A general method for the synthesis of bastaranes and isobastaranes: first total synthesis of bastadins 5, 10, 12, 16, 20, and 21

A general strategy for the synthesis of twenty naturally occurring bastadins (all but bastadin 3) is presented. A key retrosynthetic disconnection of the two amide bonds, common in all target molecules, bisects the macrocyclic core into two diaryl ether fragments, an alpha,omega-diamine (western part) and an alpha,omega-dicarboxylic acid (eastern part). Efficient preparation of the synthetically challenging o-mono or dibromo-substituted diaryl ether linkages was achieved employing the diaryl iodonium salt method. Regarding the western part, variations of the aliphatic chain were more efficiently secured by the preparation of two different alpha,omega-aminonitrile moieties. Cobalt boride mediated reduction of the nitrile functionality established the required diamines and, at the same time, provided the necessary variation of the aromatic-ring bromination pattern. Regarding the eastern part, two different dicarboxyl precursors had to be prepared in order to accommodate bromination-pattern variations. Coupling and subsequent macrolactamization of different combinations of these key intermediates may lead at will to any member of this family of marine natural products. Four bastaranes (bastadins 5, 10, 12 and 16) and two isobastaranes (bastadins 20 and 21) were synthesized as a demonstration of the flexibility and efficiency of the approach presented.     

A General Method for the Synthesis of Bastaranes and Isobastaranes: First Total Synthesis of Bastadins 5, 10, 12, 16, 20, and 21

A general strategy for the synthesis of twenty naturally occurring bastadins (all but bastadin 3) is presented. A key retrosynthetic disconnection of the two amide bonds, common in all target molecules, bisects the macrocyclic core into two diaryl ether fragments, an α,ω‐diamine (western part) and an α,ω‐dicarboxylic acid (eastern part). Efficient preparation of the synthetically challenging o‐mono or dibromo‐substituted diaryl ether linkages was achieved employing the diaryl iodonium salt method. Regarding the western part, variations of the aliphatic chain were more efficiently secured by the preparation of two different α,ω‐aminonitrile moieties. Cobalt boride mediated reduction of the nitrile functionality established the required diamines and, at the same time, provided the necessary variation of the aromatic‐ring bromination pattern. Regarding the eastern part, two different dicarboxyl precursors had to be prepared in order to accommodate bromination‐pattern variations. Coupling and subsequent macrolactamization of different combinations of these key intermediates may lead at will to any member of this family of marine natural products. Four bastaranes (bastadins 5, 10, 12 and 16) and two isobastaranes (bastadins 20 and 21) were synthesized as a demonstration of the flexibility and efficiency of the approach presented.     

Cellulose polymorphy, crystallite size, and the Segal Crystallinity Index

The X-ray diffraction-based Segal Crystallinity Index (CI) was calculated for simulated different sizes of crystallites for cellulose Iβ and II. The Mercury software was used, and different crystallite sizes were based on different input peak widths at half of the maximum peak intensity (pwhm). The two cellulose polymorphs, Iβ and II, gave different CIs despite having the same pwhm values and perfect periodicity. The higher CIs for cellulose II were attributed to a greater distance between the major peaks that are closest to the recommended 2-θ value for assessing the amorphous content. That results in less peak overlap at the recommended 2-θ value. Patterns calculated with simulated preferred orientation had somewhat higher CIs for cellulose Iβ, whereas there was very little effect on the CIs for cellulose II.     

Diblock polyampholytes grafted onto spherical particles: effect of stiffness, charge density, and grafting density

The structure of spherical brushes formed by symmetric diblock polyampholytes end-grafted onto small spherical particles in aqueous solution is examined within the framework of the so-called primitive model using Monte Carlo simulations. The properties of the two blocks are identical except for the sign of their charges. Three different chain flexibilities corresponding to flexible, semiflexible, and stiff blocks are considered at various polyampholyte linear charge densities and grafting densities. The link between the two blocks is flexible at all conditions, and the grafted segments are laterally mobile. Radial and lateral spatial distribution functions of different types and single-chain properties are analyzed. The brush structure strongly depends on the chain flexibility. With flexible chains, a disordered polyelectrolyte complex is formed at the surface of the particle, the complex becoming more compact at increasing linear charge density. With stiff blocks, the inner blocks are radially oriented. At low linear charged density, the outer blocks are orientationally disordered, whereas at increasing electrostatic interaction the two blocks of a polyampholyte are parallel and close to each other, leading to an ordered structure referred to as a polyampholyte star. As the grafting density is increased, the brush thickness responds differently for flexible and nonflexible chains, depending on a different balance between electrostatic interactions and excluded volume effects.     

