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1.
Endoscopy ; 56(4): 260-270, 2024 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-37827513

RESUMEN

BACKGROUND: The choice of polypectomy device and surveillance intervals for colorectal polyps are primarily decided by polyp size. We developed a deep learning-based system (ENDOANGEL-CPS) to estimate colorectal polyp size in real time. METHODS: ENDOANGEL-CPS calculates polyp size by estimating the distance from the endoscope lens to the polyp using the parameters of the lens. The depth estimator network was developed on 7297 images from five virtually produced colon videos and tested on 730 images from seven virtual colon videos. The performance of the system was first evaluated in nine videos of a simulated colon with polyps attached, then tested in 157 real-world prospective videos from three hospitals, with the outcomes compared with that of nine endoscopists over 69 videos. Inappropriate surveillance recommendations caused by incorrect estimation of polyp size were also analyzed. RESULTS: The relative error of depth estimation was 11.3% (SD 6.0%) in successive virtual colon images. The concordance correlation coefficients (CCCs) between system estimation and ground truth were 0.89 and 0.93 in images of a simulated colon and multicenter videos of 157 polyps. The mean CCC of ENDOANGEL-CPS surpassed all endoscopists (0.89 vs. 0.41 [SD 0.29]; P<0.001). The relative accuracy of ENDOANGEL-CPS was significantly higher than that of endoscopists (89.9% vs. 54.7%; P<0.001). Regarding inappropriate surveillance recommendations, the system's error rate is also lower than that of endoscopists (1.5% vs. 16.6%; P<0.001). CONCLUSIONS: ENDOANGEL-CPS could potentially improve the accuracy of colorectal polyp size measurements and size-based surveillance intervals.


Asunto(s)
Pólipos del Colon , Neoplasias Colorrectales , Aprendizaje Profundo , Humanos , Pólipos del Colon/diagnóstico por imagen , Colonoscopía/métodos , Neoplasias Colorrectales/diagnóstico por imagen
2.
Front Psychol ; 14: 1280041, 2023.
Artículo en Inglés | MEDLINE | ID: mdl-38106402

RESUMEN

This study aimed to investigate the changes in self-esteem levels among Chinese adolescents from 1996 to 2019. In this cross-sectional historical study, 109 articles using the Rosenberg Self-esteem Scale (SES) were selected from three Chinese and five English databases. The results showed that: (1) The self-esteem level of Chinese adolescents was positively correlated with the period, indicating that the self-esteem of Chinese adolescents was gradually increasing. (2) The increase in self-esteem level of girls was higher than that of boys. (3) The increase in the self-esteem level of only child was higher than that of non-only child. (4) The self-esteem level of rural adolescents increased year by year. However, the self-esteem level of urban adolescents was not significantly correlated with the years. (5) The changes in macro social factors can significantly predict the upward trend of the self-esteem level of Chinese adolescents.

3.
Sensors (Basel) ; 23(8)2023 Apr 08.
Artículo en Inglés | MEDLINE | ID: mdl-37112168

RESUMEN

Gearboxes are one of the most widely used speed and power transfer elements in rotating machinery. Highly accurate compound fault diagnosis of gearboxes is of great significance for the safe and reliable operation of rotating machinery systems. However, traditional compound fault diagnosis methods treat compound faults as an independent fault mode in the diagnosis process and cannot decouple them into multiple single faults. To address this problem, this paper proposes a gearbox compound fault diagnosis method. First, a multiscale convolutional neural network (MSCNN) is used as a feature learning model, which can effectively mine the compound fault information from vibration signals. Then, an improved hybrid attention module, named the channel-space attention module (CSAM), is proposed. It is embedded into the MSCNN to assign weights to multiscale features for enhancing the feature differentiation processing ability of the MSCNN. The new neural network is named CSAM-MSCNN. Finally, a multilabel classifier is used to output single or multiple labels for recognizing single or compound faults. The effectiveness of the method was verified with two gearbox datasets. The results show that the method possesses higher accuracy and stability than other models for gearbox compound fault diagnosis.

