Encapsulation and Release Characteristics of Carbon Dioxide in α-Cyclodextrin

Encapsulation and release of carbon dioxide (CO₂) into and from α-cyclodextrin (α-CD) was studied. Initial moisture content of α-CD and CO₂ pressure were found to have affected the encapsulation behavior. The increase of CO₂ pressure has constantly accelerated the encapsulation rates and increased the maximum inclusion ratio, whereas the increase of initial moisture content showed no consistent effect. The saturated α-CD solution produced the inclusion complex crystal of similar inclusion ratio to solid α-CD. The release characteristics of inclusion complexes were also monitored at various relative humidities at 25 °C. Predominantly, increase in storage humidity accelerated the release of CO₂. The inclusion complex crystal prepared from saturated α-CD solution showed the most stable release characteristic at all storage humidities investigated. The encapsulation and the release characteristics were analyzed using the first-order reaction equation and the Avrami’s equation respectively, in order to estimate the rate processes of encapsulation and release. The FT-IR spectra of inclusion complexes presented an absorption band at wavenumber around 2338 cm⁻¹, indicating CO₂ molecules resided inside the α-CD cavities in gaseous state rather than being bound to the hydroxyl groups of α-CD. Powder X-ray diffractometry was carried out to investigate the crystal lattice structure of α-CD and inclusion complexes. Scanning electron microscopy was also performed for morphological examination.     

Polymerization of coordinated monomers. XXII. Ab initio molecular orbital study on the binary radical complexes of 2-methoxycarbonyl propyl radical with boron trichloride and with boron trifluoride as a model of growing radical end

The geometrical and electronic structures of the binary radical complexes of 2-methoxycarbonyl propyl radical with boron trichloride and with boron trifluoride were determined by using an ab initio molecular orbital method. The 2-methoxycarbonyl propyl radical complex was a model of the growing radical end in the copolymerization of methyl methacrylate in the presence of boron halides. The most stable structure of the binary radical complex composed of 2-methoxycarbonyl propyl radical with boron trichloride was a twisted form in which the dihedral angle between the vinyl group and the ester group was 32°, while that of the binary radical complex composed of methyl methacrylate radical with boron trifluoride was a planar form as the free radical. The frontier orbital energy of 2-methoxycarbonyl propyl radical was lowered by 0.06 au by the coordination of boron trichloride, while that was lowered only by 0.02 au by the coordination of boron trifluoride. The polymerization mechanism was elucidated on the basis of these predictions. © 1993 John Wiley & Sons, Inc.     

Synthesis of two possible diastereomers of reticulatain-1

A convergent synthesis of two possible diastereomers of reticulatain-1 (1a and 1b) was accomplished. Comparison of the specific optical rotations of 1a and 1b did not allow for the strict determination of the absolute configuration. However, bis-(R)-MTPA esters of 1a and 1b showed a clear difference in chemical shifts in the ¹H NMR spectra. If the bis-(R)-MTPA ester of natural reticulatain-1 (1) is available, the absolute configuration of 1 will be determined. Inhibitory action of these compounds was examined with bovine heart mitochondrial complex I. Both compounds showed almost the same activity.     

Mild, powerful, and robust methods for esterification, amide formation, and thioesterification between acid chlorides and alcohols, amines, thiols, respectively

We developed two efficient practical methods for esterification, amide formation, and thioesterification between acid chlorides and alcohols, amines, thiols, respectively. The present mild and robust reaction was performed by two separate methods both by combining cheap and readily available amines, N-methylimidazole, and N,N,N′,N′-tetramethylethylenediamine (TMEDA). Method A uses catalytic N-methylimidazole and TMEDA with an equimolar amount of K₂CO₃, whereas Method B uses equimolar amounts of N-methylimidazole and TMEDA. The salient features are as follows. (i) With regard to reactivity, Method B was superior to Method A for esterification and thioesterification, whereas cost-effective Method A was superior to Method B for amide formation. (ii) Amide formation proceeded smoothly between acid chlorides and less nucleophilic and stereocongested amines such as 2,6-dichloroaniline. (iii) This protocol was applied to the successful synthesis of two agrochemicals, bromobutide and carpropamid.     

Does Gd@C82 have an anomalous endohedral structure? Synthesis and single crystal X-ray structure of the carbene adduct

We report here the results on single crystal X-ray crystallographic analysis of the Gd@C82 carbene adduct (Gd@C82(Ad), Ad = adamantylidene). The Gd atom in Gd@C82(Ad) is located at an off-centered position near a hexagonal ring in the C2v-C82 cage, as found for M@C82 (M = Sc and La) and La@C82(Ad). Theoretical calculation also confirms the position of the Gd atom in the X-ray crystal structure.     

Missing metallofullerene La@C74

The first isolation of missing metallofullerene, La@C74, as a derivative is reported. The structural determination has been performed by spectroscopic and, finally, X-ray crystallographic analysis, and the properties of La@C74 are discussed on the basis of the theoretical study.     

Polymerization of coordinated monomers. XXI. Ab initio molecular orbital study on the binary molecular complex composed of methyl methacrylate and boron trifluoride

The stereo- and electronic structures of the binary molecular complex composed of methyl methacrylate and boron trifluoride are obtained by using an ab initio molecular orbital method with an STO-3G basis set. The total energy change on the binary molecular complex formation is ?1.3 X 10^?2 Hartree (?8.2 kcal/mol). The electron transfer from methyl methacrylate to boron trifluoride and the change in the energy level of the lowest unoccupied molecular orbital of methyl methacrylate on the complex formation with boron trifluoride are much smaller than those on the complex formation with boron trichloride. A twisted form in which the dihedral angle between the vinyl plane and the ester plane is 16.9° is the most stable structure of the binary molecular complex composed of methyl methacrylate and boron trifluoride. A strong bonding overlap population between a β-hydrogen of methyl methacrylate and a fluorine of boron trifluoride is found in this conformation. © 1992 John Wiley & Sons, Inc.     

Theoretical Study of Fluorescence Spectra Utilizing the pKa Values of Acids in Their Excited States

Assignment of the fluorescence spectrum of firefly luciferin in aqueous solutions was achieved by utilizing not only emission energies but also theoretical absorption spectra and relative concentrations as estimated by pK_a values. Calculated Gibbs free energies were utilized to estimate pK_a values. These pK_a values were then corrected by employing the experimental results. It was previously thought that the main peak near 550 nm observed in the experimental fluorescence spectra at all pH values corresponds to emission from the first excited state of the luciferin dianion [Ando et al. (2010) Jpn. J. Appl. Phys. 49, 117002–117008]. However, we found that the peak near 550 nm at low pH corresponds to emission from the first excited state of the phenolate monoanion of luciferin. Furthermore, we found that the causes of the red fluorescence at pH 1–2 are not only the emission from phenol monoanion but also the emission from the protonated species at nitrogen atom in the thiazoline ring of dianion.     

Chemical transformations of 4:7,10:13-diepoxy[15]annulenone by carbonyl transposition reactions

The titled annulenone 1 could be converted into new annulenones 3 and 8 by carbonyl transposition reactions. Compound 8 can be regarded as the first 14π hydroxy-enone as a higher homolog of tropolone (6π) and hydroxy[11]annulenones (10π), and was proved to be aromatic.