Ethylene adsorption on platinum: kinetics,bonding, and relevance to catalysis

Ethylene adsorption on platinum(111) single-crystal surfaces involves two states, a di-sigma species irreversibly bonded on the clean surface, and a second pi reversible adsorption which develops at high coverages. The two states display significantly different kinetic behavior, but they can slowly interchange. This suggests an adsorption mechanism at high coverages via an initial interaction with the few metal atoms left exposed by an imperfect monolayer followed by a collective rearrangement of the neighboring molecules into a new compressed layer.     

Proton sponge and fatty acid interactions at the air-water interface. Thermodynamic, spectroscopic, and microscopic study

Mixed Langmuir and Langmuir-Blodgett (LB) films of a proton sponge, namely, diphenyl bis(octadecylamino)phosphonium bromide, and a fatty acid, docosanoic acid, with different molar ratios have been fabricated. Surface pressure versus area per molecule isotherms were registered, and the excess areas and excess Gibbs energy of mixing were calculated. Strong interactions between the proton sponge and the fatty acid take place at the air-water interface. The existence of a stoichiometric 1:1 acid-base reaction between the two components forming a complex on the water surface at high surface pressures has been demonstrated. Furthermore, the reaction had an efficiency close to 100% at the air-water interface; meanwhile, it hardly takes place in organic solvents such as chloroform or even a mixture of chloroform and dimethyl sulfoxide. The floating films were transferred to solid supports and characterized by means of several techniques including IR spectroscopy, X-ray diffraction, and atomic force microscopy, revealing the presence of highly ordered alkyl chains and a constant architecture along the different layers as well as the presence of different domains in the LB films, except those having a 1:1 proton sponge-fatty acid ratio that are homogeneous. Such domains have been interpreted as the presence of two different phases, the 1:1 complex plus the excess component in the mixture.     

Intramolecular excimer fluorescence,its solvent dependence,and photodimerization of 1,2-dianthrylethanes

Both 1,2-di(1-anthryl)ethane (I) and 1,2-di(9-anthryl) ethane (II) show two types of excimer fluorescence spectra under different conditions; one with peak at 460 nm (type-1) and the other with peak at 530 nm (type-2). Furthermore, the type-1 excimer emission shows a peculiar dependence upon the solvent polarity.     

N, N'-二取代二硫代草酰胺与二元胺反应的研究

本文研究了N, N'-二取代二硫代草酰胺与二元胺(乙二胺、1, 3-丙二胺、反-1,2-环己二胺)在二甲基亚矾中的反应。用IR、^1H NMR和四圆衍射法测定了产物的结构。实验结果表明, 反应存在着两种方式, 一种是二元胺的两个氨基反应在同一个硫代酰基的碳原子上(如乙二胺、1, 3-丙二胺)。而另一种由于立体的影响,反应在两个相邻硫代酰基的两个碳原子上(如反-1, 2-环己二胺)。     

Thermally responsive polymeric micellar nanoparticles self-assembled from cholesteryl end-capped random poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide): synthesis, temperature-sensitivity, and morphologies

