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1.
Nat Commun ; 10(1): 5401, 2019 12 16.
Artigo em Inglês | MEDLINE | ID: mdl-31844043

RESUMO

Coupling of atoms is the basis of chemistry, yielding the beauty and richness of molecules. We utilize semiconductor nanocrystals as artificial atoms to form nanocrystal molecules that are structurally and electronically coupled. CdSe/CdS core/shell nanocrystals are linked to form dimers which are then fused via constrained oriented attachment. The possible nanocrystal facets in which such fusion takes place are analyzed with atomic resolution revealing the distribution of possible crystal fusion scenarios. Coherent coupling and wave-function hybridization are manifested by a redshift of the band gap, in agreement with quantum mechanical simulations. Single nanoparticle spectroscopy unravels the attributes of coupled nanocrystal dimers related to the unique combination of quantum mechanical tunneling and energy transfer mechanisms. This sets the stage for nanocrystal chemistry to yield a diverse selection of coupled nanocrystal molecules constructed from controlled core/shell nanocrystal building blocks. These are of direct relevance for numerous applications in displays, sensing, biological tagging and emerging quantum technologies.

2.
Nat Commun ; 10(1): 2, 2019 01 02.
Artigo em Inglês | MEDLINE | ID: mdl-30602734

RESUMO

Semiconductor heterostructure nanocrystals, especially with core/shell architectures, are important for numerous applications. Here we show that by decreasing the shell growth rate the morphology of ZnS shells on ZnSe quantum rods can be tuned from flat to islands-like, which decreases the interfacial strain energy. Further reduced growth speed, approaching the thermodynamic limit, leads to coherent shell growth forming unique helical-shell morphology. This reveals a template-free mechanism for induced chirality at the nanoscale. The helical morphology minimizes the sum of the strain and surface energy and maintains band gap emission due to its coherent core/shell interface without traps, unlike the other morphologies. Reaching the thermodynamic controlled growth regime for colloidal semiconductor core/shell nanocrystals thus offers morphologies with clear impact on their applicative potential.

3.
J Phys Chem A ; 118(17): 3061-7, 2014 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-24708153

RESUMO

There is continuing interest in determining essential structural features of polymer gels, which display photoelectric and/or thermoelectric behavior. One such gel is the blend, poly(4-vinylpyridine-co-butyl methacrylate)/poly(4-vinylpyridine), dissolved in liquid pyridine. Following extended aeration of a three-component mixture, which serves as a model for the gel side chain interactions, crystallization of a new molecule, 4-isopropylpyridine hydroxide (IPPOH), occurs. X-ray diffraction, DFT modeling, and spectroscopy were used to determine the structural, electronic, and luminescent properties of the crystal. The crystal structure reveals molecules forming head-to-tail, hydrogen-bonded chains without base stacking or marked interchain interaction. The molecular chains are characterized by moderately long-lived, blue-violet luminescence excited in the near-UV. Because these photoluminescent properties resemble those of the gel from which the crystals are derived, we may posit similar structural features in the gel for which direct structural analysis is not available.

4.
Nat Mater ; 13(3): 301-7, 2014 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-24553656

RESUMO

Colloidal nanocrystal synthesis provides a powerful approach for creating unique nanostructures of relevance for applications. Here, we report that wurtzite ZnSe nanorod couples connected by twinning structures can be synthesized by means of a self-limited assembly process. Unlike for individual nanorods, the band-edge states calculated for the nanorod couples are predominantly confined to the short edges of the structure and this leads to low photoluminescence polarization anisotropy, as confirmed by single-particle fluorescence. Through a cation-exchange approach, the composition of nanorod couples can be readily expanded to additional materials, such as CdSe and PbSe. We anticipate that this family of nanorod-couple structures with distinct compositions and controlled properties will constitute an ideal system for the investigation of electronic coupling effects between individual nanorod components on the nanoscale, with relevance to applications in optics, photocatalysis and optoelectronic devices.

5.
Nat Commun ; 5: 2994, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-24389630

RESUMO

The welding and sintering of nanomaterials is relevant, for example, to form electrical contacts between metallic particles in printed electronic devices. Usually the welding of nanoparticles is achieved at high temperatures. Here we find that merging of two different metals, silver and gold nanoparticles, occurs on contact at room temperature. The merging process was investigated by experimental and molecular dynamics simulations. We discovered that the merging of these particles is driven by selective wettability of silver nanoparticles, independent of their size and shape (spheres or rods); silver behaves as a soft matter, whereas gold as a hard surface being wetted and retaining its original morphology. During that process, the silver atoms move towards the surface of the Au nanoparticles and wrap the Au nanoparticles in a pulling up-like process, leading to the wetting of Au nanoparticles.

