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21.
Motoharu Inagaki Taichi Isogai Kenta Motobayashi Kai-Qiang Lin Bin Ren Katsuyoshi Ikeda 《Chemical science》2020,11(36):9807
In surface-enhanced Raman spectra, vibrational peaks are superimposed on a background continuum, which is known as one major experimental anomaly. This is problematic in assessing vibrational information especially in the low Raman-shift region below 200 cm−1, where the background signals dominate. Herein, we present a rigorous comparison of normal Raman and surface-enhanced Raman spectra for atomically defined surfaces of Au(111) or Au(100) with and without molecular adsorbates. It is clearly shown that the origin of the background continuum is well explained by a local field enhancement of electronic Raman scattering in the conduction band of Au. In the low Raman-shift region, electronic Raman scattering gains additional intensity, probably due to a relaxation in the conservation of momentum rule through momentum transfer from surface roughness. Based on the mechanism for generation of the spectral background, we also present a practical method to extract electronic and vibrational information at the metal/dielectric interface from the measured raw spectra by reducing the thermal factor, the scattering efficiency factor and the Purcell factor over wide ranges in both the Stokes and the anti-Stokes branches. This method enables us not only to analyse concealed vibrational features in the low Raman-shift region but also to estimate more reliable local temperatures from surface-enhanced Raman spectra.Both electronic and vibrational information at the metal/dielectric interface were explicitly extracted from surface-enhanced Raman spectra. 相似文献
22.
AKIRA Isogai 《Cellulose (London, England)》1997,4(2):99-107
Low molecular weight cellulose (degree of polymerization = ca 15) was dissolved in 4-- 30% NaOD/D2O, and relationships between 1H- and 13C-chemical shifts of the cellulose and NaOD concentrations were studied in terms of the dissociation of three hydroxyl groups of cellulose in aqueous NaOH solutions. All C---H proton resonances were shifted upfield linearly with an increase in the NaOD concentration, indicating that all C---H protons of cellulose undergo the electron-shielding effect by NaOH. On the other hand, the shifting patterns of carbon resonances varied among the six carbons: C1 and C4 carbons undergo the electron-shielding effect, whereas C2, C3, C5, and C6 carbons experience the electron-deshielding effect by NaOH. Changes in 13C-chemical shifts of cellulose carbons in 4--30% NaOD/D2O indicate that C3---OH has the highest resistance to dissociation in aqueous NaOH of the three hydroxyl groups of an anhydroglucose residue. It is plausible, at least from the aspects of 13C-chemical shifts, that cellulose molecules dissolving in 20--30% NaOH behave differently from those swollen in 20--30% NaOH as alkali- cellulose 相似文献
23.
The CuX2-mediated reaction of enynal units, including ortho-alkynylbenzaldehydes, with alkynes gives a variety of haloaromatic compounds stereoselectively in good to high yields. 2,2′-Binaphthyl skeletons are also readily prepared by the reaction of ortho-alkynylbenzaldehydes and diynes. The method was applied to the synthesis of poly-substituted tetracene derivatives. 相似文献
24.
The large nonresonant Raman-scattering activities of the out-of-plane bending and torsional modes of monosubstituted benzene analogs are studied by low-frequency Raman experiments and B3LYP6-31++G(d,p) calculations. Electronic interactions between the sigma orbitals of the substituent and the pi orbitals of the ring are found to enhance the Raman activities, depending on the substituent and its conformation. In the case of tert-butylbenzene [C6H5C(CH3)3] and trimethylphenylsilane [C6H5Si(CH3)3], three single bonds which are linked to the alpha atom of the substituent have low rotational barriers around the joint bond. Nearly free rotation of the substituents leads to a significant probability for one of the single bonds to occupy a conformation close to the vertical configuration with respect to the ring at room temperature. The resultant sigma-pi electronic interaction gives rise to the large Raman activities. In contrast, those possessing a single bond in a coplanar (or nearly coplanar) configuration at the most stable equilibrium state, i.e., anisole (C6H5OCH3), thioanisole (C6H5SCH3), and N-methylaniline (C6H5NHCH3), display no prominent Raman bands for the low-frequency vibrational modes. In these molecules, the sigma-pi conjugation does not take place due to the orthogonal orientation of the orbitals. Strong conformational dependence of the sigma-pi Raman enhancement is clearly obtained for the metastable vertical conformer of thioanisole, for which Raman activities are one-order magnitude greater than those of the coplanar conformer. 相似文献
25.
Yasuhiro Isogai Anna Ishii Manabu Ishida Masahiro Mukai Motonori Ota Ken Nishikawa Tetsutaro Iizuka 《Journal of Chemical Sciences》2000,112(3):215-221
De novo design of artificial proteins is an essential approach to elucidate the principles of protein architecture and to understand
specific functions of natural proteins and also to yield novel molecules for medical and industrial aims. We have designed
artificial sequences of 153 amino acids to fit the main-chain framework of the sperm whale myoglobin structure based on the
knowledge-based energy functions to evaluate the compatibility between protein tertiary structures and amino acid sequences.
The synthesized artificial globins bind a single heme per protein molecule as designed, which show well-defined electrochemical
and spectroscopic features characteristic of proteins with a low-spin heme. Redox and ligand binding reactions of the artificial
heme proteins were investigated and these heme-related functions were found to vary with their structural uniqueness. Relationships
between the structural and functional properties are discussed. 相似文献
26.
27.
A lower (upper) bound is given for the distribution of each dj, j = k + 1, …, p (j = 1, …, s), the jth latent root of AB?1, where A and B are independent noncentral and central Wishart matrices having with rank and Wp(n, Σ), respectively. Similar bound are also given for the distributions of noncentral means and canonical correlations. The results are applied to obtain lower bounds for the null distributions of some multivariate test statistics in Tintner's model, MANOVA and canonical analysis. 相似文献
28.
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30.
Ikue Homma Takuya Isogai Tsuguyuki Saito Akira Isogai 《Cellulose (London, England)》2013,20(2):795-805
The biodegradation behavior of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose fibers (TOCs) suspended in water and TEMPO-oxidized cellulose nanofibrils (TOCNs) dispersed in water by a commercial crude cellulase was studied. Products crude cellulase-treated for 0–7 days were separated into water/ethanol-insoluble and -soluble fractions. Weight recovery ratios and viscosity-average degrees of polymerization of the water/ethanol-insoluble fractions clearly decreased with crude cellulase-treatment time, showing that both TOCs and TOCNs have biodegradability. Water/ethanol-soluble fractions were subjected to size-exclusion chromatography (SEC) with photodiode array (PDA) detection to obtain SEC elution patterns detected by reflective index and UV spectra of each SEC pattern elution slice. SEC–PDA and 13C-NMR analyses showed that glucuronosyl unit-containing molecules present on microfibril surfaces in TOCs and TOCNs were primarily cleaved by hydrolyzing enzymes present as contaminants in the crude cellulase to form glucuronic acid as one of the major water-soluble degradation compounds. After the glucuronosyl units in TOCs and TOCNs were degraded and removed from microfibril surfaces by the hydrolyzing enzymes, cellulose chains newly exposed on the microfibril surfaces were rapidly hydrolyzed by cellulases predominantly present in the crude cellulase to form cellobiose. Both TOCs and TOCNs having sodium carboxyl groups are thus biodegradable, but TOCN having free carboxyl groups had clearly low biodegradability by the crude cellulase. Thus, biodegradation behavior may be controllable by controlling the structure of carboxyl group counter ions in TOCs and TOCNs. 相似文献