Cholesteryl end-capped thermally responsive amphiphilic polymers with two different hydrophobic/hydrophilic chain-length ratios were synthesized from the hydroxyl-terminated random poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) and cholesteryl chloroformate. The hydroxyl-terminated precursor polymers with narrow molecular weight distributions were synthesized by free-radical polymerization using 2-hydroxyethanethiol as a chain-transfer agent. The aqueous solutions of the cholesteryl end-capped copolymers exhibited reversible phase transitions at temperatures slightly above human body temperature, with the lower critical solution temperature values being 37.7 and 38.2 degrees C, respectively. The critical micelle concentration values of the two cholesteryl end-capped polymers were 9 and 25 mg/L, respectively. Polymeric micellar nanoparticles were prepared from the amphiphilic polymers using a dialysis method as well as a direct dissolution method. Transmission electron microscope studies showed that the micellar nanoparticles existed in different morphologies, including spherical, star-like, and cuboid shapes. Pyrene as a model hydrophobic compound could be readily encapsulated in these polymeric nanoparticles, at loading levels of 1.0 and 0.8 mg/g for the two cholesteryl end-capped polymers, respectively. The temperature sensitivity and unusual morphology of these novel polymeric nanoparticles would make an interesting drug delivery system.     

Shear-induced conformational ordering, relaxation, and crystallization of isotactic polypropylene

The shear-induced coil-helix transition of isotactic polypropylene (iPP) has been studied with time-resolved Fourier transform infrared spectroscopy at various temperatures. The effects of temperature, shear rate, and strain on the coil-helix transition were studied systematically. The induced conformational order increases with the shear rate and strain. A threshold of shear strain is required to induce conformational ordering. High temperature reduces the effect of shear on the conformational order, though a simple correlation was not found. Following the shear-induced conformational ordering, relaxation of helices occurs, which follows the first-order exponential decay at temperatures well above the normal melting point of iPP. The relaxation time versus temperature is fitted with an Arrhenius law, which generates an activation energy of 135 kJ/mol for the helix-coil transition of iPP. At temperatures around the normal melting point, two exponential decays are needed to fit well on the relaxation kinetic of helices. This suggests that two different states of helices are induced by shear: (i) isolated single helices far away from each other without interactions, which have a fast relaxation kinetic; (ii) aggregations of helices or helical bundles with strong interactions among each other, which have a much slower relaxation process. The helical bundles are assumed to be the precursors of nuclei for crystallization. The different helix concentrations and distributions are the origin of the three different processes of crystallization after shear. The correlation between the shear-induced conformational order and crystallization is discussed.     

Disulfide- and thiol-incorporating copper catenanes: synthesis, deposition onto gold, and surface studies

Two new copper-complexed [2]catenanes have been prepared, both of which consist of two different interlocking rings. In both cases, one of the rings incorporates a disulfide bridge. The other ring contains either a single chelate (phen=1,10-phenanthroline, a bidentate ligand) or two different chelates (phen and terpy, 2,2',6',2"-terpyridine, a tridentate chelate). Deposition of these two complexes on a gold electrode surface was carried out by standard procedures, leading to reductive cleavage of the S-S bridge. The adsorbed species can be viewed as [2]catenanes for which the gold atoms of the electrode surface are an integral fragment of one of the two rings. They yield clear electrochemical responses, but no motion is observed for the catenane incorporating a phen unit and a terpy fragment in one of the two rings, regardless of the metal oxidation state. This is at odds with the behavior of the parent compound in solution, which undergoes ring-gliding motions upon electrochemical reduction or oxidation of the copper center. Near-field microscopy was used to study the deposited layers (STM and AFM). STM images suggest that the molecules do not tend to order at long range on the surface. Polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS) led to promising results: the two catenanes deposited are likely to be oriented perpendicular to the gold surface. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2111/2002/f3636_s.pdf or from the author. 1: Infrared spectra of [Cu.2]+ as a powder (black line, transmission IR spectroscopy) and as a SAM on gold (dotted line, PM-IRRAS). (Spectra offset and scaled for clarity; significant peaks marked with an asterisk.) 2: STM image (819x819 nm2) of a monolayer of [Cu.3]+ on Au(111) on mica.     

