Synthetic studies on oxindole spiro-lactones with thalliumd(III) trinitrate: A formal total synthesis of (±)-tryptoquivaline G

(±)-Tryptoquivaline G was formally synthesized through shortened steps from tryptophan, in which oxidation with thallium(III) trinitrate(TTN) was effected at the crucial stage. The present work also constitutes the first synthesis of oxindole lactones carrying 2-alkyl quinazolinones.     

Theoretical studies of the cross-linking mechanisms between cytosine and tyrosine

DNA-protein cross-linking is one of the many DNA lesions mediated by hydroxyl radicals, the most damaging among the reactive oxygen species in biological systems. Density functional theory methods are employed to investigate the complex reaction mechanisms of the formation of cytosine-tyrosine cross-links as observed in gamma-irradiated aqueous solutions of cytosine and tyrosine, as well as in gamma-irradiated nucleohistone. The majority of the radical addition mechanisms considered are found to have significant barriers and therefore to be thermodynamically unfavorable for the formation of the initial cross-linked product. Our calculated reaction potential energy surfaces suggest that a feasible complete mechanism consists of radical combination forming the initial cross-linked product, a hydrogen shuffle within the initial cross-linked product, and an acid-catalyzed dehydration reaction. Water and hydrogen-bonding interactions are suggested to play a key role in catalyzing the hydrogen-transfer step of the reaction.     

Visually precise,low-damage,single-cell spatial manipulation with single-pixel resolution

The analysis of single living cells, including intracellular delivery and extraction, is essential for monitoring their dynamic biochemical processes and exploring intracellular heterogeneity. However, owing to the 2D view in bright-field microscopy and optical distortions caused by the cell shape and the variation in the refractive index both inside and around the cells, achieving spatially undistorted imaging for high-precision manipulation within a cell is challenging. Here, an accurate and visual system is developed for single-cell spatial manipulation by correcting the aberration for simultaneous bright-field triple-view imaging. Stereo information from the triple view enables higher spatial resolution that facilitates the precise manipulation of single cells. In the bright field, we resolved the spatial locations of subcellular structures of a single cell suspended in a medium and measured the random spatial rotation angle of the cell with a precision of ±5°. Furthermore, we demonstrated the visual manipulation of a probe to an arbitrary spatial point of a cell with an accuracy of <1 pixel. This novel system is more accurate and less destructive for subcellular content extraction and drug delivery.

We achieved the low-damage spatial puncture of single cells at specific visual points with an accuracy of <65 nm.     

Aqueous Titanate Sols from Ti Alkoxide-α-Hydroxycarboxylic Acid System and Preparation of Titania Films from the Sols

Aqueous titanate sols were prepared by reactions of titanium tetraisopropoxide (TIP) with -hydroxycarboxylic acids in water. IR and Raman spectra, and elemental analyses of the precipitates obtained from the sols revealed that the carboxylates were chelated to titanium but the Ti species were polymerized to form a cluster that had a colloidal nature. Spin-coating of titania (TiO₂) thin films from these sols was also examined. Interestingly, it was found that (004) preferentially oriented anatase films with refractive index of 2.54 were obtained from TIP-lactic acid-NH₃ (1:1:1, molar ratio) aqueous sol. This crystallographic orientation was characteristic of the TIP-lactic acid-NH₃ (1:1:1) system, and was not affected by the kinds of substrates used and the heating rate of the film. TEM observation indicated that small anatase grains had already formed at 200°C. Therefore, the crystallographic orientation might depend strongly on the structure of the chemical species of the precursor solutions.     

Transition metal substituted tungstophosphoric compound catalyzed oxidation of hexanol to hexanal with hydrogen peroxide

Summary The oxidation of hexanol in the presence of the Keggin-type heteropoly compounds (HPCs) H₃PMo_nW_12-nO₄₀ (denoted as PMo_nW_12-n, n=0,1) and Na₅PW₁₁ZO₃₉ (denoted as PW₁₁Z, Z = Mn, Fe, Co, Ni, Cu and Zn) was carried out to produce hexanal and hexanoic acid. The reaction was conducted in tert-butanol (t-BuOH), using cetylpyridinium bromide (CPB) salts of HPA and 15% aqueous H₂O₂ as oxidant under mild condition. The PMoW₁₁ catalyst showed higher hexanol conversion of 25%, the lowest selectivity to hexanal of 64.4% and an efficient utilization of H₂O₂ of 34%. Over the transition metal substituted PW₁₁Z catalysts decomposition of H₂O₂ was rapid. For these PW₁₁Z catalysts, the efficient utilization of H₂O₂ decreased to 9% or even lower. By means of IR, UV-visible and GC-MS techniques the catalysts were characterized.     

