Chemical contrast in soft x-ray ptychography

The unique strengths of x-ray microscopy are high penetration depth and near-edge resonances that provide chemical information. We use ptychography, a coherent diffractive imaging technique that disposes of the requirement for isolated specimens, and demonstrate resonant imaging by exploiting resonances near the oxygen K edge to differentiate between two oxygen-containing materials. To highlight a biological system where resonant ptychography might be used for chemical mapping of unsliced cells, reconstructions of freeze-dried Deinococcus radiodurans cells at an energy of 517 eV are shown.     

Investigating Elementary Mathematics Curricula: Focus on Students With Learning Disabilities

The purpose of this study was to investigate three elementary mathematics curricula to examine the accessibility for students with learning disabilities (LD) with regards to challenges associated with working memory. We chose to focus on students' experiences when finding the area of composite shapes due to the multiple steps involved for solving these problems and the potential for these problems to tax working memory. We conducted a qualitative analysis of how each curriculum provided opportunities for students with LD to engage with these problems. During our analysis, we focused on instruction that emphasized visual representations (e.g., manipulatives, drawings, and diagrams), facilitated mathematical conversations, and developed cognitive and metacognitive skills. Our findings indicated a need for practitioners to consider how each curriculum provides instruction for storage and organization of information as well as how each curriculum develops students' thinking processes and conceptual understanding of mathematics. We concluded that all three curricula provide potentially effective strategies for teaching students with LD to solve multi‐step problems, such as area of composite shapes problems, but teachers using any of these curricula will likely need to supplement the curriculum to meet the needs of students with LD.     

Mechanistic study of photomediated triangular silver nanoprism growth

This article presents a mechanistic study of the photomediated growth of silver nanoprisms. The data show that the photochemical process is driven by silver redox cycles involving reduction of silver cations by citrate on the silver particle surface and oxidative dissolution of small silver particles by O2. Bis(p-sulfonatophenyl)phenylphosphine increases the solubility of the Ag(+) by complexing it and acts as a buffer to keep the concentration of Ag(+) at 20 microM. The silver particles serve as photocatalysts and, under plasmon excitation, facilitate Ag(+) reduction by citrate. Higher Ag(+) concentrations favor a competitive thermal process, which results in increased prism thickness.     

Infrared spectrum of matrix isolated selenoformaldehyde, CH2Se, and CD2Se

Thermolysis of highly diluted (CH2Se)3 or (CD2Se)3 in a flow of argon with subsequent quenching of the products in an matrix at 15 K yields monomeric CH2Se and CD2Se, respectively. Six fundamental vibrations upsilon1 = 2972.5, upsilon2 = 1413.3, upsilon3 = 854.2, upsilon4 = 916.4, upsilon 5 = 3052.9, and upsilon 6 = 913.2 cm(-1) and two combination bands have been observed for CH2Se as well as three fundamentals of CD2Se. The vibrational wavenumbers are compared with those of CH2O and CH2S. Matrix isolated selenoformaldehyde decomposes slowly by UV photolysis to yield the CSe molecule.     

Nafion-CNT coated carbon-fiber microelectrodes for enhanced detection of adenosine

Adenosine is a neuromodulator that regulates neurotransmission. Adenosine can be monitored using fast-scan cyclic voltammetry at carbon-fiber microelectrodes and ATP is a possible interferent in vivo because the electroactive moiety, adenine, is the same for both molecules. In this study, we investigated carbon-fiber microelectrodes coated with Nafion and carbon nanotubes (CNTs) to enhance the sensitivity of adenosine and decrease interference by ATP. Electrodes coated in 0.05 mg mL(-1) CNTs in Nafion had a 4.2 ± 0.2 fold increase in current for adenosine, twice as large as for Nafion alone. Nafion-CNT electrodes were 6 times more sensitive to adenosine than ATP. The Nafion-CNT coating did not slow the temporal response of the electrode. Comparing different purine bases shows that the presence of an amine group enhances sensitivity and that purines with carbonyl groups, such as guanine and hypoxanthine, do not have as great an enhancement after Nafion-CNT coating. The ribose group provides additional sensitivity enhancement for adenosine over adenine. The Nafion-CNT modified electrodes exhibited significantly more current for adenosine than ATP in brain slices. Therefore, Nafion-CNT modified electrodes are useful for sensitive, selective detection of adenosine in biological samples.     

