Effect of hydrostatic pressure on the fluorescence of indole derivatives

Effects of hydrostatic pressure on the fluorescence emission of L-tryptophan, N-acetyl-L-trytophanamide and indole were investigated. An increase in pressure ranging from 1 bar to 2.4 kbar results in reversible red-shifts of the emission of the three fluorophores. The pressure-induced redshift amounts to about 170 cm^–1 at 2.4 kbar, and appears related to changes in Stokes shift of the fluorophores caused by pressure effects on the dielectric constant and/or refractive index of the medium. As the pressure range investigated here is the range commonly used in studies of protein subunit association and/or folding, these observations raise the need for caution in interpreting pressure-induced spectral shifts. The significance of these observations to pressure studies of proteins is illustrated by investigation of pressure effects on human Cu,Zn Superoxide dismutase (SOD) and azurin fromPseudomonas aeruginosa. A reversible 170 cm^–1 red-shift of the emission of SOD was observed upon pressurization to 2.4 kbar. This might be interpreted as pressure-induced conformational changes of the protein. However, further studies using SOD that had been fully unfolded by guanidine hydrochloride, and fluorescence anisotropy measurements indicated that the observed red-shift was likely due to a direct effect of pressure on the fluorescence of the single tryptophan residue of SOD. Similar pressure-induced red-shifts were also observed for the buried tryptophan residue of azurin or for azurin that had been previously denatured by guanidine hydrochloride. These observations further suggest that the effective dielectric constant of the protein matrix is affected by pressure similarly to water.     

Electromagnetic and plasma perturbations induced by radio emission of the EISCAT high-frequency heating facility in the outer ionosphere of the earth

We present the results of measuring the characteristics of electromagnetic and plasma perturbations at the altitudes of the Earth’s outer ionosphere, which were obtained by the onboard equipment of the French microsatellite DEMETER when it passed through the magnetic flux tube based on a region modified by high-power HF radio emission of the EISCAT heating facility. Physical mechanisms which allow one to explain the observed phenomena are considered. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 11, pp. 925–933, November 2008.     

Amphiphilic diblock star polymer catalysts via atom transfer radical polymerization

Diblock star polymers were synthesized via atom transfer radical polymerization from a palladium porphyrin macroinitiator. The arms of the star polymers had an amphiphilic design, with the central Pd-porphyrin surrounded by a relatively hydrophobic block of poly(butyl acrylate) and terminated by a hydrophilic block of poly(oligoethyleneglycol monomethylether monomethacrylate). The size of both the interior and exterior blocks of the polymer arms were tuned over a wide range of molecular weights with the exterior block used to solubilize the stars in polar media. The star polymers showed enhanced reactivity in the oxidation of 2-furaldehyde relative to a small molecule porphyrin, suggesting that the polymer backbone aids with catalytic turnover. Oxygen diffusion studies indicate that the polymer backbone shields the porphyrin excited state from oxygen quenching. Shielding is independent of molecular weight and polymer composition, but it is not pronounced enough to retard the rate of singlet oxygen generation under preparative photooxidation conditions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4939–4951, 2006     

Bicalutamide polymorphs I and II

For a complete picture of the phase behavior of a compound exhibiting dimorphism, not only the temperature but also the pressure, the second variable of the Gibbs energy, should be taken into account. Because volume reflects the dependence of the Gibbs energy on pressure, investigating the specific volumes of a compound provides information on its phase behavior under pressure. This can be quantified using the Clapeyron equation, which leads to a so-called topological pressure–temperature phase diagram. Bicalutamide is used as a sample case and with literature data its topological phase diagram has been constructed. Even though the phase relationship between bicalutamide’s two known solid phases is monotropic at ordinary pressure, it becomes enantiotropic at higher pressure. The steep slope of the solid–solid equilibrium in the P–T diagram, 22.5 MPa K^?1, indicates that pressure has virtually no influence on it and that it is mainly entropy driven.     

