Photochromism of mixed crystals containing bisthienyl-, bisthiazolyl-, and bisoxazolylethene derivatives

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.     

四氟乙烯齐聚体的反应 四氟乙烯四、五聚体和芳香胺的反应

前已报道四氟乙烯四聚体(全氟-3,4-甲基己烯-3)(1)、五聚体(全氟-3,4-二甲基-4-乙基己烯-2)(2)和脂肪烷氧以及脂肪胺的亲核反应.本文报道化合物1,2和芳香胺如苯胺、β-萘胺的反应.由于烯烃1、2双键处于分子中间,因而当亲核试剂进攻时,双键容易发生重排,生成的末端基烯烃更具反应性,故导致一取代、二取代、三取代以及环化降解等复杂产物.     

Gibbs free energy of liquid drops on conical fibers

Small drops can move spontaneously on conical fibers. As a drop moves along the cone, it must change shape to maintain a constant volume, and thus, it must change its surface energy. Simultaneously, the exposed surface area of the underlying cone must also change. The associated surface energies should balance each other, and the drop should stop moving when it reaches a location where the free energy is a minimum. In this paper, a minimum Gibbs free energy analysis has been performed to predict where a drop will stop on a conical fiber. To obtain the Gibbs free energies of a drop at different locations of a conical fiber, the theoretical expressions for the shape of a droplet on a conical fiber are derived by extending Carroll's equations for a drop on a cylindrical fiber. The predicted Gibbs free energy exhibits a minimum along the length of the cone. For a constant cone angle, as the contact angle between the liquid and the cone increases, the drop will move toward the apex of the cone. Likewise, for a constant contact angle, as the cone angle increases, the drop moves toward the apex. Experiments in which water and dodecane were placed on glass cones verify these dependencies. Thus, the final location of a drop on a conical fiber can be predicted on the basis of the geometry and surface energy of the cone, the surface tension and volume of the liquid, and the original location where the drop was deposited.     

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.     

Moving of a nonhomogeneous, porous floc normal to a rigid plate

The boundary effect on the moving of a porous, nonhomogeneous, spherical floc normal to a rigid plate is analyzed theoretically for the case of low to medium Reynolds number. In particular, the drag force acting on the floc under various conditions is evaluated. A two-layer structure is adopted to simulate the nonhomogeneous nature of a floc. We show that if a floc is away from the plate, the streamlines surrounding the floc are distorted, but the degree of distortion becomes less significant if the floc is near the plate. The modified drag coefficient of a porous floc is orders of magnitude smaller than that of the corresponding rigid particle. For a fixed volume-averaged permeability, the effect of the presence of the plate on the behavior of a nonhomogeneous floc is more significant than that of a homogeneous floc, and this effect depends largely on the structure of a floc. The nonhomogeneous structure of a floc leads to a positive deviation from a Stokes-law-like correlation in the modified drag coefficient, and the smaller the volume-averaged permeability of a floc the greater the deviation. The presence of the plate has the effect of reducing this deviation. The nonhomogeneous structure of a floc on its modified drag coefficient is pronounced when it is close to a boundary.     

Chloroplast Biogenesis 81: Transient Formation of Divinyl Chlorophyll a Following a 2.5 ms Light Flash Treatment of Etiolated Cucumber Cotyledons

Abstract— The possible conversion of nascent divinyl (DV) chloro-phyllide a (Chlide a ) to DV chlorophyll a (Chi a during the early stages of greening in a dark divinyl-light divinyl-light/dark divinyl (DDV-LDV-LDDV) plant species was investigated. Etiolated cucumber cotyledons ( Cucu-mis sativus L .) were subjected to a 2.5 ms light flash followed by darkness. The DV and monovinyl (MV) components of the protochlorophyllide a (Pchlide a ), Chlide a , Pchlide a ester and Chi a pools were monitored quantitatively by high-resolution spectrofluorometry, immediately following the light treatments and after various periods in darkness. The light treatment photoconverted DV and MV Pchlide a to DV and MV Chlide a . Some photoconversion of MV Pchlide a ester to MV Chi a also appeared to take place. A sharp rise in the level of DV Chi a following the light treatment could not be accounted for by photoconversion of DV Pchlide a ester. It must have arisen by rapid esterification of nascent DV Chlide a. After illumination, the level of DV Chi a rose for 5 s and then declined. The implications of the transient rise and fall of DV Chi a content following illumination to the Chi a biosynthetic heterogeneity is discussed.     