4.
Chem Commun (Camb) ; 59(18): 2652-2655, 2023 Feb 28.
Artículo en Inglés | MEDLINE | ID: mdl-36779915

RESUMEN

We have developed a fluorescent quantification strategy to evaluate the uniformity and the aggregation degree of inorganic particles in polymers. This proposed strategy has been successfully used for investigating the anti-aging behaviors of composites.

5.
Open Life Sci ; 17(1): 243-247, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-35415243

RESUMEN

In this study, we explored the effect of nutrition intervention on the management of patients with novel coronavirus pneumonia (NCP). A total of 28 NCP patients receiving therapy in Ningbo First Hospital (China) were enrolled in this study. The nutrition risk was assessed using the Nutritional Risk Screening (NRS)-2002 for the patients subjected to nutrition intervention provided by the Nutritional Department in Ningbo First Hospital, China. Compared to the situation at admission, the body mass index (BMI) and weight of NCP patients were higher at the time of discharge, while no significant difference was observed (P > 0.05). The serum albumin and hemoglobin levels of NCP patients were significantly increased compared with those at admission and one week after admission (P < 0.05). The nutrition intervention can improve the nutritional status and prognosis of NCP patients.

6.
Materials (Basel) ; 14(16)2021 Aug 23.
Artículo en Inglés | MEDLINE | ID: mdl-34443273

RESUMEN

Lithium-rich manganese oxide is a promising candidate for the next-generation cathode material of lithium-ion batteries because of its low cost and high specific capacity. Herein, a series of xLi2MnO3·(1 - x)LiMnO2 nanocomposites were designed via an ingenious one-step dynamic hydrothermal route. A high concentration of alkaline solution, intense hydrothermal conditions, and stirring were used to obtain nanoparticles with a large surface area and uniform dispersity. The experimental results demonstrate that 0.072Li2MnO3·0.928LiMnO2 nanoparticles exhibit a desirable electrochemical performance and deliver a high capacity of 196.4 mAh g-1 at 0.1 C. This capacity was maintained at 190.5 mAh g-1 with a retention rate of 97.0% by the 50th cycle, which demonstrates the excellent cycling stability. Furthermore, XRD characterization of the cycled electrode indicates that the Li2MnO3 phase of the composite is inert, even under a high potential (4.8 V), which is in contrast with most previous reports of lithium-rich materials. The inertness of Li2MnO3 is attributed to its high crystallinity and few structural defects, which make it difficult to activate. Hence, the final products demonstrate a favorable electrochemical performance with appropriate proportions of two phases in the composite, as high contents of inert Li2MnO3 lower the capacity, while a sufficient structural stability cannot be achieved with low contents. The findings indicate that controlling the composition through a dynamic hydrothermal route is an effective strategy for developing a Mn-based cathode material for lithium-ion batteries.

7.
Front Psychol ; 12: 603075, 2021.
Artículo en Inglés | MEDLINE | ID: mdl-34093301

RESUMEN

There are two contending models regarding the processing of negation: the fusion model and the schema-plus-tag model. Most previous studies have centered on negation in languages such as English and Mandarin, where negators are positioned before predicates. Mongolian, quite uniquely, is a language whose negators are post-verbal, making them natural replicas of the schema-plus-tag model. The present study aims to investigate the representation process of Mongolian contradictory negative sentences to shed light on the debate between the models, meanwhile verifying the post-verbal effect of negators. A series of experiments using the sentence-picture verification paradigm supports the fusion model: (i) Mongolian contradictory negative sentences were processed by representing the actual conditions rather than the negated state of affairs at 250 ISI (interstimulus interval of 250 ms), and (ii) despite the fact that a post-verbal effect of negators was measured at 250 ISI when Mongolian and Mandarin negative sentences were compared, Mongolian-Mandarin bilinguals adopted the same representational strategy for contradictory negation in both languages.

