Chemo-switched chromatic, magnetic and structural changes with retention of molecular crystallinity, Ni(12aneS4)(BF4)2

The molecular crystal [Ni(12aneS(4))](BF(4))(2) (12aneS(4) = 1,4,7,10-tetrathiacyclododecane) displays the uncommon ability to retain its crystallinity on facile reversible hydration/dehydration without requiring polymeric bonding and despite the significant structural changes required. The flexibility of the 12aneS(4) ring facilitates rearrangement of the complex in the solid state upon absorption of two equivalents of water, with the crystal structures showing a clear topotactic relationship. The well defined chromatic, structural and magnetic changes that are both highly sensitive and easily reversed makes this complex of interest as an environmentally responsive material and as a contrasting example to the commonly reported coordination polymers.     

Homo- and heteronuclear meso,meso-(E)-ethene-1,2-diyl-linked diporphyrins: preparation, x-ray crystal structure, electronic absorption and emission spectra and density functional theory calculations

Homo- and heteronuclear meso,meso-(E)-ethene-1,2-diyl-linked diporphyrins have been prepared by the Suzuki coupling of porphyrinylboronates and iodovinylporphyrins. Combinations comprising 5,10,15-triphenylporphyrin (TriPP) on both ends of the ethene-1,2-diyl bridge M(2)10 (M(2) =H(2)/Ni, Ni(2), Ni/Zn, H(4), H(2)Zn, Zn(2)) and 5,15-bis(3,5-di-tert-butylphenyl)porphyrinato-nickel(II) on one end and H(2), Ni, and ZnTriPP on the other (M(2)11), enable the first studies of this class of compounds possessing intrinsic polarity. The compounds were characterized by electronic absorption and steady state emission spectra, (1)H?NMR spectra, and for the Ni(2) bis(TriPP) complex Ni(2)10, single crystal X-ray structure determination. The crystal structure shows ruffled distortions of the porphyrin rings, typical of Ni(II) porphyrins, and the (E)-C(2)H(2) bridge makes a dihedral angle of 50° with the mean planes of the macrocycles. The result is a stepped parallel arrangement of the porphyrin rings. The dihedral angles in the solid state reflect the interplay of steric and electronic effects of the bridge on interporphyrin communication. The emission spectra in particular, suggest energy transfer across the bridge is fast in conformations in which the bridge is nearly coplanar with the rings. Comparisons of the fluorescence behaviour of H(4)10 and H(2)Ni10 show strong quenching of the free base fluorescence when the complex is excited at the lower energy component of the Soret band, a feature associated in the literature with more planar conformations. TDDFT calculations on the gas-phase optimized geometry of Ni(2)10 reproduce the features of the experimental electronic absorption spectrum within 0.1 eV.     

High-power top-hat pulses from a Yb master oscillator power amplifier for efficient optical parametric amplifier pumping

We demonstrate shaping of high-energy broadband Yb amplifier pulses for the generation of a (sub)picosecond top-hat temporal pulse profile that significantly improves pumping efficiency of an optical parametric amplifier (OPA). Phase-only modulation is applied by an acousto-optic programmable dispersion filter. This simple scheme is scalable to a high average power due to a relatively broad bandwidth of the Yb:CaF(2) gain medium used in the amplifier that supports a sub-150-fs transform-limited pulse duration. Additionally we show that OPA seeding with supercontinuum remains possible because top-hat-shaped pulses passed through a glass block recompress to ≈200 fs with minimum satellite production.     

Temperature dependences of optical properties,chemical composition,structure,and laser damage in Ta2O5 films

Ta2O5 films are prepared by e-beam evaporation with varied deposition temperatures,annealing temperatures,and annealing times.The effects of temperature on the optical properties,chemical composition,structure,and laserinduced damage threshold(LIDT) are systematically investigated.The results show that the increase of deposition temperature decreases the film transmittance slightly,yet annealing below 923 K is beneficial for the transmittance.The XRD analysis reveals that the film is in the amorphous phase when annealed below 873 K and in thehexagonal phase when annealed at 1073 K.While an interesting near-crystalline phase is found when annealed at 923 K.The LIDT increases with the deposition temperature increasing,whereas it increases firstly and then decreases as the annealing temperature increases.In addition,the increase of the annealing time from 4 h to 12 h is favourable to improving the LIDT,which is mainly due to the improvement of the O/Ta ratio.The highest LIDT film is obtained when annealed at 923 K,owing to the lowest density of defect.     

