On the optical activity of paraffinic hydrocarbons

An expression for potential energy as a function of torsion angle about a saturated CC bond is developed analytically. This equation is used in the development of two methods for the conformational analysis of paraffins-one based on consideration only of exactly staggered conformers and one giving consideration to energy at 1° intervals of torsion angle. Two methods of assigning molecular rotations to hydrocarbon conformers are considered. Various combinations of results so obtained are compared as ways to calculate rotations for paraffins.     

Skeletal rearrangements in mass spectra. Part I. Bis-aryl compounds

Examination of a large number of spectra indicates that bis-unsaturated compounds commonly undergo a skeletal rearrangement in which part or all or the bridging moiety is eliminated, often with concomitant loss of hydrogen atoms. The spectra of labeled azobenzene, diphenyl sulfide, and their p,p′-dimethyl derivatives show that scrambling of hydrogen atoms precedes or accompanies such rearrangements, in contrast to the loss of a p-methyl group from the latter derivatives. These results are rationalized in terms of the radical site formed on one unsaturated functional group attacking the polarizable π-electrons of the other unsaturated group.     

Theoretical study of some heterocyclic amines with applications to the chemistry of 9-amino-1,2,3,4-tetrahydroacridine

9-Amino-1,2,3,4-tetrahydroacridine (THA ), a potent cholinesterase inhibitor, was recently used in the treatment of Alzheimer's disease. On attempting to prepare a dihydropyridine ? pyridinium salt-based redox chemical delivery system (CDS ) to enhance brain delivery of THA , several of the practical synthetic challenges were examined by using a theoretical MO approach. The structures, reactivities and stability of THA , derivatives of THA and a model compound, 4-aminopyridine, a simple dibasic heterocyclic amine, were studied in the framework of the AM -1 approximation. The study included the possible protonated forms of THA and 4-aminopyridine. The calculated heats of formation showed that ring nitrogen protonated forms are more stable for both THA and 4-aminopyridine. The calculated heats of formation showed that ring nitrogen protonated forms are more stable for both THA and 4-aminopyridine, consistent with experimental results. Electron delocalization is responsible for the remarkable stability of these molecules and for the observed lack of reactivity of the amino group, both in the basic and protonated forms. The site of N-alkylation of the 9-nicotinamide derivative of THA (an intermediate in the synthesis of THA -CDS ) is controlled by electronic, thermodynamic, and steric factors.     

Development of a formulation of Pirodavir using 2-hydroxypropyl-β-cyclodextrin

Pirodavir, 4-[2-[1-(6-Methyl-3-pyridazinyl)-4-piperidinyl]ethoxy]benzoic acid ethyl ester, is an antiviral compound which has low aqueous solubility (<0.01 mg/ml). The compound is a weak base (pKa 5.8) with high lipophicity (logP 4.44). Ionization of the compound increases the solubility in acidic medium to 2.3 mg/ml at pH 2.4. However, a low pH is not acceptable for nasal application as this would induce irritation. Extensive solubility studies were performed using different types of substituted cyclodextrins in order to select an appropriate derivate capable of increasing solubility to an acceptable level for formulations for nasal application. Aqueous solubility of pirodavir increased in a linear fashion with increasing concentration of most of the substituted cyclodextrins. However, using 2-hydropropyl-β-cyclodextrin (HPBCD) the solubility increased in a non-linear fashion. Based on these studies HPBCD was selected as the most appropriate excipient. To support a clinical study on the treatment of rhinovirus cold by intranasal Pirodavir formulations were developed containing up to 5 mg/ml of pirodavir and up to 10% of HPBCD. Stability of the formulations was studied and found to be acceptable.     

A characterization of subgroup containment in direct products

Using Goursat??s characterization of subgroups in a direct product, a characterization of subgroup containment in such a direct product is given. Applying this along with facts about p-groups we describe a process for obtaining the subgroup lattice of a direct product of p-groups. This process is implemented to portray the subgroup lattice of Q × Q, where Q is the quaternion group of order 8.     

Lexicographic products with high reconstruction numbers

The reconstruction number of a graph is the smallest number of vertex-deleted subgraphs needed to uniquely determine the graph up to isomorphism. Bollobás showed that almost all graphs have reconstruction number equal to three. McMullen and Radziszowski published a catalogue of all graphs on at most ten vertices with reconstruction number greater than three. We introduce constructions that generalize the examples identified in their work. In particular, we use lexicographic products of vertex transitive graphs with certain starter graphs from the work of Myrvold and from the work of Harary and Plantholt to generate new infinite families of graphs with high reconstruction numbers. In the process, we settle a question of McMullen and Radziszowski.     

Pattern avoidance for alternating permutations and Young tableaux

We define a class Ln,k of permutations that generalizes alternating (up-down) permutations and give bijective proofs of certain pattern-avoidance results for this class. As a special case of our results, we give bijections between the set A2n(1234) of alternating permutations of length 2n with no four-term increasing subsequence and standard Young tableaux of shape 〈n³〉, and between the set A2n+1(1234) and standard Young tableaux of shape 〈³n−1,2,1〉. This represents the first enumeration of alternating permutations avoiding a pattern of length four. We also extend previous work on doubly-alternating permutations (alternating permutations whose inverses are alternating) to our more general context.The set Ln,k may be viewed as the set of reading words of the standard Young tableaux of a certain skew shape. In the last section of the paper, we expand our study to consider pattern avoidance in the reading words of standard Young tableaux of any skew shape. We show bijectively that the number of standard Young tableaux of shape λ/μ whose reading words avoid 213 is a natural μ-analogue of the Catalan numbers (and in particular does not depend on λ, up to a simple technical condition), and that there are similar results for the patterns 132, 231 and 312.     

Electrophilic fluorination: the aminopyridine dilemma

An unusually high yielding fluorination of aminopyralid (3) using F-TEDA (SELECTFLUOR™) in warm water, followed by kinetic resolution (via iterative esterification/saponification) of the crude fluorination product with dry HCl in methanol produced pure ring-fluorinated pyridine 2 in an overall yield of 31% for the two steps.     

Synthesis and characterization of an amethyrin-uranyl complex displaying aromatic character

Abstract

The reaction between amethyrin and non-aqueous uranyl silylamide (UO₂[N(SiMe₃)₂]₂) under anaerobic conditions affords a bench-stable uranyl complex. UV–vis spectroscopy, cyclic voltammetry, as well as proton NMR spectroscopic analyses provide support for the conclusion that all six pyrrole subunits participate in coordination of the uranyl dication and that, upon complexation, the amethyrin-core undergoes a 2-electron oxidation to yield a formal 22 π-electron aromatic species.     

Evaluation of restricted access media for high-performance liquid chromatographic analysis of sulfonamide antibiotic residues in bovine serum.

Three commercially-available high-performance liquid chromatographic columns packed with restricted access media were evaluated for suitability in multi-residue direct injection analysis at the ng/ml level. The internal surface reversed-phase and shielded hydrophobic phase columns were not sufficiently retentive to separate all analytes from the tail of the matrix peak. Coelution of some of the analytes was also observed with these columns. The semi-permeable surface column was significantly more retentive and selective, providing good separation of analyte and matrix peaks. With this column, an analytical protocol requiring no organic solvents was developed for the assay of six sulfonamides at a detection limit of 25 ng/ml.