Characterization and corrosion properties of Ti‐O/HA composite coatings on Mg‐Zn alloy

Biodegradable magnesium alloys have been widely investigated in the field of biomaterials because they can be gradually dissolved and absorbed by the human body without long‐term existence. However, it was found that bare magnesium implants suffered from rapid corrosion. Surface modification is applied to improve the corrosion resistance and biocompatibility of magnesium implants. In this study, Ti‐O/HA composite coatings including typical flakes and nanofibers were fabricated on the Mg‐Zn alloy. The Ti‐O films were deposited on the magnesium alloy by direct current magnetron sputtering, and subsequently coated with HA flakes and nanofibers by electrochemical deposition, respectively. The obtained coatings were investigated by X‐ray diffraction, Fourier Transform Infrared spectroscopy and scanning electron microscopy. The corrosion resistance was evaluated by potentiodynamic polarization and hydrogen evolution tests in simulated body fluid at 37 °C. The results show that the compact Ti‐O films are composed of particles within the size of 100 nm, the outermost HA coatings are predominantly composed of HA and doped with Na⁺, Mg²⁺ ions and functional groups. The stronger diffraction and broader peak in nanofibers than typical flakes around 25.8° are ascribed to the preferential growth in orientation (002). The morphology of HA coatings changed from typical flakes into nanofibers with the addition of NaF, the mechanism to explain the difference is also discussed. The corrosion resistance was improved significantly by the coatings, the corrosion rates in the 10 days were 4.13, 1.77, 0.96 and 0.85 mm/y, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Electrochemical Sensing of Dissolved Hydrogen in Aqueous Solutions as a Tool to Monitor Magnesium Alloy Corrosion

Magnesium and its alloys have been the focus of the development of biodegradable metallic implant materials for years. Since water is reduced to form hydrogen gas during their corrosion, the amount and rate of hydrogen evolution, and therefore the dissolved hydrogen, could be used as an indicator to monitor and compare the corrosion. Here we report on a commercially available Clark‐Type amperometric microsensor and a simple potentiometric sensor for hydrogen to monitor the corrosion of a magnesium alloy in aqueous solutions. The sensors were compared using rare‐earth containing Mg alloy discs (Mg with 4 % Y, 2 % Nd, 0.5 % Ga, 0.5 % Dy) immersed in phosphate buffered saline (pH 7.4) and 3.5 % NaCl.     

Shadow Mask Templates for Site‐Selective Metal Exchange in Magnesium Porphyrin Nanorings

Molecular templates can be used in many different ways to control the outcome of chemical reactions. Herein, we present a new type of template‐directed synthesis. We show that templates can be used as shadow masks: The shape of the template becomes imprinted on the product because reactions only occur at sites not masked by the template. We demonstrate this effect by using oligopyridine templates to dictate the sites of demetalation when a magnesium porphyrin nanoring is treated with acid. Magnesium centers that are coordinated to the template are protected whereas uncoordinated magnesium centers are removed. After site‐selective demetalation, the template can be removed, and other cations, such as zinc(II) and copper(II), can be inserted into the free‐base porphyrin centers. This strategy provides a simple route to a wide range of heterometalated porphyrin arrays.     

Self‐Assembly of Magnesium Hydride Clusters Driven by Chameleon‐Type Ligands

While magnesium hydride complexes are generally stabilized by hard, bulky N‐donor ligands, softer ligands with a broad variety of coordination modes are shown to efficiently adapt themselves to the large variety of Mg²⁺ centers in a growing magnesium hydride cluster. A P,N‐chelating ligand is introduced that displays coordination modes between that of enamide, aza‐allyl, and phosphinomethanide. Slight changes in the ligand bite angle have dramatic consequences for the structure type. The hitherto largest neutral magnesium hydride clusters are isolated either in a nonanuclear sheet‐structure (brucite‐type) or a dodecanuclear ring structure.     

