In Situ Synthesis of 3D Flower‐Like Nanocrystalline Ni/C and its Effect on Hydrogen Storage Properties of LiAlH4

Lithium alanate (LiAlH₄) is of particular interest as one of the most promising candidates for solid‐state hydrogen storage. Unfortunately, high dehydrogenation temperatures and relatively slow kinetics limit its practical applications. Herein, 3D flower‐like nanocrystalline Ni/C, composed of highly dispersed Ni nanoparticles and interlaced carbon flakes, was synthesized in situ. The as‐synthesized nanocrystalline Ni/C significantly decreased the dehydrogenation temperature and dramatically improved the dehydrogenation kinetics of LiAlH₄. It was found that the LiAlH₄ sample with 10 wt % Ni/C (LiAlH₄‐10 wt %Ni/C) began hydrogen desorption at approximately 48 °C, which is very close to ambient temperature. Approximately 6.3 wt % H₂ was released from LiAlH₄‐10 wt %Ni/C within 60 min at 140 °C, whereas pristine LiAlH₄ only released 0.52 wt % H₂ under identical conditions. More importantly, the dehydrogenated products can partially rehydrogenate at 300 °C under 4 MPa H₂. The synergetic effect of the flower‐like carbon substrate and Ni active species contributes to the significantly reduced dehydrogenation temperatures and improved kinetics.     

Effects of Stoichiometry on the H2‐Storage Properties of Mg(NH2)2–LiH–LiBH4 Tri‐Component Systems

The hydrogen desorption pathways and storage properties of 2 Mg(NH₂)₂–3 LiH–x LiBH₄ samples (x =0, 1, 2, and 4) were investigated systematically by a combination of pressure composition isotherm (PCI), differential scanning calorimetric (DSC), and volumetric release methods. Experimental results showed that the desorption peak temperatures of 2 Mg(NH₂)₂–3 LiH–x LiBH₄ samples were approximately 10–15 °C lower than that of 2 Mg(NH₂)₂–3 LiH. The 2 Mg(NH₂)₂–3 LiH–4 LiBH₄ composite in particular began to release hydrogen at 90 °C, thereby exhibiting superior dehydrogenation performance. All of the LiBH₄‐doped samples could be fully dehydrogenated and re‐hydrogenated at a temperature of 143 °C. The high hydrogen pressure region (above 50 bar) of PCI curves for the LiBH₄‐doped samples rose as the amount of LiBH₄ increased. LiBH₄ changed the desorption pathway of the 2 Mg(NH₂)₂–3 LiH sample under a hydrogen pressure of 50 bar, thereby resulting in the formation of MgNH and molten [LiNH₂–2 LiBH₄]. That is different from the dehydrogenation pathway of 2 Mg(NH₂)₂–3 LiH sample without LiBH₄, which formed Li₂Mg₂N₃H₃ and LiNH₂, as reported previously. In addition, the results of DSC analyses showed that the doped samples exhibited two independent endothermic events, which might be related to two different desorption pathways.     

Crucial Roles of Two Hydrated Mg2+ Ions in Reaction Catalysis of the Pistol Ribozyme

Pistol ribozymes constitute a new class of small self‐cleaving RNAs. Crystal structures have been solved, providing three‐dimensional snapshots along the reaction coordinate of pistol phosphodiester cleavage, corresponding to the pre‐catalytic state, a vanadate mimic of the transition state, and the product. The results led to the proposed underlying chemical mechanism. Importantly, a hydrated Mg²⁺ ion remains innersphere‐coordinated to N7 of G33 in all three states, and is consistent with its likely role as acid in general acid base catalysis (δ and β catalysis). Strikingly, the new structures shed light on a second hydrated Mg²⁺ ion that approaches the scissile phosphate from its binding site in the pre‐cleavage state to reach out for water‐mediated hydrogen bonding in the cyclophosphate product. The major role of the second Mg²⁺ ion appears to be the stabilization of product conformation. This study delivers a mechanistic understanding of ribozyme‐catalyzed backbone cleavage.     

Hydrogen Storage Properties of Ca(BH4)2–LiNH2 System

Ca(BH₄)₂ is one of the promising candidates for hydrogen storage materials because of its high gravimetric and volumetric hydrogen capacity. However, its high dehydrogenation temperature and limited reversibility has been a hurdle for its practical applications. In an effort to overcome these barriers and to adjust the thermal stability, we make a composite system Ca(BH₄)₂–LiNH₂. Interaction of Ca(BH₄)₂ and LiNH₂ leads to decreased dehydrogenation temperatures and increased hydrogen desorption capacity in comparison to pristine Ca(BH₄)₂. More than 7 wt % of hydrogen can be detached at a temperature as low as approximately 178 °C from the cobalt‐catalyzed Ca(BH₄)₂–4 LiNH₂ system.     

