Linear dichroism amplification: adapting a long-known technique for ultrasensitive femtosecond IR spectroscopy

We demonstrate strong amplification of polarization-sensitive transient IR signals using a pseudo-null crossed polarizer technique first proposed by Keston and Lospalluto [Fed. Proc. 10, 207 (1951)] and applied for nanosecond flash photolysis in the visible by Che et al. [Chem. Phys. Lett. 224, 145 (1994)]. We adapted the technique to ultrafast pulsed laser spectroscopy in the infrared using photoelastic modulators, which allow us to measure amplified linear dichroism at kilohertz repetition rates. The method was applied to a photoswitch of the N-alkylated Schiff base family in order to demonstrate its potential of strongly enhancing sensitivity and signal to noise in ultrafast transient IR experiments, to simplify spectra and to determine intramolecular transition dipole orientations.     

Reactions with 4‐Hydroxy‐2‐methylbutananilides: Unexpected Formation of a Cyclopropanecarboxamide

The successive treatment of the N,N‐disubstituted 4‐hydroxy‐2‐methylbutanamide 2a with lithium diisopropylamide (LDA) and diphenyl phosphorochloridate (DPPCl) led to the 1‐methylcyclopropanecarboxamide 10 in good yield. This base‐catalyzed cyclization offers a new approach to cyclopropanecarboxamides. Under similar conditions, the N‐monosubstituted 4‐hydroxy‐2‐methylbutanamide 2b gave the 3‐methylpyrrolidin‐2‐one 11 . The structure of the cyclopropanecarboxamide 10 was established by X‐ray crystallography.     

Introduction of Adjacent Oxygen‐Functionalities in Dimethyl Heptalenedicarboxylates

The bromination of dimethyl 8‐methoxy‐1,6,10‐trimethylheptalene‐4,5‐dicarboxylate ( 6 ; Scheme 2) with N‐bromosuccinimide (NBS) in N,N‐dimethylformamide (DMF) leads in acceptable yields to the corresponding 9‐bromoheptalenedicarboxylate 10 (Table 1). Ether cleavage of 6 with chlorotrimethylsilane (Me₃SiCl)/NaI results in the formation of oxoheptalenedicarboxylate 13 in good yield (Scheme 4). The latter can be acetyloxylated to the (acetyloxy)oxoheptalenedicarboxylate 14 with Pb(OAc)₄ in benzene (Scheme 5). Oxo derivative 14 , in turn, can be selectively O‐methylated with dimethyl sulfate (DMS) in acetone to the (acetyloxy)methoxyheptalenedicarboxylates 15 and 15′ (Scheme 6). The AcO group of the latter can be transformed into a benzyl or methyl ether group by treatment with MeONa in DMF, followed by the addition of benzyl bromide or methyl iodide (cf. Scheme 9). Reduction of the ester groups of dimethyl 7,8‐dimethoxy‐5,6,10‐trimethylheptalene‐1,2‐dicarboxylate ( 25′ ) with diisobutylaluminium hydride (DIBAH) in tetrahydrofuran (THF) leads to the formation of the corresponding dimethanol 26′ , which can be cyclized oxidatively (IBX, dimethyl sulfoxide) to 8,9‐dimethoxy‐6,7,11‐trimethylheptaleno[1,2‐c]furan ( 27 ; Scheme 11).     

A new series of lanthanoid containing Keggin-type germanotungstates with acetate chelators: [{Ln(CH3COO)GeW11O39(H2O)}2] {Ln=Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb}

A series of head-on complexes of lanthanoid containing germanotungstates was isolated from a one pot reaction in an acetate buffer at pH 4.5. This convenient approach brought forward the [{Ln(CH₃COO)GeW₁₁O₃₉(H₂O)}₂]¹²⁻ (Ln=Eu^III, Gd^III, Tb^III, Dy^III, Ho^III, Er^III, Tm^III, and Yb^III) family with acetate chelators in the rarely observed μ₂: η²-η¹ mode. All compounds were structurally characterized using various solid state analytics, such as single crystal X-ray diffraction, FT-IR spectroscopy, and thermogravimetric analysis. The isostructural polyanions crystallize in the monoclinic system (S.G. P2₁/c). Temperature-dependent magnetic susceptibility measurements were performed on the Gd^III-complex which exhibits near perfect Curie-type behavior.     

