FLUORESCENCE SPECTRA IN LUNG WITH PORPHYRIN INJECTION

The fluorescence emission spectra from human bronchial mucosa and tumors, before and after injection of dihematoporphyrin ether/ester, have been measured with an optical multichannel analyzer from 500 to 750 nm. Fluorescence was excited with a violet krypton ion laser (average wavelength 410 nm). The autofluorescence spectra decrease monotonically with increasing wavelength except for a small broad peak near 600 nm. The spectra from tumor sites, after injection of the fluorescent porphyrin, exhibit the characteristic fluorescence emission at 630 and 690 nm, added to the autofluorescence spectrum. The spectra from control or nontumor sites are similar but the magnitude of the component due to the injected porphyrin is smaller than at a tumor site. The magnitude ratio of tumor to control site fluorescence depends on concentration of the porphyrin, tumor thickness, and time after injection. Autofluorescence degrades contrast and thus makes very thin tumors difficult to image. Subtraction of the autofluorescence background is desirable.     

On the Computational Complexity of a Rigidity Problem

Consider a structure of flexible joints connected by rigid bars.These bars will constrain the possible motions of the jointsof this structure. By "pinning down" some of the joints so thatthey cannot move further constraints will be added. In thisway the entire structure can be made rigid. A problem consideredby Bolker & Crapo (1977) and others, is that of findingthe minimum number of joints that must be pinned in order tomake a given two- or three-dimensional structure rigid. We considerthe computational complexity of this problem. Lovasz (1980)gives a somewhat complicated but polynomial time procedure forthis problem in the two-dimensional case. In this paper we showthat in three or more dimensions the problem is NP-complete,and so is unlikely to have a polynomial time algorithm.     

Advection-diffusion in reversing and oscillating flows: 2. Flows with multiple reversals

The dispersion of a passive tracer from a continuous point sourcein an estuary is modelled by a two-dimensional advection-diffusionequation with a time-varying, unidirectional velocity. Asymptoticsolutions obtained by Kay (1990, IMA J. Appl. Math., 45, 115–37)for a constant-acceleration flow are generalized to take accountof arbitrary velocity variations, and a new solution is presentedfor the case of rapidly varying acceleration around a time offlow reversal. A procedure for building up the total concentrationdistribution by linear superposition of the various types ofsolution is described. This is applied to the case of an estuarineflow, considered to consist of a constant river flow superimposedon tidal oscillations. Depending on the relative size of thesetwo components, the concentration distribution may include prominentpeaks, with concentrations which are many times higher thanthose in nearby waters. The effect of allowing the diffusioncoefficient to vary proportionally to the flow speed is shownto be small except close to the tracer source.     

An ab initio study of vibrational corrections to the electrical properties of the fluoromethanes: CH3F,CH2F2, CHF3 and CF4

Accurate SCF and MP2 quartic property hypersurfaces have been computed for the energy, dipole moments, quadrupole moments and polarizability tensors of the fluorinated methanes CF₄, CHF₃, CH₂F₂ and CH₃F, to establish accurate values of zero-point vibrational corrections to the properties. Using a consistent set of r_e geometries from density functional theory, these ZPVCs are coupled with accurate electrical properties computed using a range of correlated methods, especially BD and BD(T), and a number of purpose-built polarized basis sets, to obtain near definitive estimates of these properties that incorporate the effects of vibrational averaging. Careful attention has been paid to a critical comparison between these theoretical estimates and experimental measurements, and agreement between the two is shown to be exceptionally good. In particular, it is clear that in many instances more precise experimental results would be required in order to discriminate between different correlated results, or between the present results and those which may be obtained with larger basis sets. The work highlights the necessity to allow for the effects of zero-point vibrational averaging when comparing theory with experiment, or even when comparing different theoretical results with one another using experiment as a benchmark. It also points to the need for further precise experimental measurements of some of these properties.     

