Urocanic acid photobiology. Photochemical binding of urocanic acid to bovine serum albumin

Abstract— The photolysis of E-[ring-2-¹⁴C]urocanic acid with bovine serum albumin (BSA) leads to incorporation of radiolabel into the protein. Levels up to 68 nmol mg^?1 BSA have been observed if the irradiation is carried out in an inert atmosphere. Oxygen reduces the level slightly. It appears from gel-filtration chromatography that the label incorporation is covalent in nature.     

Nonempirical SCF-LCAO-MO calculations for (CH)+

Nonempirical molecular orbital calculations, using a minimal basis set of Slater-type atomic orbitals, are reported for the ground state of the (CH)⁺ ion. The C-H bond length calculated using optimized exponents is in excellent agreement with the experimental value, whereas the distances predicted using the conventional free atom exponents are too large by up to 17%.     

Confirmation of the currently accepted value 299 792 458 metres per second for the speed of light

The speed of light has been determined from a completely independent measurement of the wavelength and frequency of the CH₄-stabilized He-Ne laser. The wavelength is 3 392 231.40 ± 0.02 pm, the frequency 88 376 181.57 ± 0.20 MHz, and the speed of light 299 792 458.1 ± 1.9 m/s.     

Trapping of the tribromomethylanion by electron poor alkenes

α-Bromoacrylates, α-bromoacrylonitrile and diethyl alkylidenemalonates all react with bromoform and base under phase transfer conditions to give dibromocycloprapanes. When γ-bromine is present in a crotonate or an alkylidenemalonate, the intermediate derived by Michael addition of tribromomethylanion is trapped by cyclisation at that position to produce a (tribromomethyl)cyclopropane.     

Dependence of the primary normal-stress difference coefficient on molecular weight for concentrated solutions of rodlike molecules

Summary The primary normal-stress difference has been measured for concentrated solutions of rodlike and flexible chain polyamides. The solutions studied here consist of poly-p-phenyleneterephthalamide (PPT) which is believed to be rodlike in 100% H₂SO₄ and the flexible chain polyamide, polyhexamethylene adipamide (nylon 6.6), which is also dissolved in 100% sulfuric acid. For the PPT solutions the primary normal-stress difference coefficient in the limit of zero shear rate ( ₁(0)) is observed to be proportional toM _w ^12.9 whereM _w is the weight average molecular weight. For concentrated solutions of nylon 6.6, ₁(0) is found to be proportional toM _w ^7.6 which is in reasonable agreement with values reported for other flexible chain polymers. These data point out that there are some interesting differences in the primary normal stress differences for rodlike and flexible chain polymers and at the same time provide support of the recent theoretical predictions ofDoi andEdwards for concentrated solutions of entangled rodlike molecules.

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Zusammenfassung Es wurde die erste Normalspannungsdifferenz an konzentrierten Lösungen von stäbchenförmigen und flexiblen kettenförmigen Polyamiden bestimmt. Die untersuchten Lösungen bestehen aus Poly-p-Phenylenterephthalamid (PPT), bei dem man eine stäbchenförmige Konfiguration annimmt, bzw. aus Polyhexamethylenadipamid (Nylon 6.6), welches als flexibles Kettenmolekül gelöst ist, beide in 100%iger Schwefelsäure. Bei den PPT-Lösungen findet man für den ersten Normalspannungs-Koeffizienten in der Grenze verschwindender Schergeschwindigkeit ( ₁ (0)) eine Proportionalität mitM _w ^12,9 , woM _w das Gewichtsmittel des Molekulargewichts darstellt. Bei konzentrierten Lösungen von Nylon 6.6 findet man dagegen for ₁(0) Proportionalität mitM _w ^7,6 , was in vernünftiger Übereinstimmung mit den Ergebnissen anderer Autoren bei verschiedenen flexiblen Kettenmolekülen ist. Diese Ergebnisse zeigen, daß zwischen der ersten Normalspannungsdifferenz von stäbchenförmigen und flexiblen kettenförmigen Polymeren interessante Unterschiede bestehen, und stützen zugleich die neuerlichen theoretischen Voraussagen vonDoi undEdwards bezüglich konzentrierter Lösungen ineinander verhängter stäbchenförmiger Moleküle.