6.
Urology ; 80(5): 980-5, 2012 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-22990052

RESUMO

OBJECTIVE: To evaluate the importance of stone composition and crystallite size in the formation of ultimate stone burden. Crystallite is the smallest building block, which is unique in size and architecture for each type of stone component. Currently, the knowledge about the clinical importance of crystallite size is very limited. METHODS: The results of quantitative X-ray diffraction phase analysis performed on 286 kidney stones extracted during endourological surgery or expelled spontaneously were retrospectively analyzed. Stone composition and crystallite size were determined and were compared to the burden occupying the pelvicalyceal system. RESULTS: A total of 286 renal stones were analyzed. Stones were low burden and high burden in 242 and 44 of cases, respectively. We observed statistically significant association of phosphates and urates with high-burden stones in contrast to oxalates, which formed mainly low-burden stones. Crystallite sizes were available for 179 stones. Large-sized crystallites of calcium oxalate monohydrate and hydroxyl apatite formed low-burden stones, whereas small-sized crystallites formed staghorn stones. Struvite and urates had a uniform average size of crystallites. CONCLUSION: Oxalate stones have statistically significant association with smaller stones, whereas high-burden calculi are significantly associated with urates and phosphates, especially the struvite type. The smaller the crystallite size is to start with, the larger will be the ultimate stone burden. This rule is followed by calcium oxalate monohydrate and Apatite minerals.


Assuntos
Cálculos Renais/diagnóstico por imagem , Difração de Raios X/métodos , Apatitas/análise , Oxalato de Cálcio/análise , Cristalografia por Raios X , Humanos , Cálculos Renais/química , Fosfatos/análise , Radiografia , Estudos Retrospectivos , Índice de Gravidade de Doença
7.
J Phys Condens Matter ; 24(16): 164203, 2012 Apr 25.
Artigo em Inglês | MEDLINE | ID: mdl-22465965

RESUMO

Verification by imaging of the structure of 3D DNA constructs, both bare and conjugated to metal nanoparticles, is challenging. We demonstrate here two transmission electron microscopy (TEM) based methods to distinguish between fully formed tetrahedra, synthesized from DNA conjugated with gold nanoparticles (GNPs) at their vertices, and structures which are only partially formed. When deposited on a surface, fully formed tetrahedra are expected to retain their 3D pyramidal structure, while partially formed structures are expected to form a 2D structure. The first method by which 3D and 2D structures were distinguished was imaging them at different defocusing values. While for 2D structures all the four GNPs acquire Fresnel fringes at the same defocusing value, for 3D structures at least one particle is at a different plane with respect to the others, and so it acquires Fresnel fringes at a different defocusing value. The second method we show is imaging of the structures at different angles. While a single TEM image gives only a 2D projection of the structure, by combining information achieved from imaging at several tilting angles one may verify the structural construct.


Assuntos
DNA/química , Ouro/química , Imageamento Tridimensional/métodos , Nanopartículas Metálicas/química , Sequência de Bases , DNA/genética , Modelos Moleculares , Conformação Molecular , Dados de Sequência Molecular
8.
Environ Geochem Health ; 33(6): 613-22, 2011 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-21308400

RESUMO

Urinary calculi have been recognized as one of the most painful medical disorders. Tenable knowledge of the phase composition of the stones is very important to elucidate an underlying etiology of the stone disease. We report here the results of quantitative X-ray diffraction phase analysis performed on 278 kidney stones from the 275 patients treated at the Department of Urology of Hadassah Hebrew University Hospital (Jerusalem, Israel). Quantification of biominerals in multicomponent samples was performed using the normalized reference intensity ratio method. According to the observed phase compositions, all the tested stones were classified into five chemical groups: oxalates (43.2%), phosphates (7.7%), urates (10.3%), cystines (2.9%), and stones composed of a mixture of different minerals (35.9%). A detailed analysis of each allocated chemical group is presented along with the crystallite size calculations for all the observed crystalline phases. The obtained results have been compared with the published data originated from different geographical regions. Morphology and spatial distribution of the phases identified in the kidney stones were studied with scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). This type of detailed study of phase composition and structural characteristics of the kidney stones was performed in Israel for the first time.


