Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 6 de 6
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Se Pu ; 37(9): 977-982, 2019 Sep 08.
Artigo em Chinês | MEDLINE | ID: mdl-31642302

RESUMO

A high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was established for the determination of ten alkaloids in cosmetics. Extraction conditions, purification methods and instrumental parameters were optimized. The samples were ultrasonically extracted with 80% (v/v) methanol aqueous solution. The extracts were separated and filtered after centrifugation. The analytes were separated on a Waters BEH C18 column, and detected in the selected reaction monitoring mode. Ten alkaloids were quantified by the external standard method. The ten alkaloids showed good linearity with correlation coefficients (R2) greater than 0.9900. The limits of detection (LODs) and the limits of quantification (LOQs) of the ten alkaloids were in range of 5.0-12.5 µg/kg and 12.5-50.0 µg/kg, respectively. The average spiked recoveries in the cosmetics ranged from 70.91% to 116.75%, and the relative standard deviations (RSDs) ranged from 0.49% to 9.98%. The method can be used for the rapid screening and quantitative analysis of ten alkaloids in cosmetics.


Assuntos
Alcaloides/análise , Cosméticos/análise , Cromatografia Líquida de Alta Pressão , Limite de Detecção , Espectrometria de Massas em Tandem
2.
J Org Chem ; 83(19): 11905-11916, 2018 Oct 05.
Artigo em Inglês | MEDLINE | ID: mdl-30199250

RESUMO

With the aid of density functional theory (DFT) calculations, mechanistic investigations have been carried out for the nickel-catalyzed dehydrogenative cross-coupling reaction of benzaldehyde with benzyl alcohol in the presence of N-heterocyclic carbene (NHC) ligand. The overall Ni(0)/Ni(II) catalytic cycle consists of four basic steps: ligand exchange, oxidative addition, hydrogen transfer, and reductive elimination. Considerable interests are paid on detecting the transition state of the rate-determining step, with particular emphasis on the structural and electronic properties, together with clarifying the important roles of external oxidant and hydrogen acceptor. The hydrogen transfer process in the oxidative addition step is rate-determining in the whole catalytic cycle, which is accomplished by C-Ha (active Ha) activation without generating the high energy nickel hydride intermediate. Such process could be understood as the direct hydrogen transfer, instead of general concerted oxidative addition to low valent transition metal. The analysis of the bond distances, electron distributions, and orbital interactions highlights the direct hydrogen transfer mechanism. Furthermore, by exploring the influences from the electronic effect of different substrates on the reaction energy barriers, the  a,a,a-trifluoroacetophenone could accelerate the direct hydrogen transfer with low activate energy.

3.
Bioresour Technol ; 263: 17-24, 2018 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-29723845

RESUMO

SO2-ethanol-water (SEW) is a promising pretreatment for improving enzymatic digestibility of biomass through simultaneously removing hemicellulose and lignin. In this work, SEW pretreatment was performed at different cooking times (10 min-60 min) and different SO2 concentrations (0.5%-2%) to produce pretreated bamboo residues for enzymatic hydrolysis. Meanwhile, physicochemical features of the residual cellulose and lignin were analyzed to better understand how SEW improves enzymatic digestibility. Under optimized SEW pretreatment condition (1% SO2 concentration, 150 °C, 60 min), 81.7% of xylan and 80.3% of lignin were solubilized, along with 89.1% of cellulose preserved in pretreated solid. A good enzymatic digestibility (80.4%) was achieved at optimum SEW condition. Several compelling correlations (R2 > 0.7) were observable between enzymatic digestibility and physicochemical features, demonstrating the importance of SEW pretreatment abilities of hemicellulose and lignin removal, reducing cellulose's degree of polymerization, and improving the amount of sulfonyl groups imparted to the original lignin structure.


Assuntos
Etanol , Sasa/metabolismo , Dióxido de Enxofre , Celulose , Hidrólise , Lignina , Água
4.
Polymers (Basel) ; 10(8)2018 Jul 30.
Artigo em Inglês | MEDLINE | ID: mdl-30960766

