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DFT calculations shows an unexpected mechanism in the photoredox/copper-catalyzed carbocyanation of 1,3-diene, which involves CuI-only catalysis and the single electron transfer from the allyl radical to the oxidized photocatalyst.

At Quesang on the Tibetan Plateau we report a series of hand and foot impressions that appear to have been intentionally placed on the surface of a unit of soft travertine. The travertine was deposited by water from a hot spring which is now inactive and as the travertine lithified it preserved the traces. On the basis of the sizes of the hand and foot traces, we suggest that two track-makers were involved and were likely children. We interpret this event as a deliberate artistic act that created a work of parietal art. The travertine unit on which the traces were imprinted dates to between ∼169 and 226 ka BP. This would make the site the earliest currently known example of parietal art in the world and would also provide the earliest evidence discovered to date for hominins on the High Tibetan Plateau (above 4000 m a.s.l.). This remarkable discovery adds to the body of research that identifies children as some of the earliest artists within the genus Homo.

This density functional theory (DFT) study reveals a detailed plausible mechanism for the Sc-catalyzed C-H cycloaddition of imidazoles to 1,1-disubstituted alkenes to form all-carbon quaternary stereocenters. The Sc complex binds the imidazole substrate to enable deprotonative C2-H bond activation by the Sc-bound α-carbon to afford the active species. This complex undergoes intramolecular cyclization (C═C into Sc-imidazolyl insertion) with exo-selectivity, generating a β-all-carbon-substituted quaternary center in the polycyclic imidazole derivative. The Sc-bound α-carbon deprotonates the imidazole C2-H bond to deliver the product and regenerate the active catalyst, which is the rate-determining step. Calculations illuminate the electronic effect of the ancillary Cp ligand on the catalyst activity and reveal the steric bias caused by using a chiral catalyst that induce the enantioselectivity. The insights can have implications for advancing rare-earth metal-catalyzed C-H functionalization of imidazoles.

The Ganjia Basin in Xiahe County, Gansu Province, China, is located on the northeastern edge of the Tibetan Plateau. The area lies in the transitional zone between the Plateau ethnic groups dominated by ancestral Tibetans, and the Central Plains dynasties dominated by ancestral Han in history. The Ganjia Basin is therefore well suited to studying the history of the intermixing of the Han and Tibetan peoples. In this study, we collected samples of organic materials from two ancient cities, Bajiaocheng (BJC) and Sirougucheng (SRGC), in the Ganjia Basin, which were used for radiocarbon dating. Our aims were to determine the construction times and function of the cities, based on the radiocarbon ages, Bayesian age modeling, and the analysis of relevant historical records. The results are used to discuss the role of the Ganjia Basin in the conflicts between and the integration of the two ethnic groups during the historical period. We conclude that BJC was established during 663–732 CE (Common Era); its early occupation history can be divided into an initial establishment phase (670–780 CE) and a phase of regeneration (880–1030 CE). SRGC was probably built at the time of the transition between the Song and Yuan dynasties (∼1271 CE). Combining the dating results with an analysis of the architectural styles and historical records, we conclude that BJC was originally built by the Tubo Kingdom as a military stronghold, and its major functions were military, economic and religious, and to support the major eastward expansion of the Tubo. SRGC was most likely a temple-focused city intended to promote Tibetan Buddhism which was a major political and religious leadership for the Tibetans at that time, reflecting changes in the status of different religions in the Ganjia Basin. In addition, the intermixing and blending of the Han and Tibetan groups, reflected by the human activities in the Ganjia Basin, was an important demographic and cultural foundation for the formation of the culturally-diverse but spiritually-united modern Chinese people.

This work presents a density functional theory (DFT) study on the mechanism and origins of enantio- and regioselectivities in dual photoredox/chiral Bronsted acid-catalyzed asymmetric Minisci-type addition of carbon-centered radicals to N-heteroarenes [Science, 2018, 360, 419-422]. The previously proposed mechanism has been partially revised. First, photoexcited *[IrIII] is reductively quenched by TRIP anion rather than the experimentally proposed neutral radical generated from the chiral Bronsted acid cycle. Second, final product formation involves a hydrogen-atom transfer (HAT) from a neutral radical intermediate to the TRIP radical, instead of single-electron transfer (SET) to *[IrIII]. The TRIP catalyst has been shown to play a triple role by reductively quenching *[IrIII] with its anion form, activating the substrate, and inducing asymmetry. The calculated results rationalize the experimentally observed enantio- and regioselectivities and reveal that the enantioselectivity of the reaction originates from the hydrogen-bond interaction between TRIP and the N-H group of the carbon-centered radical, and the regioselectivity arises from the electron-withdrawing inductive effect from the protonated N-atom and the intramolecular hydrogen-bond interaction between the acetylamino group and the protonated pyridine ring. We also provide explanations for the experimentally observed a dramatic decrease in enantioselectivity when changing substrate or radical precursor and rationalize the solvent-controlled switch of regioselectivity.

