Effect of DNA on filament formation of tau microtubule-binding domain: structural dependence of DNA

To examine whether or not DNA accelerates the paired helical filament (PHF) formation of tau, the effect of various types of DNAs on filament formations of three-repeated and four-repeated microtubule-binding domains (3RMBD and 4RMBD, respectively) of tau protein was investigated by monitoring the change of thioflavin S fluorescence intensity, that is parallel to the filament formation. Consequently, the followings were clarified: 1) the structurally rigid double-stranded DNA such as poly(dG-dC) or calf thymus DNA has the high potency of promoting the filament formations of 3RMBD and 4RMBD, 2) the filament formation of 3RMBD was more promoted than that of 4RMBD, due to the intermolecular dimer formation of 3RMBD, 3) the DNA-promoted filament formations of these MBDs were temperature-dependent, and the single-stranded DNA such as poly(dA) or poly(dT) reversely protected 4RMBD from the molecular assembly at 20 degrees C. These are the first report on the function of DNA for the PHF formation of tau protein.     

Magnetic resonance energies of heterocyclic conjugated molecules

Magnetic resonance energy (MRE), derived from ring-current diamagnetic susceptibility, can be interpreted as a kind of aromatic stabilization energy. For polycyclic conjugated hydrocarbons, this quantity correlates well with topological resonance energy (TRE). MREs for typical heterocyclic conjugated molecules were then calculated and analyzed. It was found that even for heterocycles MRE highly correlates with TRE. Thus, the MRE concept has been firmly established as a reliable indicator of aromaticity, which mediates magnetic criteria of aromaticity with energetic ones. The conformity of heterocycles to the rule of topological charge stabilization can be checked using not only TRE but also MRE.     

Advanced dress-up chiral columns: New removable chiral stationary phases for enantioseparation of chiral carboxylic acids

This paper describes the preparation of new dress-up columns featuring reproducibly removable and replaceable chiral stationary phases. After synthesizing perfluroalkylated quinine and quinidine derivatives as chiral stationary phase compounds (F-CSPs), we adsorbed them reversibly onto a fluorous LC column through pumping of their solutions. Using this dress-up chiral column and fluorophobic elution of aqueous ammonium formate/MeOH mixtures, we could enantioseparate four racemic N-acetyl amino acids, dichlorprop, and sixteen fluorescent 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC)-derivatized amino acids. Dressing and undressing of the coated F-CSPs could be controlled by varying the fluorophilicity and fluorophobicity of the eluent. The relative standard deviations of the retention times, the retention factors, the number of theoretical plates, the enantioseparation factors, and the resolutions of each of four preparations of such dress-up columns were all less than or equal to 5.26% (from 20 repeated analyses); the reproducibilities from four different preparations were all less than or equal to 10.6%. These columns also facilitated highly sensitive and selective analyses of AQC-amino acids when detected using LC–MS/MS.     

Photochemical dynamics of indolylmaleimide derivatives

On-the-fly nonadiabatic ab initio molecular dynamics simulations have been carried out for three anionic species of indolylmaleimides (3-(1H-3-indolyl)-2,5-dihydro-1H-2,5-pyrroledione, IM) to clarify the mechanisms of photochemical reactions. The results are obtained for (i) a monovalent anion with a deprotonated indole NH group (IM(-)'), (ii) a monovalent anion with a deprotonated maleimide NH group (IM(-)') and (iii) a divalent anion with doubly deprotonated indole and the maleimide NH groups (IM(2-)). Quantum chemical calculations are treated at the three state averaged complete-active space self-consistent field level for 6 electrons in 5 orbitals with the cc-pVDZ basis set (CAS (6, 5) SCF/cc-pVDZ). Molecular dynamics simulations are performed with electronically nonadiabatic transitions included using the Zhu-Nakamura version of the trajectory surface hopping (ZN-TSH) method. It is found that the nonadiabatic transitions occur accompanied by the stretching and shrinking motions of the N(7)-C(8) bond in the case of IM(-)' and the C(11)-N(12) bond in IM(2-) rather than the twisting motion of the dihedral angle. We also found that the ultrafast S(2)→ S(1) nonadiabatic transitions occur through the conical intersection (CoIn) right after photoexcitation to S(2) in IM(-)' and IM(2-). Furthermore, the S(1)→ S(0) nonadiabatic transitions are found to take place in IM(-)'. It is concluded that IM(2-) would mainly contribute to the photoemission, because the S(1)← S(0) and S(2)← S(0) transitions of IM(-)' are dipole-forbidden transitions and, moreover, IM(2-) is found to be the only species to stay in the S(1) state without non-radiative decay.     

