Multi-shot interference approach for any kind of Bravais lattice

A mathematical scheme capable of describing the features of the photolithographic multi-beam–multi-shot approach is introduced here. We will show in detail how such a technique can reproduce any of the fourteen three-dimensional Bravais lattices. Furthermore, we will mathematically show the independence of the lattice constant of the structure from the laser wavelength. Finally, we will compare the four-beams–one-shot and the three-beams–three-shots techniques by means of simulations reproducing opal and connected FCC-like lattices.     

How Divalent Cations Interact with the Internal Channel Site of Guanine Quadruplexes

The formation of guanine quadruplexes (GQ) in DNA is crucial in telomere homeostasis and regulation of gene expression. Pollution metals can interfere with these DNA superstructures upon coordination. In this work, we study the affinity of the internal GQ channel site towards alkaline earth metal (Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺), and (post-)transition metal (Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺) cations using density functional theory computations. We find that divalent cations generally bind to the GQ cavity with a higher affinity than conventional monovalent cations (e. g. K⁺). Importantly, we establish the nature of the cation-GQ interaction and highlight the relationship between ionic and nuclear charge, and the electrostatic and covalent interactions. The covalent interaction strength plays an important role in the cation affinity and can be traced back to the relative stabilization of cations’ unoccupied atomic orbitals. Overall, our findings contribute to a deeper understanding of how pollution metals could induce genomic instability.     

Trapped Ions Interacting with Laser Fields: a Perturbative Analysis without the Rotating Wave Approximation

The Hamiltonian describing a single ion placed in a potential trap in interaction with a laser beam is studied by means of a suitable perturbative approach. It is shown, in particular, that the rotating wave approximation does not provide the correct expression, already at the first perturbative order, of the evolution operator of the system.     

Surface plasmon polariton compression through radially and linearly polarized source

We report on the possibility of realizing a radial mode on a metallic conical structure by means of a linearly polarized incident wave. This result is utilized for observing surface plasmon polaritons adiabatic compression on a tapered conical nanostructure. The ingredients for radial mode generation are described in terms of phase-matching of the components of the electromagnetic field. We conclude by showing the robustness of this approach, explaining the polaritonic behavior as a function of the device geometry.     

The onset of coulomb explosions in polyatomic molecules

With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd.     

Uniform molecular analysis using femtosecond laser mass spectrometry

The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd.     

Interpreting early land management through compound specific stable isotope analyses of archaeological soils

Compound specific stable isotope analyses of managed soils using isotope ratio mass spectrometry have been undertaken as a means of determining early land use practices. delta (15)N amino acid signals demonstrate differences between manured grassland, unmanured grassland and continuous cereal cultivation under long-term experimental land use control conditions, with delta (15)N in hydrophobic amino acids providing the most distinctive signals. Analysis of early modern/medieval and of Bronze age anthropogenic soils from Orkney demonstrates that such signals are retained in archaeological contexts. delta (13)C analyses of n- alkanoic acid components of the fossil, Bronze Age, anthropogenic soils suggest a major terrestrial input to these soils, with uniform composition of formation materials. Surficial soils demonstrate the assimilation of isotopically lighter carbon, providing a means of assessing the mobility of the n- alkanoic acids within soils and sediments. Copyright 1999 John Wiley & Sons, Ltd.     

Synthesis and biological evaluation of unprecedented ring-expanded nucleosides (RENs) containing the imidazo[4,5-d][1,2,6]oxadiazepine ring system

A small collection of ring-expanded nucleosides (RENs), containing the unprecedented bis-alkylated imidazo[4,5-d][1,2,6]oxadiazepine heterocyclic ring system, has been synthesized through a new general approach. Results of preliminary cytotoxicity tests on breast (MCF-7) and lung (A549) cancer cell lines are also reported.     

Synthesis, Stereostructure and H-bonding Patterns of a Tris-THF Compound

Abstract  

The synthesis and crystallographic analysis of a new tris-THF compound, obtained by chemical degradation of a penta-THF precursor, is reported. The molecular structure of the tris-THF compound allows to definitively assess the stereoconfiguration of the parent penta-THF compound, that was known only partially. The tris-THF compound crystallizes in the monoclinic C2/c space group with unit cell parameters a = 21.621(8), b = 7.481(4), c = 30.801(9) ?, β = 94.08(3)°, Z = 8. The final refinement converged to R ₁ = 0.0804 for 1,706 independent observed reflections having I > 2σ(I). The tris-THF compound adopts in the solid state a flexuous and wavy conformation due to the cis–trans–trans configuration of the three THF rings and to intramolecular H bonding. Molecules in the crystals form H-bonded chains that are wrapped around the crystallographic binary screw axes. The chains are also bonded to each other by H-bonding through _boxclose_boxclose_boxclose_boxclose^4 (8) R_{4}^{4} (8) and R₂² (14) R_{2}^{2} (14) ring motifs.