Characterization and cytocompatibility of polydopamine on MAO‐HA coating supported on Mg‐Zn‐Ca alloy

Magnesium has been suggested as a potential biodegradable metal for the usage as orthopaedic implants. However, high degradation rate in physiological environment remains the biggest challenge, impeding wide clinical application of magnesium‐based biomaterials. In order to reduce its degradation rate and improve the biocompatibility, micro‐arc oxidation coating doped with HA particles (MAO‐HA) was applied as the inner coating, and polydopamine (PDA) film was synthesized by dopamine self‐polymerization as the outer coating. The microstructure evolution of the coating was characterized using scanning electron microscopy (SEM), atomic force microscope (AFM), X‐ray diffraction analyses (XRD), Fourier transform infrared spectroscopy (FT‐IR), and X‐ray photoelectron spectroscopy (XPS). The results showed that PDA film had covered the entire surface of MAO‐HA coating and the pore size of MAO‐HA coating decreased. The root mean square (RMS) roughness of PDA/MAO‐HA coatings was approximately 106.46 nm, which was closer to the optimum surface roughness for cellular attachment as compared with MAO‐HA coatings. Contact angle measurement indicated that the surface wettability had been transformed from hydrophobic to hydrophilic due to the introduction of PDA. The PDA/MAO‐HA coatings exhibited better corrosion resistance in vitro, with the self‐corrosion potential increasing by 150 mV and the corrosion current density decreasing from 2.09 × 10^?5 A/cm ² to 1.46 × 10^?6 A/cm ² . In hydrogen evolution tests, the corrosion rates of the samples coated with PDA/MAO‐HA and MAO‐HA were 4.40 and 5.95 mm/y, respectively. MTS assay test and cell‐surface interactions experiment demonstrated that PDA/MAO‐HA coatings exhibited good cellular compatibility and could promote the adhesion and proliferation of MC3T3‐E1 cells.     

Magnesium‐Catalyzed Hydroboration of Terminal and Internal Alkynes

A magnesium‐catalyzed hydroboration of alkynes providing good yields and selectivities for a wide range of terminal and symmetrical and unsymmetrical internal alkynes has been developed. The compatibility with many functional groups makes this magnesium catalyzed procedure attractive for late stage functionalization. Experimental mechanistic investigations and DFT calculations reveal insights into the reaction mechanism of the magnesium catalyzed protocol.     

Biological effects of magnesium particles degradation on UMR-106 cell line: influence of fluoride treatments

Mg-based materials are promising for orthopedic, dental, and cardiovascular applications but their high degradation rate in vivo (release of Mg ions and debris particles) is cause of great concern. Protective treatments involving fluoride conversion coatings have been proposed in order to reduce corrosion rates. The aim of this study was to evaluate Mg debris biodegradation and its possible cytotoxic effects on osteoblastic cells in situ. Neutral Red dying and Acridine Orange staining techniques were used as endpoints to analyse the cytotoxic effects at 100-2000 μg/mL concentration range. Results showed a marked variation of Mg ion concentration in the culture medium after different exposure periods (1, 2, or 24h). Interestingly, the release rate of magnesium ions was dependent on the presence or absence fluoride treatment. Adverse effects induced by ≥1000 μg/mL MP doses and Mg ion concentrations higher than 480 μg/mL were observed on cells. Results showed significant differences between the concentration of Mg ions in the presence and absence of cells. This fact reveals a dynamic equilibrium mediated by Mg ion input and output in the cells that leads to the change in MP corrosion rates. Fluoride release from conversion coatings did not show cytotoxic effects.     

镁在人体模拟液中的腐蚀行为

探索了镁在人工人体模拟Hank溶液中的腐蚀行为, 发现镁在模拟液中的极化行为与在一般NaCl水溶液中相似. 电化学阻抗谱测试结果表明, 镁在模拟液中的一些具体反应对腐蚀的贡献可能比在NaCl溶液中的小. 在模拟液中, 镁腐蚀速度随时间不断变快. 这可能与模拟液中可抑制腐蚀的离子的消耗有关. 镁腐蚀产生了大量的氢气, 并使模拟液碱化. 这些结果表明, 镁虽然极有希望用作可消溶吸收的人体植入材料, 但仍有一些困难需要克服, 解决这些困难的关键在于适当地控制其腐蚀速度.     

