Polyethylene glycol-assisted sol-gel synthesis of magnetic CoFe2O4 powder as photo-Fenton catalysts in the presence of oxalic acid

Journal of Sol-Gel Science and Technology - The aim of the study was to prepare magnetic photo-Fenton catalysts based on CoFe2O4 by polyethylene glycol-assisted sol-gel method for the degradation...     

A Diazido Mannose Analogue as a Chemoenzymatic Synthon for Synthesizing Di‐N‐acetyllegionaminic Acid‐Containing Glycosides

A chemoenzymatic synthon was designed to expand the scope of the chemoenzymatic synthesis of carbohydrates. The synthon was enzymatically converted into carbohydrate analogues, which were readily derivatized chemically to produce the desired targets. The strategy is demonstrated for the synthesis of glycosides containing 7,9‐di‐N‐acetyllegionaminic acid (Leg5,7Ac₂), a bacterial nonulosonic acid (NulO) analogue of sialic acid. A versatile library of α2‐3/6‐linked Leg5,7Ac₂‐glycosides was built by using chemically synthesized 2,4‐diazido‐2,4,6‐trideoxymannose as a chemoenzymatic synthon for highly efficient one‐pot multienzyme (OPME) sialylation followed by downstream chemical conversion of the azido groups into acetamido groups. The syntheses required 10 steps from commercially available d ‐fucose and had an overall yield of 34–52 %, thus representing a significant improvement over previous methods. Free Leg5,7Ac₂ monosaccharide was also synthesized by a sialic acid aldolase‐catalyzed reaction.     

New furoquinoline alkaloid and flavanone glycoside derivatives from the leaves of Oricia suaveolens and Oricia renieri (Rutaceae)

Fractionation of the methanol extract of the leaves of Oricia renieri and Oricia suaveolens (Rutaceae) led to the isolation of 13 compounds including the hitherto unknown furoquinoline alkaloid named 6,7-methylenedioxy-5-hydroxy-8-methoxy-dictamnine (1) and a flavanone glycoside named 5-hydroxy-4′-methoxy-7-O-[α-l-rhamnopyranosyl(1?→5″)-β-d-apiofuranosyl]-flavanoside (2), together with 11 known compounds (3–13). The structures of the compounds were determined by comprehensive analyses of their 1D and 2D NMR, mass spectral data and comparison. All compounds isolated were examined for their activity against human carcinoma cell lines. The alkaloids 1, 5, 12, 13 and the phenolic 2, 8, 11 tested compounds exhibited non-selective moderate cytotoxic activity with IC₅₀ 8.7–15.9 μM whereas compounds 3, 4, 6, 7, 9 and 10 showed low activity.     

Catalytic synthesis of biodiesel from high free fatty acid-containing feedstocks

Recyclable and reusable heterogeneous diarylammonium catalysts are highly effective in catalyzing the esterification of the free fatty acid (FFA) present in greases to methyl esters to reduce the FFA content from 12-40 wt% to 0.5-1 wt%; the resulting ester-glyceride mixture (pretreated grease) could then be readily converted to methyl esters by base-catalyzed transesterification.     

On the regularity of products and intersections of complete intersections

This paper proves the formulae

for arbitrary monomial complete intersections and , and provides examples showing that these inequalities do not hold for general complete intersections.

     

Biomimetic synthesis of arteannuin h and the 3,2-rearrangement of allylic hydroperoxides

The acyl endoperoxide arteannuin H, recently reported as a novel natural product from Artemtsia annua, has been obtained in two steps from the photooxidation of dihydroartemisinic acid, thereby confirming biogenetic speculation regarding its derivation from a secondary allylic hydroperoxide. The little studied 3,2-rearrangement reaction of such allylic hydroperoxides is also discussed.     

Autoxidation of 4-amorphen-11-ol and the biogenesis of nor- and seco-amorphane sesquiterpenes from fabiana imbricata

Photooxidation of 4-amorphen-11-ol (1), recently reported as one of the major sesquiterpene natural products from the medicinal plant Fabiana imbricata, results in three allylic hydroperoxides 6, 9 and 10, which are expected from the “ene-type” reaction of molecular oxygen with the tri-substituted double bond in 1. The tertiary allylic hydroperoxide 6 undergoes carbon-carbon bond cleavage and a second autoxidation reaction to yield the more highly oxygenated seco-amorphane 11 under very mild conditions. In acid, this compound may then undergo either a second carbon-carbon bond cleavage reaction to yield nor-sesquiterpenes 2 and 3 (reported as bona fide natural products from F. imbricata, or cyclize to the sesquiterpene peroxofabianane (5), which is a presumed precursor to the natural product fabianane (4). Some mechanistic investigations concerning the two chemical processes: viz:- carbon-carbon bond cleavage and autoxidation which would account for the formation of natural products 2, 3 and 4 from 1 are reported. Tertiary allylic hydroperoxide 32, which lacks the 11-hydroxyl functional group present in 1 undergoes only C-4/C-5 carbon-carbon bond cleavage under more forcing conditions, suggesting a role for this functional group in assisting the autoxidation reactions of 4-amorphen-11-ol.     

Tunable microwave photonic notch filter using a dual-wavelength fiber laser with phase modulation

A novel tunable microwave photonic notch filter using a phase-modulated dual-wavelength fiber laser is presented. A stable dual-wavelength erbium-doped fiber laser with a linear cavity is formed by a polarization-maintaining uniform fiber Bragg grating (PM-FBG) and a polarization maintaining linearly chirped fiber Bragg grating (PM-LCFBG), both of which were fabricated on a high-birefringence (Hi-Bi) fiber. It is found that a stable room-temperature dual-wavelength operation can be achieved due to the presence of two reflection peaks arising from the orthogonal states of polarization (SOP) of the PM-FBG. Experimental results show stable dual-wavelength lasing operation with a wavelength separation of ∼0.36 nm and a large optical signal-to-noise ratio (OSNR) of over 40 dB under room temperature. The dual-wavelength fiber laser is combined with a phase modulator and a segment of single-mode fiber (SMF) as a dispersive device to form a tunable microwave photonic notch filter. By stretching the PM-FBG to tune the wavelength separation of the dual-wavelength fiber laser, a tunable microwave photonic notch filter with various free spectral ranges (FSRs) and a rejection ratio greater than 35 dB was developed.