A New Chemical Trick to Prevent House from Collapsing by Bacterial Pathogens

Metazoans often induce cell death as an ultimate strategy to prevent disastrous damage to the body under circumstances when insults, such as infection are impossible to clear. Inflammatory cell death or pyroptosis not only eliminates the replicative niche for the pathogen but also stimulates effective immune protection. A recent study by Shao, Liu and colleagues found that the Shigella flexneri effector OspC3 inactivates an inflammasome by a novel posttranslational modification termed ADP-riboxanation. This finding has greatly expanded the chemical tool box of pathogens in their manipulation of host function, which may be used to probe unrecognized signaling mechanisms.     

Retraction: Transition-metal-free synthesis of conjugated microporous polymers via amine-catalyzed Suzuki–Miyaura coupling reaction

Retraction of ‘Transition-metal-free synthesis of conjugated microporous polymers via amine-catalyzed Suzuki–Miyaura coupling reaction’ by Qingmin Liu et al., Chem. Sci., 2021, DOI: 10.1039/d1sc03970a.

We, the named authors, hereby wholly retract this Chemical Science article. This article reports the synthesis of conjugated microporous polymers using an amine-catalyzed Suzuki–Miyaura coupling reaction. This article builds upon findings first reported by Xu et al.¹ and invokes the same mechanism for Pd-free polymer synthesis. Since the publication of our article in Chemical Science, we have been made aware of concerns regarding the conclusions of the above-mentioned Nature Catalysis article, disputing the mechanisms and claims that the reactions reported are not Pd-free.^2,3 We, as the authors of this Chemical Science article, have considered these claims and, after further investigation, acknowledge that we cannot exclude the influence of residual Pd for the Suzuki coupling reaction involved. Therefore, there is sufficient doubt around the main conclusion of our work as a ‘transition-metal-free synthesis’ and so we wish to retract this article.Signed: Qingmin Liu, Shangbin Jin and Bien Tan, 18th November 2021.Retraction endorsed by May Copsey, Executive Editor, Chemical Science.     

Note: Synthesis And Crystal Structure Of A Binuclear Fumarate Complexof Copper(II) With 1,10-Phenanthroline

As dicarboxylate complexes of transition metal possess potentially useful electronic and magnetic properties, [Mehrotra and Bohra (1983). Metal Carboxylates. Academic Press, London], much interest in their synthesis and structure has been apparent recently [Kaneko and Tsuchida (1981). J. Polymer Sci . , Macromolecular Reviews, 16, 397; Holton, Lappert, Pearce and Yarrow (1983). Chem. Reviews, 83, 135]. A series of metal complexes bridged by dicarboxylates has been synthesized in our laboratory and crystal structures show versatile coordination modes for the carboxyl group [Cheng, Liu, Xu and Xu (1999). J. Coord. Chem., 48 , 495; Nie, Liu, Luo and Xu (2001). J. Coord. Chem., 53, 365]. As a part of this investigation, we have synthesized a binuclear fumarate complex of Cu(II). X-ray analysis shows considerable coordination distortion resulting from close stacking interaction of aromatic phen rings.     

Changes in energy of three types of hydrogen bonds upon excitation of aminocoumarins determined from absorption solvatochromic experiments

Absorption spectra of 6-aminocoumarin (6AC) and 7-aminocoumarins (C120 and C151) were studied in polyfluorinated alcohols: (1,1,1,3,3,3-hexafluoroisopropanol (HFIP), 2,2,2-trifluoroethanol (TFE)), in water and in methanol, and compared to those taken in 1-chloro-n-alkanes. According to our results, the observed unusual blue-shift of a long-wavelength band in absorption spectra in strong protic solvents is direct evidence of significant weakening of a NH-O hydrogen bond. The results obtained for the aminocoumarins in HFIP, which in contrast to aliphatic alcohols does not form hydrogen bonds of the acceptor type, prove that the decrease in the energy of the NH-O hydrogen bond upon excitation to the lowest S(1)-LE state is significantly greater than the increase in the energy of hydrogen bonds made by the oxygen atom of carbonyl group OH-O. It is in contrast to theoretical calculations for C151 [Y. Liu, J. Ding, R. Liu, D. Shi and J. Sun, J. Photochem. Photobiol. A, 2009, 201, 203-207]. A comparison of the absorption spectra measured in DMSO and in 1-chloro-n-alkanes shows that the energy of two N-HO hydrogen bonds considerably increases as a result of excitation. These results are consistent with those of the theoretical calculations [Y. Liu, J. Ding, R. Liu, D. Shi and J. Sun, J. Photochem. Photobiol. A, 2009, 201, 203-207; P. Zhou, P. Song, J. Liu, K. Han and G. He, Phys. Chem. Chem. Phys., 2009, 11, 9440-9449]. In this study we applied the procedure proposed by us in J. Photochem. Photobiol. A, 2006, 184, 250-264 for the determination of changes in hydrogen bond energy as a result of electronic excitation based on analysis of the absorption spectra of the probe studied in the solvents interacting with it exclusively nonspecifically and in those forming hydrogen bonds with it.     

