The synthesis of functionalized nanoscale molecular rods of defined length

We report a synthetic approach to spiro-ladder oligomers of defined length and structure that form water-soluble molecular rods. We describe the synthesis of a chiral molecular building block 1 and its assembly on solid support to form flexible chains that were then rigidified by the parallel formation of several diketopiperazine rings. Two molecular rods approximately 15 and 25 A in length were synthesized containing three and five monomers, respectively. The molecular rods were easily functionalized on both ends and were shown to have high water solubility, making them compatible with biological buffers. These molecules may find use as scaffolds for the display of ligands in chemical-biology applications and as spacers and construction materials for nanoscience applications.     

Investigation of the Structure and Properties of Crosslinked Polymers Based on Oligocarbonate Methacrylates in Film Formation

The effect of structure and flexibility of an oligomeric block of oligocarbonate methacrylates (OCM) as well as of various modifiers on the coating formation, the structure, and properties of crosslinked polymers formed under conditions of adhesive interaction has been studied. Reactivity and conversion of OCM during polymerization increase in coatings formed from oligomers with short and rigid blocks, capable of forming on the substrate a network from the ordered anisodiametric structural elements with high adhesive properties, as distinct from the globular structures appearing in the formation of the network from the oligomers with more flexible blocks. The tendencies observed have been explained with the aid of a mechanism of network formation relating the morphology of the resultant crosslinked polymers to the flexibility (conformation) of the chains of the branched polymer obtained in the initial stage of polymerization and representing a matrix of the corresponding crosslinked structures. The mode of action of modifiers is markedly dependent on the nature and flexibility of the oligomeric block.     

Redox states and associated interchain processes of thienylenevinylene oligomers

The electronic structure of successive redox states of two series of thienylenevinylene oligomers (nTVs, n=4, 5, 6, 8, and 12) that carry hexyl substituents at the alpha- or beta-positions in order to increase the solubility was investigated in detail by means of UV/ Vis/near-IR and ESR spectroscopy in solution. The nTV redox states have been fully characterized up to the dication for the shorter oligomers (n < or = 6) and up to the tetracation for the longer oligomers (n > or = 8). While the monocation radicals of the nTVs exhibit two dipole-allowed electronic transitions in the Vis/near-IR region, all the higher oxidized states invariably show a single strong absorption in the near-IR region. The electronic transitions of the various oxidized states and those of their vibronic replicas shift to lower energies with increasing conjugation length. The ESR spectra, recorded as a function of the degree of oxidation, provide evidence for the presence of electron spin in the odd-charged and the absence of spin in even-charged cations. Variable-temperature UV/Vis/near-IR and ESR spectroscopy establish that the tendency of the nTV monocation radicals to form spin-less alpha dimers in solution strongly depends on the number of solubilizing hexyl groups. While the oligomers that carry two hexyl chains at the a-positions of the terminal thiophenes (alpha-nTVs) readily form pi dimers at low temperature, the oligomers that carry hexyl groups on the beta- and beta'-positions of every thiophene ring (beta-nTVs) do not form pi dimers. Low-temperature UV/ Vis/near-IR and ESR experiments on solutions in which neutral and singly oxidized nTVs are simultaneously present, reveal the occurrence of interchain interactions between these two species, accompanied by a pronounced change in the existing disproportionation equilibrium.     

