Purification by centrifugal partition chromatography of amphiphilic compounds, glycolipids and pseudo-glycolipids synthesized by using cells

Centrifugal partition chromatography (CPC) was applied to separate amphiphilic glycolipids and pseudo-glycolipids synthesized by using cells. Neutral and acidic lipid fractions were isolated by CPC under suitable conditions respectively. Separation of neutral lipid, Gb3-type and Gb4-type oligosaccharide synthesized by using cells, was performed with a two-phase solvent system composed of chloroform-methanol-water at a volume ratio of 5:6:4. On the other hand, separation of acidic lipid, GM3-type oligosaccharide synthesized by using cells, and ganglioside extracted from rat brain were performed with a two-phase solvent system composed of butanol-ethanol-1% acetic acid at a volume ratio of 4:1:5. 8.3mg of Gb3 analogue, 5.1mg of Gb4 analogue, and 19.5mg of GM3 analogue were purified from 3.2l of culture medium obtained by incubation of African green-monkey kidney (Vero) cells with 50 microM n-dodecyl beta-lactoside using CPC.     

Total synthesis of (-)-martinellic acid via radical addition-cyclization-elimination reaction

The asymmetric total synthesis of martinellic acid, the first pyrrolo[3,2-c]quinoline alkaloid found in nature, is described. Three key steps in our synthesis of (-)-martinellic acid are the Bu(3)SnH-promoted radical addition-cyclization-elimination (RACE) reaction of an oxime ether with an alpha,beta-unsaturated ester to generate the pyrrolo[3,2-c]quinoline core, a chemoselective lactam carbonyl reduction, and guanidinylation under Mitsunobu reaction conditions. The key radical cyclization has also been investigated by using SmI(2). (-)-Martinellic acid was synthesized from commercially available methyl 4-bromo-3-methylbenzoate in fewer steps than previous syntheses and in an improved overall yield.     

Quantum processes in short and intensive electromagnetic fields

This work provides an overview of our recent results in studying two most important and widely discussed quantum processes: electron-positron pairs production off a probe photon propagating through a polarized short-pulsed electromagnetic (e.g. laser) wave field or generalized Breit–Wheeler process, and a single a photon emission off an electron interacting with the laser pules, so-called non-linear Compton scattering. We show that the probabilities of particle production in both processes are determined by interplay of two dynamical effects, where the first one is related to the shape and duration of the pulse and the second one is non-linear dynamics of the interaction of charged fermions with a strong electromagnetic field. We elaborate suitable expressions for the production probabilities and cross sections, convenient for studying evolution of the plasma in presence of strong electromagnetic fields.     

Factors influencing the swelling and elution properties of poly(vinyl alcohol) cast gels

Swelling and elution properties of physically crosslinked poly(vinyl alcohol) (PVA) cast gels depend on the network structure of the PVA and crosslink, which is characterized by the size, number, and distribution of microcrystallites. Therefore, the swelling and elution ratios can be manipulated by adept control of the conditions adopted for the preparation of gels. Among the various factors that influence the formation of microcrystallites, the temperature and relative humidity at gelation play an important role. In addition, the size of gel is also a key factor that determines the network structure of gels. To this end, this study quantitatively evaluates the macroscopic properties of swelling and elution, and the microscopic properties of the network structures in disk‐shaped PVA cast gels of the same diameter prepared by casting different weights of PVA solution in the same dish. Although the drying speed can be controlled by adjusting the three processing parameters, namely, drying temperature, humidity, and cast weight, the changes in swelling and elution ratios, microcrystallite size, and crystallinity independently depended on each parameter. Regardless of the three factors, the swelling ratio was found to correlate strongly with the elution ratio. Optimum factors to minimize the elution ratio are discussed on the basis of the change in the network structures obtained by varying the preparatory conditions. Based on the results of the systematic analyses, this study proposes a method to control the elution ratio while retaining high water‐absorbance ability. Copyright © 2015 John Wiley & Sons, Ltd.     

Sub-5-fs real-time spectroscopy of transition states in bacteriorhodopsin during retinal isomerization

By using a sub-5-fs visible laser pulse, we have made the first observation of the vibrational spectra of the transition state during trans-cis isomerization in the retinal chromophore of bacteriorhodopsin (bR(S68). No instant isomerization of the retinal occurs in spite of electron promotion from the bonding pi-orbital to the anti-bonding pi*-orbital. The difference between the in-plane and out-of-plane vibrational frequencies (about 1150-1250 and 900-1000 cm(-1), respectively) is reduced during the first time period. The vibrational spectra after this period became very broad and weak and are ascribed to a "silent state." The silent state lasts for 700-900 fs until the chromophore isomerizes to the cis-C13 = C14 conformation. The frequency of the C = C stretching mode was modulated by the torsion mode of the C13 = C14 double bond with a period of 200 fs. The modulation was clearly observed for four to five periods. Using the empirical equation for the relation between bond length and stretching frequency, we determined the transitional C = C bond length with about 0.01 angstroms accuracy during the torsion motion around the double bond with 1-fs time resolution.     