RESUMO

Lignosulfonate (LG), a water-soluble polymer from sulfite pulping process of lignocellulosic biomass, has been commercially applied as admixture for concrete. In this work, lignosulfonates were produced from alkaline lignin (AL) and enzymatic hydrolysis residue (EHR) by sulfomethylation and these lignosulfonates as water reducers for concrete were then evaluated. Results showed that 94.9% and 68.9% of lignins in AL and EHR could be sulfonated under optimum sulfomethylation conditions, respectively. The sulfonic groups in lignosulfonates from AL (AL-LG) and EHR (EHR-LG) were 1.6 mmol/g and 1.0 mmol/g, respectively. Surface tension and zeta potential analysis indicated that both AL-LG and EHR-LG can be potentially used to as dispersant for improving the fluidity of the cement paste, similarly to commercial lignosulfonate (CM-LG). Adding 0.2 wt % of AL-LG, EHR-LG, and CM-LG in the concrete, the compressive strength (28 days) of concretes increased from 38.4 Mpa to 41.6, 42.6, and 40.9 Mpa, respectively. These findings suggest that the lignosulfonate from biorefinery lignin by sulfomethylation can meet the industrial standards as water reducers for cement admixtures.

5.
Se Pu ; 33(6): 657-61, 2015 Jun.
Artigo em Chinês | MEDLINE | ID: mdl-26536771

RESUMO

A modified QuEChERS (quick, easy, cheap, effective, rugged and safe) method followed by liquid chromatography-tandem mass spectrometric analysis was developed for the determination of dimethyl yellow and diethyl yellow in yuba and dried beancurd. Yuba and dried beancurd samples were soaked by deionized water, then acetonitrile was added to extract the analytes. Sodium chloride and anhydrous magnesium sulfate were added for liquid-liquid separation. The extracts were cleaned-up by dispersive solid-phase using N-propyl diethylamine. The analytes were separated by liquid chromatography and determined by mass spectrometry. External standard method was used for quantification. The recoveries of dimethyl yellow were in the range of 73.5%-84.5% at spiked levels of 0.3, 1 and 10 kg/kg and the recoveries of diethyl yellow were in range of 70.5%-81.2% at spiked levels of 0.1,1 and 10 µg/kg; relative standard deviations of the method were lower than 11%. The limit of detection and the limit of quantification of dimethyl yellow were 0.1 µg/kg and 0.3 µg/kg, respectively; the limit of detection and the limit of quantification of diethyl yellow were 0.05 µg/kg and 0.1 µg/kg, respectively. This method can be used in rapid screening and quantitative analysis of dimethyl yellow and diethyl yellow in yuba and dried beancurd.


Assuntos
Fabaceae/química , Análise de Alimentos/métodos , Pigmentos Biológicos/análise , Cromatografia Líquida , Espectrometria de Massas em Tandem
6.
Pediatr Surg Int ; 29(12): 1273-9, 2013 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-23852556

RESUMO

BACKGROUND: Postoperative intussusception (POI) is an unusual complication in children and infants who underwent various kinds of surgery. The early recognition was difficult for its rarity and atypical presentations. This study evaluates the clinical features of POI through a literature review. METHODS: MEDLINE database was searched for relevant articles that reported the children and infants with POI since 1990 in English-language using the key word "postoperative intussusception". All published studies containing clinical data for POI in children and infants were included. Reference lists of retrieved articles were reviewed for additional cases. Detailed data of the included cases were extracted and analyzed. RESULTS: Twenty-six studies with total 127 cases of POI were included. According to the extracted data, the median age was 19 months with the male-to-female ratio 1.5:1. There were 65 operations (51.2 %) that involved gastrointestinal system, 26 cases (20.5 %) of retroperitoneal tumor resection, 12 operations (9.4 %) involved diaphragm, 8 operations (6.3 %) involved urinary system, 5 cases (3.9 %) of partial pancreatectomy, 11 cases (8.7 %) of non-abdominal operations. 75.5 % presented symptoms in the first 7 days after surgery. The prominent symptom was bilious vomiting or increased nasogastric output (87.1 % of 101 patients), following abdominal distention (74.3 %), abdominal pain (35.6 %). Six cases (5.0 %) of ileocolic POI were reduced successfully by air enema. The small bowel intussusception attributed 85.6 % of POI (95 patients). Laparotomy and manual reduction were performed in 104 cases (86.0 %). Nine patients (7.4 %) underwent intestinal resection and anastomosis. CONCLUSIONS: POI should be suspected in pediatric surgical patients who showed signs of intestinal obstruction in the early postoperative period. Early recognition and prompt management are important.


Assuntos
Intussuscepção/diagnóstico , Intussuscepção/cirurgia , Complicações Pós-Operatórias/diagnóstico , Complicações Pós-Operatórias/cirurgia , Criança , Pré-Escolar , Feminino , Humanos , Lactente , Recém-Nascido , Obstrução Intestinal/complicações , Intestinos/cirurgia , Intussuscepção/etiologia , Masculino , Complicações Pós-Operatórias/etiologia , Fatores de Risco
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA