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1.
2.
We describe the preparation of five triazene-arylene oligomers (3, 4, 7, 8, and 11) and investigations of their folding properties in aqueous solution. These oligomers contain four 2-fold rotors and populate a conformational ensemble comprising at least 10 states. Extensive 1D and 2D NMR studies as well as X-ray crystallography establish that the presence of three members of the cucurbit[n]uril family (CB[n]), CB[10], CB[7], and CB[8], results in the selective population of the (a,a,a,a)-, (a,s,s,a)-, and (a,a,a,s)-conformers. As a result of the high affinity and highly selective binding properties of the CB[n] family, it is possible to fold a single foldamer strand (3) into the CB[8].(a,a,a,s)-3 conformer by the addition of CB[8], then unfold and refold it into the CB[7].(a,s,s,a)-3.CB[7] conformer by addition of CB[7] and 3,5-dimethylaminoadamantane (17), then unfold and refold it again into the CB[10].(a,a,a,a)-3 conformer by addition of CB[10].CB[5] and aminoadamantane (18). The transformation of CB[8].(a,a,a,s)-3 into CB[7].(a,s,s,a)-3.CB[7] proceeds through the intermediacy of CB [8].(a,a,s,a)-3.CB[7], which enhances the rate of dissociation of strand 3 from CB[8]. 相似文献
3.
Electrophoresis of a sphere at an arbitrary position in a spherical cavity filled with Carreau fluid
Boundary effects on the electrophoretic behavior of a charged entity are of both fundamental and practical significance. Here, they are examined by considering the case where a sphere is at an arbitrary position in a spherical cavity under conditions of low surface potential and weak applied electrical field. Previous analyses are extended to the case of a non-Newtonian fluid, and a Carreau model is adopted for this purpose. The effects of key parameters such as the thickness of a double layer, the relative sizes of particle and cavity, the position of a particle, and the nature of a fluid on the electrophoretic mobility of a particle are discussed. Several interesting phenomena are observed. For example, if the applied electric field points toward north, the mobility of a particle has a local maximum when it is at the center of a cavity. However, if a particle is sufficiently close to the north pole of a cavity, its mobility exhibits a local minimum as its position varies. This does not occur when the particle is close to the south pole of the cavity; instead, it may move in the direction opposite to that of the applied electric field. For a Newtonian fluid, if a particle is close to the north pole of a cavity, its upward movement yields a clockwise (counterclockwise) vortex near the north pole of the cavity and a counterclockwise (clockwise) vortex near the south pole of the cavity on its right (left)-hand side. The latter is not observed for a Carreau fluid. 相似文献
4.
Mi-Seon Jeong Yongsoo Hwang Chul-Hyung Kang 《Journal of Radioanalytical and Nuclear Chemistry》2011,289(1):287-293
A deep geologic disposal is the prime option for the long-term isolation of high-level radioactive waste (HLW) in many countries.
For deeply located repositories, a radionuclide released from a failed waste container moves through the engineered and natural
barriers before it reaches a biosphere. The pseudo-colloid which a radionuclide is adsorbed on a moving natural humic or fulvic
colloid can be generated in a fractured porous medium. The size of a colloid is in general in the order of a hundred nanometer
so that its migration velocity in a fracture is higher than that of a radionuclide due to the hydrochromatic effect. A large
colloid cannot diffuse easily into a surrounding rock. Also, there are many kinds of actinides and these actinides have decay
chains. In this analysis, the canonical form solution is derived for a pseudo-colloid and a solute in a fracture and a surrounding
rock with a realistic inlet boundary condition with multi-member decay chains. It is used the Fortran based a computational
code which uses a special subroutine for the inversion of Laplace transform. Consequently, the role of the pseudo-colloid
in the fractured porous medium is important and also their decay chains aren’t neglected in the performance assessment of
the HLW. 相似文献
5.
