Structure modification of unsaturated natural products:The epoxidation of carbon-carbon double bonds in some natural products with hydrogen peroxide catalyzed by iodine

Aim To afford an environmentally benign catalytic epoxidation of carbon-carbon double bonds in organic substrates using hydrogen peroxide as an oxidant and iodine as a catalyst.Method The effects of different factors on the epoxidation of three unsaturated natural products were investigated by orthogonal design.Results The experimental results show that three unsaturated natural products are oxidized to the corresponding epoxides with hydrogen peroxide in the presence of 10%(mol/mol) of iodine at room temperature in high yields.Conclusion Iodine was found to be an efficient catalyst for the epoxidation of carbon-carbon double bonds in some unsaturated natural products with hydrogen peroxide at room temperature.

Biological Evaluation and Structure Modification of （S）-3-Aminopyrrolidine Derivatives

With our interest in （S）-3-aminopyrrolidine derivatives,we further screened inhibition activities of three hit compounds on many other kinases with the results demonstrating that this series of compounds shows better anticancer activities,which might result from the main block of PI3K/Akt signaling pathway and the inhibition of Abelson murine leukemia viral oncogene homolog（ABL） kinase,as well as some epidermal growth factors.Further structure modification demonstrates that benzylsulfonyl group is the necessary functional group contributing to the biological activity that will be helpful to guiding us to optimize these （S）-3-aminopyrrolidine derivatives.

External-Strain-Induced Raman Scattering Modification in g-C3N4 Structures

Regulation of optical properties and electronic structure of graphitic carbon nitride （g-C3N4 ） via external strain has attracted much attention due to its potential in photocatalyst and electronic devices. However, the identifi- cation of g-C3N4 structure transformation induced by strain is greatly lacking. In this work, the Raman spectra of g-C3N4 with external strain are determined theoretically based on the density function theory. Deformation induced by external strain not only regulates the Raman mode positions but also leads to a I^aman mode split- ting, which can be ascribed to crystal symmetry destruction by strain engineering. Our results suggest the use of Raman scattering in structural identification in deformed 9-C3N4 structure.

"Win-Win"Scenario of High Energy Density and Long Cycling Life in a Novel Na_(3.9)MnCr_(0.9)Zr_(0.1)(PO_(4))_(3)Cathode

The development of high-energy and long-lifespan NASICON-type cathode materials for sodium-ion batteries has always been a research hotspot but a daunting challenge.Although Na_(4)MnCr(PO_(4))_(3)has emerged as one of the most promising high-energy-density cathode materials owing to its three-electron reactions,it still suffers from serious structural distortion upon repetitive charge/discharge processes caused by the Jahn-Teller active Mn^(3+).Herein,the selective substitution of Cr by Zr in Na_(4)MnCr(PO_(4))_(3)was explored to enhance the structural stability,due to the pinning effect of Zr ions and the≈2.9-electron reactions,as-prepared Na_(3.9)MnCr_(0.9)Zr_(0.1)(PO_(4))_(3)/C delivers a high capacity retention of 85.94%over 500 cycles at 5 C and an ultrahigh capacity of 156.4 mAh g^(-1)at 0.1 C,enabling the stable energy output as high as 555.2 Wh kg^(-1).Moreover,during the whole charge/discharge process,a small volume change of only 6.7%was verified by in situ X-ray diffraction,and the reversible reactions of Cr^(3+)/Cr^(4+),Mn^(3+)/Mn^(4+),and Mn^(2+)/Mn^(3+)redox couples were identified via ex situ X-ray photoelectron spectroscopy analyses.Galvanostatic intermittent titration technique tests and density functional theory calculations further demonstrated the fast reaction kinetics of the Na_(3.9)MnCr_(0.9)Zr_(0.1)(PO_(4))_(3)/C electrode.This work offers new opportunities for designing high-energy and high-stability NASICON cathodes by ion doping.

Recent Developments in Doping and Structural Modification of Ceria-Based Catalysts

Recent development in the modification of ceria-based catalysts for exhaust gas treatment was reviewed with the dependence of redox properties on structural characters of materials. The doping of ceria with different cations such as rare earth or transition metal oxides results in improvement of structural stability, catalytic function and resistance to sintering at high temperatures. Aging and reduction treatment at high temperatures promote ceria reduction and is beneficial for oxygen storage capacity of the three-way catalysts. Chemical filing technique is very effective in modifying the redox property in the low temperature regions.

