Polyene System Research Articles

Aurantoside L, a New Tetramic Acid Glycoside with Anti-Leishmanial Activity Isolated from the Marine Sponge Siliquariaspongia japonica.

A new tetramic acid glycoside, aurantoside L (1), was isolated from the sponge Siliquariaspongia japonica collected at Tsushima Is., Nagasaki Prefecture, Japan. The structure of aurantoside L (1) composed of a tetramic acid bearing a chlorinated polyene system and a trisaccharide part was elucidated using spectral analysis. Aurantoside L (1) showed anti-parasitic activity against L. amazonensis with an IC50 value of 0.74 µM.

Photoinduced Dynamics of 13,13'-Diphenylpropyl-β-carotene.

Carotenoids are ubiquitous pigment systems in nature which are relevant to a range of processes, such as photosynthesis, but the detailed influence of substitutions at the polyene backbone on their photophysics is still underexplored. Here, we present a detailed experimental and theoretical investigation of the carotenoid 13,13'-diphenylpropyl-β-carotene using ultrafast transient absorption spectroscopy and steady-state absorption experiments in n-hexane and n-hexadecane, complemented by DFT/TDDFT calculations. In spite of their bulkiness and their potential capability to "fold back" onto the polyene system, which could result in π-stacking effects, the phenylpropyl residues have only a minor impact on the photophysical properties compared with the parent compound β-carotene. Ultrafast spectroscopy finds lifetimes of 200-300 fs for the S2 state and 8.3-9.5 ps for the S1 state. Intramolecular vibrational redistribution with time constants in the range 0.6-1.4 ps is observed in terms of a spectral narrowing of the S1 spectrum over time. We also find clear indications of the presence of vibrationally hot molecules in the ground electronic state (S0*). The DFT/TDDFT calculations confirm that the propyl spacer electronically decouples the phenyl and polyene π-systems and that the substituents in the 13 and 13' positions point away from the polyene system.

Getting to know carotenoids.

More than 600 different carotenoids have been isolated from natural sources and fully or partly characterized. Fortunately, although they are all different individual compounds, the carotenoids may be considered as a group in terms of many of their basic properties. The aim of this chapter is to help newcomers and others that are not carotenoid specialists to understand the peculiarities of carotenoids, and how best to work with them. The basic principles of structure and nomenclature of carotenoids are described (especially the IUPAC semi-systematic rules) and the chemical and physical properties on which the biological functions depend are discussed. Guidance is given on how to handle and work with carotenoids safely and reliably and reduce the risk of forming artifacts and introducing impurities. Recommendations are made about their isolation, identification by various physical methods, and spectrophotometric quantitative analysis. Structural features that determine the shape of the carotenoid molecule are discussed, especially the conjugated polyene system. This also determines the light absorption properties of carotenoids and their chemical reactivity, especially toward oxidising agents. The properties of carotenoids in situ are strongly influenced by aggregation in the aqueous environment and by interactions with other molecules in their vicinity, notably proteins and membrane lipids. Many substances that look like fragments of carotenoids have been isolated from natural sources. This chapter does not provide comprehensive coverage of these apocarotenoids, but does consider their nomenclature and numbering according to the IUPAC rules.

Increase of oxidation rate of uric acid by singlet oxygen at higher pH.

Singlet oxygen prefers to react with an electron-rich double bonds. We observed that the oxidation rate for uric acid with singlet oxygen increased with increasing pH and the oxidation rate dramatically was elevated at around pH 5.4 and 9.8, which are the acidity constants of uric acid, pKa1 and pKa2, respectively. Furthermore, we observed that the absorbance near 200 nm and the molar extinction coefficient (ɛ) increased with increasing pH, similar to the change in oxidation rate. Computer calculations by Chong [Chong, J Theor Comput Sci 2013; 1(1)] revealed that uric acid elongates its C=N conjugated diene structure with increasing pH. This is correlated with an increase in the UV absorbance of C=C double bonds near 200 nm, and may indicate higher electron density in the double bonds. Therefore, we concluded that the increased oxidation rate is due to elongation of the C=N conjugated polyene system at higher pH. On the other hand, the major products were 4-hydroxyallantoin and parabanic acid (hydrolyzed to oxaluric acid at pH 10.7), suggesting that the reaction pathways were the same regardless of pH. Finally, possible reaction schemes are presented.

Genome-Guided Discovery of Pretilactam from Actinosynnema pretiosum ATCC 31565.

Actinosynnema is a small but well-known genus of actinomycetes for production of ansamitocin, the payload component of antibody-drug conjugates against cancers. However, the secondary metabolite production profile of Actinosynnema pretiosum ATCC 31565, the most famous producer of ansamitocin, has never been fully explored. Our antiSMASH analysis of the genomic DNA of Actinosynnema pretiosum ATCC 31565 revealed a NRPS–PKS gene cluster for polyene macrolactam. The gene cluster is very similar to gene clusters for mirilactam and salinilactam, two 26-membered polyene macrolactams from Actinosynnema mirum and Salinispora tropica, respectively. Guided by this bioinformatics prediction, we characterized a novel 26-membered polyene macrolactam from Actinosynnema pretiosum ATCC 31565 and designated it pretilactam. The structure of pretilactam was elucidated by a comprehensive analysis of HRMS, 1D and 2D-NMR, with absolute configuration of chiral carbons predicted bioinformatically. Pretilactam features a dihydroxy tetrahydropyran moiety, and has a hexaene unit and a diene unit as its polyene system. A preliminary antibacterial assay indicated that pretilactam is inactive against Bacillus subtilis and Candida albicans.

Auxiliary Methoxy Aided Triphenylamine and Dicyanoisophorone Based Flurophores with Viscosity and Polarity Sensitive Intramolecular Charge Transfer

Novel, multibranched “triphenylamine based donor with added auxiliary methoxy donor and dicyanovinyl acceptor” based fluorescent molecules are developed. The dicyanoisophorone moiety is used as a configurationally locked polyene system for π-conjugation linking between donor and acceptor, to control the unnecessary intramolecular rotations in the molecule, which can to act as a rotor. The synthesized dyes show good fluorescent molecular rotor properties and strong emission solvatochromism. Auxiliary methoxy donors shift both the absorption and emission maxima towards longer wavelengths compared to known analogues, along with increased Stokes shifts. Fluorescent molecular rotor properties of the dyes are influenced by a local excited state to twisted intramolecular charge transfer state transition, which is discussed in terms of emission solvatochromism and Lippert–Mataga, Weller and Rettig polarity plots. Three different viscous solvent systems i.e., paraffin oil–dichloromethane, polyethylene glycol-400–dichloromethane and polyethylene glycol-400–N,N-dimethylformamide are used to investigate the sensitivity of rotors towards the viscosity of the environment. A maximum 16-fold enhancement in emission intensity and 0.616 × value is achieved for rotor Dye-3. The polarity effect of a binary viscous solvent system, by the virtue of intramolecular charge transfer, on the viscosity sensing properties of rotors is explained by constructing the Weller and Rettig’s plots for different viscous systems.

