Mixing of non-Newtonian fluids in steadily forced systems

We investigate mixing in a viscoelastic and shear-thinning fluid-a very common combination in polymers and suspensions. We find that competition between elastic and viscous forces generates self-similar mixing, lobe transport, and other characteristics of chaos. The mechanism by which chaos is produced is evaluated both in experiments and in a simple model. We find that chaotic flow is generated by spontaneous oscillations, the magnitude and frequency of which govern the extent of chaos and mixing.     

Periodic knolls and valleys: coexistence of solid and liquid states in granular suspensions

We report the spontaneous emergence of a doubly periodic train of sedimented knolls in a dense suspension. These solidified knolls rise out of, and coexist alongside, a sea of freely flowing liquid in a slowly rotating horizontal bottle. We apply a variable viscosity model that permits simultaneous analysis of fluidlike and solidlike behaviors that are ubiquitous in a variety of sedimenting flows. The model generates qualitative agreement with experiments, and produces new insights into mechanisms by which sedimented structures form.     

No-D NMR (no-deuterium proton NMR) spectroscopy: a simple yet powerful method for analyzing reaction and reagent solutions

[reaction: see text] The title technique is a convenient and powerful method for directly monitoring or assaying any reaction mixture or reagent solution. Examples of some common processes (Fischer esterification, lithiation, butyllithium/THF compatibility, olefin metathesis, and a quantification assay), each interrogated in its native solvent, are presented. The spectral data are easy to acquire, and the information content makes a compelling case for routine use of No-D NMR spectroscopy.     

Supramolecular catalysis at work: diastereoselective synthesis of a molecular bowl with dynamic inner space

The supramolecular assistance to Pd(0)/Cu(I)-catalyzed cyclotrimerization of stannylated norbornene 7 has been investigated to give molecular bowl 1syn in a stereoselective fashion. Following a divergent strategy, racemic norbornene 7 was synthesized in satisfactory yield. Self-coupling, promoted by Pd(0)/Cu(I) catalysis acting in synergy with CsF, yielded molecular bowl 1syn in a moderate 30% yield. The reaction diastereoselectivity is affected by the concentration of Cu(I) and Cs+: increasing quantities of the cations enhanced the syn/anti ratio of the isolated cyclotrimer from statistical (1:3) to a more desirable (4.5:1) ratio, in favor of the molecular bowl 1syn. 1H NMR spectroscopic studies suggested the coordinating affinity of 1syn toward transition metals Cu(I), Ag(I), and Au(I), to account for the observed templation effect. In particular, the tridentate 1syn has been shown to bind to one Ag(I) cation in the assembly process that is driven with enthalpy (Delta H degrees = -19 +/- 2 kcal/mol, Delta S degrees = -45 eu). The complete coordination was not cooperative, and was hypothesized to be impeded with the adverse entropy. Accordingly, density functional theory (BP86) calculations of 1syn and its mono-, bis-, and tris-Ag(I) complexes suggested that the coordination of one to three silver cations is highly exothermic. The calculations also revealed that the bowl constriction is necessary for the aromatic arms to become preorganized and bind to a silver cation(s) (Delta E approximately 8 kcal/mol). Ultimately, Ag(I) has been shown to assist the diastereoselective formation of 1syn, lending support to the notion of template-directed synthesis.     

Patterned and controlled polyelectrolyte fractal growth and aggregations

Two-dimensional patterned and controlled polyelectrolyte aggregations (e.g., tree-like ramified structures) created by microcontact printing have been demonstrated and discussed. Polyelectrolyte-micropatterned aggregations on surfaces were controlled by the micropattern size and shape of PDMS stamps. The formation of aggregates was dependent on the ink and surface conditions, and the aggregates consisted of two distinct layers; strongly adsorbed, primary uniform layers and weakly adsorbed, secondary aggregation layers positioned on top of the primary layers. The adsorption of the primary layers was strong enough not to be washed away, while the aggregated secondary layers were easily removed by washing. The aggregation of secondary layers showed typical tree-like ramified structures of fractal growth and aggregation. Directional and confined stamping led to directing and confining the growth of the fractal polyelectrolyte clusters, respectively. The micropatterned primary uniform layers were not removed by extensive washing, and they were identified by selective nickel plating and charged particle selective adsorption in which the surface formed positive and negative micropatterns. These functional and patterned surfaces have great potentials for advanced devices and sensors.     

Spectroscopic and computational studies of Co2+corrinoids: spectral and electronic properties of the biologically relevant base-on and base-off forms of Co2+cobalamin

Co(2+)cobalmain (Co(2+)Cbl) is implicated in the catalytic cycles of all adenosylcobalamin (AdoCbl)-dependent enzymes, as in each case catalysis is initiated through homolytic cleavage of the cofactor's Co-C bond. The rate of Co-C bond homolysis, while slow for the free cofactor, is accelerated by 12 orders of magnitude when AdoCbl is bound to the protein active site, possibly through enzyme-mediated stabilization of the post-homolysis products. As an essential step toward the elucidation of the mechanism of enzymatic Co-C bond activation, we employed electronic absorption (Abs), magnetic circular dichroism (MCD), and resonance Raman spectroscopies to characterize the electronic excited states of Co(2+)Cbl and Co(2+)cobinamide (Co(2+)Cbi(+), a cobalamin derivative that lacks the nucleotide loop and 5,6-dimethylbenzimazole (DMB) base and instead binds a water molecule in the lower axial position). Although relatively modest differences exist between the Abs spectra of these two Co(2+)corrinoid species, MCD data reveal that substitution of the lower axial ligand gives rise to dramatic changes in the low-energy region where Co(2+)-centered ligand field transitions are expected to occur. Our quantitative analysis of these spectral changes within the framework of time-dependent density functional theory (TD-DFT) calculations indicates that corrin-based pi --> pi transitions, which dominate the Co(2+)corrinoid Abs spectra, are essentially insulated from perturbations of the lower ligand environment. Contrastingly, the Co(2+)-centered ligand field transitions, which are observed here for the first time using MCD spectroscopy, are extremely sensitive to alterations in the Co(2+) ligand environment and thus may serve as excellent reporters of enzyme-induced perturbations of the Co(2+) state. The power of this combined spectroscopic/computational methodology for studying Co(2+)corrinoid/enzyme active site interactions is demonstrated by the dramatic changes in the MCD spectrum as Co(2+)Cbi(+) binds to the adenosyltransferase CobA.     