In 2010, geneticists reported the mitochondrial DNA and nuclear DNA sequences of a fragment of hominin phalanx found in Denisova cave, in the Altai Mountains in Russia, and the discovery of a new archaic human group which they named “Denisovans”. Subsequently, significant progress has been made in research on Denisovans. This paper reviews and summarizes recent achievements and advances in Denisovan studies, especially in chronology, archaeology, anthropology and genetics, over the past decade, with the aim of encouraging in-depth research in related fields in China. Comprehensive geochronological studies in Denisova cave suggest that Denisovans and Neanderthals may have occupied the cave during the interval of 287−55 ka (thousand years ago) and during 193−97 ka. Direct dating of hominin fossils, or of strata containing hominin fossils, indicates that Denisovans occupied the cave during 195−52 ka, while there is evidence of Neanderthals occupying the cave during 14.7−9.1 ka. These results reflect the long occupation history of Denisovans and Neanderthals in Denisova cave. In addition, the dating of the Xiahe mandible, from Baishiya karst cave (Xiahe County, Gansu Province, China) in the northeastern Tibetan Plateau, indicates that this is the first Denisovan fossil discovered outside Denisova cave, and suggests that Denisovans occupied the Tibetan Plateau at least at 160 ka, in the late Middle Pleistocene. This extends the spatial distribution of Denisovans from the Altai Mountains to the Tibetan Plateau and indicates that the Xiahe Denisovans may have been adapted to the extremely cold and hypoxic environment of the plateau. Lithic assemblages from Denisova cave include both Levallois and blade technologies produced by either Denisovans or Neanderthals, or both, who coexisted in the cave for a long time. However, preliminary analysis of lithic artifacts collected from Baishiya Karst cave indicates the dominance of simple core and flake technology. In consideration of long coexistence of two archaic humans in Denisova cave, and the archeological work in Baishiya Karst cave is still in its infancy stage, the cultural connotation of Denisovans needs further comprehensive study. Considering the long coexistence of the two archaic humans in Denisova cave, and that archeological work in Baishiya karst cave is still at a preliminary stage, the cultural connotations of the Denisovans require further comprehensive study. The fragments of Denisovan fossils found in Denisova cave provide limited evidence of the morphological characteristics of the phalanx and teeth, while the Xiahe mandible provides more extensive and important evidence of the morphological characteristics of the mandibles of Denisovans. The present study shows that the overall morphological characteristics of the phalanx are closer to those of modern humans than to Neanderthals, although the size of the molars is much greater than that those of Neanderthals and modern humans; in addition, the mandible has several features similar to those of archaic Homo sapiens in East Asia. However, due to the limited fossil evidence, the morphological differences between Denisovans and other archaic humans remain to be comprehensively documented. In addition, in contrast to the Neanderthals’ wide genetic contribution to modern humans, Denisovans only genetically contributed to modern populations in Oceania, East Asia, South Asia and America, and they exhibit a gene flow from superarchaic humans. In addition, multiple deeply differentiated branches may exist within the Denisovan population. These findings imply that Denisovans may have been more widely distributed in Asia than was previously thought and that they possess a more complex evolutionary history. At present, only one high-coverage Denisovan genome has been discovered in Denisova cave and no ancient DNA is preserved in the Xiahe mandible, which limits our understanding of other Denisovan branches. Although we still know little about Denisovans, we anticipate that future in-depth archaeological studies at Baishiya karst cave will provide additional important information on the physical morphology of Denisovans, their genetic characteristics and behavioral culture, and will elucidate the adaptation mechanism of Denisovans to high-altitude environments. In addition, we expect that an increasing number of new discoveries and multidisciplinary endeavors will shed additional light on the Denisovans and thus contribute to the study of human evolution in East Asia.

By performing density functional theory (DFT) calculation, this work aims at understanding the nonconventional meta-C-H arylation reaction of electronic-rich arenes with aryl iodide via a Pd/quinoxaline-based ligand/norbornene cooperative catalysis. The reaction is indicated to be initiated either from the ortho-C-H carbopalladation to give the meta-monoarylation product via a sequence of subsequent steps, including norbornene insertion, meta-C-H activation, oxidative addition, and reductive elimination via the Pd(II)/Pd(IV)/Pd(II) redox cycle, norbornene extrusion, and protodepalladation, or from the para-C-H carbopalladation to form the meta-diarylation product via two sequential arylation processes following similar mechanisms. The initial carbopalladation process promoted by the ligand is characterized as the rate-determining step of the reaction. The calculated mechanism shows the distinct role of the norbornene as a transient mediator that enables the final C-H arylation at the same meta-position wherever the initial carbopalladation occurs at either ortho- or para-position. The Pd/ligand/norbornene cooperative catalysis is essential for achieving the exclusive meta-selectivity of the C-H arylation of electron-rich arenes.

