits.