Search

Dye-sensitized solar cells (DSSCs) were built to probe the effect of the number of cyanocinnamic acid anchoring groups on the ring periphery of phenothiazine dyes. Two kinds of dyes, one with substitution on the N-terminal (1) and the other at the C-3 aromatic ring (2-5), have been synthesized for this purpose. Additionally, the number of cyanocinnamic acid groups have been increased to two in the case of compound 6. In the case of compounds 2-6, the N terminus was functionalized to carry methyl, 2-hydroxyethane, tris(ethylene oxide), or hexyl groups. Evidence for charge injection from the excited singlet state of phenothiazine to TiO2 was secured from femtosecond transient absorption spectral studies, wherein an ultrafast charge injection process (kCI ≈1010 -1011 s-1 ) was witnessed. The DSSCs were built on nanocrystalline TiO2 by using the traditional two-electrode method. Cell performance was better for carbon-functionalized phenothiazine dyes compared with that of nitrogen-functionalized dyes. The second cyanocinnamic group also increased the efficiency to 5.8 %.

Utilization of polyethyleneglycol (PEG) functionalized zinc phthalocyanine, (PEG)4ZnPc in (i) singlet oxygen generation, and (ii) in building energy harvesting donor-acceptor systems using fullerene, C60 as an acceptor via the well-known metal-ligand axial coordination approach is reported. The (PEG)4ZnPc was found to be capable of producing singlet oxygen with a quantum yield, ΦΔ of 0.77 in toluene, a value higher than that obtained for pristine (t-bu)4ZnPc (ΦΔ=0.54) carrying no PEG groups, revealing its usefulness in photodynamic therapy applications. Spectroscopic studies revealed efficient binding of phenylimidazole functionalized fullerene, C60Im with 1:1 stoichiometry to (PEG)4ZnPc. Binding constant K for the formation of (PEG)4ZnPc:ImC60 dyad was found to be 6×103 M−1 revealing moderate stability. Geometric and electronic studies of the dyad was arrived by B3LYP/3-21G(∗) method. The HOMO level was found to be on zinc phthalocyanine entity while the LUMO level was found to be on the C60 entity suggesting formation of (PEG)4ZnPc·+:ImC60· − charge separated state during the process of electron transfer reaction. Redox studies on the (PEG)4ZnPc:ImC60 dyad enabled accurate determination of the oxidation and reduction potentials of the donor-acceptor system, and to evaluate free-energy changes associated for the charge separation process. Kinetics of photoinduced charge separation and recombination in the (PEG)4ZnPc:ImC60 dyad was investigated using femtosecond transient absorption studies. Relatively long-lived charge separated states were confirmed for the dyad suggesting their potential usefulness in energy harvesting applications.

Sequential electron/hole transfer between energetically well-positioned entities of photosynthetic reaction center models is one of the commonly employed mechanisms to generate long-lived charge-separated states. A wealth of information, applicable towards light energy harvesting and building optoelectronic devices, has been acquired from such studies. In the present study, we report on the effect of spacer (direct or via phenoxy linkage) connecting the hole shifting agent, phenothiazine (PTZ), on photoinduced charge stabilization in subphthalocyanine-fullerene donor-acceptor conjugates. In these conjugates, the subphthalocyanine (SubPc) and fullerene (C60 ) served as primary electron donor and acceptor, respectively, while the phenothiazine entities act as hole shifting agents. The newly synthesized compounds were characterized by optical absorption and emission, computational, and electrochemical methods. The redox potentials measured using differential pulse voltammetry were used to estimate free-energy changes for charge separation, hole migration, and charge recombination processes. Using femto- and nanosecond transient absorption techniques, evidence for charge separation, and kinetics of charge separation and recombination were obtained in polar benzonitrile and nonpolar toluene solvents. In the conjugate where the phenothiazine entities are directly linked to SubPc, evidence for sequential electron transfer followed by hole shift leading to long-lived charge separated state was weak, primarily due to the delocalization of HOMO on both SubPc and PTZ entities. However, in case of the conjugate where the PTZ and SubPc are linked via phenoxy spacers, sequential electron transfer/hole shift was observed leading to the formation of long-lived charge-separated states. The present study brings out the importance of the spacer group connecting the hole shifting agent in model donor-acceptor conjugates to generate long-lived charge-separated states.

