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In this work, the break-up dynamics of a single, Newtonian droplet dispersed in an immiscible Newtonian matrix undergoing a controlled mixture of shear and extensional flow is investigated using a homemade eccentric cylinder device. Hereto, different representative supercritical flows with varying shear/elongation balance have been applied. The effect of viscosity ratio is explored using droplets with a viscosity ratio of 0.1 and 1.3, respectively. In all cases, break-up is observed to proceed through an “end-pinching” mechanism. The experimentally obtained break-up times have been compared with scaling relations known from literature for simple shear and purely extensional flow. It is found that the global break-up dynamics is still shear dominated, even for conditions where the elongational contribution comprises a substantial amount (up to 30% on average) of the mixed flow.

The methanolic extract from the leaves of the Vietnamese medicinal plant Maesa balansae showed potent in vitro and in vivo activity against the tropical protozoal parasite Leishmania infantum. Bioassay-guided purification of the extract led to the identification of six triterpenoid saponins, maesabalides I−VI (1−6), each having a strong and specific anti-leishmanial activity. Maesabalide III (3) and IV (4) were the most potent with IC50 values against intracellular amastigotes of about 7 and 14 ng/mL. In comparison, the IC50 value of sodium stibogluconate, the reference drug for treatment of leishmaniasis, is only 5.6 μg/mL. No cytotoxicity was present on a human fibroblast (MRC-5) cell line (CC50 > 32μg/mL). In vivo evaluation in the BALB/C mouse model demonstrated that >90% reduction of liver amastigote burdens was obtained 1 week after a single subcutaneous dose at 0.2−0.4 mg/kg was administered. Several chemical derivatives of maesabalides I−VI were prepared in order to study the structure−activity relationship.

A rheo-optical methodology, based on small angle light scattering and transmitted light intensity measurements, has been used to study in situ and on a time resolved basis the shear induced morphology in ternary two-phase water-gelatin−dextran mixtures. Emulsions close to the binodal line as well as far from it have been investigated. It is shown that above a critical shear rate, shear-induced mixing occurs at the length scales probed by the laser light. It is hypothesized that the shear-induced homogenization is due to the shear forces that exceed the intermolecular forces of the self-association process of the gelatin. The isothermal phase diagram at a fixed shear rate has been determined. In addition, the structure evolution after cessation of flow has been studied. When flow is stopped after homogenization, phase separation occurs almost instantaneously. When subsequently applying a low shear rate, the structure coarsens due to coalescence of the dispersed droplets. The kinetics of this coalescence process is strain controlled.

Daphnane orthoesters are the active ingredients of plant remedies from the Western, Chinese and African traditional medicine, and have provided important tools to investigate medicinally relevant processes like tumour promotion, apoptosis, neurotrophism, and VR1 activation. The occurrence, biological activity, and molecular pharmacology of these compounds will be reviewed.

Bioassay-guided fractionation of the dichloromethane extracts of the roots and the bark of Zanthoxylum usambarense led to the isolation of two physiologically active compounds, i.e. canthin-6-one 1 (fungicide) and pellitorine 4 (insecticide). Together with oxychelerythrine 2, norchelerythrine 3, (+)-sesamin 5 and (+)-piperitol-3,3-dimethylallyl ether 6, they were isolated for the first time from this plant. Copyright ­© 2002 John Wiley & Sons, Ltd.

Bioassay‐guided fractionation of the dichloromethane extracts of the roots and the bark of Zanthoxylum usambarenseled to the isolation of two physiologically active compounds, i.e. canthin‐6‐one 1(fungicide) and pellitorine 4(insecticide). Together with oxychelerythrine 2, norchelerythrine 3, (+)‐sesamin 5and (+)‐piperitol‐3,3‐dimethylallyl ether 6, they were isolated for the first time from this plant. Copyright ­© 2002 John Wiley & Sons, Ltd.