Archaeological research has documented the migration of Neolithic farmers onto the Tibetan Plateau by 4000 BC. How these incoming groups interacted, if at all, with local indigenous foragers, however, remains unclear. New archaeobotanical and zooarchaeological data from the Zongri site in the north-eastern Tibetan Plateau suggest that local foragers continued to hunt but supplemented their diet with agricultural products in the form of millet. The authors propose that, rather than being grown locally, this millet was acquired via exchange with farmers. This article highlights how indigenous foragers engaged in complex patterns of material and cultural exchange through encounters with newly arrived farmers.

Alpine ecosystems on the Tibetan Plateau are being threatened by ongoing climate warming and intensified human activities. Ecological time-series obtained from sedimentary ancient DNA (sedaDNA) are essential for understanding past ecosystem and biodiversity dynamics on the Tibetan Plateau and their responses to climate change at a high taxonomic resolution. Hitherto only few but promising studies have been published on this topic. The potential and limitations of using sedaDNA on the Tibetan Plateau are not fully understood. Here, we (i) provide updated knowledge of and a brief introduction to the suitable archives, region-specific taphonomy, state-of-the-art methodologies, and research questions of sedaDNA on the Tibetan Plateau; (ii) review published and ongoing sedaDNA studies from the Tibetan Plateau; and (iii) give some recommendations for future sedaDNA study designs. Based on the current knowledge of taphonomy, we infer that deep glacial lakes with freshwater and high clay sediment input, such as those from the southern and southeastern Tibetan Plateau, may have a high potential for sedaDNA studies. Metabarcoding (for microorganisms and plants), metagenomics (for ecosystems), and hybridization capture (for prehistoric humans) are three primary sedaDNA approaches which have been successfully applied on the Tibetan Plateau, but their power is still limited by several technical issues, such as PCR bias and incompleteness of taxonomic reference databases. Setting up high-quality and open-access regional taxonomic reference databases for the Tibetan Plateau should be given priority in the future. To conclude, the archival, taphonomic, and methodological conditions of the Tibetan Plateau are favorable for performing sedaDNA studies. More research should be encouraged to address questions about long-term ecological dynamics at ecosystem scale and to bring the paleoecology of the Tibetan Plateau into a new era.

The origin, nature and timing of prehistoric human activity on the Tibetan Plateau has become a major research topic in recent years, and great progress has been made in the study of the earliest human activity on the plateau and in the origin of modern Tibetans. The earliest human presence on the plateau has been updated by two important new studies. Rich blade assemblages found in the excavation of the Nwya Devu site shows that modern humans occupied the interior region of the Tibetan Plateau, above 4600 m a.s. l., some 30−40 thousand years ago. Recently, a study of a human mandible fossil found in Xiahe County, Gansu Province, in the northeastern Tibetan Plateau, indicated that Denisovans occupied the Tibetan Plateau at least 160000 years ago, much earlier than the arrival of modern humans to the region. The latter study also implies that the high-altitude adaptation gene, which occurs widely among modern Tibetans and Sherpa, was probably contributed by local archaic humans, like the Xiahe Denisovans. These two studies not only point to the long and complex human history in the Tibetan Plateau, but they also indicate the complexity of human evolution in the Middle and Late Pleistocene in East Asia. Whether early Holocene hunter-gatherers had already permanently settled on the Tibetan Plateau before the arrival of millet and barley agriculture after the middle Holocene, has become another major research topic in the study of the prehistoric human history of the Tibetan Plateau. However, due to the current lack of reliable evidence for the seasonality of Paleolithic site occupations in the Tibetan Plateau, the issue remains difficult to resolve. The origin of modern Tibetans has been debated for decades. A new linguistic study of the phylogeny and the time depth of the original divergence of the Sino-Tibetan language, based on Bayesian phylogenetic analysis of 109 languages, indicates that Sino-Tibetan languages diverged during some 4200 to 7800 years ago, which points to Neolithic population dispersals to the Tibetan Plateau and their close relationship with modern Tibetans. In addition, a new genetic study, based on mitochondrial DNA (mtDNA) analyses of 8277 Tibetans and 58514 individuals from the surrounding populations, has traced the genetic legacy of modern Tibetans to the historical or even Neolithic periods. Calculation of the time depth of the two common haplogroups in modern Tibetans found in this study, implies that these two groups of populations originated in northern China between 6000 and 10000 years ago and differentiated between 4000 and 5200 years ago. Both of these studies are consistent with previous archaeological studies which propose that Neolithic and Bronze Age populations moved to the Tibetan Plateau from a substantial considerable of areas in North China. More importantly, the two studies further confirm the close relationships between Neolithic millet farmers and modern Tibetans, clarifying the origin of modern Tibetans. There have also been several new Paleolithic archaeological studies of the regions surrounding the Tibetan Plateau. A deeper understanding of the Initial Upper Paleolithic in North China, Mongolia and Siberia, and new findings of the Levallois technology in the Jinsitai and Tongtian cave sites in North China, indicate a dispersal route of Paleolithic populations from the north to the Tibetan Plateau. Other studies also propose possible population migration routes in the southeastern and southwestern plateau, although archaeological evidence is currently lacking. Together with the new Paleolithic archaeological findings for the Tibetan Plateau, it appears that different human groups, including Denisovans, Neanderthals and modern humans, were living in or around the Tibetan Plateau during the Middle to Late Pleistocene. Although recent studies provide new clues for understanding their inter-relationships, additional questions have arisen, and more multidisciplinary studies are needed in the future to address them. Above all, these new studies are crucial for understanding the mechanisms by which prehistoric humans spread to and in the Tibetan Plateau, and their adaptation to the high elevation environments. In addition, they shed new light on the origin of modern humans, as well as on human evolution in East Asia during the Middle and Late Pleistocene.

