New oxindole alkaloids and iridoid from Carolina jasmine (Gelsemium sempervirens Ait. f.)

Three new gelsedine-type oxindole alkaloids, GS-1, GS-2, and GS-3, and one new iridoid, GSIR-1, were isolated from the stems and leaves of cultivated Carolina jasmine (Gelsemium sempervirens AIT. f.) and their structures were determined by spectroscopic analysis.     

Synthesis and activity of aryl benzyl methyl sulfonium salts as cationic initiators: Effect of substituent on aryl group

Benzyl o-, m-, and p-substituted phenyl methyl sulfonium salts ( 2b – 2g ) were synthesized and their activities as cationic initiators were evaluated in the bulk polymerization of phenyl glycidyl ether (PGE). Especially, their activities were estimated with respect to the effect of substituents on the aryl groups. In the polymerizations of PGE with a series of benzyl p-substituted phenyl methyl sulfonium salts, the order of their activities was found to be 2c (CH₃OCOO) > 2b (CH₃COO) > 2d (CH₃O) ～ 2a (HO). In particular, 2c was the most active initiator of all, capable of initiating the polymerization of PGE even at room temperature. In the polymerizations with 2a, 2e (m-Cl), 2f (o-CH₃), and 2g (m-CH₃), the activity of 2e was the highest of all while those of 2a, 2f , and 2g were almost the same. These results strongly suggested that the electron-withdrawing group placed on the aryl group undoubtedly enhanced the activity of the sulfonium salts as the cationic initiators.     

Structural studies of the Maillard reaction products of a protein using ion trap mass spectrometry

The early stage products of the Maillard reaction of egg white lysozyme with D-glucose were studied. Incubation with D-glucose at 50 degrees C for 20 days caused reaction on the Lys and Arg residues of lysozyme as follows: all of the six Lys residues and 10 of the 11 Arg residues in lysozyme reacted with D-glucose; Arg 61 did not react with D-glucose. The Lys residues reacted with D-glucose with 1 mol of dehydration per mole of residue, and the Arg residues reacted with 2 mol of dehydration per mole of residue. The major constituent of the Amadori product with the epsilon-amino group of the Lys residue and the D-glucose was found to be the beta-pyranose form. The structure of the early stage product of the Maillard reaction of a protein with a sugar is the same as that of an amino acid with a sugar.     

Photodissociation of CO from [Ru3(mu3-O)(mu-OOCCH3)6(CO)L2] in acetonitrile, where L = pyridine, 4-cyanopyridine and methanol

Photodissociation of CO from oxo-centered trinuclear ruthenium clusters [Ru3(mu3-O)(mu-OOCCH3)6(CO)L2] (L = pyridine (py): 1; 4-cyanopyridine (cpy): 2; methanol: 3) dissolved in organic solvents has been examined. Upon photolysis (> or = 290 nm, a 450-W Xe lamp), an absorption peak at 585 nm observed for 1 in CH3CN decreases its intensity and a new absorption band appears and grows at 896 nm. This spectral change, presenting isosbestic points, corresponds to photosubstitution of CO in 1 to form [Ru3(mu3-O)(mu-OOCCH3)6(CH3CN)(py)2] 4. Photoexcitation of carbonyl complexes 2 and 3 in CH3CN also affords the corresponding CH3CN-coordinated complexes [Ru3(mu3-O)(mu-OOCCH3)6(CH3CN)(cpy)2] 6 and [Ru3(mu3-O)(mu-OOCCH3)6(CH3CN)3] 7, respectively. The photosubstitution reactions (excitation wavelength, > or = 290 nm) are well described by the first-order kinetics: k = 7.3 x 10(-4) s(-1) for 1, 4.9 x 10(-4) s(-1) for 2 and 5.1 x 10(-4) s(-1) for 3 (298 K). In the presence of a 100-fold excess of py, photolysis of 1 yields a tris(py) complex [Ru3(mu3-O)(mu-OOCCH3)6(py)3] 5 via photochemical loss of CO followed by coordination of py. The overall reaction (photochemical and thermal) is also confirmed by 1H NMR spectroscopy. The dissociative character of the photosubstitution is supported by negligible effects of the concentration of the entering pyridine molecule, the nature of solvents and the type of terminal monodentate ligands (other than CO) attached to the cluster. Quantum yield measurements with varied excitation wavelengths have shown that absorption bands located in the UV region (< 400 nm) play a principal role in photosubstitution, whereas an absorption band in the visible region (centered at approximately 580 nm), ascribed to an "intracluster" charge transfer, is not at all responsible for photosubstitution.     

