An S‐Oxygenated [NiFe] Complex Modelling Sulfenate Intermediates of an O2‐Tolerant Hydrogenase

To understand the molecular details of O₂‐tolerant hydrogen cycling by a soluble NAD⁺‐reducing [NiFe] hydrogenase, we herein present the first bioinspired heterobimetallic S‐oxygenated [NiFe] complex as a structural and vibrational spectroscopic model for the oxygen‐inhibited [NiFe] active site. This compound and its non‐S‐oxygenated congener were fully characterized, and their electronic structures were elucidated in a combined experimental and theoretical study with emphasis on the bridging sulfenato moiety. Based on the vibrational spectroscopic properties of these complexes, we also propose novel strategies for exploring S‐oxygenated intermediates in hydrogenases and similar enzymes.     

Locating Dynamic Species with X‐ray Crystallography and NMR Spectroscopy: Acetone in p‐tert‐Butylcalix[4]arene

The exact location and orientation of dynamic species in structural studies continues to be a serious challenge, yet it is of paramount importance in modeling guest–host interactions so as to improve our understanding of the multiple weak interactions that govern many chemical and biological processes. The acetone guest in the tBC (p‐tert‐butylcalixarene) host presents such a challenge, as initial guest positions obtained from single crystal X‐ray diffraction (XRD) are incompatible with the ²H NMR spectrum. A detailed consideration of the diffraction data showed that more complicated structural models could be constructed that were consistent with the NMR data and still yielded satisfactory diffraction residuals. These models agree that one acetone methyl group is inserted into the deep cavity, and that it exchanges with the second methyl group outside. The outside methyl group in turn can switch positions with the carbonyl group, but the distribution of the methyl and carbonyl groups over the two sites is not equal. One factor that poses additional difficulty in deciding between models is whether the actual space group is tetragonal (P4/n), or twinned monoclinic (P2/n). All of the structural models considered here disagree substantially with the one proposed in an earlier publication.     

Synthesis,Spectroscopy, X‐ray Crystallography,and DFT Computations of Nanosized Phosphazenes

Nanoparticles of nine phosphazenes with general formula 4‐CH₃C₆H₄S(O)₂N=PX₃ [X = Cl ( A ), NC₄H₈ ( 1 ), NC₆H₁₂ ( 2 ), NC₄H₈N–C(O)OC₂H₅ ( 3 ), NC₄H₈N–C(O)OC₆H₅ ( 4 ), NC₄H₈O ( 5 ), NHCH₂–C₄H₇O ( 6 ), N(CH₃)(C₆H₁₁) ( 7 ), NHCH₂–C₆H₅ ( 8 ), and 2‐NH‐NC₅H₄ ( 9 )] were synthesized using ultrasonic method and characterized by ¹H, ¹³C, ³¹P NMR, FT‐IR, fluorescence, as well as UV/Vis spectroscopy and additionally with XRD, FE‐SEM, N₂ sorption, and elemental analysis. The ³¹P NMR spectra of compounds 1 – 9 reveal the most up field shift δ(³¹P) for 9 at –11.45 ppm reflecting the most electron donation of 2‐aminopyridinyl rings through resonance to the phosphorus atom. The ¹H, ¹³C NMR spectra of 7 exhibit two sets of signals for the hydrogen and carbon atoms of its two isomers present in the solution state in 1:4 ratio. The FE‐SEM micrographs illustrate that the nanoparticles of compounds 1 – 9 have spherical morphology and a size of 27–42 nm. From the XRD patterns, the crystal sizes were estimated to about 24–86 nm. The highest bandgap was measured for 3 (3.81 eV) whereas the smallest was measured for 8 (3.50 eV). The structures of two polymorphs of compound 5 ( 5 , 5′ ) were determined by X‐ray crystallography at 120 K. Both of these polymorphs are triclinic with P1 space group but 5 has a doubled unit cell volume and two symmetrically independent molecules ( 5a and 5b ). In structures 5a and 5′ , the phosphorus and all endocyclic atoms of two morpholinyl rings display disorder, whereas the molecule 5b does not show disorder. The strong intermolecular O–H ··· O hydrogen bonds plus weak intermolecular C–H ··· O and C–H ··· N interactions create three‐dimensional polymers in the crystalline networks of 5 and 5′ . The DFT computations illustrate that molecule 5b is more stable than 5a by –1.1062 and –0.9779 kcal · mol^–1 at B3LYP and B3PW91 levels, respectively. The NBO calculations presented sp³d hybridization for phosphorus and sulfur atoms and sp², sp³ hybrids for the nitrogen and oxygen atoms.     

