NMR studies of conformations and molecular recognition of pyridinio-appended and nicotinamide-appended β-cyclodextrin

Abstract

The conformations of pyridinio-appended β-cyclodextrin (CDP⁺) and nicotinamide-appended β-cyclodextrin (CDNA⁺) were studied by NMR spectroscopy. The orientations of the pyridine residue of CDP⁺ and the nicotinamide residue of CDNA⁺ were determined by using a combination of NMR spectroscopic techniques. NMR spectra indicate that the shapes of the cavities of CDP⁺ and CDNA⁺ were changed after forming complexes. This change depended on the shape of the guest. CDNA⁺ could separate the ¹H resonances at the Cβ position of racemic tryptophan into two sets of resonances for each enantiomer.     

Synthesis of 3-Alkylidenecepham-4-carboxylic Acid derivatives by Samarium(II) Iodide Reduction

Samarium(II) iodide promoted reductive deacetoxylation of 7-aminocephalosporanic acid derivatives to synthesize 3-alkylidenecepham-4-carboxylates, which could be valuable intermediates for the synthesis of new cephalosporin antibiotics, was investigated.     

The Synergistic Effect of a Bimetallic Catalyst for the Synthesis of Carbon Nanotube Aerogels and their Predominant Chirality

Synthesis of continuous spinnable carbon nanotube (CNT) fibers is the most promising method for producing CNT fibers for commercial applications. The floating-catalyst chemical vapor deposition (FC-CVD) method is a rapid process that achieves catalyst formation, CNT nucleation and growth, and aerogel-like sock formation within a few seconds. However, the formation mechanism is unknown. Herein, the progress of CNT fiber formation with bimetallic catalysts was studied, and the effect of catalyst composition to CNT fiber synthesis and their structural properties was investigated. In the case of bimetallic catalysts, the carbon source rapidly decomposes and generates various secondary hydrocarbon species, such as CH₄, C₂H₄, C₂H₂, C₃H₆, and C₄H₁₀ whereas monometallic catalysts generate only CH₄ and C₂H₄ on decomposition. CNT fiber formation with Fe₁Ni₀ begins about 400 mm from the reactor entrance, whereas CNT formation with Fe_0.8Ni_0.2 and Fe_0.5Ni_0.5 begins at about 500 and 300 mm, respectively. The formed CNT bundles and individual CNTs are oriented along the gas flow at these locations. The enhanced rate of fiber formation and lowering of growth temperature associated with bimetallic catalysts is explained by the synergistic effects between the two metals. The synthesized CNTs become predominantly semiconducting with increasing Ni contents.     

Synthesis and investigation of photovoltaic properties for polymer semiconductors based on porphyrin compounds as light-harvesting units

We reported on two polymer semiconducting copolymers based on porphyrin compounds, poly[9,9-dioctylfluorene-co-5,15-bis(hexoxybenzyl)-10,20-bis(benzo-4-yl)porphyrin] (PFPor) and poly[9-(heptadecan-9-yl)carbazole-co-5,15-bis(hexoxybenzyl)-10,20-bis(benzo-4-yl)porphyrin] (PCPor), for use as organic photovoltaic materials. The thermal, optical, electrochemical, and photovoltaic properties of the two polymers were investigated. In addition, PC₆₁BM and PC₇₁BM were introduced as acceptor materials to confirm the acceptor effect in bulk heterojunction photovoltaic devices. Moreover, in order to establish acceptor effects, morphologies of polymer/PCBM blend films were analyzed through atomic force microscopy (AFM). PFPor and PCPor exhibited the best device performance with power conversion efficiencies (PCE) of 0.62% and 0.76%, respectively, upon the introduction of PC₇₁BM as the acceptor in the device where 86 wt.% of the PC₇₁BM was contained in the active layer (pol:PC₇₁BM = 1:6, w/w).     

Two Gel States of a PEO‐PPO‐PEO Triblock Copolymer Formed by Different Mechanisms

Two gel states of a PEO‐PPO‐PEO (Pluronic P103) triblock copolymer in water are investigated using small‐angle X‐ray scattering, rheology and differential scanning calorimetry. The first gel state turns out to be the hexagonal microphase while the second gel state, showing turbidity change with four distinct regions, is somewhat disrupted. The second gel is moreover not thermoreversible as evidenced by rheology. Based upon the present study, two different gelation mechanisms for aqueous PEO‐PPO‐PEO solutions are proposed.     

Synthesis and thermal properties of disiloxane-arylene polymers by dehydrocoupling polymerization of bis(dimethylsilyl)arylene with water

Disiloxane-arylene polymers having phenylene, biphenylene, and fluorenylene groups as arylene units were synthesized by dehydrocoupling polymerization of corresponding bis(silane) derivatives with water. The reactivity of Si-H was not affected by the structure of aromatic groups in the reaction. The polymers containing biphenylene and fluorenylene units are amorphous and show higher glass transition temperatures than the polymer from 1,4-bis(dimethylsilyl)benzene.     

Airborne particulates (PM2.5/PM10) monitoring in Korea by instrumental neutron activation analysis

Instrumental neutron activation analysis was used for the analysis of 25 trace elements in airborne particulate matter (PM) for air pollution monitoring. For the collection of air samples, the Gent stacked filter unit low volume sampler and two types of Nuclepore polycarbonate filters were employed. Samples were collected at selected sampling dates in suburban and industrial regions of Daejon city in the Republic of Korea. Mass concentrations and black carbon of PM were measured, and enrichment factors were calculated. The results were used to describe the emission sources and their correlation patterns.