Magnesocene‐Based Electrolytes: A New Class of Electrolytes for Magnesium Batteries

Unlike ferrocene, bis(η⁵‐cyclopentadienyl)magnesium (magnesocene, MgCp₂) is slightly dissociated in solvents, such as ethers, resulting in electrolyte solutions with low conductivity. MgCp₂/tetrahydrofuran solutions make possible reversible magnesium plating and stripping with low over‐potentials for many cycles. The Mg deposits appear with a cauliflower‐like morphology. IR and NMR spectroscopy confirm that the electrolyte is stable and not decomposed during prolonged cycling. The anodic stability limit is in the range of 1.5 V (at platinum) and 1.8 V versus Mg/Mg²⁺ (at stainless steel), which may be sufficient for low‐voltage cathode materials. MgCp₂ is a first example of a completely new class of halide‐free electrolytes, which may open up a new research direction for future magnesium metal and magnesium‐ion batteries.     

Alkali‐Metal‐Mediated Magnesiations of an N‐Heterocyclic Carbene: Normal,Abnormal, and “Paranormal” Reactivity in a Single Tritopic Molecule

Herein the sodium alkylmagnesium amide [Na₄Mg₂(TMP)₆(nBu)₂] (TMP=2,2,6,6‐tetramethylpiperidide), a template base as its deprotonating action is dictated primarily by its 12 atom ring structure, is studied with the common N‐heterocyclic carbene (NHC) IPr [1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene]. Remarkably, magnesiation of IPr occurs at the para‐position of an aryl substituent, sodiation occurs at the abnormal C4 position, and a dative bond occurs between normal C2 and sodium, all within a 20 atom ring structure accommodating two IPr²⁻. Studies with different K/Mg and Na/Mg bimetallic bases led to two other magnesiated NHC structures containing two or three IPr⁻ monoanions bound to Mg through abnormal C4 sites. Synergistic in that magnesiation can only work through alkali‐metal mediation, these reactions add magnesium to the small cartel of metals capable of directly metalating a NHC.     

Solvothermal Synthesis and Crystal Structure of One‐Dimensional Chains of Anhydrous Zinc and Magnesium Formate

Reaction of the zinc or magnesium formate dihydrates in formic acid under solvothermal conditions results in the formation of single crystals of the anhydrous metal(II) formates β‐Zn(OOCH)₂ and β‐Mg(OOCH)₂. Both structures form one‐dimensional chains of μ‐oxygen‐bridged metal atoms. Single crystal diffraction studies reveal that β‐zinc formate represents the first structure in which chains of oxygen‐bridged metal atoms are connected by alternating single, double and triple oxygen atom bridges resulting in the first observation of corner, edge and face sharing coordination octahedra within a single chain. Polycrystalline material can be obtained by dehydration reaction of zinc formate dihydrate. β‐magnesium formate is the crystalline product that is obtained by annealing the amorphous intermediate phase after dehydration of magnesium formate dihydrate.     

Strukturen von polaren Magnesiumorganylen: Synthese und Struktur von Basen‐Addukten des Bis(cyclopentadienyl)magnesiums

Structures of Polar Magnesium Organyls: Synthesis and Structure of Base Adducts of Bis(cyclopentadienyl)magnesium Eight donor‐acceptor complexes of bis(cyclopentadienyl)magnesium ( 1 ) with N‐ and O‐donor Lewis bases have been synthesized and characterized by X‐ray structure analysis. With acetonitrile, dimethoxyethane, diethyleneglycoldimethylether, dioxane, and tetramethylethylenediamine simple 1:1 adducts are formed ( 2 – 6 ). In some cases a change of the hapticity of one cyclopentadienylring from η⁵ to η² or η¹ is observed ( 4 – 6 ). In the adduct with pentamethyldiethylenetriamine ( 7 ) one C₅H₅‐ring is removed from the magnesium atom forming the cation [Mg(C₅H₅)(PMDTA)]⁺ and an uncoordinated five‐ring anion. With the crown ether 15‐crown‐5 the two ionic Mg compounds 8 and 9 are formed which have a [Mg(15‐crown‐5)L₂]²⁺‐cation [L = pyridine, THF] and two uncoordinated cyclopentadienyl anions. Cyclopentadienyl‐methyl‐magnesium reacts with 15‐crown‐5 to the salt [Mg(CH₃)(15‐crown‐5)]⁺ C₅H₅^? ( 10 ) which has also a free cyclopentadienyl anion.     