创新型化学专业学生培养的课程体系改革与实践

主要介绍兰州大学为了培养创新型化学专业人才进行的化学专业课程体系教学改革与实践。希望能够对今后的化学专业课程体系教学改革提供一些借鉴。     

Instructions to Authors

Editorial Policy
Analysis and Testing Technology and Instruments, published quarterly, is a journal reporting new technology, theory, method and achievements in the fields of modern instrumental analysis and testing technologies. It is sponsored by the Unified Plan Bureau of the Chinese Academy of Sciences （CAS）, the Analysis and Testing Center of Lanzhou Branch of CAS and Lanzhou Institute of Chemical Physics of CAS.     

An Accurate Barrier for the Hydrogen Exchange Reaction from Valence Bond Theory: Is this Theory Coming of Age?

One of the landmark achievements of quantum chemistry, specifically of MO-based methods that include electron correlation, was the precise calculation of the barrier for the hydrogen-exchange reaction (B. Liu, J. Chem. Phys. 1973, 58, 1925; P. Siegbahn, B. Liu, J. Chem. Phys. 1978, 68, 2457). This paper reports an accurate calculation of this barrier by two recently developed VB methods that use only the eight classical VB structures. To our knowledge, the present work is the first accurate ab initio VB barrier that matches an experimental value. Along with the accurate barrier, the VB method provides accurate bond energies and diabatic quantities that enable the barrier height to be analyzed by the VB state correlation diagram approach, VBSCD (S. Shaik, A. Shurki, Angew. Chem. 1999, 111, 616; Angew. Chem. Int. Ed. Engl. 1999, 38, 586). This is a proof of principal that VB theory with appropriate account of dynamic electron correlation can achieve quantitative accuracy of reaction barriers, and still retain a compact and interpretable wave function. A sample of S(N)2 barriers and dihalogen bonding energies, which are close to CCSD(T) and G2(+) values, show that the H(3) problem is not an isolated case, and while it is premature to conclude that VB theory has come of age, the occurrence of this event is clearly within sight.     

Time-dependent four-component relativistic density-functional theory for excitation energies. II. The exchange-correlation kernel

We extend our previous formulation of time-dependent four-component relativistic density-functional theory [J. Gao, W. Liu, B. Song, and C. Liu, J. Chem. Phys. 121, 6658 (2004)] by using a noncollinear form for the exchange-correlation kernel. The new formalism can deal with excited states involving moment (spin)-flipped configurations which are otherwise not accessible with ordinary exchange-correlation functionals. As a first application, the global potential-energy curves of 16 low-lying omega omega-coupled electronic states of the AuH molecule have been investigated. The derived spectroscopic parameters, including the adiabatic and vertical excitation energies, equilibrium bond lengths, harmonic and anharmonic vibrational constants, fundamental frequencies, and dissociation energies, are grossly in good agreement with those of ab initio multireference second-order perturbation theory and the available experimental data.     

A new force field model for the simulation of transport properties of imidazolium-based ionic liquids

A new, non-polarizable force field model (FFM) for imidazolium-based, room-temperature ionic liquids (RTILs), 1-ethyl-3-methyl-imidazolium tetrafluoroborate and 1-butyl-3-methyl-imidazolium tetrafluoroborate, has been developed. Modifying the FFM originally designed by Liu et al. (J. Phys. Chem. B, 2004, 108, 12978-12989), the electrostatic charges on interacting sites are refined according to partial charges calculated by explicit-ion density functional theory. The refined FFM reproduces experimental heats of vaporization, diffusion coefficients, ionic conductivities, and shear viscosities of RTILs, which is a significant improvement over the original model (Zh. Liu, Sh. Huang and W. Wang, J. Phys. Chem. B, 2004, 108, 12978-12989). The advantages of the proposed procedure include clarity, simplicity, and flexibility. Expanding the functionality of our FFM conveniently only requires modification of the electrostatic charges. Our FFM can be extended to other classes of RTILs as well as condensed matter systems in which the ionic interaction requires an account of polarization effects.     