MAlH4(M=Li,Na)储氢材料*

氢能是一种新型的清洁能源,有望替代碳经济,而氢的储存是氢能应用的关键。近年来,研究集中在具有储氢容量高和可逆性好等优点的固态储氢材料上。许多新型储氢材料不断出现,其中以MAlH₄(M=Li, Na)为代表的金属复合氢化物体系被认为是最有前景的储氢材料之一。本文综述了MAlH₄(M=Li, Na)作为可逆储氢材料的研究现状,主要从吸放氢反应、储氢性能、反应机理、理论计算和存在的问题等方面进行了讨论,并指出其相关发展趋势。     

In Situ Synchrotron X-ray Diffraction Studies of Hydrogen-Desorption Properties of 2LiBH4–Mg2FeH6 Composite

Adding a secondary complex metal hydride can either kinetically or thermodynamically facilitate dehydrogenation reactions. Adding Mg₂FeH₆ to LiBH₄ is energetically favoured, since FeB and MgB₂ are formed as stable intermediate compounds during dehydrogenation reactions. Such “hydride destabilisation” enhances H₂-release thermodynamics from H₂-storage materials. Samples of the LiBH₄ and Mg₂FeH₆ with a 2:1 molar ratio were mixed and decomposed under three different conditions (dynamic decomposition under vacuum, dynamic decomposition under a hydrogen atmosphere, and isothermal decomposition). In situ synchrotron X-ray diffraction results revealed the influence of decomposition conditions on the selected reaction path. Dynamic decomposition of Mg₂FeH₆–LiBH₄ under vacuum, or isothermal decomposition at low temperatures, was found to induce pure decomposition of LiBH₄, whilst mixed decomposition of LiBH₄ + Mg and formation of MgB₂ were achieved via high-temperature isothermal dehydrogenation.     

Template‐Free Preparation of Volvox‐like CdxZn1−xS Nanospheres with Cubic Phase for Efficient Photocatalytic Hydrogen Production

Volvox‐like Cd_xZn_1?xS solid solutions with a cubic zinc blend structure were synthesized through a template‐free ethylene glycol process. Cd(Ac)₂ ? 2 H₂O, Zn(Ac)₂ ? 2 H₂O, and thiourea are used as the starting materials and dissolved in ethylene glycol. These reaction precursors and solvent not only contributed to control over the formation of the volvox‐like spherical geometry, but also exerted vigorous domination for existence of cubic‐phase Cd_xZn_1?xS nanostructures. As‐prepared volvox‐like Cd_xZn_1?xS nanospheres have a diameter of around 100 nm with extensional shells. These samples show excellent photocatalytic H₂ evolution activity from water splitting under visible‐light irradiation without any cocatalyst or scaffolding, owing to their tunable band gap, cubic zinc blend structure, and unique hierarchical porous structure with a high surface area (as high as 95.2 m² g^?1).     

Reaction Pathways Determined by Mechanical Milling Process for Dehydrogenation/Hydrogenation of the LiNH2/MgH2 System

The dehydrogenation/hydrogenation processes of the LiNH₂/MgH₂ (1:1) system were systematically investigated with respect to balller milling and the subsequent heating process. The reaction pathways for hydrogen desorption/absorption of the LiNH₂/MgH₂ (1:1) system were found to depend strongly on the milling duration due to the presence of two competing reactions in different stages (i.e., the reaction between Mg(NH₂)₂ and MgH₂ and that between Mg(NH₂)₂ and LiH), caused by a metathesis reaction between LiNH₂ and MgH₂, which exhibits more the nature of solid–solid reactions. The study provides us with a new approach for the design of novel hydrogen storage systems and the improvement of hydrogen‐storage performance of the amide/hydride systems.     

Superlight and Superflexible Three‐Dimensional Semiconductor Frameworks A(X≡Y)4 (A=Si,Ge; X/Y=C,B, N) with Tunable Optoelectronic and Mechanical Properties from First‐Principles

Silicon carbide materials, as leading wide band gap semiconductors, hold significant importance in semiconductor technologies. Herein, diamond‐like 3D materials with low density, but high elasticity properties, have been designed from first‐principles calculations. They are porous single‐crystalline materials composed of sp³‐hybridized silicon (or germanium) and sp‐type C≡C (or B≡N) linear moieties; their stabilities are comparable to those of recently prepared SiC₄ materials. Moreover, such wide band gap semiconductors have strong absorption over a wide UV range and exhibit superlight, superflexible, and incompressible mechanical properties, and their optoelectronic and mechanical properties can be well tuned through structural modifications. Such features provide high potential for practicable application under extreme conditions, and suggest promising applications for the design of UV optoelectronic devices.     

