Theoretical prediction on the insertion reactions of stannylenoid H2SnLiF with CH3X and SiH3X (X = F, Cl, Br).

Density functional theory was used to study the insertion reaction of stannylenoid H2SnLiF with CH3X, SiH3X (X = F, Cl, Br). Comparing the reaction barrier of H2SnLiF with CH3X, SiH3X, it can be found that the order of the difficulty of insertion reaction is F > Cl > Br. The insertion reaction potential barrier of SiH3X is lower than that of CH3X, which means that SiH3X is easier to react. According to the calculation results, the reaction law in THF solvent is consistent with that in vacuum, while in THF solvent, the barrier is lower and therefore more prone to reactions. This work provides theoretical support for the reaction properties of stannylenoids.

High reusability and adsorption capacity of acid washed calcium alginate/chitosan composite hydrogel spheres in the removal of norfloxacin.

Calcium alginate (CA) hydrogel spheres were widely used as adsorbents to remove organics, but their adsorption capacities and reusability to some antibiotics are unsatisfactory. In this study, calcium alginate/chitosan (CA/CTS) hydrogel spheres were prepared as precursors. Acid-washed CA/CTS (CA/CTS-M) hydrogel spheres (310.6 mg/g) behaved much better adsorption capacity of norfloxacin (NOR) than CA (69.5 mg/g) and CA/CTS (87.7 mg/g) hydrogel spheres. Astonishingly, after being reused for 15 cycles, CA/CTS-M has no loss of NOR adsorption capacity. In the original idea, acid wash was expected to remove the chitosan in CA/CTS hydrogel spheres for obtaining a larger specific surface area. Both scanning electron microscopy and Brunauer-Emmett-Teller test showed that acid wash can remove CTS from CA/CTS hydrogel spheres to increase the specific surface area. However, part of the chitosan remained in CA/CTS-M, having a role to enhance the structural stability of the material, because the acid-washed CA (about 2 mm) has a significantly smaller diameter than CA/CTS-M (about 3 mm). According to the influence of pH and density functional theory calculations, electrostatic attraction is the key driving force of NOR adsorption. Importantly, acid wash led to more negative-charged surface characterized by Zeta potential, which is the main reason of the significantly enhanced adsorption capacity of CA/CTS-M in removal of NOR. In short, CA/CTS-M hydrogel spheres are environment friendly and highly stable adsorbents with high adsorption capacity in the removal of NOR.

Insight into the addition reactions of stannylenoid H2SnLiF with ethylene.

CONTEXT: Tetrylenoids, R2EXM (E = Si, Ge, and Sn; X = electronegative group; M = alkali metal), have electrophilic and nucleophilic properties just like carbenoid. As the products of carbenoid compounds with olefins, the cyclopropane fraction has been found to be biologically active in many natural and artificial compounds. Can carbenoid analogues of stannylenoid facilitate similar cyclopropanation reactions? METHODS: Addition reaction of the stannylenoid compound H2SnLiF with ethylene was investigated using density function theory (DFT) at the M062X/def2-TZVP level. The single-point energy calculations were performed on the basis of QCISD/def2-TZVP level. RESULTS: Two possible pathways were found for the addition reaction of H2SnLiF (R1) with ethylene (R2). The most favorable path is the two successive reactions of H2SnLiF and ethylene through the ternary ring product c-H2Sn(CH2)2 (P1) and then the formation of the five-membered ring product (P2). Solvation-related studies have shown that addition reactions are more likely to occur in the presence of THF solvents. This work provides theoretical support for the reactions of stannylenoid with olefins.

Theoretical investigation on the addition reaction of the germylenoid H2GeLiCl with acetone.

In this work, theoretical calculations were performed on the addition reaction of the germylenoid H2GeLiCl with acetone. The DFT M06-2X method was used to optimize the geometries of the whole stationary points on the potential energy surfaces and the QCISD method to calculate the single-point energy. The results reveal that the addition reaction of H2GeLiCl with acetone firstly generates an oxagermacyclopropane c-H2GeOC(CH3)2 and then c-H2GeOC(CH3)2 further reacts with acetone along two possible pathways, pathway I and pathway II, in which the 2,4-dioxagermolane is formed at the end of pathway I and 2,5-dioxagermolane is formed at the end of pathway II, respectively. According to the calculated barrier heights, we can deduce that the pathway I is more favorable than pathway II. The computational results suggest that this reaction model can provide new inspiration for the synthesis of heterocyclic germanium compounds.