Refolding foldamers: triazene-arylene oligomers that change shape with chemical stimuli

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].     

Photochromic reactions of diarylethenes in single crystals with intermolecular O--H...N hydrogen-bonding networks

The crystal structures and photochromic performance of a single crystal of a diarylethene derivative possessing carboxyl groups, 1,2-bis(5-carboxyl-2-methyl-3-thienyl)perfluorocyclopentene (1 a), and cocrystals of 1 a with 4,4'-, 2,4'-, and 2,2'-bipyridines were examined. In crystal 1 a, a discrete cyclic structure was observed, in which four 1 a molecules are linked through hydrogen bonds between the carboxyl groups. In the homocrystal, photoreactive and photoinactive conformers of 1 a exist in the ratio of 1:1. In the cocrystals of 1 a with bipyridines, O--HN-type hydrogen bonds between 1 a and pyridyl groups were formed, and all 1 a molecules are fixed in a photoreactive conformation. Both the homocrystal 1 a and the cocrystals showed photochromic performances, and color variation from bluish-violet to cyan was observed, depending on the conformation of the packed diarylethene molecules.     

Evidence for a simple monatomic ideal glass former: the thermodynamic glass transition from a stable liquid phase

Under cooling, a liquid can undergo a transition to the glassy state either as a result of a continuous slowing down or by a first-order polyamorphous phase transition. The second scenario has so far always been observed in a metastable liquid domain below the melting point where crystalline nucleation interfered with the glass formation. We report the first observation of the liquid-glass transition by a first-order polyamorphous phase transition from the equilibrium stable liquid phase. The observation was made in a molecular dynamics simulation of a one-component system with a model metallic pair potential. In this way, the model, demonstrating the thermodynamic glass transition from a stable liquid phase, may be regarded as a candidate for a simple monatomic ideal glass former. This observation is of conceptual importance in the context of continuing attempts to resolve the long-standing Kauzmann paradox. The possibility of a thermodynamic glass transition from an equilibrium melt in a metallic system also indicates a new strategy for the development of bulk metallic glass-forming alloys.     

Synthesis of 3, 4, 4a, 5, 6, 7, 8, 8a α-Octahydro-4a β, 8α-Dimethyl-2(1H)-Naphthalenones from the Wieland-Miescher Ketone

Conversion of the Wieland-Miescher ketone to a bicyclic dienophile capable of providing the AB rings of the picrasane skeleton of the guassinoids required the introduction of a C-8α methyl group in a 2-decalone. Among the routes explored, the conversion of the Wieland-Miescher ketone to a 4,4a,5,6,7,8-hexahydro-4aβ-methyl-8-methylene-2(3H)-napthalenone and subsequent reduction to a 3,4,4a,5,6,7,8,8aα-octahydro-4aβ,8α-dimethyl-2(1H)-napthalenone proved most useful.     

Tautomeric equilibrium between penta- and hexacoordinate silicon chelates. A chloride bridge between two pentacoordinate silicons.

The reaction of O-trimethylsilyl-1,1-dimethyl-2-trifluoroacetylhydrazine (1a) with chloromethyl(methyl)dichlorosilane affords an unexpected equilibrium mixture, 10a right arrow over left arrow 11a, between a neutral hexacoordinate silicon chelate with a covalent chloro ligand (10a) and an ionic pentacoordinate silicon complex (11a). The equilibrium reaction consists formally of a migration of the covalent chloro ligand from silicon to an adjacent ammonium nitrogen, as a chloride anion, and thus constitutes a novel type of tautomeric reaction. Crystallographic and NMR data provide evidence for the reaction. Temperature, solvent, substituent, and counterion effects on the tautomeric equilibrium are discussed: when the temperature of the mixture is raised, the equilibrium ratio 10a/11a increases. Formation of the mixture in toluene, a nonionizing solvent, shifts the equilibrium completely toward the neutral 10a. When the initial hydrazide has a phenyl (11c) or a hydrogen (11b) group as substituent, rather than CF3, the equilibrium is shifted to the ionic side. Replacement of the chloride counterion by triflate, using trimethylsilyl triflate, shifts the 10a/11a mixture to the ionic side. Low-temperature NMR monitoring of the stepwise formation of 10/11 was carried out and provided insight into the reaction mechanism. In an attempt to grow crystals of 11c, the pentacoordinate tautomer analogue, an unprecedented chloride-bridged disiloxane complex, with two pentacoordinate silicons sharing a common axial chloro ligand, crystallized and was characterized and described.     

