μ-Biphenyl-3,3′,4,4′-tetra­carboxyl­ato-κ2 O 3:O 3′-bis­[triaqua­(2,2′-bipyridyl-κ2 N,N′)nickel(II)] hexa­hydrate

The asymmetric unit of the title complex, [Ni2(C16H6O8)(C10H8N2)2(H2O)6]·6H2O, contains one NiII atom, one 2,2′-bipyridine ligand, three coordinated water mol­ecules, one-half of a fully deprotonated biphenyl-3,3′,4,4′-tetra­carboxyl­ate anion and three lattice water mol­ecules. The NiII atom displays a distorted NiN2O4 octa­hedral coordination formed by one carboxyl­ate O atom, three water O atoms and two N atoms of the chelating ligand. The complete biphenyl-3,3′,4,4′-tetra­carboxyl­ate ligand displays inversion symmetry and links two symmetry-related NiII atoms into a binuclear complex. Neighbouring complex mol­ecules are linked through O—H⋯O hydrogen bonds into a three-dimensional structure. Additional O—H⋯O hydrogen bonds between the lattice water mol­ecules help to consolidate the crystal packing

Acinetobacter baumannii: an evolving and cunning opponent

Acinetobacter baumannii is one of the most common multidrug-resistant pathogens causing nosocomial infections. The prevalence of multidrug-resistant A. baumannii infections is increasing because of several factors, including unregulated antibiotic use. A. baumannii drug resistance rate is high; in particular, its resistance rates for tigecycline and polymyxin—the drugs of last resort for extensively drug-resistant A. baumannii—has been increasing annually. Patients with a severe infection of extensively antibiotic-resistant A. baumannii demonstrate a high mortality rate along with a poor prognosis, which makes treating them challenging. Through carbapenem enzyme production and other relevant mechanisms, A. baumannii has rapidly acquired a strong resistance to carbapenem antibiotics—once considered a class of strong antibacterials for A. baumannii infection treatment. Therefore, understanding the resistance mechanism of A. baumannii is particularly crucial. This review summarizes mechanisms underlying common antimicrobial resistance in A. baumannii, particularly those underlying tigecycline and polymyxin resistance. This review will serve as a reference for reasonable antibiotic use at clinics, as well as new antibiotic development

Ligand field effect tuned magnetic behaviors of two chain compounds based on MnIII3O units: From slow magnetic relaxation to metamagnetism

Two chain compounds built with anti-anti acetate bridged Mn III3O units, [Mn3O(Clppz)3(EtOH) 4(OAc)]n (1) and [Mn3O(Clppz) 3(EtOH)2(OAc)]n (2), were synthesized and characterized. The magnetic studies indicate that 1 is a single-chain magnet with two slow magnetization relaxation processes which has for the first time been found in this type of chain complex, while 2 shows a field-induced metamagnetic behavior. The quite different magnetic behaviors resulted from the different number of coordinated ethanol molecules on the MnIII 3O unit, four ethanol molecules for 1, and two ethanol molecules for 2. The best fittings to the experimental magnetic susceptibilities gave J 1 = -2.72 cm-1, J2 = -4.34 cm-1, zJ = 1.24 cm-1 for 1 and J1 = -5.91 cm-1, J 2 = -0.98 cm-1, zJ = 1.71 for 2 above 30 K. The positive zJ values indicate the presence of weak ferromagnetic interactions between the trinuclear units via acetate bridges in 1 and 2. ? The Royal Society of Chemistry 2013

Mechanism for Selective Binding of Aromatic Compounds on Oxygen-Rich Graphene Nanosheets Based on Molecule Size/Polarity Matching

Selective binding of organic compounds is the cornerstone of many important industrial and pharmaceutical applications. Here, we achieved highly selective binding of aromatic compounds in aqueous solution and gas phase by oxygen-enriched graphene oxide (GO) nanosheets via a previously unknown mechanism based on size matching and polarity matching. Oxygen-containing functional groups (predominately epoxies and hydroxyls) on the nongraphitized aliphatic carbons of the basal plane of GO formed highly polar regions that encompass graphitic regions slightly larger than the benzene ring. This facilitated size match–based interactions between small apolar compounds and the isolated aromatic region of GO, resulting in high binding selectivity relative to larger apolar compounds. The interactions between the functional group(s) of polar aromatics and the epoxy/hydroxyl groups around the isolated aromatic region of GO enhanced binding selectivity relative to similar-sized apolar aromatics. These findings provide opportunities for precision separations and molecular recognition enabled by size/polarity match–based selectivity