Terpenoids from the Marine-Derived Fungus Aspergillus sp. RR-YLW-12, Associated with the Red Alga Rhodomela confervoides.

Two new meroterpenoids, aspermeroterpenes D and E (1 and 2), two new ophiobolin-type sesterterpenoids, the C-18 epimers of 18,19-dihydro-18-methoxy-19-hydroxyophiobolin P (6 and 7), and two new drimane-type sesquiterpenoids, 3S-hydroxystrobilactone A (8) and 6-epi-strobilactone A (9), along with 11 known terpenoids (3-5 and 10-17) were isolated from the cultures of the algicolous fungus Aspergillus sp. RR-YLW-12, derived from the red alga Rhodomela confervoides. The structures and relative configurations of new compounds were established by detailed spectroscopic analysis of NMR and HRMS experiments, and the absolute configurations were assigned by X-ray diffraction experiments and comparison of their experimental and calculated ECD spectra. Compound 1 features a rare 6/6/6/6/5 pentacyclic system with a meroterpenoid skeleton, and the structure of terretonin E (3) was revised in this study. Compound 4 showed significant inhibitory activities against three microalgae, Prorocentrum donghaiense, Heterosigma akashiwo, and Chattonella marina, with IC50 values of 10.5, 5.2, and 3.1 µg/mL, respectively.

Total Synthesis of the Proposed Microcyclamides MZ602 and MZ568.

The first convergent total synthesis for the proposed structures of microcyclamides MZ602 (1) and MZ568 (2) has been accomplished in 11 linear steps with 12.5 and 16.8% overall yield, respectively. Key features of the syntheses include a one-pot cascade reaction to construct core Boc-l-Ile-Thz-OAllyl fragment 5, and a removable pseudoproline (ΨMe,Me pro) inducer assisted cyclization of thiazole-containing all-l linear peptides. The spectral data (1H NMR, 13C NMR, and HRMS) of synthetic MZ602 (1) were quite similar to those of the proposed natural microcyclamide MZ602, except to an opposite sign of the optical rotation value. Surprisingly, the synthetic MZ568 (2) presented large discrepancies in characteristic spectral data from those of the reported natural product, although the absolute configuration of key intermediate 36 was unambiguously determined by single-crystal X-ray analysis in our work. These findings revealed that the proposed structures of natural microcyclamides MZ602 and MZ568 required revision.

Hymerhabdrin A, a novel diterpenoid with antifouling activity from the intertidal sponge Hymerhabdia sp.

Hymerhabdrin A (1), a diterpenoid possessing a novel 6/6/5 fused-ring skeleton, together with four known sterols were isolated from an intertidal marine sponge Hymerhabdia sp. Their structures were elucidated by extensive spectroscopic methods, and the relative and absolute configurations of 1 were determined by NOESY analysis and electronic circular dichrosim calculations, respectively. Hymerhabdrin A (1) exhibited significant antifouling activity against Balanus amphitrite larval with LC50 (lethal concentration 50) value of 3.6 µg ml-1.

Substitution Reactions of the Aluminum Chlorogermylenoid H2GeClAlCl2 with HF, H2O, NH3, HCl, H2S, and PH3.

Quantum chemical calculations have been performed for the substitution reactions of the aluminum chlorogermylenoid H2GeClAlCl2 with HF, H2O, NH3, HCl, H2S, and PH3 to get more insights into the reactivity of H2GeClAlCl2. The theoretical calculated results indicated that the substitution reactions of H2GeClAlCl2 with HF, H2O, NH3, HCl, H2S, and PH3 proceeded in a concerted manner. There were one transition state and one intermediate which connected the reactants and the products along the potential energy surface. The six substitution reactions of H2GeClAlCl2 with HF, H2O, NH3, HCl, H2S, and PH3 are compared with the addition reaction s of H2Ge with these hydrides. And based on the calculated results we concluded that the substitution reactions of H2GeClAlCl2 with these hydrides involve two steps, one is dissociation onto H2Ge with AlCl3, and the other is the addition reactions of H2Ge with HF, H2O, NH3, HCl, H2S, and PH3.

Chemical constituents and their bioactivities from the fruits of Vitex negundo var. cannabifolia.

Phytochemical investigation of the fruits of Vitex negundo var. cannabifolia led to the isolation of 22 compounds (1-22). Their structures were elucidated mainly by spectroscopic analysis and comparison with the literature data. Among them, compounds 1 and 2 were two new artificial lignans. Primary bioassay showed that the polymethoxyflavones 9-12 displayed moderate-to-weak cytotoxicity against human HepG2 and rat C6 cell lines, while the triterpenoids 13-17 exhibited significant brine shrimp lethality with LC50values of 7.5-29.4 µM.