Design, synthesis, and biological evaluation of platensimycin analogues with varying degrees of molecular complexity

The molecular design, chemical synthesis, and biological evaluation of two distinct series of platensimycin analogues with varying degrees of complexity are described. The first series of compounds probes the biological importance of the benzoic acid subunit of the molecule, while the second series explores the tetracyclic cage domain. The biological data obtained reveal that, while the substituted benzoic acid domain of platensimycin is a highly conserved structural motif within the active compounds with strict functional group requirements, the cage domain of the molecule can tolerate considerable structural modifications without losing biological action. These findings refine our present understanding of the platensimycin pharmacophore and establish certain structure-activity relationships from which the next generation of designed analogues of this new antibiotic may emerge.     

Nanoscratch-induced deformation behaviour in B4C particle reinforced ultrafine grained Al alloy composites: a novel diagnostic approach

We report on the novel application of nanoscratch characterization to provide insight into the plasticity mechanisms responsible for the behaviour of composites. Accordingly, we conduct deformation characterization with nanoscratch testing (DCNT) to study the deformation behaviour of two B₄C reinforced ultrafine grained Al alloy tri-modal composites with average B₄C particle sizes of ~1–6?μm and ~500?nm, respectively. To highlight the type of mechanistic information revealed in a DCNT study of composites, we concentrate on the influence of B₄C particle size on deformation mechanisms.     

RP‐HPLC determination of phenylalkanoids and monoterpenoids in Rhodiola rosea and identification by LC‐ESI‐TOF

An HPLC method permitting the simultaneous determination of fourteen analytes (phenylalkanoids and monoterpenoids) from the roots of Rhodiola rosea was developed. A separation was achieved within 35 min using C₁₈ column material and a water–acetonitrile mobile phase, both containing a 0.05% phosphoric acid gradient system and a temperature of 53°C. The method was validated for linearity, repeatability, limits of detection and limits of quantification. The limits of detection and limits of quantification of 14 phenylalkanoids and monoterpenoids were found to be 0.20–1.0 and 0.5–3.5 µg/mL, respectively. The wavelengths used for quantification of phenylalkanoids and monoterpenoids with a diode array detector were 205, 220 and 251 nm. The method was used to analyze the roots of two species of Rhodiola and commercial extracts of R. rosea and provides preliminary evidence of phytochemical differences between North American and Eurasian populations of R. rosea. LC–mass spectrometry coupled with electrospray ionization (ESI) interface method is described for the identification of phenylalkanoids and monoterpenoids in various Rhodiola samples. This method involved the use of the [M + H]⁺, [M + NH₄]⁺ and [M + Na]⁺ ions in the positive ion mode with extractive ion monitoring (EIM). Copyright © 2009 John Wiley & Sons, Ltd.     

Pharmacokinetics of ICG and HPPH-car for the detection of normal and tumor tissue using fluorescence, near-infrared reflectance imaging: a case study

We present in vivo fluorescent, near-infrared (NIR), reflectance images of indocyanine green (ICG) and carotene-conjugated 2-devinyl-2-(1-hexyloxyethyl) pyropheophorbide (HPPH-car) to discriminate spontaneous canine adenocarcinoma from normal mammary tissue. Following intravenous administration of 1.0 mg kg-1 ICG or 0.3 mg kg-1 HPPH-car into the canine, a 25 mW, 778 nm or 70 mW, 660 nm laser diode beam, expanded by a diverging lens to approximately 4 cm in diameter, illuminated the surface of the mammary tissue. Successfully propagating to the tissue surface, ICG or HPPH-car fluorescence generated from within the tissue was collected by an image-intensified, charge-coupled device camera fitted with an 830 or 710 nm bandpass interference filter. Upon collecting time-dependent fluorescence images at the tissue surface overlying both normal and diseased tissue volumes, and fitting these images to a pharmacokinetic model describing the uptake (wash-in) and release (wash-out) of fluorescent dye, the pharmacokinetics of fluorescent dye was spatially determined. Mapping the fluorescence intensity owing to ICG indicates that the dye acts as a blood pool or blood persistent agent, for the model parameters show no difference in the ICG uptake rates between normal and diseased tissue regions. The wash-out of ICG was delayed for up to 72 h after intravenous injection in tissue volumes associated with disease, because ICG fluorescence was still detected in the diseased tissue 72 h after injection. In contrast, HPPH-car pharmacokinetics illustrated active uptake into diseased tissues, perhaps owing to the overexpression of LDL receptors associated with the malignant cells. HPPH-car fluorescence was not discernable after 24 h. This work illustrates the ability to monitor the pharmacokinetic delivery of NIR fluorescent dyes within tissue volumes as great as 0.5-1 cm from the tissue surface in order to differentiate normal from diseased tissue volumes on the basis of parameters obtained from the pharmacokinetic models.