Unraveling the effect of Al doping on CO adsorption at ZnO(101̄0)

Understanding the effect of Al doping on CO adsorption at ZnO(10$\bar{1}$0) is crucial for designing a high-performance CO gas sensor. In this work, we investigated the adsorption properties of CO on pristine and Al-doped ZnO(10$\bar{1}$0) by performing DFT+U calculations. It is found that the doping of Al on ZnO(10$\bar{1}$0) induces the semiconductor-to-metal transition and thus enhances the conductance of the substrate. Compared to the pristine ZnO(10$\bar{1}$0), the adsorption energy of CO on the Al-doped surfaces is significantly enhanced since Al doping has the effect of strengthening the adsorption bond. The bonding analysis reveals that CO adsorbs on pristine ZnO(10$\bar{1}$0) via the sole σ-dative donation between the CO HOMO 5σ and the empty states of the Zn cation while π-back donation from filled states of Zn or Al cations to the CO 2π* LUMO is facilitated on the Al-doped surfaces. The π-back donation also results in the red-shift of the CO stretching frequency on the Al-doped surfaces, contrasting to the blue-shift on the pristine surface. The simulated results demonstrate that the doping of Al to a three-fold coordinated site on ZnO(10$\bar{1}$0) is highly beneficial for boosting the performance of the CO gas sensor. Our theoretical investigation provides fundamental insights into the effect of Al doping on the sensing mechanism for CO at the ZnO(10$\bar{1}$0) surface.

Al doping enhances the adsorption of CO on ZnO(10$\bar{1}$0) by facilitating π-back donation from the surface to CO.     

Global diabatic potential energy surfaces for the BeH2+ system and dynamics studies on the Be+(2P) + H2(X1Σg+) → BeH+(X1Σ+) + H(2S) reaction

The Be⁺(²P) + H₂(X¹Σ_g⁺) → BeH⁺(X¹Σ⁺) + H(²S) reaction has great significance for studying diabatic processes and ultracold chemistry. The first global diabatic potential energy surfaces (PESs) which are correlated with the lowest two adiabatic states 1²A′ and 2²A′ of the BeH₂⁺ system are constructed by using the neural network method. Ab initio energy points are calculated using the multi-reference configuration interaction method with the Davidson correction and AVQZ basis set. The diabatic energies are obtained from the transformation of ab initio data based on the dipole moment operators. The topographical characteristics of the diabatic PESs are described in detail, and the positions of crossing between the V^d₁₁ and V^d₂₂ are pinpointed. On new diabatic PESs, the time-dependent quantum wave packet method is carried out to study the mechanism of the title reaction. The results of dynamics calculations indicate the reaction has no threshold and the product BeH⁺ is excited to high vibrational states easily. In addition, the product BeH⁺ tends to backward scattering at most collision energies.

The first global diabatic potential energy surfaces for the Be⁺(²P) + H₂(X¹Σ_g⁺) → BeH⁺(X¹Σ⁺) + H(²S) reaction are constructed.     

Deformation mechanism in Al0.1CoCrFeNi Σ3(111)[11̄0] high entropy alloys – molecular dynamics simulations

High entropy alloys (HEAs), composed of multiple components with equal or near atomic proportions, have extraordinary mechanical properties and are expected to bear the impact of high-speed forces in armor protection structure materials. In order to understand the deformation behaviour of HEAs under tensile and compressive loading, molecular dynamics simulations were performed to reveal the deformation mechanism and mechanical properties of three crystal structures: Al_0.1CoCrFeNi HEAs without grain boundaries (perfect HEAs), Al_0.1CoCrFeNi HEAs with grain boundaries of Σ3(111)[1$\bar{1}$0] (GBs HEAs) and grain boundaries of Σ3(111)[1$\bar{1}$0] with chemical cluster HEAs (cluster-GBs HEAs). The mechanical properties of the three models at the same strain rate were discussed. Then, the mechanical properties at different strain rates were analyzed. The movement and direction of internal dislocations during the deformation process were investigated. The simulation results show that the GBs HEAs and the cluster-GBs both play an important role in the deformation and failure of the HEAs. Under tensile loading, three behaviour stages of deformation were observed. Cluster-GBs HEAs have a larger yield strength and Young''s modulus than that of GBs and perfect HEAs. The higher the strain rate is, the greater the stress reduction rate. Under compressive loading, there are only two behaviour stages of deformation. Cluster-GBs HEAs also have the largest yield strength. Under tensile and compressive deformation, Shockley partial dislocations of 1/6 <112> are dominant and their moving direction and effect on mechanical properties are discussed.