Modeling the reaction mechanisms of the amide hydrolysis in an N-(o-carboxybenzoyl)-L-amino acid

Reaction mechanisms of the amide hydrolysis from the protonated, neutral, and deprotonated forms of N-(o-carboxybenzoyl)-l-amino acid have been investigated by use of the B3LYP density functional method. Our calculations reveal that in the amide hydrolysis the reaction barrier is significantly lower in solution than that in the gas phase, in contrast with the mechanism for imide formation in which the solvent has little influence on the reaction barrier. In the model reactions, the water molecules function both as a catalyst and as a reactant. The reaction mechanism starting from the neutral form of N-(o-carboxybenzoyl)-l-amino acid, which corresponds to pH 0-3, is concluded to be the most favored, and a concerted mechanism is more favorable than a stepwise mechanism. This conclusion is in agreement with experimental observations that the optimal pH range for amide hydrolysis of N-(o-carboxybenzoyl)-l-leucine is pH 0-3 where N-(o-carboxybenzoyl)-l-leucine is predominantly in its neutral form. We suggest that besides the acid-catalyzed mechanism the addition-elimination mechanism is likely to be an alternative choice for cleaving an amide bond. For the reaction mechanism initiated by protonation at the amidic oxygen (hydrogen ion concentration H(0) < -1), the reaction of the model compound with two water molecules lowers the transition barrier significantly compared with that involving a single water molecule.     

Determination of protein phosphorylation by extracellular signal-regulated kinase using capillary electrophoresis and matrix-assisted laser desorption ionization time-of-flight mass spectrometry

Extracellular signal-regulated kinase (ERK) is a key regulatory enzyme mediating cell responses to mitogenic stimulation and is one of the key components in linking growth factor receptor activation to serine/threonine protein phosphorylation processes. Phosphorylation reaction by ERK plays an important role in many signal transduction pathways. ERK phosphorylates numerous substrates such as MBP, microtubule-associated protein 2 (MAP2) and nuclear protein. In particular, MBP is a substrate commonly employed for the detection of ERK activity and contains the consensus primary sequence PRT97P. In this paper, we compared the degree of the phosphorylation reaction of MBP substrate peptides by ERK with the three different MBP substrate peptides, MBP1(KNIVTPRTPPPSQGK), MBP2(VPRTPGGRR) and MBP3(APRTPGGRR) in order to select an efficient substrate peptide for phosphorylation reaction by ERK. The results showed that the MBP3 peptide is the most efficient substrate for phosphorylation reaction by ERK. Using MBP3 peptide, the phosphorylation reaction of MBP by ERK was monitored with both matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and capillary electrophoresis (CE). Our results demonstrate the feasibility of the CE method, the method being a simple and reliable technique in determining and characterizing various kinds of enzyme reaction especially including kinase enzymes.     

Reaction of α-haloester having internal double bond with the low-valent metal complex

The α-haloester having an internal double bond was allowed to react with a catalytic amount of Pd(PPh₃)₄ to afford a cyclized product in a fairly good yield and the same product was obtained by treatment with Pd(OAc)₂ to ketene silyl acetal.     

Quantitative interrogation of protein co-aggregation using multi-color fluorogenic protein aggregation sensors

Co-aggregation of multiple pathogenic proteins is common in neurodegenerative diseases but deconvolution of such biochemical process is challenging. Herein, we developed a dual-color fluorogenic thermal shift assay to simultaneously report on the aggregation of two different proteins and quantitatively study their thermodynamic stability during co-aggregation. Expansion of spectral coverage was first achieved by developing multi-color fluorogenic protein aggregation sensors. Orthogonal detection was enabled by conjugating sensors of minimal fluorescence crosstalk to two different proteins via sortase-tag technology. Using this assay, we quantified shifts in melting temperatures in a heterozygous model protein system, revealing that the thermodynamic stability of wild-type proteins was significantly compromised by the mutant ones but not vice versa. We also examined how small molecule ligands selectively and differentially interfere with such interplay. Finally, we demonstrated these sensors are suited to visualize how different proteins exert influence on each other upon their co-aggregation in live cells.

A little leak will sink a great ship! We prepared a series of multi-color protein aggregation sensors and developed a dual-color thermal shift assay to simultaneously and quantitatively report on protein co-aggregation of two different proteins.     

Synthesis of Zeolite L. Tuning Size and Morphology

Summary. A convenient synthesis of zeolite L is presented. The size of the crystals can be tuned between 30 and 6000nm, spanning a volume range of seven orders of magnitude. The zeolite L crystals, which typically feature a cylindrical morphology, are synthesized with various aspect ratios ranging from elongated to disc-shaped. The importance of obtaining zeolite crystals with well-defined size and morphology is discussed in view of potential applications of zeolite L containing organic dye molecules as guests.This revised version was published online in February 2005. In the previous version the issue was not marked as a special issue, and the issue title and the editor was missing