8.
Zhonghua Nan Ke Xue ; 26(2): 160-166, 2020 Feb.
Artículo en Chino | MEDLINE | ID: mdl-33346421

RESUMEN

OBJECTIVE: To investigate the protective effect of Jinkui Shenqi Pills (JSP) against cyclophosphamide-induced testis injury (TI) and its anti-oxidation mechanism in mice. METHODS: Thirty male mice were equally divided into a blank control, a TI model control and a JSP treatment group. The mice in the JSP treatment group were treated intragastrically with JSP and the blank controls with normal saline at 1.2 g/kg qd for 7 days, and then the animals in both the TI model control and JSP treatment groups were injected intraperitoneally with cyclophosphamide at 50 mg/kg, once a week, for 35 days, to induce testis injury. After modeling, all the mice were weighed and sacrificed, followed by detection of the serum T content, measurement of the testis weight, examination of semen parameters in the caudad epididymis, and determination of the levels of super oxide dismutase (SOD) and malondialdehyde (MDA) in the testis tissue and the expressions of relevant genes by qRT-PCR. RESULTS: The mice of the TI model control group, compared with the blank controls, showed significant decreases in the body weight (ï¼»34.63 ± 1.92ï¼½ vs ï¼»48.32 ± 1.64ï¼½ g, P<0.05), testis weight (ï¼»80.00 ± 3.90ï¼½ vs ï¼»140.00 ± 6.10ï¼½ mg, P<0.05), testicular organ coefficient (ï¼»0.22 ± 0.01ï¼½ vs ï¼»0.31 ±0.03ï¼½%, P<0.05), sperm motility (ï¼»48.66 ± 8.08ï¼½% vs ï¼»89.33 ± 4.04ï¼½%, P<0.05), sperm concentration (ï¼»28.42 ± 5.26ï¼½ vs ï¼»77.67 ± 8.73ï¼½ ×106/ml, P<0.05), and levels of serum T (ï¼»8.75 ± 0.96ï¼½ vs ï¼»21.75 ± 1.71ï¼½ pg/ml, P<0.05) and SOD (ï¼»140.82 ± 10.08ï¼½ vs ï¼»358.52 ± 40.41ï¼½ U/mg prot, P<0.05), but remarkable increases in the sperm deformity rate (ï¼»37.33 ± 2.08ï¼½ vs ï¼»15.33±1.53ï¼½%, P<0.05) and MDA level (ï¼»54.89±6.09ï¼½ vs ï¼»30.21±2.17ï¼½ nmol/ng prot, P<0.05). The mice of the JSP treatment group, in comparison with the TI model controls, exhibited markedly increased body weight (ï¼»39.80±2.89ï¼½ vs ï¼»34.63±1.92ï¼½g, P<0.05), testis weight (ï¼»130.00 ± 11.00ï¼½ vs ï¼»80.00 ± 3.90ï¼½ mg, P<0.05), testicular organ coefficient (ï¼»0.28 ± 0.01ï¼½ vs ï¼»0.22 ± 0.01ï¼½%, P<0.05), sperm motility (ï¼»76.00 ± 5.29ï¼½% vs ï¼»48.66 ± 8.08ï¼½%, P<0.05), sperm concentration (ï¼»56.08 ± 4.29ï¼½ vs ï¼»28.42 ± 5.26ï¼½ ×106/ml, P<0.05), and levels of serum T (ï¼»15.50 ± 1.29ï¼½ vs ï¼»8.75 ± 0.96ï¼½ pg/ml, P<0.05) and SOD (ï¼»206.59 ± 16.38ï¼½ vs ï¼»140.82 ± 10.08ï¼½ U/mg prot, P<0.05), but decreased sperm deformity rate (ï¼»25.01 ± 2.99ï¼½% vs ï¼»37.33 ± 2.08ï¼½%, P<0.05) and MDA level (ï¼»35.84 ± 3.61ï¼½ vs ï¼»54.89 ± 6.09ï¼½ nmol/ng prot, P<0.05). The mRNA expressions of NOQ-1, Nrf2 and HO-1 in the testis tissue were significantly lower and that of Caspase-3 remarkably higher in the TI model control than in the blank control group (P<0.05), while those of Nrf2 and HO-1 significantly higher and that of Caspase-3 markedly lower in the JSP treatment group than in the TI model controls (P<0.05). Histopathological images displayed reduced layers of spermatogenic cells in the seminiferous tubules, complete exfoliation of the spermatogenic cells in some of the tubules and decreased number of sperm cells in the TI model controls, which were all found normal in the JSP treatment group. CONCLUSIONS: Jinkui Shenqi Pills can effectively inhibit cyclophosphamide-induced testis injury, which may be related to its effect of regulating the gene expression of the Nrf2 signaling pathway and enhancing the activity of antioxidant enzymes.