Photochromic performance of diarylethene single crystals was controlled by crystal engineering using non-covalent aromatic-aromatic interactions as the directional intermolecular force. A diarylethene derivative with two pentafluorophenyl groups, 1,2-bis(2-methyl-5-pentafluorophenyl-3-thienyl)perfluorocyclopentene (1a), formed stoichiometric co-crystals with benzene (Bz) and naphthalene (Np) by aryl-perfluoroaryl interactions. Face-to-face pi-stacking interactions between the pentafluorophenyl groups of 1a and the aromatic molecules are responsible for 2:1 and 1:1 stoichiometric compositions in 1a/Bz and 1a/Np co-crystals, respectively. The diarylethene underwent thermally stable and photoreversible photochromic reactions in a homo-crystal of 1a and co-crystals 1a/Bz and 1a/Np. The absorption spectra of the photogenerated closed-ring isomers varied depending on the conformation of the diarylethene molecules packed in the crystals. The diarylethene 1a also formed 1:1 stoichiometric co-crystals with different kinds of diarylethenes, 1,2-bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene (2a) and 1,2-bis[2-methyl-5-(1-naphthyl)-3-thienyl]perfluorocyclopentene (3a). Both co-crystals 1a/2a and 1a/3a showed photochromism. Although 1a, 2a, and 3a underwent efficient photocyclization reactions in their homo-crystals, highly selective photocyclization reactions of 2a or 3a were observed in the co-crystals. The selective reactions were confirmed by HPLC and X-ray crystallography. Excited energy transfers from 1a to 2a and from 1a to 3a are considered to occur and cause the selective reactions. 相似文献
6.
Iwaki T 《The Journal of chemical physics》2006,125(22):224901
Recently, it has been revealed that a semiflexible polyelectrolyte chain can form a partially folded conformation stably as a result of an electrostatic interaction. Interestingly, there are cases where the appearance of this structure requires a high-salt condition of a solution. In order to solve this problem, we consider the double equilibrium of the formation of loops and their aggregation on a single-chain polymer. First, an aggregate with a typical surface energy is examined as a test case. The basic nature of the folding transition is discussed with regard to the chemical potential of loop structures. Next, we consider a charged aggregate for which the interior is completely neutralized by counter ions. In this model, a partially folded chain appears with a high-salt condition. Based on this model, screened interactions between surface charges and a toroidal shape of a folded structure are considered essential factors bihind this phenomenon. 相似文献
7.
Controlled Dynamic Helicity of a Folded Macrocycle Based on a Bisterephthalamide with a Twofold Z‐Shaped Structure
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Dr. Ryo Katoono Keiichi Kusaka Prof. Dr. Kenshu Fujiwara Prof. Dr. Takanori Suzuki 《化学:亚洲杂志》2014,9(11):3182-3187
Dynamic helicity in a folded macrocycle and control of the helical preference are described. We designed macrocycle 1 with a dual mode of folding through the integration of two flexible units that are arranged twice to form a cyclic structure. As a folding unit, we used a terephthalamide skeleton and a Z‐shaped hydrocarbon: the former acted as a control unit to induce a preference of a particular sense of dynamic helicity and the latter was just a spacer. A terephthalamide unit provided a binding site for capturing a ditopic hydrogen‐bonding guest when it adopted helically folded syn forms (M/P). Thus, only the terephthalamide unit controlled the helical sense of dynamic helicity in a folded macrocycle through the supramolecular transmission of chirality upon complexation with a chiral ditopic guest. In addition, chirality on a host could also contribute to the control of the helical preference in a folded macrocycle, which led to exceptionally enhanced chiroptical signals. 相似文献
8.
Single crystals composed of two or three different kinds of diarylethenes, having similar geometrical structures but different colors in the closed-ring isomers, 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene (1a), 1,2-bis(5-methyl-2-phenyl- 4-thiazolyl)perfluorocyclopentene (2a), and 1,2-bis(5-methyl-2-phenyl-4-oxazolyl)perfluorocyclopentene (3a) have been prepared in an attempt to form single crystals which exhibit different colors, depending on illumination wavelengths. When 1a and 2a are mixed in ethanol and the content of 2a in the feed is higher than that of 1a, only a needle-shaped crystal is obtained. The crystal shape is similar to that of 2a. On the other hand, high content of 1a in the feed leads to formation of a block-shaped crystal, of which the shape is similar to that of 1a. At a feed ratio of 1:1 for 1a and 2a, two types of crystals such as needle- and block-shapes are obtained from the same batch. Mixed crystals composed of three kinds of derivatives 1a/2a/3a have also been prepared. A crystal composed of the three derivatives in the molar ratio of 32 (1a):53 (2a):15 (3a) was obtained. X-ray analysis proved that 1a and 3a are packed in the crystal lattice of 2a. The mixed crystal 1a/2a/3a changed color from colorless to yellow, red, and blue upon irradiation with light of appropriate wavelengths. 相似文献
9.