Multi-metal complexation and partially templated synthesis of metal clusters by using triangular trisaloph ligands

On the basis of the concept of partial template, triangular trisaloph ligands 2a and 2b reacted with excess Zn^II to give heptanuclear Zn clusters with a similar geometry. The Zn complex of 2c, which was difficult to be prepared according to a previous procedure, was synthesized in high yield in a one-pot fashion. Various multi-nuclear complexes of 2a with Mn, Co, Ni, and Cu were also produced, although the trinuclear Mn^II and Co^II complexes were smoothly oxidized to the Mn^III and Co^III complexes.     

Simultaneous chiral resolution of monosaccharides as 8-aminonaphthalene-1,3,6-trisulfonate derivatives by ligand-exchange CE using borate as a central ion of the chiral selector

Six reducing monosaccharides (mannose, galactose, fucose, glucose, xylose, and arabinose) were derivatized with 8-aminonaphthalene-1,3,6-trisulfonate (ANTS). Based on the chiral ligand-exchange principle using borate as a central ion of the chiral selector and (S)-3-amino-1,2-propanediol (SAP) as a chiral selector ligand, all of the six ANTS-monosaccharides were simultaneously enantioseparated using absorbance at 245 nm for detection. The optimum conditions for both high resolution and moderately short migration time consisted of 200 mM SAP-200 mM borate buffer (pH 9.2) containing 10% ACN as a BGE at 30 degrees C with an applied voltage of +30 kV. It was revealed that the proposed chiral ligand-exchange CE using the SAP-borate system was applicable to enantioseparation of not only diols but also polyols.     

Spectroscopic investigation of cationic comb-type copolymers/DNA interaction: interpolyelectrolyte complex enhancement synchronized with DNA hybridization

We have demonstrated that cationic comb-type copolymers consisting of a polycation backbone and abundant grafts of water-soluble polymers stabilize DNA hybrids. Furthermore, the copolymers were found to accelerate strand exchange reaction between a double-stranded DNA and its complementary single-stranded DNA. In this article, we investigated the effects of PLL-g-Dex on base pairs of a self-complementary DNA octamer, d(GGAATTCC). The soluble interpolyelectrolyte complex (IPEC) between the DNA and copolymer allowed us to characterize the complex by using spectroscopic methods under physiological ionic condition. Chemical shifts of nucleobase proton signals were not changed by PLL-g-Dex. Furthermore, the copolymer slightly changed the von't Hoff DeltaH accompanying the helix-coil transition of the octamer. These results indicated that the base pairs of the duplex DNA in the IPEC were not perturbed by the polycationic copolymer. It was obviously shown by temperature dependencies of proton and phosphorus NMR spectra that DNA/copolymer interaction was considerably enhanced in response to ds DNA formation. An increase in the density and total number of DNA negative charges upon hybrid formation likely caused the higher affinity of the copolymer with the ds form over that of the copolymer with the ss form. The IPEC formation of CCCs with DNA, however, seems highly sensitive to the coil-helix transition of the DNA.     

Heterogeneous Pd/C-catalyzed ligand-free, room-temperature Suzuki-Miyaura coupling reactions in aqueous media

A mild and efficient ligand-free Suzuki-Miyaura coupling reaction catalyzed by heterogeneous Pd/C was developed. Aryl bromides and triflates undergo the cross-coupling with aryl boronic acids in excellent yields without the presence of any additives in aqueous media at room temperature. Aryl vinyl boronic acids are also applicable to this coupling reaction and provide the trans-stilbene derivatives in high yields. The application of wet-type Pd/C to the coupling reaction was achieved without any loss of activity under aerobic conditions, and the reuse of Pd/C is feasible for a fifth run without significant loss of activity. Inductively coupled plasma (ICP) mass-spectrometric analysis of the filtrate from the reaction mixture of 4-bromonitrobenzene with phenylboronic acid demonstrated that the palladium metal hardly leached into the solution within the limits of the detector (<1 ppm), thus suggesting that the present Suzuki-Miyaura reaction proceeded by heterogeneous catalysis.     

Possible mechanism of proton transfer through peptide groups in the H-pathway of the bovine cytochrome c oxidase

The peptide group connecting Tyr440 and Ser441 of the bovine cytochrome c oxidase is involved in a recently proposed proton-transfer path (H-path) where, at variance with other pathways (D- and K-paths), a usual hydrogen-bond network is interrupted, thus making this proton propagation rather unconventional. Our density-functional based molecular dynamics simulations show that, despite this anomaly and provided that a proton can reach a nearby water, a multistep proton-transfer pathway can become a viable pathway for such a reaction: a proton is initially transferred to the carbonyl oxygen of a keto form of the Tyr440-Ser441 peptide group [-CO-NH-], producing an imidic acid [-C(OH)-NH-] as a metastable state; the amide proton of the imidic acid is then transferred, spontaneously to the deprotonated carboxyl group of the Asp51 side chain, leading to the formation of an enol form [-C(OH)=N-] of the Tyr440-Ser441 peptide group. Then a subsequent enol-to-keto tautomerization occurs via a double proton-transfer path realized in the two adjacent Tyr440-Ser441 and Ser441-Asp442 peptide groups. An analysis of this multistep proton-transfer pathway shows that each elementary process occurs through the shortest distance, no permanent conformational changes are induced, thus preserving the X-ray crystal structure, and the reaction path is characterized by a reasonable activation barrier.