Asunto(s)
Medicamentos Herbarios Chinos/farmacología , Factor 2 Relacionado con NF-E2/metabolismo , Motilidad Espermática , Testículo/metabolismo , Animales , Ciclofosfamida , Expresión Génica , Masculino , Ratones , Factor 2 Relacionado con NF-E2/genética , Transducción de Señal , Recuento de Espermatozoides , Espermatozoides , Testículo/efectos de los fármacos
10.
Hua Xi Kou Qiang Yi Xue Za Zhi ; 38(2): 117-121, 2020 Apr 01.
Artículo en Chino | MEDLINE | ID: mdl-32314881

RESUMEN

The outbreak of corona virus disease (COVID-19) has raised concerns among dentists to develop strategies to prevent infection of dental equipment, materials, and patients during an epidemic period. Strategies following the National Laws and Standards of China and local standards of several provinces for controlling cross-infection and instituting protective measures for medical staff in dental clinics during an epidemic period are discussed. A proposal is put forth for dental clinics that will face similar situations in the future. Further research is warranted to address potential problems that will be encountered under such dire circumstances.


Asunto(s)
Infecciones por Coronavirus , Coronavirus , Clínicas Odontológicas , Control de Infecciones , Betacoronavirus , COVID-19 , China , Equipo Dental , Brotes de Enfermedades , Humanos , Pandemias , Neumonía Viral , SARS-CoV-2
11.
Anal Chem ; 92(1): 1628-1634, 2020 01 07.
Artículo en Inglés | MEDLINE | ID: mdl-31826615

RESUMEN

Oxygen vacancy is known to act as a reactive center in oxides to produce radicals. Currently, X-ray photoelectron spectra (XPS) become a unique spectral tool for analyzing oxygen vacancy based on the differences in atomic number ratios between metal ions and lattice oxygen. In this work, it was found that the superoxide radical (O2•-)-luminol electrochemiluminescence (ECL) intensity linearly increases with increasing the oxygen vacancy concentrations of TiO2 samples coated on the electrodes. An experimental study of the mechanism demonstrates that an increase in oxygen vacancy concentrations could lead to an increase in the generation of O2•-, resulting in an increase in the O2•--related luminol ECL signals. Accordingly, we have developed a rapid and simple O2•--luminol ECL platform to detect oxygen vacancy in TiO2 samples, based on the relationship between O2•- generation and oxygen vacancy. The proposed ECL platform exhibits good reproducibility and stability through the parallel ECL measurements. Moreover, the feasibility is verified by analyzing the oxygen vacancy concentrations in different TiO2 samples with varying the Co, Cr, Fe, and N doping concentrations. The oxygen vacancy concentrations obtained by the proposed ECL method could match well with those obtained by conventional XPS measurements. Our successful construction of the ECL platform will significantly promote the development of the oxygen vacancy detection in oxides and deepen the understanding of the relationship between oxygen vacancy and radicals.