The first complexes containing both a sulfur atom and a hydroxamate moiety coordinated to a biologically relevant transition metal were synthesized as models for the structure of inhibited peptide deformylases. Two of these [(N(2)S)Zn(hydroxamate)] complexes were characterized by X-ray crystallography. The first contains a thioether and a simple hydroxamate, the second a thiolate and a N-substituted hydroxamate. Isolation of a complex with a thiolate and a simple hydroxamate group was not possible. 相似文献
10.
G. Becker 《无机化学与普通化学杂志》1981,480(9):38-48
Acyl- and Alkylidenephosphines. XVIII. Monoacetyl- and Diacetylphosphine When triacetylphosphine 3a is treated with methanol 4 or benzyl alcohol 6 P? C(O) bonds are cleaved and a mixture of diacetyl- 2a and monoacetylphosphine 1a is formed. The thermally labile phosphine 1a decomposes completely within a few hours at +20°C; but 2a also reacts slowly within days to give triacetylphosphine 3a and further unknown compounds. As it is found by nmr-spectroscopic studies the acidic hydrogen atoms of monoacetylphosphine 1a are both bound to phosphorus. In liquid diacetylphosphine 2a or in solutions of this compound, However, there exists an equilibrium between the keto tautomer K- 2a with a PH and the enol tautomer E- 2a with an O? H? O group; compared with pentane-2,4-dione 8a the keto tautomerpredo minates in 2a . As in 1,3-diketones a low temperature and a small dielectric constant of the solvent increase the amount of enol tautomer E- 2a present. The 1H-nmr resonance of the enolic hydrogen atom is observed at very low field (δ = 18,3 ppm). 相似文献
11.
The electrophoresis of a rigid sphere in a Carreau fluid normal to a large disk is analyzed theoretically under the conditions of low surface potential and weak applied electric field. Previous analyses are extended to the case where a disk can be charged, and a more realistic electrostatic force formula is applied. We show that the qualitative behavior of a sphere depends largely on its distance from a disk, the thickness of double layer, and the nature of a fluid. In general, the presence of a disk has the effect of increasing the conventional hydrodynamic drag on a sphere, and a decrease in the thickness of the double layer surrounding a sphere has the effect of enhancing the shear-thinning effect. However, this might not be the case if a sphere is uncharged and a disk is charged, where the osmotic pressure field and the induced charge on the sphere surface can be significant. The shear-thinning effect is important only if the thickness of double layer is sufficiently thick. This result can play a significant role in practice such as in electrophoretic deposition, where the deposition electrode is charged and the fluid medium is usually of shearing-thinning nature. 相似文献
12.
Enamines 8a-e could be chlorinated by equimolar amounts of N-chlorosuccinimide (9) generating monochloroenamines 10a-e; 10a and 10d were isolated as pure substances. Two equivalents of 9 afforded the dichloroenamines 12a,c from 8a,c. Interaction of the chlorinated enamines 10a-e and 12a,c with cyanide gave morpholino-azabicyclohexane derivatives. 10a-d, thereby, led to exo-cyano-isomers lla-c; 12a,c generated endo-cyano compounds 13a,c. In the case of the ethoxycarbonylated chloroenamine 10e a mixture of diastereomeric products 11e and 14e resulted from the analogous reaction. Reduction of 11a and 14e with lithium aluminum hydride produced a pair of diastereomeric triamines 15 and 16. A tricyclic diazasystem 19 was formed from the reaction of cyanide with the carbamoylated chloroenamine 18. Monochloroenamine 10a and dichloroenamine 12a showed a significant mutagenic behaviour in the Ames test. 相似文献
13.
