Structure elucidation with lanthanide-induced shifts 5. Evaluation of the binding ability of various functional groups

The equilibrium binding constants have been evaluated for the association in CCl₄ of the lanthanide shift reagent. Eu(fod)₃, with a series of adamantane derivatives containing a variety of different functional groups. It is shown that if steric effects are held constant the binding abilities of the adamantane derivatives exhibit a good correlation with the proton affinities of the methyl analogs containing the same functional groups. The results permit the prediction of binding strength of other functional groups with Eu(dpm)₃ as well as with Eu(fod)₃ and thus can be of great assistance in planning and interpreting the results of experiments with lanthanide shift reagents.Part 4:D. J. Raber, M. D. Johnston, jr., C. M. Campbell, C. M. Janks, andP. Sutton, Org. Mag. Res.11, 323 (1978).     

Structure determination of mycolactone C via total synthesis

[structure: see text] By total synthesis, mycolactone C has been established as an approximately 1:1 mixture of Z-Delta4'5'- and E-Delta4'5'-geometric isomers of C12'-deoxymycolactones A and B.     

Synthesis and structure of ditetrabutylammonium tetrachlorodioxoneptunium(VI)

The reaction of a stock solution of NpO₂² + in 2 M HCl with two equivalents of tetrabutylammonium chloride in 6 M HCl results in the preparation of the title compound. This compound, [NBu₄]₂[NpO₂Cl₄], is isostructural with the uranium analogue, [NBu₄]₂[UO₂Cl₄]. The anion of the complex, [NpO₂Cl₄]²–, adopts a pseudooctahedral geometry common to six-coordinate actinyl complexes in which the neptunium metal is coordinated by two trans axial oxo groups with NpO(oxo) bond lengths of 1.733(5)Å, and four equatorial chloride ligands with Np–Cl bond lengths in the range 2.637(2)–2.676(2)Å. The neptunyl ONpO bond angle is 178.6(3)°. Charge balance of the neptunyl tetrachloride anion is maintained by two tetrabutylammonium cations. This complex crystallizes in the monoclinic space group P2₁/n (a = 15.416(4), b = 15.362(4), c = 18.479(5)Å, = 108.147(6)°, V = 4158.4(19)ų, Z = 4).     

The Dirichlet problem on quadratic surfaces

We give a fast, exact algorithm for solving Dirichlet problems with polynomial boundary functions on quadratic surfaces in such as ellipsoids, elliptic cylinders, and paraboloids. To produce this algorithm, first we show that every polynomial in can be uniquely written as the sum of a harmonic function and a polynomial multiple of a quadratic function, thus extending a theorem of Ernst Fischer. We then use this decomposition to reduce the Dirichlet problem to a manageable system of linear equations. The algorithm requires differentiation of the boundary function, but no integration. We also show that the polynomial solution produced by our algorithm is the unique polynomial solution, even on unbounded domains such as elliptic cylinders and paraboloids.

     

Therelationship between professional operatic soprano voice and high range spectral energy

Operatic sopranos need to be audible over an orchestra yet they are not considered to possess a singer's formant. As in other voice types, some singers are more successful than others at being heard and so this work investigated the frequency range of the singer's formant between 2000 and 4000 Hz to consider the question of extra energy in this range. Such energy would give an advantage over an orchestra, so the aims were to ascertain what levels of excess energy there might be and look at any relationship between extra energy levels and performance level. The voices of six operatic sopranos (national and international standard) were recorded performing vowel and song tasks and subsequently analyzed acoustically. Measures taken from vowel data were compared with song task data to assess the consistency of the approaches. Comparisons were also made with regard to two conditions of intended projection (maximal and comfortable), two song tasks (anthem and aria), two recording environments (studio and anechoic room), and between subjects. Ranking the singers from highest energy result to lowest showed the consistency of the results from both vowel and song methods and correlated reasonably well with the performance level of the subjects. The use of formant tuning is considered and examined.     

Novel imprinted soluble microgels with hydrolytic catalytic activity

The synthesis and kinetic characterisation of soluble imprinted acrylamide based microgels incorporating arginine and tyrosine derivatives as additional functional monomers is reported.     

Porphyrin-acetylene-thiophene polymer wires

5,15-Bis[acetylene-4-(ethylenedioxy)thiophene]-10,20-bis(4-carboxyphenyl)porphyrin was synthesized by a Sonogashira coupling and polymerized to fibres; TEM and AFM images show uniform porphyrin wires with a length of several micrometers and a thickness of less than 4 nm.     

Development of an accelerated low-pH reversed-phase liquid chromatography column stability test

The important experimental design criteria for an accelerated low-pH RPLC column stability test are discussed. The influence of method variables on the amount and rate of retention-loss and the final optimized parameters for the accelerated low-pH RPLC stability test are presented. The retention-loss curves for selected C8 and C18 stationary phases are compared. These studies indicate that ligand chain length, functionality and bonding density play an important role in determining the low-pH stability of a stationary phase. Additionally, elemental analysis data are used to infer the mechanism responsible for the observed retention-loss under low-pH conditions.