Oligomeric rods of alkyl- and hydridogallium imides

Reaction of [RGa(NMe(2))(2)](2), where R = Me, Et, Bu, and Hx, with ammonia at 150 degrees C in an autoclave produced insoluble white powders formulated as oligomers of [RGaNH](n). The analogous reaction between NH(3) and MeGa[N(SiMe(3))(2)](2) at low temperature (<25 degrees C) formed an isolable intermediate, [MeGa(mu-NH(2))N(SiMe(3))(2)](2), that was characterized using single-crystal X-ray diffraction. Infrared spectroscopy and X-ray diffraction of the oligomers were consistent with a rodlike structure comprised of six-membered, [RGaNH](3) rings stacked perpendicular to the long axis of the rod. The method of synthesis, formula, and diffraction results suggested a structural similarity between the alkyl, [RGaNH](n)(), and the previously reported hydride, [HGaNH](n). The structural and electronic properties of rods having the general formula H(3)[(HXYH)(3)](n)H(3) (XY = GaN, GeC; n = 1-9) were investigated using density functional theory. Atomic electronegativity differences between the group 13/15 and 14/14 systems were found to play important roles in the geometrical structures of the two rods and also caused significant differences in the electronic structures. Energetically, it was found to be increasingly favorable to add additional cyclotrigallazane rings to the GaN rods, while for the GeC rods, there was a roughly constant energy cost associated with each additional ring. The electric dipole moments of the GaN rods increased substantially with length; in the GeC rods, charge separation occurred to a much smaller extent and had a polarization opposite to that found in GaN. In addition, increased dipole moments correlated with smaller electronic excitation energies, as predicted by time-dependent density functional theory. All of the powders exhibited luminescence in the visible spectrum at room temperature. Structure observed in the photoluminescence spectra of [HGaNH](n) and [MeGaNH](n) was interpreted as arising from rods of different length.     

DNA oligomers having a diazapyrenium dication (DAP2+); synthesis and DNA cleavage activities.

Aiming at the creation of functionalized antisense DNA oligomers possessing site-selective DNA cleaving activity, viologen and a related compound, diazapyrenium dication (DAP2+), were selected and introduced into oligodeoxyribonucleotides as a functionalized molecule. The conjugation of these functionalized molecules with DNA proceeded smoothly by using standard H-phosphonate chemistry. A part of the DAP(2+)-tethered DNA oligomers was synthesized by a combination of solid support method and liquid phase technique. Viologen-tethered DNA oligomers showed no significant activity toward DNA cleavage in spite of their characteristic ESR spectra. On the other hand, it was observed that the DAP(2+)-tethered DNA oligomers formed more stable duplexes with their complementary strands than the corresponding wild type, and these molecules effectively cleaved the complementary strands at the specific site of 2-3 bases away from the modified phosphoramidate linkage. The effect of position and length of the linker arm on the selectivity in the cleavage reaction was also investigated, and it was found that introduction at the 3'- or 5'-end phosphate site is more favorable, probably due to duplex stabilization.     

Radical polymerization of tetrafluoroethylene that forms a colloid solution and gel of oligomers

As the concentration of tetrafluoroethylene (TFE) in the solvent increases, its polymerization is shown to be accompanied by a transformation of the resulting homogeneous solution of oligomers into a colloid one, which then transforms into gel. The micron-sized colloid particles consist of oligomers and solvent molecules, whose number per TFE unit in the oligomer decreases from 15–20 at the threshold of dense phase formation to 4–6 in a gel. A kinetic model of polymerization was suggested. In this model, the chain propagation is limited by monomer diffusion to the growing macroradical and the chain transfer (oligomer formation and regeneration of the prime radical) is limited by the reaction of the growing macroradical with the solvent molecule. The model that allows for the decrease in the diffusion coefficients with increasing of the oligomer chain length and their local concentration leads to a spatially inhomogeneous molecular mass distribution, with long oligomers accumulated in the vicinity of the macroradical and short ones in the distant zone. The formation of colloid particles and gel occurs when the concentration of long oligomers shaped as rigid rods exceeds the critical value for the dense phase formation and the percolation threshold, respectively. The transition from the initial spatial distribution to the equilibrium distribution described by the phase diagram was considered using the model of viscoelastic separation so that phases retain spatial continuity.     