Masanori Fujinami Satoshi Jinno Masafumi Fukuzumi Takumi Kawaguchi Koichi Oguma Takashi Akahane 《Analytical sciences》2008,24(1):73-79
A production method for a positron microprobe using a beta+-decay radioisotope (22Na) source has been investigated. When a magnetically guided positron beam was extracted from the magnetic field, the combination of an extraction coil and a magnetic lens enabled us to focus the positron beam by a factor of 10 and to achieve a high transport efficiency (71%). A 150-nm-thick Ni(100) thin film was mounted at the focal point of the magnetic lens and was used as a remoderator for brightness enhancement in a transmission geometry. The remoderated positrons were accelerated by an electrostatic lens and focused on the target by an objective magnetic lens. As a result, a 4-mm-diameter positron beam could be transformed into a microprobe of 60 microm or less with 4.2% total efficiency. The S parameter profile obtained by a single-line scan of a test specimen coincided well with the defect distribution. This technique for a positron microprobe is available to an accelerator-based high-intensity positron source and allows 3-dimensional vacancy-type defect analysis and a positron source for a transmission positron microscope. 相似文献
14.
Y. Clerc M. Dubos N. Bihoreau L. Delamourd C. Brasseur B. Gond M. Goyffon J. Saint-Blancard 《Applied biochemistry and biotechnology》1987,14(3):241-251
Glutaraldehyde hemoglobin polymerization gives too many high polymers, resulting in a too viscous solution. We describe here
an alternate method leading to superior results, as compared to the classical one. This method includes a molecular fractionation
step using a tangential flow ultrafiltration that secondarily lowers the unpolymerized tetramer’s content of a mildly polymerized,
pyridoxylated hemoglobin solution (Pyr-Poly Hb). This leads to an adequately polymerized product with a lesser high polymer
content, implying a lower viscosity. We thus obtain a pyridoxylated, polymerized molecular fractionated solution presenting
suitable features as a blood substitute: A 7.5 g% hemoglobin 2 g% albumin solution had a 16% unpolymerized tetramer’s ratio,
a 1.8 mPas viscosity, a P50 of 2.8 kPa, a Hill coefficient of 2.1, a binding coefficient of 1.3 mL/g, a colloid osmotic pressure of 2.4 kPa, and a methemoglobin
concentration of 3% Male Sprague-Dawley rats undergoing an isovolumic blood exchange with this Pyr-Poly Hb solution, down
to a 2% hematocrit, present a mean survival time of 20 h. 相似文献
15.
Wolfgang Quapp 《Theoretical chemistry accounts》1989,75(6):447-460
Gradient extremals are curves in configuration space denned by the condition that the gradient of the potential energy is an eigenvector of the Hessian matrix. Solutions of a corresponding equation go along a valley floor or along a crest of a ridge, if the norm of the gradient is a minimum, and along a cirque or a cliff or a flank of one of the two if the gradient norm is a maximum. Properties of gradient extremals are discussed for simple 2D model surfaces including the problem of valley bifurcations. 相似文献
16.
We present an identity for an unbiased estimate of a general statistical distribution. The identity computes the distribution density from dividing a histogram sum over a local window by a correction factor from a mean-force integral, and the mean force can be evaluated as a configuration average. We show that the optimal window size is roughly the inverse of the local mean-force fluctuation. The new identity offers a more robust and precise estimate than a previous one by Adib and Jarzynski [J. Chem. Phys. 122, 014114 (2005)]. It also allows a straightforward generalization to an arbitrary ensemble and a joint distribution of multiple variables. Particularly we derive a mean-force enhanced version of the weighted histogram analysis method. The method can be used to improve distributions computed from molecular simulations. We illustrate the use in computing a potential energy distribution, a volume distribution in a constant-pressure ensemble, a radial distribution function, and a joint distribution of amino acid backbone dihedral angles. 相似文献
17.
