Probing the Influence of Amino Acids on Photoluminescence from Carbon Nanotubes Suspended with DNA

The quantitative analysis of amino acid levels in the human organism is required for the early clinical diagnosis of a variety of diseases. In this work the influence of 13 amino acid doping on the photoluminescence (PL) from the semiconducting single-walled carbon nanotubes (SWNTs) suspended with single-stranded DNA (ssDNA) in water has been studied. Amino acid doping leads to the PL enhancement and the strongest increase was found after cysteine doping of the nanotube suspension while addition of other amino acids yielded the significantly smaller effect. The emphasis of cysteine molecules is attributed to presence of the reactive thiol group that turns cysteine into reducing agent that passivates the p-defects on the nanotube sidewall and increases the PL intensity. The reasons of PL enhancement after doping with other amino acids are discussed. The response of nanotube PL to cysteine addition depends on the nanotube aqueous suspension preparation with tip or bath sonication treatment. The enhancement of the emission from different nanotube species after cysteine doping was analyzed too. It was shown that the increase of the carbon nanotube PL at addition of cysteine allows successful monitoring of the cysteine concentration in aqueous solution in the range of 50–1000 μM.     

Effect of iron doping on the hydrophobicity of titanium dioxide film: experiment and simulation

In this study, we carried out experiments and molecular dynamics simulations to identify the effect of Fe doping on the hydrophobicity of a titanium dioxide film. TiO₂ and Fe-doped TiO₂ films were fabricated in situ by atomic layer deposition without annealing. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterise the crystal structure and elemental composition. Iron doping resulted in the TiO₂ becoming more hydrophobic at a macroscopic level, as estimated by atomic force microscopy observations and static contact angle measurements. Furthermore, the effect of iron doping on the structure and kinetics of water molecules on the exterior of TiO₂ were studied by molecular dynamics simulations. On the basis of the XPS results, the Fe-TiO₂ surface matrix has a Ti:Fe ratio of 36:5. In addition, the density distribution of oxygen and hydrogen atoms indicate that interfacial water molecules enter the Fe-TiO₂ film more easily and hydrogen atoms in the water molecules are oriented upward at the interface. The self-diffusion coefficients indicate that iron doping makes the TiO₂ more hydrophobic, which is consistent with the macroscopic test results.     

Surface science of diamond: Familiar and amazing

The crystal structure of diamond is identical with that of its more common semiconductor relatives silicon and germanium. Consequently, a number of surface properties in terms of reconstructions, surface states and surface band diagrams are similar as in the case of Si or Ge. But diamond also exhibits a number of unusual and potentially very useful surface properties. Particularly when the surface dangling bonds are saturated by monovalent hydrogen atoms (donor-like), surface states are removed from the gap, the electron affinity changes sign and becomes negative, and the material becomes susceptible to an unusual type of transfer doping where holes are injected by acceptors located at the surface instead of inside the host lattice. These surface acceptors can in the simplest case be adsorbed molecules conveniently chosen by their electron affinity, but they can also be solvated ions within atmospheric water layers or electrolytes in contact with the hydrogenated diamond surface. In this article the surface properties of diamond will be reviewed with special emphasis on this new kind of doping mechanism.     

Boron doping of silicon by excimer laser irradiation in a reactive atmosphere

UV excimer lasers have been used to dope semiconductors by a one-step process in which the laser serves both to melt a controlled thickness of a sample placed in dopant ambient and to photodissociate the dopant molecules themselves. Here we report the boron doping of silicon by means of an ArF (193 nm) excimer laser. Dopant atoms are obtained by photolysis of BCl₃ or pyrolysis of BF₃ molecules. The doping is performed both in gas ambient and using only an adsorbed layer. We have investigated the dependence of doping parameters such as laser pulse repetition and gas pressure on the subsequent boron impurity profiles and the dopant incorporation rate. These results indicate that the laser doping process is dopant-flux limited for BF₃ and externally rate limited for BCl₃.     

纳米MgO掺杂聚乙烯微观特性的分子动力学模拟研究

电力系统高压电缆的主要绝缘材料为聚乙烯,为了提升聚乙烯的热稳定性以及减弱水分对其的渗透能力,采用纳米MgO掺杂聚乙烯,利用分子动力学模拟方法建立包含低密度聚乙烯(LDPE)、不同颗粒半径的MgO纳米团簇以及相同质量分数水分的复合模拟模型.研究结果表明,水分会降低复合体系的玻璃化温度,MgO的掺杂则会提高复合体系的玻璃化温度,减弱聚乙烯分子链的运动并减小复合体系的自由体积,使得复合体系结构更加稳定,从而增强了聚乙烯材料的热稳定性能.此外发现水分子的扩散随着温度的上升而增大,纳米MgO的添加会与水分子形成氢键抑制水分子的扩散,同时自由体积的缩减使水分子的溶解度系数与扩散系数都减小,导致水分子的渗透能力减弱,更难以渗透进聚乙烯材料破坏其结构.研究结果可为聚乙烯的水树枝生长以及老化过程的抑制提供有益的参考.     

