Tryptophan photooxidation promoted by new hybrid materials prepared by condensation of naphthalene imides with silicate by the sol–gel process

Three novel hybrid organic/inorganic materials were synthesized from 4-substituted (NO₂, Br, H) 1,8-naphthalene imide-N-propyltriethoxysilane by the sol–gel process. These materials were obtained as a xerogel and partially characterized. The ability to photosensitize the oxidation and degradation of tryptophan indole ring by these materials was studied through photophysical and photochemical techniques. Although the derivatives containing Br and NO₂ as substituent do not cause efficient tryptophan photodamage, the hybrid material obtained from 1,8-naphthalic anhydride is very efficient to promote tryptophan photooxidation. By using laser flash photolysis it was possible to verify the presence of naphthalene imide transient radical species. The presence of oxygen causes an increase of the yield of radical formation. These results suggest that the mechanism of photodegradation of tryptophan occurs by type I, i.e. the transient radical (TrpH⁺) formed by the direct reaction of the triplet state of the naphthalene imide moiety with tryptophan. Thus a inorganic–organic hybrid material that can be used to promote the oxidation of biomolecules was obtained.     

Effect of reaction conditions on product distribution from the co-pyrolysis of α-amino acids with glucose

The effect of reaction conditions on product distribution from the co-pyrolysis of amino acids with glucose was studied. Three different amino acids, proline, tryptophan and asparagine, were studied. Some experiments were also conducted with aspartic acid, glutamic acid and glutamine. Equimolar binary mixtures of each amino acid and glucose were pyrolyzed at 300 °C to obtain low temperature char (LTC) and low temperature tar (LTT). The LTC in each case was then pyrolyzed further at 625 °C to obtain high temperature char (HTC) and high temperature tar (HTT). In a few experiments, the LTT and HTT were also pyrolyzed at 870 °C (secondary cracking) to obtain the final tars (LTFT and HTFT, respectively) and study the formation of polycyclic aromatic compounds (PACs) via secondary reactions. Experiments were also conducted at different amino acid/glucose molar ratio or at a temperature of 200 °C. All the experiments were performed in an inert atmosphere. The extent of interaction between the amino acids and glucose was determined by comparing the observed results to that calculated from the separate pyrolyses of amino acids and glucose. At 200 °C, the co-pyrolysis led to lower LTC yields relative to the calculated yields. At 300 and 625 °C the yields of LTC and HTC were mostly higher whereas those of LTT and HTT were lower than the calculated yields, except for asparagine and aspartic acid where the observed and calculated LTC yields were comparable. Although proline formed no char in the absence of glucose, it gave a significant amount of nitrogen-containing char when co-pyrolyzed with glucose. The pyrolysis tars contained a number of nitrogenous products not observed from the pyrolysis of amino acids alone. After the secondary cracking, the product changed from mainly single-ring heterocycles to PACs and, in some cases, PAHs.     

Absorption and fluorescence characteristics of photo-activated adenylate cyclase nano-clusters from the amoeboflagellate Naegleria gruberi NEG-M strain

The spectroscopic characteristics of BLUF (BLUF = sensor of blue light using flavin) domain containing soluble adenylate cyclase (nPAC = Naegleria photo-activated cyclase) samples from the amoeboflagellate Naegleria gruberi NEG-M strain is studied at room temperature. The absorption and fluorescence spectroscopic development in the dark was investigated over two weeks. Attenuation coefficient spectra, fluorescence quantum distributions, fluorescence quantum yields, and fluorescence excitation distributions were measured. Thawing of frozen nPAC samples gave solutions with varying protein nano-cluster size and varying flavin, tyrosine, tryptophan, and protein color-center emission. Protein color-center emission was observed in the wavelength range of 360-900 nm with narrow emission bands of small Stokes shift and broad emission bands of large Stokes shift. The emission spectra evolved in time with protein nano-cluster aging.     

维生素K3的激发三重态与色氨酸、酪氨酸电子转移氧化反应的激光闪光光解研究

利用时间分辨的激光闪光光解技术研究了乙腈-水混合溶液(1:1,V/V)中2-甲基萘醌(通常称为维生素K3)的激发三重态对色氨酸、酪氨酸的光敏氧化机理.通过瞬态吸收光谱的变化可以推断维生素K3的激发三重态可以与色氨酸、酪氨酸发生电子转移反应,反应形成的维生素K3阴离子自由基的吸收峰可以直接从瞬态吸收谱图中观察到.维生素K3与色氨酸、酪氨酸的电子转移反应的速率分别为1.1×109和0.6×109L·mol-1·s-1.吉布斯自由能(ΔG)的计算结果表明维生素K3的激发三重态与色氨酸、酪氨酸电子转移反应在热力学上是可行的.     