Build grain boundaries for Al_0.1CoCrFeNi Σ3(111)[1$\bar{1}$0] HEA and elucidate the deformation behavior under tensile and compressive loading.     

Study on the growth of Al-doped ZnO thin films with (112̄0) and (0002) preferential orientations and their thermoelectric characteristics

In this work, using a conventional magnetron sputtering system, Al-doped ZnO (AZO) films with (11$\bar{2}$0) and (0002) preferential orientations were grown on r-sapphire and a-sapphire substrates, respectively. The effect of substrate and deposition temperature on the growth of AZO films and their preferential orientations were investigated. The crystallographic characteristics of AZO films were characterized by X-ray diffraction (XRD). The surface morphology of AZO films was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). It is found that the lattice mismatch between AZO and substrate determines the growth of AZO films and their preferential orientations. The thermoelectric properties are strongly dependent on the crystal grain shape and the grain boundaries induced by the preferred orientation. The highly connected and elongated grains lead to high thermoelectric properties. The in-plane anisotropy performances of thermoelectric characteristics were found in the (11$\bar{2}$0) preferential oriented ZnO films. The in-plane power factor of the (11$\bar{2}$0) preferential oriented ZnO films in the [0001] direction was more than 1.5 × 10⁻³ W m⁻¹ K⁻² at 573 K, which is larger than that of the (0002) preferential oriented ZnO films.

In this work, using a conventional magnetron sputtering system, Al-doped ZnO (AZO) films with (11$\bar{2}$0) and (0002) preferential orientations were grown on r-sapphire and a-sapphire substrates, respectively.     

Structural investigations of La0.6Sr0.4FeO3−δ under reducing conditions: kinetic and thermodynamic limitations for phase transformations and iron exsolution phenomena

The crystal structure changes and iron exsolution behavior of a series of oxygen-deficient lanthanum strontium ferrite (La_0.6Sr_0.4FeO_3−δ, LSF) samples under various inert and reducing conditions up to a maximum temperature of 873 K have been investigated to understand the role of oxygen and iron deficiencies in both processes. Iron exsolution occurs in reductive environments at higher temperatures, leading to the formation of Fe rods or particles at the surface. Utilizing multiple ex situ and in situ methods (in situ X-ray diffraction (XRD), in situ thermogravimetric analysis (TGA), and scanning X-ray absorption near-edge spectroscopy (XANES)), the thermodynamic and kinetic limitations are accordingly assessed. Prior to the iron exsolution, the perovskite undergoes a nonlinear shift of the diffraction peaks to smaller 2θ angles, which can be attributed to a rhombohedral-to-cubic (R$\bar{3}$c to Pm$\bar{3}$m) structural transition. In reducing atmospheres, the cubic structure is stabilized upon cooling to room temperature, whereas the transition is suppressed under oxidizing conditions. This suggests that an accumulation of oxygen vacancies in the lattice stabilize the cubic phase. The exsolution itself is shown to exhibit a diffusion-limited Avrami-like behavior, where the transport of iron to the Fe-depleted surface-near region is the rate-limiting step.

A dependence of structural transformation and iron exsolution on chemical environment and reducing conditions is proven for the perovskite La_0.6Sr_0.4FeO_3−δ.     

The effect of strain on water dissociation on reduced rutile TiO2(110) surface

The effect of external uniaxial strain on water dissociation on a reduced rutile TiO₂(110) surface has been theoretically studied using first-principles calculations. We find that when the tensile strain along [1$\bar{1}$0] is applied, the energy barrier of water dissociation substantially decreases with the increase of strain. In particular, water almost automatically dissociates when the strain is larger than 3%. Besides, the water dissociation mechanism changes from indirect to direct dissociation when the compressive strain is larger than 1.3% along [1$\bar{1}$0] or 3% along [001]. The results strongly suggest that it is feasible to engineer the water dissociation on the reduced rutile TiO₂(110) surface using external strain.

The tensile strain along [1$\bar{1}$0] on the reduced TiO₂(110) surface can greatly promote the dissociation of water, the compressive strain along [001] and [1$\bar{1}$0] can change the dissociation mechanisms.     