Kinetics and mechanism of the dehydration of HCO₃^- catalyzed by Zn(II) and Cu(II) complexes of novel tripod ligand

1172-1175The observed rate constants of the dehydration reaction of HCO3- catalyzed by Zn(II) and Cu(II) complexes of novel tripod ligand have been measured both in 70% (v/v) alcohol solution and in aqueous solution by stopped-flow method. Reasonable explanation for the difference between the rate constants in 70% (v/v) alcohol solution and in aqueous solution has been proposed. The direction of reaction curve is changed in aqueous solution when the pH is greater than 7.6. The results are discussed and the mechanism is proposed

Multiple interactions in Zn(II) ternary systems of phenanthroline bridging polyaza ligand and adenosine, 5'-triphosphate

287-291The stability of Zn(II) ternary complexes of phenanthroline bridging polyaza ligand and ATP have been determined using potentiometric pH titrations, 1H and 31P NMR spectra. Protonated metal complexes interact with the polyphosphate chain of the nucleotide substrate by coordination, electrostatic and H-bonding interactions, as well as stacking interactions bctween the phenanthroline moiety of L and the nucleoside residue of ATP. Moreover, ion-π-donor, hydrophobic and even vander Waals interactions may exist in the ternary systems. The recognition of nucleotides is promoted by adding Zn(II) to the receptor/substrate system. Zn(II) acts as n "messenger" to bridge the polyamine and ATP, which in turn leads to competition between the mixed ligands in binding zinc ion. Thus, the supramolecules formed by self-assembly are good models to mimic the active center of the ATPase

La(III) complex of phenanthroline bridging polyamine as efficient catalyst for the hydrolysis of ATP

1076-1080The hydrolysis of ATP catalyzed by protonated ligand 2, 9-di[(2'-ethylamino)ethylene-aminomethyl]-1, 10-phenanthroline·4HCl.H2O(L) or its La(III) complex has been studied at pH 7.6 using 31P NMR spectroscopy. The two systems have a rate of 12.1×10-4 mol.dm-3 and 159×10-4 mol.dm-3 , which is about 5- and 59-fold as fast as that of free ATP respectively. La(III) complex of L is a more efficient catalyst for ATP hydrolysis than metal ion alone, which has a rate enhancement ratio about 5. High catalytic efficiency has been achieved through the effective activation of ATP by La(III) complex and the availability of a good intramolecular nucleophile. The phosphoramidate intermediate at 2.88 ppm in L/ATP system has not been observed in La(III)/L/ATP system. The mechanism for ATP hydrolysis catalyzed by complex of ‘‘hard’’ metal ion has been given. The effects of metal ion mediated by polyaza ligand in controlling the recognition of the substrate and the attacking on phosphorous counter have been discussed

Synthesis and magnetic property of a one-dimensional 3d-4f heterometallic triple-chain complex

A heterometallic triple-chain complex [CuTb2(mal)(4)(H2O)(6)]center dot 2H(2)O (CuTb2, H(2)mal = D-malic acid) and its isomorphous CuY2 and ZnTb2 have been prepared and characterized, whose magnetic properties are studied by comparison with its analogues. The results indicate that the Cu center dot center dot center dot Tb interactions in CuTb2 are antiferromagnetic. Published by Elsevier B.V.National Natural Science Foundation of China [21001073, 20971084]; Excellent Young Teacher Foundation of Shanghai Municipal Education Commission; Innovation Foundation of Shanghai Universit

Chitosan Nanoparticles to Enhance the Inhibitory Effect of Natamycin on Candida albicans

Fungal keratitis is a stubborn fungal infection that is widespread worldwide. It can even affect the health and life of a patient. At present, natamycin (NAT) is the first-line drug in the treatment of fungal keratitis, despite its disadvantages of clinical use, such as low drug bioavailability and poor water solubility. Herein, inspired by the adhesion properties of chitosan and its excellent drug loading and antifungal properties, we designed simple natamycin-chitosan nanoparticles (NAT-NPs) to investigate the feasibility of chitosan with NAT for eye treatment. Results showed that the NAT-NPs increased the antifungal effect of NAT due to the antifungal feature of chitosan NPs. Therefore, NAT-NPs are expected to become potential candidates for the treatment of fungal keratitis due to their high bacteriostasis