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1.
Sci Rep ; 10(1): 5126, 2020 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-32198378

RESUMO

The present study evaluates the role of graphene oxide's (GO's) peroxidase-like and inherent/carbocatalytic properties in oxidising silver nitrate (AgNO3) to create graphene nanocomposites with silver nanoparticles (GO/Ag nanocomposite). Activation of peroxidase-like catalytic function of GO required hydrogen peroxide (H2O2) and ammonia (NH3) in pH 4.0 disodium hydrogen phosphate (Na2HPO4). Carbocatalytic abilities of GO were triggered in pH 4.0 deionised distilled water (ddH2O). Transmission electron microscope (TEM), scanning electron microscope (SEM), cyclic voltammetry (CV) and UV-Vis spectroscopy aided in qualitatively and quantitatively assessing GO/Ag nanocomposites. TEM and SEM analysis demonstrated the successful use of GO's peroxidase-like and carbocatalytic properties to produce GO/Ag nanocomposite. UV-Vis analysis indicated a higher yield in optical density values for GO/Ag nanocomposites created using GO's carbocatalytic ability rather than its peroxidase-like counterpart. Additionally, CV demonstrated that GO/Ag nanocomposite fabricated here is a product of an irreversible electrochemical reaction. Our study outcomes show new opportunities for GO as a standalone catalyst in biosensing. We demonstrate a sustainable approach to obtain graphene nanocomposites exclusive of harmful chemicals or physical methods.

3.
J Vis Exp ; (143)2019 01 10.
Artigo em Inglês | MEDLINE | ID: mdl-30688310

RESUMO

The work presents an experiment that allows the study of many fundamental physical processes, such as photon pressure, diffraction of light or the motion of charged particles in electrical fields. In this experiment, a focused laser beam pointing upwards levitate liquid droplets. The droplets are levitated by the photon pressure of the focused laser beam which balances the gravitational force. The diffraction pattern created when illuminated with laser light can help measure the size of a trapped droplet. The charge of the trapped droplet can be determined by studying its motion when a vertically directed electrical field is applied. There are several reasons motivating this experiment to be remotely controlled. The investments required for the setup exceeds the amount normally available in undergraduate teaching laboratories. The experiment requires a laser of Class 4, which is harmful to both skin and eyes and the experiment uses voltages that are harmful.


Assuntos
Laboratórios , Óptica e Fotônica/métodos , Eletricidade , Eletrodos , Lasers , Interface Usuário-Computador
4.
J Phys Chem Lett ; 9(21): 6179-6184, 2018 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-30380894

RESUMO

In nanofabrication, just as in any other craft, the scale of spatial details is limited by the dimensions of the tool at hand. For example, the smallest details of direct laser writing with far-field light are set by the diffraction limit, which is approximately half of the used wavelength. In this work, we overcome this universal assertion by optically forging graphene ripples that show features with dimensions unlimited by diffraction. Thin sheet elasticity simulations suggest that the scaled-down ripples originate from the interplay between substrate adhesion, in-plane strain, and circular symmetry. The optical forging technique thus offers an accurate way to modify and shape 2D materials and facilitates the creation of controllable nanostructures for plasmonics, resonators, and nano-optics.

5.
J Environ Manage ; 218: 402-415, 2018 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-29704835

RESUMO

Natural resource (NR) exploitation often gives rise to conflict. While most actors intend to manage collectively used places and their NRs sustainably, they may disagree about what this entails. This article accordingly explores the origin of NR conflicts by analysing them in terms of competing pathways to sustainability. By comparing conflicts over mine establishments in three places in northern Sweden, we specifically explore the role of place-based perceptions and experiences. The results indicate that the investigated conflicts go far beyond the question of metals and mines. The differences between pathways supporting mine establishment and those opposing it refer to fundamental ideas about human-nature relationships and sustainable development (SD). The study suggests that place-related parameters affect local interpretations of SD and mobilisation in ways that explain why resistance and conflict exist in some places but not others. A broader understanding of a particular conflict and its specific place-based trajectory may help uncover complex underlying reasons. However, our comparative analysis also demonstrates that mining conflicts in different places share certain characteristics. Consequently, a site-specific focus ought to be combined with attempts to compare, or map, conflicts at a larger scale to improve our understanding of when and how conflicts evolve. By addressing the underlying causes and origins of contestation, this study generates knowledge needed to address NR management conflicts effectively and legitimately.


