Structure and mechanical properties of pincers for freshwater lobster

The mineral phases and structure of pincer for the freshwater lobster were analyzed and observed by using X-ray diffraction and field-emission scanning electronic microscope with energy dispersive spectroscopy, and the mechanical properties of pincer were determined by using nano-indenter and micro-tribometer. The results showed that the pincers contained Ca, Mg, C, O, Na, etc. elements and there were many amorphous mineral phases in the lobster pincers. There were many concave hollows and convex domes with seta on the surface of pincer, and some spines were observed on the surface of seta, which exhibited non-smooth surface. The exoskeleton of pincer consisted of epicuticle, exocuticle and endocuticle, and the microstructure of exocuticle and endocuticle displayed the twisted plywood structure with chitin protein fibers. The mean hardness and elastic modulus on the surface of fresh pincers were 0.27 GPa and 5.28 GPa, respectively. With the increase in distance from the surface, the hardness and elastic modulus all decreased gradually. This indicated that the transition of hardness and elastic modulus occurred from exocuticle to endocuticle. When the heat treatment temperature was lower than 200°C, the values of hardness and elastic modulus fluctuated slightly, while they increased at the temperature beyond 200°C. As the pincers slid against Si3N4 balls in water and air, the friction coefficients in water were higher than those in air. The research could provide a bio-inspired basis for the structural design of composite materials and anti-friction surface.

髋关节撞击综合征

髋关节撞击综合征是一种常见的、可引起慢性髋关节疼痛及髋关节屈曲和内收受限的疾病,是髋关节骨性关节炎常见的病因。根据不同的解剖异常可分为Cam凸轮碰撞和Pincer钳形碰撞两型。髋关节X线正位片可观察到股骨头颈之间的凹陷度不足,表现为股骨头突起部向外侧伸延、头与颈间的凹陷减少或消失。CT及MRI能发现不明显的股骨头颈交界处及髋臼的解剖异常。而显示关节盂缘病变和邻近软骨病变及软骨下囊性变和滑膜疝,MRI较X线平片及CT更准确。主要就髋关节撞击综合征的临床、分型及影像学表现予以综述。

井底螺杆马达试验台架夹紧钳的设计和计算

对井底螺杆马达试验台架的螺旋夹紧钳所受的切向和轴向载荷进行了力学分析,推导出了切向和轴向总夹紧力的计算式,得出单只夹紧钳的设计参数。另外还提出了主要部件的应力分析假设和设计依据。

Current concepts in management of femoroacetabular impingement

Femoroacetabular impingement(FAI)is an increasingly recognized condition,which is believed to contribute to degenerative changes of the hip.This correlation has led to a great deal of interested in diagnosis and treatment of FAI.FAI can be divided into two groups:cam and pincer type impingement.FAI can lead to chondral and labral pathologies,that if left untreated,can progress rapidly to osteoarthritis.The diagnosis of FAI involves a detailed history,physical exam,and radiographs of the pelvis.Surgical treatment is indicated in anatomic variants known to cause FAI.The primary goal of surgical treatment is to increase joint clearance and decrease destructive forces being transmitted through the joint.Treatment has been evolving rapidly over the past decade and includes three primary techniques:open surgical dislocation,mini-open,and arthroscopic surgery.Open surgical dislocation is a technique for dislocating the femoral head from the acetabulum with a low risk of avascular necrosis in orderto reshape the neck or acetabular rim to improve joint clearance.Mini-open treatment is performed using the distal portion of an anterior approach to the hip to visualize and to correct acetabular and femoral head and neck junction deformities.This does not involve frank dislocation.Recently,arthroscopic treatment has gained popularity.This however does have a steep learning curve and is best done by an experienced surgeon.Short-to mid-term results have shown relatively equal success with all techniques in patients with no or only mild evidence of degenerative changes.Additionally,all techniques have demonstrated low rates of complications.

