Stability of 2-D colloidal particle aggregates held against flow stress in an ultrasound trap

The formation of a two-dimensional aggregate of 25 microm latex particles in a 1.5 MHz ultrasound standing wave (USW) field and its disintegration in a flow were studied. The aggregate was held in the pressure node plane, which allowed continuous microscope observation and video recording of the processes. The trajectories and velocities of the particles approaching the formation site were analyzed by particle image velocimetry (PIV). Since the direct radiation force on the particles dominated the drag due to acoustic streaming, the acoustic pressure profile in the vicinity of the aggregate was quantifiable. The drag coefficients D(coef) for 2- to 485-particle aggregates were estimated from the balance of the drag force FD and the buoyancy-corrected gravitational force during sedimentation on termination of the ultrasound when the long axis of the aggregate was in the vertical plane. D(coef) were calculated from FD as proportional to the aggregate velocity. Experiments on particle detachment by flow (in-plane velocity measured by PIV) from horizontal aggregates suspended in deionized water and CaCl2 solution of different concentrations showed that the mechanical strength of the aggregates depended on the acoustic pressure amplitude P0 and ionic strength of the solution. In deionized water the flow velocity required to detach the first single particle from an aggregate increased from 1 mm s-1 at P0 = 0.6 MPa to 4.2 mm s-1 at P0 = 1.4 MPa. The balance of forces acting on particles in a USW trap is discussed. The magnitude of the shear stress employed ( approximately 0.05 Pa) and separation forces suggests that this technique can be applied to studying the mechanical responses of cell aggregates to hydrodynamic flow, where cell-cell interaction can be separated from the effects of solid substrata.     

Imaging photoelectron transmission through self-assembled monolayers: the work-function of alkanethiols coated gold

In this paper, we present a new approach for studying the electronic properties of self-assembled monolayers and their interaction with a conductive substrate, the low-energy photoelectron imaging spectroscopy (LEPIS). LEPIS relies on imaging of photoelectrons ejected from a conductive substrate and subsequently transmitted through organic monolayers. Using this method, we measure the relative work-function of alkanethiols of different length on gold substrate, and we are able to follow the changes occurring when the surface coverage is varied. We also computed the work-function of model alkanethiols using a plane-wave density functional theory approach, in order to demonstrate the correlation between changes in the work-function with the monolayer organization and density.     

Chiral separation of Huperzine A using CE - method validation and application in pharmaceutical formulations

The aim of this work is the development, validation and application of an MEKC method for the chiral separation of Huperzine A. Huperzine A is an important compound that is used to treat Alzheimer's disease. However, only the (?)‐form of this compound is biologically active and behaves as a potential acetylcholinesterase inhibitor. Therefore, the separation of the (?)‐form from the (+)‐form is of greatest importance. Optimal conditions, regarding resolution and analysis time, were established by altering several experimental parameters, such as temperature, field strength, pH, type and concentration of BGE and chiral selector. A major problem that had to be solved in this study was the low intensity and efficiency of the peaks. More parameters were examined, such as the addition of modifiers, to optimize further the separation, and particularly the efficiency. Baseline enantioseparation was achieved by using a BGE of 50 mM acetate (pH 5.0), supplemented with 0.2% w/v poly(sodium N‐undecanoyl‐ll ‐alanyl‐valinate) and 10% v/v tert‐butanol. Finally, the optimum conditions were applied to a pharmaceutical formulation, to demonstrate the ability of the method to control the purity of the (?)‐Huperzine A in pharmaceutical formulations.     

Synthesis and Biological Evaluation of the Novel Growth Inhibitor Streptol Glucoside,Isolated from an Obligate Plant Symbiont

The plant Psychotria kirkii hosts an obligatory bacterial symbiont, Candidatus Burkholderia kirkii, in nodules on their leaves. Recently, a glucosylated derivative of (+)-streptol, (+)-streptol glucoside, was isolated from the nodulated leaves and was found to possess a plant growth inhibitory activity. To establish a structure–activity relationship study, a convergent strategy was developed to obtain several pseudosugars from a single synthetic precursor. Furthermore, the glucosylation of streptol was investigated in detail and conditions affording specifically the α or β glucosidic anomer were identified. Although (+)-streptol was the most active compound, its concentration in P. kirkii plant leaves extract was approximately ten-fold lower than that of (+)-streptol glucoside. These results provide compelling evidence that the glucosylation of (+)-streptol protects the plant host against the growth inhibitory effect of the compound, which might constitute a molecular cornerstone for this successful plant-bacteria symbiosis.     

