Spatially resolved piezo-spectroscopic characterizations for the validation of theoretical models of notch-root stress fields in ceramic materials

The main aim of this work is a precise experimental assessment of the local stress fields developed at the notch-root in a ruby crystal, selected as a paradigm brittle material, by means of photo- and electron-stimulated luminescence techniques. Our approach takes advantage of the piezo-spectroscopic (PS) effect, which consists of a spectral shift of the luminescence emitted by the material due to lattice strain. Highly spatially resolved stress maps were extensively collected at the notch-root and spectral shifts monitored for the chromophoric (R-lines) fluorescence observed in a single-crystalline ruby sample. Experimental data were analyzed and compared to the theoretical solutions of notch-root stress fields given by Filippi and by Creager-Paris. Due to its inherent simplifications, the Creager–Paris solution was found leading to underestimation of the maximum stress value piled up in the material, while the Filippi’s solution represented a more suitable approximation for the stress field developed at the notch-root.     

6‐Di­methoxy­methyl‐1‐methoxy­carbonyl­bi­cyclo­[3.1.0]­hex‐2‐ene‐2‐carboxyl­ic acid

The title compound, C₁₂H₁₆O₆, prepared by a standard synthetic method, was determined by single‐crystal X‐ray crystallography to exist with a cyclo­propane ring fused to a cyclo­pentene ring. Comparison of the unit‐cell dimensions and space group of this material with those of a crystal of the same material prepared using a route involving pig liver esterase hydro­lysis shows them to be identical.     

Practical selective monohydrolysis of bulky symmetric diesters: Comparing with sonochemistry

The conditions of the practical selective monohydrolysis of symmetric diesters we previously reported have been modified and applied to selective monohydrolysis of bulky symmetric diesters. While ultrasound is generally considered effective for two-phase reactions, its effect actually turned out to be rather marginal. Instead, use of a larger proportion of a polar aprotic co-solvent, DMSO, and aqueous KOH helped enhance the reaction rates and improve the yields of the half-esters. The reactions are simple, mild and practical without special devices.     

Di-tert-butylsilylene (DTBS) group-directed α-selective galactosylation unaffected by C-2 participating functionalities

We have discovered an unusual α-galactosylation using phenylthioglycoside of 4,6-O-di-tert-butylsilylene (DTBS)-protected galactose derivatives as a glycosyl donor, which was not hampered by the neighboring participation of C-2 acyl functionality such as NTroc and OBz. The power of the DTBS effect has been exemplified by the coupling reaction with various glycosyl acceptors.     

Synthesis of a capillarisin sulfur-analogue possessing aldose reductase inhibitory activity by selective isopropylation

We describe the synthesis of 2-[(4-hydroxyphenyl)thio]-7-isopropoxy-5,6-dimethoxy-4H-chromen-4-one 2 from 3,4,5-trimethoxyphenol 6 via the key intermediate, 3-iodo-7-isopropoxy-5,6-dimethoxy-4H-chromen-4-one 3. An important feature of this synthetic scheme involves selective alkylation, which can be achieved by two different routes. One route involves the selective isopropylation of a triacetate derivative 4 under basic conditions. The second route employs the selective demethylation of a trimethoxy derivative 5 under acidic conditions followed by isopropylation. The product of these alternative routes, compound 3, is then converted to a capillarisin sulfur analogue 2 in a one-pot reaction via the imidazolyl intermediate 22.     

13C NMR spectroscopic studies of the behaviors of carbonyl compounds in various solutions

¹³C NMR spectroscopic studies were performed for carbonyl compounds having a hydroxyl group, a carboalkoxy group, an acetoxy group, or a carboxyl group in various solvents with different polarities for observation of their behaviors of ¹³C NMR chemical shifts of carbonyl carbons in solutions. It was found that the chemical shifts of the carbonyl carbons in ¹³C NMR have good correlation with the empirical parameter for solvent polarities, E_T^N, depending on the structures. Inter- or intramolecular hydrogen bonding and dipolar-dipolar interactions appear to play a key role in this observation.     

Photoreactivity of amino acids: tryptophan-induced photochemical events via reactive oxygen species generation.

Tryptophan (Trp), an aromatic amino acid, is a constituent of peptides/proteins and is also a precursor of serotonin, kynurenine derivatives, and nicotinamide adenine dinucleotides. There have been a number of reports on photochemical reactions involving peptides/proteins which contain Trp that showed significant photodegradation, dimerization, and photoionization. The photochemical properties of Trp have not been fully elucidated, and this would provide novel insight into the handling of Trp-containing peptides/proteins. Consequently, we have been trying to evaluate the photochemical properties of Trp, as well as other essential amino acids, focusing on their photosensitivity, photodegradation, and their ability to induce lipid peroxidation. Among all the essential amino acids tested, Trp exhibited the maximal level of superoxide anion generation under 18 h of light exposure (30000 lux). UV spectral analysis of Trp suggested the absorbability of UVA/B light, and exposure of Trp, in both solid and solution states, to UVA/B light resulted in significant photodegradation (t(0.5): 18 h) and gradual color changes. In addition, photoirradiated Trp generated lipoperoxidant, a causative agent of photoirritation, and this might be associated with ROS generation.     

