Synthesis of novel chiral bisoxazoline ligands with a spiro[4,4]-1,6-nonadiene skeleton

A new type of chiral bisoxazoline ligands 1 based on spiro[4,4]-1,6-nonadiene backbone was easily prepared in six steps from racemic spiro[4,4]-nonane-1,6-dione, with the Pd-catalyzed coupling of the enol triflates with CO and amino alcohols as the key steps for the construction of the oxazoline moiety. The structure of the ligand (R,S,S)-1b was unambiguously established by X-ray crystallographic analysis. The chiral Cu(II) complex generated in situ from the combination of spiro bisoxazoline ligand (S,S,S)- 1c and Cu(OTf)₂ was effective in the catalysis of asymmetric chlorination of the β-ketoester, methyl 1-oxo-2,3-dihydro-1H- in-dene-2-carboxylate, affording the corresponding chlorinated derivative in 99% yield with 17% ee.     

Diastereoselective addition of lithium enolate of γ-substituted α-diazoacetoacetate to <Emphasis Type="Italic">N</Emphasis>-sulfinyl imines

Highly diastereoselective addition of lithium enolate of γ-substituted α-diazoacetoacetate to chiral N-sulfinyl imines has been developed. The addition products were further subjected to photo-induced Wolff rearrangement or Rh(II)-catalyzed intramolecular N–H insertion to afford chiral 4,5-disubstituted 2-oxo and 3-oxo pyrrolidines, respectively.     

Seasonal variations and environmental controls on stalagmite calcite crystal growth in Heshang Cave,central China

Stalagmite growth rates are usually considered to reflect changes in paleoclimate and paleoenvironment. However, how exactly growth rates are affected by climate and environment is still unclear. We launched a monitoring and modeling program that lasted approximately 4 years on two active drip sites in Heshang Cave, central China. We collected comprehensive quantitative data on growth rates, cave temperature, CO₂ concentration, drip rate and drip-water chemistry to better understand the relationship between stalagmite growth and cave environment. By laying out glass substrates, we successfully grew stalagmite calcite crystals with rhombic characteristics, and quantified growth rates by measuring the long and short axes of calcite crystals under a microscope. Combined with coeval environmental data, we explicitly examined the roles of cave temperature, drip rate and drip-water chemistry in controlling the micro-scale growth of stalagmite calcite. Results show that growth of stalagmite calcite crystals at two drip sites exhibited similar seasonal variations − generally faster in the summer months, at ∼3 μm d⁻¹, and slower during the late winter to early spring, at ∼1.5 μm d⁻¹. Variations in calcite growth rates were mainly determined by changes in cave temperature, with the growth rate increasing by 8.1%/°C and 6.6%/°C at the two locations. This indicates the potential use of stalagmite growth rates as a seasonal-resolution paleo-temperature proxy in some ventilated caves. On the other hand, the effect of drip rate and drip-water Ca²⁺ and SIC values on growth rates were not significant.     

Variations in equilibrium line altitude of the Qiyi Glacier,Qilian Mountains,over the past 50 years

Based on observations of the equilibrium line altitude (ELA) of the Qiyi Glacier in the Qilian Mountain, we established a statistical model between ELA and its major influencing factors, warm season air temperature (air temperature averages for September, July and August) and cold season precipitation (total precipitation in the period January through March). Warm season air temperature was the leading climatic factor influencing ELA variations. The glacier ELA ascends (descends) 172 m when warm season air temperature increases (decreases) by 1°C, and ascends (descends) 62 m when cold season precipitation decreases (increases) by 10%. In the period 1958–2008, the glacier ELA showed a general increasing trend, ascending 230 m and reaching its highest altitude in 2006 at 5131 m a.s.l., close to the glacier summit. If future climate is similar to that in the period 2001–2008, the Qiyi Glacier will not stabilize until it retreats by 2.08 km.     