Estimation of Jones matrix,birefringence and entropy using Cloude-Pottier decomposition in polarization-sensitive optical coherence tomography: erratum

An erratum is presented to correct errors in the equations in [Biomed. Opt. Express 7(9), 3551–3573 (2016)].OCIS codes: (110.4500) Optical coherence tomography, (170.4500) Optical coherence tomography, (170.4470) Ophthalmology, (120.2130) Ellipsometry and polarimetryIn our paper [1], several errors in the equations have been found and are corrected as below.Equation (22) of [1] should read Hnoise(Ei¯)=∑j=12−ζj(i)log4(ζj(i)),(22) where the negative sign and the base 4 of the logarithm were described correctly. We note that the same base of the logarithm has to be used for the entropy throughout the processing flow.In addition, Eq. (28) was erroneously presented in [1], which algebraically resulted in 1 regardless of the signals and noises. It was related to the erroneous definition of Eq. (27) in [1]. Equation (27) should be defined to include the bias of the noises as [s0″(1)s1″(1)s2″(1)s3″(1)]:=[|g1H|2¯+|g1V|2¯|g1H|2¯−|g1V|2¯2Re[g1Hg1V*¯]2Im[g1Hg1V*¯]]=[|g1H|2¯+|g1V|2¯|g1H|2¯−|g1V|2¯2Re[E1HE1V*¯]2Im[E1HE1V*¯]]=[|g1H|2¯+|g1V|2¯|g1H|2¯−|g1V|2¯2|E1H|¯|E1V|¯cosδ2|E1H|¯|E1V|¯sinδ]=[|g1H|2¯+|g1V|2¯|g1H|2¯−|g1V|2¯2|g1H|2¯−|n1H|2¯|g1V|2¯−|n1V|2¯cosδ2|g1H|2¯−|n1H|2¯|g1V|2¯−|n1V|2¯sinδ],(27) which is based on Eq. (25) of [1]. Equation (28) of [1] should then read P(1)={s1″(1)}2+{s2″(1)}2+{s3″(1)}2s″0(1)=(|g1H|2¯−|g1V|2¯)2+4(|g1H|2¯−|n1H|2¯)(|g1V|2¯−|n1V|2¯)|g1H|2¯+|g1V|2¯.(28)Consequently, Eqs. (43)-(46) of [1] should readP(ε1¯)=(|ε1H|2¯−|ε1V|2¯)2+4(|ε1H|2¯−Var(ε1H))(|ε1V|2¯−Var(ε1V))|ε1H|2¯+|ε1V|2¯,(43)P(ε2¯)=(|ε2H|2¯−|ε2V|2¯)2+4(|ε2H|2¯−Var(ε2H))(|ε2V|2¯−Var(ε2V))|ε2H|2¯+|ε2V|2¯,(44)P(ε1¯|ε2¯)=(|ε1H|2¯−|ε1V|2¯)2+4(|ε1H|2¯−Var(ε1H|ε2¯))(|ε1V|2¯−Var(ε1V|ε2¯))|ε1H|2¯+|ε1V|2¯,(45)P(ε2¯|ε1¯)=(|ε2H|2¯−|ε2V|2¯)2+4(|ε2H|2¯−Var(ε2H|ε1¯))(|ε2V|2¯−Var(ε2V|ε1¯))|ε2H|2¯+|ε2V|2¯.(46)In Eq. (28), |g1H|2¯−|n1H|2¯ and |g1V|2¯−|n1V|2¯ should be non-negative in principle, but can be negative in practice. If these parameters are negative in the data processing, they are set as zero to avoid physically undefined values of P⁽¹⁾. Similar operations are also applied to Eqs. (43)-(46).In addition, the last sentence of Section 2.5 shown in the following should be deleted because it was presented incorrectly and did not make sense in [1]; “The absolute-squared expected values of the matrix elements in Eq. (24) or (29) that are used in Eqs. (35)-(42) are calculated as |g1H|2¯−|n1H|2¯ and similarly for all other elements.”Since all of the equations were correctly implemented in our processing software of [1], no change is required in the results.     

Anisotropic crystallite size distributions in LiFePO4 powders

The anisotropic crystallite sizes in high-performance LiFePO₄ powders were measured by XRD and compared with the particle sizes found by TEM image analysis. Lognormal particle size distribution functions were determined for all three main crystallographic axes. A procedure was developed to determine the fraction of the composite particles which consists of several crystallites and contains small- and large-angle boundaries. In a sample with the most anisotropic crystallites (ratio of volume-weighted mean crystallite sizes $\bar{L}$_V[001]/$\bar{L}$_V[010] = 1.41) the number of the composite particles was at least 30%.

Large composite particles of LiFePO₄ powders registered by TEM with at least 30% amount are recorded by XRD as smaller crystallites with at least 45% amount.     