A new minor diketopiperazine from the sponge-derived fungus Simplicillium sp. YZ-11.

Chemical investigation of the cultures of a sponge-derived fungus Simplicillium sp. YZ-11 led to the isolation of a new minor diketopiperazine alkaloid cyclo-(2-hydroxy-Pro-Gly) (1) and a natural lactone (S)-dihydro-5-[(S)- hydroxyphenylmethyl]-2(3H)-furanone (2), together with five known ergostane-type sterols (3-7). Their structures were established based on extensive spectroscopic methods ((1)H and (13)C NMR, (1)H-(1)H COSY, HSQC and HMBC) and optical rotation analysis.

New insights into the insertion reactions of germylenoid H2GeLiF with RH (R = F, OH, NH2).

In the present work, a new pathway of the insertion reactions of H2GeLiF with RH (R = F, OH, NH2) was investigated using DFT B3LYP and QCISD methods. The geometries of the stationary points on the potential energy surfaces in the reactions were optimized at the B3LYP/6-311 + G (d, p) level and then the single-point energies were calculated at the QCISD/6-311++G (d, p) level. The calculated results indicated that the initial step of all the reactions is the isomerization of the p-complex structure to a three-membered-ring structure. After isomerization, the insertion reactions of three-membered-ring H2GeLiF with RH (R = F, OH, NH2) take place. The QCISD/6-311++G (d, p)//B3LYP/6-311 + G (d, p) calculated potential energy barriers of the three reactions were 89.77, 137.40, and 167.45 kJ mol(-1), respectively. Under the same situation, the insertion reactions should occur easily in the following order H-F > H-OH > H-NH2. Compared with the direct insertion reactions of H2GeLiF with RH (R = F, OH, NH2), the two-step insertions have lower activation barriers and should be more favorable.

Insight into the substitution reactions of silylenoid H2SiLiF with GeH3X (X = F, Cl, Br): a theoretical study.

The unique substitution reactions of the three-membered-ring silylenoid H2SiLiF with GeH3X (X = F, Cl, Br) were investigated using ab initio and density functional theory calculations. All stationary points on the potential energy surfaces were optimized at the B3LYP/6-311 + G (d, p) level of theory and the QCISD method was then used to calculate the single-point energies. Theoretical calculations predicted that the substitution reactions of H2SiLiF with GeH3X proceed via two reaction paths (I and II), while forming the same product H2FSi-GeH3. In either pathway, there is one precursor complex (Q), one transition state (TS), and one intermediate (IM) connecting the reactants and products. The substitution reaction barriers of H2SiLiF with GeH3X for path I (48.49, 42.71, and 38.71 kJ mol(-1)) decreased with the increase for the same-family element X from up to down in the periodic table, whereas the substitution barriers for path II (6.51, 22.04, and 23.62 kJ mol(-1)) increased with the increase in atomic number of X (X = F, Cl, Br). Path II was more favorable than path I. All the substitution reactions of H2SiLiF with GeH3X were exothermic. The elucidation of the unique mechanism of these substitution reactions suggests a new reaction mode of silicon-germanium bond formation.

A new reaction mode of germanium-silicon bond formation: insertion reactions of H2GeLiF with SiH3X (X = F, Cl, Br).

A combined density functional and ab initio quantum chemical study of the insertion reactions of the germylenoid H2GeLiF with SiH3X (X = F, Cl, Br) was carried out. The geometries of all the stationary points of the reactions were optimized using the DFT B3LYP method and then the QCISD method was used to calculate the single-point energies. The theoretical calculations indicated that along the potential energy surface, there were one precursor complex (Q), one transition state (TS), and one intermediate (IM) which connected the reactants and the products. The calculated barrier heights relative to the respective precursors are 102.26 (X = F), 95.28 (X = Cl), and 84.42 (X = Br) kJ mol(-1) for the three different insertion reactions, respectively, indicating the insertion reactions should occur easily according to the following order: SiH3-Br > SiH3-Cl > SiH3-F under the same situation. The solvent effects on the insertion reactions were also calculated and it was found that the larger the dielectric constant, the easier the insertion reactions. The elucidations of the mechanism of these insertion reactions provided a new reaction model of germanium-silicon bond formation.