Ammonia borane-enabled hydrogen transfer processes:Insights into catalytic strategies and mechanisms

Transfer hydrogenation(TH) with in situ generated hydrogen donor is of great importance in reduction reactions, and an alternative strategy to traditional hydrogenation processes involving pressurized molecular hydrogen. Ammonia borane(NH3BH3, AB) is a promising material of hydrogen storage, and it has attracted much attention in reductive organic transformations owing to its high activity, good atom economy, nontoxicity, sustainability, and ease of transport and storage. This review focuses on summarizing the recent progress of AB-mediated TH reactions of diverse substrates including nitro compounds, nitriles, imines, alkenes, alkynes, carbonyl compounds(ketones and aldehydes), carbon dioxide,and N-and O-heterocycles. Syntheses protocols(metal-containing and metal-free), the effect of reaction parameters, product distribution, and variation of reactivity are surveyed, and the mechanism of each reaction involving the action mode of AB as well as structure-activity relationships is discussed in detail. Finally, perspectives are presented to highlight the challenges and opportunities for AB-enabled TH reactions of unsaturated compounds.

EFFECT OF ELECTRON DONORS ON THE SELECTIVE HYDROGENATION OF DIENE TO MONOENE OVER HETEROGENIZED Pd CATALYST

In the selective hydrogenation of diene (or alkyne) using heterogenized homogeneous catalyst, the high selectivity of monoene formation only appears in a very short time interval. The addition of suitable electron donors can decrease or even cease the monoene hydrogenation and thereby keep the high monoene selectivity after reaching its maximum.

Hydrogenic donor impurity states and intersubband optical absorption spectra of monolayer transition metal dichalcogenides in dielectric environments

The hydrogenic donor impurity states and intersubband optical absorption spectra in monolayer transition metal dichalcogenides(ML TMDs) under dielectric environments are theoretically investigated based on a two-dimensional(2D)nonorthogonal associated Laguerre basis set. The 2D quantum confinement effect together with the strongly reduced dielectric screening results in the strong attractive Coulomb potential between electron and donor ion, with exceptionally large impurity binding energy and huge intersubband oscillator strength. These lead to the strong interaction of the electron with light in a 2D regime. The intersubband optical absorption spectra exhibit strong absorption lines of the non-hydrogenic Rydberg series in the mid-infrared range of light. The strength of the Coulomb potential can be controlled by changing the dielectric environment. The electron affinity difference leads to charge transfer between ML TMD and the dielectric environment, generating the polarization-electric field in ML TMD accompanied by weakening the Coulomb interaction strength. The larger the dielectric constant of the dielectric environment, the more the charge transfer is, accompanied by the larger polarization-electric field and the stronger dielectric screening. The dielectric environment is shown to provide an efficient tool to tune the wavelength and output of the mid-infrared intersubband devices based on ML TMDs.

Electronic States of a Shallow Hydrogenic Donor Impurity in Different Shaped Semiconductor Quantum Wells

The shallow hydrogenic donor impurity states in square, V-shaped, and parabolic quantum wells are studied in the framework of effective-mass envelope-function theory using the plane wave basis. The first four impurity energy levels and binding energy of the ground state are more easily calculated than with the variation method. The calculation results indicate that impurity energy levels decrease with the increase of the well width and decrease quickly when the well width is small. The binding energy of the ground state increases until it reaches a maximum value, and then decreases as the well width increases. The results are meaningful and can be widely applied in the design of various optoelectronie devices.

New possible silver lining for pancreatic cancer therapy:Hydrogen sulfide and its donors