Assuntos
Conservação dos Recursos Naturais , Mineração , Humanos , Suécia
6.
Nano Lett ; 17(10): 6469-6474, 2017 10 11.
Artigo em Inglês | MEDLINE | ID: mdl-28926715

RESUMO

Atomically thin materials, such as graphene, are the ultimate building blocks for nanoscale devices. But although their synthesis and handling today are routine, all efforts thus far have been restricted to flat natural geometries, since the means to control their three-dimensional (3D) morphology has remained elusive. Here we show that, just as a blacksmith uses a hammer to forge a metal sheet into 3D shapes, a pulsed laser beam can forge a graphene sheet into controlled 3D shapes in the nanoscale. The forging mechanism is based on laser-induced local expansion of graphene, as confirmed by computer simulations using thin sheet elasticity theory.

7.
Anticancer Res ; 37(4): 1825-1830, 2017 04.
Artigo em Inglês | MEDLINE | ID: mdl-28373447

RESUMO

AIM: To quantify the impact of decreased margins for two treatment techniques, three-dimensional conformal radiotherapy (3D-CRT) and volumetric-modulated arc therapy (VMAT), on local control in curative treatment of prostate cancer. MATERIALS AND METHODS: The planning target volume (PTV) margins were decreased in steps of 1 mm from 10 to 1 mm. Treatment plans using 3D-CRT and VMAT technique were produced for all margin sizes and the dose to the neuro vascular bundles (NVB), that was not included in the PTV, was investigated. RESULTS: Due to the more conformal dose delivery using VMAT, the dose to the NVB decreased more rapidly by VMAT compared to the 3D-CRT plans. The dose difference was significant for margins from 1-7 mm. CONCLUSION: One should be very cautious before clinical routines are changed, bearing in mind whether the change means more conformal treatment technique, smaller margins or target segmentation in different imaging modalities.


Assuntos
Adenocarcinoma/radioterapia , Recidiva Local de Neoplasia/diagnóstico , Neovascularização Patológica/etiologia , Neoplasias da Próstata/radioterapia , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia Conformacional/efeitos adversos , Radioterapia de Intensidade Modulada/efeitos adversos , Adenocarcinoma/patologia , Humanos , Masculino , Gradação de Tumores , Recidiva Local de Neoplasia/etiologia , Prognóstico , Neoplasias da Próstata/patologia , Dosagem Radioterapêutica
8.
Phys Chem Chem Phys ; 17(1): 209-16, 2015 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-25381806

RESUMO

Photo-oxidation of individual, air-suspended single walled carbon nanotubes (SWCNTs) is studied by femtosecond laser spectroscopy and imaging. Individual SWCNTs are imaged by four wave mixing (FWM) microscopy under an inert gas (Ar or N2) atmosphere. When imaging is performed in an ambient air atmosphere, the decay of the FWM signal takes place. Electron microscopy shows that SWCNTs are not destroyed and the process is attributed to photoinduced oxidation reactions which proceed via a non-linear excitation mechanism, when irradiation is performed with ∼30 fs pulses in the visible spectral region (500-600 nm). Photo-oxidation can be localized in specific regions of SWCNTs within optical resolution (∼300 nm). The effect of photo-oxidation on Raman spectra was studied by irradiating a local spot on an individual SWCNT and comparing the spectra of irradiated and non-irradiated regions of the same tube. It is shown at an individual nanotube level that oxidation leads to a decrease of the intensity of the Raman signal and an upshift of the G-band.

9.
Nanoscale ; 7(7): 2851-5, 2015 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-25492105

RESUMO

We demonstrate a simple all-optical patterning method for graphene, based on laser induced two-photon oxidation. By tuning the intensity and dose of irradiation, the level of oxidation is controlled, the band gap is introduced and electrical and optical properties are continuously tuned. Complex patterning is performed for air-suspended monolayer graphene and for graphene on substrates. The presented concept allows development of all-graphene electronic and optoelectronic devices with an all-optical method.

10.
Gut Pathog ; 5(1): 42, 2013 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-24350840

RESUMO

BACKGROUND: Widely considered probiotic organisms, Bifidobacteria are common inhabitants of the alimentary tract of animals including insects. Bifidobacteria identified from the honey bee are found in larval guts and throughout the alimentary tract, but attain their greatest abundance in the adult hind gut. To further understand the role of Bifidobacteria in honey bees, we sequenced two strains of Bifidobacterium cultured from different alimentary tract environments and life stages. RESULTS: Reflecting an oxygen-rich niche, both strains possessed catalase, peroxidase, superoxide-dismutase and respiratory chain enzymes indicative of oxidative metabolism. The strains show markedly different carbohydrate processing capabilities, with one possessing auxiliary and key enzymes of the Entner-Doudoroff pathway. CONCLUSIONS: As a result of long term co-evolution, honey bee associated Bifidobacterium may harbor considerable strain diversity reflecting adaptation to a variety of different honey bee microenvironments and hive-mediated vertical transmission between generations.