Energy Stabilities,Magnetic Properties,and Electronic Structures of Diluted Magnetic Semiconductor Zn1-xMnxS(001) Thin Films

We investigate the electronic and magnetic properties of the diluted magnetic semiconductors Zn_1-xMn_xS(001) thin films with different Mn doping concentrations using the total energy density functional theory. The energy stability and density of states of a single Mn atom and two Mn atoms at various doped configurations and different magnetic coupling state were calculated. Different doping configurations have different degrees of p-d hybridization, and because Mn atoms are located in different crystal-field environment, the 3d projected densities of states peak splitting of different Mn doping configurations are quite different. In the two Mn atoms doped, the calculated ground states of three kinds of stable configurations are anti-ferromagnetic state. We analyzed the 3d density of states diagram of three kinds of energy stability configurations with the two Mn atoms in different magnetic coupling state. When the two Mn atoms are ferromagnetic coupling, due to d-d electron interactions, density of states of anti-bonding state have significant broadening peaks. As the concentration of Mn atoms increases, there is a tendency for Mn atoms to form nearest neighbors and cluster around S. For such these configurations, the antiferromagnetic coupling between Mn atoms is energetically more favorable.     

Thermodynamic, dynamic, structural, and excess entropy anomalies for core-softened potentials

Using molecular dynamic simulations, we study three families of continuous core-softened potentials consisting of two length scales: a shoulder scale and an attractive scale. All the families have the same slope between the two length scales but exhibit different potential energy gap between them. For each family three shoulder depths are analyzed. We show that all these systems exhibit a liquid-liquid phase transition between a high density liquid phase and a low density liquid phase ending at a critical point. The critical temperature is the same for all cases suggesting that the critical temperature is only dependent on the slope between the two scales. The critical pressure decreases with the decrease of the potential energy gap between the two scales suggesting that the pressure is responsible for forming the high density liquid. We also show, using the radial distribution function and the excess entropy analysis, that the density, the diffusion, and the structural anomalies are present if particles move from the attractive scale to the shoulder scale with the increase of the temperature indicating that the anomalous behavior depends only in what happens up to the second coordination shell.     

Oligo(p-phenyleneethynylene)-functionalized Perylenebisimidetriad: Synthesis, Photophysical Properties, and Self-assembly

The rod‐like oligo(p‐phenylene ethynylene)‐functionalized perylene bisimide triad was synthesized and characterized. Aggregation behavior in solvents of different polarity was investigated by absorption and fluorescent spectroscopy. The results showed that stronger aggregations took place in low‐polarity slovent. The experiments also indicated that the energy and electron transfer might takeplace between the two chromophores during the photoinduced excitation. Highly ordered two‐dimensional assemblies could be observed at solid/liquid interfaces.     

Methylene excitation energies,transition probabilities,and frequency dependent polarizabilities

The electronic structure of the low-lying valence states of the polyatomic free radical methylene (CH₂) is investigated at two different geometries using multiconfigurational self-consistent field (MC SCF) and multiconfigurational random phase approximation (MC TDHF MC RPA) techniques. Oscillator strengths and polarizabilities of CH₂ are also examined with the MC TDHF MC RPA.     

Excited-state kinetics in the photolysis of azoethane and hexafluoroazomethane at 366 nm,up to one atmosphere pressure,and from room temperature to 150°C

The photochemistry of azoethane and hexafluoroazomethane at 366 nm has been reinvestigated up to 1 atm pressure, and over a range of temperature from 27 to 150°C. The Stern-Volmer type quenching plots primarily demonstrate the decomposition of a single electronic and vibrationally excited state for azoethane, but competitive photodissociation from two different electronic and vibrationally excited states, which was previously postulated for hexafluoroazomethane and azoisopropane, is confirmed for hexafluoroazomethane. It is concluded, however, that two different electronic and vibrationally excited photodissociating states are present in azoethane photolysis, but that one of them is difficult to detect, at least by the present approach Photosensitization with biacetyl at 436 nm also causes the dissociation of azoethane, and this is probably from the vibrationally equilibrated first triplet state. The energy barrier for this process was found to be 5.0 kcal/mol.     