Click mechanochemistry: quantitative synthesis of "ready to use" chiral organocatalysts by efficient two-fold thiourea coupling to vicinal diamines

Mechanochemical methods of neat grinding and liquid-assisted grinding have been applied to the synthesis of mono- and bis(thiourea)s by using the click coupling of aromatic and aliphatic diamines with aromatic isothiocyanates. The ability to modify the reaction conditions allowed the optimization of each reaction, leading to the quantitative formation of chiral bis(thiourea)s with known uses as organocatalysts or anion sensors. Quantitative reaction yields, combined with the fact that mechanochemical reaction conditions avoid the use of bulk solvents, enabled solution-based purification methods (such as chromatography or recrystallization) to be completely avoided. Importantly, by using selected model reactions, we also show that the described mechanochemical reaction procedures can be readily scaled up to at least the one-gram scale. In that way, mechanochemical synthesis provides a facile method to fully transform valuable enantiomerically pure reagents into useful products that can immediately be applied in their designed purpose. This was demonstrated by using some of the mechanochemically prepared reagents as organocatalysts in a model Morita-Baylis-Hillman reaction and as cyanide ion sensors in organic solvents. The use of electronically and sterically hindered ortho-phenylenediamine revealed that mechanochemical reaction conditions can be readily optimized to form either the 1:1 or the 1:2 click-coupling product, demonstrating that reaction stoichiometry can be more efficiently controlled under these conditions than in solution-based syntheses. In this way, it was shown that excellent stoichiometric control by mechanochemistry, previously established for mechanochemical syntheses of cocrystals and coordination polymers, can also be achieved in the context of covalent-bond formation.     

Application of bare gold nanoparticles in open-tubular CEC separations of polyaromatic hydrocarbons and peptides

In this study, bare gold nanoparticles (GNPs) immobilized in the sol-gel-pretreated fused-silica (FS) capillary as a stationary phase for open-tubular capillary electrochromatography (OT-CEC) are for the first time shown to be able to separate both hydrophobic polyaromatic hydrocarbons (PAHs) as well as hydrophilic cationic antimicrobial peptides. Model mixture of four PAHs, naphthalene, fluorene, phenanthrene, and anthracene, was resolved by OT-CEC in the GNP-modified FS capillaries using the hydro-organic background electrolyte (BGE) composed of 20 mmol/L sodium phosphate buffer, pH 7, modified with ACN at 8:2 v/v ratio. On the other hand, three synthetic analogues of an antimicrobial peptide mastoparan PDD-B, basic tetradecapeptides INWKKLGKKILGAL-NH(2), INSLKLGKKILGAL-NH(2) and NWLRLGRRILGAL-NH(2), were separated in aqueous acidic BGEs, pH 2.1-3.1, composed of weak acids (formic and acetic) or amphoteric amino or imino acids (aspartic or iminodiacetic), utilizing the advantage of a slow reversed (anodic) EOF and slightly positive charge of the GNP-modified FS capillary suppressing the adsorption of cationic peptides on the inner capillary wall and improving their resolution.     

J/ψ polarization in pp collisions at √s=7 TeV

The ALICE Collaboration has studied J/ψ production in pp collisions at √s=7 TeV at the LHC through its muon pair decay. The polar and azimuthal angle distributions of the decay muons were measured, and results on the J/ψ polarization parameters λ(θ) and λ(φ) were obtained. The study was performed in the kinematic region 2.5相似文献   

Radiative decays and the nature of heavy quarkonia

We argue that the photon spectra in radiative decays of various heavy quarkonium states provide important information on their nature. If two of these states are in the strong coupling regime, we are able to produce a parameter-free model-independent formula, which holds at next-to-leading order and includes both direct and fragmentation contributions. When the formula is checked against recent CLEO data it favors Y(2S) and Y(3S) in the strong coupling regime and disfavors Y(1S) in it.     

Ag60纳米颗粒[{Cl@Ag12}@Ag48(dppm)12]的结构(其中dppm=双(二苯基膦基)甲烷

本文合成一种新的双膦连接Ag₆₀纳米团簇[{Cl@Ag₁₂}@Ag₄₈(dppm)₁₂],并通过X射线晶体学进行表征. 二十面体的银处于核心位置,里面是中心氯化物组成,外面有48 个银原子/离子的包裹,顶端是12个双(二苯基膦基)甲烷(dppm)配体. 同时利用密度泛函理论对阳离子[{Cl@Ag₁₂}@Ag₄₈(dppm)₁₂]⁺进行计算,以确定该结构是否对应于核心数n=58的超原子. DFT计算的优化结构与X射线一致,但是HOMO-LUMO的能差并不能保证其超级稳定性.     

锚杆支护方式对深埋洞室隔冲击效果影响的数值模拟研究

与浅埋洞室相比,随着埋深增加而产生的高地应力现象使深埋洞室安全性评价更加复杂。本研究在考虑地应力平衡的前提下,采用有限元与无限元相结合的方法,对冲击荷载作用下深埋洞室的锚杆支护方式进行了设计与优化。计算结果表明：在平衡初始地应力之后,Mises应力会随着锚杆长度、疏密程度的增加略有增长。当锚杆长度和疏密程度增至某一特定值时,洞室洞壁的位移和塑性应变将达到最小值,洞室围岩将达到相对安全状态。锚杆间隔布置下,长锚杆数量的增加将提高洞室围岩的安全性。当对洞室拱脚进行重点支护时,整个洞壁的位移均有所减小。