11.
J Mol Biol ; 425(22): 4323-33, 2013 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-23816837

RESUMO

Guanine monophosphate (GMP) synthetase is a bifunctional two-domain enzyme. The N-terminal glutaminase domain generates ammonia from glutamine and the C-terminal synthetase domain aminates xanthine monophosphate (XMP) to form GMP. Mammalian GMP synthetases (GMPSs) contain a 130-residue-long insert in the synthetase domain in comparison to bacterial proteins. We report here the structure of a eukaryotic GMPS. Substrate XMP was bound in the crystal structure of the human GMPS enzyme. XMP is bound to the synthetase domain and covered by a LID motif. The enzyme forms a dimer in the crystal structure with subunit orientations entirely different from the bacterial counterparts. The inserted sub-domain is shown to be involved in substrate binding and dimerization. Furthermore, the structural basis for XMP recognition is revealed as well as a potential allosteric site. Enzymes in the nucleotide metabolism typically display an increased activity in proliferating cells due to the increased need for nucleotides. Many drugs used as immunosuppressants and for treatment of cancer and viral diseases are indeed nucleobase- and nucleoside-based compounds, which are acting on or are activated by enzymes in this pathway. The information obtained from the crystal structure of human GMPS might therefore aid in understanding interactions of nucleoside-based drugs with GMPS and in structure-based design of GMPS-specific inhibitors.


Assuntos
Carbono-Nitrogênio Ligases/química , Carbono-Nitrogênio Ligases/metabolismo , Multimerização Proteica , Sequência de Aminoácidos , Escherichia coli/química , Escherichia coli/enzimologia , Humanos , Cinética , Modelos Moleculares , Dados de Sequência Molecular , Ligação Proteica , Conformação Proteica , Domínios e Motivos de Interação entre Proteínas , Alinhamento de Sequência , Especificidade por Substrato
12.
J Chem Inf Model ; 51(2): 267-82, 2011 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-21309544

RESUMO

Molecular docking plays an important role in drug discovery as a tool for the structure-based design of small organic ligands for macromolecules. Possible applications of docking are identification of the bioactive conformation of a protein-ligand complex and the ranking of different ligands with respect to their strength of binding to a particular target. We have investigated the effect of implicit water on the postprocessing of binding poses generated by molecular docking using MM-PB/GB-SA (molecular mechanics Poisson-Boltzmann and generalized Born surface area) methodology. The investigation was divided into three parts: geometry optimization, pose selection, and estimation of the relative binding energies of docked protein-ligand complexes. Appropriate geometry optimization afforded more accurate binding poses for 20% of the complexes investigated. The time required for this step was greatly reduced by minimizing the energy of the binding site using GB solvation models rather than minimizing the entire complex using the PB model. By optimizing the geometries of docking poses using the GB(HCT+SA) model then calculating their free energies of binding using the PB implicit solvent model, binding poses similar to those observed in crystal structures were obtained. Rescoring of these poses according to their calculated binding energies resulted in improved correlations with experimental binding data. These correlations could be further improved by applying the postprocessing to several of the most highly ranked poses rather than focusing exclusively on the top-scored pose. The postprocessing protocol was successfully applied to the analysis of a set of Factor Xa inhibitors and a set of glycopeptide ligands for the class II major histocompatibility complex (MHC) A(q) protein. These results indicate that the protocol for the postprocessing of docked protein-ligand complexes developed in this paper may be generally useful for structure-based design in drug discovery.


Assuntos
Modelos Moleculares , Proteínas/metabolismo , Solventes/química , Cristalografia por Raios X , Entropia , Fator Xa/metabolismo , Inibidores do Fator Xa , Glicoproteínas/química , Glicoproteínas/metabolismo , Antígenos HLA/metabolismo , Ligantes , Peptidomiméticos/metabolismo , Ligação Proteica , Proteínas/química
13.
FEBS J ; 277(23): 4920-30, 2010 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-21054786