Assuntos
Cálculos Renais/química , Cálculos Renais/diagnóstico por imagem , Minerais/análise , Humanos , Israel , Cálculos Renais/patologia , Microscopia Eletrônica de Varredura , Minerais/química , Radiografia , Espectrometria por Raios X , Difração de Raios X
9.
Nat Mater ; 9(10): 810-5, 2010 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-20852616

RESUMO

Cage structures exhibit inherent high symmetry and beauty, and both naturally occurring and synthetic molecular-scale cages have been discovered. Their characteristic high surface area and voids have led to their use as catalysts and catalyst supports, filtration media and gas storage materials. Nanometre-scale cage structures have also been synthesized, notably noble-metal cube-shaped cages prepared by galvanic displacement with promising applications in drug delivery and catalysis. Further functionality for nanostructures in general is provided by the concept of hybrid nanoparticles combining two disparate materials on the same system to achieve synergistic properties stemming from unusual material combinations. We report the integration of the two powerful concepts of cages and hybrid nanoparticles. A previously unknown edge growth mechanism has led to a new type of cage-structured hybrid metal-semiconductor nanoparticle; a ruthenium cage was grown selectively on the edges of a faceted copper(I) sulphide nanocrystal, contrary to the more commonly observed facet and island growth modes of other hybrids. The cage motif was extended by exploiting the open frame to achieve empty cages and cages containing other semiconductors. Such previously unknown nano-inorganic cage structures with variable cores and metal frames manifest new chemical, optical and electronic properties and demonstrate possibilities for uses in electrocatalysis.

10.
J Am Chem Soc ; 131(47): 17406-11, 2009 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-19894717

RESUMO

Gold growth on CdS nanorods and on seeded CdSe/CdS nanorods with and without illumination at different temperatures was studied. Two competing mechanisms were identified: thermal and light-induced growth. The thermal mechanism leads to growth of small gold particles at defects along the rod body and can be suppressed at lower temperatures. This control is attributed to a phase transition of the alkyl chains of the surface amine ligands to a static phase at lower temperatures, blocking the Au precursor's access to the nanorod surfaces. While a long-chain (C18) amine shows effective blocking at 293 K, a shorter chain (C12) amine shows the same result only at 273 K; however, in the case of a bulky trialkylamine, defect growth was observed even at 273 K. Light-induced growth leads to selective deposition of gold on one end of the rods. The tip was shown to grow on sulfur-rich facets of the nanorod, producing end-on and angled tip orientations. Growth under illumination with decreased temperature provides a highly selective synthesis of hybrid semiconductor nanorods with a single gold tip. Such anisotropic semiconductor-metal hybrids are of interest for self-assembly and photocatalysis and as building blocks in optoelectronic devices.

11.
Langmuir ; 25(4): 2501-3, 2009 Feb 17.
Artigo em Inglês | MEDLINE | ID: mdl-19166274

RESUMO

It was found that during the evaporation of water from a droplet of a silver nanoparticles dispersion a self-assembly process leads to the coalescence of the nanoparticles at room temperature and eventually results in a 3D, micrometer-sized dendrite. Direct in situ HR-TEM observation of coalescence events of individual nanoparticles revealed that during this process a transformation of the nanoparticles' crystal structure takes place, from the common fcc silver structure to the unusual hcp structure. It was found that even-though a majority of the nanoparticles in the dispersion have the fcc structure the obtained dendrites are characterized by the hcp structure, reflecting the crystal structure transformation due to the coalescence process.

13.
Langmuir ; 24(3): 722-33, 2008 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-18163657

RESUMO

Crystallization of carbamazepine (CBZ), an antiepileptic drug, precipitated from confined spaces of nonionic microemulsions was investigated. The study was aimed to correlate the structure of the microemulsion [water-in-oil (W/O), bicontinuous, and oil-in-water (O/W)] with the crystalline structure and morphology of solid CBZ. The precipitated CBZ was studied by DSC, TGA, powder XRD, single-crystal XRD, SEM, and optical microscopy. The results suggest that the microstructure of the microemulsions influences the crystallization process and allows crystallizing polymorphs that exhibit different crystal structure and habits. W/O nanodroplets orient the crystallizing CBZ molecules to form a prismlike anhydrous polymorphic form with monoclinic unit cell and P21/n space group. Bicontinuous structures lead to platelike dihydrate crystals with orthorhombic unit cell and Cmca space group. The O/W nanodroplets cause the formation of needlelike dihydrate crystals with monoclinic unit cell and P21/c space group. The morphological features of solid CBZ remain predetermined by the basic symmetry and parameters of its unit cell. Precipitation of CBZ pseudopolymorphs from supersaturated microemulsion is discussed in terms of oriented attachment that provides perfect packing of numerous separately nucleated ordered nuclei of CBZ into microscale platelets and then into macroscopic crystals. Crystallization from microemulsion media enabling one to obtain the drug (CBZ) with predicted structure and morphology should be of great significance for pharmaceutical applications.