铜基N-杂环Pincer配合物的合成、表征以及对芳香化合物的催化研究

将Pincer形配体2,6-双(5-叔丁基-1H-吡唑-3-基)吡啶(H 2 L)与CuBr 2反应,合成一种新的配合物[H 2LCuBr 2](H 2L=2,6-双(5-叔丁基-1H-吡唑-3-基)吡啶),并进行元素分析、紫外-可见(UV-Vis)光谱、傅里叶变换红外光谱(FT IR)和热重分析等表征.在70℃条件下的乙腈溶液中,以过氧化氢为氧化剂,以H 2 LCuBr 2为催化剂,分别对芳族底物如异丙苯、苯乙烯、α-甲基苯乙烯和苯甲醇进行了氧化催化活性测试.实验证明该催化剂对苯甲醇、苯乙烯和α-甲基苯乙烯的氧化表现出良好的催化活性,主要产品分别为苯甲醛、苯甲醛和苯乙酮.苯甲醇在8 h内转化率为51.77%,选择性95.46%;苯乙烯在4 h内转化率为94.84%,选择性81.07%;α-甲基苯乙烯在4 h内转化率为99.80%,选择性97.91%.通过对苯甲醇氧化反应的质谱跟踪监测,提出了合理的催化反应机理.

Synthesis and reactivity of cobalt dinitrogen complex supported by nonsymmetrical pincer ligand

A nonsymmetrical PNN pincer ligand[6-(^(t)Bu_(2)PNH)C_(5)H_(4)N-2-(3-Mes)C_(3)H_(2)N_(2)]and its corresponding cobalt-N_(2)complex were synthesized and characterized.By the stoichiometric reaction of the PNN ligand lithium salt with CoCl_(2),the complex 3,(PNN)CoCl,was obtained.Then,reduction of 3 with NaBHEt3under a dinitrogen atmosphere yielded complex 5,(PNN)Co(Ⅰ)(η^(1)-N_(2)).Single-crystal X-ray analysis,IR spectrum,and DFT calculations revealed that the dinitrogen in 5 was only weakly reduced by the cobalt center.The reactions of 5 with carbon monoxide and 2,6-dimethylphenyl isocyanide gave carbonyl and isocyanide complexes 6 and 7 with the release of N_(2),respectively.Furthermore,these cobalt complexes,especially complex 5,demonstrated the capacity to convert dinitrogen to N(TMS)_(3)with moderate efficiency.

Aromatic and olefinic C–H alkenylation by catalysis with spirocyclic NHC Ru(Ⅳ) pincer complex

Catalyst innovation lies at the heart of transition-metal-catalyzed reaction development. In this article, we have explored the C(sp2)–H alkenylation activity with novel spirocyclic N-heterocyclic carbene(NHC)-based cyclometalated ruthenium pincer catalyst system, SNRu-X. After screening catalyst and condition, a high valent Ru(Ⅳ) dioxide(X = O_(2)) species has demonstrated superior reactivity in the catalytic alkenylation of aromatic and olefinic C–H bonds with unactivated alkenyl bromides and triflates. This reaction has achieved the easy construction of a wide range of(hetero)aromatic alkenes and dienes, in good to excellent yields with exclusive selectivity. Preliminary mechanistic studies indicate that this reaction may proceed through a single electron transfer(SET) triggered oxidative addition, by doing so, providing valuable complementary to classical alkenylation reactions that are dependent on activated alkenyl precursors.

Pincer Ru with a single stereogenic identity for highly efficient asymmetric transfer hydrogenation of ketones

The asymmetric reduction of carbonyl compounds by means of the Ru-chiral diphosphine-chiral diamine catalysts is widely useful in organic synthesis where high levels of enantioselectivities have been attributed to multiple ligand chiral elements as well as essential stereochemical matching synergies within them.Described here is the design and discovery of new pincer-type Ru-catalysts that feature only single stereogenic element within ligands,yet the such significantly simplified structure is demonstrated to be well competent for effecting asymmetric reductions as well as kinetic resolutions over a broad range of highly functionalized ketones/alcohols,including heteroaryl substituted substrates that were challenging by known catalyst systems.Alcohols were furnished not only in excellent enantioselectivities,but with turnover numbers(up to 100,000 TONs)that reach the highest levels known to date in asymmetric transfer hydrogenation of ketones.This work should help shed light on the intricate origin of enantioselection in these important processes,and further stimulate rational understanding as well as optimization of chiral catalysts towards efficiency and simplicity.

