Synthesis and Metal Complexes of Thiourea Ligands Containing Carbohydrate‐Derived Substituents

Two glucose‐derived thiourea derivatives, 2a and 2b , were prepared by addition of the corresponding amino sugars to a solution of 4‐nitrobenzoyl isothiocyanate (Scheme 1). The thioureas were isolated as colorless solids in good yields and were fully characterized by NMR spectroscopy, optical rotation, elemental analysis, and also by single‐crystal X‐ray diffraction. Attempts to obtain Cu^II and Ni^II bis(chelate) complexes with these thioureas failed. However, the C(1)‐protected thiourea derivative 2a reacted with orthopalladated acetato‐bridged dimers to afford the corresponding monomeric Pd^II complexes 3 and 4 (Scheme 2). In these compounds, the thiourea coordinates to the metal as monoanionic O,S chelate ligand, which was confirmed by X‐ray crystallography.     

On the convergence of kernel estimators of probability density functions

Summary The properties of the characteristic function of the fixed-bandwidth kernel estimator of a probability density function are used to derive estimates of the rate of almost sure convergence of such estimators in a family of Hilbert spaces. The convergence of these estimators in a reproducing-kernel Hilbert space is used to prove the uniform convergence of variable-bandwidth estimators. An algorithm employing the fast Fourier transform and heuristic estimates of the optimal bandwidth is presented, and numerical experiments using four density functions are described. This research was supported by the United States Air Force, Air Force Office of Scientific Research, Under Grant Number AFOSR-76-2711.     

Electron paramagnetic resonance and scanning tunneling microscopy investigations on the formation of F(+) and F(0) Color centers on the surface of thin MgO(001) films

The formation of surface color centers (F(S) centers) by electron bombardment of thin MgO(001) films is investigated using electron paramagnetic resonance and low-temperature scanning tunneling microscopy. At low electron doses both techniques indicate the formation of singly occupied color centers (F(S)(+)), whereas at high electron doses the doubly occupied type (F(S)(0)) is dominant. It is suggested that with increasing electron dose F(S)(+) centers are transformed into F(S)(0). Tunneling spectra of individual F(S)(0) centers reveal a large distribution of energetic positions of occupied and unoccupied states, which is caused by local variations of the coordination number of the defects and explains the broad signals usually detected with integrating spectroscopic techniques.     

A measurement of polarization in π−p→ K°Λ° at 5 GeV/c

We have measured the Λ° polarization in π^?p→ K°Λ° at 5 GeV/c, using a data sample of 3709 events. The polarization is positive for small t, passes through zero near t = ?0.3 (GeV/c)², and becomes large and negative at larger t, consistent with a value of ?1.0 for t between ?0.7 and ?1.6(GeV/c)².     

Properties of low-lying levels of59Co

Levels up to 3,016 keV in⁵⁹Co were studied using the⁵⁹Co (p, p′y) and⁵⁶Fe (α, py) reactions. Level energies, branching ratios, mean lifetimes and spins were obtained for a number of levels.