Density functional theory (DFT) calculations were performed to investigate the photosensitizer-free visible-light-mediated gold-catalyzed cis-difunctionalization of alkynes with aryl diazonium salts. The detailed reaction mechanism is established, and the observed regio- and chemoselectivities are rationalized. The results are compared to those of the rhodium-catalyzed cis-difunctionalization of alkynes. It is indicated that the excitation of the aryl diazonium salt initiates the photocatalytic cycle, and the following single-electron transfer between the Au(I) catalyst and the excited aryl diazonium salt affords the key aryl radical. Both gold- and rhodium-catalyzed reactions involve two major steps: alkyne insertion into the M-N or M-C bond (M = Au, Rh), and C-C or C-N reductive elimination from the M(III) center. The cis-difunctionalized product can be obtained by the trimethylsilyl (TMS)-substituted alkyne through the gold catalysis or by the Ph-substituted alkyne through the rhodium catalysis. The catalyst-dependent reactivity switch of TMS- and Ph-substituted alkynes is attributed to the catalyst-induced shift of the rate-determining step.

Using the marine biological valuation method, we selected five ecosystem components, namely, phytoplankton, microzooplankton, macrozooplankton, macrobenthos, and nekton, to evaluate the marine biodiversity value of Jiangsu’s offshore areas in 2006 (early-term coastal development) and 2014 (mid-term coastal development), and the impact of human activities on the values were analyzed based on the differences between the two time periods. In general, the biological value (BV) of the Jiangsu offshore area changed in the context of high-intensity human activities, disrupting the original spatial pattern of the natural geographical attributes indicated by the BV in 2006. From the perspective of various ecosystem components, the impact on macrobenthos is long-lasting and significant, the impact on plankton is temporary and recoverable, and the presence of offshore structures leads to the formation of new habitats that attract new species and more predators (fishes), with the BV of nekton in the radial sand ridge area being higher than that in other marine areas. The results of our approach confirm the importance of areas that were previously identified for protection (particularly in the central regions). Our results also highlight the value of currently unprotected sites, mainly in the northern and southern regions. Highlighting the impact of high-intensity human activities on the BV of Jiangsu lays a foundation for developing future marine spatial plans and provides a scientific reference and basis for administrative departments to develop marine management decisions.

This work presents a DFT study on the mechanism and origin of catalyst-controlled divergent reactivity in the synthesis of benzo-heterocycles from o-alkynylbenzamides by Au(I)/Pt(IV) catalysis. The results indicate that the transformations proceed via a nucleophilic cyclization process. In the Au(I) catalysis, the preferred O-attack mode mainly originates from the symmetry match in the dominant bond-forming interaction between the lone-pair orbital of carbonyl-O and the in-plane alkyne π* orbital, and the electronic property of the ligand controls the O-5-exo-dig/O-6-endo-dig selectivity. The preference for the N-attack mode in Pt(IV) catalysis is attributed to the stronger coordinate capability of carbonyl-O than amino-N in the substrate to PtCl4, and the regioselective N-6-endo-dig or N-5-exo-dig cyclization depends on the stronger electrostatic interaction between the amino-N and alkynyl-Cβ atoms. The theoretical results provide a fundamental understanding of why and how gold and platinum complexes catalyze the cyclization of o-alkynylbenzamides with different chemo- and regioselectivities.

