Chloracylierung und Bromacylierung von Carbonylverbindungen: Eine in Vergessenheit geratene Carbonylreaktion. I. Präparative Anwendungsbreite

Chloroacylation and bromoacylation of carbonyl compounds: A forgotten carbonyl reaction. I. Scope of the reaction Aliphatic, α,β-unsaturated and aromatic aldehydes as well as aliphatic ketones react with acyl halides to (α-haloalkyl)esters. These bifunctional derivates contain two leaving groups of different reactivity. The scope of this scarcely of this scarcely known carbonyl reaction is discussed.     

Light-driven horseradish peroxidase cycle by using photo-activated methylene blue as the reducing agent

In this work, the regeneration of native horseradish peroxidase (HRP), following the consecutive reduction of oxo-ferryl pi-cation (compound I) and oxo-ferryl (compound II) forms, was observed by UV-visible spectrometry and electron paramagnetic resonance (EPR) in the presence of methylene (MB+), in the dark and under irradiation. In the dark, MB+ did not affect the rate of HRP compound I and II reduction, compatible with hydrogen peroxide as the solely reducing species. Under irradiation, the dye promoted a significant increase in the native HRP regeneration rate in a pH-dependent manner. Flash photolysis measurements revealed significant redshift of the MB+ triplet absorbance spectrum in the presence of native HRP. This result is compatible with the dye binding on the enzyme structure leading to the increase in the photogenerated MB* yield. In the presence of HRP compound II, the lifetime of the dye at 520 nm decreased approximately 75% relative to the presence of native HRP that suggests MB* as the heme iron photochemical reducing agent. In argon and in air-saturated media, photoactivated MB+ led to native HRP regeneration in a time- and concentration-dependent manner. The apparent rate constant for photoactivated MB+-promoted native HRP regeneration, in argon and in air-saturated medium and measured as a function of MB+ concentration, exhibited saturation that is suggestive of dye binding on the HRP structure. The dissociation constant (KMB) observed for the binding of dye to HRP was 5.4+/-0.6 microM and 0.57+/-0.05 microM in argon and air-saturated media, respectively. In argon-saturated medium, the rate of the conversion of HRP compound II to native HRP was significantly higher, k2argon=(2.1+/-0.1)x10(-2) s(-1), than that obtained in air-equilibrated medium, k2air=(0.73+/-0.02)x10(-2) s(-1). Under these conditions the efficiency of photoactivated MB(+)-promoted native HRP regeneration was determined in argon and air-equilibrated media as being, respectively: k2/KMB=3.9x10(3) and 12.8x10(3) M(-1) s(-1).     

Photochemically generated stable cation radical of phenothiazine aggregates in mildly acid buffered solutions

This work characterizes, for the first time, the photochemical behavior of the antipsychotic drugs thioridazine (TR), trifluoperazine (TFP), and fluphenazine (FP) influenced by the aggregation state of the molecules. Samples of monomeric and aggregated forms of phenothiazines were submitted to 20 min of irradiation at 254 nm for intervals of 1, 5, 10, 15, 20, or 25 days. In high phenothiazine concentrations, the irradiation led to the appearance of absorbance bands in the visible region peaking at 633 nm for TR and 509 nm for FP and TFP. In the dark, at room temperature and at 4 degrees C, these bands disappeared, after approximately 15 and approximately 60 min, respectively, but reappeared after a new irradiation session. These visible bands were assigned to stable cation radicals that were characterized by direct EPR measurements and by flash photolysis. Photogenerated stable cation radicals in the phenothiazine aggregates at room temperature are formed probably due to the stacking of the thiazine phenyl moieties. For the monomeric forms of phenothiazines, the spectral changes observed during the irradiation suggested the formation of sulfoxide and hydroxylated derivates. Oxidized derivates were detected by mass spectrometry of the aggregated forms of phenothiazines (>100 microM) only in the samples irradiated for more than 20 days. In contrast, monomeric phenothiazines were totally converted to the oxidized forms after 20 min of irradiation. Surface tension measurements of phenothiazines revealed that, in concentrations above 100 microM, the drugs formed aggregates. In the case of TR, small-angle X-ray scattering measurements indicated that this compound forms large lamellar-like aggregates in aqueous solutions.     

Age, sex, and vowel dependencies of acoustic measures related to the voice source

The effects of age, sex, and vocal tract configuration on the glottal excitation signal in speech are only partially understood, yet understanding these effects is important for both recognition and synthesis of speech as well as for medical purposes. In this paper, three acoustic measures related to the voice source are analyzed for five vowels from 3145 CVC utterances spoken by 335 talkers (8-39 years old) from the CID database [Miller et al., Proceedings of ICASSP, 1996, Vol. 2, pp. 849-852]. The measures are: the fundamental frequency (F0), the difference between the "corrected" (denoted by an asterisk) first two spectral harmonic magnitudes, H1* - H2* (related to the open quotient), and the difference between the "corrected" magnitudes of the first spectral harmonic and that of the third formant peak, H1* - A3* (related to source spectral tilt). The correction refers to compensating for the influence of formant frequencies on spectral magnitude estimation. Experimental results show that the three acoustic measures are dependent to varying degrees on age and vowel. Age dependencies are more prominent for male talkers, while vowel dependencies are more prominent for female talkers suggesting a greater vocal tract-source interaction. All talkers show a dependency of F0 on sex and on F3, and of H1* - A3* on vowel type. For low-pitched talkers (F0 < or = 175 Hz), H1* - H2* is positively correlated with F0 while for high-pitched talkers, H1* - H2* is dependent on F1 or vowel height. For high-pitched talkers there were no significant sex dependencies of H1* - H2* and H1* - A3*. The statistical significance of these results is shown.     