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With 3 figures and 2 tables     

First results of electron cooling experiments at LEAR

The first results are presented of electron cooling experiments in the Low-Energy Antiproton Ring (LEAR) at CERN, performed with a proton beam of about 50 and 21 MeV. The number of stored protons ranged from 10⁷ to 3 × 10⁹. Cooling times of the order 1 s and proton drag rates of up to 0.7 MeV/s were obtained. The capture of cooling electrons by protons producing hydrogen atoms was used to derive an effective electron temperature (0.25 eV). From the angular profile of the neutral hydrogen beam an upper limit of 3π mm.mrad could be deduced for the horizontal equilibrium proton-beam emittance. The lowest equilibrium momentum spread was 2 × 10⁵ (FWHM), as derived from the analysis of the longitudinal Schottky signal. This Schottky signal exhibited an unusual behaviour with beam intensity and under certain conditions showed a doublepeak structure which was associated with collective beam noise. For very cold beams transverse instabilities were observed, which resulted in a rapid spill-off of protons and a stabilization at lower intensities. The threshold of these instabilities was raised by heating the proton or the electron beam. The cooling of a bunched proton beam was investigated. The reduction of the proton momentum spread led to bunch lengths of about 2 m, containing 3 × 10⁸ protons.     

Diffraction characteristics of planar absorption gratings

Planar (co)sinusoidal conductivity (absorption) transmission gratings are analyzed using rigorous coupled-wave theory. The first-order and higher-order diffraction efficiencies are determined over the entire range of possible conductivities and Bragg angles of incidence (or equivalently, grating periods) for H-mode polarization incident plane waves. The maximum possible first diffracted order efficiency is found to be 5.26%. Rigorous results are compared to approximate results from the Raman-Nath theory and the two-wave first-order coupled-wave (Kogelnik) theory. A regime parameter, , is defined which delineates the regions of Raman-Nath diffraction behavior ( < 1) and the region of two-wave first-order diffraction theory behavior ( > 1). Likewise, the angular selectivity characteristics of conductivity gratings are determined from rigorous theory and are compared with corresponding results from approximate theory.     

Use of phosphoimidazolide-activated guanosine to investigate the nucleophilicity of spermine and spermidine.

Guanosine 5'-phosphate 2-methylimidazolide (2-MeImpG), a labile phosphoimidazolide analog of guanosine triphosphate, was used to test the reactivity of the natural polyamines (PAs), spermine (spm) and spermidine (spd). The products are the guanosine 5'-phosphate-polyamine derivatives (PA-pG: spd-pG and spm-pG) which are quite stable in the range 4 < pH < 11. Our study is the first of which we are aware that reports on the nucleophilicity of these amines. The main findings are as follows. (i) HPLC analysis of the products indicates the formation of only two of the three possible spd products and only one of the two possible spm products. These results can be explained if only the primary amino groups of the two polyamines are reactive, while the secondary amino groups are rendered unreactive by a steric effect. The reactions of 2-MeImpG and other phosphoimidazolide derivatives of nucleosides (ImpNs) with primary and secondary monoamines support this interpretation (Kanavarioti et al. J. Org. Chem. 1995, 60, 632). (ii) The product ratio of the two spd-pG adducts derived from the primary amino groups varies between 2.40 and 0.71 in the range 6.1 < or equal to pH < or equal to 11.9. Such small variation in the product ratio can only be rationalized by the similar, but not identical, basicity of the two primary amino groups and provides strong support for a previously reported model for polyamine ionization (Onasch et. al. Biophys. Chem. 1984, 19, 245). (iii) On the basis of our kinetic determinations conditions at which the nucleophilicity of these amines is at a minimum and at which other interactions with ImpNs could be tested can be chosen.