Excited State Dynamics of Selected All-trans C40 Xanthophyll Carotenoids

Abstract We investigated the excited state dynamics of selected all-trans C40 xanthophyll carotenoids by ultrafast pump-supercontinuum probe (PSCP) spectroscopy in the spectral range 350–770 nm upon photoexcitation by a femtosecond laser (ca. 80 fs pulse length) near 500 nm in acetone. The following carotenoids were selected considering a systematic variation of the number and position of carbonyl (CO) and hydroxyl (OH) functional groups on the β-ionone rings and the change of the effective conjugation length of the polyene system: β-cryptoxanthin (1), echinenone (2), 3-hydroxyechinenone (3), 3′-hydroxyechinenone (4), canthaxanthin (5), adonirubin (6) and astaxanthin (7). The carotenoids featuring an increasing conjugation length, for example, (1), (3) and (6), showed a systematically shorter S1 lifetime of 8.7, 6.2 and 4.7 ps, respectively. Carotenoids with OH groups adjacent to a CO group showed slightly broader steady-state and transient absorption bands, but the influence on the S1 lifetime was minor compared to the case of CO substitution. Moreover, in all cases we observed clearly visible “S* signals”, namely a longer-lived characteristic S0 → S2 red-edge absorption and a negative signal in the S0 → S2 bleach region. This spectral signature is assigned to highly vibrationally excited molecules in the ground electronic state S0 * which are generated by internal conversion from S1. The S0 * species cool with a time constant of 9.2–9.6 ps in the case of the keto-substituted carotenoids (2)–(7), whereas we obtain a larger value of 13.2 ps for (1) which does not have a keto group. Our findings are supported by results from a global kinetic analysis procedure.

Structurally modified indocyanine green dyes. Modification of the polyene linker

We have prepared a series of indocyanine green dicarboxylic acid derivatives (9a,b, 4, 10, 13) with modified polyene linkers in an attempt to increase the structural rigidity of the polyene linker and thereby the fluorescent yield. Incorporation of five- and six-membered rings into the polyene system led to lower florescent yield for 9a,b, 4 and 10, but shortening the chain by two carbon atoms led to an increase in fluorescent yield for 13.

Fullerene-containing polymers: UV spectroscopic study

A spectral method is developed to determine the content of fullerene in polymers formed in its presence during the free-radical polymerization and copolymerization of methyl methacrylate, allyl methacrylate, allyl chloride, and styrene. The method is based on measurement of absorption coefficients for the ππ*-excited transition of fullerene cores at 330 nm that is due to their insertion into a polymer chain and the related distortion of the closed polyene system of carbon-carbon bonds.

A Simple and Novel Approach To Delineating Stereochemistry of Electrocyclic Reactions

The dynamic stereochemistry of electrocyclic reactions (a class of pericyclic reactions) stems from the operation of either conrotatory (con) or disrotatory (dis) mode of ring-closing and ring-opening processes. Difficulty is often encountered in depicting product stereochemistry resulting from such movements of substituents. A novel, simple, straightforward, and quick approach to delineating product stereochemistry of such reactions is presented. In this approach, the stereochemical properties of reactant and product in electrocyclic reactions are classified as either syn (S) or anti (A). The two substituents at the ends of conjugated polyene system or σ bond of cyclic system in reactant or product are designated as S or A. The product stereochemistry is then delineated as follows: reactant stereochemistry × mode = product stereochemistry, resulting in S × con = S; A × con = A; S × dis = A; and A × dis = S. The procedure is illustrated with several examples of electrocyclic and related pericyclic reactions that are appropriate for an upper-level undergraduate or first-year master’s level organic chemistry course.

Ground-state properties of the retinal molecule: from quantum mechanical to classical mechanical computations of retinal proteins

Retinal proteins are excellent systems for understanding essential physiological processes such as signal transduction and ion pumping. Although the conjugated polyene system of the retinal chromophore is best described with quantum mechanics, simulations of the long-timescale dynamics of a retinal protein in its physiological, flexible, lipid-membrane environment can only be performed at the classical mechanical level. Torsional energy barriers are a critical ingredient of the classical force-field parameters. Here we review briefly current retinal force fields and discuss new quantum mechanical computations to assess how the retinal Schiff base model and the approach used to derive the force-field parameters may influence the torsional potentials.

