Densely Functionalized Macrocyclic Sesquiterpene Pyridine Alkaloids from Maytenus austroyunnanensis.

Eleven densely functionalized new dihydro-ß-agarofuran sesquiterpenoid derivatives, named maytenoids A-K (1-11), as well as one known analog, were isolated and characterized from Maytenus austroyunnanensis. Their structures were assigned based on analysis of spectroscopic data and X-ray crystallography. Compounds 1-9 are macrocyclic sesquiterpene pyridine alkaloids generated by the respective acylation of the hydroxy groups at C-3 and C-13 of dihydro-ß-agarofuran sesquiterpenoids via diverse pyridine dicarboxylic acids. Compounds 1, 2, 5-10, and 12 exhibited significant inhibitory effects on NO production at 10 µM in lipopolysaccharide (LPS)-stimulated BV2 cells.

Two New Cytotoxic Maytansinoids Targeting Tubulin from Trewia nudiflora.

Two new maytansinoids, N-methyltreflorine (1: ) and methyltrewiasine (2: ), were isolated from the dried fruits of Trewia nudiflora, together with three known congeners (3:  - 5: ). Their structures were elucidated by spectroscopic methods, and the absolute configuration of 1: and 2: was determined by X-ray crystallographic analysis. Compounds 1:  - 5: exhibited strong cytotoxicity against human tumor cell lines, including HeLa, MV-4 - 11, and MCF-7, with IC50 values ranging from 0.12 to 11 nM. Compounds 1: and 4: also showed inhibitory activity against the MCF-7/ADR cell line with IC50 values of 13 and 28 nM, respectively. Compounds 1: and 2: significantly inhibited tubulin polymerization in vitro with IC50 values of 3.6 and 3.2 µM, respectively.

Comparative study on corrosion inhibition of N doped and N,S codoped carbon dots for carbon steel in strong acidic solution.

Carbon steel is the most widely used engineering material, and its corrosion is one of the main areas of concern in many industries. The most practical approach to control this problem is to use corrosion inhibitors. Currently, because of their good water solubility, excellent chemical stability, low cost and nontoxic features, carbon dots (CDs), especially heteroatom-doped CDs, have been developed as green corrosion inhibitors, but the corrosion inhibition efficiency and underlying mechanisms of single- or dual-element doping have not yet been accurately compared and analyzed. Inspired by this, eco-friendly nitrogen-doped and nitrogen, sulfur codoped CDs (N-CDs and N,S-CDs) are prepared via a one-step hydrothermal process, and a comparative study on their inhibition performance for carbon steel corrosion in strong acidic solution is performed. The results show that both N-CDs and N,S-CDs can restrain the corrosion of carbon steel, and their inhibition efficiency increases with increasing concentration and immersion time, reaching approximately 87.9% (N-CDs) and 96.4% (N,S-CDs) at 200 ppm after 1 h of immersion. Molecular dynamics simulation indicates that the strong interaction ability between N,S-CDs and the Fe substrate leads to higher corrosion inhibition performance than the single N doping case, benefiting from the multi-anchor adsorption of N,S-CDs on carbon steel in a strong acidic solution. Therefore, the facile preparation, eco-friendliness and high corrosion inhibition performance of N,S-CDs will provide a new approach for designing highly efficient carbon dots and broadening the application of carbon dots in the corrosion field.

Nitrogen and sulfur Co-doped carbon dots as ecofriendly and effective corrosion inhibitors for Q235 carbon steel in 1 M HCl solution.

Novel nitrogen and sulfur co-doped carbon dots (N,S-CDs) were synthesized via a hydrothermal procedure using citric acid (CA) and thiourea (TU) as precursors, and the corresponding corrosion protection performance was first investigated for Q235 carbon steel in 1 M HCl solution. Experimental results indicated that N,S-CDs as mixed-type corrosion inhibitors could effectively prevent Q235 carbon steel from corrosion in 1 M HCl solution, and the corrosion inhibition efficiency was improved with the increase in N,S-CD concentration. The maximum value was achieved at 400 ppm of N,S-CDs at 25 °C, which was approximately 96.6%, 94.6% and 90.55%, according to the potentiodynamic polarization curves, EIS results and weight loss measurement, respectively. Additionally, with the temperature ranging from 25 to 55 °C, the inhibition efficiency obtained from the weight loss measurement was enhanced from 90.55% to 94.04%. Such superior inhibition effect was assigned to the physisorption and chemisorption of N,S-CDs on the Q235 carbon steel surface, which was also be confirmed by XPS analysis. The adsorption of N,S-CDs onto a steel substrate conformed to the Langmuir adsorption isotherm.

Effective Corrosion Inhibition of Carbon Steel in Hydrochloric Acid by Dopamine-Produced Carbon Dots.