Orientational ordering in polymer composites with nanofillers: the osmotic pressure effect

Phase behavior of short double-stranded DNA molecules dissolved in the water-containing polymer matrix is considered theoretically. Flexible-chain polymer molecules are assumed to be neutral. The phase behavior of DNA fragments is shown to be governed by the effective attraction, occurring due to polyvalent cations dissolved in water, and the osmotic pressure of the flexible-chain polymer.     

Low-frequency spectroscopy of four-photon scattering of laser radiation in aqueous solutions of biopolymers

Four-photon scattering (FPS) spectroscopy is used to record rotational resonances of H₂O and H₂O₂ molecules in aqueous solutions of DNA and denatured DNA within a range of ±10 cm^-1 with a spectral resolution of 3 GHz. The resonance contribution of rotational transitions of these molecules in solutions was found to be considerably larger than that in distilled water. This fact is interpreted as a manifestation of the specific properties of a hydrate layer at the interface between water and DNA or denatured DNA molecules. An analysis of the FPS spectra shows that the concentration of H₂O₂ molecules in the hydrate layer of the DNA molecule increases threefold after denaturation. In addition, the FPS spectra of aqueous solutions of α-chymotrypsin protein with concentrations of 0-20 mg cm^-3 were measured in the spectral range of ±7 cm^-1. It is found that the velocity of hypersound in the protein aqueous solution, which is measured by the shift of the Mandelstam—Brillouin scattering spectrum components, is a cubic function of the concentration and reaches 3000 m/s at 20 mg/cm³.     

Violet-to-red photoluminescence of spiro-TAD organic films doped with different organic dyes

Photoluminescence (PL) and photoluminescence excitation (PLE) spectra of undoped spiro-TAD films and spiro-TAD films doped either by the organic dyes coumarin 7 or DCM as well as by both of these dyes simultaneously were investigated at different dye concentrations. A widened PL spectrum caused by doping was encountered and violet-to-red emission was obtained. It was established that excitation of the dyes is realized most efficiently through spiro-TAD. The overall integral PL intensity of the coumarin 7 doped films increased with dye concentration due to the suppression of nonradiative recombination in the film caused by a transfer of spiro-TAD excitation energy to the dye molecules. Mainly radiative energy transfer from semiconductor to dye molecules occurs in the case of DCM doping. No mutual influence on the luminescence of both dyes in the spiro-TAD film was observed and as a consequence, the PL band intensity of each dye can be adjusted separately.     

Organic low-dimensional structure electroluminescent material characteristics and devices

Photoluminescence (PL) characteristics of organic doped films are studied as a function of dopant concentration, doped layer thickness. The luminescence properties of doped films are decided by Förster energy transfer rate between host and guest and fluorescence quenching effect of guest. For Alq:rubrene doped film at 5% doping level, we fabricated and characterized organic doped quantum-well structure device, and observed significant quantum size effect. For Alq:QAD doping system, at low doping level of 0.4%, the intermolecular spacing between QAD molecules is relatively large, the interaction between neighboring QAD molecules is very small due to the strong localization of the carriers in the single QAD molecules, the PL properties of Alq:QAD doped films only depends on the PL properties of single isolated QAD molecules, which is somewhat similar to the inorganic quantum dot structure. We also reported the electroluminescent performance of the Alq:QAD system.     

掺杂二氧化钛纳米管对有机电致发光性能的影响

在聚合物电致发光器件中，通过在不同功能层中掺杂二氧化钛纳米管来改善器件的性能.由于二氧化钛纳米管具有p型传导特性，可以显著增大空穴传输层中载流子的迁移率.由于二氧化钛纳米管在发光层中可以增大发光材料分子的刚性，从而减少无辐射跃迁.当把二氧化钛纳米管掺杂到空穴缓冲层中时，由于其与有机分子的强相互作用，一方面降低了空穴的传导性，同时也减少了界面淬灭发光的缺陷态的产生. 关键词： 二氧化钛纳米管 聚合物电致发光 掺杂     