TDPAD measurements with highly oriented pyrolytic graphite using the19F(p,p′)19F* and19F(α, n)22Na* reactions

The TDPAD technique has been used to investigate quadrupole interactions of¹⁹F*(E _x =197 keV,J ^π=5/2⁺,T _1/2=88.5 ns) and²²Na*(E _x =583 keV,J ^π=1⁺,T _1/2=243 ns) in highly oriented pyrolytic graphite (HOPG). For¹⁹F* a single static quadrupole interaction was found with field gradientV _ZZ =3.24(19) × 10¹⁸ V/cm². For the case of²²Na* no quadrupole interaction was detected, leading to the conclusion that |QV _ZZ |<5.2(5) × 10¹⁵ b V/cm². TakingQ=0.06 b for the 583 keV state on the basis ofB(E2) measurements and theoretical estimates, we find that |V _ZZ | <8.7(8) × 10¹⁶ V/cm². The data demonstrate the advantages of using HOPG as a host material for the study of quadrupole interactions. Former Central Bureau for Nuclear Measurements (CBNM).     

Radar studies of ionospheric dusty plasma phenomena

We discuss the influence of charged dust on radar observations in the Earth ionosphere. This region in the upper Earth atmosphere can be described as a partially ionized, low‐temperature plasma. Plasma parameters vary by orders of magnitude spatially and in time. Dust particles influence the charge balance, in some cases dusty plasma condition is met. The polar mesospheric echoes are an example of dust plasma interactions observed with radar. The mesosphere is a region where atmospheric temperature decreases with altitude and can reach frost point temperature. The formation of the polar mesospheric radar echoes involves neutral atmosphere dynamics, which is latitude dependent and it involves charged dust particles, especially icy dust that forms in the polar summer mesosphere. Charged dust can also influence incoherent scatter that results from electromagnetic waves scattering off electrons, where the electrons are coupled to other charged components. Observers rarely report charged dust signatures in the incoherent scatter spectra; we show that there is a good chance for doing so with improved observations. The incoherent scatter can possibly also be used to estimate the amount of charged dust in the direct vicinity of a meteor, as we show based on the order of magnitude considerations. This prospect of new observational results makes theoretical investigations of radio‐wave scattering in the presence of charged dust with size distributions worthwhile.     

Tyrosine alkyl esters as prodrug: the structure and intermolecular interactions of <Emphasis Type="SmallCaps">l</Emphasis>-tyrosine methyl ester compared to <Emphasis Type="SmallCaps">l</Emphasis>-tyrosine and its ethyl and <Emphasis Type="Italic">n</Emphasis>-butyl esters

l-Tyrosine alkyl esters are used as prodrugs for l-tyrosine. Although prodrugs are often designed for their behavior in solution, understanding their solid-state properties is the first step in mastering drug delivery. The crystal structure of l-tyrosine methyl ester has been determined and compared to published structures of l-tyrosine and its ethyl and n-butyl esters. It is almost isostructural with the other esters: it crystallizes in the orthorhombic chiral space group P2₁2₁2₁, a = 5.7634(15) Å, b = 12.111(2) Å, c = 14.3713(19) Å, V = 1003.1(4) Å³ with Z′ = 1. Their main packing motif is a C(9) infinite hydrogen-bond chain, but the conformation of l-tyrosine methyl ester is different from the other two: eclipsed versus U-shaped, respectively. The published structure of the ethyl ester, which was incomplete, has been confirmed by X-ray powder diffraction data. Because l-tyrosine methyl ester is very stable (28 years stored at room temperature), and its hydrolysis rate is relatively low, it should be one of the better prodrugs among the alkyl esters of tyrosine.     

Crystal structure and thermal expansion of N,N,N′,N′-tetrakis-[(1H,2,4-triazol-1-yl)methyl]-ethane-1,2-diamine

Structural Chemistry - The crystal structure of N,N,N′,N′-tetrakis-[(1H,2,4-triazol-1-yl)methyl]-ethane-1,2-diamine has been fully determined at six different temperatures by X-ray...