Chemical images of marine bio-active compounds by surface enhanced Raman spectroscopy and transposed orthogonal partial least squares (T-OPLS)

Surface enhanced Raman spectroscopy combined with transposed Orthogonal Partial Least Squares (T-OPLS) was shown to produce chemical images of the natural antibacterial surface-active compound 1,1,3,3-tetrabromo-2-heptanone (TBH) on Bonnemaisonia hamifera. The use of gold colloids functionalised with the internal standard 4-mercapto-benzonitrile (MBN) made it possible to create images of the relative concentration of TBH over the surfaces. A gradient of TBH could be mapped over and in the close vicinity of the B. hamifera algal vesicles at the attomol/pixel level.     

Activation of Al2O3 by a long-ranged chemical bond mechanism

On the basis of density functional theory calculations, a novel bond mechanism with chemical strength but of long-ranged character is proposed. As compared to adsorption on a sole oxide or metal, the mechanism is found to enhance the bond strength between an adsorbate and an oxide in contact with a metal. As a model system, NO2 adsorption on alpha-Al2O3(0001) either in contact with Ag(111) or small Agn clusters is used. The observed phenomenon rests on charge transfer and modification of the oxide-metal interface. The mechanism is general in nature and the implication for heterogeneous catalysis is discussed.     

Multiphoton electron angular distributions from laser-aligned CS2 molecules

Laser-aligned carbondisulfide (CS2) molecules are singly ionized by multiphoton absorption from intense, linearly polarized 25 fs laser pulses. The angular distribution of the photoelectrons exhibits a significant dependence on the angle between the polarizations of the aligning and ionizing laser fields. The widely used strong-field approximation predicts angular distributions in qualitative agreement with the experimental data but fails at a quantitative level.     

Polymeric liquids in extension: fluid mechanics or rheometry?

We use a transient 3D free surface finite element method to simulate flow of entangled polymer fluids in the dual cylinder wind-up extensional rheometer. The constitutive equations are K-BKZ integral representations of the Doi–Edwards models with and without the independent alignment approximation (IA). It is demonstrated that the actual kinematics in this rheometer is a mixture of planar and uniaxial extension. Moreover, the ratio of planar to uniaxial deformation is highly dependent upon whether IA is invoked. Without IA, the flow has a tendency toward planar extension, while it tends to be more uniaxial with IA invoked. As a second illustration of the techniques, we simulate the phenomenon of delayed rupture after rapid extension of entangled polymer systems. It is demonstrated that this phenomenon can be explained on the basis of the Doi–Edwards model in terms of a Considere-type instability after chain stretch relaxation.     

A non‐planar peptide bond in l‐seryl‐l‐valine

The C^α—C′—N—C^α (ω) torsion angle of the peptide bond in the crystal structure of the title compound, C₈H₁₆N₂O₄, is 157.37 (15)°. This is the second‐largest deviation from planarity observed for a small linear peptide.