The fluoroformyloxyl radical geometry and ground-state rotational spectra of the free FC18O2· radical

The rotational spectra of the isotopically substituted free fluoroformyloxyl radical FC(18)O(2·) were measured using the Prague millimeter-wave high-resolution spectrometer. More than 110 rotational-fine-hyperfine transition lines were observed and assigned to appropriate quantum numbers in the frequency range of 235-270 GHz. The obtained transition frequencies were analyzed with standard effective Hamiltonians to acquire a set of precise rotational, centrifugal-distortion, fine, and hyperfine structure molecular constants. Merging the new FC(18)O(2·) isotopologue molecular parameters with those previously obtained for the ordinary FC(16)O(2)[middle dot] radical, the substitution molecular geometry in the ground vibronic state was evaluated. The molecular parameters for both radical isotopologues were also calculated by several quantum chemistry methods and their calculated mutual ratios are in remarkable agreement with the experimental FC(16)O(2·)/FC(18)O(2·) parameter ratios. The measurements, assignments of the 18-oxygen isotopologue FC(18)O(2·) radical millimeter-wave transitions, as well as the derivation of the fluoroformyloxyl radical ground-state geometry have been carried out for the first time.     

Azobenzene on Cu(110): adsorption site-dependent diffusion

Azobenzene and its derivatives can undergo reversible trans-cis isomerizations when irradiated with light, making them potential candidates for optically sensitive materials and devices. The adsorption and diffusion of azobenzene on the Cu(110) surface was investigated with a variable-temperature scanning tunneling microscope. The trans-isomer was observed and found to occupy two adsorption geometries-an energetically stable and a metastable state. Diffusion occurred along the closed-packed [1 -1 0] direction of the surface, and the diffusivity for the two adsorption states was found to differ by approximately 1 order of magnitude.     

Metal-catalyzed phosphodiester cleavage: secondary 18O isotope effects as an indicator of mechanism

Information about the transition states of metal-catalyzed hydrolysis reactions of model phosphate compounds has been obtained through determination of isotope effects (IEs) on the hydrolysis reactions. Metal complexation has been found to significantly alter the transition state of the reaction from the alkaline hydrolysis reaction, and the transition state is quite dependent on the particular metal ion used. For the diester, ethyl p-nitrophenyl phosphate, the nonbridge 18O effect for the hydrolysis reactions catalyzed by Co(III) 1,5,9-triazacyclononane and Eu(III) were 1.0006 and 1.0016, respectively, indicative of a slightly associative transition state and little net change in bonding to the nonbridge oxygen. The reaction catalyzed by Zn(II) 1,4,7,10-tetraazacyclododecane had an 18O nonbridge IE of 1.0108, showing the reaction differs significantly from the reaction of the noncomplexed diester and resembles the reactions of triesters. Reaction with Co(III) 1,4,7,10-tetraazacyclododecane showed an inverse effect of 0.9948 reflecting the effects of bonding of the diester to the Co(III). Lanthanide-catalyzed hydrolysis has been observed to have unusually large 15N effects. To further investigate this effect, the 15N effect on the reaction catalyzed by Ce(IV) bis-Tris propane solutions at pH 8 was determined to be 1.0012. The 15N effects were also measured for the reaction of the monoester p-nitrophenyl phosphate by Ce(IV) bis-Tris propane (1.0014) and Eu(III) bis-Tris propane (1.0012). These smaller effects at pH 8 indicate that a smaller negative charge develops on the nitrogen during the hydrolysis reaction.     

Diameters of 3-sphere quotients

Let G⊂O(4) act isometrically on S³. In this article we calculate a lower bound for the diameter of the quotient spaces S³/G. We find it to be , which is exactly the value of the lower bound for diameters of the spherical space forms. In the process, we are also able to find a lower bound for diameters for the spherical Aleksandrov spaces, Sn/G, of cohomogeneities 1 and 2, as well as for cohomogeneity 3 (with some restrictions on the group type). This leads us to conjecture that the diameter of Sn/G is increasing as the cohomogeneity of the group G increases.     

ChemInform Abstract: Spectroscopic and Structural Studies of Difluorophosphoryl Azide F2P(O)N3, Difluorophosphoryl Isocyanate F2P(O)NCO,and Difluorophosphoric Acid Anhydride,F2(O)POP(O)F2.

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