RESUMO

Human hypoxanthine-guanine phosphoribosyltransferase (HPRT) (EC 2.4.2.8) catalyzes the conversion of hypoxanthine and guanine to their respective nucleoside monophosphates. Human HPRT deficiency as a result of genetic mutations is linked to both Lesch-Nyhan disease and gout. In the present study, we have characterized phosphoribosyltransferase domain containing protein 1 (PRTFDC1), a human HPRT homolog of unknown function. The PRTFDC1 structure has been determined at 1.7 Å resolution with bound GMP. The overall structure and GMP binding mode are very similar to that observed for HPRT. Using a thermal-melt assay, a nucleotide metabolome library was screened against PRTFDC1 and revealed that hypoxanthine and guanine specifically interacted with the enzyme. It was subsequently confirmed that PRTFDC1 could convert these two bases into their corresponding nucleoside monophosphate. However, the catalytic efficiency (k(cat)/K(m)) of PRTFDC1 towards hypoxanthine and guanine was only 0.26% and 0.09%, respectively, of that of HPRT. This low activity could be explained by the fact that PRTFDC1 has a Gly in the position of the proposed catalytic Asp of HPRT. In PRTFDC1, a water molecule at the position of the aspartic acid side chain position in HPRT might be responsible for the low activity observed by acting as a weak base. The data obtained in the present study indicate that PRTFDC1 does not have a direct catalytic role in the nucleotide salvage pathway.


Assuntos
Hipoxantina Fosforribosiltransferase/química , Hipoxantina Fosforribosiltransferase/metabolismo , Sequência de Aminoácidos , Clonagem Molecular , Cristalografia por Raios X , Guanina/metabolismo , Guanosina Monofosfato/metabolismo , Humanos , Hipoxantina/metabolismo , Hipoxantina Fosforribosiltransferase/genética , Técnicas In Vitro , Cinética , Metaboloma , Modelos Moleculares , Dados de Sequência Molecular , Conformação Proteica , Estrutura Quaternária de Proteína , Estrutura Terciária de Proteína , Homologia de Sequência de Aminoácidos , Homologia Estrutural de Proteína , Especificidade por Substrato
14.
ACS Nano ; 4(11): 6780-6, 2010 Nov 23.
Artigo em Inglês | MEDLINE | ID: mdl-20939509

RESUMO

Femtosecond four-wave-mixing (FWM) experiments of individual suspended semiconducting single-walled carbon nanotubes (SWCNTs) are presented. The chiral indices of the tubes were determined by electron diffraction as (28,14) and (24,14) having diameters of 2.90 and 2.61 nm, respectively. The diameter and semiconducting character of the tubes were additionally confirmed by resonance Raman measurements. The FWM signal showed electronic response from the SWCNTs. The results demonstrate that ultrafast dynamics of individual SWCNTs can be studied by FWM spectroscopies.

15.
ACS Nano ; 4(6): 3356-62, 2010 Jun 22.
Artigo em Inglês | MEDLINE | ID: mdl-20524681

RESUMO

We demonstrate controllable and gate-tunable negative differential resistance in carbon nanotube field-effect transistors, at room temperature and at 4.2 K. This is achieved by effectively creating quantum dots along the carbon nanotube channel by patterning the underlying, high-kappa gate oxide. The negative differential resistance feature can be modulated by both the gate and the drain-source voltage, which leads to more than 20% change of the current peak-to-valley ratio. Our approach is fully scalable and opens up a possibility for a new class of nanoscale electronic devices using negative differential resistance in their operation.


Assuntos
Nanoestruturas/química , Nanoestruturas/ultraestrutura , Nanotecnologia/instrumentação , Transistores Eletrônicos , Cristalização/métodos , Impedância Elétrica , Desenho de Equipamento , Análise de Falha de Equipamento , Substâncias Macromoleculares/química , Teste de Materiais , Conformação Molecular , Óxidos/química , Tamanho da Partícula , Propriedades de Superfície
16.
J Med Chem ; 52(9): 3108-11, 2009 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-19354255

RESUMO

Poly(ADP-ribose) polymerases (PARPs) activate DNA repair mechanisms upon stress- and cytotoxin-induced DNA damage, and inhibition of PARP activity is a lead in cancer drug therapy. We present a structural and functional analysis of the PARP domain of human PARP-3 in complex with several inhibitors. Of these, KU0058948 is the strongest inhibitor of PARP-3 activity. The presented crystal structures highlight key features for potent inhibitor binding and suggest routes for creating isoenzyme-specific PARP inhibitors.


Assuntos
Inibidores Enzimáticos/química , Inibidores Enzimáticos/farmacologia , Inibidores de Poli(ADP-Ribose) Polimerases , Poli(ADP-Ribose) Polimerases/química , Biocatálise/efeitos dos fármacos , Cristalografia por Raios X , Inibidores Enzimáticos/metabolismo , Humanos , Modelos Moleculares , Poli(ADP-Ribose) Polimerases/metabolismo , Conformação Proteica , Especificidade por Substrato
17.
Nano Lett ; 9(2): 643-7, 2009 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-19152310

RESUMO

We demonstrate 100 ns write/erase speed of single-walled carbon nanotube field-effect transistor (SWCNT-FET) memory elements. With this high operation speed, SWCNT-FET memory elements can compete with state of the art commercial Flash memories in this figure of merit. The endurance of the memory elements is shown to exceed 104 cycles. The SWCNT-FETs have atomic layer deposited hafnium oxide as a gate dielectric, and the devices are passivated by another hafnium oxide layer in order to reduce surface chemistry effects. We discuss a model where the hafnium oxide has defect states situated above, but close in energy to, the band gap of the SWCNT. The fast and efficient charging and discharging of these defects is a likely explanation for the observed operation speed of 100 ns which greatly exceeds the SWCNT-FET memory speeds of 10 ms observed earlier for devices with conventional gate oxides.