Sprout damage which results in poor breadmaking quality due to enzymatic activity of alpha-amylase is one of the important grading factors of wheat in Canada. Potential of near-infrared (NIR) hyperspectral imaging was investigated to detect sprouting of wheat kernels. Artificially sprouted, midge-damaged, and healthy wheat kernels were scanned using NIR hyperspectral imaging system in the range of 1000-1600 nm at 60 evenly distributed wavelengths. Multivariate image analysis (MVI) technique based on principal components analysis (PCA) was applied to reduce the dimensionality of the hyperspectral data. Three wavelengths 1101.7, 1132.2, and 1305.1 nm were identified as significant and used in analysis. Statistical discriminant classifiers (linear, quadratic, and Mahalanobis) were used to classify sprouted, midge-damaged, and healthy wheat kernels. The discriminant classifiers gave maximum accuracy of 98.3 and 100% for classifying healthy and damaged kernels, respectively. Refereed/Peer-reviewed

Novel photosynthetic reaction center model compounds of the type donor2 -donor1 -acceptor, composed of phenothiazine, BF2 -chelated dipyrromethene (BODIPY), and fullerene, respectively, have been newly synthesized using multistep synthetic methods. X-ray structures of three of the phenothiazine-BODIPY intermediate compounds have been solved to visualize the substitution effect caused by the phenothiazine on the BODIPY macrocycle. Optical absorption and emission, computational, and differential pulse voltammetry studies were systematically performed to establish the molecular integrity of the triads. The N-substituted phenothiazine was found to be easier to oxidize by 60 mV compared to the C-substituted analogue. The geometry and electronic structures were obtained by B3LYP/6-31G(dp) calculations (for H, B, N, and O) and B3LYP/6-31G(df) calculations (for S) in vacuum, followed by a single-point calculation in benzonitrile utilizing the polarizable continuum model (PCM). The HOMO-1, HOMO, and LUMO were, respectively, on the BODIPY, phenothiazine and fullerene entities, which agreed well with the site of electron transfer determined from electrochemical studies. The energy-level diagram deduced from these data helped in elucidating the mechanistic details of the photochemical events. Excitation of BODIPY resulted in ultrafast electron transfer to produce PTZ-BODIPY(.+) -C60 (.-) ; subsequent hole shift resulted in PTZ(.+) -BODIPY-C60 (.-) charge-separated species. The return of the charge-separated species was found to be solvent dependent. In nonpolar solvents the PTZ(.+) -BODIPY-C60 (.-) species populated the (3) C60 * prior to returning to the ground state, while in polar solvent no such process was observed due to relative positioning of the energy levels. The (1) BODIPY* generated radical ion-pair in these triads persisted for few nanoseconds due to electron transfer/hole-shift mechanism.

A multimodular donor-acceptor tetrad featuring a bis(zinc porphyrin)-(zinc phthalocyanine) ((ZnP-ZnP)-ZnPc) triad and bis-pyridine-functionalized fullerene was assembled by a "two-point" binding strategy, and investigated as a charge-separating photosynthetic antenna-reaction center mimic. The spectral and computational studies suggested that the mode of binding of the bis-pyridine-functionalized fullerene involves either one of the zinc porphyrin and zinc phthalocyanine (Pc) entities of the triad or both zinc porphyrin entities leaving ZnPc unbound. The binding constant evaluated by constructing a Benesi-Hildebrand plot by using the optical data was found to be 1.17×10(5) M(-1), whereas a plot of "mole-ratio" method revealed a 1:1 stoichiometry for the supramolecular tetrad. The mode of binding was further supported by differential pulse voltammetry studies, in which redox modulation of both zinc porphyrin and zinc phthalocyanine entities was observed. The geometry of the tetrad was deduced by B3LYP/6-31G* optimization, whereas the energy levels for different photochemical events was established by using data from the optical absorption and emission, and electrochemical studies. Excitation of the zinc porphyrin entity of the triad and tetrad revealed ultrafast singlet-singlet energy transfer to the appended zinc phthalocyanine. The estimated rate of energy transfer (k(ENT)) in the case of the triad was found to be 7.5×10(11) s(-1) in toluene and 6.3×10(11) s(-1) in o-dichlorobenzene, respectively. As was predicted from the energy levels, photoinduced electron transfer from the energy-transfer product, that is, singlet-excited zinc phthalocyanine to fullerene was verified from the femtosecond-transient spectral studies, both in o-dichlorobenzene and toluene. Transient bands corresponding to ZnPc(⋅+) in the 850 nm range and C60(⋅-) in the 1020 nm range were clearly observed. The rate of charge separation, k(CS), and rate of charge recombination, k(CR), for the (ZnP-ZnP)-ZnPc(⋅+):Py2C60(⋅-) radical ion pair (from the time profile of 849 nm peak) were found to be 2.20×10(11) and 6.10×10(8) s(-1) in toluene, and 6.82×10(11) and 1.20×10(9) s(-1) in o-dichlorobenzene, respectively. These results revealed efficient energy transfer followed by charge separation in the newly assembled supramolecular tetrad.