How a single stretched polymer responds coherently to a minute oscillation in fluctuating environments: An entropic stochastic resonance

Within the cell, biopolymers are often situated in constrained, fluid environments, e.g., cytoskeletal networks, stretched DNAs in chromatin. It is of paramount importance to understand quantitatively how they, utilizing their flexibility, optimally respond to a minute signal, which is, in general, temporally fluctuating far away from equilibrium. To this end, we analytically study viscoelastic response and associated stochastic resonance in a stretched single semi-flexible chain to an oscillatory force or electric field. Including hydrodynamic interactions between chain segments, we evaluate dynamics of the polymer extension in coherent response to the force or field. We find power amplification factor of the response at a noise-strength (temperature) can attain the maximum that grows as the chain length increases, indicative of an entropic stochastic resonance (ESR). In particular for a charged chain under an electric field, we find that the maximum also occurs at an optimal chain length, a new feature of ESR. The hydrodynamic interaction is found to enhance the power amplification, representing unique polymer cooperativity which the fluid background imparts despite its overdamping nature. For the slow oscillatory force, the resonance behavior is explained by the chain undulation of the longest wavelength. This novel ESR phenomenon suggests how a biopolymer self-organizes in an overdamping environment, utilizing its flexibility and thermal fluctuations.     

Drying of colloidal solutions of fluoroalkyl oligomers

The change in the supramolecular structure upon drying (solvent removal) of colloidal solutions of fluoroalkyl oligomers at atmospheric pressure has been studied using atomic force microscopy. In an initial colloidal solution, micrometer-sized particles of the dense phase consist of randomly oriented oligomers in the form of rigid rods of a 3–5 nm length forming a porous framework filled with solvent molecules, which solvate the oligomer chains. The drying-induced capillary pressure, which in nanosized pores is of the same order of magnitude as the solvation energy, leads to framework deformation, collapse of the pores, and the formation of lamellar and dendritic structures on a 50–100 nm scale. The ordering of these structures (formation of blocks of parallel oriented fibers typical of a fluoroplastic) increases as the heat-treatment temperature and the drying rate are increased, increasing the roughness of the surface (ratio of real to smooth surface area) and its hydrophobicity.     

Determination of rate constants for radical telomerization chain growth and transfer from the molecular-mass distribution of oligomer

The ratio of rate constant for growth and transfer X(n), as a function of the chain length n has been found from the measured molecular-mass distributions of the products of tetrafluoroethylene telomerization in acetone, ethyl acetate, chloroform, and carbon tetrachloride. For all these telogens, the function increases by a factor of 1.5–2.5 in the range of n from 2 to 5, is almost constant for n of 6 to 10, and increases by a factor of 7–10 in the range of n from 12 to 20. This behavior of the function X(n) has been explained in terms of the model of diffusion-controlled propagation and kinetic chain transfer. The model takes into account the change in the diffusion nature of oligomers in the form of rigid rods with an increase in their length. A sharp increase in X(n) occurs when the oligomers that accumulate in the environment of growing macroradical sterically restrict the withdrawal of the forming oligomer to the bulk by an effective solid angle, which decreases with the increasing oligomer length and becomes minimal in the region of formation of colloidal particles.     

The influence of the salt concentration on the aggregation behavior of viscoelastic detergents

The influence of excess NaCl on the properties of viscoelastic detergent solutions of Cetypyridiniumsalicylate (CPySal) has been studied by static and dynamic light scattering, electric birefringence and rheological measurements. It is obeserved that the rodlike micelles of length L which are present in these solutions and which are responsible for their elastic properties grow in length with the increase of the NaCl concentration. As long as the rods are shorter than their mean distance, their length can be determined from the rheological and electric birefringence measurements. For very small shear fields these solutions behave as Newtonian fluids. The viscosity of the solution increases strongly when the rods begin to overlap. Solutions with overlapping rods are elastic. It is postulated from the results that the cmc_II (the critical concentration above which rods are present) and the length L of the rods are partially determined by the intermicellar interaction energy. It is furthermore postulated that this intermicellar interaction energy has an influence on the polydispersity of the rods and seems to make the rods relatively monodisperse.     

