Biosynthetically Inspired Syntheses of Secu′amamine A and Fluvirosaones A and B

Presented here is a concise synthesis of secu′amamine A, and fluvirosaones A and B from readily available allosecurinine and viroallosecurinine. The key C2‐enamine derivative of (viro)allosecurinine, the presumed biosynthetic precursors of these natural products, was accessed, for the first time, by a VO(acac)₂‐mediated regioselective Polonovski reaction. Formal hydration and 1,2‐amine shift of this pluripotent enamine compound afforded secu′amamine A. Formal oxidative [3+2] cycloaddition reaction between this enamine and TMS‐substituted methallyl iodide reagent paved the way to the precursors of fluvirosaones A and B. The relative stereochemistry at the C2 position of these advanced intermediates governs the fate of 1,2‐amine shift leading to fluvirosaones A and B. The syntheses of potential biosynthetic precursors and investigations of their chemical reactivities have provided insights regarding the biogenesis of these natural products.     

Biosynthetically Inspired Syntheses of Secu′amamine A and Fluvirosaones A and B

Presented here is a concise synthesis of secu′amamine A, and fluvirosaones A and B from readily available allosecurinine and viroallosecurinine. The key C2-enamine derivative of (viro)allosecurinine, the presumed biosynthetic precursors of these natural products, was accessed, for the first time, by a VO(acac)₂-mediated regioselective Polonovski reaction. Formal hydration and 1,2-amine shift of this pluripotent enamine compound afforded secu′amamine A. Formal oxidative [3+2] cycloaddition reaction between this enamine and TMS-substituted methallyl iodide reagent paved the way to the precursors of fluvirosaones A and B. The relative stereochemistry at the C2 position of these advanced intermediates governs the fate of 1,2-amine shift leading to fluvirosaones A and B. The syntheses of potential biosynthetic precursors and investigations of their chemical reactivities have provided insights regarding the biogenesis of these natural products.     

Phosphinate selective hosts and importance of CH hydrogen bonding for affinity modulation toward anion guests

Even though phosphinate and its analogs are very important guests in nature, the artificial receptors which are capable of selective recognition of phosphinate are rare. Here, we report a series of acetate and phosphinate selective hosts (1, 2 and 3) which utilize amide NH and aliphatic CH groups as hydrogen bonding donors. In this series of receptors, even though the amide NH hydrogen bonding element was found to be the most significant, by varying the polarity of CH group, the magnitude of recognition could be modulated considerably. The affinities of host 3 against all the tested anion guests showed significantly higher affinities compared with those of hosts 1 and 2, and this could be attributed to the difference of CH group polarities among the receptors 1, 2 and 3. C_α-H hydrogen in host 3 is the most highly polarized by the charged pyridinium group. Therefore, it is the strongest host in this series of hosts. From the experiments shown here, we demonstrated the importance of CH hydrogen bonding element as a decisive modulating moiety for anionic recognition.     

Synthesis and characterization of novel polyimides bearing a side chain composed of stilbene mesogen and undecyl spacer and the alignment ability of nematic liquid-crystal molecules

Four different polyimides with side chains containing undecyl spacers and 4-fluorostilbene mesogen end groups were prepared, and their structures and the controllability of the liquid-crystal (LC) alignment with rubbing were investigated. From X-ray scattering and differential scanning calorimetry data, pyromellitic dianhydride (PMDA)-, benzophenone-3,3′,4,4′-tetracarboxylic dianhydride (BTDA)-, and 4,4′-oxydi(phthalic anhydride) (ODPA)-based polyimides were shown to have layered structures and short-range ordering. Pretilt angles of LCs on the rubbed surfaces were 1–9°, depending on the rubbing density and backbone. In particular, the long undecyl spacers caused the mesogenic stilbene end groups to lie next to the main chain, resulting in a reduction in the pretilt angles. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1800–1809, 2001     

In vivo labeling method of cyclosporin A with [14C-methyl]-S-adenosyl-L-methionine can evaluate a potency of cyclosporin A-producing mutant

Cyclosporin A synthetase activity ofTolypocladium inflatum can be estimated by measuring its N-methyltransferase activity. In vivo N-methyltransferase activity of cyclosporin A synthetase of cells was measured by in vivo [¹⁴C-methyl] labeling assay, which was designed for actively growing cells. After the cells were incubated with 0.025 μCi of [¹⁴C-methyl]-S-adenosyl-l-methionine, [¹⁴C-methyl] labelled cyclosporin A and its analogs inside the cells were extracted with ethylacetate and¹⁴C radioactivity of the ethylacetate extract of the cells was counted. When various mutant cells grown on agar plate medium after ultraviolet irradiation or N-methyl-N’-nitroso-guanidine treatment were applied to in vivo [¹⁴C-methyl] labeling assay, these mutants showed a broad range of in vivo N-methyltransferase activity. Poor correlation was found between in vivo N-methyltransferase activity of cyclosporin A synthetase of the mutant grown on agar plate and the actual amount of cyclosporin A production in shake-flask culture. However, when the cells grown on the shake-flask culture were applied in the in vivo [¹⁴C-methyl] labeling assay, a better correlation was resulted. In vivo N-methyltransferase activity reached the maximum value at about 150 h, and then declined quickly, but cyclosporin A was synthesized for 200 h during fermentation. Specific in vivo N-methyltransferase activity was not greatly influenced by culture age during fermentation. The major product of in vivo [¹⁴C-methyl] labeling assay was identified as cyclosporin A, and only trace amounts of other cyclosporin analogues were detected. Therefore, the results suggest that in vivo labeling method with [C¹⁴-methyl]-S-adenosyl-l-methionine can easily compare a potency of cyclosporin A-producing mutant during fermentation.     

