Highly Reactive Nonheme Iron(III) Iodosylarene Complexes in Alkane Hydroxylation and Sulfoxidation Reactions

High‐spin iron(III) iodosylarene complexes bearing an N‐methylated cyclam ligand are synthesized and characterized using various spectroscopic methods. The nonheme high‐spin iron(III) iodosylarene intermediates are highly reactive oxidants capable of activating strong C? H bonds of alkanes; the reactivity of the iron(III) iodosylarene intermediates is much greater than that of the corresponding iron(IV) oxo complex. The electrophilic character of the iron(III) iodosylarene complexes is demonstrated in sulfoxidation reactions.     

Efficient one-pot synthesis of biologically interesting diverse furo[2,3-b]pyran-6-ones by rhodium(II)-catalyzed cascade reactions of diazo compound with ethynyl compounds

Rhodium(II)-catalyzed reactions of diazo compound and a variety of ethynyl compounds were carried out. These reactions provide a rapid route for preparing a variety of furo[2,3-b]pyran-6-one derivatives in one-pot via cascade reactions of metal carbenoid reaction/ketene formation/[2+2]cycloaddition/ring expansion.     

Relationships between unfolded configurations of proteins and dynamics of folding to the native state

We compare folding trajectories of chymotrypsin inhibitor (CI2) using a dynamic Monte Carlo scheme with Go-type potentials. The model considers the four backbone atoms of each residue and a sphere centered around C^β the diameter of which is chosen according to the type of the side group. Bond lengths and bond angles are kept fixed. Folding trajectories are obtained by giving random increments to the φ and ψ torsion angles with some bias toward the native state. Excluded volume effects are considered. Two sets of 20 trajectories are obtained, with different initial configurations. The first set is generated from random initial configurations. The initial configurations of the second set are generated according to knowledge-based neighbor dependent torsion probabilities derived from triplets in the Protein Data Bank. Compared to chains with randomly generated initial configurations, those generated with neighbor-dependent probabilities (i) fold faster, (ii) have better defined secondary structure elements, and (iii) have less number of non-native contacts during folding. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3667–3678, 2006     

InGaAs/InP heterojunction-channel tunneling field-effect transistor for ultra-low operating and standby power application below supply voltage of 0.5 V

An In_0.53Ga_0.47As/InP heterojunction-channel tunneling field-effect transistor (TFET) with enhanced subthreshold swing (S) and on/off current ratio (I_on/I_off) is studied. The proposed TFET achieves remarkable characteristics including S of 16.5 mV/dec, on-state current (I_on) of 421 μA/μm, I_on/I_off of 1.2 × 10¹² by design optimization in doping type of In_0.53Ga_0.47As channel at low gate (V_GS) and drain voltages (V_DS) of 0.5 V. Comparable performances are maintained at V_DS below 0.5 V. Moreover, an extremely fast switching below 100 fs is accomplished by the device. It is confirmed that the proposed TFET has strong potentials for the ultra-low operating power and high-speed electron device.     

Determination of Neonicotinoid Pesticides in Propolis with Liquid Chromatography Coupled to Tandem Mass Spectrometry

In this study, a method was developed for the determination of five neonicotinoid pesticides (acetamiprid, clothianidin, imidacloprid, thiacloprid, and thiamethoxam) in propolis. Two sample preparation methods were tested: solid-phase extraction and the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method. The identities of analytes were confirmed using liquid chromatography–tandem mass spectrometry (LC-MS/MS) in the selected reaction monitoring mode. Solid-phase extraction resulted in cleaner extracts; therefore, the SPE-LC-MS/MS method was validated according to the SANTE protocol in triplicate at two spiking levels (10 ng/g and 50 ng/g). The average recoveries of analytes ranged from 61% to 101%, except for clothianidin (10–20%). The LOD ranged from 0.2 ng/g to 4.4 ng/g, whereas the LOQ was in the range of 0.8 ng/g–14.7 ng/g. In order to compensate for the matrix effect, matrix-matched calibration was used. Good accuracy (relative error: 1.9–10.4%) and good linearity (R² > 0.991) were obtained for all compounds. The optimised method was applied to 30 samples: 18 raw propolis and 12 ethanol tinctures. Acetamiprid, imidacloprid, and thiacloprid were detectable in seven samples but were still below the LOQ. This study is the first to report the determination of several neonicotinoid residues in propolis.     

Total Synthesis of (+)‐Machaeriols B and C and of Their Enantiomers with a Cannabinoid Structure

An efficient and concise synthesis of the biologically interesting (+)‐machaeriol B ( 2 ) and its enantiomer 5 was accomplished from O‐phenylhydroxylamine ( 7 ) in four steps (Scheme 2). In addition, the first total synthesis of natural (+)‐machaeriol C ( 3 ) and its enantiomer 6 was achieved from the readily available ester 15 in eight steps (Scheme 4). The key strategies in the syntheses of 2 and 5 involved benzofuran formation through a [3,3]‐sigmatropic rearrangement and trans‐hexahydrodibenzopyran formation by a domino aldol‐type/hetero‐Diels–Alder reaction. In the case of 3 and 6 , the key steps were stilbene formation by a Horner–Wadsworth–Emmons reaction and trans‐hexahydrodibenzopyran formation by domino reactions.     

Long cycles in fullerene graphs

It is conjectured that every fullerene graph is hamiltonian. Jendrol’ and Owens proved [J. Math. Chem. 18 (1995), pp. 83–90] that every fullerene graph on n vertices has a cycle of length at least 4n/5. In this paper we, improve this bound to 5n/6 − 2/3.     

含碗形CTV侧基的甲基丙烯酸酯类单体和聚合物

采用三聚法合成外围基团中含羟十一碳氧基的CTV衍生物(CTV-H),然后结合柱层析分离技术合成和分离出外围基团中含单甲基丙烯酸酯基团的CTV衍生物(CTV-M).以CTV-M为单体,本体聚合得到含碗形CTV侧基的甲基丙烯酸酯类聚合物(BPM).CTV-H和CTV-M都具有热致液晶性,是新的碗状液晶.SAXS和WAXD测定表明,液晶结构为六方柱相(Φh),柱直径为4.4 nm和4.8 nm,与理论计算结果相符.而BPM没有液晶性,呈非晶态.     

Nonhomogeneous state of stress,strain, and swelling in amorphous polymer networks

The total free energy of an amorphous, crosslinked polymer is given as ΔA = ΔA_mix + ΔA_el, where ΔA_mix indicates the free energy of mixing of the crosslinked polymer and the solvent to which the network is exposed throughout the deformation process; ΔA_el indicates the elastic free energy of the network as a function of strain, including the effect of dilation with the solvent. The explicit forms of the mixing and the elastic free energies are obtained from the molecular theory of rubber elasticity. Recent developments in this field allow accurate representation of the behavior of swollen networks under strain. Expressions for the stress in terms of strain and swelling ratio are obtained from the free energy. Formulation of boundary-value problems are discussed. Bending of a cuboid subject to the action of a swelling agent is analyzed as an example. Material parameters are chosen for a crosslinked amorphous network. The distribution of stresses, strains, and solvent in the bent cuboid are calculated numerically. The magnitude of moments applied at the two ends are calculated for different degrees of flexure. Results are compared with those obtained for the same network in the dry state.