As one of the most lethal diseases,pancreatic cancer shows a dismal overall prognosis and high resistance to most treatment modalities.Furthermore,pancreatic cancer escapes early detection during the curable period because early symptoms rarely emerge and specific markers for this disease have not been found.Although combinations of new drugs,multimodal therapies,and adjuvants prolong survival,most patients still relapse after surgery and eventually die.Consequently,the search for more effective treatments for pancreatic cancer is highly relevant and justified.As a newly re-discovered mediator of gasotransmission,hydrogen sulfide(H2S)undertakes essential functions,encompassing various signaling complexes that occupy key processes in human biology.Accumulating evidence indicates that H2S exhibits bimodal modulation of cancer development.Thus,endogenous or low levels of exogenous H2S are thought to promote cancer,whereas high doses of exogenous H2S suppress tumor proliferation.Similarly,inhibition of endogenous H2S production also suppresses tumor proliferation.Accordingly,H2S biosynthesis inhibitors and H2S supplementation(H2S donors)are two distinct strategies for the treatment of cancer.Unfortunately,modulation of endogenous H2S on pancreatic cancer has not been studied so far.However,H2S donors and their derivatives have been extensively studied as potential therapeutic agents for pancreatic cancer therapy by inhibiting cell proliferation,inducing apoptosis,arresting cell cycle,and suppressing invasion and migration through exploiting multiple signaling pathways.As far as we know,there is no review of the effects of H2S donors on pancreatic cancer.Based on these concerns,the therapeutic effects of some H2S donors and NO-H2S dual donors on pancreatic cancer were summarized in this paper.Exogenous H2S donors may be promising compounds for pancreatic cancer treatment.

Alcohol-assisted hydrodeoxygenation as a sustainable and cost-effective pathway for biomass derivatives upgrading

Hydrodeoxygenation(HDO)is one of the most promising strategies for the upgrading of biomass-derived compounds to chemicals and fuels.However,the conventional HDO process accompanied by insecure high-pressure H_(2)leads to the hefty infrastructure cost on the industrial scale and inevitably trigger overall hydrogenation which is considered as an uncontrollable and risky approach.Accordingly,the developments of alcohol-assisted HDO can be viewed as a sustainable and cost-effective alternative.This review critically summarizes the potentials and challenges of alcohol-assisted strategy from diverse perspectives including safety,economics and catalytic efficiency.Based on the discrepancies of in-situ hydrogen generation,the alcohol-assisted strategy is divided into combined reforming-HDO route and catalytic transfer hydrogenation/hydrogenolysis(CTH)route.Furthermore,describe different catalytic behaviors and elaborate their applications among several upgrading processes of representative biomass model compounds,aiming to illustrate their potentials in biomass utilization.The influence of alcohols is highlighted because they act both hydrogen donor and solvent.At last,the current challenges and perspectives of alcohol-assisted HDO are proposed for further development and improvement.

Activatable and Self-Monitoring Hydrogen Sulfide-Based Molecular Senomorphics for Visualized Regulation of Cellular Senescence

Specific regulation of the senescence-associated secretory phenotype(SASP)is vital to block senescence-induced detrimental cellular plasticity.Recently,some chemical compounds called senomorphics have demonstrated such potential,but it remains challenging to achieve site-specific activation and real-time monitoring of the action of senomorphics,posing great obstacles for transformable applications.Here,we report a tailor-made hydrogen sulfide(H_(2)S)donor(Lyso-FH_(2)S-Gal)as a new class of molecule senomorphics for spatially controlled delivery of H_(2)S for visualization of regulation of cellular senescence.It comprises four functional moieties in a single molecular structure,including a lysosome-targeting group for cell recognition,a lysosomal enzyme-cleaved scaffold for site-specific activation,thiocarbamate as the H_(2)S precursor,and a switchable fluorophore for concurrent selfreporting of H_(2)S release and senescence imaging.Lyso-FH_(2)S-Gal exhibited remarkable response selectivity,sustained H_(2)S release,and 141-fold fluorescence enhancement.In cellular models,Lyso-FH_(2) S-Gal preferentially enriched in senescent cells over nonsenescent cells,and alleviated the levels of SASP and reactive oxygen species(ROS)in senescent cells,while remaining inert in nonsenescent cells.More impressively,it efficiently inhibited the SASPmediated crosstalk between senescent cells and surrounding nonsenescent cells,thereby preventing senescence propagation.This work offers a useful molecular tool with the hope for controlled intervention of senescence-related important biological processes.

