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1.
Inelastic electron tunneling spectroscopy (IETS) is a relatively new form of vibrational spectroscopy which is able to address problems previously unsolved by either IR or Raman. It is particularly useful for surface analysis. 相似文献
2.
ABSTRACT Copolymers of 1,5-dioxepan-2-one (DXO) and e-caprolactone (?-CL), δ-valerolactone (δ-VL) or L-lactide (LLA) have been synthesized and characterized. High molecular weight copolymers were obtained using stannous-2-ethyl hexanoate as catalyst in bulk. Reactivity ratios for the copolymerization of DXO and δ-VL were determined at 110°C as rVL=0.5 and rDXO=2.3. At high conversion, depolymerization of δ-VL occurred, resulting in lower molecular weight and variations in the copolymer composition. Physical properties, such as crystallinity and melting temperature of the DXO-copolymers proved to be strongly dependent on the choice of comonomer and on the molar composition of the copolymers. DXO appears to be incorporated into the poly-?-caprolactone (PCL) crystals and to some extent into the poly-δ-valerolactone (PVL) crystals, resulting in a more gradual decrease in crystallinity with increasing amount of DXO. 相似文献
3.
Jeongyun Heo Thomas A. Sobiech Hilliard L. Kutscher Lee Chaves Dinesh K. Sukumaran Shanta Karki Admire Dube Paras N. Prasad Jessica L. Reynolds 《Macromolecular bioscience》2021,21(1)
A nanoformulation composed of curdlan, a linear polysaccharide of 1,3‐β‐linked d ‐glucose units, hydrogen bonded to poly(γ ‐glutamic acid) (PGA), was developed to stimulate macrophage. Curdlan/PGA nanoparticles (C‐NP) are formulated by physically blending curdlan (0.2 mg mL?1 in 0.4 m NaOH) with PGA (0.8 mg mL?1). Forster resonance energy transfer (FRET) analysis demonstrates a heterospecies interpolymer complex formed between curdlan and PGA. The 1H‐NMR spectra display significant peak broadening as well as downfield chemical shifts of the hydroxyl proton resonances of curdlan, indicating potential intermolecular hydrogen bonding interactions. In addition, the cross peaks in 1H‐1H 2D‐NOESY suggest intermolecular associations between the OH‐2/OH‐4 hydroxyl groups of curdlan and the carboxylic‐/amide‐groups of PGA via hydrogen bonding. Intracellular uptake of C‐NP occurs over time in human monocyte‐derived macrophage (MDM). Furthermore, C‐NP nanoparticles dose‐dependently increase gene expression for TNF‐α, IL‐6, and IL‐8 at 24 h in MDM. C‐NP nanoparticles also stimulate the release of IL‐lβ, MCP‐1, TNF‐α, IL‐8, IL‐12p70, IL‐17, IL‐18, and IL‐23 from MDM. Overall, this is the first demonstration of a simplistic nanoformulation formed by hydrogen bonding between curdlan and PGA that modulates cytokine gene expression and release of cytokines from MDM. 相似文献
4.
H.K. Wong B.Y. Jin H.Q. Yang J.E. Hilliard J.B. Ketterson 《Superlattices and Microstructures》1985,1(3):259-264
We report measurements on the superconducting properties of V/Fe superlattices with various layer thicknesses. These samples were prepared with a novel UHV evaporator which can produce up to twenty different samples in the same run. The Fe layer, a strong pair breaker, suppresses the superconducting transition temperature in a systematic way. When the V layer thickness is on the order of the BCS coherence length and the Fe layer is only a few atomic planes thick, a 2D–3D crossover has been observed in the temperature dependence of the parallel upper critical field HC2∥. This implies the coexistence of superconductivity and ferromagnetismm. We observe three dimensional behavior for thinner Fe layers (~1 atomic plane) and two dimensional behavior for thicker Fe layers (greater than 10 atomic planes). 相似文献
5.