Solvent effects on electrophilicity

Continuum solvent effect on the electrophilicity index recently proposed by Parr and co-workers (Parr, R. G.; von Szentpaly, L.; Liu, S. J. Am. Chem. Soc. 1999, 121, 1922) is discussed in detail. Solvent effect is introduced using the self-consistent isodensity polarized continuum model (SCI-PCM). A linear relationship is found between the change in electrophilicity index and the solvation energy as represented in the frame of the reaction field theory. The effect of a polarizable environment on the global electrophilicity is examined for a series of 18 well-known electrophiles presenting a wide diversity in structure and bonding properties. It is found that solvation enhances the electrophilicity power of neutral electrophilic ligands but attenuates this power in charged and ionic electrophiles.     

Contribution of the Sedimentation and Coalescence Mechanisms to the Separation of Concentrated Water-in-Oil Emulsions

Crude oil is, in the vast majority of cases, produced together with formation water in the form of water/oil emulsions. Until recently oil/water separators were simply designed using Stokes' law. In order to improve the design of these separators the two main contributing mechanisms, sedimentation and coalescence, have to be better understood. This article presents a method that distinguishes the respective contributions of the sedimentation and coalescence mechanisms. Two series of experiments have been carried out, the first with a system heavily charged in surfactant that only allows sedimentation of the emulsions droplets. The second with a much lower surfactant concentration allows both sedimentation and coalescence to take place. By comparing the separation velocities of the oil/emulsion interfaces of the two series of experiments, it seems possible to determine the contribution of the two mechanisms towards the separation.     

Erratum: General peroxidase activity of a parallel G-quadruplex-hemin DNAzyme formed by Pu39WT - a mixed G-quadruplex forming sequence in the Bcl-2 P1 promoter

This is a correction to the following paper: General peroxidase activity of a parallel G-quadruplex-hemin DNAzyme formed by Pu39WT - a mixed G-quadruplex forming sequence in the Bcl-2 P1 promoter, Bo Liu, Da Li* and Hong Shang*, Chemistry Central Journal 2014, 8:43 (1 July 2014).     

Pair-correlated speed distributions for the OH+CH4/CD4 reactions: Further remarks on their classical trajectory calculations in a quantum spirit

Ten years ago, Liu and co-workers measured pair-correlated speed distributions for OH+CH₄/CD₄ reactions by means of velocity map imaging (VMI) techniques at a collision energy of ∼10 kcal/mol [B. Zhang, W. Shiu, J. J. Lin and K. Liu, J. Chem. Phys 122, 131102 (2005); B. Zhang, W. Shiu and K. Liu, J. Phys. Chem. A 109, 8989 (2005)]. Recently, two of us could semi-quantitatively reproduce these measurements by performing full-dimensional quasi-classical trajectory calculations in a quantum spirit on an ab-initio potential energy surface of their own [J. Espinosa-Garcia and J. C. Corchado, Theor. Chem. Acc. (2015) 134: 6; J. Phys. Chem. B 120, 1446 (2016)]. The goal of the present work is to show that these results can be significantly improved by adding a few more constraints in order to better comply with the restrictions imposed by VMI. Overall, the level of agreement between theory and experiment is remarkable owing to the large dimensionality of the reactions under scrutiny. This is an encouraging result considering the computational challenges of quantum scattering calculations for such large processes.     

Examining the robustness of first-principles calculations for metal hydride reaction thermodynamics by detection of metastable reaction pathways

First principles calculations have played a useful role in screening mixtures of complex metal hydrides to find systems suitable for H(2) storage applications. Standard methods for this task efficiently identify the lowest energy reaction mechanisms among all possible reactions involving collections of materials for which DFT calculations have been performed. The resulting mechanism can potentially differ from physical reality due to inaccuracies in the DFT functionals used, or due to other approximations made in estimating reaction free energies. We introduce an efficient method to probe the robustness of DFT-based predictions that relies on identifying reactions that are metastable relative to the lowest energy reaction path predicted with DFT. An important conclusion of our calculations is that in many examples DFT cannot unambiguously predict a single reaction mechanism for a well defined metal hydride mixture because two or more mechanisms have reaction energies that differ by a small amount. Our approach is illustrated by analyzing a series of single step reactions identified in our recent work that examined reactions with a large database of solids [Kim et al., Phys. Chem. Chem. Phys. 2011, 13, 7218].