Chemical Synthesis of Burkholderia Lipid A Modified with Glycosyl Phosphodiester‐Linked 4‐Amino‐4‐deoxy‐β‐L‐arabinose and Its Immunomodulatory Potential

Modification of the Lipid A phosphates by positively charged appendages is a part of the survival strategy of numerous opportunistic Gram‐negative bacteria. The phosphate groups of the cystic fibrosis adapted Burkholderia Lipid A are abundantly esterified by 4‐amino‐4‐deoxy‐β‐L ‐arabinose (β‐L ‐Ara4N), which imposes resistance to antibiotic treatment and contributes to bacterial virulence. To establish structural features accounting for the unique pro‐inflammatory activity of Burkholderia LPS we have synthesised Lipid A substituted by β‐L ‐Ara4N at the anomeric phosphate and its Ara4N‐free counterpart. The double glycosyl phosphodiester was assembled by triazolyl‐tris‐(pyrrolidinyl)phosphonium‐assisted coupling of the β‐L ‐Ara4N H‐phosphonate to α‐lactol of β(1→6) diglucosamine, pentaacylated with (R)‐(3)‐acyloxyacyl‐ and Alloc‐protected (R)‐(3)‐hydroxyacyl residues. The intermediate 1,1′‐glycosyl‐H‐phosphonate diester was oxidised in anhydrous conditions to provide, after total deprotection, β‐L ‐Ara4N‐substituted Burkholderia Lipid A. The β‐L ‐Ara4N modification significantly enhanced the pro‐inflammatory innate immune signaling of otherwise non‐endotoxic Burkholderia Lipid A.     

Preparation and Catalytic Activity of a Novel Nanocrystalline ZrO2@C Composite for Hydrogen Storage in NaAlH4

Sodium alanate (NaAlH₄) has attracted intense interest as a prototypical high‐density hydrogen‐storage material. However, poor reversibility and slow kinetics limit its practical applications. Herein, a nanocrystalline ZrO₂@C catalyst was synthesized by using Uio‐66(Zr) as a precursor and furfuryl alcohol (FA) as a carbon source. The as‐synthesized ZrO₂@C exhibits good catalytic activity for the dehydrogenation and hydrogenation of NaAlH₄. The NaAlH₄‐7 wt % ZrO₂@C sample released hydrogen starting from 126 °C and reabsorbed it starting from 54 °C, and these temperatures are lower by 71 and 36 °C, respectively, relative to pristine NaAlH₄. At 160 °C, approximately 5.0 wt % of hydrogen was released from the NaAlH₄‐7 wt % ZrO₂@C sample within 250 min, and the dehydrogenation product reabsorbed approximately 4.9 wt % within 35 min at 140 °C and 100 bar of hydrogen. The catalytic function of the Zr‐based active species is believed to contribute to the significantly reduced operating temperatures and enhanced kinetics.     

4‐Aryl‐3,5‐bis(arylethynyl)aryl‐4H‐1,2,4‐triazoles: Multitasking Skeleton as a Self‐Assembling Unit

The synthesis of a series of 4‐aryl‐3,5‐bis(arylethynyl)aryl‐4H‐1,2,4‐triazoles derivatives is reported and the influence exerted by peripheral substitution on the morphology of the aggregates generated from these 1,2,4‐triazoles is investigated by SEM imaging. The presence of paraffinic side chains results in long fibrillar supramolecular structures, but unsubstituted triazoles self‐assemble into thinner ribbons and needle‐like aggregates. The crystals obtained from methoxy‐substituted triazoles have been utilised to elaborate a model that helps to justify aggregation of the investigated 1,2,4‐triazoles, in which the operation of arrays of C?H???π non‐covalent interactions plays a significant role. The results presented herein demonstrate the ability of simple molecules to behave as multitasking scaffolds with different properties, depending on peripheral substitution. Thus, although 1,2,4‐triazoles without long paraffinic side chains exhibit optical waveguiding behaviour, triazoles endowed with peripheral paraffinic side chains exhibit hexagonal columnar mesomorphism.     

