Effect of C7-Substituent on Self-Assembly of Chlorosomal Chlorophylls

Abstract

Bacteriochlorophyll d analogues that possessed a series of bulky substituents of OMe, OCOMe, and OCO ^t Bu at the C7¹-position were synthesized (Zn-complexes of methyl 7¹-substituted-3-(1-hydroxy-methyl)pyropheophorbide a). Aggregation behavior of these pigments was examined in comparison with a natural-type compound (C7¹-H) to elucidate the effects of size of the C7¹-moiety on self-assembly of the chlorins. These C7¹-substituted Zn-chlorins formed self-aggregates in 1% THF/hexane. The aggregates gave almost the same visible absorption bands, especially a ca. 2000-cm^?1 red-shifted Q_y peak; the spectra were essentially similar to those of the natural-type Zn-chlorin (C7¹-H). All the aggregates of the C7¹-substituted compounds showed similar exciton-type CD couplets in the red-shifted Q_y region, which were different from the feature of the couplet of the C7¹-H Zn-chlorin aggregate. These spectral data suggested that the C7¹-moiety did not interrupt the intermolecular linkages between chlorin molecules but altered the supramolecular structure which influences the long-range chirality.     

The potential use of electrospun polylactic acid nanofibers as alternative reinforcements in an epoxy composite system

This pilot study elaborates the development of novel epoxy/electrospun polylactic acid (PLA) nanofiber composites at the fiber contents of 3, 5, and 10 wt % to evaluate their mechanical and thermal properties using flexural tests and differential scanning calorimetry (DSC). The flexural moduli of composites increase remarkably by 50.8 and 24.0% for 5 and 10 wt % fiber contents, respectively, relative to that of neat epoxy. Furthermore, a similar trend is also shown for corresponding flexural strengths being enhanced by 31.6 and 4.8%. Fractured surface morphology with scanning electron microscopy (SEM) confirms a full permeation of cured epoxy matrix into nanofiber structures and existence of nondestructive fibrous networks inside large void cavities. The glass transition temperature (T_g) of composites increases up to 54–60 °C due to embedded electrospun nanofibers compared to 50 °C for that of epoxy, indicating that fibrous networks may further restrict the intermolecular mobility of matrix in thermal effects. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 618–623     

Model Waveforms of Slow-Tail Sferics

Radiophysics and Quantum Electronics - We simulate numerically the propagation of slow-tail sferics, which occupy a wide frequency band from 1 Hz to 10 kHz, in the spherical Earth–ionosphere...     

Enhancement of Light Absorption Ability of Synthetic Chlorophyll Derivatives by Conjugation with a Difluoroboron Diketonate Group

The enhancement of the light absorption ability of synthetic chlorophyll derivatives is demonstrated. Chlorophyll derivatives directly conjugated with a difluoroboron 1,3‐diketonate group at the C3 position were synthesized from methyl pyropheophorbide‐d through Barbier acylmethylation of the C3‐formyl moiety, oxidation of the C3‐carbinol, and difluoroboron complexation of the diketonate. Electronic absorption spectra in a diluted solution showed that the synthetic conjugates gave an absorption band at λ=400–500 nm, with a Qy band shifted to a longer wavelength of λ≈700 nm. DFT calculations demonstrated that the absorption bands and redshifts were ascribable to the coupling of the LUMO of chlorin with that of the difluoroboron diketonate moiety. The introduction of a pyrenyl group at the C3³‐position of the conjugate afforded an additional charge‐transfer band over λ=500 nm, producing a pigment that bridged the green gap in standard chlorophylls.     

Radiation-induced polymerization of 3-octylthiophene

In order to develop a new synthetic method and to study mechanism of oxidative polymerization of conducting polymers, polymerization of 3-octylthiophene in several organic solvents by γ-irradiation was examined. Polymers bimodal distribution with molecular weights at 500–1000 and 2000–3000 were generated by the irradiation of chloroform solutions. The values of monomer conversion (G(?M)) decreased from 445 to 10 with doses from 0.99 kGy to 594 kGy. The large G(?M) values and dose dependence of G(?M) cannot be explained with widely accepted mechanism for electrochemical polymerization or chemical oxidative polymerization. Another mechanism, which proceeds through chain reactions, is proposed. This mechanism explains the large G(?M) and the dependence on the dose.     

Non-linear dielectric spectra of ferroelectric liquid crystals

Abstract

The non-linear dielectric relaxation spectroscopy has been recently developed and applied to soft materials such as polymers. We have applied this new method to the S*_C phases of some ferroelectric liquid crystals. Under a weak AC electric field, the original and third order harmonic frequency components of electric displacement are proportional to the first and third powers of the applied electric field, respectively. The linear spectrum obtained from the original frequency component shows the relaxation of Debye type and the third order non-linear spectrum shows the relaxation with an extended form of Debye type to the non-linear case. The third order non-linear dielectric increment is found to be negative, which implies that the dielectric non-linearity of the liquid crystal in the S*_C phase is due to the saturation of molecular dipole moments induced by the applied electric field. The temperature dependence of the linear and third order non-linear spectra in the S*_C phase are also studied. Both spectra do not change their forms much through the whole temperature range of the S*_C phase. In the vicinity of the S_A–S*_C transition temperature, the critical behaviour is more remarkable in the third order spectrum than in the linear one.