Hexagonal VO2 particles: synthesis,mechanism and thermochromic properties

Monoclinic vanadium dioxide VO₂ (M) with hexagonal structure is synthesized by hydrothermal method, and the phase evolution is evidenced. Interestingly, the hexagonal morphology comes into being as a result of the low-energy coherent interfaces, (21$\bar{1}$)₁//(2$\bar{1}$$\bar{1}$)₂ and (2$\bar{1}$$\bar{1}$)₁//(020)₂. The size of hexagonal particles is well controlled by changing the concentration of precursor solutions. Hexagonal particles exhibit excellent thermochromic properties with a narrow hysteresis of 5.9 °C and high stability. In addition, the phase transition temperature can be substantially reduced down to 28 °C by simply W doping.

Monoclinic vanadium dioxide VO₂ (M) with hexagonal structure is synthesized by hydrothermal method, and the phase evolution is evidenced.     

Analysis of ventilatory ratio as a novel method to monitor ventilatory adequacy at the bedside

Introduction

Due to complexities in its measurement, adequacy of ventilation is seldom used to categorize disease severity and guide ventilatory strategies. Ventilatory ratio (VR) is a novel index to monitor ventilatory adequacy at the bedside. VR=(V˙Emeasured×PaCO2measured)/(V˙Epredicted×PaCO2ideal). V˙Epredicted is 100 mL.Kg^-1.min^-1 and Pa_{CO2 ideal} is 5 kPa. Physiological analysis shows that VR is influenced by dead space (V_D/V_T) and CO2 production (V˙CO2). Two studies were conducted to explore the physiological properties of VR and assess its use in clinical practice.

Methods

Both studies were conducted in adult mechanically ventilated ICU patients. In Study 1, volumetric capnography was used to estimate daily V_D/V_T and measure V˙CO2 in 48 patients. Simultaneously, ventilatory ratio was calculated using arterial blood gas measurements alongside respiratory and ventilatory variables. This data was used to explore the physiological properties of VR. In Study 2, 224 ventilated patients had daily VR and other respiratory variables, baseline characteristics, and outcome recorded. The database was used to examine the prognostic value of VR.

Results

Study 1 showed that there was significant positive correlation between VR and VD/VT (modified r = 0.71) and V˙CO2 (r = 0.14). The correlation between VR and V_D/V_T was stronger in mandatory ventilation compared to spontaneous ventilation. Linear regression analysis showed that V_D/V_T had a greater influence on VR than V˙CO2 (standardized regression coefficient 1/1-V_D/V_T: 0.78, V˙CO2: 0.44). Study 2 showed that VR was significantly higher in non-survivors compared to survivors (1.55 vs. 1.32; P < 0.01). Univariate logistic regression showed that higher VR was associated with mortality (OR 2.3, P < 0.01), this remained the case after adjusting for confounding variables (OR 2.34, P = 0.04).

Conclusions

VR is an easy to calculate bedside index of ventilatory adequacy and appears to yield clinically useful information.     

Direct β-selectivity of α,β-unsaturated γ-butyrolactam for asymmetric conjugate additions in an organocatalytic manner

The β-selective asymmetric addition of γ-butyrolactam with cyclic imino esters catalyzed by a bifunctional chiral tertiary amine has been developed, which provides an efficient access to optically active β-position functionalized pyrrolidin-2-one derivatives in both high yield and enantioselectivity (up to 78% yield and 95 : 5 er). This is the first catalytic method to access chiral β-functionalized pyrrolidin-2-one via a direct organocatalytic approach.

The asymmetric addition of γ-butyrolactam with cyclic imino esters catalyzed by (DHQD)₂AQN has been developed, which provides an access to β-position functionalized pyrrolidin-2-one derivatives in high levels yield and enantioselectivity.