X-Ray Analysis of a Novel Spirocyclic Diglycoside, a Degradation Product of the Antibiotics Papulacandin A, B and C Structure 4 has been established for a novel spirocyclic diglycoside which is a degradation product of the antibiotics papulacandin A, B and C. By X-ray analysis the diglycoside was shown to consist of a galactose moiety connected by a β-1, 4-linkage to a glucose. This diglycoside is further connected by a spiro union to a oxaindan-diol moiety. 相似文献
18.
Kobayashi K Ishii K Sakamoto S Shirasaka T Yamaguchi K 《Journal of the American Chemical Society》2003,125(35):10615-10624
The guest- or solvent-induced assembly of a tetracarboxyl-cavitand 1 and a tetra(3-pyridyl)-cavitand 2 into a heterodimeric capsule 1.2 in a rim-to-rim fashion via four intermolecular CO(2)H.N hydrogen bonds has been investigated both in solution and in the solid state. In the (1)H NMR study, a 1:1 mixture of1a and 2a (R = (CH(2))(6)CH(3)) in CDCl(3) gave a mixture of various complicated aggregates, whereas this mixture in CDCl(2)CDCl(2) or p-xylene-d(10) exclusively produced the heterodimeric capsule 1a.2a. It was found that an appropriate 1,4-disubstituted-benzene is a suitable guest for inducing the exclusive formation of 1a.2a in CDCl(3). The ability of a guest to induce the formation of guest-encapsulating heterodimeric capsule, guest@(1a.2a), increased in the order p-ethyltoluene < 1-ethyl-4-methoxybenzene < or = 1-ethyl-4-iodobenzene < or = 1,4-dibromobenzene < 1-iodo-4-methoxybenzene < or= 1,4-dimethoxybenzene < or = 1,4-diiodobenzene. The (1)H NMR study revealed that a CH-halogen interaction between the inner protons of the methylene-bridge rims (-O-H(out)CH(in)-O-) of the 1a and 2a units and the halogen atoms of 1,4-dihalobenzenes and a CH-pi interaction between the methoxy protons of 1,4-dimethoxybenzene and the aromatic cavities of the 1a and 2a units play important roles in the formation of 1,4-dihalobenzene@(1a.2a) and 1,4-dimethoxybenzene@(1a.2a), respectively. A preliminary single-crystal X-ray diffraction analysis of guest@(1b.2b) (R = (CH(2))(2)Ph; guest = 1-iodo-4-methoxybenzene or p-xylene) confirmed that the guest encapsulated in 1b.2b is oriented with the long axis of the guest along the long axis of 1b.2b and that the iodo and the methoxy groups of the encapsulated 1-iodo-4-methoxybenzene are specifically oriented with respect to the cavities of the 2b and 1b units, respectively. 相似文献
19.
Bianchi I Forlani R Minetto G Peretto I Regalia N Taddei M Raveglia LF 《Journal of combinatorial chemistry》2006,8(4):491-499
An efficient strategy for the solution-phase parallel synthesis of a library of pyrrole-amides is described. Key reactions include functional homologation of beta-ketoesters with a set of aldehydes followed by oxidation to produce a series of differently substituted 1,4-dicarbonyl compounds. Rapid cyclization using a microwave-assisted Paal-Knorr reaction provided a set of 24 pyrrole esters that were further functionalized through a trimethylaluminum-mediated aminolysis to obtain a larger library of 288 diverse pyrrole-3-amides. The tetrasubstitution allows a good exploration of the chemical space around the central pyrrole core. The last step was entirely automated with a Bohdan Myriad personal synthesizer. 相似文献
20.
A.A. Kulikovsky 《Electrochemistry communications》2010,12(12):1780-1783
A model of a partially degraded catalyst layer (CL) in a fuel cell is reported. The degradation is modeled as a lowering of the exchange current density in a sub-layer at the membrane/CL interface. Degradation of 30 to 40% of the CL thickness may dramatically increase the polarization voltage. At a large current density, the voltage loss in such a two-layer system is close to the loss in a fully degraded CL. Estimates of this effect for a PEMFC cathode and a DMFC anode are performed. 相似文献