Full assignment of the proton and carbon-13 nmr spectra of 2,3,6 -tri-o-methyl-β-cyclodextrin

The proton and carbon-13 NMR spectra of 2,3,6 -tri-O-methyl-β-cyclodextrin in deuteriochloroform have been fully and unambiguously assigned using homonuclear and selective heteronuclear spin decoupling and two-dimensional homo- and heteronudear correlation NMR spectroscopy. Corrections are made to some earlier literature assignments.     

A reversible safety-catch method for the hydrogenolysis of N-benzyl moieties

The benzyl groups of β-hydroxy-N-benzyl sulfonamides are labile toward hydrogenolysis-unlike N-benzyl sulfonamides lacking the β-hydroxy moiety. We find that N-acyl-N-benzyl sulfonamides undergo hydrogenolysis under very mild conditions. Based upon these observations, we developed a reversible safety-catch method using tert-butoxycarbonyl moieties to activate N-benzyl sulfonamides toward hydrogenolysis. We also explored the utility of the safety-catch activation method for other nitrogen-based functionality such as N-benzyl carboxamides, imides, and related functionality.     

Phase transformation in He+ and H+ ion irradiated type 304 stainless steel

γ (fcc)→α (bcc) phase transformation in type 304 stainless steel has been observed after irradiation of He⁺ and H⁺ ions up to fluence levels of 10¹⁷ and 10¹⁹ ions/cm², respectively. Depth selective conversion Mössbauer spectroscopy and surface-sensitive X-ray diffractometry were employed to study the effect of irradiation. It is shown that the amount of the ion induced phase is highly sensitive to the fluence, the ion species and depth from the surface. It is worth noting that H⁺ ion irradiation is rather ineffective in inducing the transformation.     

Stability of a microwave heated fluid Layer

When a time harmonic electromagnetic wave impinges on a slaba certain portion of the wave creates heat within the slab throughdipolar and ohmic heating. The electrical and thermal propertiesof the material dictate the dynamical nature of the heatingprocess, as well as the steady-state temperature profile. Thematerial considered here is a slab of fluid. We consider thecase where the fluid is bounded by thin rigid layers of transparentmaterial. The steady-state heating profile governs the typesof convective motions that can occur and also affects the stabilitycharacteristics of temperature, pressure and velocity perturbationsintroduced in the slab. The main objective here is to examinesuch stability characteristics, initially in the linear regime.Both rigid-rigid and rigid-free configurations are considered.     

Use of a urea and guanidine-HCl-propanol solvent system to purify a growth inhibitory glycopeptide by high-performance liquid chromatography

Reversed-phase high-performance liquid chromatography was used to purify an inhibitory glycopeptide where resolution and recovery were enhanced by using urea or guanidine-HCl-isopropanol-water as a solvent system. Isopropanol alone or other solvent systems that have been proposed for such purification steps were not effective in eluting hydrophobic proteins from the reversed-phase column. The application of the urea or guanidine-HCl solvent systems in the separation and purification of membrane proteins, and other hydrophobic macromolecules, could greatly enhance recovery and efficiency of purification.     

Isotopic oxygen exchange rates between [V18O42]12− and water

Summary From kinetic studies of¹⁸O-exchange between aqueous solutions of K₁₂V₁₈O₄₂ · 16H₂O and water it is concluded that [V₁₈O₄₂]^12– exists as a discrete ion in this medium. The rate of exchange is relatively slow (t_1/2 ca. 6×10⁴s at 0°C) and obeys the McKay equation within the precision obtainable. The sensitivity of the ion to its environment in the solid state, leading to induced exchange, prevented a decision as to whether all oxygens are kinetically equivalent. It is clear, however, that the ions remains intact for long periods in solution in the absence of air.     

Stability of m-matrix products

We investigate various types of stability for powers and products of nonsingular M-matrices. Stability of the matrix powers is categorized according to the length of the longest simple circuit in the digraph of the matrix, while stability of the general products is categorized by the order of the matrices. Additional results are given regarding stability of the Hadamard product of M-matrices and for matrices whose digraph has a longest simple circuit of length two.     

The NP-completeness column: An ongoing guide

This is the fifteenth edition of a quarterly column that covers new developments in the theory of NP-completeness. The presentation is modeled on that used by M. R. Garey and myself in our book “Computers and Intractability: A Guide to the Theory of NP-Completeness,“ W. H. Freeman & Co., New York, 1979 (hereinafter referred to as “[G & J]”; previous columns will be referred to by their dates). A background equivalent to that provided by [G & J] is assumed, and, when appropriate, cross-references will be given to that book and the list of problems (NP-complete and harder) presented there. Readers who have results they would like mentioned (NP-hardness, PSPACE-hardness, polynomial-time-solvability, etc.) or open problems they would like publicized, should send them to David S. Johnson, Room 2C-355, AT & T Bell Laboratories, Murray Hill, NJ 07974 (CSNET address: dsj.btl@csnet-relay). Please include details, or at least sketches, of any new proofs; full papers are preferred. If the results are unpublished, please state explicitly that you would like them to be mentioned in the column. Comments and corrections are also welcome. For more details on the nature of the column and the form of desired submissions, see the December 1981 issue of this Journal.