Homogeneously alloyed CdSxSe1-x nanocrystals: synthesis, characterization, and composition/size-dependent band gap

Alloy nanocrystals provide an additional degree of freedom in selecting desirable properties for nanoscale engineering because their physical and optical properties depend on both size and composition. We report the pyrolytic synthesis of homogeneously alloyed CdS(x)Se(1-x) nanocrystals in all proportions. The nanocrystals are characterized using UV-visible absorption spectroscopy, transmission electron microscopy, X-ray diffractrometry, and Rutherford backscattering spectrometry to determine precisely structure, size, and composition. The dependence of band gap on nanocrystal size and composition is elucidated, yielding a bowing constant of 0.29, in agreement with bulk values. In addition, the morphology of the resultant nanocrystals can be altered by changing the reaction conditions, generating structures ranging from homogeneous, spherical nanocrystals to one-dimensional gradient nanorods.     

DNA-protein cross-linking: model systems for pyrimidine-aromatic amino acid cross-linking

[reaction: see text] We have synthesized simple model systems to explore the possibility of photo-cross-linking between the pyrimidine bases and the side chains of the aromatic amino acids. Thymine/phenylalanine and thymine/tyrosine models gave cross-links, and thymine/tryptophan models gave complex mixtures; the cytosine/phenylalanine model was unreactive. The quantum yields for the model cross-linking reactions were 18-46 times smaller than those for thymine dimer formation. Biphotonic excitation contributes little to the yield of these reactions.     

Multiple-spot optical tweezers created with microlens arrays fabricated by proton beam writing

We report two different applications for using arrays of microlenses on glass substrate to facilitate multiple-spot optical trapping of colloidal microbeads. The array of microlenses was made of SU8 or PMMA resist and created by a combination of Proton-Beam writing followed by thermal reflow processes. Firstly, similar to previous reports [8, 9, 10 ], the lenses were utilized as an optical element in generating multiple laser spot arrays that were subsequently focused down to impose a microbead array. In addition, we demonstrated the feasibility of a novel approach of integrating the microlens array into a sample chamber to provide localized optical trapping. PACS 07.60.Pb; 41.75.Ak; 42.15.Eq; 42.65.Jx; 42.79.Bh     

Determination of the collisionally activated dissociation of a substituted indole by orthogonal acceleration quadrupole time-of-flight mass spectrometry

The use of orthogonal acceleration quadrupole time-of-flight (Q-TOF) mass spectrometry to determine the collisionally activated dissociation (CAD) of a test compound 1-(3-[5-[1,2,4-triazol-4-yl]-1H-indol-3-yl]propyl)-4-(2-[3-fluorophenyl]ethyl)piperazine is described. At unit-mass resolution the identity of many ions is ambiguous because of the complexity of the resulting product ion spectrum. Using the high resolution capabilities of the Q-TOF instrument, exact masses for each fragment were determined. These data were used to infer molecular formulas for each fragment through software interpretation and, by further applying chemical intuition, the majority of ions were fully assigned. Additionally, by utilizing in-source fragmentation at high cone voltage, analyses of second-generation products allowed derivation of a consistent sequential fragmentation pathway. This study clearly demonstrates the power of Q-TOF mass spectrometry to elucidate complex product ion spectra.     

A comparison of ten different methods for the analysis of saturates, olefins, benzene, total aromatics, and oxygenates in finished gasolines

The Technical Committee 19 of the European Committee for Standardization (CEN/TC19) in the "Lisbon resolution" requested to evaluate replacement methods to the fluorescent indicator absorption (FIA) (American Standardization for Testing and Material D 1319) method for the determination of aromatics and olefins in gasolines. In the same resolution it was requested to review the two existing methods for the determination of benzene content of gasolines, anticipating lower limit values in future European gasoline specifications. As a result of this request, a round robin (RR) was organized in which 8 gasoline samples are analyzed using 10 different methods in 33 laboratories. The methods used in the RR include, apart from the FIA method, one-dimensional gas chromatography (GC) and multidimensional GC, with and without specific detectors and spectroscopic analysis methods. This study describes these methods in short, gives an evaluation of the results of the RR, and draws a conclusion on the outcome.     

K(π 1)'s for Artin Groups of Finite Type

We construct K( 1)'s for Artin groups of type C _n and D _n , using the lattice of elements preceding a Coxeter element in the partial order defined by reflection length.     