Magnesium Halide‐promoted Ring‐opening Reaction of Cyclic Ether in the Presence of Phosphine Halide

A new route to the direct preparation of H‐phosphinate esters has been explored. The ring‐opening reaction of cyclic ether (tetrahydrofuran or tetrahydropyrane) was carried out with magnesium halide in the presence of phosphine halide (PRCl₂ or PCl₃). The process is straightforward and all the reagents are relatively cheap and readily available. Magnesium halide‐mediated THF ring‐opening (S_N2@C) and the subsequent S_N2@P elementary reactions that giving rise to the intermediate of haloalkyl phosphinates have been discussed based on our experimental findings ( Path I : S_N2@C−+S_N2@P). Another possible route, the direct S_N2 between THF (nucleophile) and phosphine halide (electrophile) that followed by THF ring opening by halide dissociated from phosphine halide ( Path II: S_N2@P−+S_N2@C), was also proposed. However, path II is the least likely reaction path because neutral THF is not a good nucleophile. H‐phosphinate esters could be readily available in the subsequent hydrolysis process. Considering the ionic bond strength in magnesium halides and the nucleophilicity of halides dissociated from MgX₂ in protic solvents like water, MgBr₂ is recommended for ring‐opening reactions of cyclic ethers.     

β‐Diketiminate Stabilized Magnesium Hydroxide,Heterobimetallic, and Halide Complexes: Synthesis and X‐ray Structural Studies

The controlled hydrolysis of heteroleptic magnesium amide, LMgN(SiMe₃)₂ (L = CH[C(Me)N(2,6‐iPr₂C₆H₃)]₂) with water afforded the corresponding hydroxide [LMg(OH)·THF]₂ as air and moisture sensitive compound. The presence of a sterically bulky β‐diketiminate ligand prevents the self‐condensation reaction of this hydroxide complex. Single crystal X‐ray analysis shows that the hydroxide is dimeric in the solid state. Reaction of the magnesium amide or LMg(Me)·OEt₂ with LAlMe(OH) generates the heterobimetallic species containing the Mg–O–Al moiety. Additionally, the reaction of methylmagnesiumchloride with the free ligand leads to complex L′MgCl (L′ = CH[Et₂NCH₂CH₂N(CMe)]₂). As revealed by the crystal structure, L′MgCl is a solvent free monomeric magnesium chloride complex that is analogues to the Grignard reagent.     

Microelectrode Sensing of Adenosine/Adenosine‐5′‐triphosphate with Fast‐Scan Cyclic Voltammetry

Adenosine and adenosine‐5′‐triphosphate (ATP) are important extracellular signaling molecules. Here, we studied adenosine and ATP using fast‐scan cyclic voltammetry at carbon‐fiber microelectrodes. Although ATP and adenosine have similar oxidation potentials, ATP oxidation current was highly dependent on buffer pH and divalent cation concentrations but adenosine current was not. Therefore, they can be distinguished by adding a divalent cation chelator or calibrating electrodes at different pH values. The enzymatic degradation of adenosine by adenosine deaminase was monitored in a mixture of adenosine and ATP in presence of EDTA (ethylenediaminetetraacetate). This sensing method is promising for enzyme kinetics or in vitro studies.     

Single‐Molecule Sensing of Environmental pH—an STM Break Junction and NEGF‐DFT Approach

Sensors play a significant role in the detection of toxic species and explosives, and in the remote control of chemical processes. In this work, we report a single‐molecule‐based pH switch/sensor that exploits the sensitivity of dye molecules to environmental pH to build metal–molecule–metal (m‐M‐m) devices using the scanning tunneling microscopy (STM) break junction technique. Dyes undergo pH‐induced electronic modulation due to reversible structural transformation between a conjugated and a nonconjugated form, resulting in a change in the HOMO–LUMO gap. The dye‐mediated m‐M‐m devices react to environmental pH with a high on/off ratio (≈100:1) of device conductivity. Density functional theory (DFT) calculations, carried out under the non‐equilibrium Green’s function (NEGF) framework, model charge transport through these molecules in the two possible forms and confirm that the HOMO–LUMO gap of dyes is nearly twice as large in the nonconjugated form as in the conjugated form.     