Specific Cα-C Bond Cleavage of β-Carbon-Centered Radical Peptides Produced by Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry

Radical-driven dissociation (RDD) of hydrogen-deficient peptide ions [M???H?+?H]^·+ has been examined using matrix-assisted laser dissociation/ionization in-source decay mass spectrometry (MALDI-ISD MS) with the hydrogen-abstracting matrices 4-nitro-1-naphthol (4,1-NNL) and 5-nitrosalicylic acid (5-NSA). The preferential fragment ions observed in the ISD spectra include N-terminal [a]?+?ions and C-terminal [x]⁺, [y?+?2]⁺, and [w]⁺ ions which imply that β-carbon (Cβ)-centered radical peptide ions [M???Hβ?+?H]^·+ are predominantly produced in MALDI conditions. RDD reactions from the peptide ions [M???Hβ?+?H]^·+ successfully explains the fact that both [a]⁺ and [x]⁺ ions arising from cleavage at the Cα-C bond of the backbone of Gly-Xxx residues are missing from the ISD spectra. Furthermore, the formation of [a]⁺ ions originating from the cleavage of Cα-C bond of deuterated Ala(d3)-Xxx residues indicates that the [a]⁺ ions are produced from the peptide ions [M???Hβ?+?H]^·+ generated by deuteron-abstraction from Ala(d3) residues. It is suggested that from the standpoint of hydrogen abstraction via direct interactions between the nitro group of matrix and hydrogen of peptides, the generation of the peptide radical ions [M???Hβ?+?H]^·+ is more favorable than that of the α-carbon (Cα)-centered radical ions [M???Hα?+?H]^·+ and the amide nitrogen-centered radical ions [M???H_N?+?H]^·+, while ab initio calculations indicate that the formation of [M???Hα?+?H]^·+ is energetically most favorable.

Open image in new window

Graphical Abstract ?

     

Hydrogel Formation Using New L‐Lysine‐Based Low‐Molecular‐Weight Compounds with Positively Charged Pendant Chains

Low‐molecular‐weight compounds based on L ‐lysine with alkylpyridinium or ‐imidazolium groups have been synthesized and studied for their gelation behavior in H₂O. Most compounds formed gels below a concentration of 2.5 weight‐%, the pyridinium bromide 2a and the 1‐methyl‐1H‐imidazolium bromide 3 even at 0.1 weight‐%. The minimum gel concentration (MGC) necessary for hydrogelation increased with increasing length of the Lys N^α‐alkanoyl chain, but the gelation ability concomitantly decreased. Electron‐microscopic images demonstrated that these hydrogelators create a three‐dimensional network in H₂O by entanglement of self‐assembled nanofibers. A fluorescence study with 8‐anilinonaphthalene‐1‐sulfonic acid (ANS) proved that some hydrophobic aggregates are formed at hydrogelator concentrations below an MGC of less than 50 μM (0.004%). FT‐IR, ¹H‐NMR, and Fluorescence studies indicated that the driving forces for the self‐assembly into nanofibers are mainly hydrophobic interactions and H‐bonding between amide groups.     

Recycling nanoparticles stabilized in water-in-CO2 microemulsions for catalytic hydrogenations

Catalytic hydrogenations of olefins took place effectively in supercritical CO2 with Pd0 nanoparticles dispersed in the fluid phase using a water-in-CO2 microemulsion consisting of water, sodium bis(2-ethylhexyl) sulfosuccinate (AOT) as a surfactant, and 1-octanol as a cosolvent. The hydrogenated products dissolved in supercritical CO2 can be separated from the octanol solution containing AOT microemulsions with Pd0 nanoparticles by phase separation (upper phase, supercritical CO2 with hydrogenated products; lower phase, 1-octanol containing AOT microemulsions with Pd0 nanoparticles) accompanied by reduction of CO2 pressure. After collecting the hydrogenated products by flowing the upper CO2 phase to a collection vessel, the Pd0 nanoparticles remaining in the lower phase can be redispersed into supercritical CO2 by pressurizing the system to a pressure where a homogeneous phase is attained. The redispersed nanoparticles can be reused as catalysts for the next runs of the hydrogenations. Triphenylethylene was hydrogenated to 1,1,2-triphenylethane at conversions of 100% (1st-3rd runs), >99% (4th run), and >96% (5th run) using the recycled Pd0 nanoparticles. The feasibility of using other organic solvents as cosolvents is also studied in the present paper.     

In situ observation of molecular diffusion in solid supports using two-photon fluorescence microscopy

We demonstrate that two-photon fluorescence microscopy is a useful tool for monitoring the diffusion of molecules through polymeric solid supports. As a proof of principle, TentaGel beads were bound to a cover slip, and diffusion of Rhodamine 6G through single beads was observed in real time. Diffusion experiments performed in 40 different beads indicate that there is a considerable degree of heterogeneity in diffusion rates from bead to bead.     

Swelled plastics in supercritical CO2 as media for stabilization of metal nanoparticles and for catalytic hydrogenation

Swelled plastics in supercritical carbon dioxide provide unique environments for stabilizing palladium and rhodium nanoparticles and for catalytic hydrogenation. Complete hydrogenation of benzene to cyclohexane can be achieved in 10 minutes using the plastic stabilized Rh nanoparticles at 50 degrees C in supercritical CO(2). High efficiency, reusability, and rapid separation of products are some advantages of the plastic stabilized metal nanoparticles for catalytic hydrogenation in supercritical CO(2).     

Structure elucidation and synthesis of lycoposerramine-B, a novel oxime-containing Lycopodium alkaloid from Lycopodium serratum Thunb

A new alkaloid, lycoposerramine-B (1), containing an oxime function, was isolated from the club moss Lycopodium serratum Thunb. The structure of 1 was elucidated by spectroscopic analysis, including J-resolved HMBC spectroscopy, and confirmed by its synthesis from the known alkaloid, serratinine (3).