Directly Knitted Ruthenium Pincer Complexes with Enhanced Activity as Recyclable Single-Site Catalysts for Hydrogenation of CO_(2)to Methanol

Considering the importance of the valorization of CO_(2),a number of phosphine-containing ruthenium pincer complexes have been successfully heterogenized using a“direct knitting”strategy without any premodification.The resulting porous organometallic polymers(POMPs)with high specific-surface areas,hierarchical pores,and uniformly dispersed Ru single-sites exhibited outstanding catalytic activity toward the N-formylation of diverse amines with CO_(2).Besides excellent turnover number(TON,5×10^(5))and turnover frequency(TOF,5592 h-1),the obtained formamides were readily hydrogenated to methanol with the same catalyst.Consequently,an amine-assisted direct hydrogenation system of CO_(2)to methanol was established by POMPs with higher activity and TON(1.46×10^(4))than their molecular precursors,shedding light on the direct valorization of CO_(2)and carbon neutral recycling.

Catalytic alkane dehydrogenations

Olefins find widespread applications in the synthesis of polyolefins and fine chemicals. With an increasing demand for olefins, the technologies for alkane dehydrogenation have drawn much attention. Several types of heterogeneous catalysts have found applications in industry for the dehydrogenation of light alkanes, mainly ethane, propane, and butane. In the past three decades, a number of transition-metal complexes,particularly pincer-ligated iridium complexes, have been developed as the homogeneous catalysts for alkane dehydrogenations. The homogeneous catalyst systems operate under much milder conditions compared with the heterogeneous systems, and some systems exhibit good activity and high regioselectivity in dehydrogenation of alkanes longer than butane.

Colorimetric recognition of melamine in milk using novel pincer zinc complex stabilized gold nanoparticles

A convenient colorimetric approach for visual detection of melamine in raw milk was realized by using gold nanoparticles(AuNPs)stabilized by an unsymmetrical terpyridyl zinc complex with a thymine fragment at one terminal and a quaternary ammonium salt at the other.Even without pre-addition of melamine or relative additives,obvious color change from red to blue was observed by naked eye in the presence of trace amount of melamine,which was attributed to the alternation of aggregation state of AuNPs caused by the selective binding between the thymine fragment and melamine via triple hydrogenbonding interactions.Remarkably,the detection limit for melamine was as low as 2.4 ppb,providing a highly sensitive and efficient approach for the visual detection of melamine.

Development of unique dianionic Ir(Ⅲ) CCC pincer complexes with a favourable spirocyclic NHC framework

A new type of dianionic Ir(Ⅲ) CCC pincer complexes(SNHC-Ir, 1a–1c) is successfully designed and synthesized by developing a one-step methodology, which involves an initial coordination of Ir(I) with the NHC and subsequent metallation of double sp2C–H bonds. This method is considerably useful over those reported by using strong coordination ligand or carbonic anion exchange,and would provide an alternative efficient template of organometallics synthesis. Experimental and density functional theory(DFT) calculation results indicate that the spirocyclic framework is a favourable factor for the facile formation and stabilization of these complexes. Primary investigation shows that chloride 1b can well catalyze homo and hetero addition of styrene derivatives and remote olefin isomerization, which represents the first catalytic application of the dianionic CCC pincer complexes.

A self-catalytic role of methanol in PNP-Ru pincer complex catalysed dehydrogenation

Extracting hydrogen from methanol is a safe and cost-efficient strategy for fuel supply. This process was realized recently at a mild condition with excellent efficiency by ruthenium pincer catalysts. Despite the experimental success, the associated mechanism remains under debate. With the aid of density functional theory(DFT) calculations, an updated and self-consistent mechanism which involves Me OH-catalysed dehydrogenation of ruthenium hydride intermediate and pre-protonation of the pincer ligand was present herein. This mechanism is kinetically favoured over the previously-proposed water- or formic- acid-participated ones and more consistent with the optimal experimental condition where strong base and neat methanol solvent are used.

Cobalt-catalyzed asymmetric hydrogenation of ketones:A remarkable additive effect on enantioselectivity

A chiral cobalt pincer complex,when combined with an achiral electron-rich mono-phosphine ligand,catalyzes efficient asymmetric hydrogenation of a wide range of aryl ketones,affording chiral alcohols with high yields and moderate to excellent enantioselectivities(29 examples,up to 93%ee).Notably,the achiral mono-phosphine ligand shows a remarkable effect on the enantioselectivity of the reaction.