The study on the effect of the substitution of K2CO3 with Ca(OH)2 on kinetics on CO2–lignite coal gasification

Research on Chemical Intermediates - Three kinds of lignite were mixed with K2CO3 and Ca(OH)2 and were gasified with CO2 to investigate the effect that the addition of Ca(OH)2 had on the...     

Wettability of the morphologically and compositionally varied surfaces prepared from blends of well ordered comb-like polymer and polystyrene

Phase-separated surfaces of blends of polystyrene (PS) and well ordered comb-like polymer, poly[(oxy(decylsulfonylmethyl)ethylene)] (CH(3)-10SE), were prepared by spin casting polymer mixtures. Various surface morphologies, such as holes, islands, connected islands and pillars, were prepared by changing the blend compositions. Due to the influence of the CH(3)-10SE domain with a well ordered molecular conformation, a very low energy surface (≈22mN/m) was created, which is close to the value of the pure polymer (≈20mN/m), even when the blends contained only 20wt.% of the pure polymer. Furthermore, by selective etching the PS domain in the blend surfaces, the advancing contact angles of water and n-hexadecane were highly increased from 113.5° and 43.2° for the pure CH(3)-10SE surface to 133.3° and 67.2° for the CH(3)-10SE structural surfaces with holes prepared using the solvent etching method, respectively. The result of the water advancing contact angles measured on the samples immersed in water over 20days showed that the film stability of CH(3)-10SE could be improved considerably by even adding small amounts of PS.     

Design, Modeling, Fabrication, and Evaluation of the Air Amplifier for Improved Detection of Biomolecules by Electrospray Ionization Mass Spectrometry

Through a multi-disciplinary approach, the air amplifier is being evolved as a highly engineered device to improve detection limits of biomolecules when using electrospray ionization. Several key aspects have driven the modifications to the device through experimentation and simulations. We have developed a computer simulation that accurately portrays actual conditions and the results from these simulations are corroborated by the experimental data. These computer simulations can be used to predict outcomes from future designs resulting in a design process that is efficient in terms of financial cost and time. We have fabricated a new device with annular gap control over a range of 50 to 70 μm using piezoelectric actuators. This has enabled us to obtain better aerodynamic performance when compared to the previous design (2× more vacuum) and also more reproducible results. This is allowing us to study a broader experimental space than the previous design which is critical in guiding future directions. This work also presents and explains the principles behind a fractional factorial design of experiments methodology for testing a large number of experimental parameters in an orderly and efficient manner to understand and optimize the critical parameters that lead to obtain improved detection limits while minimizing the number of experiments performed. Preliminary results showed that several folds of improvements could be obtained for certain condition of operations (up to 34 folds).     

Cation-pi-anion interaction: a theoretical investigation of the role of induction energies

Cation-pi and the corresponding anion-pi interactions have in general been investigated as binary complexes despite their association with counterions. However, a recent study of the ammonia channel highlights the important but overlooked role of anions in cation-pi interactions. In an effort to examine the structural and energetic consequences of the presence of counterions, we have carried out detailed ab initio calculations on some model cation-pi-anion ternary complexes and evaluated the nonpair potential terms, three-body contributions, and attractive and repulsive energy components of the interaction energy. The presence of the anion in the vicinity of the pi system leads to a large redistribution of electron density and hence leads to an inductive stabilization. The resulting electronic and geometrical changes have important consequences in both chemical and biological systems. Compared to cation-pi-anion ternary complexes, the magnitude of the cation-pi interaction in pi-cation-anion ternary complexes is markedly lower because of charge transfer from the anion to the cation.     

Characterization of supercooling suppression of microencapsulated phase change material by using DSC

Supercooling suppression of microencapsulated n-tetradecane was measured using differential scanning calorimetry. Results indicate that the degree of supercooling is positively affected by the amount and type of nucleating agent present in bulk and microencapsulated n-tetradecane which it is used as a phase change material (MPCM). Results also demonstrate that the melting point of the n-tetradecane is fairly independent of nucleating agent concentration (0 – 4%). Conversely, the latent heat of fusion of n-tetradecane decreases considerably with nucleating agent amount and the initiation of crystallization point is inversely proportional to cooling rate.