Partial Difference Sets with Paley Parameters

Partial difference sets with parameters (,k,,µ) = (,(– 1)/2, ( – 5)/4,( – 1)/4) are called Paleypartial difference sets. By using finite local rings, we constructa family of Paley PDSs for abelian p-groups with any given exponent.Furthermore, we prove some non-existence results on Paley PDSs.Using these results, we prove that Paley PDSs exist in a rank2 abelian group if and only if the group is isomorphic to Z_p^r x Z_{p ^r} where p is an odd prime.     

Development of electrochemical processes for nitrene generation and transfer

An electrochemical strategy for running nitrogen-transfer reactions on chemically inert anode surfaces has been developed. The generation and trapping of highly reactive nitrene-transfer reagents can be accomplished under mild conditions on platinum electrodes. The key factor that accounts for the high levels of chemoselectivity in this process is the phenomenon of overpotential. We have found that molecules that are similar in terms of propensity toward oxidation can be differentiated on the basis of their affinity to a given electrode surface. Thereby, reactive species can be selectively generated in the presence of acceptor molecules of interest. Specifically, a wide range of structurally dissimilar olefins can be transformed into the corresponding aziridines in the presence of N-aminophthalimide. Likewise, nitrene generation in the presence of sulfoxides leads to their chemoselective transformation into the corresponding sulfoximines. In this paper we discuss the underlying mechanistic foundation of these reactions.     

195Pt-NMR. Spectroscopy. The direct measurement of the values 1J (195Pt, 14N) and chemical shift data for the complexes trans-[PtCl2(C2H4) (substituted pyridine)]

The values ⁿJ (¹⁹⁵Pt, ¹⁴N) are shown to be measurable directly from the ¹⁹⁵Pt spectrum for a variety of complexes containing nitrogen ligands. The sample temperature can play an important role in determining the width of the ¹⁹⁵Pt signal. ¹⁹⁵Pt chemical shifts for the complexes trans-[PtCl₂(C₂H₄) (substituted pyridine)] have been measured. Methyl substitution at the 2- and 6-positions produces a relatively large downfield shift.     

Negative ion atmospheric pressure ionization mass spectrometry: Ionization of aromatic hydrocarbons

A corona discharge atmospheric pressure ionization source generates the reagent ions, OH^? and O^? ions in addition to better known O₂^? ions, when ambient air is used as the carrier. All three ions are gas-phase bases that could form negative ions from organics via proton abstraction. Ionization of simple aromatic hydrocarbons by O₂^? is thermodynamically not feasible. Simple aromatic hydrocarbons are ionized only by O^? and/or OH^? to form [M ? H]^? ions. However, [M ? H]^? ions do not appear in the mass spectrum as they undergo stabilization via clustering with predominantly oxygen atoms.     

Multiply charged ions in ionspray tandem mass spectrometry

Multiply charged anions of some 30 species containing multiple carboxylic, sulphonic and/or phosphoric groups generated by ionspray were studied by using tandem mass spectrometry (MS/MS). Two trends emerged: (1) lower-charged ions are preferentially evaporated, and (2) for more highly charged ions, evaporability is a function of ion size. Triply and quadruply charged ions were observed for azo dyes with molecular masses in the 700-900 Dalton range. Daughter-ion mass spectra of selected multiply charged ions are presented.     

Diethylaminosulfur trifluoride-mediated intramolecular cyclization of 2-hydroxycycloalkylureas to fused bicyclic aminooxazoline compounds and evaluation of their biochemical activity against β-secretase-1 (BACE-1)

A series of unique bicyclic aminooxazolines were synthesized and found to exhibit micromolar inhibition of β-secretase-1 (BACE-1). The aminooxazolines were procured by an intramolecular diethylaminosulfur trifluoride (DAST)-mediated ring closure of a benzylic urea onto a secondary alcohol.