Synthesis,characterization and reactivity of a neutral antimony(Ⅲ) complex

Pincer complexes are widely used in organometallic and coordination chemistry.The role of antimony as a central donor atom in pincer ligands has been extensively explored in recent years.Although phenylenediamine derived PXP(X=B,Al,C,Si,Ge,Sn,N) type ligands exhibit diverse reactivity,analogues species based on antimony have been reported less frequently.Herein,we report a new PSbP complex and evaluate its reactivity.These species will broaden the family of phenylenediamine derived pincer complexes.

Functional Organometallics

1 Results The lecture will address aspects of functional organometallics related to the development of novel organometallic materials.In chromium complexes of fused arenes-regio-and diastereoselectively accessible by chromium-templated benzannulation of arylcarbenes by alkynes[1]-a haptotropic migration of the chromium fragment along the π-face of fused arenes is controlled by both thermodynamics and the substitution pattern of the arene and the metal coligand sphere,and can be applied towards an organo...

Carbon-halogen bond activation by a structurally constrained phosphorus(Ⅲ)platform

Theσ-bond activation by main group element has received enormous attention from theoretical and experimental chemists.Here,the reaction of C-X(X=Cl,Br,I)bonds in benzyl and allyl halides with a pincer-type phosphorus(Ⅲ)species was reported.A series of structurally robust phosphorus(Ⅴ)compounds were formed via the formal oxidative addition reactions of C-X bonds to the phosphorus(Ⅲ)center.Density functional theory calculations show that the nucleophilic addition process is more favorable than the direct oxidative addition mechanism.Isomerization of bent structures of phosphorus(Ⅲ)compound to poorly nucleophilic compounds to undergo further C-X bond activation can be rationalized by frontier molecule orbital analysis.This study not only provides a deep understanding of the reactivity of phosphorus(Ⅲ)species but also demonstrates a potential of main group elements for the small-molecule activation.

Visual recognition of melamine in milk via selective metallo-hydrogel formation

A series of novel six-coordinated terpyridine zinc complexes,containing ammonium salts and thymine fragment at the two terminals,have been designed and synthesized,which can function as highly sensitive visualized sensors for melamine detection via selective metallo-hydrogel formation.After fully characterization by various techniques,the complementary triple-hydrogen-bonding between the thymine fragment and melamine,as well as π-π stacking interactions may be responsible for the selective metallo-hydrogel formation.In light of the possible interference aroused by milk ingredients(proteins,peptides and amino acids) and legal/illegal additives(urine,sugars and vitamins),a series of control experiments are therefore involved.To our delight,this visual recognition is highly selective,no gelation was observed with the selected milk ingredients or additives.Remarkably,this new developed protocol enables convenient and highly selective visual recognition of melamine at a concentration as low as 10 ppm in raw milk without any tedious pretreatment.

Synthesis of chiral 1,3-bis(1-(diarylphosphoryl)ethyl)-benzenes via Ir-catalyzed double asymmetric hydrogenation of bis(diarylvinylphosphine oxides)

A class of chiral 1,3-bis(diarylphosphinoethyl)benzenes, which are key intermediates for the synthesis of PCP-type chiral pincer ligands, were prepared in high diastereomeric ratios and excellent ee values via double asymmetric hydrogenation of the corresponding bis(diarylvinylphosphine oxide) substrates using a SpinPhox/Ir(I) complex as the catalyst. The hydrogenation product 5a was readily transformed into the corresponding borane-protected chiral PCP-type pincer ligand 7a with high enantiomeric excess, exemplifying a viable synthetic route to optically active chiral PCP pincer ligands.

Pincer iridium(Ⅲ)-catalyzed enantioselective C(sp3)-H functionalization via carbenoid C–H insertion of 3-diazooxindoles with 1,4-cyclohexadiene

The asymmetric carbenoid C–H insertion of 3-diazooxindoles into 1,4-cyclohexadiene has been accomplished in the presence of chiral bis(imidazoline) NCN pincer iridium(Ⅲ) complexes as the catalysts. With a catalyst loading of 0.5 mol%, the reactions proceeded smoothly at 0℃ to afford a variety of chiral 3-substituted oxindoles in good yields with moderate to excellent enantioselectivities(up to 99% ee). The protocol exhibits good functional group tolerance with respect to 3-diazooxindoles and is readily scaled up to 2 mmol scale without any loss in activity and enantioselectivity. Density functional theory(DFT)calculations have been performed to better understand the reaction mechanism and to explain the stereochemical outcome of the reactions.