DFT calculations have been performed to gain insight into the mechanism of production 5-hydroxymethylfurfural (HMF) from fructose catalyzed by a representative imidazolium-based ionic liquid (IL), 1-butyl-3-methyl-imidazolium bromide ([BMIM]Br). The overall barrier of the catalytic conversion is found to be 41.5 kcal/mol, which is in contrast to 75.6 kcal/mol located in previous literature. Different from the mechanism proposed in the literature, which Br anion of IL interacts with the hydroxyl group of the substrate via H-bonding to induce the dehydration process, while cation of IL acts as a spectator, the present calculations emphasize the collaboration of cation and anion of IL.

Past human genetic diversity and migration between southern China and Southeast Asia have not been well characterized, in part due to poor preservation of ancient DNA in hot and humid regions. We sequenced 31 ancient genomes from southern China (Guangxi and Fujian), including two ∼12,000- to 10,000-year-old individuals representing the oldest humans sequenced from southern China. We discovered a deeply diverged East Asian ancestry in the Guangxi region that persisted until at least 6,000 years ago. We found that ∼9,000- to 6,000-year-old Guangxi populations were a mixture of local ancestry, southern ancestry previously sampled in Fujian, and deep Asian ancestry related to Southeast Asian Hoabinhian hunter-gatherers, showing broad admixture in the region predating the appearance of farming. Historical Guangxi populations dating to ∼1,500 to 500 years ago are closely related to Tai-Kadai and Hmong-Mien speakers. Our results show heavy interactions among three distinct ancestries at the crossroads of East and Southeast Asia.

Climatic change that affects biological productivity is often argued to be a primary force influencing human activities during the glacial period. To test this assumption, we combine in-site pollen, paleoclimatic, and archaeological data from the Dadiwan site and nearby areas on the western Loess Plateau (WLP) that date to Marine Oxygen Isotope Stage (MIS) 3. Our comparison of multiple datasets suggests that regional human activities increased when the vegetation around the Dadiwan area shifted from forest steppe in the early MIS 3 (59–46.7 ka) to steppe in the middle to late MIS 3 (46.7–29.5 ka). Our results indicate that regional human activities increased again during the late MIS 3 when the amount of precipitation was higher, as indicated by the lower Artemisia proportion. We suggest that increased precipitation on the WLP enhanced the above-ground biomass production and may be responsible for an increase in human activity and population in this region.

Wang, T.; Yu, W.; Zou, X.; Zhang, D.; Li, B.; Wang, J., and Zhang, H., 2018. Zooplankton community responses and the relation to environmental factors from established offshore wind farms within the Rudong coastal area of China. The goal of this study was to examine the responses of the zooplankton community to the establishment of an OWF, the causes of any observed effects, and their relation to environmental factors in the study area. This article describes the results of an investigation into the zooplankton community and the main environmental factors affecting that community based on data obtained from three cruises in May, August, and November of 2015 in the area of the Longyuan OWF in Rudong, China. This study analyzed the spatiotemporal distribution of zooplankton, including data obtained before the construction of the wind farm, to assess any postconstruction change in the zooplankton community. Data from the zooplankton community were analyzed using canonical correlation analysis, redun...

The formation of polycyclic aromatic hydrocarbons (PAHs) on the C11H11 potential energy surface involved in the reactions of a phenyl radical (C6H5) with cis-3-penten-1-yne (cis-C1HC2–C3HC4H–C5H3, referred to as C5H6) and its three radicals (CHC–ĊCH–CH3, CHC–CHĊ–CH3, and cis-CHC–CHCH–ĊH2, referred to as the C3-, C4-, and C5-radicals with the same chemical components, C5H5) assisted by H atoms is investigated by performing combined density functional theory (DFT) and ab initio calculations. Five potential pathways for the formation of PAHs have been explored in detail: Pathways I–II correspond to the reaction of C6H5 with C5H6 at the C1 and C2 position, and Pathways III–V involve the reaction of C6H5 with the C3-, C4-, and C5-radicals with the assistance of H atoms. The initial association of C6H5 with C5H6 or C5H5 is found to be highly exothermic with only minor barriers (1.4–7.1 kcal mol−1), which provides a large driving force for the formation of PAHs. The hydrogen atom is beneficial for the ring enlargement and ring formation processes. The present calculations predict 9 potential PAHs, six (CS6, CS10, CS13, CS26, CS28 and CS29) of which are indicated to be energetically more favorable along Pathways I, III, IV and V at low temperature. The calculated barriers for the formation of these PAHs are around 19.2–38.0 kcal mol−1. All PAHs products could be formed at flame temperature, for the medium barriers are easily overcome in various flame conditions. The theoretical results supplement the PAH formation pathway and provide help to understand PAH growth mechanism.

