Baryon multipole moments in the single quark transition model

It is shown that the predictions of the single quark transition model of the electromagnetic transitions of baryons can be expressed in a highly simplified form by the simultaneous use of multipole moments at the quark level and at the baryon level. The predictions so expressed are applied to the latest ‘world average’ photoproduction amplitudes and an excellent fit is obtained. The model also fits electroproduction amplitudes to within the errors. It is argued that the electromagnetic decays of baryon resonances to dileptons are of particular interest and widths for these processes are estimated.     

Photodissociation spectra and the assignment of low-lying states in butadiene and toluene cations

The photodissociation spectra of gas-phase butadiene and toluene cations are discussed and compared with optical absorption spectra, photoelectron spectra, and theoretical results of both all-valence-electron and π-electron types.     

Reaction of the thiolsulfonate group with the aromatic nucleus: A new ring closure

The double ring closure of N,N-bis[2- (alkyl- or arylsulfonylthio)ethyl]anilines to form 2,3,5,6-tetrahydro[1,4]thiazino[4,3,2-de][1,4]benzothiazines, a new ring system, is reported. The effects of various benzene ring substituents upon the ring closure are described.     

Infrared-enhanced multiphoton dissociation of iodobenzene cations

When gas-phase iodobenzene cations in an ion cyclotron resonance spectrometer are irradiated simultaneously with visible 610 nm and IR 977 cm⁻¹ photons, the visible two-photon process is enhanced by a factor of up to three. The experimental pressure and intensity dependences can be modeled using a set of rate equations for the evolution of the populations of different internal energy levels. Modeling suggests that the major mechanism for the mixed visible/IR process is the absorption of several IR photons, followed by the absorption of one visible photon which brings about dissociation: that the visible photoexcitation cross section decreases with increasing ion internal energy: that IR pumping does not compete successfully with relaxation processes near dissociation threshold: and that the IR radiative relaxation time is constant ≈ 500 ms.     

Partial geometry of dimension three

This paper introduces the concept of a partial geometry of dimension three, extending the concept of an (r, k, t) partial geometry (which may be called of dimension two) due to Bose. An association scheme is defined on this system which is then shown to form a partially balanced incomplete block design based on an association scheme with three associate classes.     

Pole-placement controllers for linear systems with point delays

This paper presents a robust control algorithm for plants involvingboth internal (i.e. in the state) and external (i.e. in theoutput or input) known point delays. Several stabilizing controllerstructures are given and analysed for the case of perfectlymodelled plants with known parameters. The parametrized partsof two of the controller structures involve delays, while thoseof the two remaining controllers are delay-free. However, auxiliarycompensating signals which weight the plant input and outputintegrals are incorporated in all the controller structuresfor stabilization and model matching purposes.     

Computer-aided molecular modeling of a D2-agonist dopamine pharmacophore

Summary Using computer-aided molecular modeling techniques to analyze models recently proposed for the receptor binding sites of dopaminergic agonists, we superimposed the chemical structures of various compounds that mimic the pharmacological behavior of dopamine, as well as inactive enantiomers, on a postulated three-dimensional frame of reference. We analyzed the vector directionalities of the lone pairs of the nitrogen common to these molecules, and the acidic hydrogen of phenols (in aminoindanes, aminotetralins, apomorphines,p-phenol-piperazines, octahydrobenzo(g)quinolines, octahydrobenzo(f)quinolines, and benzazepines) or of nitrogen (in ergoline-type compounds and related structures). This model, when expressed as distances from that of the reference compound pergolide, correlates with the dopaminergic binding affinity observed in compounds previously reported to act on the dopaminergic system in the central nervous system (CNS). The regression analysis of log K_D with respect to the distances of the vectors of the acidic hydrogen support the hypothesis that these compounds bind to the receptor as donors in hydrogen bond formation.     

Tuning the metal-metal bonds in the linear tricobalt compound Co3(dpa)(4)Cl2: bond-stretch and spin-state isomers

Sixteen crystal structures have been determined for the Co3(dpa)(4)Cl2 (1) molecule in the following five crystalline solvates: 1.0.85(C2H5)(2)O.0.15CH2Cl2 (at 120, 213, 296 K); 1.C(4)H(8)O (at 120, 295 K); 1.C(6)H(6) (at 170, 213, 260, 316 K); 1.C(6)H(12) (at 120, 213, 295 K); and 1.1.75C(7)H(8).0.5C(6)H(14) (at 90, 110, 170, 298 K). For 1.0.85(C(2)H(5))(2)O.0.15CH2Cl2 the molecule of 1 is almost symmetrical at 120 K (Co-Co distances of 2.3191(3) and 2.3304(3) A) and remains so at 296 K (2.2320(3) and 2.3667(4) A). For 1.C(4)H(8)O the Co(3) chain is precisely symmetric at both 120 and 295 K though the Co-Co distances increase from 2.3111(4) to 2.3484(4) A as the temperature rises. Compound 1.C(6)H(6) is isomorphous with 1.C(4)H(8)O at 213 and 295 K and has rigorously symmetrical molecules at these two temperatures. Between 213 and 120 K the space group changes from Pccn to P2(1)/c, so that a symmetrical arrangement is no longer required and the two Co-Co distances then differ slightly (by 0.013 A). For 1.C(6)H(6) there is a phase change between 316 K (Pca2(1)) and 260 K (Pna2(1)). At all four temperatures, however, the molecule is almost symmetrical, with the two independent Co-Co distances never differing by more than 0.026 A. 1.1.75C(7)H(8).0.5C(6)H(14) contains, at all temperatures between 90 and 298 K, two crystallographically independent molecules, each of which is distinctly unsymmetrical at 298 K (Co-Co distances of 2.312(2) and 2.442(2) A for one and 2.310(2) and 2.471(2) for the other). In the first of these the distances converge to a much smaller separation (0.056 A) at 90 K while in the second the difference decreases to only 0.006 A at 90 K. Magnetic susceptibility measurements from 1.8 to 350 K indicate in each case that a gradual spin crossover, from a doublet to a quartet state, occurs over this temperature range.     

A molecular approach to flavor synthesis. I. Menthol esters of varying size and polarity

For a series of menthol esters of increasing size and polarity, “mintyness” decreased rapidly as molecular weight increased. For molecular weights above about 700, the compounds were tasteless to a significant proportion of the taste panel. As polarity increased, the “sweet minty” taste of hydrophobic menthol esters became increasingly bitter, until water-soluble menthol esters were strongly bitter. Bitterness was still apparent in quite high-molecular-weight water-soluble esters; a different receptor may be involved for bitterness than for mint. An overall hypothesis relating flavor to molecular solubility parameters is proposed.