Assuntos
Carbamazepina/química , Anticonvulsivantes/química , Anticonvulsivantes/isolamento & purificação , Varredura Diferencial de Calorimetria , Carbamazepina/isolamento & purificação , Cristalização , Cristalografia por Raios X , Emulsões , Luz , Microscopia Eletrônica de Varredura , Modelos Moleculares , Difração de Pó , Espalhamento de Radiação , Termodinâmica
14.
J Pharm Biomed Anal ; 46(4): 676-82, 2008 Mar 13.
Artigo em Inglês | MEDLINE | ID: mdl-18191358

RESUMO

Clopidogrel bisulphate (CLP) is a pharmaceutical compound with a novel mechanism of action for the reduction of atherosclerotic events. Only two crystalline forms (CLP I and CLP II) among the six known polymorphs of CLP have therapeutic activity. The structure of the CLP I polymorph is unknown and the structure of the CLP II polymorph is known only partially. Two techniques of X-ray diffraction quantitative phase analysis have been developed in this work for the quantification of CLP I and CLP II in their mixtures. The first technique is based on use of the whole powder pattern decomposition method (WPDM). WPDM was realized through Powder Cell for Windows v.2.4 (PCW) freeware. The second technique is based on the classical direct method. Metrological characterization and comparison of methods have been performed on the mixtures with known phase composition as well as on the real samples with varying phase content. Quantitative phase analyses of 120 specimens containing mixtures of forms I and II of CLP were performed using both developed techniques. Absolute and relative errors and reproducibility of both methods were found to be very similar. The statistical analysis of obtained results revealed that the WPDM gives higher accuracy. We found that the limit of quantification using both methods is 1.0-1.5wt.% of phase content in the mix.


Assuntos
Ticlopidina/análogos & derivados , Difração de Raios X/métodos , Clopidogrel , Ticlopidina/química
15.
J Phys Chem B ; 110(50): 25421-9, 2006 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-17165989

RESUMO

We explore the growth mechanism of gold nanocrystals onto preformed cadmium sulfide nanorods to form hybrid metal nanocrystal/semiconductor nanorod colloids. By manipulating the growth conditions, it is possible to obtain nanostructures exhibiting Au nanocrystal growth at only one nanorod tip, at both tips, or at multiple locations along the nanorod surface. Under anaerobic conditions, Au growth occurs only at one tip of the nanorods, producing asymmetric structures. In contrast, the presence of oxygen and trace amounts of water during the reaction promotes etching of the nanorod surface, providing additional sites for metal deposition. Three growth stages are observed when Au growth is performed under air: (1) Au nanocrystal formation at both nanorod tips, (2) growth onto defect sites on the nanorod surface, and finally (3) a ripening process in which one nanocrystal tip grows at the expense of the other particles present on the nanorod. Analysis of the hybrid nanostructures by high-resolution TEM shows that there is no preferred orientation between the Au nanocrystal and the CdS nanorod, indicating that growth is nonepitaxial. The optical signatures of the nanocrystals and the nanorods (i.e., the surface plasmon and first exciton transition peaks, respectively) are spectrally distinct, allowing the different stages of the growth process to be easily monitored. The initial CdS nanorods exhibit band gap and trap state emission, both of which are quenched during Au growth.