鲱精DNA纤维水合状态的振动谱特征

利用拉曼散射光谱测试技术，对不同温度处理后获得的各种相对湿度下的鲱精ＤＮＡ纤维进行脱氧核苷Ｃ—Ｈ振动与结合水Ｏ—Ｈ振动行为分析，以揭示其中结合水的数量特征。结果表明，运用２５９２６×Ｉ２９６４／Ｉ３０２４新指标所获数据与文献报道的小牛胸腺ＤＮＡ水合状态拉曼数据不同，但与小牛胸腺ＤＮＡ、鲑精ＤＮＡ的红外、Ｘ射线衍射、重量分析及差示扫描量热分析所得数据相吻合，证明拉曼分析公式的修订是成功的。鲱精ＤＮＡ纤维应与上述二种ＤＮＡ纤维具有同样的水合状态，每核苷酸对含有９～１４个结合水分子。     

Influences of Al doping on the electronic structure of Mg(0001) and dissociation properties of H2

By using the density functional theory method, we systematically study the effects of the doping of an Al atom on the electronic structures of the Mg(0001) surface and on the dissociation behaviors of H₂ molecules. We find that for the Al-doped surfaces, the surface relaxation around the doping layer changes from expansion of a clean Mg(0001) surface to contraction, due to the redistribution of electrons. After doping, the work function is enlarged, and the electronic states around the Fermi energy have a major distribution around the doping layer. For the dissociation of H₂ molecules, we find that the energy barrier is enlarged for the doped surfaces. In particular, when the Al atom is doped at the first layer, the energy barrier is enlarged by 0.30 eV. For different doping lengths, however, the dissociation energy barrier decreases slowly to the value on a clean Mg(0001) surface when the doping layer is far away from the top surface. Our results well describe the electronic changes after Al doping for the Mg(0001) surface, and reveal some possible mechanisms for improving the resistance to corrosion of the Mg(0001) surface by doping of Al atoms.     

Electrical resistance response of polyaniline films to water, ethanol, and nitric acid solution

<正>This paper reports on electrical resistance vs.aging time for the response of polyanihne films under exposure to water,ethanol and nitric acid(HNO_3) solution.Camphor sulfonic acid-doped polyanihne films were prepared by a "doping-dedoping-redoping" method,the morphology and microstructures of the films were characterized by a scanning electron microscope and an x-ray diffractometer,the electrical resistance was measured by a four-probe method.It was found that a lower amount of water molecules infiltrating the film can decrease the film's resistance possibly due to an enhancement of charge carrier transfer between polyanihne chains,whereas excessive water molecules can swell inter-chain distances and result in a quick increase of resistance.The resistance of the film under exposure to ethanol increases and becomes much larger than the original value.However,HNO3 solution can decrease the film's resistance sharply possibly owing to doping effect of protonic acid.These results can help to understand the conduction mechanism in polyaniline films,and also indicate that the films have potential application in chemical sensors.     

Synthesis and characterization of doxorubicin hydrochloride drug molecule-intercalated DNA nanostructures

In this paper, we demonstrate the feasibility of constructing DNA nanostructures (i.e. DNA rings and double-crossover (DX) DNA lattices) with appropriate doxorubicin hydrochloride (DOX) concentration and reveal significant characteristics for specific applications, especially in the fields of biophysics, biochemistry and medicine. DOX-intercalated DNA rings and DX DNA lattices are fabricated on a given substrate using the substrate-assisted growth method. For both DNA rings and DX DNA lattices, phase transitions from crystalline to amorphous, observed using atomic force microscopy (AFM) occurred above a certain concentration of DOX (at a critical concentration of DOX, 30 μM of [DOX]_C) at a fixed DNA concentration. Additionally, the coverage percentage of DNA nanostructures on a given substrate is discussed in order to understand the crystal growth mechanism during the course of annealing. Lastly, we address the significance of optical absorption and photoluminescence characteristics for determining the appropriate DOX binding to DNA molecules and the energy transfer between DOX and DNA, respectively. Both measurements provide evidence of DOX doping and [DOX]_C in DNA nanostructures.     

Photoinduced flavin-tryptophan electron transfer across vesicle membranes generates magnetic field sensitive radical pairs

ABSTRACT

Due to the photobiology of the flavoproteins DNA photolyase and cryptochrome, electron transfer reactions between flavins and tryptophan are of significant biological relevance. In addition, electron transfer across vesicle membranes has also seen much attention. In this work, we study the electron transfer reaction between flavins and tryptophan across lipid bilayer membranes in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine small unilamellar vesicles using time-resolved optical absorption microspectroscopy and magnetically affected reaction yield spectroscopy. We demonstrate that riboflavin tetrabutyrate is embedded in the vesicle bilayer and can undergo electron transfer with tryptophan molecules in either the inner water pool or the bulk solution. Remarkably, flavin mononucleotide encapsulated in the inner water pool can undergo electron transfer across the vesicle bilayer to generate a magnetically sensitive radical pair with tryptophan molecules located in the bulk solution. The observed kinetics suggest that back electron transfer occurs between radical pairs generated by diffusive reencounter, either in the vesicle surface water or via electron hopping through degenerate electron exchange.     