Structure-activity relationships of oxime compounds as flotation collectors by DFT calculations

The relationships between the structure of oxime compounds(R^(1)R^(2)C=NOH,R^(1)/R^(2)=alkyl groups) with different substituents and their corresponding flotation performances were studied. The analyses of density functional theory(DFT) calculations illustrated that the introduced phenyl group at the R^(1) position could enhance the acidity,while the heptyl group could effectively increase the hydrophobicity and benefit van der Waals interactions. Meanwhile,the introduced amino group at the R^(2) position could provide cationic sites to interact with negatively charged surfaces of minerals, while the introduced hydroxyl group could provide additional action sites to form stable chelates with metal ions. Based on the structure-activity relationships, structural optimization was carried out to obtain three efficient collectors, which possessed superior flotation separation performances, proving the effectiveness of the structural modification to oxime compounds in this work.

Effect of fluence and ambient environment on the surface and structural modification of femtosecond laser irradiated Ti

Under certain conditions, ultrafast pulsed laser interaction with matter leads to the formation of self-organized conical as well as periodic surface structures （commonly reffered to as, laser induced periodic surface structures, LIPSS）. The purpose of the present investigations is to explore the effect of fsec laser fluence and ambient environments （Vacuum ＆ 02） on the formation of LIPSS and conical structures on the Ti surface. The surface morphology was investigated by scanning electron microscope （SEM）. The ablation threshold with single and multiple （N = 100） shots and the existence of an incubation effect was demonstrated by SEM investigations for both the vacuum and the 02 environment. The phase analysis and chemical composition of the exposed targets were performed by x-ray diffraction （XRD） and energy dispersive x-ray spectroscopy （EDS）, respectively. SEM investigations reveal the formation of LIPSS （nano ＆ micro）. FFT d-spacing calculations illustrate the dependence of periodicity on the fluence and ambient environment. The periodicity of nano-scale LIPSS is higher in the case of irradiation under vacuum conditions as compared to 02. Furthermore, the 02 environment reduces the ablation threshold. XRD data reveal that for the 02 environment, new phases （oxides of Ti） are formed. EDS analysis exhibits that after irradiation under vacuum conditions, the percentage of impurity element （A1） is reduced. The irradiation in the 02 environment results in 15% atomic diffusion of oxygen.

Structural Modification for Antitumor Nitrogenous Steroids

Natural steroids have been showing notable cytotoxic activities, which are quite interesting lead compounds for the development of anticancer drug including estramustine and prednimustine. Considering that these semi-synthetic molecules are nitrogen mustard functionalized steroidal derivatives, the present review is focused on the methodologies of introducing nitrogen atom or nitrogen-containing heterocycles on A^D rings or side chains of steroids, and analysis of the structure-activity relationship（SAR） for these man-made cytotoxic steroids.

Structure and Anti-HIV Activity of Betulinic Acid Analogues

Firstly discovered in 1980s, human immunodeficiency virus （HIV） continues to affect more and more people. However, there is no effective drug available for the therapy of HIV infection. Betulinic acid existing in various medicinal herbs and fruits exhibits multiple biological effects, especially its outstanding anti-HIV activity, which has drawn the attentions of many pharmacists. Among the derivatives of betulinic acid, some compounds exhibited inhibitory activities at the nanomolar concentration, and have entered phase II clinical trials. This paper summarizes the current investigations on the anti-HIV activity of betulinic acid analogues, and provides valuable data for subsequent researches.

Optimal Structural Modifications of a Gun Tripod for Desired Natural Frequencies

Sensitivity analysis and structural modification techniques are used to investigate the structural modifications of a machine gun tripod which suffers from severe vibration during firing due to the resonance. The finite element analysis and modal test techniques are used to determine the natural frequencies of the machine gun. The sensitivities of natural frequencies with respect to the structural parameters of the tripod are obtained by the method of sensitivity analysis, and they can be used as an indication for the structural modification of the tripod so as to shift the natural frequencies effectively. By the structural modification techniques, finally, the optimal structural modifications of the tripod for desired natural frequencies are made to avoid the resonance, and this optimal structural modification is verified by re-analysis of the modified structure and the vibration contrast between original structure and modified structure. The research resulted in a successful structural modification for desired natural frequencies, which can avoid the resonance and thereby greatly improve the shooting precision of the machine gun during firing.