MO-Calculation of the Optical Activity of Oligopeptides. II. Open-chain conformations. Comparison with some cyclic systems

Using the Frozen Core (FC) MO procedure described in a previous communication, we have computed the long-wavelength chiroptic properties of oligopeptides in the parallel-chain (PC) pleated sheet conformation, in the poly (L -proline) I and poly (L -proline) II conformations. The main features of the computed results are: (a) In the PC pleated sheet conformation the π–π* transition with the highest positive rotatory strength appears at shorter wavelength than the π–π* transition with highest negative rotatory strength and is polarized mainly perpendicularly to the chain axis. There is an analogy between the computed PC pleated sheet spectrum and that calculated for a cyclohexapeptide of low symmetry, in a conformation which is probably stabilized by intra-annular hydrogen bonds. (b) In the polyproline I conformation the computed π–π* transition with highest positive rotatory strength is also the longest-wavelength π–π* transition and is polarized mainly along the helix axis. There is an analogy between this spectrum and that calculated for cyclo(tri-L -proline) of symmetry C₃. (c) The poly-proline II CD. spectrum may be qualitatively reproduced only by invoking very strong n – π interaction. The local n –π mixing parameter Λ must take on values ?3 eV, which is of the order of a nearest-neighbor core resonance integral between atomic 2p orbitals of same spatial orientation. The question concerning the structural reasons for this situation is raised. As far as comparisons with experimental data are possible, qualitative agreement is obtained.     

Electronic Properties and Optical Activity of Oligopeptides. III. Some cyclohexapeptides with glycine,L- and D-alanine

The wavelength range of the CD. spectra of some cyclohexapeptides containing different sequences of glycine, L - and D -alanine is extended down to 170 nm. This allows a relatively complete recording of the (n ? π*) and (π° ? π*) Cotton effects. Some striking spectral changes are observed on going from one molecule to another. The relative influence of L - and D -alanyl residues is discussed: Some spectra may be qualitatively related to each other by considering the effect of an L -residue at position q in the ring to cancel partially with the effect of a D -residue at position q ± 3. Assuming these cyclopeptides to occur in a hydrogen-bonded pleated sheet structure, certain dominant changes in the spectra are interpreted as reflecting a transition of the overall backbone conformation from one which is closer to the (optically inactive) symmetry C_i to another which is closer to the (optically active) symmetry C₂. An attempt is made to relate the influence of L - and D -substituents within hairpin bends of the pleated sheet structure to an amide sector rule.     

Photochemical reduction of cytochrome c by a 1,4,5,8-naphthalenediimide radical anion

Steady-state UV irradiation of aqueous solutions containing cytochrome c (cyt c) and N,N'-bis(2-phosphonoethyl)-1,4,5,8-naphthalenediimide (BPNDI), a water-soluble aromatic imide, resulted in the reduction of the heme iron from the Fe(III) to the Fe(II) oxidation state. The reaction kinetics were followed by the increase of the ferrocytochrome c absorbance band at 549 nm. The rate of the photochemical reaction was pH dependent, reaching its maximum values over the pH range 4-7. Addition of electrolyte (NaCl) at pH 5 resulted in a decrease in the reaction rate, as expected for reactions between oppositely charged species. Flash photolysis studies revealed that the actual reductant in the reaction was a photogenerated BPNDI radical anion, which transferred an electron to the cyt c heme iron. The participation of imide radicals in the process was confirmed by the ready reduction of cyt c by BPNDI radicals chemically generated with sodium dithionite.     

Photoinduced electron transfer between cytochrome c and a novel 1,4,5,8-naphthalenetetracarboxylic diimide with amphiphilic character

N-dodecyl-N'-(2-phosphonoethyl)-1,4,5,8-naphthalenetetracarboxylic diimide (DNDI) is a novel naphthalenic diimide with amphiphilic character. DNDI was synthesized through the sequential reaction of 1,4,5,8-naphthalenetetracarboxylic dianhydride, first with dodecylamine and then with 2-aminoethylphosphonic acid. Fluorescence measurements showed that DNDI forms excimers in water at sufficiently high concentrations. The fluorescence quantum yield of DNDI in diluted solutions is sensitive to the polarity of the microenvironment, decreasing as going from water to less polar solvents. This property allowed to monitor the incorporation of DNDI into cetyl trimethyl ammonium bromide (CTAB) micelles, with a binding constant of 1.2x10(4) M-1. UV irradiation (365 nm) of solutions containing DNDI and the redox protein cytochrome c (cyt c) resulted in the reduction of the heme iron from the Fe(III) to the Fe(II) state, a reaction that was inhibited by the incorporation of DNDI into CTAB micelles. DNDI formed host-guest complexes with alpha-cyclodextrin (alpha-CD) through the inclusion of the dodecyl group, resulting in an increased aqueous solubility of the compound.     

Projection theorems in hyperbolic space

We establish Marstrand-type projection theorems for orthogonal projections along geodesics onto m-dimensional subspaces of the hyperbolic n-space by a geometric argument. Moreover, we obtain a Besicovitch–Federer type characterization of purely unrectifiable sets in terms of these hyperbolic orthogonal projections.