Metal-free organocatalytic asymmetric transformations have successfully captured considerable enthusiasm of chemists as powerful methods for the synthesis of various kinds of useful chiral compounds ranging from the preparation of biologically important molecules through to novel materials.¹ Chiral pyrrolidin-2-ones have been recognized as important structural motifs that are frequently encountered in a variety of biologically active natural and synthetic compounds.² In particular, the β-position functionalized pyrrolidin-2-one backbones, which can serve as key synthetic precursors for inhibitory neurotransmitters γ-aminobutyric acids (GABA),³ selective GABA_B receptor agonists⁴ as well as antidepressant rolipram analogues,⁵ have attracted a great deal of attention. Therefore, the development of highly efficient, environmentally friendly and convenient asymmetric synthetic methods to access these versatile frameworks is particularly appealing.As a direct precursor to pyrrolidin-2-one derivatives, recently, α,β-unsaturated γ-butyrolactam has emerged as the most attractive reactant in asymmetric organometallic or organocatalytic reactions for the synthesis of chiral γ-position functionalized pyrrolidin-2-ones (Scheme 1). These elegant developments have been achieved in the research area of catalytic asymmetric vinylogous aldol,⁶ Mannich,⁷ Michael⁸ and annulation reactions⁹ in the presence of either metal catalysts or organocatalysts (a, Scheme 1). These well-developed catalytic asymmetric methods have been related to the γ-functionalized α,β-unsaturated γ-butyrolactam to date. However, in sharp contrast, the approaches toward introducing C-3 chirality at the β-position of butyrolactam through a direct catalytic manner are underdeveloped (b, Scheme 1)¹⁰ in spite of the fact that β-selective chiral functionalization of butyrolactam can directly build up α,β-functionalized pyrrolidin-2-one frameworks.Open in a separate windowScheme 1Different reactive position of α,β-unsaturated γ-butyrolactam in catalytic asymmetric reactions.So far, only a few metal-catalytic enantioselective β-selective functionalized reactions have been reported. For examples, a rhodium/diene complex catalyzed efficient asymmetric β-selective arylation^10a and alkenylation^10b have been reported by Lin group (a, Scheme 2). Procter and co-workers reported an efficient Cu(i)–NHC-catalyzed asymmetric silylation of unsaturated lactams (b, Scheme 2).^10c Despite these creative works, considerable challenges still exist in the catalytic asymmetric β-selective functionalization of γ-butyrolactam. First, the scope of nucleophiles is limited to arylboronic acids, potassium alkenyltrifluoroborates and PhMe₂SiBpin reagents. Second, the catalytic system and activation mode is restricted to metal/chiral ligands. To our knowledge, an efficient catalytic method to access chiral β-functionalized pyrrolidin-2-one via a direct organocatalytic approach has not yet been established. Therefore, the development of organocatalytic asymmetric β-selective functionalization of γ-butyrolactam are highly desirable. In conjunction with our continuing efforts in building upon chiral precedents by using chiral tertiary amine catalytic system,¹¹ we rationalized that the activated α,β-unsaturated γ-butyrolactam might serve as a β-position electron-deficient electrophile. This γ-butyrolactam may react with a properly designed electron-rich nucleophile to conduct an expected β-selective functionalized reaction of γ-butyrolactam under a bifunctional organocatalytic fashion, while avoiding the direct γ-selective vinylogous addition reaction or β,γ-selective annulation as outlined in Scheme 2. Herein we report the β-selective asymmetric addition of γ-butyrolactam with cyclic imino esters¹² catalyzed by a bifunctional chiral tertiary amine, which provides an efficient and facile access to optically active β-position functionalized pyrrolidin-2-one derivatives with both high diastereoselectivity and enantioselectivity.Open in a separate windowScheme 2β-Selective functionalization of γ-butyrolactam via metal- (previous work) or organo- (this work) catalytic approach.To begin our initial investigation, several bifunctional organocatalysts¹³ were firstly screened to evaluate their ability to promote the β-selective asymmetric addition of γ-butyrolactam 2a with cyclic imino ester 3a in the presence of 15 mol% of catalyst loading at room temperature in CH₂Cl₂ (entries 1–6,

Defect structure in δ-Bi5PbY2O11.5

A detailed study of the defect structure in a di-substituted δ-Bi₂O₃ type phase, δ-Bi₅PbY₂O_11.5, is presented. Using a combination of conventional Rietveld analysis of neutron diffraction data, reverse Monte Carlo (RMC) analysis of total neutron scattering data and ab initio molecular dynamics (MD) simulations, both average and local structures have been characterized. δ-Bi₅PbY₂O_11.5 represents a model system for the highly conducting δ-Bi₂O₃ type phases, in which there is a higher nominal vacancy concentration than in the unsubstituted parent compound. Uniquely, the methodology developed in this study has afforded the opportunity to study both oxide-ion vacancy ordering as well as specific cation–cation interactions. Oxide-ion vacancies in this system have been found to show a preference for association with Pb²⁺ cations, with some evidence for clustering of these cations. The system shows a non-random distribution of vacancy pair alignments, with a preference for 〈100〉 ordering, the extent of which shows thermal variation. MD simulations indicate a predominance of oxide-ion jumps in the 〈100〉 direction.

Total neutron scattering analysis and ab initio MD simulations reveal details of oxide ion vacancy ordering and migration pathways.     