Differentiation between [1,2,4]triazolo[1,5‐a] pyrimidine and [1,2,4]triazolo[4,3‐a]‐ pyrimidine regioisomers by 1H?15N HMBC experiments

The condensation of malonoaldehyde derivatives with either a 3‐amino‐[1,2,4]‐triazole or a 3,5‐diamino‐[1,2,4]‐triazole precursor was studied. In agreement with previous reports, two different bicycles, namely, bearing the regioisomeric [1,2,4]triazolo[1,5‐a]pyrimidine ( 1 ) or[1,2,4] triazolo [4,3‐a]pyrimidine ( 2 ) structural surrogates, could be obtained. We found that, depending on the triazole precursor, only one regioisomer resulted, either of the 1 or 2 series. We also observed that these two structural surrogates could be unambiguously differentiated by indirectly measuring their ¹⁵N chemical shifts by ¹H? ¹⁵N HMBC experiments. The occasional conversion of [1,2,4]triazolo[4,3‐a]pyrimidines to the [1,2,4]triazolo[1,5‐a]pyrimidine counterparts could be unequivocally determined by ¹⁵N NMR data. Copyright © 2010 John Wiley & Sons, Ltd.     

热处理对[NiFe/Cu/Co/Cu]_n多层纳米线磁性能的影响

采用双槽控电位法在阳极氧化铝(AAO)模板中制备了有序均一的[NiFe/Cu/Co/Cu]n多层纳米线阵列,并在不同温度下进行了热处理.利用X射线衍射(XRD)对热处理前后多层线的晶体结构进行了测试.考察了不同退火温度对多层线矫顽力、剩磁比、巨磁电阻(GMR)效应、磁灵敏度的影响.随热处理温度升高,多层纳米线中磁性微晶晶型取向越来越明显,晶体结构更均匀;多层纳米线的矫顽力和剩磁比先增大后减小.300°C下多层纳米线矫顽力达到最大值,GMR最大值可达59%,对应的磁电阻灵敏度(SV)为0.233%Oe-1.     

Combined computational and crystallographic study of the oxidised states of [NiFe] hydrogenase

[NiFe] hydrogenases catalyse the reaction H₂↔2H⁺+2e⁻. Several states of the enzyme have been observed by spectroscopic methods. Among these, the two most oxidized states, called the unready Ni–A and Ni–SU states, have been especially intriguing, because they take a much longer time to activate than the corresponding ready Ni–B and Ni–SI states. It has recently been suggested that the unready states actually contain a (hydro)peroxide bridge between the Ni and Fe ions, in contrast to the hydroxide bridge in the ready states. In this paper, we use quantum refinement (crystallographic refinement, in which the molecular mechanics [MM] calculations, normally employed to supplement the crystallographic data, are replace by more accurate quantum mechanics [QM] calculations), combined QM/MM calculations, and accurate energy estimates to study the nature of a recent oxidised crystal structure of [NiFe] hydrogenase from Desulfovibrio fructosovorans. We show that the structure contains a mixture of several states in the active site. The experimental data is best explained by structures with a hydroxide bridge but with two of the cysteine ligands (one bridging and one terminal) partly oxidised. When the terminal Cys-543 ligand is oxidised, the sulphur occupies an alternative position, observed in several crystal structures. The Glu-25 residue, that forms a hydrogen bond to this sulphur, also changes position. A peroxide ligand may exist as a minor component in the crystal and the suggested structure is supported by the calculations. We suggest that oxidised states are slow-equilibrium mixtures of structures with a peroxide bound and structures with oxidised Cys residues, and that the former can be activated by replacement of the protonated peroxide with a H₂ or CO ligand, as has been observed in electrochemical experiments.     

Aerobic Damage to [FeFe]‐Hydrogenases: Activation Barriers for the Chemical Attachment of O2

[FeFe]‐hydrogenases are the best natural hydrogen‐producing enzymes but their biotechnological exploitation is hampered by their extreme oxygen sensitivity. The free energy profile for the chemical attachment of O₂ to the enzyme active site was investigated by using a range‐separated density functional re‐parametrized to reproduce high‐level ab initio data. An activation free‐energy barrier of 13 kcal mol^?1 was obtained for chemical bond formation between the di‐iron active site and O₂, a value in good agreement with experimental inactivation rates. The oxygen binding can be viewed as an inner‐sphere electron‐transfer process that is strongly influenced by Coulombic interactions with the proximal cubane cluster and the protein environment. The implications of these results for future mutation studies with the aim of increasing the oxygen tolerance of this enzyme are discussed.     

Biomimetic Hydrogenation Catalyzed by a Manganese Model of [Fe]‐Hydrogenase

[Fe]‐hydrogenase is an efficient biological hydrogenation catalyst. Despite intense research, Fe complexes mimicking the active site of [Fe]‐hydrogenase have not achieved turnovers in hydrogenation reactions. Herein, we describe the design and development of a manganese(I) mimic of [Fe]‐hydrogenase. This complex exhibits the highest activity and broadest scope in catalytic hydrogenation among known mimics. Thanks to its biomimetic nature, the complex exhibits unique activity in the hydrogenation of compounds analogous to methenyl‐H₄MPT⁺, the natural substrate of [Fe]‐hydrogenase. This activity enables asymmetric relay hydrogenation of benzoxazinones and benzoxazines, involving the hydrogenation of a chiral hydride transfer agent using our catalyst coupled to Lewis acid‐catalyzed hydride transfer from this agent to the substrates.     