Evaluation of the β value of the phenylene unit by probing exchange interaction between two nitroxides

Oligophenylene molecular rods with bicyclo[2.2.2]octane having two nitronyl nitroxide radicals were synthesized to investigate the decay constant of p-phenylene. By the measurement and simulation of the ESR spectra of the biradicals with different rod length, it was found that the exchange interaction was decreased with the decay constant β of 0.51 ± 0.01 ?(-1). This result indicates that the spin-spin exchange interaction between neutral radicals has a decay constant similar to the molecular conductance.     

Helical pitch of m-phenylene ethynylene foldamers by double spin labeling

To investigate the helical conformation of oligo(m-phenylene ethynylene)s, a pair of TEMPO spin labels were appended to the backbone. The two TEMPO radicals were separated by the four, five, and six repeating units. ESR spectra of the labeled oligomers were measured in chloroform and in ethyl acetate solvents in which the oligomers are disordered and folded, respectively. The measurement and analysis of ESR spectra revealed that six repeating units make one helical turn.     

Electronic coherence dynamics in trans-polyacetylene oligomers

Electronic coherence dynamics in trans-polyacetylene oligomers are considered by explicitly computing the time dependent molecular polarization from the coupled dynamics of electronic and vibrational degrees of freedom in a mean-field mixed quantum-classical approximation. The oligomers are described by the Su-Schrieffer-Heeger Hamiltonian and the effect of decoherence is incorporated by propagating an ensemble of quantum-classical trajectories with initial conditions obtained by sampling the Wigner distribution of the nuclear degrees of freedom. The electronic coherence of superpositions between the ground and excited and between pairs of excited states is examined for chains of different length, and the dynamics is discussed in terms of the nuclear overlap function that appears in the off-diagonal elements of the electronic reduced density matrix. For long oligomers the loss of coherence occurs in tens of femtoseconds. This time scale is determined by the decay of population into other electronic states through vibronic interactions, and is relatively insensitive to the type and class of superposition considered. By contrast, for smaller oligomers the decoherence time scale depends strongly on the initially selected superposition, with superpositions that can decay as fast as 50 fs and as slow as 250 fs. The long-lived superpositions are such that little population is transferred to other electronic states and for which the vibronic dynamics is relatively harmonic.     

Study on the intermediate of photooxidative degradation of phenylenevinylene oligomers

The results of the investigation on photooxidative degradation of five phenylenevinylene oligomers are as follows. The sequence of the photodegradation rate in self-sensitized reaction is the same as that in the biacetyl-sensitized reaction and the rate of photooxidative degradation increases upon the incorporation of electron-donating groups and decreases upon the incorporation of electron-accepting groups on the oligomers. The self-sensitized reaction rate of oligomers increases as the solvent changing from benzene to deuterated benzene and decreases with the addition of the singlet oxygen (¹O₂) scavenger. ¹O₂ is shown to be the main reactive intermediate in self-sensitized photolysis of phenylenevinylene oligomers, which was directly confirmed by ESR spin trapping experiments.     

对苯撑乙烯低聚物光氧化降解研究

五种对苯撑乙烯低聚物的光氧化降解反应表明,给电子基团能促进其光氧化降解,而吸电子基团却能提高它们的光稳定性,这为用分子修饰的方法提高对苯撑乙烯类发光材料的稳定性提供了理论基础。在自敏化和染料敏化的光氧化降解反应中,五种低聚物的降解速率顺序完全一致,意味着单线态氧（1O2）是其光氧化降解反应过程中的主要中间体,ESR自旋捕获实验进一步证实了上述诊断。     

Polymerization of Diphenylbutadiyne Derivatives in Solution by Free Radical Initiator

In order to study free radical reactions of aromatic diacetylenes, the reaction of diphenyldiacetylene with di‐t‐butylperoxide was carried out in 1,2‐dichlorobenzene. The presence of t‐butoxy radicals considerably accelerated product formation, and oligomers with number average molecular weights of 700–2000 were obtained. There is no fragment of the t‐butyl group in the oligomers obtained according with the ¹H‐NMR spectrum. Furthermore, it is impossible that the t‐butoxy radicals would have initiated the oligomerization. The intense ESR spectra observed during the reaction at 130°C are due to the diradicals of oligomeric diphenylbutadiyne. It was concluded that the oligomerization proceeds via coupling of diradicals, and not the successive addition of radicals to monomers. The purified product oligomers did not contain carbonyl groups indicating there was no oxidation, and their ESR spectra have revealed that these oligomers contained a substantial amount of living free radicals stable in air at room temperature. The reason why high polymers are not obtained is the steric effect of oligomeric diradicals for coupling, as well as probable cyclization.     