RING-OPENING PHOTOREACTIONS OF CYTOSINE AND 5-METHYLCYTOSINE WITH ALIPHATIC ALCOHOLS

Abstract Several reports in the late 1950s and early 1960s indicated that ultraviolet irradiation of dilute solutions of cytosine or 5-methylcytosine in aliphatic alcohols, such as methanol or ethanol, leads to reaction mixtures containing products with an absorption maximum around 300 nm. The present work reports the isolation and characterization of the products responsible for this absorption in the photochemical reactions of cytosine and 5-methylcytosine with methanol, ethanol and 2-propanol at concentrations in the neighborhood of 200 μM. Under these conditions the reactions have been shown, in each nucleobase/alcohol system, to give almost exclusively a single type of primary photopro-duct; each product shows an absorption maximum in the region of 300 nm. Structural analysis showed the products to be alcohol adducts with an ester linkage at C2 of the ring-opened base and an enamine structure at C6. For example, in the case of the reaction of cytosine with methanol, the product is N-carbomethoxy-3-aminoacrylamidine (IIIa). The occurrence of this type of photoreaction suggests a mode by which alcoholic functional groups on amino acid side chains could contribute to photoinduced DNA-protein cross-linking.     

MODULES FOR RELATIVE YANGIANS (FAMILY ALGEBRAS) AND KAZHDAN-LUSZTIG POLYNOMIALS

Let g be a complex simple Lie algebra and let mod U (g) be the category of finite dimensional U (g)-modules. The relative Yangian Y _V (g) with respect to the pair g, V: V ∈ mod U (g) is defined to be the g invariant subalgebra of End V ? U (g) with respect to the natural “diagonal” action. According to recent work (see [12, Sect. 5] and references therein), the finite dimensional simple modules of the Yangians for g?=?sl(n) or the twisted Yangians for g?=?sp(2n), so(n) are described by the simple modules of relative Yangians Y _V (g) : V ∈ mod U (g). Here a classification of the simple modules of a relative Yangian is obtained simply and briefly as an advanced exercise in Frobenius reciprocity inspired by a Bernstein–Gelfand equivalence of categories [2]. An unexpected fact is that the dimension of these modules are determined by the Kazhdan-Lusztig polynomials, and conversely the latter are described in terms of dimensions of certain extension groups associated to finite dimensional modules of relative Yangians.     

Advection-Diffusion in Reversing and Oscillating Flows: 1. The Effect of a Single Reversal

Motivated by the need to understand effluent dispersion in shallowtidal waters, a two-dimensional analysis of advection and diffusionin a reversing flow has been carried out. The flow speed varieslinearly with time, passing through zero at time t=0. A pointsource discharges contaminant into this flow at a steady rate,so that water which is close to the source around the time offlow reversal will become highly contaminated. Thus a peak inthe contaminant concentration field will appear, moving downstreamafter the reversal at a speed close to that of the flow. Thisconcentration peak has certain characteristics similar to acloud of contaminant from an instantaneous discharge at t=0.The solution of the advection-diffusion equation is in the formof an integral of concentration fields due to instantaneousreleases of contaminant at all previous times. At large timesafter the flow reversal, asymptotic analysis yields good approximationsto this integral. The use of Laplace's method is equivalentto ignoring longitudinal diffusion (the boundary-layer approximation);however, the expansion obtained in this way is not uniformlyvalid near the concentration peak, indicating that longitudinaldiffusion plays an important role in the development of thispeak. Uniformly valid expansions are obtained for the concentrationaround the peak, and also around the source where the boundary-layerapproximation always breaks down. Numerical integration hasalso been carried out, the results being used to produce contourplots of concentration for various times either side of theflow reversal.     

PHOTOCHEMISTRY OF MEROCYANINE 540

The photophysical properties of merocyanine 540 have been determined in methanol solution over a modest temperature range. Triplet state population is inefficient (the limiting triplet quantum yield being 0.25) due to rapid isomerization of the central double bond from the first excited singlet state. Activation energies have been measured for isomerization from the excited singlet state (20 kJ mol-1) and for conversion of the resultant cis-isomer back to the original trans-form (63 kJ mol-1), both processes involving formation of a twisted species. The dye is easily oxidized to give an unstable adduct which decomposes on the sub-ms timescale. Reversible redox chemistry occurs upon excitation in the presence of electron acceptors. These various observations are discussed in terms of the known chemotherapeutic activity of MC540 and it is concluded that the most probable mechanisms for cytotoxicity involve either local thermal disruption of cell membranes or in situ photogeneration of toxins derived from breakdown of the dye.