Fullerene C60-perylene-3,4:9,10-bis(dicarboximide) light-harvesting dyads: spacer-length and bay-substituent effects on intramolecular singlet and triplet energy transfer

Novel covalent fullerene C(60)-perylene-3,4:9,10-bis(dicarboximide) (C(60)-PDI) dyads (1-4) were synthesized and characterized. Their electrochemical and photophysical properties were investigated. Electrochemical studies show that the reduction potential of PDI can be tuned relative to C(60) by molecular engineering through altering the substituents on the PDI bay region. It was demonstrated using steady-state and time-resolved spectroscopy that a quantitative, photoinduced energy transfer takes place from the PDI moiety, acting as a light-harvesting antenna, to the C(60) unit, playing the role of energy acceptor. The bay-substitution (tetrachloro [1 and 2] or tetra-tert-butylphenoxy [3 and 4]) of the PDI antenna and the linkage length (C(2) [1 and 3] or C(5) [2 and 4]) to the C(60) acceptor are important parameters in the kinetics of energy transfer. Femtosecond transient absorption spectroscopy indicates singlet-singlet energy-transfer times (from the PDI to the C(60) unit) of 0.4 and 5 ps (1), 4.5 and 27 ps (2), 0.8 and 12 ps (3), and 7 and 50 ps (4), these values being ascribed to two different conformers for each C(60)-PDI system. Subsequent triplet-triplet energy-transfer times (from the C(60) unit to the PDI) are slower and in the order of 0.8 ns (1), 6.2 ns (2), 2.7 ns (3), and 9 ns (4). Nanosecond transient absorption spectroscopy of final PDI triplet states show a marked influence of the bay substitution (tetrachloro- or tetra-tert-butylphenoxy), and triplet-state lifetimes (10-20 micros) and the PDI triplet quantum yields (0.75-0.52) were estimated. The spectroscopy showed no substantial solvent effect upon comparing toluene (non-polar) to benzonitrile (polar), indicating that no electron transfer is occurring in these systems.     

Nonelectrolyte-Induced CP Variation of TX-114＋TBAB System

The effects of nonelectrolytes(ureas,amino acids,sugars)on the cloud point(CP)of nonionic surfactantTriton X-114(TX-114)and tetra-n-butylammonium bromide(TBAB)system were studied.Ureas as well as thioureasincreased the CP.Behaviors of amino acids depended upon their nature.Nonpolar and uncharged polar anlino acidswere less effective in changing the CP.However,tryptophan and phenylalanine increased the CP sharply.Acidicamino acid(aspartic acid)and sugars decreased the CP.The results were explained in terms of their effect on waterstructure.Amino acids got solubilized either in the micellar interior or in the bulk phase.     

Benzophenone and zinc(II) phthalocyanine dichromophores-labeled poly (aryl ether) dendrimer: synthesis,characterization and photoinduced energy transfer

A series of benzophenone chromospheres and zinc(II) phthalocyanine dichromophores labeled poly (aryl benzyl ether) dendrimer (G_n-DZnPc(BP)_8n, n = 1?2) were synthesized. Their structures were characterized by elemental analysis, ¹H NMR, IR, UV–vis and matrix-assisted laser desorption/ionization time-of-flight spectrometry (MALDI-TOF MS). Their photophysical properties were examined by steady-state and time-resolved fluorescence methods. Both the poly (aryl benzyl ether) dendrimer and BP terminal chromophores had a significant effect on photophysical properties of the zinc(II) phthalocyanine core. Time-resolved spectroscopic measurements indicated that the lifetime of benzophenone (donor) chromophore was longer than that of the zinc(II) phthalocyanine (acceptor). The fluorescence of the peripheral benzophenone chromophores was quenched by the phthalocyanine group attached to the focal point. All of these observations suggest that an intramolecular singlet energy transfer occurs in G_n-DZnPc(BP)_8n molecules. The light-harvesting abilities of these molecules increased with generations due to an increase in the number of benzophenone chromophores. The energy transfer efficiencies were ca. 0.49 and 0.68 for generations 1 and 2, respectively, and the rate constants of the singlet-singlet energy transfer were ca. 10⁸ s^?1. The rate constants changed inconspicuously with increase of dendron generations. The intramolecular singlet-singlet energy transfer is proposed to proceed mainly via a Förster-type interaction mechanism involving the dendrimer backbone as a scaffold to hold the peripheral benzophenone chromophores and the phthalocyanine core together. This dendrimer was an effective new energy transmission complex with high efficiency and could be used as a potential light-harvesting system.     

A simple method for determination of erythritol,maltitol, xylitol,and sorbitol in sugar‐free chocolates by capillary electrophoresis with capacitively coupled contactless conductivity detection

In this work, a novel and simple analytical method using capillary electrophoresis (CE) with capacitively coupled contactless conductivity detection (C⁴D) is proposed for the determination of the polyols erythritol, maltitol, xylitol, and sorbitol in sugar‐free chocolate. CE separation of the polyols was achieved in less than 6 min, and it was mediated by the interaction between the polyols and the borate ions in the background electrolyte, forming negatively charged borate esters. The extraction of the polyols from the samples was simply obtained using ultra‐pure water and ultrasonic energy. Linearity was assessed by calibration curves that showed R² varying from 0.9920 to 0.9976. The LOQs were 12.4, 15.9, 9.0, and 9.0 μg/g for erythritol, maltitol, xylitol, and sorbitol, respectively. The accuracy of the method was evaluated by recovery tests, and the obtained recoveries varied from 70 to 116% with standard deviations ranging from 0.2 to 19%. The CE‐C⁴D method was successfully applied for the determination of the studied polyols in commercial samples of sugar‐free chocolate.     