The relationship of theory and practice in mathematics teacher professional development: an activity theory perspective

This paper describes certain interactions between the activity of “teaching” and the activity of “researching” in which the teachers participate in a 52-h professional development course aiming to introduce them to research in mathematics education as a tool for inquiry in their teaching. The teachers are involved in different research tasks such as: reading and presenting research papers; analyzing classroom dialogues and tasks; and designing, implementing, and evaluating collaboratively a classroom teaching intervention. From an activity theory (AT) perspective, and in particular Engeström’s (2001) third generation AT, distinguish two activity systems, the activity system of research and the activity system of teaching, to identify links that the participating teachers make. These links indicate the development of an inquiring stance to mathematics teaching and learning as a means of professional learning.     

Towards preparative-scale, biocatalytic alkene reductions

Simple strategies for using alkene reductase enzymes to produce gram-scale quantities of both (R)- and (S)-citronellal have been developed. The methodology is easily accessible to non-specialist laboratories, allowing alkene reductases to be added to the toolbox of routine synthetic transformations.     

Assessing Surface Permeabilities from Transient Guest Profiles in Nanoporous Host Materials

Easy come, easy go? Transport resistances on particle surfaces are important for mass transfer in nanoporous materials and bulk diffusion in crystals. Interference microscopy and IR micro‐imaging are shown to be excellent tools for determining such transport resistances. By studying short‐chain‐length alkane guest molecules in crystals of the metal–organic framework compound Zn(tbip) a data collection of surface permeabilities is established.

     

Ensemble Measurement of Diffusion: Novel Beauty and Evidence

Recording the evolution of concentration profiles in nanoporous materials opens a new field of diffusion research with particle ensembles. The technique is based on the complementary application of interference microscopy and IR micro‐imaging. Combining the virtues of diffusion measurements with solids and fluids, it provides information of unprecedented wealth and visual power on transport phenomena in molecular ensembles. These phenomena include the diverging uptake and release patterns for concentration‐dependent diffusivities, the mechanisms of mass transfer at the fluid–solid interface and opposing tendencies in local and global concentration evolution.     

Coordination complexes of iron(III) with 3-hydroxy-2(1H)-pyridinone, 2,3-dihydroxybenzoic acid and 3,4-dihydroxybenzoic acid: preparation and characterization in the solid state

Summary The synthesis and study of a number of new iron(III) complexes of the ligands 3-hydroxy-2(1H)-pyridinone (3,2-opoH), 2,3-dihydroxybenzoic acid (2,3-dhbH₃) and 3,4-dihydroxybenzoic acid (3,4-dhbH₃) are described. These complexes have the formulae [Fe(3,2-opo)₂Cl]·PrⁿOH, K[Fe(2,3-dhbH)₂(H₂O)₂], [Fe(2,3-dhb)(H₂O)₂], K[Fe-(3,4-dhbH)₂(H₂O)₂], [Fe(3,4-dhb)(H₂O)₂] and K₆[Fe(3,4-dhb)₃]·3H₂O. The complexes were characterized by elemental analyses. X-ray powder patterns, t.g.a./d.t.g. techniques, magnetic susceptibilities and spectroscopic (u.v.-vis., i.r. and variable-temperature ⁵⁷Fe-M?ssbauer) studies. Monomeric octahedral structures are assigned for the 1∶2 2,3-dhbH²⁻ complex and the 1:3 3,4-dhb³⁻ compound. Dinuclear and/or oligonuclear structures are tentatively proposed for the remaining complexes in the solid state. In [FeL(H₂O)₂] (L³⁻ = 2,3-dhb³⁻ or 3,4-dhb³⁻), iron(III) appears to be 5-coordinate. Both oxygens of 3,2-opo⁻ participate in coordination, while the dihydroxybenzoato ligands exhibit various coordination modes, depending mainly on the positions of the hydroxy groups, their anionic charge and the ligand∶metal molar ratio used.     

One-pot efficient synthesis of novel fused pentacyclic indolopyridobenzimidazoles and pyridoimidazopyridoindoles from the reaction of pyranoindolones with 1,2-diaminobenzenes and 2,3-diaminopyridines

The synthesis of a number of novel, fully conjugated, planar pentacyclic 5H-indolo[3′,2′:4,5]pyrido[1,2-a][1,3]benzimidazoles (8) and 11H-pyrido[3″,2″:4′,5′]imidazo[1′,2′:1,6]pyrido[3,4-b]indoles (12) by a one-pot reaction of pyranoindolones with substituted o-phenylenediamines or 2,3-diaminopyridines is described. In the case of 2,3-diaminopyridines the reaction proceeds regioselectively affording only regioisomers 12. Structural assignments of the new compounds as well as complete assignment of ¹H and ¹³C NMR signals were based on the analysis of their ¹H and ¹³C NMR (1D and 2D), IR, MS and elemental analysis data. Plausible mechanisms are proposed.