Study on 1,3,5‐Triazine Chemistry in Dehydrocondensation: Gauche Effect on the Generation of Active Triazinylammonium Species

The reaction of 2‐chloro‐4,6‐dimethoxy‐1,3,5‐triazine (CDMT) with various nitrogen‐containing compounds, particularly tertiary amines (tert‐amines), has been studied for the preparation of 2‐(4,6‐dimethoxy‐1,3,5‐triazinyl)trialkylammonium salts [DMT‐Am(s)]. DMT‐Ams derived from aliphatic tert‐amines exhibited activity for the dehydrocondensation between a carboxylic acid and an amine to form an amide in a model reaction. Based on a conformational analysis of DMT‐Ams and tert‐amines by NMR and X‐ray diffraction methods, we concluded that a β‐alkyl group maintained in a gauche relationship with the nitrogen lone pair of tert‐amines significantly hinders the approach of CDMT to the nitrogen. Thus, trimethylamine and quinuclidine without such alkyl groups readily react with CDMT whereas triethylamine, possessing two or three such gauche β‐alkyl groups in the stable conformations, does not react at all. The theory of “gauche β‐alkyl group effect” proposed here provides useful guidelines for the preparation of DMT‐Ams possessing various tertiary amine moieties. An investigation of the dehydrocondensation activity of tert‐amines in a CDMT/tert‐amine system that involves in situ generation of DMT‐Am, showed that the gauche effect of the β‐alkyl group becomes quite pronounced; the yield of the amide decreases significantly with tert‐amines possessing an unavoidable gauche β‐alkyl group. Thus, the tert‐amine/CDMT systems are useful for judging whether tert‐amines can readily react with CDMT without isolation of DMT‐Ams.     

Intrinsic self‐initiating thermal ring‐opening polymerization of 1,3‐benzoxazines without the influence of impurities using very high purity crystals

A phenol/aniline type monofunctional benzoxazine monomer, PH‐a , is synthesized and highly purified to study the intrinsic thermal ring‐opening polymerization of benzoxazines without the influence of any impurity. The successful synthesis of the monomer and its corresponding chemical structure are confirmed by Fourier transform infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance (¹H NMR) spectroscopy. Purity of the compound is evaluated through differential scanning calorimetry (DSC) as well as elemental analysis (EA). Moreover, the thermal behavior of benzoxazine monomer toward polymerization is also studied by DSC, indicating that the highly purified benzoxazine monomer actually polymerize upon heating. The results present evidence of an intrinsic tendency for 1,3‐benzoxazines to undergo thermally induced ring‐opening polymerization upon heating only without any impurity participating during the reaction. This reveals that polybenzoxazines can be obtained by both the traditional thermally accelerated (or activated) polymerization, where impurities or purposefully added initiators are involved in the reaction; or, by the classic thermal polymerization, where only heat is enough to initiate the reaction. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3434–3445     

N‐Substituted Azacalixphyrins: Synthesis,Properties, and Self‐Assembly

Pre‐ and postintroduction of substituents with respect to the macrocyclization step leads to previously unknown N‐substituted azacalixphyrins. The stepwise synthetic approach has been studied in detail to highlight the key role of the N‐substituents of the precursors and/or intermediates in terms of reactivity. Based on a combined experimental and theoretical investigation, the relationship between the properties of the macrocycles and their degree of substitution is rationalized. Depending on the nature of the N‐substituents, the formation of supramolecular ribbon‐like structures could also be observed, as demonstrated by combined TEM, SEM, AFM, and FTIR experiments.     

Effect of the Peptidic Scaffold in Copper(II) Coordination and the Redox Properties of Short Histidine‐Containing Peptides

A linear decapeptide containing three His and one Asp residues and a β‐turn‐inducing dProPro unit was synthesised. A detailed potentiometric, mass spectrometric and spectroscopic study showed that at a 1:1 ratio of C_Cu/C_peptide this peptide formed a major [CuH(O_dPro?Asp)]²⁺ species (pH range 5.5–7.0), in which the Cu²⁺ ion was bound to the His and Asp residues in square‐planar or square‐pyramidal geometries. The stability constant corrected for protonated species (log K*=9.33) is almost equal to the value obtained for the parent [CuH(O?Asp)]²⁺ species (log K*_CuH(O‐Asp)=9.28), but lower than that obtained for the cyclic [CuH(C?Asp)]²⁺ complex (log K*_CuH(C‐Asp)=10.79) previously published. Thus, the replacement of the ProGly unit by the stronger β‐turn‐inducing dProPro unit did not generate a more stable copper(II) species, although the O_dPro?Asp peptide was structured in solution, as shown by circular dichroism (CD) spectroscopy. Interestingly, the calculated value of K_eff showed that this peptide behaved similarly to the O?Asp or C?Asp counterparts, depending on the pH value. The cyclic voltammetry data indicated that the most easily reducible species were [CuH(O?Asp)]²⁺ (E′⁰=262 mV versus a normal hydrogen electrode (NHE)) and [CuH(O_dPro?Asp)]²⁺ (E′⁰=294 mV versus NHE) complexes, the peptidic scaffolds of which are open. A lower value was obtained for [CuH(C?Asp)]²⁺ (E′⁰=24 mV versus NHE). A different degree of non‐reversibility was observed for the three copper(II) complexes; this could reflect a different degree of flexibility in their respective peptidic scaffolds.     

