Concise Total Synthesis of (-)-Bipolarolide D.

Here we report the first and concise total synthesis of a complex ophiobolin-derived sesterterpene, bipolarolide D, which hinges on two strategic applications of pentafulvene: (1) enantioselective pentafulvene-involved [6+2] cycloaddition; (2) regioselective and diastereoselective pentafulvene-involved Heck cyclization. Late-stage selective allylic addition to the ketone moiety facilitates the successful installation of the side chain. This strategy enabled the accomplishment of its first enantioselective total synthesis through a modular approach. This synthesis will facilitate the investigation of relevant biological activities and provide a synthetic blueprint for utilizing fulvenes as versatile synthons in other complex natural product synthesis.

Precise determination of the molybdenum isotopic composition of urine by multiple collector inductively coupled plasma mass spectrometry.

RATIONALE: Molybdenum (Mo) is predominantly expelled from the human body in urine. Consequently, urinary variability in the concentration and isotopic composition of Mo may encode valuable clinical information. To access this information, however, it is first necessary to develop and demonstrate a rapid, accurate and precise methodology capable of concentrating Mo from urine for isotope analysis. METHODS: The utility of N-benzoyl-N-phenylhydroxylamine (BPHA) to effectively separate and purify Mo from urine samples without the need for acid digestion was tested. Following this approach, applying a double-spike mass bias correction, we determined the Mo isotopic compositions of a set of urine samples by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). RESULTS: Based on replicate analyses of an in-house urine standard, this approach demonstrates an external precision on δ98/95 Mo values of better than 0.08‰ (2SD, n = 15). Application to a sample set collected from healthy individuals in Guangzhou, China, provides the first suite of δ98/95 Mo measurements from urine samples. Samples from the female participants show δ98/95 Mo (‰) values (1.31 ± 0.19‰, Ave ± 2SD, n = 14) that are consistently lower than those from the male participants (1.55 ± 0.16‰, Ave ± 2SD, n = 17). CONCLUSIONS: The employed methodology is suitable for rapid, low-blank and high-throughput Mo isotope analysis of urine samples. Although resolvable δ98/95 Mo variability is seen in this preliminary dataset, the mechanism driving this variability is unknown. High-precision Mo isotopic analysis might be added to the urinalysis tool-kit, with the potential to provide valuable clinical information in the future.

Synergistic effects of chitosan-guanidine complexes on enhancing antimicrobial activity and wet-strength of paper.

Chitosan-guanidine complexes were prepared by reacting chitosan and polyhexamethylene guanidine hydrochloride or crosslinked polyhexamethylene guanidine hydrochloride in the presence of sodium tripolyphosphate as a crosslinking agent. The complexes, used as functional additives for paper, synergistically improved wet-strength and antimicrobial activities. In comparison with the control sample, the wet/dry strength ratio of hand-sheets treated with the complexes was increased from 2.65% up to 23.3%. The MIC values of the chitosan-PHGH and chitosan-PHGHE complexes against Escherichia coli were 15.6 and 31.2 microg mL(-1), respectively, thus demonstrating excellent antimicrobial activity. Hand-sheets treated with the complexes exhibited antibacterial activity against E. coli and Staphylococcus aureus. The release of the guanidine polymers included in the complexes was dynamically monitored using UV and the results showed the amount released exceeded 80%. Atomic force microscopy images indicated that the antimicrobial mechanism of the complexes was likely due to membrane damage.

Adsorption properties of crosslinked carboxymethyl-chitosan resin with Pb(II) as template ions.

In the current study, we attempt to find a new adsorbent material based on chitosan to improve adsorption selectivity for heavy metals, so that the crosslinked N,O-carboxymethyl-chitosan resin with Pb(II) as template ions (crosslinked CMC template) were synthesized by using CMC adsorbed Pb(II) ions crosslinked with glutaraldehyde. The effects on adsorption capacities such as amount of crosslinking agent, degree of substitution of CMC, pH value of the initial solution and adsorption time were investigated. The adsorption experiments demonstrated the crosslinked CMC template has high adsorption selectivity for Pb(II) ions in solution containing single metal ions or coexistence of three metals ions of Cu(II), Zn(II) and Pb(II). Furthermore, it was investigated that the crosslinked CMC template has a good reusability and stability as compared to CMC. Finally, we studied the adsorption mechanism by FTIR spectra and XPS analysis. The results reveal that the adsorption of crosslinked CMC template and CMC for Pb(II) is a chelation process.

Adsorption kinetics of Cu(II) ions using N,O-carboxymethyl-chitosan.

A series of N,O-carboxymethyl-chitosan (N,O-CMC) with different degree of substitution (DS) were prepared by using chitosan (CTS) and monochloroacetic acid under various conditions. The adsorption properties of N,O-CMC were evaluated. The results revealed that N,O-CMC is suitable for adsorbent to removal Cu(II) ion. The parameters for the adsorption of Cu(II) ions by N,O-CMC were also determined. It was shown that the samples of N,O-CMC had given good correlation with Langmuir's isotherm model and that the adsorption kinetics of Cu(II) could be best described by the pseudo-second-order model. It was also observed that the adsorption capacity seemed to be dependent on pH value in solution, the DS of samples and ionic strength. Furthermore, the maximum adsorption capacity of the monolayer was 162.5 mg of Cu(II) per gram of polymer with DS of 0.96. FTIR and X-ray photoelectron spectroscopy revealed that Cu(II) ions and N,O-CMC formed a chelate complex.

[Study on D-glucosamine-zn (II) complexes by IR spectral analysis].

In this paper, a series of glucosamine-Zn(II) complexes were synthesized by the reaction of D-glucosamine hydrochloride with ZnSO4 at different pH values. The physical properties and the IR spectra of glucosamine-ZnSO4 complexes were investigated. The absorption at 3346 and 3292 cm(-1) shifted to 3300 cm(-1) due to O--H and N--H stretching, one at 1617 cm(-1) shifted to 1530 cm(-1) due to N-H stretching, and one at 1094 cm(-1) disappeared due to secondary alcohol --OH stretching. But 1033 cm(-1) with primary alcohol --OH did not shift, suggesting that both the amino and secondary hydroxyl groups of glucosamine are coordinated to Zn(II). The results showed that the coordination ability of Zn(II) to glucosamine was enhanced with the pH value increasing, however, the coordination ability weakened when pH value was more than 6.5. So pH 6.5 is an optimal coordination condition for glucosamine-ZnSO4 complexes. The complexes of D-glucosamine with different zinc salts (zinc sulfate, zinc nitrate, zinc acetate, and zinc chloride) were also synthesized at the same pH value, and zinc chloride had weaker coordination ability than other zinc salts. Their IR spectra indicated that glucosamine-Zn(II) complexes with different zinc salts had different coordination model, and only glucosamine-ZnSO4 complex had fixed ratio of coordination under the condition of pH 6.5. The structure of the complex seems to correspond to [Zn(glucosamine)]SO4 7H2O at pH 6.5.