Homo‐ and Heteronuclear meso,meso‐(E)‐Ethene‐1,2‐diyl‐Linked Diporphyrins: Preparation,X‐ray Crystal Structure,Electronic Absorption and Emission Spectra and Density Functional Theory Calculations

Homo‐ and heteronuclear meso,meso‐(E)‐ethene‐1,2‐diyl‐linked diporphyrins have been prepared by the Suzuki coupling of porphyrinylboronates and iodovinylporphyrins. Combinations comprising 5,10,15‐triphenylporphyrin (TriPP) on both ends of the ethene‐1,2‐diyl bridge M₂10 (M₂=H₂/Ni, Ni₂, Ni/Zn, H₄, H₂Zn, Zn₂) and 5,15‐bis(3,5‐di‐tert‐butylphenyl)porphyrinato‐nickel(II) on one end and H₂, Ni, and ZnTriPP on the other ( M₂11 ), enable the first studies of this class of compounds possessing intrinsic polarity. The compounds were characterized by electronic absorption and steady state emission spectra, ¹H NMR spectra, and for the Ni₂ bis(TriPP) complex Ni₂10 , single crystal X‐ray structure determination. The crystal structure shows ruffled distortions of the porphyrin rings, typical of Ni^II porphyrins, and the (E)‐C₂H₂ bridge makes a dihedral angle of 50° with the mean planes of the macrocycles. The result is a stepped parallel arrangement of the porphyrin rings. The dihedral angles in the solid state reflect the interplay of steric and electronic effects of the bridge on interporphyrin communication. The emission spectra in particular, suggest energy transfer across the bridge is fast in conformations in which the bridge is nearly coplanar with the rings. Comparisons of the fluorescence behaviour of H₄10 and H₂Ni10 show strong quenching of the free base fluorescence when the complex is excited at the lower energy component of the Soret band, a feature associated in the literature with more planar conformations. TDDFT calculations on the gas‐phase optimized geometry of Ni₂10 reproduce the features of the experimental electronic absorption spectrum within 0.1 eV.     

Watching Nanoparticles Form: An In Situ (Small‐/Wide‐Angle X‐ray Scattering/Total Scattering) Study of the Growth of Yttria‐Stabilised Zirconia in Supercritical Fluids

Understanding nanoparticle‐formation reactions requires multi‐technique in situ characterisation, since no single characterisation technique provides adequate information. Here, the first combined small‐angle X‐ray scattering (SAXS)/wide‐angle X‐ray scattering (WAXS)/total‐scattering study of nanoparticle formation is presented. We report on the formation and growth of yttria‐stabilised zirconia (YSZ) under the extreme conditions of supercritical methanol for particles with Y₂O₃ equivalent molar fractions of 0, 4, 8, 12 and 25 %. Simultaneous in situ SAXS and WAXS reveals a quick formation (seconds) of sub‐nanometre amorphous material forming larger agglomerates with subsequent slow crystallisation (minutes) into nanocrystallites. The amount of yttria dopant is shown to strongly affect the crystallite size and unit‐cell dimensions. At yttria‐doping levels larger than 8 %, which is known to be the stoichiometry with maximum ionic conductivity, the strain on the crystal lattice is significantly increased. Time‐resolved nanoparticle size distributions are calculated based on whole‐powder‐pattern modelling of the WAXS data, which reveals that concurrent with increasing average particle sizes, a broadening of the particle‐size distributions occur. In situ total scattering provides structural insight into the sub‐nanometre amorphous phase prior to crystallite growth, and the data reveal an atomic rearrangement from six‐coordinated zirconium atoms in the initial amorphous clusters to eight‐coordinated zirconia atoms in stable crystallites. Representative samples prepared ex situ and investigated by transmission electron microscopy confirm a transformation from an amorphous material to crystalline nanoparticles upon increased synthesis duration.     

Vibrational frequencies and structural determination of tetraazidogermane

The vibrational frequencies and corresponding normal mode assignments of tetraazidogermane are examined theoretically using the Gaussian98 set of quantum chemistry codes. All normal modes were successfully assigned to one of seven types of motion predicted by a group theoretical analysis (N-N-N asymmetric stretch, N-N-N symmetric stretch, Ge-N stretch, N-N-N bend, Ge-N-N bend, N-Ge-N bend, and N-Ge-N-N torsion) utilizing the S(4) symmetry of the molecule. The molecular orbitals of Ge(N(3))(4) are examined.     

Higher-order Brunnian structures and possible physical realizations

We consider few-body bound state systems and provide precise definitions of Borromean and Brunnian systems. The initial concepts are more than a hundred years old and originated in mathematical knot-theory as purely geometric considerations. About thirty years ago they were generalized and applied to the binding of systems in nature. It now appears that recent generalization to higher-order Brunnian structures may potentially be realized as laboratory-made or naturally occurring systems. With the binding energy as measure, we discuss possibilities of physical realization in nuclei, cold atoms, and condensedmatter systems. Appearance is not excluded. However, both the form and the strengths of the interactions must be rather special. The most promising subfields for present searches would be in cold atoms because of external control of effective interactions, or perhaps in condensed-matter systems with nonlocal interactions. In nuclei, it would only be by sheer luck due to a lack of tunability.     