In emulsions and immiscible polymer blends linear conservative dichroism is known to be very sensitive to flow-induced microstructural changes during flow. The same holds for the excess or interfacial contribution to the first normal stress. Similarities have already been observed between these two properties in blends. Here it is investigated whether this similarity reflects a more quantitative relationship. The interfacial normal stress can be described by means of an interface anisotropy tensor. Therefore, the measured dichroism will be compared with the calculated components of this anisotropy tensor for different flow histories. These include steady-state shear flow, sudden increase in shear rate, relaxation with droplet breakup, and oscillatory flow. In all cases a proportionality factor is obtained. For strongly deformed droplets direct theoretical evidence for a quantitative relationship between rheology and rheo-optics in blends is provided. To extend this relationship to a larger window of shear rates, the size dependence of the scattering has to be taken into account.

Flow small-angle light scattering and linear conservative dichroism are used to follow, in situ and time resolved, the flow-induced changes of the microstructure in viscous emulsions such as immiscible polymer blends. A dilute system consisting of poly(butadiene) droplets dispersed in a poly(isobutene) matrix has been used as a model system. Contrary to earlier rheo-optical work on such materials, the structure has been probed in the plane formed by the flow and the velocity gradient directions. In this manner, shape anisotropy as well as the orientation angle can be monitored continuously for droplet sizes where microscopic observation becomes difficult or even impossible. During steady-state shear flow the size-dependent orientation of the droplets could be detected. It is shown that the various morphological stages caused by a sudden increase in shear rate can be identified and quantified:  droplet deformation and rotation, fibril formation, and development of interfacial instabilities leading to breakup and reorientation of the resulting small droplets. These latter stages result in very characteristic light-scattering patterns. Values for anisotropy and orientation are derived from dichroism and light-scattering data and compared with theoretical results for the case of affine droplet deformation.

Droplet breakup in immiscible polymer blends after a sudden substantial increase in shear rate is studied using small-angle light scattering experiments. During the breakup of the fibrils, secondary streaks are visible in the scattering pattern, which indicate the occurrence of Rayleigh instabilities. A high-resolution camera allows quantitative determination of the evolution of the wavelength of the disturbances during the disintegration process. It is shown that this process is time-controlled rather than strain-controlled as suggested by theory.

Several quinone type compounds were isolated from the hexane, dichloromethane, and ethyl acetate extracts of the roots of Pentas longiflora. The hexane extract afforded two new compounds, [(3α,3‘α,4β,4‘β)-3,3‘]-dimethoxy-cis-[4,4‘-bis(3,4,5,10-tetrahydro-1H-naphtho[2,3-c]pyran)]-5,5‘,10,10‘-tetraone (1) and cis-3,4-dihydroxy-3,4-dihydromollugin (2), together with six known compounds, namely, pentalongin, mollugin, trans-3,4-dihydroxy-3,4-dihydromollugin, methyl-2,3-epoxy-3-prenyl-1,4-naphthoquinone-2-carboxylate, tectoquinone, and 3-hydroxymollugin. From the dichloromethane extract were isolated the three known compounds 3-methoxymollugin, methyl-3-prenyl-1,4-naphthoquinone-2-carboxylate, and scopoletin, while the ethyl acetate extract afforded the known 2-methoxy-3-methylanthraquinone.

A new homoprenylated benzochromene, methyl-5,10-dihydroxy-7-methoxy-3-methyl-3-[4-methyl-3-pentenyl]-3H-benzo[f]chromene-9-carboxylate (1), was isolated from the roots of Pentas bussei, collected from Kenya. The structure of this new compound was determined by spectroscopic data interpretation.

The bioassay-guided fractionation of a dichloromethane extract from the roots of Synaptolepis kirkii using neuronal viability as a model allowed the isolation of the new daphnane orthoester kirkinine (1a) as a powerful neurotrophic constituent.

A new type of tetracyclic naphthoquinone, named isagarin (1), was isolated from the hexane extract of the roots of Pentas longiflora. On the basis of spectral and X-ray diffraction analysis this compound was identified as 1,4-epoxy-4-methyl-1,2,4,5-tetrahydronaphtho[2.3-d]oxepin-6,11-dione.