A synthetic ditryptophan conjugate that rescues bacteria from mercury toxicity through complexation

The synthesis of ditryptophan-pyridine conjugates and their binding to mercury ions is described. Conjugate 3 shows an excellent ability to sequester mercury from solution and rescue bacterial growth in a concentration-dependent survival assay. It is proposed that such compounds, composed primarily of bioessential/biodegradable components, could be potentially used as sequestrating agents for the removal of Hg(II) ions in detoxification strategies.     

Investigation of the association behaviors between biliverdin and bovine serum albumin by fluorescence spectroscopy

The interaction between biliverdin and bovine serum albumin (BSA) has been studied by steady fluorescence spectroscopy, synchronous fluorescence and resonance light scanning spectra. The binding of biliverdin to BSA quenches the tryptophan residue fluorescence and the results show that both static and dynamic quenching occur together with complex formation. The binding constant and binding sites of biliverdin to BSA at pH 7.1 are calculated to be 3.33 × 10⁸ L/mol and 1.54, respectively, according to the double logarithm regression curve. In addition, the distance between the biliverdin and BSA is estimated to be 1.25 nm using Föster's equation on the basis of the fluorescence energy transfer. Furthermore the synchronous fluorescence spectra show that the microenvironment of the tryptophan residues has not obvious changes, which obeys the phase distribution model. Finally, the thermodynamic data show that biliverdin molecules enter the hydrophobic cavity of BSA via hydrophobic interaction.     

Chemiluminescence Behavior and Application of Ce (IV)-Tween20-Tryptophan System

It was observed that the chemiluminescence intensity from the reaction of Ce (IV) with Tween20 was greatly enhanced in the presence of tryptophan, and the possible reaction mechanism was explored. Based on the reaction, a sequential injection procedure with chemiluminescence detection was developed for the determination of tryptophan. Under the optimum conditions, a linear dynamic range of 0.2–8.0 μM, a 3σ detection limit of 0.15 μM and a coefficient of variation of 0.7% at 3.0 μM level were obtained. The method was applied to the determination of tryptophan in beer and amino acid injections.     

Tryptophanbestimmung im Gehirn Spezifische fluorimetrische Methode in Gegenwart von Analoga und Metaboliten

Zusammenfassung Es wurde eine Methode zur Bestimmung von Tryptophan in Gehirn ausgearbeitet. Diese führt in Gegenwart von Formaldehyd und Salpetersäure zu einem Fluorophor (Typ Norharman), der — im Gegensatz zu ähnlichen Formaldehydreaktionen mit HCl u. a. — nur von Tryptamin schwach gestört wird. Serotonin, 5-Hydroxytryptophan, Xanthurensäure, 3Hydroxyanthranilsäure und 5-Hydroxyindolessigsäure stören die fluorimetrische Bestimmung (374/450 nm) nicht. Es kann sogar auf vorherige DC-Trennung verzichtet werden. Geschlechts- und altersspezifische Unterschiede des Tryptophangehalts im Rattenhirn sind nicht stark ausgeprägt.

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Determination of tryptophan in the brain. specific fluorimetric method in presence of analogues and metabolites

Summary A method for the determination of tryptophan in the brain was developed, which is based on the formation of a fluorophore (374/450 nm) in the presence of formaldehyde and nitric acid. In contrast to similar methods which use formaldehyde and hydrochloric acid, tryptamine interferes only weakly. Serotonin, 5-hydroxytryptophan, xanthurenic acid, 3-hydroxyanthranilic acid and 5-hydroxyindoleacetic acid do not interfere, t.l.c. separation prior to fluorophore formation can be omitted. Influence of sex and age on the tryptophan content in rat brain are not very marked.

     

Tryptophan analysis simultaneously with other amino acids in gas phase hydrochloric acid hydrolyzates using the Pico-TagTM Work Station

Summary Classical liquid phase hydrolysis of proteins with hydrochloric acid in the presence of tryptamine [3-(2-aminoethyl)indole] has shown that tryptophan can be protected from destruction. An exhaustive study has been made to establish the optimum conditions for protein hydrolysis, in the gas phase using the Pico-Tag^TM Work Station, as a function of time and temperature. The amino acid content, including tryptophan and cyst(e)ine, of standard proteins such as lysozyme, human albumin and -chymotrypsin were determined as phenylthiocarbamyl (PTC) derivatives. On 5 m Hypersil columns (15×4.6 mm) the quantitation of twenty PTC amino acids requires 22 minutes. The reproducibility of the measurements was 5.8% (relative standard deviation) or less.