添加叔丁醇钾对Mg(NH2)2-2LiH体系储氢性能的影响

叔丁醇钾(C_4H_9OK)的添加显著改善了Mg(NH_2)_2-2LiH体系的储氢性能。添加0.08 mol C_4H_9OK的Mg(NH_2)_2-2LiH-0.08C_4H_9OK样品表现出最佳储氢性能。该样品的起始放氢温度仅为70℃,较Mg(NH_2)_2-2LiH原始样品降低了60℃;130℃完全放氢后,该样品可在50℃开始吸氢,较原始样品降低了50℃。Mg(NH_2)_2-2LiH-0.08C_4H_9OK样品可在150℃的等温条件下50min内迅速放出质量分数3.82%的氢气,完全放氢后可在120℃的等温条件下50 min内快速吸收质量分数4.11%的氢气,表现出良好的吸放氢动力学性能。C_4H_9OK的添加降低了样品放氢反应的表观活化能和反应焓变,改善了放氢反应的动力学和热力学性能,从而降低了放氢反应温度。进一步的放氢反应机理研究发现,在180℃之前,C_4H_9OK对Mg(NH_2)_2-2LiH体系的放氢起催化改性作用;温度继续升高后,C_4H_9OK将会分解并参与放氢反应最终生成Li_3K(NH_2)_4。     

Mechanistic Investigation of the Dipolar [2+2] Cycloaddition–Cycloreversion Reaction between 4‐(N,N‐Dimethylamino)phenylacetylene and Arylated 1,1‐Dicyanovinyl Derivatives To Form Intramolecular Charge‐Transfer Chromophores

The kinetics and mechanism of the formal [2+2] cycloaddition–cycloreversion reaction between 4‐(N,N‐dimethylamino)phenylacetylene ( 1 ) and para‐substituted benzylidenemalononitriles 2 b – 2 l to form 2‐donor‐substituted 1,1‐dicyanobuta‐1,3‐dienes 3 b – 3 l via the postulated dicyanocyclobutene intermediates 4 b – 4 l have been studied experimentally by the method of initial rates and computationally at the unrestricted B3LYP/6‐31G(d) level. The transformations were found to follow bimolecular, second‐order kinetics, with ${{\rm{\Delta }}H_{{\rm{exp}}}^{ {\ne} } }$ =13–18 kcal mol^?1, ${{\rm{\Delta }}S_{{\rm{exp}}}^{ {\ne} } }$ ≈?30 cal K^?1 mol^?1, and ${{\rm{\Delta }}G_{{\rm{exp}}}^{ {\ne} } }$ =22–27 kcal mol^?1. These experimental activation parameters for the rate‐determining cycloaddition step are close to the computational values. The rate constants show a good linear free energy relationship (ρ=2.0) with the electronic character of the para‐substituents on the benzylidene moiety in dimethylformamide (DMF), which is indicative of a dipolar mechanism. Analysis of the computed structures and their corresponding solvation energies in acetonitrile suggests that the rate‐determining attack of the nucleophilic, terminal alkyne carbon onto the dicyanovinyl electrophile generates a transient zwitterion intermediate with the negative charge developing as a stabilized malononitrile carbanion. The computational analysis predicted that the cycloreversion of the postulated dicyanocyclobutene intermediate would become rate‐determining for 1,1‐dicyanoethene ( 2 m ) as the electrophile. The dicyanocyclobutene 4 m could indeed be isolated as the key intermediate from the reaction between alkyne 1 and 2 m and characterized by X‐ray analysis. Facile first‐order cycloreversion occurred upon further heating, yielding as the sole product the 1,1‐dicyanobuta‐1,3‐diene 3 m .