18.
Peptides ; 29(9): 1588-95, 2008 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-18550224

RESUMO

Our understanding of the central regulation of food intake and body weight has increased tremendously through implication of a high number of neuropeptides. However, lack of all-embracing studies have made comparison difficult in the past. The objective of this study was to demonstrate the relative importance of the different neuropeptides in terms of involvement in appetite regulatory mechanisms. We quantified expression levels of 21 hypothalamic neuropeptides and circulating levels of leptin, insulin, corticosterone, adrenocorticotropic hormone, ghrelin and adiponectin in rats after acute food deprivation and chronic food restriction using validated quantitative real-time PCR and hormone measurements. Body weight, insulin and leptin were reduced whereas corticosterone was increased by both acute food deprivation and chronic food restriction. Our results confirmed the relative importance in body weight homeostasis of neuropeptide Y and proopiomelanocortin, which were increased and decreased as predicted. The expression of other neuropeptides previously attributed central roles in body weight homeostasis, e.g. melanin-concentrating hormone and orexin, appeared to be less affected by the treatments. Moreover, the expression of dynorphin, galanin-like peptide and neuropeptide B was dramatically reduced after both treatments. This suggests that the latter neuropeptides--although previously known to be involved in body weight homeostasis--may be of unexpected importance in states of negative energy balance.


Assuntos
Ingestão de Energia/fisiologia , Privação de Alimentos/fisiologia , Hormônios/sangue , Hipotálamo/metabolismo , Neuropeptídeos/biossíntese , Animais , Glicemia/metabolismo , Dinorfinas/sangue , Peptídeo Semelhante a Galanina/sangue , Masculino , Neuropeptídeos/sangue , Ratos , Ratos Sprague-Dawley
19.
J Mol Biol ; 379(1): 136-45, 2008 May 23.
Artigo em Inglês | MEDLINE | ID: mdl-18436240

RESUMO

Tankyrases are recently discovered proteins implicated in many important functions in the cell including telomere homeostasis and mitosis. Tankyrase modulates the activity of target proteins through poly(ADP-ribosyl)ation, and here we report the structure of the catalytic poly(ADP-ribose) polymerase (PARP) domain of human tankyrase 1. This is the first structure of a PARP domain from the tankyrase subfamily. The present structure reveals that tankyrases contain a short zinc-binding motif, which has not been predicted. Tankyrase activity contributes to telomere elongation observed in various cancer cells and tankyrase inhibition has been suggested as a potential route for cancer therapy. In comparison with other PARPs, significant structural differences are observed in the regions lining the substrate-binding site of tankyrase 1. These findings will be of great value to facilitate structure-based design of selective PARP inhibitors, in general, and tankyrase inhibitors, in particular.


Assuntos
Domínio Catalítico , Tanquirases/química , Zinco/química , Motivos de Aminoácidos , Sequência de Aminoácidos , Sítios de Ligação , Desenho de Fármacos , Inibidores Enzimáticos/química , Humanos , Dados de Sequência Molecular , Estrutura Molecular
20.
Artigo em Inglês | MEDLINE | ID: mdl-18051061

RESUMO

This paper presents a novel method for phase unwrapping for phase sensitive reconstruction in MR imaging. The unwrapped phase is obtained by integrating the phase gradient by solving a Poisson equation. An efficient solver, which has been made publicly available, is used to solve the equation. The proposed method is demonstrated on a fat quantification MRI task that is a part of a prospective study of fat accumulation. The method is compared to a phase unwrapping method based on region growing. Results indicate that the proposed method provides more robust unwrapping. Unlike region growing methods, the proposed method is also straight-forward to implement in 3D.


Assuntos
Tecido Adiposo/anatomia & histologia , Artefatos , Água Corporal , Aumento da Imagem/métodos , Interpretação de Imagem Assistida por Computador/métodos , Técnica de Subtração , Imagem Corporal Total/métodos , Adulto , Algoritmos , Feminino , Humanos , Masculino , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
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