Pt-tetraethynylethene molecular scaffolding: synthesis and characterization of a novel class of organometallic molecular rods

The series of monodisperse Pt-bridged TEE oligomers 3a-f was prepared by oxidative Glaser-Hay oligomerization of monomer 7 under end-capping conditions. These novel molecular rods extend in length from 3.3 nm (monomeric 3a) to 12.1 nm (hexameric 3 f). Their isolation was achieved by high performance gel permeation chromatography (GPC), and their purification was best monitored by analytical GPC in combination with matrix-assisted laser-desorption-ionization mass spectrometry (MALDI-TOF MS). The mass spectra of each oligomer revealed the molecular ion or its sodium complex as parent ion together with a clean, highly characteristic fragmentation pattern. Delayed addition of the end-capping reagent PhC(triple bond)CH to the oligomerization mixture afforded polymer 10 with an average of approximately 32 repeat units and a remarkably narrow molecular weight distribution (Mw/Mn=1.06), which is indicative of a living polymerization process. UV/Vis spectral data as well as measurements of the second hyperpolarizability gamma by third harmonic generation (THG) revealed a nearly complete lack of pi-electron delocalization along the oligomeric backbone. The Pt atoms act as true insulating centers, and the Pt-C(sp) bonds hardly possess any pi character. The synthesis of the molecular rods 3a-f provides another demonstration of the power of oxidative acetylenic homocouplings for the preparation of unusual nanoarchitecture.     

Structure and Dynamics of Molecular Rods in Membranes: Application of a Spin‐Labeled Rod

Molecular rods consisting of a hydrophobic backbone and terminally varying functional groups have been synthesized for applications for the functionalization of membranes. In the present study, we employ a spin‐labeled analogue of a recently described new class of molecular rods to characterize their dynamic interactions with membranes. By using the different approaches of ESR and NMR spectroscopy, we show that the spin moiety of the membrane‐embedded spin‐labeled rod is localized in the upper chain/glycerol region of membranes of different compositions. The rod is embedded within the membrane in a tilted orientation to adjust for the varying hydrophobic thicknesses of these bilayers. This orientation does not perturb the membrane structure. The water solubility of the rod is increased significantly in the presence of certain cyclodextrins. These cyclodextrins also allow the rods to be extracted from the membrane and incorporated into preformed membranes. The latter will improve the future applications of these rods in cellular systems as stable membrane‐associated anchors for the functionalization of membrane surfaces.     

Recent progress in JAERI alanineESR dosimetry system

Alanine/ESR (electron spin resonance) dosimetry system has been developed on the basis of precise, mass-productive alanine dosimeters of various shapes, and easy-handling ESR reading system. Polymers as binders enable us to mass-produce homogeneous and dimensionally uniform alanine dosimeters of different shapes and thickness relative to penetration range of radiations, for instance, rods for gamma and X-rays, and thin films for electrons and heavy charged particles. They also allow us to simplify parameters of ESR operation exclusively for specific dosimeters and to achieve good reproducibility of measurement. An easy-handling ESR spectrometric reading system was developed on the basis of custom-made ESR spectrometer with a permanent magnet, and automated with auxiliary interfaces and a personal computer. Alanine/ESR dosimetry in JAERI works for domestic and international transfer dosimetry, for simple and reliable routine dosimetry in radiation processing, and for dosimetry of short-penetration range radiations.     

ESR Study of Photopolymerization of Epoxy-Acrylate Oligomers

Photopolymerization and thermal polymerization of epoxy-acrylate oligomers were studied by ESR at room temperature.