In present study, novel nitrogen doped carbon dots (NCDs) are synthesized using a green material-dopamine-as a precursor and studied as corrosion inhibitors for Q235 carbon steel in 1 M HCl solution. According to the electrochemical results, it is found that NCDs acting as a mixed-type corrosion inhibitor can effectively retard the acid corrosion of carbon steel, and their inhibition efficiency increases with the concentration increasing from 50 to 400 ppm. The highest inhibition efficiency is 96.1% in the presence of 400 ppm NCDs at room temperature. Additionally, the adsorption of NCDs obeys the Langmuir adsorption isotherm. In addition, weight loss results show that the inhibition efficiency in the presence of 400 ppm NCDs increases with prolonged exposure time and rising temperature (298-328 K), owing to the strong adsorption of NCDs on the steel surface, and the η value is 92.2% at 60 h of immersion and 86.2%, 89.1%, 90.6% and 92.9% at 298, 308, 318 and 328 K, respectively. Surface analysis by scanning electron microscope (SEM), laser scanning confocal microscope (LSCM) and X-ray photoelectron spectroscopy (XPS) further proves the formation of a protective NCD film on the steel surface.

Correction: The corrosion behaviors of multilayer diamond-like carbon coatings: influence of deposition periods and corrosive medium.

[This corrects the article DOI: 10.1039/C6RA05527C.].

Correction: Corrosion and tribocorrosion performance of multilayer diamond-like carbon film in NaCl solution.

[This corrects the article DOI: 10.1039/C5RA21207C.].

Determination of maytansinoids in Trewia nudiflora using QuEChERS extraction combined with HPLC.

Three maytansinoids with strong cytotoxicities, dehydrotrewiasine, maytanbutine, and trewiasine, were isolated and identified from Trewia nudiflora, and maytanbutine was obtained from this plant for the first time. A quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction combined with high-performance liquid chromatography (HPLC) was established to determine the three maytansinoids in T. nudiflora. The effects of major factors on the extraction efficiency of the QuEChERS method were evaluated and the optimal conditions using acetonitrile-ethyl acetate (1:1, v/v) as the extraction solvent and PestiCarb as the clean-up sorbents were established. Compared with Soxhlet extraction (SE) and ultrasonic-assisted extraction (UAE), the QuEChERS method was easy-to-operate and afforded a cleaner extract. A phenomenex HyperClone BDS C18 column was used for HPLC analysis. Methanol-acetonitrile-water was chosen as mobile phase for gradient elution. Method validation showed that all analytes showed good linearity (r > 0.999) over the investigated ranges and satisfactory recoveries ranging from 95.0% to 105.0%. The developed QuEChERS-HPLC method was simple, efficient, and applicable to the determination of maytansinoids in T. nudiflora.

Dopamine@Nanodiamond as novel reinforcing nanofillers for polyimide with enhanced thermal, mechanical and wear resistance performance.

In this study, to achieve a homogeneous dispersion of nanodiamond (ND) in a polyimide (PI) matrix and a strong interfacial adhesion between ND and the PI matrix, a biomimetic nondestructive dopamine chemistry was employed for surface modification of ND. FTIR and Raman spectroscopy studies revealed that self-polymerization of dopamine could produce thinner polydopamine (PDA) layers on the ND surface via spontaneous oxidation and the intermolecular cross-linking reaction of PDA molecules. The structure and morphology of PDA-ND were studied by FTIR, SEM, and Raman spectroscopy, which verified the π-π interactions between PDA and ND. The facile dispersion of PDA-ND in a polyamic acid prepolymer made it possible to obtain PI/ND composites with no obvious ND aggregation. The effect of PDA-ND nanoparticles on the thermal, mechanical and tribological properties of the resulting PI/PDA-ND composites were evaluated, and the results showed that the incorporation of PDA-ND could increase the hardness, tensile strength, storage modulus, as well as the wear resistance properties. PI/PDA-ND composites prepared in this study showed that PDA-ND is a promising nanoreinforcing filler for PI composites.

Multilayer Regulation of Atomic Boron Nitride Films to Improve Oxidation and Corrosion Resistance of Cu.

The boron nitride (BN) monolayer (1L) with high impermeability and resistivity seems to hold promise as a long-term corrosion barrier for Cu under ambient condition, which is supported by recent researches. Here, we perform a complete study of the alternating temperature tests (the sample is exposed in air for 30 days and subsequently heated at 200 °C for 2 h) and electrochemical measurements on 1L and multilayer BN-coated Cu foils. Results imply that the BN-coated Cu foils are less oxidized than uncoated Cu foils after alternating temperature tests, regardless of the layers of BN. Particularly, the oxidation process proceeds slowly in multilayers because most of the underlying defects are covered with BN layers to suppress the oxygen diffusion in the vertical direction and the oxidation mainly occurs on the wrinkled region of BN films. Electrochemical analyses reveal that the BN layers provide an effective physical barrier against the corrosive medium and inhibit the electron diffusion because of their high electrical insulating behavior and the corrosion resistance of the samples increases with increasing BN layers. These findings indicate that BN films with adequate layers are good candidates for oxidation and corrosion protection at the atomic level, which is vital to many industrial and academic applications.