Ultrafast excited state dynamics and spectroscopy of 13,13′-diphenyl-β-carotene

Ultrafast transient broadband absorption spectroscopy based on the Pump-Supercontinuum Probe (PSCP) technique has been applied to characterize the excited state dynamics of the newly-synthesized artificial β-carotene derivative 13,13'-diphenyl-β-carotene in the wavelength range 340-770 nm with ca. 60 fs cross-correlation time after excitation to the S(2) state. The influence of phenyl substitution at the polyene backbone has been investigated in different solvents by comparing the dynamics of the internal conversion (IC) processes S(2)→ S(1) and S(1)→ S(0)* with results for β-carotene. Global analysis provides IC time constants and also time-dependent S(1) spectra demonstrating vibrational relaxation processes. Intramolecular vibrational redistribution processes are accelerated by phenyl substitution and are also solvent-dependent. DFT and TDDFT-TDA calculations suggest that both phenyl rings prefer an orientation where their ring planes are almost perpendicular to the plane of the carotene backbone, largely decoupling them electronically from the polyene system. This is consistent with several experimental observations: the up-field chemical shift of adjacent hydrogen atoms by a ring-current effect of the phenyl groups in the (1)H NMR spectrum, a small red-shift of the S(0)→ S(2)(0-0) transition energy in the steady-state absorption spectrum relative to β-carotene, and almost the same S(1)→ S(0)* IC time constant as in β-carotene, suggesting a similar S(1)-S(0) energy gap. The oscillator strength of the S(0)→ S(2) transition of the diphenyl derivative is reduced by ca. 20%. In addition, we observe a highly structured ground state bleach combined with excited state absorption at longer wavelengths, which is typical for an "S* state". Both features can be clearly assigned to absorption of vibrationally hot molecules in the ground electronic state S(0)* superimposed on the bleach of room temperature molecules S(0). The S(0)* population is formed by IC from S(1). These findings are discussed in detail with respect to alternative interpretations previously reported in the literature. Understanding the dynamics of this type of artificial phenyl-substituted carotene systems appears useful regarding their future structural optimization with respect to enhanced thermal stability while keeping the desired photophysical properties.

Stereospecific preparation of (1 E,3 E,5 E)-3.4-difluoro-1,6-diphenylhexatriene and (2 E,4 E,6 E)-diethyl-4,5-difluoroocta-2,4,6-trienedioate

Palladium(0) catalyzed coupling of β-bromostyrene ( E/ Z = 89/11) with ( E)-(1,2-difluoro-1,2-ethenediyl)bis[tributylstannane], 1, in DMF at room temperature stereospecifically gave only (1 E,3 E,5 E)-3,4-difluoro-1,6-diphenylhexatriene. Similarly, palladium(0) catalyzed coupling of ( E)-ethyl 3-bromoacrylate as the vinyl halide precursor stereospecifically gave (2 E,4 E,6 E)-diethyl-4,5-difluoroocta-2,4,6-trienedioate. This work demonstrates that a non-fluorine-containing vinyl bromide will selectively undergo coupling with 1 and enable the stereospecific preparation of a mixed polyene system. The ( E)-ethyl 3-bromoacrylate coupling with 1 illustrates that mixed functionalized hexatriene systems can be easily accessed via this methodology. The X-ray structure of (2 E,4 E,6 E)-diethyl-4,5-difluoroocta-2,4,6-trienedioate confirmed its structure.

ChemInform Abstract: Charge‐Transfer Interactions in Organic Functional Materials

AbstractReview: 130 refs.

Charge-Transfer Interactions in Organic Functional Materials.

Our goal in this review is three-fold. First, we provide an overview of a number of quantum-chemical methods that can abstract charge-transfer (CT) information on the excited-state species of organic conjugated materials, which can then be exploited for the understanding and design of organic photodiodes and solar cells at the molecular level. We stress that the Composite-Molecule (CM) model is useful for evaluating the electronic excited states and excitonic couplings of the organic molecules in the solid state. We start from a simple polyene dimer as an example to illustrate how interchain separation and chain size affect the intercahin interaction and the role of the charge transfer interaction in the excited state of the polyene dimers. With the basic knowledge from analysis of the polyene system, we then study more practical organic materials such as oligophenylenevinylenes (OPVn), oligothiophenes (OTn), and oligophenylenes (OPn). Finally, we apply this method to address the delocalization pathway (through-bond and/or through-space) in the lowest excited state for cyclophanes by combining the charge-transfer contributions calculated on the cyclophanes and the corresponding hypothetical molecules with tethers removed. This review represents a step forward in the understanding of the nature of the charge-transfer interactions in the excited state of organic functional materials.