We demonstrate a method to count small numbers of atoms held in a deep, microscopic optical dipole trap by collecting fluorescence from atoms exposed to a standing wave of light that is blue detuned from resonance. While scattering photons, the atoms are cooled by a Sisyphus mechanism that results from the spatial variation in light intensity. The use of a small blue detuning limits the losses due to light-assisted collisions, thereby making the method suitable for counting several atoms in a microscopic volume. 相似文献
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7.
Lisa J. Hilliard D.Steven Foulk Harvey S. Gold Carl E. Rechsteiner 《Analytica chimica acta》1981,133(3):319-327
Ultraviolet-visible and fluorescence spectra have long been utilized for qualitative and quantitative purposes despite numerous complicating factors. In this study, anthracene, 1-naphthol, and 9-acetylanthracene are used as model systems to distinguish solventinduced effects via multiple regression techniques. The ability to predict changes in spectral peak locations and quantum efficiencies arising from solute—solvent interactions is critical to the development of a versatile computer-searchable library of electronic spectra. 相似文献
8.
RD Harris WS Baker Van Stipdonk MJ RM Crooks EA Schweikert 《Rapid communications in mass spectrometry : RCM》1999,13(14):1374-1380
A suite of keV polyatomic or 'cluster' projectiles was used to bombard unoxidized and oxidized self-assembled monolayer surfaces. Negative secondary ion yields, collected at the limit of single ion impacts, were measured and compared for both molecular and fragment ions. In contrast to targets that are orders of magnitude thicker than the penetration range of the primary ions, secondary ion yields from polyatomic projectile impacts on self-assembled monolayers show little to no enhancement when compared with monatomic projectiles at the same velocity. This unusual trend is most likely due to the structural arrangement and bonding characteristics of the monolayer molecules with the Au(111). Copyright 1999 John Wiley & Sons, Ltd. 相似文献
9.
Surface modification of silica nanoparticles to reduce aggregation and nonspecific binding 总被引:1,自引:0,他引:1
Bagwe RP Hilliard LR Tan W 《Langmuir : the ACS journal of surfaces and colloids》2006,22(9):4357-4362
In this article, a systematic study of the design and development of surface-modification schemes for silica nanoparticles is presented. The nanoparticle surface design involves an optimum balance of the use of inert and active surface functional groups to achieve minimal nanoparticle aggregation and reduce nanoparticle nonspecific binding. Silica nanoparticles were prepared in a water-in-oil microemulsion and subsequently surface modified via cohydrolysis with tetraethyl orthosilicate (TEOS) and various organosilane reagents. Nanoparticles with different functional groups, including carboxylate, amine, amine/phosphonate, poly(ethylene glycol), octadecyl, and carboxylate/octadecyl groups, were produced. Aggregation studies using SEM, dynamic light scattering, and zeta potential analysis indicate that severe aggregation among amine-modified silica nanoparticles can be reduced by adding inert functional groups, such as methyl phosphonate, to the surface. To determine the effect of various surface-modification schemes on nanoparticle nonspecific binding, the interaction between functionalized silica nanoparticles and a DNA chip was also studied using confocal imaging/fluorescence microscopy. Dye-doped silica nanoparticles functionalized with octadecyl and carboxylate groups showed minimal nonspecific binding. Using these surface-modification schemes, fluorescent dye-doped silica nanoparticles can be more readily conjugated with biomolecules and used as highly fluorescent, sensitive, and reproducible labels in bioanalytical applications. 相似文献
10.
A Mukherjee M Dasgupta DJ Hinde CR Morton AC Berriman RD Butt JO Newton H Timmers 《Pramana》2001,57(1):195-198
Fusion cross-sections for the 7Li + 12C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy
evaporation residues with energies below 3 MeV could not be separated out from the α-particles in the spectrum and hence their
contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections
due to the breakup of 7Li may not be significant for 7Li + 12C reaction at energies around the barrier. 相似文献