Disjoint 3‐Cycles in Tournaments: A Proof of The Bermond–Thomassen Conjecture for Tournaments

We prove that every tournament with minimum out‐degree at least contains k disjoint 3‐cycles. This provides additional support for the conjecture by Bermond and Thomassen that every digraph D of minimum out‐degree contains k vertex disjoint cycles. We also prove that for every , when k is large enough, every tournament with minimum out‐degree at least contains k disjoint cycles. The linear factor 1.5 is best possible as shown by the regular tournaments.     

The Steiner Problem on Surfaces of Revolution

While the Steiner problem has been extensively studied in the Euclidean plane, it remains an open problem to solve the Steiner problem on arbitrary non-planar (piecewise smooth) surfaces. We suggest an algorithm for solving the n-point Steiner problem on surfaces of revolution which have a non-decreasing generating function by constructing an isometric framework on a plane endowed with a weighted distance metric, thus propelling a new analytical avenue for studying the Steiner problem on surfaces with non-constant curvature.     

Energy gradients in combined fragment molecular orbital and polarizable continuum model (FMO/PCM) calculation

The analytic energy gradients for the combined fragment molecular orbital and polarizable continuum model (FMO/PCM) method are derived and implemented. Applications of FMO/PCM geometry optimization to polyalanine show that the structures obtained with the FMO/PCM method are very close to those obtained with the corresponding full ab initio PCM methods. FMO/PCM (RHF/6‐31G* level) is used to optimize the solution structure of the 304‐atom Trp‐cage miniprotein and the result is in agreement with NMR experiments. The key factors determining the relative stability of the α‐helix, β‐turn and the extended form in solution are elucidated for polyalanine. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Direct modification of hydrogen/deuterium-terminated diamond particles with polymers to form reversed and strong cation exchange solid phase extraction sorbents

We describe direct polymer attachment to hydrogen and deuterium-terminated diamond (HTD and DTD) surfaces using a radical initiator (di-tert-amyl peroxide, DTAP), a reactive monomer (styrene) and a crosslinking agent (divinylbenzene, DVB) to create polystyrene encapsulated diamond. Chemisorbed polystyrene is sulfonated with sulfuric acid in acetic acid. Surface changes were followed by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFT). Finally, both polystyrene-modified DTD and sulfonated styrene-modified DTD were used in solid phase extraction (SPE). Percent recovery and column capacity were investigated for both phenyl (polystyrene) and sulfonic acid treated polystyrene SPE columns. These diamond-based SPE supports are stable under basic conditions, which is not the case for silica-based SPE supports.     

Implementation of droplet-membrane-droplet liquid-phase microextraction under stagnant conditions for lab-on-a-chip applications

In the current work, droplet-membrane-droplet liquid-phase microextraction (LPME) under totally stagnant conditions was presented for the first time. Subsequently, implementation of this concept on a microchip was demonstrated as a miniaturized, on-line sample preparation method. The performance level of the lab-on-a-chip system with integrated microextraction, capillary electrophoresis (CE) and laser-induced fluorescence (LIF) detection in a single miniaturized device was preliminarily investigated and characterized. Extractions under stagnant conditions were performed from 3.5 to 15 μL sample droplets, through a supported liquid membrane (SLM) sustained in the pores of a small piece of a flat polypropylene membrane, and into 3.5-15 μL of acceptor droplet. The basic model analytes pethidine, nortriptyline, methadone, haloperidol, and loperamide were extracted from alkaline sample droplets (pH 12), through 1-octanol as SLM, and into acidified acceptor droplets (pH 2) with recoveries ranging between 13 and 66% after 5 min of operation. For the acidic model analytes Bodipy FL C₅ and Oregon Green 488, the pH conditions were reversed, utilizing an acidic sample droplet and an alkaline acceptor droplet, and 1-octanol as SLM. As a result, recoveries for Bodipy FL C₅ and Oregon Green 488 from human urine were 15 and 25%, respectively.     

Potential‐driven peptide extractions across supported liquid membranes: Investigation of principal operational parameters

Fundamental experiments on electromembrane extraction were performed to increase the basic knowledge about the current and the mass transfer of target peptides and background electrolyte ions. Three peptides (angiotensin 2, bradykinin, and enkephalin) were extracted from 500 μL aqueous donor solution (1 mM HCl, positive electrode), through a 200 μm supported liquid membrane (SLM) of 1‐octanol/di‐isobutylketon/di‐(2‐ethylhexyl) phosphate (55:35:10 w/w/w) sustained in the pores of a porous hollow fiber, and into 25 μL aqueous acceptor solution (50 mM HCl, negative electrode) present inside the lumen of the fiber by the application of an electrical potential (50 V) and agitation (1050 rpm). Recoveries were typically in the range of 55–65% after 5 min of extraction and were principally determined by the chemical composition of the SLM and by the applied voltage. The electrical current in the system was measured during the extraction and was close to 350 μA. The current arose to some extent from mass transfer of the target peptides, but the major contribution was due to a background current from di‐(2‐ethylhexyl) phosphate in the SLM and from mass transfer of background electrolytes. Operation at relatively low background current was important to maintain a stable system.