Dehydration of raffinose pentahydrate: structures of raffinose 5‐, 4.433‐, 4.289‐ and 4.127‐hydrate at 93 K

Raffinose [or O‐α‐D‐galactopyranosyl‐(1→6)‐α‐D‐glucopyranosyl‐(1→2)‐β‐D‐fructofuranoside] pentahydrate, C₁₈H₃₂O₁₆·5H₂O, (I), and three lower hydrates, namely the 4.433‐, (II), 4.289‐, (III), and 4.127‐hydrated, (IV), forms, obtained in the course of the dehydration of (I), have been studied. The unit cells in the space group P2₁2₁2₁ are of similar dimensions for all the crystals. The conformation of the raffinose molecules remains almost the same across the four crystal structures. The raffinose molecules are linked into a three‐dimensional hydrogen‐bonded network involving all the –OH groups, the ring and glycosidic O atoms, and the water molecules. Six water sites were identified in the structures of (II), (III) and (IV), of which W1, W4 and W6 (W = water) are partially occupied with their populations coupled. W1, W4 and one of the –OH groups of the galactose ring form an infinite hydrogen‐bonding chain around a 2₁ axis parallel to the a axis (denoted chain A), and W6 and the same –OH group form a similar chain (chain A′) disordered with chain A. The occupancy ratio of chain A to chain A′ for N‐hydrates (N is a hydration number between 4 and 5) is (N− 4):(5 −N). The transformation of chain A to chain A′ as part of the dehydration process has little effect on the rest of the structure. Thus, the dehydration proceeds without significant impact on the crystal structure.     

Toxicity of Methanol and Formaldehyde Towards <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> as Assessed by DNA Microarray Analysis

To assess the toxicity of the C1 compounds methanol and formaldehyde, gene expression profiles of treated baker’s yeast were analyzed using DNA microarrays. Among approximately 6,000 open reading frames (ORFs), 314 were repressed and 375 were induced in response to methanol. The gene process category “energy” comprised the greatest number of induced genes while “protein synthesis” comprised the greatest number of repressed genes. Products of genes induced by methanol were mainly integral membrane proteins or were localized to the plasma membrane. A total of 622 and 610 ORFs were induced or repressed by formaldehyde, respectively. More than one-third of the genes found to be strongly repressed by formaldehyde belonged to the “protein synthesis” functional category. Conversely, genes in the subcategory of “nitrogen, sulfur, and selenium metabolism” within “metabolism” and in the category of “cell rescue, defense, and virulence” were up-regulated by exposure to formaldehyde. Our data suggest that membrane structure is a major target of methanol toxicity, while proteins were major targets of formaldehyde toxicity.     

Top-down analysis of protein isoprenylation by electrospray ionization hybrid quadrupole time-of-flight tandem mass spectrometry; the mouse Tgamma protein

Protein isoprenylation, an important post-translational modification with a lipid, involves the selective attachment of two types of isoprenoids, farnesyl (C15) and geranylgeranyl (C20). The isoprenoid is linked via a thioether bond to the C-terminal cysteine residue of a variety of cellular proteins, including the heterotrimeric G protein gamma-subunits. One member of the G protein family, transducin (Talpha/Tbetagamma), plays a central role in visual transduction, and the structure-function relationship has been extensively studied with purified proteins, predominantly with bovine transducin that was shown to be farnesylated at the C-terminal cysteine residue of the gamma-subunit (Tgamma). We report here the structure of the C-terminal modification of mouse Tgamma, which has not yet been elucidated owing to the low amount of protein that can be isolated from the mouse retina. Electrospray ionization mass spectrometry (ESI-MS) of the high-performance liquid chromatography (HPLC)-purified Tgamma was in good agreement with the calculated mass of the farnesylated and methylated form of mouse Tgamma (Pro1-Cys70). A 'top-down' analysis of intact Tgamma using an ESI hybrid quadrupole time-of-flight (TOF) tandem mass spectrometer provided isoprenyl-specific ions that were observed to produce ions separated by 204 Da from the conventional (unmodified) precursor ion or the C-terminal sequence ions. Such characteristic fragmentation on an isoprenoid observed in top-down analysis could be useful in general for determining the type of isoprenylation as well as probing the site of modification in the protein sequence.