Cadinane-type sesquiterpenes from the roots of Taiwania cryptomerioides Hayata

Five new cadinane-type sesquiterpenes, 15-acetoxy-T-muurolol (1), isokhusinodiol (2), cadin-10(14)-ene-4beta,5alpha-diol (3), cadinane-4beta,5alpha,10beta-triol (4), and muurolane-4beta,5beta,10beta-triol (5), together with five known compounds, T-cadinol (6), T-muurolol (7), alpha-cadinol (8), delta-cadinol (9), and khusinodiol (10), were isolated from the roots of Taiwania cryptomerioides. The structure of the new constituents were elucidated through chemical and spectral studies.     

Synthesis of Mg-Al and Zn-Al-layered double hydroxide nanocrystals using laser ablation in water

In this paper, we report our results on the synthesis of Mg-Al and Zn-Al-layered double hydroxides using the laser ablation in the liquid technique. To prepare these layered double hydroxides (LDH) we first began with the laser generation of a Mg (or zinc) target submerged in deionized water and then ablated an aluminum target submerged in the previously prepared Mg-deionized water suspensions (Mg-dw) to produce Mg-Al LDH and in Zn-dw to prepare Zn-Al LDH. In these ablation tests, the Mg ablation duration was selected to vary from 5 to 60 min, while the Al ablation duration was kept constant at 30 min for all samples. The generated Mg-Al LDH was a gel-like and well crystallized nanoparticles of a rod-like shape and were arranged in a well-organized pattern. When the Mg ablation duration between 25 and 35 min, the synthesized nanocrystals were stoichiometric with a formula of Mg₆Al₂(OH)₁₈4.5(H₂O), the interlayer distance (d_(0 0 3)-spacing) was 7.8 Å and the average grain size was 8.0 nm. The synthesized Zn-Al LDH revealed various lamellar thin plate-like nanostructures of hexagonal morphologies. The average diameters of these structures was about 500 nm and the thickness of a single layer was approximately about 6.0 nm. The XRD diffraction peaks were indexed in hexagonal lattice with a_o=3.07 Å and c_o=15.12 Å. These indexes were (0 0 2), (0 0 4), and (0 0 8) and the corresponding interlayer distances, d-spacing (Å), were 7.56 (0 0 2), 3.782 (0 0 4), and 1.891 (0 0 8), respectively.     

ENHANCED POOL BOILING HEAT TRANSFER WITH SURFACE ATTACHMENT

Abstract

A pool boiling experiment with either water or Freon-113 was conducted to investigate nucleate boiling from a heated wall with either a spherical or a cylindrical attachment. The result revealed that nucleate boiling can be enhanced by applying a horizontal cylindrical attachment to a vertical heated wall, owing to the favorable thermal environment characterized by a small-gradient liquid temperature profile within the restricted regions between the attachment and the heated wait. Nucleate boiling is enhanced in terms of a lower wall superheat required for incipient boiling and more bubbles generated than from an open heated wall. As a result of the enhanced nucleate boiling, heal transfer of the vertical heated wall above the attachment was improved due to excessive bubbles moving upward along the heated wall, causing removal of the thermal layer near the wall and evaporation of the thin liquid film between the bubbles and the wall. The boiling curve hysteresis with Freon-113 was significantly reduced as a result. The effects of diameter, length and surface roughness of the cylindrical attachment were also investigated.     

New Lignans from the Roots of Taiwania cryptomerioides Hayata

The five new lignans designated 3′,4′‐de‐O‐methylenehinokinin ( 1 ), taiwaninolide ( 2 ), 8′‐hydroxysavinin ( 3 ), isoguamarol ( 4 ), and 4′‐O‐methylsalicifolin ( 5 ), as well as the new 4‐(3,4‐dimethoxybenzyl)dihydro‐3‐(4‐hydroxybenzyl)furan‐2(3H)‐one ( 6 ) were isolated from the roots of Taiwania cryptomerioides, besides the three known compounds hinokinin ( 8 ), savinin ( 9 ), and 3,4‐de‐O‐methylenehinokinin ( 7 ). The structures of the new constituents were elucidated through chemical and spectral studies. A compound previously isolated from the heartwood of Chamaecyparis obtusa var. formosana was assigned structure 1 ; however, this structure has now been revised to be 3,4‐de‐O‐methylenehinokinin ( 7 ).     