Recent development on Rh(III)-catalyzed synthesis of indolines from arylnitrones and alkynes provides an efficient redox-neutral method integrating C–H activation with O-atom transfer. Here density functional theory calculations were performed on the mechanism of a representative model system: [Cp*Rh]2+-catalyzed reaction of phenylnitrone with 1-phenylpropyne. The results suggest that the catalytic cycle involves a Rh(III)–Rh(I)–Rh(III) transformation and consists of C–H activation, alkyne insertion/O-atom transfer, and cyclization-protonation. The C–H activation, the rate-determining step, proceeds via a self-assisted deprotonation mechanism. The alkyne prefers the insertion into Rh–C(sp2) bond rather than Rh–O bond. The calculations locate an intermediate containing an enol unit, which plays a crucial role in facilitating the cyclization process. The theoretical results provide an explanation for the puzzling experimental observations. The regioselectivity of the reaction is stemmed from the electronic effect rather than steric effect and controlled by the alkyne insertion step. The improved yield with the addition of pivalic acid is attributed to the strong deprotonation capability of pivalate, which significantly facilitates the C–H activation via the concerted metalation–deprotonation (CMD) mechanism.

To illustrate the formation mechanism of normal and abnormal N-heterocyclic carbene–carbon dioxide adducts (NHC–CO2 and aNHC–CO2), we implement density functional theory calculations on the reactions of two imidazolium-based ionic liquids ([C2C1Im][OAc] and [C2C1Im][CH3SO3]) with CO2. The reaction of [C2C1Im][OAc] with CO2 is mimicked using the gas phase model, implicit solvent model, and combined explicit–implicit solvent model. In the gas phase, the calculated barriers at 125 °C and 10 MPa are 12.1 kcal/mol for the formation of NHC–CO2 and 22.5 kcal/mol for the formation of aNHC–CO2, and the difference is significant (10.4 kcal/mol). However, the difference becomes less important (1.5 kcal/mol) as the solvation effect is considered more realistically using the combined explicit–implicit solvent model, rationalizing the experimental observation of aNHC–CO2 adduct in the [C2C1Im][OAc]–CO2 system. The anion of the ionic liquid is shown to play a substantial role, which can adjust the reactivity of imidazol...

The reaction mechanisms of PAH formation from phenyl radical (C6H5) to naphthalene via C2H3 (C2H3-Path) and C4H4 (C4H4-Path) were investigated by the G3(MP2, CC) method. The hydrogen abstraction, ring closure, cis–trans isomerization, and disproportionation reactions were considered, as well as their occurred sequence. The results showed that H-abstraction reactions occurred more easily than H-dissociation reactions. The cis–trans conversion reactions in sub-routes of C2H3-Path and C4H4-Path provided the largest barriers of 51, 53, and 36 kcal/mol along their routes, which illustrated that the cis–trans isomerization was energetically costly in the PAH formation process. The entrance barriers of C2H2-Path, C2H3-Path, and C4H4-Path are 6, 8, and 3 kcal/mol, respectively, which indicates that it is easier to add C4H4 to C6H5 compared with adding C2H2 to C2H3. C2H3 additions were highly exothermic with reaction energies greater than 110 kcal/mol, and compared with C2H2 additions, C2H3 additions were irreversible. However, C2H2-Path, C2H3-Path and C4H4-Path involved energy barriers of 20, 32, and 36 kcal/mol, respectively. Considering the high temperature in combustion and the approximate concentrations of C2H3 and C4H4, all three of these pathways could lead to naphthalene in some combustion flames.

As a new type of catalytic borylations, the Rh-catalytic borylation reaction of aryl cyanides has been reported experimentally (Tobisu et al. J. Am. Soc. Chem. 2012, 134, 115). Here, to aid experimental designs of the novel type of borylation reactions, we theoretically predict Rh-catalytic borylations of two alternative substrates of aryl cyanides, i.e. aryl acetylene and aryl ethylene. Both borylation and diborylation pathways have been calculated in details for each substrate. It is found that aryl ethylene prefers to the borylation product via the β-H elimination mechanism, in contrast, aryl acetylene favors the diborylation product by inserting the C C bond into the Rh B bond. The theoretical results are expected to be helpful for the preparation of organoboron compounds.

Supplementary Information

Denisovans are members of a hominin group who are currently only known directly from fragmentary fossils, the genomes of which have been studied from a single site, Denisova Cave1–3 in Siberia. They are also known indirectly from their genetic legacy through gene flow into several low-altitude East Asian populations4,5 and high-altitude modern Tibetans6. The lack of morphologically informative Denisovan fossils hinders our ability to connect geographically and temporally dispersed fossil hominins from Asia and to understand in a coherent manner their relation to recent Asian populations. This includes understanding the genetic adaptation of humans to the high-altitude Tibetan Plateau7,8, which was inherited from the Denisovans. Here we report a Denisovan mandible, identified by ancient protein analysis9,10, found on the Tibetan Plateau in Baishiya Karst Cave, Xiahe, Gansu, China. We determine the mandible to be at least 160 thousand years old through U-series dating of an adhering carbonate matrix. The Xiahe specimen provides direct evidence of the Denisovans outside the Altai Mountains and its analysis unique insights into Denisovan mandibular and dental morphology. Our results indicate that archaic hominins occupied the Tibetan Plateau in the Middle Pleistocene epoch and successfully adapted to high-altitude hypoxic environments long before the regional arrival of modern Homo sapiens. Fossil evidence indicates that Denisovans occupied the Tibetan Plateau in the Middle Pleistocene epoch and successfully adapted to this high-altitude hypoxic environments long before the regional arrival of modern Homo sapiens.