Asymmetric distribution of pathogenic low wall shear stress of the bilateral subclavian arteries: two case reports

The effects of increasing blood flow on the pathogenic wall shear stress (pWSS) of subclavian arteries (SAs) are currently unclear. Patient-specific models of the SA were constructed based on computed tomographic images from two patients. Using the Ansys Fluent 19.0 transient laminar flow solver, the finite volume method was chosen to solve the Navier–Stokes equation governing fluid behavior. The time-averaged wall shear stress, ratio of risk area, cumulative ratio of risk area (P¯), ratio of risk time, and ratio contour of risk time were calculated to describe the temporal and spatial distributions of pWSS. Virtually all pWSS occurred during the diastolic phase. The P¯was 2.3 and 1.29 times higher on the left than on the right in Patients 1 (P1) and 2 (P2), respectively. Increasing the blood flow volume of the left SA by 20%, 40%, and 60% led to a 9.27%, 15.10%, and 20.99% decrease inP¯ for P1 and a 5.74%, 11.55%, and 17.14% decrease in P¯ for P2, respectively, compared with baseline values. In conclusion, the left SA showed greater diastolic pWSS than the right SA, and increasing the blood flow volume reduced the pWSS in the left SA.     

Phosphine-catalyzed [3 + 2] annulation of β-sulfonamido-substituted enones with trans-α-cyano-α,β-unsaturated ketones for the synthesis of highly substituted pyrrolidines

To synthesize highly substituted pyrrolidines, we developed a phosphine-catalyzed [3 + 2] annulation of β-sulfonamido-substituted enones with trans-α-cyano-α,β-unsaturated ketones. We prepared a series of pyrrolidines under mild conditions with high yields and moderate-to-good diastereoselectivities. A catalytic mechanism for this reaction is suggested.

To synthesize highly substituted pyrrolidines, we developed a phosphine-catalyzed [3 + 2] annulation of β-sulfonamido-substituted enones with trans-α-cyano-α,β-unsaturated ketones.

Nucleophilic phosphine catalysis is a practical and powerful synthetic approach to obtain heterocyclic compounds using various annulation reactions, the advantages of which are it being mild and metal-free, ecologically friendly, and inexpensive.¹ Phosphine-catalyzed intermolecular [3 + 2],² [4 + 1],³ [2 + 2 + 1]⁴ and intramolecular annulations are often used to obtain pyrrole derivatives. Intermolecular [3 + 2] annulations of imines and phosphorus ylides formed in situ from allenoates, alkynes, or Morita–Baylis–Hillman carbonates under the presence of phosphine catalysts are especially the most widely used approach to synthesize pyrrolidine derivates. In these reactions, phosphorus ylides act as C–C–C synthons for the [3 + 2] annulations with a C N bond converting to a pyrrolidine ring (Scheme 1). However, literature reports on exploring new activation modes, namely, phosphorus ylides acting as C–C–N synthons for the [3 + 2] annulations, are rare.Open in a separate windowScheme 1Pyrrolidine ring formation through reaction of phosphorus ylides act as C–C–C and C–C–N synthons.β-Sulfonamido-substituted enones could be used as C–C–N synthons to form various N-based heterocycles. Catalytically activated (by amines) β-sulfonamido-substituted enones act as nucleophiles towards electron-deficient olefins or imines during [3 + 2] annulation reactions. Du''s⁵ and Pan''s groups⁶ have made outstanding contributions to this field.⁷ In 2018, Guo''s group developed a Bu₃P-catalyzed [5 + 1] annulation of γ-sulfonamido-substituted enones with N-sulfonyl-imines to obtain chiral 2,4-di-substituted imidazolidines. They also synthesized γ-sulfonamido-substituted enones attacked by phosphine catalyst and acting as C–C–C–C–N synthon (see Scheme 2).⁸ Recently, Guo et al.⁹ used β-sulfonamido-substituted enone as a phosphine acceptor as well as a C–C–N synthon for the [3 + 2] annulation with sulfamate-derived cyclic imines (see Scheme 2). Using of β-sulfonamido-substituted enone as a novel phosphine acceptor is very promising for phosphine-catalyzed reactions. Inspired by Guo''s work, we further extended the substrate scope of this reaction from sulfamate-derived cyclic imines to unsaturated ketones for the construction of pyrrolidine rings. Therefore, in this work, we report phosphine-catalyzed [3 + 2] annulation of β-sulfonamido-substituted enones and trans-α-cyano-α,β-unsaturated ketones, to synthesize highly substituted pyrrolidines (see Scheme 2), which are among the primary building blocks and the core structures of natural and bioactive compounds.¹⁰Open in a separate windowScheme 2Phosphine-catalyzed annulation of γ-sulfonamido-substituted enones and β-sulfonamido-substituted enones.We first used trans-α-cyano-α,β-unsaturated ketone 1a and β-sulfonamido-substituted enone 2a as model substrates to obtain optimum reaction conditions. Tertiary phosphine catalysts were screened with 1,2-dichloroethane (DCE) as solvent at room temperature (see † Thus, the optimum reaction conditions were determined as follows: using 20 mol% of PMe₃ as catalyst, CHCl₃ as solvent at room temperature.Optimization of reaction conditions^a

