Porphyrin analogs in bacterial photosynthesis

The electron transfer process in bacterial reaction centers is investigated. It is found that the side indole group Trp M252 in Rb sphaeroides (Trp M250 in Rps viridis) assists tunneling electron transfer by a distance of ∼14Å from pheophytin to quinone. Reported at the VIIIth International Conference on Spectroscopy of Porphyrins and Their Analogs, Minsk, September 22–26, 1998. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 496–500, July–August, 1999.     

The investigation of oxidized silver nanoparticles prepared by thermal evaporation and radio-frequency sputtering of metallic silver under oxygen

The investigation of oxidized silver nanoparticles by the photoemission (XPS, UPS) and HRTEM methods was performed. The nanoparticles of oxidized silver were obtained in the vacuum chamber by two methods of synthesis: thermal evaporation of silver nanoparticles followed by transferring in convective gas flow and sputtering of oxidized clusters under the action of plasma. Both methods indicated that oxygen interaction with silver nanoparticles depends strongly on its size. It was shown that the chemical bonding of oxygen species stabilized on small particles differs from the oxygen species adsorbed on bulk silver surfaces (monocrystals, foils and large particles). The low charged oxygen with molecular type of bonding stabilizes on particles of size approximately 5 nm and smaller. Increasing particle size leads to the dissociation of molecular oxygen species and the formation of strongly charged oxygen composed of oxide nanoparticles like Ag₂O or AgO type. The presence of extended defects in the microdomain large nanoparticles facilitates the formation of Ag₂O or AgO layers covering metallic nanosilver.     

The electrochemistry of arylated anthraquinones in room temperature ionic liquids

Arylated anthraquinone derivatives of different sizes and different π‐basicities have been prepared, and the electrochemical behaviour of these substances has been studied on screen printed graphite electrodes in the three room temperature ionic liquids (RTILs), 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([C₄MIM][PF₆]), 1‐hexyl‐3‐methylimidazolium hexafluorophosphate ([C₆MIM][PF₆]) and 1‐octyl‐3‐methylimidazolium hexafluorophosphate ([C₈MIM][PF₆]). Half redox potentials for the first and second one electron reduction waves were identified, and the diffusion coefficient values were estimated from cyclic voltammetry measurements. The influence of the nature of the RTIL and of the substitution pattern of the anthraquinone on the solvodynamic radii were studied. A correlation of the reductive potentials with the corresponding Hammett constants of the substituents was tested. Copyright © 2013 John Wiley & Sons, Ltd.     

Selectivity in the Aerobic Dearomatization of Phenols: Total Synthesis of Dehydronornuciferine by Chemo‐ and Regioselective Oxidation

We describe a selective aerobic oxidation of meta‐biaryl phenols that enables rapid access to functionalized phenanthrenes. Aerobic oxidations attract interest due to their efficiency, but remain underutilized in complex molecule settings due to challenges of selectivity. We discuss these issues in the context of Cu catalysis, and highlight the advantages of confining oxygen activation and substrate oxidation to the catalyst's inner‐coordination sphere. This gives rise to predictable selectivity that we use for a concise synthesis of the aporphine dehydronornuciferine.     

Structural characterization of oxidized lumiflavin hydrochloride hydrate: Comparison with the hydrogen bonding at the cofactor of flavoproteins

In order to examine the possibility of hydrogen bonding around the flavin ring, an X-ray diffraction study of the title compound was undertaken. Crystals of lumiflavin hydrochloride hydrate [2(C₁₃H₁₂N₄O₂) 4 HCl 7 H₂O] are triclinic, space group ,Z=2,a=11.064(1),b=17.903(1),c=9.891(1)Å, =111.9(6), -96.4(8), =91.6(7)°. We present the crystal structure of this compound and compare it with other flavin derivatives and with the structure of the active site of some flavoproteins.     

An unusual Mannich type reaction of tertiary aromatic amines in aqueous micelles

An efficient, unusual Mannich type reaction of tertiary aromatic amines, formaldehyde and 1,3-dicarbonyl compounds is described in aqueous micelles catalyzed by boric acid to afford dialkylaminoarylated 1,3-dicarbonyls. In this unusual Mannich type reaction, tertiary aromatic amines react with formaldehyde to generate an N-alkyl-N-(4-methylenecyclohexa-2,5-dienylidene)alkylaminium intermediate (aza quinone methide), which undergoes nucleophilic addition with 1,3-dicarbonyl compounds. The reaction is highly regioselective, and exclusively para functionalized products are formed in high yields.     

Aromatic Monochlorination Photosensitized by DDQ with Hydrogen Chloride under Visible‐Light Irradiation

Photochlorination of aromatic substrates by hydrogen chloride with 2,3‐dichloro‐5,6‐cyano‐p‐benzoquinone (DDQ) occurs efficiently to produce the corresponding monochlorinated products selectively under visible‐light irradiation. The yields for the chlorination of phenol were 70 % and 18 % for p‐ and o‐chlorophenol, respectively, without formation of further chlorinated products. The photoinduced chlorination is initiated by electron transfer from Cl^? to the triplet excited state of DDQ. The radical intermediates involved in the photochemical reaction have been detected by time‐resolved transient absorption measurements.     

高效液相色谱法测定药品中的二硫苏糖醇和氧化型二硫苏糖醇

建立了高效液相色谱法同时测定药品中二硫苏糖醇(DTT)和氧化型二硫苏糖醇(DTTox)含量。采用Waters X-Bridge C18柱(250×4.6mm,5μm)分离,流动相为体积比为30∶70的甲醇-水(含0.02%三氟乙酸),检测波长为210nm。结果表明,DTT和DTTox在选定质量浓度范围内呈良好的线性关系(r0.999),DTT和DTTox的检出限(S/N=3)为0.02μg/mL,定量限(S/N=10)为0.07μg/mL。平均加标回收率分别为99.32%、99.49%,相对标准偏差分别为2.34%、2.23%。该方法简单、准确,灵敏度高,重复性好,适用于药品中DTT和DTTox的检测。