Synthesis of through‐space conjugated polymers containing [2.2]paracyclophane and thieno[3,4‐b]pyrazine in the main chain

We synthesized through‐space conjugated polymers with [2.2]paracyclophane and thieno[3,4‐b]pyrazine units in the main chain by the Sonogashira–Hagihara coupling reaction. The obtained polymers were soluble in common organic solvents, and homogeneous thin films were readily obtained from the polymer solutions by spin‐coating techniques. The polymers exhibited the extension of the conjugation length via the through‐space interaction. The polymers showed orangish‐red emission with peak maxima of around 610 nm in diluted solutions and their thin films, which were derived from the thieno[3,4‐b]pyrazine moieties. The optical and electrochemical behaviors of the polymers containing pseudo‐para‐ and pseudo‐ortho‐linked [2.2]paracyclophane were identical. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Cu(II)‐supported graphene quantum dots modified NiFe2O4: A green and efficient catalyst for the synthesis of 4H‐pyrimido[2,1‐b]benzothiazoles in water

NiFe₂O₄ nanoparticles are modified by graphene quantum dots (GQDs) and utilized to stabilize the Cu(II) nanoparticles as a novel magnetically retrievable catalytic system (Cu(II)/GQDs/NiFe₂O₄) for green formation of 4H‐pyrimido[2,1‐b]benzothiazoles. The prepared catalyst can be isolated assisted by an outer magnet and recovered for five courses without significant reduction in its efficiency. The as‐prepared magnetic heterogeneous nanocomposite was characterized by UV–Vis, FT‐IR, XRD, EDS, VSM, TEM, and ICP. Performing the reactions in environmentally friendly and affordable conditions (water), the low catalyst percentage, high yield of products, short reaction times, and easy workup are the merits of this protocol.     

Diastereo‐ and Enantioselective Palladium‐Catalyzed Dearomative [3+2] Cycloaddition of 3‐Nitroindoles

Diastereo‐ and enantioselective cycloaddition of 3‐nitroindoles with vinyl aziridine was realized under Pd‐catalysis using commercially available Walphos as the ligand, affording pyrroloindolines in high yields with high diastereo‐ and enantioselectivities. The reaction can be scaled up to a gram scale and the reaction products are easily converted to amino pyrroloindoline and other pyrroloindoline derivatives.     

Photophysical Properties and Photoinduced Electron Transfer between[60]Fullerene—containing Cyclic Sulphoxide [C60—C60H8SO]and Tetrathiafulvalene（TTF） by Laser Flash Photolysis

Photoinduced electron transfer(PET) processes between C60-C6H8SO and Tetrathiafulvalene(TTF) have been studied by nanosecond laser photolysis.Quantrm yiekds(φet) and rate constants of electron transfer(ket) from TTF to excited triplet state of[60] fullerene-containing cyclic sulphoxide in benzonitrile(BN) have been evaluated by observing the transient absorption bands in the NIR region.With the decay of excited triplet state of [60]fullerene-containing cyclic suplhoxide,the rise of radical anion of [60]fullerene-containing cyclic sulphoxinde is observed.     

Stereoselective Synthesis of Pillar[4]arene[1]cis‐diepoxy‐p‐dione and X‐Ray Crystal Structure of Host–Guest System

Herein, we successfully develop a novel route to give rise to polarity for the pillararenes by the introduction of oxygenated functionalities into pillar[5]arene to stereoselectively synthesize the pillar[4]arene[1]cis ‐diepoxy‐p ‐dione. Its host–guest properties with different dinitrile molecules were also investigated and characterized by NMR and X‐ray crystallography.     

Synthesis and characterization of a [5.5]paracyclophane‐containing silicon by NMR spectroscopy and X‐ray crystallography

The synthesis and characterization of 1,3,10,12‐tetraoxo‐2,11‐(diphenylsilylene)[5.5]par‐acyclophane obtained by reaction of 1,4‐benzenedimethanol and dichlorodiphenylsilane is reported. The structure was established by mass spectrometry; ¹H, ¹³C, and ²⁹Si NMR; and X‐ray diffraction analysis. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 351–354, 1999     

新的杯[4]芳烃衍生物通过缔合乙腈进行自插入的X-射线衍射和密度泛函理论研究

合成和表征了一个新的杯[4]芳烃衍生物，11,23-二羟亚胺甲基-25,27-二羟基-26,28-二丙氧基杯[4]芳烃 (B)及其与乙腈生成的组成为B·2CH₃CN的化合物。¹H NMR显示，在B·2CH₃CN中B采取锥型构象，X-射线衍射分析确证在溶液中所发现的构象。在晶格网络中存在着B·2CH₃CN以二聚体形式的自插入现象。在B3LYP/6-311G(d)水平上计算了该自插入二聚体中的非共价相互作用能，并对基集叠加误差进行了校正。在二聚体中的B·2CH₃CN，一个CH₃CN通过与羟亚胺基形成氢键使之稳定，结合能为–5.02 kJ·mol^-1，另一个CH₃CN则通过与另一个羟亚胺基形成氢键以及与另一B·2CH₃CN中B苯环空腔间的C–H···π相互作用使之稳定，结合能分别为–14.23 kJ·mol^-1和–3.77 kJ·mol^-1。自插入的驱动能为–7.54 kJ·mol^-1。