Interspecies variation in survival and growth of filamentous heterotrophic bacteria in response to UVC radiation

Ultraviolet radiation is an important environmental constraint on the evolution of life. In addition to its harmful effects, ultraviolet radiation plays an important role in generating genetic polymorphisms and acting as a selective agent. Understanding how prokaryotes cope with high radiation can give insights on the evolution of life on Earth. Four representative filamentous bacteria from the family Cytophagaceae with different pigmentation were selected and exposed to different doses of UVC radiation (15-32,400Jm(-2)). The effect of UVC radiation on bacterial survival, growth and morphology were investigated. Results showed high survival in response to UVC for Rudanella lutea and Fibrisoma limi, whereas low survival was observed for Fibrella aestuarina and Spirosoma linguale. S. linguale showed slow growth recovery after ultraviolet exposure, R. lutea and F. limi showed intermediate growth recovery, while F. aestuarina had the fastest recovery among the four tested bacteria. In terms of survival, S. linguale was the most sensitive bacterium whereas R. lutea and F. limi were better at coping with UVC stress. The latter two resumed growth even after 2h exposure (～10,800Jm(-2)). Additionally, the ability to form multicellular filaments after exposure was tested using two bacteria: one representative of the high (R. lutea) and one of the low (F. aestuarina) survival rates. The ability to elongate filaments due to cell division was preserved but modified. In R. lutea 10min exposure reduced the average filament length. The opposite was observed in F. aestuarina, where the 5 and 10min exposures increased the average filament length. R. lutea and F. limi are potential candidates for further research into survival and resistance to ultraviolet radiation stress.     

Synthesis of epitaxial graphene on rhodium from 3-pentanone

The synthesis of high quality single layer graphene on rhodium, g/Rh(111), is reported. The graphene layers are grown at 1060 K by low pressure chemical vapor deposition (CVD) using 3-pentanone as a precursor molecule. The presented growth technique shows an easy high quality production method for epitaxial graphene monolayers. The chemical composition and structural properties of such self-assembled monolayers were characterized by X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED). Scanning Tunneling Microscopy (STM) confirms the formation of a 3 nm super cell and a unique surface morphology which establishes the potential of g/Rh(111) as a template for molecules.     

Wave Relations

The wave equation (free boson) problem is studied from the viewpoint of the relations on the symplectic manifolds associated to the boundary induced by solutions. Unexpectedly, there is still something to say about this simple, well-studied problem. In particular, boundaries which do not allow for a meaningful Hamiltonian evolution are not problematic from the viewpoint of relations. In the two-dimensional Minkowski case, these relations are shown to be Lagrangian. This result is then extended to a wide class of metrics and is conjectured to be true also in higher dimensions for nice enough metrics. A counterexample where the relation is not Lagrangian is provided by the Misner space.     

Dynamics of a Strongly Coupled Polaron

We study the dynamics of large polarons described by the Fröhlich Hamiltonian in the limit of strong coupling. The initial conditions are (perturbations of) product states of an electron wave function and a phonon coherent state, as suggested by Pekar. We show that, to leading order on the natural time scale of the problem, the phonon field is stationary and the electron moves according to an effective linear Schrödinger equation.     

Optimal estimates on free boundary propagation in thin-film flow

We present a method for the derivation of lower bounds on free boundary propagation for the thin-film equation, one of the most prominent examples of a higher-order degenerate parabolic equation. In particular, we obtain sufficient conditions for instantaneous forward motion of the free boundary, upper bounds on waiting times, as well as lower bounds on asymptotic propagation rates. Our estimates coincide (up to a constant factor) with the previously known reverse bounds and are therefore optimal. To the best of our knowledge, these results constitute the first lower bounds on free boundary propagation for any higher-order degenerate parabolic equation. Our technique is based on new monotonicity formulas for solutions to the thin-film equation which involve weighted entropies with singular weight functions. It turns out that our method is not restricted to the thin-film equation, but also applicable to other higher-order parabolic equations like quantum drift-diffusion equations. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,characterization, spectrophotometric and electrochemistry studies,and DNA cleavage of copper(II) complexes of a new azacrown bis-macrocycle and its mono-cyclic analogue

A new azacrown bis-macrocycle (5) and its mono–cyclic analogue (7) were synthesized and characterized by FT-IR, ¹H NMR, ¹³C NMR, DEPT ¹³C NMR, MS, and elemental analysis. The reaction with copper(II) nitrate yielded the corresponding complexes, formulated as Cu(5)(NO₃)₂·3H₂O (8), and Cu(7)(NO₃)₂·2.5H₂O (9). Also the stoichiometries of the complexes were determined in alcoholic solution and the results show that for both complexes the ratio of ligand to metal was 1:1 in methanol. The redox behavior of both complexes has been studied by cyclic voltammetry in DMF. Cyclic voltamogram of 8 shows quasi-reversible Cu^II/Cu^I redox couple whereas 9 shows a reversible Cu^II/Cu^I redox couple. Mono- and bis-macrocycle copper(II) complexes (8 and 9 respectively) cleaved plasmid pGS2 DNA by using an oxidative mechanism with 3- mercaptopropionic acid (MPA) as the reductant under aerobic conditions. The bis-macrocycle copper(II) complex 8 showed higher cleavage efficiency than their mono-macrocycle analogue 9 at the same Cu²⁺ concentration.