Using light and a molecular switch to 'lock' and 'unlock' the Diels-Alder reaction

Light is used to 'gate' the Diels-Alder reaction using a photoresponsive dithienylfuran backbone and turn the reversibility of the Diels-Alder reaction 'off' and 'on' at 100 °C. These features make the reported system an excellent candidate for developing the next generation of self-healing polymers and photothermal drug delivery vehicles.     

On the swelling behavior of poly(N-Isopropylacrylamide) hydrogels exposed to perfluoroalkyl acids

Per- and polyfluoroalkyl substances (PFAS) have rapidly accumulated in the environment due to their widespread use prior to commercial discussion in the early 21st century, and their slow degradation has magnified concerns of their potential toxicity. Monitoring their distribution is, therefore, necessary to evaluate and control their impact on the health of exposed populations. This investigation evaluates the capability of a simple polymeric detection scheme for PFAS based on crosslinked, thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) hydrogels. Surveying swelling perturbations induced by several hydrotropes and comparable hydrocarbon analogs, tetraethylammonium perfluorooctane sulfonate (TPFOS) showed a significantly higher swelling ratio on a mass basis (65.5 ± 8.8 at 15°C) than any of the other analytes tested. Combining swelling with the fluorimetric response of a solvachromatic dye, nile red, revealed the fluorosurfactant to initiate observable aggregation (i.e., its critical aggregation concentration) at 0.05 mM and reach saturation (i.e., its charge neutralization concentration) at 0.5 mM. The fluorosurfactant was found to homogeneously distribute throughout the polymer matrix with energy dispersive X-ray spectroscopy, marking the swelling response as a peculiar nexus of fluorinated interfacial positioning and delocalized electrostatic repulsion. Results from the current study hold promise for exploiting the physiochemical response of PNIPAM to assess TPFOS's concentration.     

Quantification techniques of mass-separation and ion yield for the detection of radioactive isotopes

Journal of Radioanalytical and Nuclear Chemistry - This research demonstrates two methods of quantifying ion yield efficiency using an inductively coupled plasma mass spectrometer. The mass...     

An observation concerning the vanishing topology of certain isolated determinantal singularities

We extend the results about the vanishing topology of isolated Cohen–Macaulay codimension 2 singularities from a previous article by Frühbis-Krüger and Zach (On the vanishing topology of isolated Cohen–Macaulay codimension 2 singularities. arXiv:1501.01915, 2015). Due to the Hilbert–Burch theorem, these singularities have a canonical determinantal structure and a well behaved deformation theory, which, in particular, yields a unique Milnor fiber. Studying the case of possibly non-isolated singularities in the Tjurina transform, as introduced in Frühbis-Krüger and Zach (2015), we reveal that in dimension 3 and 2 there is always exactly one special vanishing cycle in degree 2 closely related to the determinantal structure of the singularity.

     

Infrared spectroscopy and structures of manganese carbonyl cations,Mn(CO)<Stack><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript><Superscript>+</Superscript></Stack> (<Emphasis Type="Italic">n</Emphasis> = 1−9)

Manganese carbonyl cations of the form Mn(CO) _n ⁺ (n = 1−9) are produced in a molecular beam by laser vaporization in a pulsed nozzle source. Mass selected infrared photodissociation spectroscopy in the carbonyl stretching region is used to study these complexes and their “argon-tagged” analogues. The geometries and electronic states of these complexes are determined by comparing their infrared spectra to theoretical predictions. Mn(CO)₆⁺ has a completed coordination sphere, consistent with its predicted 18-electron stability. It has an octahedral structure in its singlet ground state, similar to its isoelectronic analogue Cr(CO)₆. Charge-induced reduction in π back-bonding leads to a decreased red-shift in Mn(CO)₆⁺ (υ_CO = 2106 cm⁻¹) compared with Cr(CO)₆ (υ_CO = 2003 cm⁻¹). The spin multiplicity of Mn⁺(CO) _n complexes gradually decreases with progressive ligand addition. MnCO⁺ is observed as both a quintet and a septet, Mn(CO)₂⁺ is observed only as a quintet, while Mn(CO)_3,4⁺ are both observed as triplets. Mn(CO)₅⁺ and Mn(CO)₆⁺ are both singlets, as are all larger complexes.     

Confinement potential in the dual monopole Nambu–Jona–Lasinio model with dual Dirac strings

Interquark confinement potential is calculated in the dual monopole Nambu–Jona–Lasinio model with dual Dirac strings suggested in [2,3] as a functional of the dual Dirac string length. The calculation is carried out by explicit integration over quantum fluctuations of a dual-vector field (monopole–antimonopole collective excitation) around the Abrikosov flux line and string shape fluctuations. The contribution of the scalar field (monopole–antimonopole collective excitation) exchange is taken into account in the tree approximation because of the London limit regime. The dominant role of quantum fluctuations for the formation of the linearly rising part of the confinement potential is argued. Received: 10 November 1998 / Revised version: 10 May 1999 / Published online: 12 August 1999     

Structural and magnetic phase transitions in CoxNi1−xMnGe system under pressure

The interaction of magnetic (T_c) an first-order distortion-type structural (T_D) transitions in the Co_xNi_1?xMnGe system was investigated using an ac susceptibility method under hydrostatic pressure up to 1.3 GPa. For all compositions T_C increases and T_D decreases with pressure. At the first triple point (0.3–0.6 GPa depending on x) these transitions go through a simultaneous magnetic-structural transition, as observed by Anzai and Ozawa in NiMnGe. However, for the composition x = 5, at the second triple point (at 0.8 GPa) the magnetic transition separates from the structural one, with T_C greater than T_D. This appears to be the first example of physically different, first and second-order phase transitions merging at a particular value of an external parameter, i.e. pressure P_TR1 and decoupling again at P_TR2 > P_T1. The (P, T) phase diagrams and the nature of the triple points are discussed using a simple Landau-type theory