To better understand the efficient transformation of glucose to fructose catalyzed by chromium chlorides in imidazolium-based ionic liquids (ILs), density functional theory calculations have been carried out on a model system which describes the catalytic reaction by CrCl2 in 1,3-dimethylimidazolium chlorine (MMImCl) ionic liquid (IL). The reaction is shown to involve three fundamental processes: ring opening, 1,2-H migration, and ring closure. The reaction is calculated to exergonic by 3.8 kcal/mol with an overall barrier of 37.1 kcal/mol. Throughout all elementary steps, both CrCl2 and MMImCl are found to play substantial roles. The Cr center, as a Lewis acid, coordinates to two hydroxyl group oxygen atoms of glucose to bidentally rivet the substrate, and the imidazolium cation plays a dual role of proton shuttle and H-bond donor due to its intrinsic acidic property, while the Cl– anion is identified as a Bronsted/Lewis base and also a H-bond acceptor. Our present calculations emphasize that in the rate...

The magnetic Fe3O4@β-cyclodextrin (β-CD) nanocomposites were fabricated via Fe ions and β-CD in one pot and characterized as a heterogeneous Fenton-like catalyst that may be used for the degradation of 4-chlorophenol (4-CP). The catalytic capacity of Fe3O4@β-CD was evaluated on the basis of various parameters, including pH, H2O2 concentration and catalyst loading, with regards to the pseudo-first-order kinetics of 4-CP degradation. In addition, iron leaching, the effect of radical scavengers and reusability of the Fe3O4@β-CD nanocomposite were also studied. The results showed that Fe3O4@β-CD exhibited a higher catalytic ability than that Fe3O4 toward 4-CP degradation, the observed rate constants (kobs) were 0.0373 min−1 for Fe3O4@β-CD, and 0.0162 min−1 for Fe3O4, which may be ascribed to the construction of a ternary complex (Fe2+–β-CD–pollutant) that allowed the produced hydroxyl radicals (·OH) to directly attack the contaminant and simultaneously enhanced the solubility of the organic pollutant. Fe3O4@β-CD also exhibited an enhancement effect for chlorobenzene (CB) degradation with the kobs of 0.0392 min−1 (kobs = 0.0099 min−1 for Fe3O4), which may be due to a synergistic effect in the Fe3O4@β-CD composite. Furthermore, Fe3O4@β-CD has an excellent catalytic activity, stable mechanical strength and adequate reusability. A possible reaction pathway of 4-CP degradation dominated by ·OH was proposed according to analyses of the degradation intermediates and chloride ions. The host-guest interaction between β-CD and 4-CP were examined with density functional theory (DFT) calculations, expounding the unicity of degraded intermediate owing to the specific spatial selectivity of β-CD. The findings of this study provide a novel material used in the Fenton-like process for the degradation of contaminants.

G-rich aptamers have been widely applied to develop various sensors for detecting proteins, small molecules, and cations, which is based on the target-induced conformational transfer from single strand to G-quadruplex. However, the transforming process is unclear. Here, with PW17 as an aptamer example, the forming process of G-quadruplex induced by K(+) is investigated by circular dichroism spectroscopy, electrospray ionization mass spectroscopy, and native gel electrophoresis. The results demonstrate that PW17 undergoes a conformational transforming process from loose and unstable to compact and stable G-quadruplex, which is strictly K(+) concentration-dependent. The process contains three stages: (1) K(+) (0.5 mM) could induce PW17 forming a loose and unstable G-quadruplex; (2) the compact and stable K(+)-stabilized G-quadruplex is almost formed when K(+) is equal to or larger than 7 mM; and (3) when K(+) ranges from 0.5 mM to 7 mM, the transformation of K(+)-stabilized PW17 from loose and unstable to compact and stable occurs. Interestingly, dimeric G-quadruplex through 5'-5' stacking is involved in the forming process until completely formed at 40 mM K(+). Moreover, the total process is thermodynamically controlled. With PW17 as a sensing probe and PPIX as a fluorescent probe for detection of K(+), three linear fluorescent ranges are observed, which corresponds to the three forming stages of G-quadruplex. Clarifying the forming process provides a representative example to deeply understand and further design aptamer-based biosensers and logic devices.