Total synthesis of lodopyridone

A convergent total synthesis of the structurally unprecedented alkaloid lodopyridone was achieved using a cross-coupling of an iodopyridone fragment with a quinolinethiazolylstannane. Key features of the syntheses of the pentasubstituted 4-pyridone were a regioselective bromination of a 4-pyridone derived from kojic acid, a subsequent Cu-mediated introduction of the thioether, and a directed lithiation/iodination step. A chemoselective Negishi cross-coupling of a dibromothiazole and a quinolinylzinc reagent was used to assemble the chloroquinolinethiazol moiety.     

An accurate density functional theory based estimation of pK(a) values of polar residues combined with experimental data: from amino acids to minimal proteins

We report a scheme for estimating the acid dissociation constant (pK(a)) based on quantum-chemical calculations combined with a polarizable continuum model, where a parameter is determined for small reference molecules. We calculated the pK(a) values of variously sized molecules ranging from an amino acid to a protein consisting of 300 atoms. This scheme enabled us to derive a semiquantitative pK(a) value of specific chemical groups and discuss the influence of the surroundings on the pK(a) values. As applications, we have derived the pK(a) value of the side chain of an amino acid and almost reproduced the experimental value. By using our computing schemes, we showed the influence of hydrogen bonds on the pK(a) values in the case of tripeptides, which decreases the pK(a) value by 3.0 units for serine in comparison with those of the corresponding monopeptides. Finally, with some assumptions, we derived the pK(a) values of tyrosines and serines in chignolin and a tryptophan cage. We obtained quite different pK(a) values of adjacent serines in the tryptophan cage; the pK(a) value of the OH group of Ser13 exposed to bulk water is 14.69, whereas that of Ser14 not exposed to bulk water is 20.80 because of the internal hydrogen bonds.     

Synthesis, properties, and redox behavior of di(1-azulenyl)(2- and 3-thienyl)methyl cations and dications composed of two di(1-azulenyl)methylium units connected with 2,5-thiophenediyl and 2,5-thienothiophenediyl spacers

The titled stable monocations, di(1-azulenyl)(2- and 3-thienyl)methyl cations 7a,b and 8a,b and dications composed of two di(1-azulenyl)methylium units connected with 2,5-thiophenediyl and 2,5-thieno[3,2-b]thiophenediyl spacers 9a,b and 10a,b were prepared by hydride abstraction of the corresponding methane derivatives. These mono- and dications 7a,b, 8a,b, 9a,b, and 10a,b showed high stability with large pK(R)+ values. The values of monocations 7a,b and 8a,b were 11.2-11.8 +/- 0.1 and 11.4-12.4 +/- 0.1, respectively. Two cation units in dications 9a,b and 10a,b were neutralized via one step at the pH of 11.1-11.7 +/- 0.1, which corresponds to the average of the pK(R)+ values of the dications and half-neutralized monocations. Electrochemical behavior of 7a,b, 8a,b, 9a,b, and 10a,b was examined by cyclic voltammetry (CV). Formation of the thienoquinoid products 18a,b and 19a,b from 9a,b and 10a,b was characterized by UV-vis spectroscopy under electrochemical reduction conditions. Chemical reduction of 9a,b and 10a,b with Zn powder in acetonitrile afforded 18a,b and 19a,b as deep-colored crystals, which exhibited rather high electron-donating ability.     