Nanomotor-based H_(2)S donor with mitochondrial targeting function for treatment of Parkinson’s disease

Reduction of endogenous hydrogen sulfide(H_(2)S)is considered to have an important impact on the progress of Parkinson’s disease(PD),thus exogenous H_(2)S supplementation is expected to become one of the key means to treat PD.However,at present,it is difficult for H_(2)S donors to effectively penetrate the blood brain barrier(BBB),selectively release H_(2)S in brain,and effectively target the mitochondria of neuron cells.Herein,we report a kind of nanomotor-based H_(2)S donor,which is obtained by free radical polymerization reaction between L-cysteine derivative modified-polyethylene glycol(PEG-Cys)and 2-methacryloyloxyethyl phosphorylcholine(MPC).This kind of H_(2)S donor can not only effectively break through BBB,but also be specifically catalyzed by cystathionineβ-synthase(CBS)in neurons of PD site in brain and 3-mercaptopyruvate sulfurtransferase(3-MST)in mitochondria to produce H_(2)S,endowing it with chemotaxis/motion ability.Moreover,the unique chemotaxis effect of nanomotor can realize the purpose of precisely targeting brain and the mitochondria of damaged neuron cytopathic diseases.This kind of nanomotor-based H_(2)S donor is expected to enrich the current types of H_(2)S donors and provide new ideas for the treatment of PD.

A ROS-responsive,self-immolative and self-reporting hydrogen sulfide donor with multiple biological activities for the treatment of myocardial infarction

Myocardial infarction(MI),as one of the leading causes of global death,urgently needs effective therapies.Recently,hydrogen sulfide(H2S)has been regarded as a promising therapeutic agent for MI,while its spatiotemporally controlled delivery remains a major issue limiting clinical translation.To address this limitation,we designed and synthesized a novel H2S donor(HSD-R)that can produce H2S and emit fluorescence in response to reactive oxygen species(ROS)highly expressed at diseased sites.HSD-R can specifically target mitochondria and provide red fluorescence to visualize and quantify H2S release in vitro and in vivo.Therapeutically,HSD-R significantly promoted the reconstruction of cardiac structure and function in a rat MI model.Mechanistically,myocardial protection is achieved by reducing cardiomyocyte apoptosis,attenuating local inflammation,and promoting angiogenesis.Furthermore,inhibition of typical pro-apoptotic genes(Bid,Apaf-1,and p53)played an important role in the anti-apoptotic effect of HSD-R to achieve cardioprotection,which were identified as new therapeutic targets of H2S against myocardial ischemia injury.This ROS-responsive,self-immolative,and fluorescent H2S donor can serve as a new theranostic agent for MI and other ischemic diseases.

Electron energy states in a two-dimensional GaAs quantum ring with hydrogenic donor impurity in the presence of magnetic field

Using the finite element method, we investigate the lowest and first few excited state energies in a two- dimensional GaAs quantum ring （QR） with a hydrogenic donor impurity and effective mass approximation under a uniform magnetic field perpendicular to the ring plane. We study in detail the dependence of the energy spectrum with different angular momentum on the inner radius, the outer radius and width of the QR, the magnetic field and impurity position. The results reveal that the electron energies increase with the inner radius while decrease with the outer radius and width of the QR; for a fixed ring, the magnetic field induces the increase of the electron energies. Moreover, the existence of impurity reduces energy levels, and the energy levels depend highly on the impurity position, which decreases as the impurity is far away from the center of the QR. Also, the dependence of the angular momentum on the energy spectrum is analyzed in detail.

Hydrothermal conversion of lignin and black liquor for phenolics with the aids of alkali and hydrogen donor

The potentials of phenolic productions from lignin and black liquor(BL)via hydrothermal technology with the aids of alkalis and hydrogen donors were investigated,by conducting batch experiments in micro-tube reactors with 300℃ sub-critical water as the solvent.The results showed that all the employed alkalis improved lignin degradation and thus phenolics production,and the strong alkalis additionally manifested deoxygenation to produce more phenolics free of methoxyl group(s).Relatively,hydrogen donors more visibly facilitated phenolics formation.Combination of strong alkali and hydrogen donors exhibited synergistically positive effects on producing phenolics(their total yield reaching 22 wt%)with high selectivities to phenolics,among which the yields of catechol and cresols respectively peaked 16 and 3.5 wt%.BL could be hydrothermally converted into phenolics at high yields(approaching 10 wt%with the yields of catechol and cresols of about 4 and 2 wt%,respectively)with the aids of its inherent alkali and hydrogen donors,justifying its cascade utilization.