Total synthesis of marinostatin, a serine protease inhibitor isolated from the marine bacterium Pseudoallteromonas sagamiensis

Marinostatin (MST) (1) isolated from a marine organism is a serine protease inhibitor consisting of 12 amino acids with two internal ester linkages that are formed between the β-hydroxyl and β-carboxyl groups, Thr³-Asp⁹ and Ser⁸-Asp¹¹. We synthesized MST by a regioselective esterification procedure employing two sets of orthogonally removable protecting groups at the side-chains of Asp and Ser/Thr. We optimized the esterification conditions to preferentially form the intramolecular ester linkages without any significant aspartimide (Asi) formation at Asp⁹ and Asp¹¹. The inhibitory potency of the synthetic MST against subtilisin (Ki, 0.6 nM) was comparable with a reported value for native MST (1.5 nM).     

Automatic analyzer for highly polar carboxylic acids based on fluorescence derivatization–liquid chromatography

A sensitive, versatile, and reproducible automatic analyzer for highly polar carboxylic acids based on a fluorescence derivatization–liquid chromatography (LC) method was developed. In this method, carboxylic acids were automatically and fluorescently derivatized with 4‐(N,N‐dimethylaminosulfonyl)‐7‐piperazino‐2,1,3‐benzoxadiazole (DBD‐PZ) in the presence of 4‐(4,6‐dimethoxy‐1,3,5‐triazin‐2‐yl)‐4‐methylmorpholinium chloride by adopting a pretreatment program installed in an LC autosampler. All of the DBD‐PZ‐carboxylic acid derivatives were separated on the ODS column within 30 min by gradient elution. The peak of DBD‐PZ did not interfere with the separation and the quantification of all the acids with the exception of lactic acid. From the LC‐MS/MS analysis, we confirmed that lactic acid was converted to an oxytriazinyl derivative, which was further modified with a dimethoxy triazine group of 4‐(4,6‐dimethoxy‐1,3,5‐triazin‐2‐yl)‐4‐methylmorpholinium chloride (DMT‐MM). We detected this oxytriazinyl derivative to quantify lactic acid. The detection limits (signal‐to‐noise ratio = 3) for the examined acids ranged from 0.19 to 1.1 µm , which correspond to 95–550 fmol per injection. The intra‐ and inter‐day precisions of typical, highly polar carboxylic acids were all <9.0%. The developed method was successfully applied to the comprehensive analysis of carboxylic acids in various samples, which included fruit juices, red wine and media from cultured tumor cells. Copyright © 2014 John Wiley & Sons, Ltd.     

Analysis of photodecomposition of gaseous chlorobenzene by KrF excimer laser.

Gaseous monochlorobenzene was irradiated with KrF excimer laser (248 nm) under reduced pressure. The photodecomposition was an apparent first order reaction. When the system contained no additive gas, the photolysis was found to give benzene (conversion yield: 49%) in the gas phase and many unidentified products in the solid phase. On the other hand, in the presence of oxygen, carbon dioxide (10%), carbon monoxide (16%), hydrogen chloride (52%) and acetylene (2%) are produced and the peaks shown on the gas chromatogram of the solid phase were effectively suppressed.     

Simultaneous determination of D- and L-serine in rat brain microdialysis sample using a column-switching HPLC with fluorimetric detection

Both D- and L-serine in rat brain microdialysis sample were simultaneously determined by pre-column fluorescence derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), separation of the derivatives on ODS column, TSKgel ODS-80TsQA, followed by Pirkle type chiral columns, Sumichiral OA-2500 (S), which gave a sufficient enantiomeric separation of NBD-D-serine and NBD-L-serine, and fluorimetric detection at a wavelength of 540 nm with an excitation wavelength of 470 nm. The peaks of NBD-D-serine and NBD-L-serine in the rat brain microdialysis sample were clearly found, and the validation study showed satisfactory results; the precision and accuracy were within 5.14 and 109%, respectively. Using the proposed HPLC method, the time-course profile of D-serine concentration in rat prefrontal cortex following intraperitoneal administration of D-serine was investigated. As a consequence, D-serine appeared to be rapidly distributed in the brain, and then decreased gradually with time in the extracellular fluid of the rat prefrontal cortex. The proposed HPLC method will be useful for in vivo studies on D-serine, which acts as a coagonist for N-methyl-D-aspartate receptor, to the extracellular fluid of rat brain.     

Crystal and molecular structure of an (S)-(+)-enantiomer of modafinil, a novel wake-promoting agent

The (+)-enantiomer of modafinil [(RS)-2-(diphenylmethylsulfinyl)acetamide], a novel wake-promoting agent, was clarified to be S-configuration by X-ray crystal structure analysis. The crystal consists of two crystallographically independent conformers that are different at the torsion angles around the sulfinylacetamide moiety, and this results from the molecular packing requirement to form a two-dimensional hydrogen-bonding network via neighboring amide groups in the crystal. The crystal structure is characterized by the formation of alternative hydrophobic and hydrophilic layers, which are formed among the symmetry-translated assemblies of diphenylmethyl and sulfinylacetamide moieties, respectively. The spatial orientation between the diphenyl and amide groups is believed to be important for the activity of modafinil.