Adsorption of azide-functionalized thiol linkers on zinc oxide surfaces

A comprehensive understanding of the interactions between organic molecules and a metal oxide surface is essential for an efficient surface modification and the formation of organic–inorganic hybrids with technological applications ranging from heterogeneous catalysis and biomedical templates up to functional nanoporous matrices. In this work, first-principles calculations supported by experiments are used to provide the microstructural characteristics of (10$\bar{1}$0) surfaces of zinc oxide single crystals modified by azide terminated hydrocarbons, which graft on the oxide through a thiol group. On the computational side, we evaluate the specific interactions between the surface and the molecules with the chemical formula N₃(CH₂)_nSH, with n = 1, 3, 6, 9. We demonstrate that the molecules chemisorb on the bridge site of ZnO(10$\bar{1}$0). Upon adsorption, the N₃(CH₂)_nSH molecules break the neutral (Zn^δ+–O^δ−) dimers on ZnO(10$\bar{1}$0) resulting in a structural distortion of the ZnO(10$\bar{1}$0) substrate. The energy decomposition analysis revealed that such structure distortion favors the adsorption of the molecules on the surface leading to a strong correlation between the surface distortion energy and the interaction energy of the molecule. An azide-terminated thiol with three methylene groups in the hydrocarbon chain N₃(CH₂)₃SH was synthesized, and the assembly of this linker on ZnO surfaces was confirmed through atomic force microscopy. The bonding to the inorganic surface was examined via X-ray photoelectron spectroscopy (XPS). Clear signatures of the organic components on the oxide substrates were observed underlying the successful realization of thiol-grafting on the metal oxide. Temperature-dependent and angle-resolved XPS were applied to examine the thermal stability and to determine the thickness of the grafted SAMs, respectively. We discuss the high potential of our hybrid materials in providing further functionalities towards heterocatalysis and medical applications.

Studying the interaction between organic molecules and metal oxide surfaces is key to the development and modification of organic–inorganic hybrids for application in heterogeneous catalysis, biomedical implants, and functional nanoporous matrices.     

Pressure-induced stability and polymeric nitrogen in alkaline earth metal N-rich nitrides (XN6, X = Ca,Sr and Ba): a first-principles study

Multi-nitrogen or polynitrogen compounds can be used as potential high energy-density materials, so they have attracted great attention. Nitrogen can exist in alkaline earth metal nitrogen-rich (N-rich) compounds in the form of single or double bonds. In recent years, to explore N-rich compounds which are stable and easy to synthesize has become a new research direction. The N-rich compounds XN₆ (X = Ca, Sr and Ba) have been reported under normal pressure. In order to find other stable crystal structures, we have performed XN₆ (X = Ca, Sr and Ba) exploration under high pressure. We found that SrN₆ has a new P$\bar{1}$ phase at a pressure of 22 GPa and an infinite nitrogen chain structure, and BaN₆ has a new C2/m phase at 110 GPa, with an N₆ ring network structure. Further, we observed that the infinite nitrogen chain and the N₆ ring network structure contain typical covalent bonds formed by the hybridization of the sp² and sp³ orbitals of N, respectively. It is found that both SrN₆ and BaN₆ are semiconductor materials and the N-2p orbital plays an important role in the stability of the crystal structure for P$\bar{1}$-SrN₆ and C2/m-BaN₆. Because of the polymerization of nitrogen in the two compounds and their stabilities under high pressure, they can be used as potential high energy-density materials. The research in this paper further promotes the understanding of alkaline earth metal N-rich compounds and provides new information and methods for the synthesis of alkaline earth metal N-rich compounds (XN₆, X = Ca, Sr and Ba).

The Fddd-SrN₆ structure can transform into P$\bar{1}$-SrN₆, and polymerized to infinite nitrogen chain structures at P = 22 GPa. For BaN₆, the Fmmm-BaN₆ structure can transform into C2/m-BaN₆, and polymerized to N₆ ring network structure at P = 110 GPa.     

