Reaction of metal-Carbene complexes with vinyllithium reagents

The reaction of vinyllithium with (CO)₅CrC(OCH₃)C₆H₅ (Ic) at?78° followed by the treatment with HCl at ?78° gave 43% (Z)-1-methoxy-1-phenylpropene (IIIa) and 21% 1,4-dimethoxy-1,4-diphenyl-1,3-butadiene (IVa) and no trace of a vinylphenylcarbene complex or its expected decomposition products. IIIa and IVa are proposed to arise from electrophilic attack at the carbon-carbon double bond of a σ-allychromium intermediate. The reaction of phenyllithium with (CO)₅CrC(OCH₃)CH=CHC₆H₅ (V) gave 9% (CO)₅CrC(OCH₃)CH₂CH- (C₆H₅)₂(VI) and 17% (E)-1-methoxy-1,3-diphenylpropene (VII). Reaction of V with lithium diphenylcuprate gave 30% of the conjugate addition product VI.     

1,3,4-Oxadiazole-containing hybrids as potential anticancer agents: Recent developments,mechanism of action and structure-activity relationships

Chemotherapy is an important therapeutic approach for the treatment of cancer. Currently, many anticancer drugs are available in the market that plays an important role in cancer treatment, but concerns such as, drug resistance and side effects create an urgent need for the development of new anti-tumor drugs with high potency and less side effects. Heterocycles are of great interest due to their fascinating anticancer activity. Among them, 1,3,4-oxadiazoles showed attracting anti-tumor activity and its derivatives are under clinical trials for the treatment of cancer. Hybridization of 1,3,4-oxadiazole moiety with other heterocyclic pharmacophoresis a promising approach to overcome various disadvantages of current anticancer drugs such as drug resistance, toxicity, and other side effects. Thus, 1,3,4-oxadiazole-heterocycle hybrids occupy a significant position in the discovery of anti-tumor drugs. Among the reported oxadiazole-based hybrids reviewed here, compounds 45i, 59j, and 62x showed the highest anticancer activity with IC₅₀ values in the nanomolar range. This review summarizes the recent developments in the anticancer potential, structure–activity relationships, and mechanisms of actions of 1,3,4-oxadiazole-heterocycle hybrids.     

Investigation of droplets impinging on a deep pool: transition from coalescence to jetting

An experimental investigation of droplets impinging vertically on a deep liquid pool of the same fluid was conducted. Coalescence and jetting as two of the main regimes were identified and studied. Five fluids, distilled water, technical ethanol, n-pentane, methanol and 1-propanol were used for providing different liquid-phase physical properties with density from 600 to 1,000 kg/m³, viscosity from 0.20 to 2.00 mPa s, and surface tension from 13.7 to 72.0 mN/m. Except for the experimental run of n-pentane, which was carried out in n-pentane saturated vapor, the ambient gas for the other experiments was air. The impact processes of micro-level (diameter below 1 mm) droplets were captured using a high-speed camera with a backlight. The observations, velocity and diameter ranges of the experimental runs were described, and based on them, the effects of the liquid-phase properties were studied. It was found that both low viscosity and low surface tension can increase the instability during impact processes. By curve-fitting, the transition from coalescence to jetting was characterized by using two models, one employing the Weber number (We) and the Ohnesorge number (Oh), and one employing the Froude number (Fr) and the Capillary number (Ca). Both models characterize the coalescence-jetting threshold well. The We-Oh model was based on a commonly used model from Cossali et al. (in Exp Fluids 22:463–472, 1997) for characterizing coalescence-splashing. For the small droplet diameters (below 1 mm) considered in this study, it was required to modify the We-Oh model with a diameter-dependent term to fit the sharp change in thresholds for fluids with relatively high viscosity. The Fr-Ca model has not previously been presented in the literature. A comparison of the two models with literature data (Rodriguez and Mesler, J Colloid Interface Sci 106(2):347–352, 1985) indicates that they are also valid for impacts of droplets with diameters above 1mm. Calculation methods to generalize the two models were proposed.     

Transition between coalescence and bouncing of droplets on a deep liquid pool

This study focused on the bouncing of sub-millimetric droplets (below 0.7 mm) of three different fluids, distilled water, technical ethanol and 1-propanol on a deep liquid pool of the same fluids. Four different flow regimes including low-energy-collision coalescence, bouncing, high-energy-collision coalescence, and partial coalescence were observed in the experiments. These regimes were plotted in velocity-diameter diagrams, which showed that there was a diameter limit, D ≈ 0.2 mm, above which the low-energy-collision coalescence was inhibited. The contact time, in which the impinging droplets and the liquid surface interacted in the bouncing process, was studied, and the results showed the same characteristic time scale of the contact time as those of Richard et al. (in Nature 417, 2002, 811) and Thoroddsen and Takehara (in Phys. Fluids 12 (6), 2000, 1265–1267). The restitution coefficients for all fluids were investigated, and the water data agreed well with the values reported in the literature (Bach et al., J. Fluid. Mech. 518, 2004, 157–185; Jayaratne and Mason, Proc. R. Soc. Lond. A 280 (1383), 1964, 545–565). Based on stable restitution coefficients, which varied with fluids, the effects from both viscosity and surface tension were discussed. Further, a correlation (K = We · Oh^−0.58) was generalized to characterize the two transitions between coalescence (both high-energy- and low-energy-collision types) and bouncing, and a comparison with the model and data of Huang and Zhang (in Petrol Sci. 5, 2008, 62–66) showed that the generalized model characterized the coalescence-bouncing threshold well for the experimental fluids in the present study and oil with much higher viscosity.     

Unusual mechanisms can dominate reactions at hyperthermal energies: an example from O(3P) + HCl --> ClO + H

An unusual mechanism in the reaction, O(3P) + HCl --> ClO + H, dominates at hyperthermal collision energies. This mechanism applies to collision geometries in which the H atom in the HCl molecule is oriented toward the reagent O atom. As the Cl-O bond forms, the H atom experiences a strong repulsive force from both the O and Cl atoms. The ClO product scatters forward with respect to the initial velocity of the O atom, and the H atom scatters backward. This mechanism accounts for more than half the reactive trajectories at energies >110 kcal mol-1, but it does not involve motion near the minimum energy path, which favors an SN2-like reaction mechanism where the H atom is oriented away from the reagent O atom during the collision.     

Concerted and stepwise proton-coupled electron transfers in aquo/hydroxo complex couples in water: oxidative electrochemistry of [Os(II)(bpy)(2)(py)(OH(2))](2+)

Successive oxidation of transition metal(II) aqua complexes (M(II)OH(2) to M(III)OH) is a domain in which proton-coupled electron transfer reactions are extremely common. The mechanism of these PCET reactions-concerted or stepwise-is an important issue in the understanding and design of natural or artificial systems catalyzing the formation of dioxygen by four-electron oxidation of water. Concerted proton-coupled electron transfer from an aqua metal(II) to a hydroxo metal(III) complex requires the close proximity of a proton-accepting group with a pK value between those of the aqua complexes. Otherwise, stepwise electron-proton or proton-electron pathways involving high-energy intermediates are followed. Concerted proton-electron pathways involving water as proton-acceptor or proton-donor group are inefficient. Cyclic voltammetry of the title complex in buffered aqueous solution and re-examination of previous results for the same complex attached to an electrode surface are used to establish these conclusions, which provide a starting point on the route to higher degrees of oxidation, such as those involved in the catalysis of water oxidation.     

Hyperthermal reactions of O and O2 with a hydrocarbon surface: direct C-C bond breakage by O and H-atom abstraction by O2

A C-C bond-breaking reaction has been observed when a beam containing hyperthermal oxygen was directed at a continuously refreshed saturated hydrocarbon liquid (squalane) surface. The dynamics of this C-C bond-breaking reaction have been investigated by monitoring time-of-flight and angular distributions of the volatile product, OCH3 or H2CO. The primary product is believed to be the methoxy radical, OCH3, but if this radical is highly internally excited, then it may undergo secondary dissociation to form formaldehyde, H2CO. Either the primary or the secondary product may scatter directly into the gas phase before thermal equilibrium with the surface is reached, or they may become trapped on the surface and desorb in thermal equilibrium with the surface. Direct, single-collision scattering events that produce a C-C bond-breaking product are described with a kinematic picture that allows the determination of the effective surface mass encountered by an incident O atom, the atom-surface collision energy in the center-of-mass frame, and the fraction of the center-of-mass collision energy that goes into translation of the scattered gaseous product and the recoiling surface fragment. The dynamical behavior of the C-C bond-breaking reaction is compared with that of the H-atom abstraction reaction, which was the subject of an earlier study. Another reaction, H-atom abstraction by O2 (which is present in the hyperthermal beam), has also been observed, and the dynamics of this reaction are compared with the inelastic scattering dynamics of O2 and the dynamics of H-atom abstraction by O. The dynamics involving direct inelastic and reactive scattering of O2 are also described in terms of a kinematic picture where the incident O2 molecule is viewed as interacting with a local region of the surface.     

内埋炸药下超高韧性水泥基复合材料的抗爆性能

为研究超高韧性水泥基复合材料(ultra-high toughness cementitious composites, UHTCC)在内埋炸药爆炸下的抗爆性能和损伤破坏规律,对不同炸药埋深下的UHTCC和高强混凝土(high-strength concrete, HSC)进行了内埋炸药抗爆实验。得到了两种材料靶体的破坏状态,并利用接触爆炸的实验结果计算出了两种材料的抗爆性能参数。结果表明,在相同条件下,UHTCC抗爆性能优于高强混凝土。为了进一步探究UHTCC的抗压强度、抗拉强度以及拉伸韧性对靶体在内埋炸药下抗爆性能的影响,首先,采用改进的K&C模型对炸药埋深为40 mm的超高韧性水泥基复合材料靶体进行数值模拟,模拟结果与实验结果基本吻合,并根据数值模拟的结果得到了爆炸冲击波沿靶体径向衰减速度大于轴向衰减速度这一规律,验证了数值模型的有效性;然后,通过调整改进K&C模型中与抗压强度、抗拉强度以及拉伸韧性相关的参数,数值预测了不同抗压强度、抗拉强度以及拉伸韧性下UHTCC靶体的破坏状态,发现增强UHTCC的韧性可以有效防止靶体发生整体性破坏,增大UHTCC的抗拉强度可以减小靶体迎爆面的开坑直径,增大UHTCC的抗压强度对减小开坑直径效果不明显。