Network analysis of protein-protein interaction

Residue networks are constructed by defining the residues as the vertices and atom contacts between them as the edges. The residue network of a protein complex is divided into two types of networks, i.e. the hydrophobic and the hydrophilic residue networks. By analyzing the network parameters, it is found that the correct binding complex conformations are of both higher sum of the interface degree values and lower characteristic path length than those incorrect ones. These features reflect that the correct bind-ing complex conformations have better geometric and/or residue type complementarity, and the correct binding modes are very important for preserving the characteristic path lengths of native protein complexes. In addition, two scoring terms are proposed based on the network parameters, in which the characteristics of the entire complex shape and residue type complementarity are taken into account. These network-based scoring terms have also been used in conjunction with other scoring terms, and the new multi-term scoring HPNCscore is devised in this work. It can improve the discrimination of the combined scoring function of RosettaDock more than 12%. This work might enhance our knowledge of the mechanisms of protein-protein interactions and recognition.     

Wetting behavior and interfacial characteristic of Sn-Ag-Cu solder alloy on Cu substrate

Wettability of molten Sn-Ag-Cu alloy on Cu substrate has been determined by sessile drop method, as well as its dependence on time and temperature. It was found that the evolution of contact angle at the alloy’s melting point experienced four different stages. Especially, the contact angle was unstable and fluctuant in stage II, and gradually decreased in stage III mainly due to a chemical reaction between Sn-Ag-Cu alloy and Cu substrate. The contact angle decreased with increasing temperature, but increased slightly at 629 K, for another chemical reaction occurred. Interfacial characteristic has been further investigated by examining the sample’s cross section. Intermetallic compounds of Cu6Sn5 and β-Sn phase were found at the interface of Sn-Ag-Cu/Cu.     

A phase field study for influence of elastic energy on L1<Subscript>0</Subscript>→L1<Subscript>2</Subscript> transient ordering in Ni<Subscript>75</Subscript>Al<Subscript>17</Subscript>Zn<Subscript>8</Subscript>

The influence of the elastic energy on L1₀→L1₂ transient ordering transformation was investigated by microscopic phase field method. It is found that there are three stages experienced in atomic ordering: solute clustering+L10 short range ordering → L1₀ long range ordering → L1₂ long range ordering. Before the formation of the high ordered L1₂ phase, it has firstly taken place the transformation from matrix to L1₀ phase, and then held the L1₀→L1₂ secondary transformation. Elastic energy is proved to take little effect on the stage of short range ordering, but as the elastic energy is multiplied, it obviously shortened the course of the solute clustering, and speeded up the proceeding of the L1₀ long range ordering transition. Accordingly, the increased elastic energy also strengthens the single crystalline directionality of L1₀ phase projecting on 2D plane and makes the ordered degree of Al and Zn atoms enhanced. With the temperature elevation, Al’s and Zn’s ordered degree decreased in L10 phase.     

Built-in electric field influence on impurity-free vacancy disordering of InGaAs/InP quantum well structure

Built-in electric field may enhance or retard the impurity-free vacancy disordering (IFVD) during rapid thermal annealing (RTP) by imposing a drift on charged point defects. Built-in electric field is at the interface between dielectric layer and top layer of the structure. Subsequent rapid thermal annealing leads to different intermixing results due to different field directions on InP cap layers in different doping types. Experimental results also show different influences of the built-in field on the two...     

A wide tuning range electro-optic filter based on long-period waveguide grating

We present the design of an electro-optic filter with polarization insensitivity based on a long period waveguide grating. The filter exhibits an ultra-large wavelength tuning range of exceeding 35 nm and covering the whole C band (1530 to 1565 nm) in a bias voltage range from −84 to 84 V. In the whole tuning range, the transmission coefficients for quasi TE modes are over 97% and the 3 dB bandwidths are below 0.8 nm. The wavelength sensitivity to the tunable voltage is about 0.208 nm/V. This electro-optic filter can be used in dynamic WDM networks for fast wavelength scanning/selection, communication channel reconfiguration, and optical switching.     

Advances in the synthesis and reactivity of 2-pyranylidene carbene complexes

Pyranylidene carbene complexes bearing a pyran ring carbene ligand represent a unique kind of organometallic species due to their special structures and reactivity. In this review, we present a comprehensive summary on the synthesis and reactivity of pyranylidene carbene complexes during the past four decades.