Assuntos
Compostos de Cádmio/química , Coloides/síntese química , Ouro/química , Nanoestruturas/química , Sulfetos/química , Ar , Compostos de Cádmio/síntese química , Coloides/química , Microscopia Eletrônica de Transmissão , Nanotubos/química , Óptica e Fotônica , Tamanho da Partícula , Sensibilidade e Especificidade , Sulfetos/síntese química , Propriedades de Superfície , Difração de Raios X
16.
Angew Chem Int Ed Engl ; 45(47): 8001-5, 2006 Dec 04.
Artigo em Inglês | MEDLINE | ID: mdl-17080480
17.
J Am Chem Soc ; 128(1): 257-64, 2006 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-16390155

RESUMO

A complex InAs/CdSe/ZnSe core/shell1/shell2 (CSS) structure is synthesized, where the intermediate CdSe buffer layer decreases strain between the InAs core and the ZnSe outer shell. This structure leads to significantly improved fluorescence quantum yield as compared to previously prepared core/shell structures and enables growth of much thicker shells. The shell growth is done using a layer-by-layer method in which the shell cation and anion precursors are added sequentially allowing for excellent control, and a good size distribution is maintained throughout the entire growth process. The CSS structure is characterized using transmission electron microscopy, as well as by X-ray diffraction and X-ray photoelectron spectroscopy which provide evidence for shell growth. The quantum yield for CSS with small InAs cores reaches over 70%-exceptional photoluminescence intensity for III-V semiconductor nanocrystals. In larger InAs cores there is a systematic decrease in the quantum yield, with a yield of approximately 40% for intermediate size cores down to a few percent in large cores. The CSS structures also exhibit very good photostability, vastly improved over those of organically coated cores, and transformation into water environment via ligand exchange is performed without significant decrease of the quantum yield. These new InAs/CdSe/ZnSe CSS nanocrystals are therefore promising near-IR chromophores for biological fluorescence tagging and optoelectronic devices.

18.
Langmuir ; 21(13): 5659-62, 2005 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-15952803

RESUMO

The NAD(P)H-mediated growth of Au nanoparticles (NPs) in the presence of ascorbic acid, AuCl4-, and cetyltrimethylammonium bromide leads to the formation of shaped NP structures consisting of dipods, tripods, and tetrapods. The shaped particles exhibit a red-shifted plasmon absorbance at lambda = 680 nm, consistent with the existence of a longitudinal plasmon exciton. High-resolution transmission electron microscopy analysis of the tripod and tetrapod structures reveals directional growth along the <211> and <010> directions, respectively. The shaped Au NPs could be generated by a biocatalytic process using alcohol dehydrogenase, NAD+, and ethanol, and the resulting blue color provides a colorimetric test for ethanol.


Assuntos
NADP/química , NAD/química , Nanoestruturas/química , Ácido Ascórbico , Catálise , Cristalografia , Compostos de Ouro , Microscopia Eletrônica , Modelos Moleculares , Oxirredução
19.
Nano Lett ; 5(1): 21-5, 2005 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-15792406

RESUMO

The H(2)O(2)-mediated enlargement of Au nanoparticles (NPs) and the growth mechanism are described. In addition to the deposition of gold on the NP faces, the formation of nanocrystalline clusters at the intersection of the faces is observed. The detachment of the latter nanoclusters provides additional seeds for the deposition of gold. The biocatalyzed generation of H(2)O(2) in the presence of O(2)/glucose and glucose oxidase enabled the development of an optical biosensor for glucose.


Assuntos
Técnicas Biossensoriais , Glucose/análise , Ouro/química , Catálise , Glucose/química , Glucose Oxidase/química , Peróxido de Hidrogênio/química , Microscopia Eletrônica de Transmissão , Nanoestruturas , Oxigênio/química , Análise Espectral
20.
J Am Chem Soc ; 127(8): 2650-5, 2005 Mar 02.
Artigo em Inglês | MEDLINE | ID: mdl-15725022

RESUMO

Enantioselective surfactant-templated thin films were fabricated through the sol-gel (SG) process. The enantioselectivity is general in the sense that it discriminates between pairs of enantiomers not used for the imprinting process. The chiral cationic surfactant (-)-N-dodecyl-N-methylephedrinium bromide (1) was used as the surfactant template, and after its extraction chiral domains were created. The chiral discriminative feature of these films was examined by challenging with pure enantiomer solutions for rebinding. Selective adsorption was shown using (R)- and (S)-propranolol, (R)-2 and (S)-2, respectively, and (R)- and (S)-2,2,2-trifluoro-1-(9-anthryl)ethanol, (R)-3 and (S)-3, respectively, as the chiral probes. The selective adsorption was measured by fluorescence analysis, and the chiral selectivity factors were found to be 1.6 for 2 and 2.25 for 3. In both cases, (R)-enantiomer was adsorbed preferably. The resulting material was characterized by transmission electron microscopy, by diffraction, and by surface area measurements, and was found to be semicrystalline with short-range ordered domains (50 A) of hexagonal symmetry.

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