Comparison of negative and positive ion electrospray ionization mass spectra of calmodulin and its complex with trifluoperazine

The protein calmodulin (apoCaM) undergoes a conformational change when it binds calcium. This structure of the protein (Ca4CaM) is a dumbbell-shaped molecule that undergoes a further profound conformational change on binding of the antipsychotic drug trifluoperazine (TFP). Experimental conditions were developed to prepare samples of apoCaM, Ca4CaM and Ca4CaM/TFP that were substantially free of sodium. The effects of the conformational changes of calmodulin on the charge-state distributions observed in positive ion and negative ion electrospray ionization (ESI) mass spectra were examined. Conversion of apoCaM into Ca4CaM was concomitant with a change in the negative ion ESI mass spectrum whereby the 16- ion was the most abundant ion observed for the apo form and the 8- ion was the most abundant for the complex. In contrast, in the positive ion ESI mass spectra of apoCaM and Ca4CaM, the most abundant species in each case was the 8+ ion. When a complex of Ca4CaMwith TFP was prepared, the most abundant species was the 5+ ion. This is consistent with a conformational change of Ca4CaM that rendered some basic sites inaccessible to ionization in the ESI process. Using the same Ca4CaM/TFP mixture, no complex with TFP was observed in negative ion ESI mass spectra. These observations are discussed in the context of the structural changes that are known to occur in calmodulin, and suggestions are made to explain the apparently conflicting data. The results reported here reflect on the validity of using differences in charge-state distributions observed in ESI mass spectra to assess conformational changes in proteins.     

Multiphoton-Excited Visible Emission by Serotonin Solutions

Nonlinear excitation of the neurotransmitter serotonin (5HT) in aqueous solution is shown to generate a blue-green-emitting photoproduct in addition to UV fluorescence characteristic of native 5HT. The visible emission rate in diffusional steady-state measurements scales as the sixth power of excitation intensity, demonstrating that absorption of six near-IR photons is required to generate emission of one visible photon. Transient measurements reveal that this process is composed of two sequential nonlinear steps, the first excited by four photons and the second by two photons. These results, in combination with measurements of multiphoton-excited serotonin UV fluorescence, support a model in which 5HT is photochemically transformed as a consequence of four-photon absorption (E_tot?6 eV) to a photoproduct that then emits in the visible region via two-photon excitation. A minimum bound of ?10^-51 cm⁴ s photon^-1 is observed for the two-photon emission action cross section at 830 nm. Photoionization, rather than reaction with a dissolved oxygen species, appears to be the primary mechanism for generation of the blue-green-emitting photoproduct. The peak intensities required to generate significant blue-green emission (?5 times 10¹¹ W cm^-2 from 80 MHz 150 fs titanium: sapphire laser pulses) are approximately five-fold higher than are typically used in two-photon laser scanning microscopy but are still substantially lower than the estimated intensity needed to induce dielectric breakdown of water.     

Speciation analysis of arsenic in groundwater from Inner Mongolia with an emphasis on acid-leachable particulate arsenic

Arsenic in drinking water affects millions of people around the world. While soluble arsenic is commonly measured, the amount of particulate arsenic in drinking water has often been overlooked. We report here determination of the acid-leachable particulate arsenic and soluble arsenicals in well water from an arsenic-poisoning endemic area in Inner Mongolia, China. Water samples (583) were collected from 120 wells in Ba Men, Inner Mongolia, where well water was the primary drinking water source. Two methods were demonstrated for the determination of soluble arsenic species (primarily inorganic arsenate and arsenite) and total particulate arsenic. The first method used solid phase extraction cartridges and membrane filters to separate arsenic species on-site, followed by analysis of the individual arsenic species eluted from the cartridges and filters. The other method uses liquid chromatography separation with hydride generation atomic fluorescence detection to determine soluble arsenic species. Analysis of acidified water samples using inductively coupled plasma mass spectrometry provided the total arsenic concentration. Arsenic concentrations in water samples from the 120 wells ranged from <1 to ∼1000 μg L⁻¹. On average, particulate arsenic accounted for 39 ± 38% (median 36%) of the total arsenic. In some wells, particulate arsenic was six times higher than the soluble arsenic concentration. Particulate arsenic can be effectively removed using membrane filtration. The information on particulate and soluble arsenic in water is useful for optimizing treatment options and for understanding the geochemical behavior of arsenic in groundwater.     

Properties of Some Wool Keratin Copolymers

The properties of keratin following the formation of polymers in situ have been studied. It is important to determine any effects of the initiatory system on keratin in order to assess the role of the added polymer, The water content of the copolymer usually differs from that of the keratin and polymer measured as separate entities and influences the observed physical properties. Deposition of polymer has little direct effect on properties unless reaction with the keratin structure occurs. Observed physical properties suggest that polymer is predominately formed in the matrix component.