Influence of Structural Modification on Work-hardening Behaviour of Type 316 Stainless Steel

Work-hardening behaviour of type 316 austenitic stainless steel having difFerent initial dislocation structures introduced by swaging to various levels is analysed by a simplified Kock's model which takes into account the structural changes through the dislocation accumulation and annihilation process during deformation. The dislocation accumulation and annihilation factors show a temperature and structure dependence. The dislocation annihilation factor shows a plateau or decreasing tendency in the dynamic strain ageing (DSA) temperature range. This is attributed as either due to dislocation accumulation being more pronounced than dislocation annihilation or as due to precipitates being formed at DSA temperatures acting as obstacles to dislocation motion in the DSA temperature range.

Recent Progress in Structural Modification and Activities on Panax notoginseng Saponins

This paper reviews recent progress in the structural modification and activities on Panax notoginseng saponins(PNS).PNS can not only improve the function of cardio-cerebral system,central nervous system and immune system,but also reveal anticancer,anti-aging and anti-oxidation activities.In order to solve the problem of low bioavailability and poor absorbability of PNS in vivo,usually,the researchers modified the structure of PNS with three methods:glycoside cleavage(including acid hydrolysis,sulfation,etc.),biotransformation method(including enzyme hydrolysis,microbial transformation)and combinatorial chemical method.It was found that the structural modification sites of PNS were single,mainly aimed at C-3,C-6 and C-20,which provided a new perspective for the structural modification of PNS.Therefore,structural modification on PNS with high yield and ready availability are significant in the discovery of new active ingredients and industrialization.Derivatives of PNS are applied to research of structure-activity relationship,which is beneficial to the development of new medicines.

STUDY ON MECHANISM OF MODIFICATION OF HLA ANTIGEN CAMOUFLAGED BY DIVERSE mPEGs

Objective To study mechanism of various effects of HLA antigen camouflaged by differentmPEGs. Methods Effects of the modification of HLA antigen camouflaged by various mPEGs were detected by microlymphocytotoxicity test. The ability of modification was detected by SDS-PAGE. The mechanism of the modification was depicted by the three-dimensional structure of HLA antigen. Results The specific reaction between HLA-A2 antigen and its antibody were completely blocked by mPEG-BTC and mPEG-SPA. mPEG-MAL did not camouflage HLA antigen. The diversity of the modification of HLA antigen camouflaged by varied mPEGs was closely associated with the amides displayed on the surface of HLA antigen. Conclusion Only the amides which were exposed to the surface of HLA antigen can be camouflaged by mPEG. The amides on the surface of three-dimensional structure of HLA-A2 antigen determine the effect of the modification by various mPEGs.

Modification strategies for non-aqueous, highly proton-conductive benzimidazole-based high-temperature proton exchange membranes

High-temperature proton exchange membranes(HT-PEMs) possess excellent thermal and outstanding electrochemical stability, providing an avenue to realize high-temperature proton exchange membranes fuel cells(HT-PEMFCs) with both superior power density and long-term durability. Unfortunately, polybenzimidazole(PBI), a typical material for conventional HT-PEMs, fails to compromise the high nonaqueous proton conductivity and high mechanical properties, thus hindering their practical applications.Achieving efficient nonaqueous proton conduction is crucial for HT-PEMFC, and many insightful research works have been done in this area. However, there still lacks a report that integrates the host-guest interactions of phosphoric acid doping and the structural stability of polymers to systematically illustrate modification strategies. Here, we summarize recent advancements in enhancing the nonaqueous proton conduction of HT-PEMs. Various polymer structure modification strategies, including main chain and side group modification, cross-linking, blocking, and branching, are reviewed. Composite approaches of polymer, including compounding with organic porous polymers, filling the inorganic components and modifying with ionic liquids, etc., are also covered in this work. These strategies endow the HT-PEMs with more free volume, nanophase-separated structure, and multi-stage proton transfer channels, which can facilitate the proton transportation and improve their performance. Finally, current challenges and future directions for further enhancements are also outlined.

