Supramolecular design for multivalent interaction: maltose mobility along polyrotaxane enhanced binding with concanavalin A

High molecular mobility of maltose-conjugated alpha-cyclodextrins (alpha-CDs) along a poly(ethylene glycol) (PEG) chain due to the mechanically locked structure of polyrotaxanes enhanced multivalent interactions between maltose and concanavalin A (Con A). When maltose groups are conjugated with alpha-CDs that were threaded onto a PEG capped with benzyloxycarbonyl l-tyrosine (polyrotaxane), Con A-induced hemagglutination was greatly inhibited by polyrotaxanes with a certain threading % of alpha-CDs. Such an inhibitory effect was significantly superior to the other type of conjugates, in which poly(acrylic acid) was used as a backbone for maltose conjugation. The spin-spin relaxation time (T2) of the maltose C(1) proton in the polyrotaxane at a typical alpha-CD threading % was significantly larger than that of any other conjugate, which was well related to the inhibitory effect. Therefore, we concluded that the high mobility of maltose groups along the polyrotaxane structure contributes to enhanced Con A recognition.     

Hemilabile amidomonophosphine ligand-rhodium(I) complex-catalyzed asymmetric 1,4-addition of arylboronic acids to cycloalkenones

The asymmetric 1,4-addition reaction of arylboronic acids with cycloalkenones was catalyzed by 1 mol % of an amidomonophosphine-rhodium(I) catalyst in a 10:1 mixture of 1,4-dioxane and water at 100 degrees C, affording 3-arylcycloalkanones in reasonably high enantioselectivity and high yields. It was revealed by NMR, IR, and X-ray spectroscopies that this bidentate amidomonophosphine behaves as a hemilabile ligand that contains a hard donor site in addition to the soft donor in a molecule. Phosphorus atom strongly bonds to rhodium(I), and the amide carbonyl oxygen is coordinatively labile. The reaction efficacy of phenylboronic acid with cyclopent-2-en-1-one was significantly dependent on the possibility of coordination of the amide carbonyl oxygen to rhodium(I).     

Vapor pressure measurements in carrier gas containing ligand vapor using the transpiration technique

The vapor pressures of 1,1,1-trifluoro-2,4-pentanedionates were measured in 0.1–10 mm Hg using the transpiration technique with helium or helium containing the ligand vapor as carrier gas. The injection chamber of a gas chromatograph equipped with a ligand vapor generator was used. The vapor pressure of bis(1,1,1-trifluoro-2,4-pentanedionato)nickel(II) was measured for the first time, stabilized in ligand vapor atmosphere. The vapor pressures of standard samples (naphthalene and benzoic acid) agreed well with previously reported values.     

Stereochemistry of reaction products of 1,3-dimethylthymine epoxide with amines

Reaction of 1,3-dimethylthymine epoxide with amines afforded cis and trans adducts, stereostructures of which were elucidated and treatment of trans adduct with boron trifluoride etherate afforded cis adduct; mechanism for the isomerization is presented.     

Development of high-resolution optical scanning fluorescence microscopy

Instrumentation of a high-resolution optical scanning fluorescence microscope is presented. This instrument provides a fluorescent image of the structural surface of various kinds of thin membrane samples with high resolution on the molecular scale. For this instrument, a new excitation optical tip and a three-dimensional scanning unit have been designed. The optical tip consists of a sharpened optical fibre covered with evaporated aluminium in vacuo, on which the top has a pinhole. The optical tip is mounted in the centre of a crosslinked piezoelectric scanning head. On thez-axis, a piezoelectric positioner is equipped with a differential micrometer mechanism. All operations are controlled with a micro-computer system.The scanning area in this instrument is 4000*4000 nm₂ for measurements of biological specimens. Several optical scanning microscopic images as well as the STM image are presented.     

Synthesis of thiophene-containing hybrid calixphyrins of the 5,10-porphodimethene type

The synthesis, structure, and optical and electrochemical properties of thiophene-containing hybrid calixphyrins are reported. The 5,10-porphodimethene type 14pi- and 16pi-S,N2,X-hybrid calixphyrins (X = NH, O, S) were prepared by acid-promoted dehydrative condensation between a thiatripyrrane and the corresponding 2,5-bis[hydroxy(phenyl)methyl]heteroles followed by DDQ oxidation. Both crystallographic and spectroscopic analyses of the newly prepared hybrid calixphyrins have revealed that the combination of heteroles explicitly influences the electronic structures of the pi-conjugated framework. The 14pi-S,N2,X-hybrid calixphyrins have proven to be fluorescent in solution.     

Discrimination and identification of the six aromatic positional isomers of trimethoxyamphetamine (TMA) by gas chromatography-mass spectrometry (GC-MS)

A reliable and accurate GC-MS method was developed that allows both mass spectrometric and chromatographic discrimination of the six aromatic positional isomers of trimethoxyamphetamine (TMA). Regardless of the trifluoroacetyl (TFA) derivatization, chromatographic separation of all the investigated isomers was achieved by using DB-5 ms capillary columns (30 m x 0.32 mm i.d.), with run times less than 15 min. However, the mass spectra of the nonderivatized TMAs, except 2,4,6-trimethoxyamphetmine (TMA-6), showed insufficient difference for unambiguous discrimination. On the other hand, the mass spectra of the TFA derivatives of the six isomers exhibited fragments with significant intensity differences, which allowed the unequivocal identification of all the aromatic positional isomers investigated in the present study. This GC-MS technique in combination with TFA derivatization, therefore, is a powerful method to discriminate these isomers, especially useful to distinguish the currently controlled 3,4,5-trimethoxyamphetmine (TMA-1) and 2,4,5-trimethoxyamphetmine (TMA-2) from other uncontrolled TMAs.     

Rapid induction of thermoreversible hydrogel formation based on poly(propylene glycol)-grafted dextran inclusion complexes

Poly(propylene glycol) (PPG)-grafted dextran was synthesized by conjugating amino-terminated PPG with hydroxyl groups of dextran, and its inclusion complexation property was investigated. The average number of grafted PPG per dextran was changeable in the range of 1.1 to 38.5. The formation of inclusion complexes between the PPG grafts and β-cyclodextrins (β-CDs) and their crystalline structures were characterized by ¹³C CP/MAS NMR and X-ray spectroscopies. These hydrogel systems showed a thermally reversible sol–gel transition based on supramolecular assembly and dissociation between host and guest moieties. The results of rheological measurements and sol–gel transition temperature of the hydrogels suggested that the aggregated channel-type crystalline domain was critical to control the transition temperature in terms of initial feed molar ratio of PPG and β-CD and the graft number of PPG constituents. These thermoreversible hydrogel systems showed rapid gelation properties, which may be useful for biomedical application, especially injectable drug delivery systems.

Sol–gel phase transition of ICs between PPG-grafted dextrans and β-CDs. (conc. of IC was fixed at 20 wt.-%).