带有非线性收获和妊娠时滞的微分代数捕食者-食饵系统的稳定性及Hopf分支

本文研究了一类同时带有非线性食饵收获和捕食者妊娠时滞的微分代数捕食者-食饵系统的稳定性及Hopf分支问题.利用了分支理论和稳定性理论,以捕食者妊娠时滞作为系统的分支参数,获得了所提出的新系统在正平衡点处系统稳定性的相关判据条件和Hopf分支的产生条件.推广了一般带有线性收获和时滞的微分代数捕食者-食饵系统的结论.     

Comparative genomics for understanding the structure,function and sub-cellular localization of hypothetical proteins in Thermanerovibrio acidaminovorans DSM 6589 (tai)

The Thermanerovibrio acidaminovorans DSM 6589 (tai) is a unique bacterium isolated from anaerobic sludge bed reactor from sugar refinery in Netherland. The comparative genomic studies for understanding the hypothetical proteins in T. acidaminovorans DSM 6589 (tai) were carried out using different bioinformatic tools and web servers. In all 320 hypothetical proteins were screened from the total available genome. The Insilico function prediction for 320 hypothetical proteins was achieved by using different online servers like CDD-Blast, Interproscan and pfam whereas, the structure prediction for 202 hypothetical proteins were deciphered by using protein structure prediction server (PS2 server). The sub-cellular localization for the identified proteins was predicted by the use of cello v2.5 for 320. The study carried out has helped us to understand the structures and functions of unknown proteins available in T. acidaminovorans DSM 6589 (tai) through comparative genomic approach.     

OPTIMAL FISH HARVESTING FOR A POPULATION MODELED BY A NONLINEAR PARABOLIC PARTIAL DIFFERENTIAL EQUATION

As the human population continues to grow, there is a need for better management of our natural resources in order for our planet to be able to produce enough to sustain us. One important resource we must consider is marine fish populations. We use the tool of optimal control to investigate harvesting strategies for maximizing yield of a fish population in a heterogeneous, finite domain. We determine whether these solutions include no‐take marine reserves as part of the optimal solution. The fishery stock is modeled using a nonlinear, parabolic partial differential equation with logistic growth, movement by diffusion and advection, and with Robin boundary conditions. The objective for the problem is to find the harvest rate that maximizes the discounted yield. Optimal harvesting strategies are found numerically.     

A simple route to incorporate redox mediator into carbon nanotubes/Nafion composite film and its application to determine NADH at low potential

Several new sugar glasses were investigated for their potential in solid-matrix luminescence. Both solid-matrix fluorescence (SMF) and solid-matrix phosphorescence (SMP) properties were obtained, and two heterocyclic aromatic amines were employed as model compounds. In addition to glucose glasses, which were investigated previously, fructose, ribose, xylose, galactose, maltose, and glucose with poly(acrylic acid) (PAA) were studied. Detailed experimental conditions were obtained for each sugar-glass system. In addition, NaI was investigated as a heavy-atom salt in the sugar-glass systems to enhance the SMP of the heterocyclic aromatic amines. The SMF intensity was the strongest in maltose and glucose with PAA for 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and in maltose for 2-amino-9H-pyrido[2,3-b]indole (AαC). The largest SMP signals for PhIP with and without NaI were acquired in glucose with PAA. For AαC with NaI, the strongest SMP signal was obtained in maltose. Limits of detection were obtained for PhIP in the several sugar-glass systems, and the lowest limit of detection was 0.04 pmol/mg of PhIP in maltose with NaI present. An extensive study was carried out using both SMF and SMP to determine if neutral and/or protonated species of PhIP and AαC were in the sugar-glass systems. General guidelines such as glass transition temperature and solubility are discussed for selecting a sugar glass as a solid matrix.     

Porphyrin light-harvesting arrays constructed in the recombinant tobacco mosaic virus scaffold

We have demonstrated the construction of multiple porphyrin arrays in the tobacco mosaic virus (TMV) supramolecular structures by self-assembly of recombinant TMV coat protein (TMVCP) monomers, in which Zn-coordinated porphyrin (ZnP) and free-base porphyrin (FbP) were site-selectively incorporated. The photophysical properties of porphyrin moieties incorporated in the TMV assemblies were also characterized. TMV-porphyrin conjugates employed as building blocks self-assembled into unique disk and rod structures under the proper conditions as similar to native TMV assemblies. The mixture of a ZnP donor and an FbP acceptor was packed in the TMV assembly and showed energy transfer and light-harvesting activity. The detailed photophysical properties of the arrayed porphyrins in the TMV assemblies were examined by time-resolved fluorescence spectroscopy, and the energy transfer rates were determined to be 3.1-6.4x10(9) s(-1). The results indicate that the porphyrins are placed at the expected positions in the TMV assemblies.