2,3,4,5‐Tetraethylpentela‐cyclo‐pentadienide (2,3,4,5‐Tetraethylpentolide) der Erdalkalimetalle Magnesium,Calcium, Strontium und Barium

2,3,4,5‐Tetraethylpentela‐cyclo‐pentadienides (2,3,4,5‐Tetraethylpentolides) of the Alkaline Earth Metals Magnesium, Calcium, Strontium, and Barium The reaction of bis(cyclopentadienyl)‐1‐zircona‐2,3,4,5‐tetraethyl‐cyclo‐penta‐2,4‐diene with ECl₃ (E = P, As, Sb) yields 1‐chloro‐tetraethylphosphole ( 1 ), ‐arsole ( 2 ) und ‐stibole ( 3 ). The reduction of these pentoles gives in a first step the corresponding octaethyldiphospholyle ( 4 ), ‐diarsolyle ( 5 ) and ‐distibolyle ( 6 ). Further reduction of these dipentolyles with magnesium and calcium leads in the presence of the corresponding dihalides to the formation of magnesium chlorid (2,3,4,5‐tetraethylphospholide) ( 7 ), ‐arsolide) ( 8 ) and ‐stibolide) ( 9 ) and calcium chlorid (2,3,4,5‐tetraethylphospholide) ( 10 ), ‐arsolide) ( 11 ) and ‐stibolide) ( 12 ), respectively. In the absence of alkaline earth metal dihalides no reaction is observed. For the larger metals strontium and barium the reduction of the dipentolyles succeeds in THF also without the addition of halides and the 1,1′‐dipentela‐octaethylstrontocene [E = P ( 13 ), As ( 14 ), Sb ( 15 )] as well as ‐barocene [E = P ( 16 ), As ( 17 ), Sb ( 18 )] are isolated halogen‐free. The strontocene crystallizes as a THF adduct whereas the barocene precipitates coligand‐free but with a chain structure. The molecular structures of 7 , 10 , and 16 are discussed.     

Application of a C?C Bond‐Forming Conjugate Addition Reaction in Asymmetric Dearomatization of β‐Naphthols

A C C bond‐forming conjugate reaction was successfully applied to the enantioselective dearomatization of β‐naphthols. A C(sp2) C(sp3) bond is formed by using propargylic ketones as reactive partners. Good to excellent Z/E ratios and ee values were obtained by employing an in situ generated magnesium catalyst. Further transformations of the Z‐configured C C double bond in the products were achieved under mild reaction conditions. Moreover, the stereocontrolling element of this magnesium‐catalyzed dearomatization reaction was explored by computational chemistry.     

体外电化学测试对镁合金体内降解行为的预测

可生物降解镁合金因同时具有优良的生物相容性和力学性能,在生物医学界显示出其作为新型骨科内植入物的巨大潜在优势和市场前景。目前,作为制约镁合金医用产业化的关键因素,即过快的降解速率已经成为研究重点。本文回顾了体外电化学测试技术对镁合金抗腐蚀性能的研究,并分析了模拟腐蚀体系对镁合金腐蚀行为的影响;同时评估了电化学测试方法作为快速有效预测镁合金体内降解性能前期分析手段的可行性与局限性。最后,对如何发展更合理的体外电化学测试技术来预测镁合金体内降解提出了可能的解决方法及构思。     

Monomeric Magnesium and Calcium Complexes containing the Rigid,Dianionic 1, 2‐Bis[(2, 5‐di‐tert‐butylphenyl)imino]acenaphthene (dtb‐BIAN) and 1, 2‐Bis[(2‐biphenyl)imino]acenaphthene (bph‐BIAN) Ligands

The new rigid bidentate nitrogen ligands 1, 2‐bis[(2, 5‐di‐tert‐butylphenyl)imino]acenaphthene ( 1 ) (dtb‐BIAN) and 1, 2‐bis[(2‐biphenyl)imino]acenaphthene ( 2 ) (bph‐BIAN) have been synthesized by condensation of 1, 2‐acenaphthylenedione with 2, 5‐di‐tert‐butylaniline and 2‐aminobiphenyl, respectively. Reduction of 1 and 2 with magnesium and calcium results in the formation of the monomeric metal complexes [(dtb‐BIAN)Mg(THF)₂] ( 3 ), [(bph‐BIAN)Mg(DME)₂] ( 4 ), and [(bph‐BIAN)Ca(THF)₃] ( 5 ). Compounds 1 — 5 have been characterized by C/H analyses, IR, ¹H NMR, and ¹³C NMR spectra, the structures of 2 , 3 , and 5 have been estimated by single crystal X‐ray diffraction.