12.
Chem Commun (Camb) ; 55(39): 5563-5566, 2019 May 09.
Artículo en Inglés | MEDLINE | ID: mdl-31025674

RESUMEN

In this study, we discovered that a clear decrease in the electrochemiluminescence (ECL) intensities of luminol occurred upon increasing the electron donating capacity of amides. Therefore, herein, a novel ECL probe was used for the first time to screen the strength of the hydrogen bonds formed between HOO˙ radicals and amides. This proposed hydrogen bonding strength-sensitive ECL probe has a significant prospect in distinguishing the hydrogen bonding strength of different radicals.

13.
J Nanosci Nanotechnol ; 19(2): 780-785, 2019 02 01.
Artículo en Inglés | MEDLINE | ID: mdl-30360153

RESUMEN

Silver plate was found to prevent spoilage of foods thousands year ago and Ag nanoparticle is known to have great antibacterial activity. In this study, Ag nanoparticles with low than 10 nm average diameter were prepared in the present of glucose. A hypothetical "molecular cage" was built by glucose molecules in solution to limit the chemical reaction in a tiny space and to control the size and morphology of Ag nanoparticles. A possible synthesis mechanism of Ag nanoparticles in confined space was proposed. Escherichia coli and Staphylococcus aureus were used to investigate the antibacterial activity of the synthesized Ag nanoparticles. Compared with the Ag nanoparticles obtained by conventional chemical precipitation method, the Ag nanoparticles synthesized in our study have better antibacterial activities for both Escherichia coli and Staphylococcus aureus in low concentrations.


Asunto(s)
Nanopartículas del Metal , Plata , Antibacterianos/farmacología , Escherichia coli , Pruebas de Sensibilidad Microbiana , Plata/farmacología , Staphylococcus aureus
14.
J Hazard Mater ; 353: 89-98, 2018 07 05.
Artículo en Inglés | MEDLINE | ID: mdl-29635178

RESUMEN

A "molecular cage" was possibly built in glucose alkaline solution to limit the chemical reaction in a tiny space to control the size and morphology of HA nanoparticles. A possible reaction mechanism of HA nanoparticles confined space synthesis was proposed in this work. The super-small HA nanoparticles were successfully obtained in the first time in mild and green condition which had a 7 nm diameter. The adsorptions to Pb2+, Zn2+, Ni2+, Cd2+ ions in their mixture solution by the synthesized HA nanoparticles were studied. The adsorbent showed huge adsorption capacities for the targets (Pb2+ = 3289 mg/g, Zn2+ = 3150 mg/g, Ni2+ = 3061 mg/g and Cd2+ = 2784 mg/g), which indicated an excellent performance of the synthesized nano material in water treatment. Freundlich equation analysis and SEM images of the adsorption products suggested multilayer adsorptions to the targets, and a new recrystalline type adsorption on the surface of the host was found. Some Ca atoms in HA nanoparticles were also found to be substituted by the heavy metallic elements in the initial stage of the adsorptions. The synthesized nano material exhibits better application prospect in wastewater treatment field for its easy synthesis, low-cost and environmental friendly properties.

15.
RSC Adv ; 8(10): 5127-5135, 2018 Jan 29.
Artículo en Inglés | MEDLINE | ID: mdl-35542416

RESUMEN

In the current work, MCM-41/polydimethylsiloxane (PDMS) mixed matrix membrane (MMM) was prepared for effective n-butanol pervaporation from a model aqueous solution. In order to improve the compatibility between MCM-41 and PDMS, different types of silane coupling agents including n-propyltrimethoxysilane (PTMS), n-octyltrimethoxysilane (OTMS), n-dodecyltrimethoxysilane (DTMS) and n-hexadecyltrimethoxysilane (HDTMS) were used to modify the MCM-41. The results showed that the highest n-butanol separation performance was achieved by bonding 20 wt% of PTMS-modified MCM-41 with PDMS. Under these conditions, total flux of 1476 g m-2 h-1 was obtained when separating a 1.5 wt% n-butanol aqueous solution at 55 °C. The total flux increased by nearly 40% compared to the pure PDMS membrane with no obvious changes of the n-butanol separation factor at the same time. The curing process of the casting solution was also significantly improved after MCM-41 modification.