New Cadinane‐Type Sesquiterpenes from the Roots of Taiwania cryptomerioides Hayata

Six new cadinane‐type sesquiterpenes, (1β,4β,5α,10α)‐1,4‐epoxymuurolan‐5‐ol ( 1 ), (4α,10β)‐4,10‐dihydroxycadin‐1(6)‐en‐5‐one ( 2 ), (2β,3α,4β,6β)‐2,3‐dihydroxycadin‐1(10)‐en‐5‐one ( 3 ), (2β,3α)‐α‐corocalene‐2,3‐diol ( 4 ), (7S)‐α‐calacoren‐14‐ol ( 5 ), and (8β,9β,10β)‐8,9‐epoxycalamenene‐3,10‐diol ( 6 ) together with one known compound, (8β,9β,10β)‐8,9‐epoxycalamenen‐10‐ol ( 7 ), were isolated from the roots of Taiwania cryptomerioides. The structures of the new constituents were essentially elucidated by spectral evidence.     

New abietane and seco-abietane diterpenes from the roots of Taiwania cryptomerioides

Four new diterpenes, 3-oxosaprorthoquinone (1), 3-oxomicrostegiol (2), 3-oxoisotaxodione (3), and taiwaninal (4), together with two known compounds, 3-oxosapriparaquinone (5) and 6-dehydrohinokiol (6), were isolated from the roots of Taiwania cryptomerioides. The structures of 1-4 were principle elucidated based on spectral evidence.     

Novel Antifungal Dimers from the Roots of Taiwania cryptomerioides

Five new dimer compounds, namely Taiwaniacryptodimers A–E (1–5), were isolated from the methanol extract of the roots of Taiwania cryptomerioides. Their structures were established by mean of spectroscopic analysis and comparison of NMR data with those of known analogues. Their antifungal activities were also evaluated. Our results indicated that metabolites 1, 2, 4, and 5 displayed moderate antifungal activities against Aspergillus niger, Penicillium italicum, Candida albicans, and Saccharomyces cerevisiae.     

Continuous-distribution kinetics for degradation of polybutylene terephthalate (PBT) in supercritical methanol

The depolymerization of polybutylene terephthalate (PBT) in supercritical methanol was investigated by using a batch autoclave reactor. Continuous kinetics analysis was applied to experimental data. It was observed that PBT could dissolve into supercritical methanol quickly and decompose completely in a homogeneous phase. PBT with average molecular weight of about 29 700 was converted to oligomer with that of 4200 within 10 min and with that of 2700 in 15 min at 513 K and converted into monomer completely within 22 min. The main reaction products decomposed of PBT were dimethylterephthalate (DMT) and 1, 4-butanediol (BG) by methanolysis. The yields of monomer components of the decomposition products, including byproducts were measured. The yields of DMT and BG could reach 94.5% and 70.1%, respectively, at 563 K for 75 min. Based on the qualitative and quantitative analyses of the products, a depolymerization-reaction scheme was proposed to explain the reaction mechanism, i.e. the degradation of PBT in supercritical methanol mainly includes random scission and chain-end scission reactions and side reactions for monomer components. With the process of degradation, some oligomers could be decomposed into small molecular products by side reactions. Continuous-distribution kinetics theory was developed to analyze the decomposition behavior. The energy of activation for the random scissions of PBT in the supercritical methanol was 86.53 kJ/mol.     

Two novel 9,11-seco-11-norabietanes from the roots of Taiwania cryptomerioides

Two novel 9,11-seco-11-norabietanes, namely taiwanlactones A (1) and B (2), together with 3β-hydroxysugiol (3) and 6α-hydroxysugiol (4), were isolated from the roots of Taiwania cryptomerioides. Their structures were elucidated through spectral studies. The absolute configuration of 1 was elucidated by a modified Mosher’s method. The biotransformation mechanisms of 1 and 2 were proposed.     

Selection criteria for solvent and coagulation medium in view of macrovoid formation in the wet phase inversion process

Sponge‐like and finger‐like structures are two distinct membrane structures commonly observed in membranes produced by the wet immersion process. An index Φ calculated solely from solubility parameters was defined as an indicator of the membrane structure. The Φ values of four polymers, poly(methyl metharylate), polysulfone, cellulose acetate, and poly(vinylidene fluoride), in various solvent‐nonsolvent pairs were calculated and compared with the corresponding membrane structures. It was found that the finger‐like structure often occurred at higher Φ values. Although the Φ value represents mostly the thermodynamics nature of a system, as an index for prior selection of solvent‐nonsolvent pairs for a particular polymer, a general rule of thumb was developed. Taking 15% polymer concentration and 300 μm casting thickness as a referential casting condition, selecting solvent‐nonsolvent pairs with Φ values higher than 0.25 is suggested, when a finger‐like structure is desired. The polymer concentration in the casting solution and the casting thickness will also affect the membrane structure. If a higher polymer concentration needs to be used, selection of a polymer‐solvent‐nonsolvent system with a Φ value much higher than 0.25 is suggested, or keeping the casting thickness lower than 300 μm to obtain a finger‐like membrane structure. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1495–1502, 1999