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21.
The relations between the Hellmann-Feynman forces in laboratory fixed (L-) and relative (R-) coordinate systems are clarified. In the usualL-coordinate system, the force is interpreted as force on nucleus, while in theR-coordinate system, it means force on whole particles consisting of the electrons and nuclei of each interacting subsystem. From a perturbation theoretical viewpoint, the concept of the force on whole particles correctly corresponds to the perturbation energy and is superior to the force on the nucleus. 相似文献
22.
Toshikatsu Koga 《International journal of quantum chemistry》1984,25(2):347-354
The recently proposed method of using momentum densities for interatomic interactions is applied to the long-range force between the ground-state hydrogen atom and the proton, and the results are compared with those from using the position density based on the electrostatic Hellmann–Feynaman theorem. A new physical interpretation of the long-range force is obtained, which is complementary to that in position space. It is found that some perturbative changes in the position density do not accompany changes in the momentum density. 相似文献
23.
F. Kokai Y. Koga Y. Kakudate M. Kawaguchi S. Fujiwara M. Kubota K. Fukuda 《Applied Physics A: Materials Science & Processing》1994,59(3):299-304
Laser-ionization Time-Of-Flight (TOF) mass-spectrometric studies have been carried out on the 532 nm and 1064 nm laser ablation products from a nitrogen-rich polymer. The polymer used had an elemental composition of C6.0N8.9H3.4 and consisted of C=N, C-N, and N-H chemical bonds. The TOF mass spectra observed were composed of various peaks (150 amu) depending on the ablation laser wavelength. The primary peaks were assigned to C+, CN+, CHnN+
2 (n=1–3) and C2H2N+
3 for 532 nm ablation, and C+, C+
3, HCN+, HCCN+, CH2NH+, HNCN+, H3NCN+, and C4H4N+
7 for 1064 nm ablation. The flight velocity distributions with peak velocities ranging from 8.6×103 cm/s to 3.8×104 cm/s were measured for these products. The distinct velocity distributions observed between small and large products indicate the presence of two origins in the fragment ejection process from the polymer for both 532 nm and 1064 nm ablation. Furthermore, we suggest an importance of the translational energy of the fragments for the product generation in the laser plume. 相似文献
24.
A novel approach to the mimicking of enzyme-catalyzed bond-forming reactions has been examined using multifunctionalized chiral crown ethers. In addition to the 18-crown-6 moiety as a binding site, the host have one thiol and one thio ester with an N-protected alpha-amino acid or a peptide, and have successfully achieved peptide synthesis in an enzyme-mimetic reaction mode. This new method involves the following three key reactions. (1) Intra-complex thiolysis: the host carries out the rapid intra-complex thiolysis of alpha-amino acid ester salts to form the dithioester, corresponding to the assembly of two guests by the host. (2) Amide formation: intramolecular aminolysis occurs between the bound guests to form the amide bond. (3) Peptide chain elongation: as the thiol reactive group is regenerated, the above two reactions are repeated to elongate the peptide chain. Formal turnover of the enzyme model has been demonstrated by the synthesis of a tetrapeptide derivative by the repetition of the above processes. 相似文献
25.
Koga T Taguchi K Kinoshita T Higuchi M 《Chemical communications (Cambridge, England)》2002,(3):242-243
A novel artificial protein with simple primary structure, poly(gamma-methyl-L-glutamate)-grafted polyallylamine, has been prepared and the resultant peptide has shown a unique property of pH-regulated conformation and morphology. 相似文献
26.
27.
Yoshio Imai Hiroshi Koga 《Journal of polymer science. Part A, Polymer chemistry》1973,11(10):2623-2632
New thermally stable poly(imide-oxoisoindolobenzothiadiazine dioxides) (PIOD) have been prepared by the three-step cyclopolycondensation reaction of diaminobenzenesulfonamides with aromatic tetracarboxylic dianhydrides. The polymerization proceeded through the formation of poly(amic acid-sulfonamides) (PAAS), followed by cyclodehydration to yield polyimide-sulfonamides (PIS), which were subsequently converted to PIOD at 300°C. PAAS having inherent viscosities in the range of 0.1–0.5 in N-methyl-2-pyrrolidone (NMP) were obtained in approximately quantitative yield. PIOD were insoluble in most organic solvents, whereas PAAS and PIS were soluble in NMP and dimethyl sulfoxide. Differential thermal analysis and thermogravimetric analysis indicated that PIOD began to decompose at 460°C in air. The cyclodehydration of the model compounds was also investigated. 相似文献
28.
For 357 subshells of the 53 neutral atoms He through Xe in their ground states, the two-electron intracule (relative motion)
<u
k
>
nl
and extracule (center-of-mass motion) <R
k
>
nl
subshell moments in position space are examined as well as their counterparts <v
k
>
nl
and <P
k
>
nl
in momentum space, where n and l are the principal and azimuthal quantum numbers of the atomic subshell, respectively. It is clarified that between the intracule
and extracule moments the “2
k
-rule” is strictly valid, which means <u
k
>
nl
= 2
k
<R
k
>
nl
and <v
k
>
nl
= 2
k
<P
k
>
nl
for any nl subshell. Theoretical analysis also proves that for a particular case of k = +2, two relations <u
2>
nl
= (N
nl
−1)<r
2>
nl
and <v
2>
nl
= (N
nl
−1)<p
2>
nl
hold exactly, where N
nl
(≥2) is the number of electrons in the subshell nl, and <r
k
>
nl
and <p
k
>
nl
are the familiar one-electron subshell moments in position and momentum spaces, respectively. The latter equality establishes
a new and rigorous relation between the second electron-pair moments in momentum space and the total energy of an atom through
the virial theorem. For k=+1, −1, and −2, the numerical Hartree-Fock results for the 357 subshells show that there are approximate but accurate linear
relations between <u
k
>
nl
and <r
k
>
nl
and between <v
k
>
nl
and <p
k
>
nl
, in which the proportionality constant in each space depends on n,l, and k.
Received: 27 April 1998 / Accepted: 29 May 1998 / Published online: 28 August 1998 相似文献
29.
The reaction process of the thermal dehydration of dilithium tetraborate trihydrate, Li2B4O73H2O, was reinvestigated from a viewpoint of reaction kinetics. On the basis of the results of thermogravimetry, constant rate thermal analysis, powder X-ray diffractometry, infrared spectroscopy and scanning electron microscopy, it was confirmed that the reaction proceeds via three consecutive kinetic steps characterized by different activation energies. The first and second kinetic steps, accompanied by the destruction of the original crystal structure of the reactant, seem to be assigned to the surface and internal reactions, respectively. During the third kinetic step, the thermal dehydration of hydrated amorphous intermediate, produced at the second kinetic step, and crystallization of the final dehydration product, Li2B4O7, are likely to take place concurrently.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
30.
Kenji Koga Kazunori Odashima 《Journal of inclusion phenomena and macrocyclic chemistry》1989,7(1):53-60
A series of water-soluble cyclophanes, made by connecting two diarylmethane units and two bridging chains via four nitrogens, were found to provide hydrophobic cavities of definite shape and size for forming inclusion complexes with various organic compounds in aqueous solution. Some chemical modifications of these cyclophanes are described.This paper is dedicated to Professor D. J. Cram to celebrate his honor in receiving the 1987 Nobel Prize in Chemistry. 相似文献