Isolation and structural characterization of a non-diketopiperazine phytotoxin from a potato pathogenic Streptomyces strain

Two Streptomyces spp. strains responsible for potato common scab infections in Uruguay which do not produce diketopiperazines were identified through whole-genome sequencing, and the virulence factor produced by one of them was isolated and characterized. Phylogenetic analysis showed that both pathogenic strains can be identified as S. niveiscabiei, and the structure of the phytotoxin was elucidated as that of the polyketide desmethylmensacarcin using MS and NMR methods. The metabolite is produced in yields of ～200?mg/L of culture media, induces deep necrotic lesions on potato tubers, stuns root and shoot growth in radish seedlings, and is comparatively more aggressive than thaxtomin A. This is the first time that desmethylmensacarcin, a member of a class of compounds known for their antitumor and antibiotic activity, is associated with phytotoxicity. More importantly, it represents the discovery of a new virulence factor related to potato common scab, an economically-important disease affecting potato production worldwide.     

Relative humidity effects in dip-pen nanolithography of alkanethiol mixtures

In the dip-pen nanolithography of a binary alkanethiol mixture of mercaptohexadecanoic acid (MHA) and 1-octadecanethiol (ODT) at a relative humidity (RH) of less than 80%, two distinct phases of MHA and ODT were patterned. However, on ramping up the RH to greater than 80%, only MHA was observed to pattern. This effect was reversible, as shown by the fact that two distinct thiol regions were again patterned on lowering the RH. This segregation could be exploited for generating exclusive MHA (hydrophilic) templates for subsequent architectures from a mixture of alkanethiols driven solely by the RH.     

Optimum flat-top airfoils in viscous hypersonic flow

The problem of determining the shape of the lower surface of a flat-top airfoil which maximizes the lift-to-drag ratio at hypersonic speeds is considered. The body is assumed to be slender with the flat upper surface parallel to the free-stream direction. The total drag is made up of pressure drag, base drag, and skin-friction drag. The local pressure coefficient used is that of the tangent-wedge approximation; the base pressure coefficient is assumed constant; and the local skin-friction coefficient is that for laminar flow. The extremal problem is solved with the use of the methods of the calculus of variations, and results are obtained by using numerical techniques on the resulting equations. It is seen that the optimum shape is a flat plate followed by a slightly convex shape which is nearly a wedge. The results for these airfoils are compared with those of the optimum wedge and the optimum flat plate-wedge. For all practical purposes, either of the above simple shapes can be used in place of the variational optimum, the latter being the more nearly identical.This research was supported in part by the Air Force Office of Scientific Research, Office of Aerospace Research, US Air Force, Grant No. AF-AFOSR-69-1744.     

On the validity of stochastic rate equations in finite systems with finite-strength interactions

Starting with the Hamiltonian for a linear harmonic chain of 2N particles of massm and one of massM, we have carried out numerical calculations for the momentum autocorrelation function of the mass defect particle for chains with finite numberN of mass points and for nonzero values of the mass ratio=m/M. These results have been compared with the well-known exponential relaxation of the momentum autocorrelation function which is found to be the rigorous result when passing to the thermodynamic and weak-coupling limit. In these limits, the dynamics of the mass defect particle is exactly described by a Fokker-Planck equation, i.e., a stochastic equation of motion. We have shown that, to an excellent approximation, an exponential relaxation of the momentum autocorrelation function is obtained for mass ratios as high as=0.1 and for chains with only 50 particles. Thus, for the harmonic chain considered here, the stochastic equations of motion can be applied to a very good approximation far outside the usually imposed thermodynamic and weak-coupling limits.Supported in part by the Advanced Research Projects Agency of the Department of Defense as monitored by the U.S. Office of Naval Research under Contract N00014-69-A-0200-6018 and by the National Science Foundation under Grant GP28257X.     

Stereoselective synthesis of myo-inositol via ring-closing metathesis: a building block for glycosylphosphatidylinositol (GPI) anchor synthesis

Here we report a concise stereoselective synthesis of myo-inositol via ring-closing metathesis. A readily available bis-Weinreb amide of D-tartrate served as a key intermediate. [reaction: see text]     

Synthetic studies of polyene macrolides,synthesis of a C29–37 fragment for amphotericin B and nystatin

An enantioselective synthesis of a C29–37 fragment common to both amphotericin B $\text{1}$ and nystatin $\text{2}$ is described from ethyl 3(S)-hydroxybutanote.     

Estimation of states and parameters in continuous non-linear systems with discrete observations

We consider a class of continuous non-linear systems defined by the ordinary differential equation x = f(x, t) + g(x, t)u, where u is an unknown input representing noise or disturbances. The object is to estimate states and parameters in these systems by means of a fixed number of discrete observations y_i = h(x(t_i), t_i) + v_i, 1 ? i ? m, where the v_i represents unknown errors in the measurements y_i. No statistical assumptions are made concerning the nature of the unknown input u or the unknown measurement errors v_i. A weighted least squares criterion is defined as a measure of the optimal estimate. A result concerning the existence of solutions of the differential equation which minimize the criterion is presented. The necessary conditions for an optimal estimate, a set of Euler-Lagrange equations and multi-point discontinuous non-linear boundary conditions, are given. The multi-point problem is converted to an equivalent continuous two-point boundary value problem of larger dimension in the case in which the observations are assumed to be linear functions of the state. A pair of equivalent quasilinearization algorithms is defined for the two-point system and the multi-point system. Quadratic convergence for these algorithms is proved.