16.
Clin Nutr ; 37(2): 516-521, 2018 04.
Artículo en Inglés | MEDLINE | ID: mdl-28040302

RESUMEN

BACKGROUND: The most typical chronic liver disease in children and adolescents is non-alcoholic fatty liver disease (NAFLD). The dietary addition of ω-3 polyunsaturated fatty acids (PUFAs) provides a promising therapy for children with NAFLD due to its convenience and safety; however, several studies suggested contradictory results for PUFA supplementation in children. Hence, we performed a systematic review and meta-analysis to evaluate the effectiveness of PUFA supplementation in children with NAFLD. METHODS: Published randomized controlled trials (RCTs) that evaluated the effectiveness of the dietary addition of PUFA in children with NAFLD were considered. The primary result was the alteration in hepatic steatosis grade on ultrasound after treatment. The secondary outcomes included alanine aminotransferase (ALT), aspartate aminotransferase (AST), C-reactive protein (CRP) and components of metabolic syndrome. Predefined sensitivity analysis was also performed to explore possible explanations for heterogeneity in the evaluations. RESULTS: In total, 4 studies with 263 subjects were identified. PUFA supplementation was associated with significantly improved hepatic steatosis grade on ultrasound (risk difference: 25%, 95% CI: 12-38%), without heterogeneity (P = 0.27, I2 = 24%). Sensitivity analysis confirmed the robustness of our findings. PUFA supplementation could decrease AST levels after 6 months, but could only reduce ALT levels after 12 months. PUFA did not have a significant effect on most components of metabolic syndrome and the CRP level. CONCLUSION: ω-3 PUFA supplementation can improve liver steatosis and liver functions, and it is a potential food supplementation to treat NAFLD in children.


Asunto(s)
Ácidos Grasos Omega-3/uso terapéutico , Enfermedad del Hígado Graso no Alcohólico/tratamiento farmacológico , Adolescente , Niño , Humanos , Ensayos Clínicos Controlados Aleatorios como Asunto , Resultado del Tratamiento
17.
Chem Commun (Camb) ; 53(38): 5283-5286, 2017 May 09.
Artículo en Inglés | MEDLINE | ID: mdl-28443872

RESUMEN

Three novel bis(Triol)-functionalized Anderson cluster derivatives (POM-L-POM, POM-L, L-POM-L) were efficiently synthesized, which manifest interesting self-assembly and synergistic effects. They provided strong support in synthons, applications in syntheses and properties for designing organic-inorganic hybrid chains.

18.
FEMS Microbiol Lett ; 350(2): 154-60, 2014 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-24236444

RESUMEN

The Per-ARNT-Sim (PAS) domain serine/threonine kinase PAS kinase is involved in energy flux and protein synthesis. In yeast, PSK1 and PSK2 are two partially redundant PASK homologs. We recently generated PSK2 deletion mutant and showed that Psk2 acts as a nutrient-sensing protein kinase to modulate Ultradian clock-coupled respiratory oscillation in yeast. Here, we show that deletion of PSK1 increased the sensitivity of yeast cells to oxidative stress (H2 O2 treatment) and partially inhibited cell growth; however, the growth of the PSK2-deleted mutant was similar to that of the wild type. Superoxide dismutase-1 (SOD1) mRNA and protein levels were lower in PSK1-deletion mutant than the wild type. The mRNA levels of stress response genes CTT1, HSP104, ATH1, NTH1 and SOD2 were similar in both the PSK1-deleted mutant and wild-type yeast. Furthermore, intracellular accumulation of reactive oxygen species (ROS) was noted in PSK1-deleted mutant. These results suggest that PSK1 induces SOD1 expression to protect against oxidative stress in yeast.


