Homo-Coupling of Terminal Alkynes Using a Simple, Cheap Ni(dppe)Cl₂/Ag₂O Catalyst System

<div><p></p><p>A simple Ni(dppe)Cl₂/Ag₂O combination has been established as an efficient catalyst system for the homo-coupling of aromatic terminal alkynes. This reaction proceeds under mild conditions and can be applied to alkynone substrates. Various aromatic 1,3-diynes were obtained in good to excellent yields.</p></div

Mid–Late Cretaceous igneous activity in South China: the Qianjia example, Hainan Island

<p>Both Pacific and Neo-Tethys plates had major influences on the Cretaceous magmatisms in southeastern China. The subduction of the Neo-Tethys plate is, however, not well studied. This paper reports zircon U–Pb ages, Lu–Hf isotopes, whole-rock geochemistry, and Sr–Nd isotopes for the Qianjia intrusive rocks in Hainan Island, southeast China. LA-inductively coupled plasma mass spectrometry zircon U–Pb dating of granites and dark enclave monzonite in the area yield magmatic crystallization ages of ca. 100 Ma, which are consistent with other Late Cretaceous granites, e.g. Baocheng, Tunchang, and Yaliang. Both rocks show high-K calc-alkaline compositions and metaluminous to weakly peraluminous signatures belonging to I-type rocks. They are enriched in the alkalis, Rb, Th, U, K, and light rare earth elements, depleted in Nb, Ta, Ti, and P, and characterized by high Al₂O₃ contents (14–15 wt%) and high Mg^# values (50–53). Among them, some of granodiorites have geochemical affinities of adakitic rocks. Zircon <i>ε</i>_Hf(<i>t</i>) values range from −5.97 to −1.18, with fairly constant whole-rock Sr–Nd isotopes (<i>I</i>_Sr = 0.7084–0.7086; <i>ε</i>_Nd(<i>t</i>) = −4.97 to −4.29) similar with those of the Cretaceous mafic dikes (136–81 Ma) in Hainan Island, which are the result of partial melting of subduction-related sub-continental lithospheric mantle. Combined with Sr–Nd isotopes and negative Hf isotope, Qianjia intrusive rocks were likely derived from hybrid melts of underplated continental crust-derived with mantle-derived, then experienced varied degrees of fractional crystallization. According to the latest geophysical, sedimentological, and geochemical data, previous authors identified a Cretaceous E–W-trend subduction zone in the northern margin of the South China Sea. Combined with the southern margin magmatisms (110–80 Ma) and magmatisms of ~120 Ma distributed east–west ward from the Philippines to the Vietnam, We preferred that the subduction of the E–W-trend Neo-Tethys plate was the main geodynamic mechanism which induced the Cretaceous large-scale magmatisms in the southern margin of South China Block.</p

Difference of Gaussians (DOG) model.

<p>(A) The center-surround receptive filed organization is assumed to be fitted by two Gaussian curves: the narrower positive Gaussian representing the excitatory center or the CRF, while the broader negative Gaussian represents the inhibitory surround or the nCRF. K_e and a represent the strength and the space constants for the CRF, and K_i and b, those of the nCRF. The summation profile (R) of the model is represented as the difference of the two integrals of Gaussians. (B) A V1 neuron with suppressive summation. Dashed and dotted curves represent integrals of the excitatory and inhibitory components and the solid curve the linear combination of the two components that best fits the summation data.</p

Origin of Early Cretaceous Guandian adakitic pluton in central eastern China: partial melting of delaminated lower continental crust triggered by ridge subduction

<p>Early Cretaceous adakite or adakitic plutons are widely distributed in central eastern China, e.g. lower Yangtze river belt (LYRB), the south Tan–Lu fault (STLF), and the Dabie orogen. Their genesis, however, remains controversial. In this contribution, we present detailed geochemical and geochronological study on the Guandian pluton in central Anhui Province, eastern China, which has been formerly regarded as a part of the north belt in the LYRB and lately classified in the STLF. Namely, it is located near the boundary between ridge subduction related slab melting and partial melting of lower continental crust (LCC). The Guandian pluton consists of quartz monzonite and is metaluminous and high-K calc-alkaline according to the chemical composition. The samples show high SiO₂ (59.15–62.32%), Al₂O₃ (14.51–15.39%), Sr (892–1184 ppm), Sr/Y (56.74–86.32), and low Y (12.65–18.05 ppm), similar to typical geochemical features of adakite. The Guandian adakitic rocks also exhibit high K₂O (2.88–3.86%), MgO (3.89–5.24%), and Mg# (55–60), negative anomalies of high field strength elements (e.g. Nb, Ta, and Ti), and positive anomalies of Ba, Pb, and Sr. LA-ICP-MS zircon U–Pb dating yielded a weighted average age of 129.2 ± 0.7 Ma. Calculations of zircon Ce⁴⁺/Ce³⁺ (6.97–145) and (Eu/Eu*)_N (0.23–0.42) on the basis of <i>in situ</i> zircon trace element analysis indicate that the magma had a lower oxygen fugacity relative to the ore-bearing adakites in the LYRB and Dexing, which is consistent with the fact of ore-barren in the research area. In combination with previous research, we propose that Guandian adakitic pluton was formed by partial melting of delaminated LCC triggered by Early Cretaceous ridge subduction of the Pacific and Izanagi plates. During ridge subduction, physical erosion destructed the thickened LCC and resulted in delamination, while thermal erosion facilitated partial melting of the delaminated LCC.</p

The histogram of changes in strength of surround suppression for FSUs and RSUs.

<p>The △SI indicate the difference between SI_high and SI_low. The arrows indicate the average, which was 0.02 for FSUs and 0.08 for RS-Units (P >0.05).</p

Difference of Gaussians (DOG) model.

<p>(A) The center-surround receptive filed organization is assumed to be fitted by two Gaussian curves: the narrower positive Gaussian representing the excitatory center or the CRF, while the broader negative Gaussian represents the inhibitory surround or the nCRF. K_e and a represent the strength and the space constants for the CRF, and K_i and b, those of the nCRF. The summation profile (R) of the model is represented as the difference of the two integrals of Gaussians. (B) A V1 neuron with suppressive summation. Dashed and dotted curves represent integrals of the excitatory and inhibitory components and the solid curve the linear combination of the two components that best fits the summation data.</p

The spatial summation curves of two V1 neurons at high and low contrast.

<p>The red and blue line represents a FSU and a RSU for each. The curve with solid symbols represents the spatial summation curve measured at high contrast and the curve with open symbols at low contrast.</p

Classification of the FS-Units and RS-Units.

<p>(A) Shown were representative traces, recording from two neurons in V1 cat. (B) The recorded action potential waveforms were averaged and normalized. (C) The distribution of waveform durations was significant bimodal according to Hartigan’s dip test (P < 0.01). (D) The scatterplots of each cell’s peak firing rate versus spike duration. The average of peak firing rates for FSUs was significant stronger than those of RSUs (P = 0.0003). The blue and red solid line indicate the average of peak firing rate of RSUs and FSUs for each.</p

The scatter plot of the estimates of surround suppression at high contrast versus low contrast.

<p>The solid circle and hollow diamond indicate RSUs and FSUs, respectively.</p