Preparation and purification of substrate amounts of radioactive as well as non-radioactive dolichyl diphosphate N-acetylglucosamine and dolichyl diphosphate chitobiose made it possible to test and characterize tentatively the first three reactions of the dolichol pathway (enzyme I–III). The test conditions are described in detail. All three enzymes were solubilized from yeast membranes with detergents. Enzyme II and III were purified to give a purification factor of 35-fold and 70-fold, respectively. The reactions required divalent metal ions with an optimum concentration of 10 mM Mg2+. Enzyme II was stimulated almost to the same extent also by Ca2+. The Km values for UDP-N-acetylglucosamine for enzyme I and II were 15 and 10 μM, respectively, and for GDP-mannose (enzyme III) 7 μM. The apparent Km values for the lipophilic acceptor was 180 μM for enzyme I (dolichyl phosphate), 40 μM for enzyme II (dolichyl diphosphate N-acetylglucosamine) and 17 μM for enzyme III (dolichyl diphosphate chitobiose). The corresponding V values were approximately 1, 10, and 50 nmol × h−1× mg protein−1. All reactions were inhibited by nucleoside diphosphates.

The complex chemical behaviour of 2-phosphaindolizines 1 (1,3-azaphospholo[1,5-a]pyridines) towards metal carbonyl compounds was studied. (η1-2-Phosphaindolizine)M(CO)5 complexes 2–4 (M = Cr, Mo, W) were formed from 1 and [(THF)M(CO)5], the cis-L2Cr(CO)4 complex 5f from 1f and tetracarbonyl(norbornadiene) chromium(0). The reaction of 2-phosphaindolizines 1e, 1f, or 1g with tricarbonyl(cycloheptatriene)molybdenum(0) or tricarbonyl(mesitylene)tungsten(0) yielded σ-complexes of the types L2M(CO)4or L3M(CO)3 rather than isolable π-complexes. In one case a strong upfield signal (δ31P = 6.1) was observed with a coordination shift of Δδ = –161.7, which is typical for π-coordination. Prolonged reaction or work-up led, however, to dismutation yielding 1g and the fac-L3Mo(CO)3 complex 6g. X-ray structure analysis of 2a indicates an increased 10π-delocalization compared with 1a and a changed conformation of the acyl substituent. The influence of substituents and metals on the 31P and 13C complexation chemical shifts and coupling constants is discussed.

Initial allyl cation geometry appears to be irrelevant with respect to the stereochemistry of cycloadducts in the intramolecular 4+3 cycloaddition of alkoxyallylic cations derived from alkoxyallylic sulfones.

The first complete study of relative stereocontrol in an intramolecular 4+3 cycloaddition has been performed. Thus, CH2Cl2 solutions of alkoxyallylic sulfones 5, 7, and 9 were treated with TiCl4 at −78°C to give diastereomeric cycloadducts in fair yield. For 5 and 7 diastereoselectivity was low, but suggested that allylic cation geometry plays a small but definitive role in determining the diastereomer distribution in the cycloadducts. For the cycloaddition reaction of 9, cation geometry is irrelevant and the cycloadduct is obtained in very high diastereomeric purity.

The thiazole-diamide series (1) has been identified as highly potent γ-secretase inhibitors. Several representative compounds showed IC50 values of

Human activities such as industrial development, burning of fossil fuels, deforestation and even agriculture practices are changing the composition of Earth's atmosphere. There is a growing concern that greenhouse gases released by these activities, such as carbon dioxide, may cause global warming which, in turn, would have dramatic social, economic and political impacts. The paper examines the global warming contribution of automobiles in Canada and compares various alternative transportation fuels in terms of their emissions of greenhouse gases and global warming potential. Energy conservation, improved fuel economy, and the use of certain alternative transportation fuels can significantly reduce the emissions of greenhouse gases from automobiles. Although automobiles in Canada make a rather small contribution to overall emissions of greenhouse gases in the global context, reducing the emissions of greenhouse gases seems to be a step in the right direction. Many individual measures, each having a modest impact on greenhouse gas emissions, can have a dramatic impact on the rate of climatic change when combined.

Lignin, a naturally occurring polymer, was isolated from sawdust and used as a substitute in phenol formaldehyde resins. Thus lignin-phenol formaldehyde adhesives for plywood with lignin-phenol ratios of 50:50, 60:40, 70:30, 80:20 and 90:10 were prepared. Glue shear strength for these adhesives was tested by preparing three-ply plywood panels. The adhesives showed a dry bond strength varying from 0.57 to 0.82 MPa. The glue shear strength for cold water resistance tests varied from 0.16 to 0.25 MPa, indicating that even 80% replacement of phenol with lignin is capable of producing a bond quality acceptable for cold water resistant grade plywood.