A review of structural modification and biological activities of oleanolic acid

Oleanolic acid(OA),a pentacyclic triterpenoid,exhibits a broad spectrum of biological activities,including antitumor,antiviral,antibacterial,anti-inflammatory,hepatoprotective,hypoglycemic,and hypolipidemic effects.Since its initial isolation and identification,numerous studies have reported on the structural modifications and pharmacological activities of OA and its derivatives.Despite this,there has been a dearth of comprehensive reviews in the past two decades,leading to challenges in subsequent research on OA.Based on the main biological activities of OA,this paper comprehensively summarized the modification strategies and structureactivity relationships(SARs)of OA and its derivatives to provide valuable reference for future investigations into OA.

Recent advances in structural modification on graphitic carbon nitride(g-C_(3)N_(4))-based photocatalysts for high-efficiency photocatalytic H_(2)O_(2)production

To date,extensively high demand for hydrogen peroxide(H_(2)O_(2))has been predominantly supplied by the anthraquinone process for several worldwide applications,encompassing wastewater treatment,environmental remediation,and chemical synthesis.However,the compacted manufacturing,massive energy input and the release of tremendous wastes have restricted commercialization feasibility.Regards to mitigate such issues,the photocatalytic H_(2)O_(2)production by utilizing g-C_(3)N_(4)catalysts has endowed a greener,sustainable and promising alternative,considering that it involves water and oxygen as reactants in the present of sunlight as energy input.Herein,we have manifested a comprehensive overview of the research progress for g-C_(3)N_(4)-based semiconductors for photocatalytic H_(2)O_(2)generation.This review has systematically elucidated state-of-the-art development of different modifications on g-C_(3)N_(4)to unravel the fundamental mechanism of H_(2)O_(2)evolution via oxygen reduction reaction(ORR)and water oxidation reaction(WOR).In addition,the contribution made by vacancy introduction,doping,heterogenization,and co-catalyst passivation with respect to photoefficiency enhancement have been clarified.Furthermore,the current challenges and perspective of future development directions on photocatalytic H_(2)O_(2)production have also been highlighted.As such,g-C_(3)N_(4)stands as the next step toward advancement in the configuration and modulation of high-efficiency photocatalysts.

An Efficient Synthesis and Screening of Osteostatin analogues by Using Pooling Strategy

An efficient synthesis and screening of twenty one osteostatin(OSN) analogues were achieved by using pooling strategy. Three analogues were found to retain almost the same activity of inhibiting bone resorption in rat as that of OSN. Therefore, it is possible to develop partially modified OSN surrogate with higher enzymic stability.

Synthesis and Anti-tumor Activity of Novel Glycyrrhetinic Acid Derivatives

Twenty-five derivatives of glycyrrhetinic acid（GA） modified on the A-ring,at C30 and C11 positions were synthesized.Their in vitro cytotoxicity against various cancer cell lines[henrietta lacks strain of cancer cells（HeLa）,human hepatocellular liver carcinoma cells（HepG2） and human gastric carcinoma cells（BGC-823）] was evaluated by standard MTT[3-（4,5-dimethyl-2-thiazol-yl）-2,5-diphenyl-2H-tetrazolium bromide] assay.All the tested derivatives were found to have stronger cell growth inhibitory than their parent compound GA.Among them,compounds 3a,5a,and 8d have similar activity on HeLa cell line,and compound 8a has similar activity on HeLa,HepG2 and BGC-823 cell lines as Gefitinib.

A novel modified paclitaxel-loaded discoidal recombinant high-density lipoproteins:Preparation,characterizations and in vivo evaluation

This study is one of the first to focus on the unexpected drug leakage from discoidal recombinant high-density lipoproteins(d-rHDLs)as a consequence of remodeling process,mainly associated with lecithin-cholesterol acyltransferase(LCAT)during their metabolic process.Here,a newly monocholesterylsuccinate(CHS)modified paclitaxel-loaded drHDLs(cP-d-rHDLs)were constructed successfully through structural modification,thus aiming to improve the performance of d-rHDLs.And next their in vitro physiochemical properties and pharmacokinetics in SpragueeDawley rats were elaborately investigated.Collectively our studies demonstrated that cP-d-rHDLs,whose remodeling behaviors were restrained effectively after structural modification,exhibited more excellent and promising properties as novel delivery vehicles for anti-cancer agents.