Quasi-nanowires from fluorescent semiconductor nanocrystals on the surface of oriented DNA molecules

Ordered structures in the form of quasi-nanowires were obtained from CdSe/ZnS fluorescent semiconductor nanoparticles of spherical (quantum dots) or rodlike (quantum rods) form by their electrostatic deposition on DNA molecules with subsequent stretching of the molecules on a solid substrate. Positively charged nanoparticles were fixed along the negatively charged backbones of DNA molecules by electrostatic interactions in an aqueous solution of a mixture of DNA with quantum particles at different stoichiometric ratios. Strands of single DNA molecules with quantum particles fixed along them were immobilized and stretched on hydrophobic surfaces using the molecular combing technique. It is shown that, by varying the nanoparticle charge and the stoichiometry of complexes of DNA with particles, it is possible to create fluorescent structures with predetermined morphology and properties.     

Amphoteric and controllable doping of carbon nanotubes by encapsulation of organic and organometallic molecules

By using first principles calculations, we show that fine tuning of both p- and n-type doping can be realized on single-wall carbon nanotubes (SWNTs) by tuning the electron affinity or ionization potential of the organic and organometallic molecules encapsulated inside SWNTs. This novel type of SWNT-based material offers great promise for molecular electronics because of its air stability, synthetic simplicity and the abundance of organic and organometallic molecules.     

Micromechanics of base pair unzipping in the DNA duplex

All-atom molecular dynamics (MD) simulations of DNA duplex unzipping in a water environment were performed. The investigated DNA double helix consists of a Drew-Dickerson dodecamer sequence and a hairpin (AAG) attached to the end of the double-helix chain. The considered system is used to examine the process of DNA strand separation under the action of an external force. This process occurs in vivo and now is being intensively investigated in experiments with single molecules. The DNA dodecamer duplex is consequently unzipped pair by pair by means of the steered MD. The unzipping trajectories turn out to be similar for the duplex parts with G·C content and rather distinct for the parts with A·T content. It is shown that during the unzipping each pair experiences two types of motion: relatively quick rotation together with all the duplex and slower motion in the frame of the unzipping fork. In the course of opening, the complementary pair passes through several distinct states: (i) the closed state in the double helix, (ii) the metastable preopened state in the unzipping fork and (iii) the unbound state. The performed simulations show that water molecules participate in the stabilization of the metastable states of the preopened base pairs in the DNA unzipping fork.     

Changes in the zero-point energy of the protons as the source of the binding energy of water to A-phase DNA

The measured changes in the zero-point kinetic energy of the protons are entirely responsible for the binding energy of water molecules to A phase DNA at the concentration of 6 water molecules/base pair. The changes in kinetic energy can be expected to be a significant contribution to the energy balance in intracellular biological processes and the properties of nano-confined water. The shape of the momentum distribution in the dehydrated A phase is consistent with coherent delocalization of some of the protons in a double well potential, with a separation of the wells of 0.2??.     

有机混合薄膜中的F(o)rster能量转移

通过掺杂不同的染料有机电致发光器件可以得到不同颜色的光发射。掺杂小分子有机材料?p酸四甲酯perylene-3,4,9,10-tetracarboxylicacid(TMEP)到蓝色发光聚合物poly(N-vinyl-carbazole)聚乙烯基咔唑(PVK),得到了很好的绿光发射。TEMP掺杂质量分数为0.01时,295. 5nm激发波长的荧光光谱可以明显观察到在420 nm处PVK和530 nm处TEMP的发射峰值;当TMEP掺杂质量分数达到0.05～0.10之间,器件的电致发光光谱和荧光光谱发射峰几乎完全被TEMP的绿光所占据。光谱的转移归因于从聚合物PVK到小分子有机材料TMEP的Forster能量转移。荧光光谱中随着TMEP掺杂浓度的的增大发射峰值有明显的红移,这种现象被归因于在TMEP高浓度掺杂情况下激基缔合物的形成。激基缔合物的形成从TMEP在薄膜状态下与溶液状态下的荧光光谱的比较中得到证实。