The clarification of the genetic origins of present-day Tibetans requires an understanding of their past relationships with the ancient populations of the Tibetan Plateau. Here we successfully sequenced 67 complete mitochondrial DNA genomes of 5200 to 300-year-old humans from the plateau. Apart from identifying two ancient plateau lineages (haplogroups D4j1b and M9a1a1c1b1a) that suggest some ancestors of Tibetans came from low-altitude areas 4750 to 2775 years ago and that some were involved in an expansion of people moving between high-altitude areas 2125 to 1100 years ago, we found limited evidence of recent matrilineal continuity on the plateau. Furthermore, deep learning of the ancient data incorporated into simulation models with an accuracy of 97% supports that present-day Tibetan matrilineal ancestry received partial contribution rather than complete continuity from the plateau populations of the last 5200 years.

Denisovans are members of a hominin group who are currently only known directly from fragmentary fossils, the genomes of which have been studied from a single site, Denisova Cave

The mechanisms and chemoselectivities on the Au(I)-catalyzed intermolecular condensation between homopropargyl alcohols and terminal alkynes were investigated by performing DFT calculations. The reaction was indicated to involve three stages: transformation of the homopropargyl alcohol (R1) via intramolecular cyclization to the cyclic vinyl ether (R1′), formation of the C-2-arylalkynyl cyclic ether (P1) via hydroalkynylation of R1′ with phenylacetylene (R2), and conversion from P1 to 2,3-dihydro-oxepine (P2). The results revealed the origin of the reaction divergence and rationalized the experimental observations that a 1:3 reactant stoichiometric ratio affords P1 as the major product, whereas the 1:1.1 ratio results in P2 in high yield. The reactant stoichiometric ratio-controlled divergent reactivity is attributed to different catalytic activities of the gold catalyst toward different reaction stages. In the 1:3 situation, the excess R2 induces the Au catalyst toward its dimerization and/or hydration, i...

Understanding the mechanism for the catalyzed cleavage of the β-O-4 ether linkage in lignin is crucial to developing efficient strategies for depolymerizing lignin. In this work, veratrylglycerol-β-guaiacyl ether (VG) was used as a lignin model compound in a theoretical investigation of the mechanism for the cleavage of the β-O-4 bond as catalyzed by the acidic ionic liquid (IL) 1-H-3-methylimidazolium chloride ([HMIM]Cl). The reaction was found to involve two processes-dehydration and hydrolysis-in which the cation functions as a Brønsted acid (donating a proton) and the anion acts as a nucleophile (promoting dehydration) or interacts with the substrate through hydrogen bonding, stabilizing the intermediate. These roles of the anion and cation of [HMIM]Cl explain why the [HMIM]Cl medium catalyzes the depolymerization of lignin. In addition, calculations predict that adding formaldehyde during the depolymerization of VG prevents the condensation of VG without significantly altering the mechanism of depolymerization, thus suggesting a method for potentially improving the efficiency of lignin depolymerization.

Recently the Kennedy group reported a unique successive N-methylene C–H bond activation on N-heterocyclic triruthenium carbene complexes. Here, density functional theory calculations have been performed on this reaction to clarify the molecular-level mechanism of the two C–H bond activations. The calculated results indicated that the reaction occurs sequentially through the following steps: phosphine ligand dissociation from the Ru center followed by rearrangement of ligands on Ru center, the first C–H bond oxidative addition to Ru, the elimination of the first CO ligand with recoordination of the phosphine ligand, the second CO ligand elimination followed by the second C–H bond activation, and hydride migrations between Ru centers. The rate-determining step is the first C–H bond activation, which needs to overcome a barrier of 37.9 kcal mol−1.

While the catalytic conversion of glucose to 5-hydroxymethyl furfural (HMF) catalyzed by SO3H-functioned ionic liquids (ILs) has been achieved successfully, the relevant molecular mechanism is still not understood well. Choosing 1-butyl-3-methylimidazolium chloride [C4SO3HmimCl] as a representative of SO3H-functioned IL, this work presents a density functional theory (DFT) study on the catalytic mechanism for conversion of glucose into HMF. It is found that the conversion may proceed via two potential pathways and that throughout most of elementary steps, the cation of the IL plays a substantial role, functioning as a proton shuttle to promote the reaction. The chloride anion interacts with the substrate and the acidic proton in the imidazolium ring via H-bonding, as well as provides a polar environment together with the imidazolium cation to stabilize intermediates and transition states. The calculated overall barriers of the catalytic conversion along two potential pathways are 32.9 and 31.0 kcal/mol, respectively, which are compatible with the observed catalytic performance of the IL under mild conditions (100 °C). The present results provide help for rationalizing the effective conversion of glucose to HMF catalyzed by SO3H-functionalized ILs and for designing IL catalysts used in biomass conversion chemistry.