High-pressure phase transition of AB3-type compounds: case of tellurium trioxide

Tellurium trioxide, TeO₃, is the only example of a trioxide adopting at ambient conditions the VF₃-type structure (a distorted variant of the cubic ReO₃ structure). Here we present a combined experimental (Raman scattering) and theoretical (DFT modelling) study on the influence of high pressure (exceeding 100 GPa) on the phase stability of this compound. In experiments the ambient-pressure VF₃-type structure (R$\bar{3}$c symmetry) is preserved up to 110 GPa. In contrast, calculations indicate that above 66 GPa the R$\bar{3}$c structure should transform to a YF₃-type polymorph (Pnma symmetry) with the coordination number of Te⁶⁺ increasing from 6 to 8 upon the transition. The lack of this transition in the room-temperature experiment is most probably connected with energetic barriers, in analogy to what is found for compressed WO₃. The YF₃-type phase is predicted to be stable up to 220 GPa when it should transform to a novel structure of R$\bar{3}$ symmetry and Z = 18. We analyse the influence of pressure on the band gap of TeO₃, and discuss the present findings in the context of structural transformations of trioxides and trifluorides adopting an extended structure in the solid state.

Tellurium trioxide, TeO₃, is the only example of a trioxide adopting at ambient conditions the VF₃-type structure (a distorted variant of the cubic ReO₃ structure).     

Donor moieties with D–π–a framing modulated electronic and nonlinear optical properties for non-fullerene-based chromophores

Herein, a series of non-fullerene-based substantial chromophores (FHD1–FHD6) with a D–π–A framework was designed from a synthesized non-fullerene compound (FH) via structural tailoring with various donor moieties. The FH and its designed derivatives were optimized with frequency analysis at the M06/6-311G (d,p) level to confirm their true minima on potential energy surfaces. These optimized geometries were utilized to perform further analyses, such as absorption, natural bonding orbital (NBO), frontier molecular orbital (FMO), and nonlinear orbital (NLO) analyses at the aforesaid level. Quantum chemical study revealed that all the designed chromophores exhibited a lower band gap than that of the parent molecule with the exception of FHD3. Furthermore, density of states (DOS) analysis supported the findings from the FMO study, and this agreement revealed that the efficient charge was transferred from the HOMO to the LUMO. The NBO investigations disclosed that all the compounds comprised donor moieties with positive charges and acceptors having negative charges. Interestingly, π-conjugated linkers were also found with positive charges, showing an effective donating property. These NBO findings explicated that FHD1–FHD6 exhibited an efficient push–pull mechanism. The λ_max values of the designed chromophores were observed to be greater than the reference compound. The average polarizability 〈α〉, first hyperpolarizability (β_tot), and second hyperpolarizability 〈γ〉 values of FHD2 were found to be 2.170 × 10⁻²², 3.150 × 10⁻²⁷, and 4.275 × 10⁻³² esu, respectively, while all the other derivatives had been reported in the relevant range. Efficient NLO data revealed that FH-based derivatives may contribute significantly toward NLO technology.

Herein, a series of non-fullerene-based substantial chromophores (FHD1–FHD6) with a D–π–A framework was designed from a synthesized non-fullerene compound (FH) via structural tailoring with various donor moieties.     

Nonadiabatic dynamics studies of the H(2S) + RbH(X1Σ+) reaction: based on new diabatic potential energy surfaces

The global diabatic potential energy surfaces (PESs) that correspond to the ground (1²A′) and first excited states (2²A′) of the RbH₂ system PES are constructed based on 17 786 ab initio points. The neural network method is used to fit the PESs and the topographic features of the new diabatic PESs are discussed in detail. Based on the newly constructed diabatic PESs, the dynamics calculations of the H(²S) + RbH(X¹Σ⁺) → Rb(5²S) + H₂(X¹Σ_g⁺)/Rb(5²P) + H₂(X¹Σ_g⁺) reactions are performed using the time-dependent wave packet method. The dynamics properties of these two channels such as the reaction probabilities, integral cross sections, and differential cross sections (DCSs) are calculated at state-to-state level of theory. The nonadiabatic effects are discussed in detail, and the results indicate that the adiabatic results are overestimated from the dynamics values. The DCSs of these two channels are forward biased, which indicates that the abstraction mechanism plays a dominant role in the reaction.

Global diabatic potential energy surfaces (PESs) of RbH₂ system that correspond to 1²A′ and 2²A′ electronic states were built. Using the new PESs, the dynamics studies of the H + RbH reaction were performed.