Asunto(s)
Regulación Fúngica de la Expresión Génica/genética , Estrés Oxidativo/genética , Proteínas Serina-Treonina Quinasas/genética , Proteínas de Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/genética , Superóxido Dismutasa/genética , Mutación/genética , Proteínas Serina-Treonina Quinasas/metabolismo , Especies Reactivas de Oxígeno/análisis , Especies Reactivas de Oxígeno/metabolismo , Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/fisiología , Proteínas de Saccharomyces cerevisiae/metabolismo , Superóxido Dismutasa/metabolismo , Superóxido Dismutasa-1
19.
J Hazard Mater ; 262: 64-70, 2013 Nov 15.
Artículo en Inglés | MEDLINE | ID: mdl-24012961

RESUMEN

This paper reports the fabrication of layered double hydroxide (LDH)/conductive polymer multilayer films by alternate assembly of exfoliated ZnAl-LDH nanosheets and polyaniline (PANI) on silicon wafer substrates using the layer-by-layer (LBL) deposition technology. UV-vis absorption spectroscopy indicates a stepwise and regular growth of the (LDH/PANI)n multilayer films upon increasing deposition cycles. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrate that the surfaces of the films are microscopy smooth and uniform with a thickness of 2 nm per bilayer. Furthermore, the resulting (LDH/PANI)n multilayer films possess high selectively response to ammonia at room temperature. The presence of LDH nanosheets plays a critical role on the gas sensing for the pure PANI film has very low response to ammonia. The LBL assembly process based on LDH combines the conducting polymer and nano-inorganic material, which provides opportunities to develop new inorganic-organic films for gas sensing.


Asunto(s)
Amoníaco/análisis , Compuestos de Anilina/química , Hidróxidos/química , Microscopía de Fuerza Atómica , Microscopía Electrónica de Rastreo , Espectrofotometría Ultravioleta , Difracción de Rayos X
20.
J Phys Chem B ; 115(37): 10877-91, 2011 Sep 22.
Artículo en Inglés | MEDLINE | ID: mdl-21809878

RESUMEN

Diurea cross-linked bridged silsesquioxanes (BSs) C(10)C(n)C(10) derived from organosilane precursors, including decylene chains as side spacers and alkylene chains with variable length as central spacers (EtO)(3)Si-(CH(2))(10)-Y-(CH(2))(n)-Y-(CH(2))(10)-Si(OEt)(3) (n = 7, 9-12; Y = urea group and Et = ethyl), have been synthesized through the combination of self-directed assembly and an acid-catalyzed sol-gel route involving the addition of dimethylsulfoxide (DMSO) and a large excess of water. This new family of hybrids has enabled us to conclude that the length of the side spacers plays a unique role in the structuring of alkylene-based BSs, although their morphology remains unaffected. All the samples adopt a lamellar structure. While the alkylene chains are totally disordered in the case of the C(10)C(7)C(10) sample, a variable proportion of all-trans and gauche conformers exists in the materials with longer central spacers. The highest degree of structuring occurs for n = 9. The inclusion of decylene instead of propylene chains as side spacers leads to the formation of a stronger hydrogen-bonded urea-urea array as evidenced by two dimensional correlation Fourier transform infrared spectroscopic analysis. The emission spectra and emission quantum yields of the C(10)C(n)C(10) materials are similar to those reported for diurea cross-linked alkylene-based BSs incorporating propylene chains as side spacers and prepared under different experimental conditions. The emission of the C(10)C(n)C(10) hybrids is ascribed to the overlap of two distinct components that occur within the urea cross-linkages and within the siliceous nanodomains. Time-resolved photoluminescence spectroscopy has provided evidence that the average distance between the siliceous domains and the urea cross-links is similar in the C(10)C(n)C(10) BSs and in oxyethylene-based hybrid analogues incorporating propylene chains as side spacers (diureasils), an indication that the longer side chains in the former materials adopt gauche conformations. It has also allowed us to demonstrate for the first time that the emission features of the urea-related component of the emission of alkylene-based BSs depend critically on the length of the side spacers.

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