Nematicidal effects of cysteine proteinases against sedentary plant parasitic nematodes

Cysteine proteinases from the fruit and latex of plants, such as papaya, pineapple and fig, have previously been shown to have substantial anthelmintic efficacy, in vitro and in vivo, against a range of animal parasitic nematodes. In this paper, we describe the in vitro effects of these plant extracts against 2 sedentary plant parasitic nematodes of the genera Meloidogyne and Globodera. All the plant extracts examined caused digestion of the cuticle and decreased the activity of the tested nematodes. The specific inhibitor of cysteine proteinases, E-64, blocked this activity completely, indicating that it was essentially mediated by cysteine proteinases. In vitro, plant cysteine proteinases are active against second-stage juveniles of M. incognita and M. javanica, and some cysteine proteinases also affect the second-stage juveniles of Globodera rostochiensis. It is not known yet whether these plant extracts will interfere with, or prevent invasion of, host plants

Nanorheology of polymers

When polymers are confined in a narrow gap to a thickness comparable to the size of the molecule, new dynamic behavior emerges. The effective shear moduli are enhanced compared with the bulk, relaxation times are prolonged and nonlinear responses set in at lower shear rates. Key experimental findings discussed include static surface forces, linear shear dynamic moduli and nonlinear shear dynamic moduli, with special attention given to polymer melts and tethered block copolymers. Future areas of opportunity in this field are emphasized

NANORHEOLOGY OF CONFINED POLYMER MELTS .3. WEAKLY ADSORBING SURFACES

Polymer melts confined between weakly adsorbing surfaces terminated with methyl groups (close-packed self-assembled monolayers of condensed octadecyltriethoxysilane, OTE) were studied in regard to surface forces (static forces to compress the polymer films to a given thickness) and shear rheology. The experiments involved a surface forces apparatus modified for dynamic mechanical shear oscillation. The polymers were an atactic poly(phenylmethylsiloxane), PPMS, with chain length from 31 to 153 skeletal bonds. Three principal conclusions emerged. First, the equilibrated surface force between OTE was zero down to the same small thickness (17 +/- 2 Angstrom) regardless of molecular weight. This decisively confirms theoretical predictions for the surface forces of polymer chains in equilibrium with a bulk reservoir. Second, enhanced effective shear moduli (measured in the Linear-response regime) were observed only at this thickness of measurable surface force. This accompaniment of surface force and enhanced shear modulus was also seen in the case of strong adsorption. But in that case, these phenomena scaled with the molecular size of the polymer, approximately its radius of gyration (R(G)); here these phenomena appeared at a single film thickness. Third, the effective elastic shear modulus G' under confinement was rubberlike in magnitude, indicating enormously slower relaxation than in the bulk fluid. This relaxation was slower, the higher the polymer molecular weight. This third conclusion is qualitatively similar to the case for these same PPMS polymers confined between strongly adsorbing surfaces. It suggests that, even in the case of weak adsorption, geometrical confinement enhances entanglement interactions between polymer chains

SELF-ASSEMBLED MONOLAYERS ON MICA FOR EXPERIMENTS UTILIZING THE SURFACE FORCES APPARATUS

Strongly bound, closely packed self-assembled monolayers of condensed alkyltriethoxysilanes were formed on mica and other substrates with a packing density of about 20 Angstrom(2)/molecule. Techniques to exploit these monolayers in the surface forces apparatus (SFA) are described. The length of the alkyl chain of the amphiphiles was 18 carbons (methyl functionality at the terminus) or 20 and 22 carbons (vinyl functionality at the terminus). The thickness of both monolayers, determined independently by ellipsometry and by in situ SFA measurement, was consistent with models in which the alkyl chains were directed away from the surface in all-trans conformations. The average tilt angle of the alkyl chains, determined by Fourier transform infrared spectroscopy, was 13 +/- 5 degrees from the surface normal. The surface energies of the monolayers, determined by in situ SFA measurement of the pull-off forces and contact-area diameters, agreed with independent estimates from contact angle measurements. The monolayer surfaces were of a high degree of smoothness: when undecane (C11H24) fluid was confined between the surfaces, oscillatory force-distance profiles were measured over a range of liquid thickness similar to that over which oscillatory forces were measured between unmodified mica surfaces. The amount of water in the hydrolysis solutions greatly affected the ability to self-assemble as a tightly-bound monolayer, and the optimal water concentration was determined. All monolayers were resistant to attack by nonpolar solvents. The vinyl-terminated species could be chemically converted to the hydroxyl form, thereby creating a polar surface without apparent change in the organization of the monolayer

STICK TO SLIP TRANSITION AND ADHESION OF LUBRICATED SURFACES IN MOVING CONTACT

The friction of dry self-assembled monolayers, chemically attached to a solid surface and comprising a well-defined interface for sliding, is compared to the case of two solids separated by an ultrathin confined liquid. The monolayers were condensed octadecyltriethoxysilane (OTE). The liquid was squalane (C30H62), a film 2.0 nm thick confined between parallel plates of mica. The method of measurement was a surface forces apparatus, modified for oscillatory shear. The principal observations were the same in both cases: (1) Predominantly elastic behavior in the linear response state was followed by a discontinuous transition to a mostly dissipative state at larger deformations. The elastic energy stored at the transition was low, of the order of 0.1 kT per molecule. This transition was exactly repeatable in repetitive cycles of oscillation and reversible with pronounced hysteresis. (2) The dissipative stress in the sliding state was almost independent of peak sliding velocity when this was changed over several decades. Significant (although smaller) elastic stress also persisted, which decreased with increasing deflection amplitude but was almost independent of oscillation frequency. (3) The adhesive energy in the sliding state was significantly reduced from that measured at rest. This similarity of friction in the two systems, dry and wet sliding, leads us to speculate that, similar to plastic deformation of solids, sliding in the confined liquid films is the result of slippage along an interface

STRUCTURE OF CONFINED ALKANE LIQUIDS

Polymer integral equation theory is employed to calculate structural properties of undecane and short polymer liquids confined between Parallel plates. A strong dependence is found on the strength of fluid-surface interactions which is consistent with solvation force measurements using both strongly attractive mica and weakly repulsive hydrocarbon surfaces