Fast fringe-field switching of vertically aligned liquid crystals between high-haze translucent and haze-free transparent states

We report control of the haze value in a liquid crystal (LC) cell driven by a fringe electric field. When a fringe field is applied to a vertically aligned (VA) cell, a large spatial phase difference with a short grating period is induced in the LC layer. The average grating period of a VA cell driven by a fringe field is a quarter of the pitch of the interdigitated electrodes, which is half of the grating period of a VA cell driven by an in-plane field. Moreover, a sharper spatial phase profile is built around the edges of the interdigitated electrodes, which led to a high haze of 84.3% in the translucent state. The device was haze-free in the transparent state owing to the use of an LC layer without a polymer structure. To increase the haze value of the LC device while retaining a short response time, we developed an LC cell with crossed interdigitated electrodes where a large spatial phase difference is induced with little dependence on the azimuth angle. By applying a fringe electric field to a 20 μm thick LC cell using crossed interdigitated electrodes, we demonstrated a very high haze of 95.4% and a response time of less than 5 ms.     

Statistical mechanics of three-dimensional vesicles

We consider a lattice model of three-dimensional vesicles in which the boundary of the vesicle is a self-avoiding plaquette surface, homeomorphic to a sphere. Surfaces with fixed area can enclose a variety of different volumes and we associate a fugacity with the enclosed volume to mimic the effect of a pressure difference across the surface. Pairs of plaquettes which share a common edge can be in the same plane or normal to each other and we associate a fugacity with adjacent pairs of plaquettes at right angles to represent a surface stiffness term. We discuss the behaviour of the surfaces in the infinite surface area limit, as a function of these two fugacities.     

Boron/nitrogen substitution of the central carbon atoms of the biphenalenyl diradical π dimer: a novel 2e-12c bond and large NLO responses

On the basis of the famous staggered biphenalenyl diradical π dimer 1, the eclipsed biphenalenyl (1a), with no centrosymmetry, was obtained by rotating a layer of 1 by 60° around its central axis. Furthermore, the central carbon atoms of 1 and 1a were substituted by boron and nitrogen atoms to form 2 and 2a with a novel 2e-12c bond. We found that the novel 2e-12c bond is formed by the electron pair of the occupied orbital of the phenalenyl monomer substituted by the nitrogen atom and the unoccupied orbital of the phenalenyl monomer substituted by the boron atom. As a result of the novel 2e-12c bond, 2 and 2a exhibit a fascinating interlayer charge-transfer transition character, which results in a significant difference in the dipole moments (Δμ) between the ground state and the crucial excited state. The values of Δμ for 2 and 2a are 6.4315 and 6.9253 Debye, clearly larger than the values of 0 and 0.0015 Debye for 1 and 1a. Significantly, the boron/nitrogen substitution effect can greatly enhance the first hyperpolarizabilities (β(0) ) of 2 and 2a with a novel 2e-12c bond compared with 1 and 1a with a traditional 2e-12c bond: 0 and 19 a.u. for 1 and 1a are much lower than 3516 and 12272 a.u. for 2 and 2a. Furthermore, the interaction energies (E(int) )of 2 and 2a are larger than those of 1 and 1a, which could be considered as a signature of reliability for the newly designed dimers. Our present work will be beneficial for further theoretical and experimental studies on the properties of molecules with the novel 2e-12c bond.     

Modeling of the pseudo-colloids migration for multi-member decay chains with a arbitrary flux boundary condition in a fractured porous medium

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.     

Effect of charged boundary on electrophoresis: Sphere in spherical cavity at arbitrary potential and double-layer thickness

The boundary effect on electrophoresis is investigated by considering a spherical particle at an arbitrary position in a spherical cavity. Our previous analysis is extended to the case where the effect of double-layer polarization can be significant. Also, the effect of a charged boundary, which yields an electroosmotic flow and a pressure gradient, thereby making the problem under consideration more complicated, is investigated. The influences of the level of the surface potential, the thickness of double layer, the relative size of a sphere, and its position in a cavity on the electrophoretic behavior of the sphere are discussed. Some results that are of practical significance are observed. For example, if a positively charged sphere is placed in an uncharged cavity, its mobility may have a local minimum as the thickness of the double layer varies. If an uncharged sphere is placed in a positively charged cavity, the mobility may have a local minimum as the position of the sphere varies. Also, if the size of a sphere is fixed, its mobility may have a local minimum as the size of a cavity varies. These provide useful information for the design of an electrophoresis apparatus.