EPR, optical, infrared and Raman spectral studies of Actinolite mineral

Electron paramagnetic resonance (EPR), optical, infrared and Raman spectral studies have been performed on a natural Actinolite mineral. The room temperature EPR spectrum reveals the presence of Mn(2+) and Fe(3+) ions giving rise to two resonance signals at g = 2.0 and 4.3, respectively. The resonance signal at g = 2.0 exhibits a six line hyperfine structure characteristic of Mn(2+) ions. EPR spectra have been studied at different temperatures from 123 to 433 K. The number of spins (N) participating in the resonance at g = 2.0 has been calculated at different temperatures. A linear relationship is observed between log N and 1/T in accordance with Boltzmann law and the activation energy was calculated. The paramagnetic susceptibility (chi) has been calculated at different temperatures and is found to be increasing with decreasing temperature as expected from Curie's law. From the graph of 1/chi versus T, the Curie constant and Curie temperature have been evaluated. The optical absorption spectrum exhibits bands characteristic of Fe(2+) and Fe(3+) ions. The crystal field parameter Dq and the Racah parameters B and C have been evaluated from the optical absorption spectrum. The infrared spectral studies reveal the formation of Fe(3+)--OH complexes due to the presence of higher amount of iron in this mineral. The Raman spectrum exhibits bands characteristic of Si--O--Si stretching and Mg?OH translation modes.     

Effective PET and ICT switching of boradiazaindacene emission: a unimolecular, emission-mode, molecular half-subtractor with reconfigurable logic gates

[reaction, structure: see text] We report a unimolecular system functioning as a combinatorial logic circuit for half-subtractor. The emission characteristics can be modulated by chemical inputs, and when followed at two different wavelengths, two functionally integrated logic gates XOR and INHIBIT are obtained. Both logic gates function in the emission mode, and with very large differences in the signal intensity allowing unequivocal assignment of logic-0 and logic-1.     

Solubility,diffusivity, and mobility of n-pentane and ethanol in poly(1-trimethylsilyl-1-propyne)

The diffusion coefficient of ethanol and of n-pentane in PTMSP, at 27°C, was measured as a function of concentration up to a penetrant content of about 12% by weight, for polymer samples obtained through different processes; differential sorptions and desorptions with vapor phases were considered. In the case of ethanol a nonmonotonous behavior was observed for the diffusivity, while in the case of n-pentane the same property was found to monotonously decrease with increasing the penetrant content. The sorption isotherms were also reported, indicating that n-pentane exhibits a typical dual mode behavior, while ethanol follows an unusual s-shape curve. The chemical potential of the dissolved penetrants, calculated directly from the isotherms, shows the very different importance of the energetic interactions of the two penetrants with the polymer units. In spite of the remarkably different concentration dependencies observed for both solubility and diffusivity of the two penetrants, the mobility factors are in both cases monotonously decreasing with the penetrant concentration, and follow very similar trends. The significant differences observed for the concentration dependence of the diffusion coefficients are, thus, associated to the thermodynamic contributions, which are very different for n-pentane and ethanol. Different polymeric films, obtained through different solvent evaporation processes, show quite different solubility, diffusivity and mobility for both ethanol and n-pentane. On the other hand, the ratio between the mobility of the two penetrants as well as the slope of mobility as function of the concentration remains the same for all the different samples inspected. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2245–2258, 1997     

Microwave Dielectric Relaxation of Bound Water to Silica, Alumina, and Silica-Alumina Gel Suspensions

By the use of a time domain reflectomery method, dielectric measurements were carried out on silica, alumina, and silica-alumina gel suspensions (five types with composition varying between 0.3 < Si/Al atomic ratio <0.8) in the frequency range of 100 kHz to 20 GHz. For all the gels, a relaxation peak due to bound water was observed. This peak locates at around 1-10 MHz, indicating that the peak is a decade or 10 decades lower than those of biological polymers such as an aqueous DNA solution. The silica and alumina gels have a different bound water structure, judging from the fact that the peaks are different in their locations and shapes between the two gels. The silica-alumina gels exhibit two different peaks other than the peak of bulk water. The sum of the relaxation strength on the two peaks is proportional to the monolayer capacity obtained from water vapor isotherms. The shape of the one peak holds that of the silica gel, whereas the other retains that of alumina gel, and furthermore the ratio of the relaxation strength on the former peak to that on the latter depends on Si/Al atomic ratio. It is suggested that both peaks are caused by the orientation of bound water molecules. Copyright 1999 Academic Press.