Efficient synthesis and biological evaluation of demethyl geranylgeranoic acid derivatives

Synthetic retinoids have generated in the fields of dermatology and oncology due to their potent anti-proliferative and differentiation activities. We efficiently synthesized different demethyl geranylgeranoic acid (GGA) analogs, and evaluated their biological activities. Among the demethyl analogs synthesized, 3-demethyl derivative exhibited the highest anti-proliferative activity in HL-60 cells. In addition, a 3-demethyl derivative induced apoptosis more potently than 9Z-retinoic acid. These activities were due to the high binding affinity of 3-demethyl derivative for retinoid receptors. We found that, in a conjugated polyene system combined with a methyl substituent, the position of the methyl played an important role in the regulation of gene transcription and apoptosis-inducing activity. These results provided useful information on the structure-activity relationships of GGA derivatives that function as acyclic retinoic acid analogs. This information is likely to be useful in the development of new anti-cancer drugs.

Role of the triplet state in the green emission peak of polyfluorene films: A time evolution study

The blue emission of ethyl-hexyl substituted polyfluorene (PF2/6) films is accompanied by a low energy green emission peak around 500 nm in inert atmosphere. The intensity of this 500 nm peak is large in electroluminescence (EL) compared to photoluminescence (PL) measurements. Furthermore, the green emission intensity reduces dramatically in the presence of molecular oxygen. To understand this, we have modeled various nonradiative processes by time dependent quantum many body methods. These are (i) intersystem crossing to study conversion of excited singlets to triplets leading to a phosphorescence emission, (ii) electron-hole recombination (e-hR) process in the presence of a paramagnetic impurity to follow the yield of triplets in a polyene system doped with paramagnetic metal atom, and (iii) quenching of excited triplet states in the presence of oxygen molecules to understand the low intensity of EL emission in ambient atmosphere, when compared with that in nitrogen atmosphere. We have employed the Pariser-Parr-Pople Hamiltonian to model the molecules and have invoked electron-electron repulsions beyond zero differential approximation while treating interactions between the organic molecule and the rest of the system. Our time evolution methods show that there is a large cross section for triplet formation in the e-hR process in the presence of paramagnetic impurity with degenerate orbitals. The triplet yield through e-hR process far exceeds that in the intersystem crossing pathway, clearly pointing to the large intensity of the 500 nm peak in EL compared to PL measurements. We have also modeled the triplet quenching process by a paramagnetic oxygen molecule which shows a sizable quenching cross section especially for systems with large sizes. These studies show that the most probable origin of the experimentally observed low energy EL emission is the triplets.

Inhibitors of Sterol Biosynthesis as Staphylococcus aureus Antibiotics

Inhibitors of Sterol Biosynthesis as <i>Staphylococcus aureus</i> Antibiotics

Physicochemical and Photophysical Studies on Porphyrin-Based Donor−Acceptor Systems: Effect of Redox Potentials on Ultrafast Electron-Transfer Dynamics

We report new polychromophoric complexes, where different porphyrin (P) derivatives are covalently coupled to a redox active Mo center, MoL*(NO)Cl(X) (L* is the face-capping tridentate ligand tris(3,5-dimethylpyrazolyl) hydroborate and X is a phenoxide/pyridyl/amido derivative of porphyrin). The luminescence quantum yields of the bichromophoric systems (1, 2, and 5) were found to be an order of magnitude less than those of their respective porphyrin precursors. Transient absorption measurements revealed the formation of the porphyrin radical cation species (P(.)(+)) and photoinduced electron transfer from the porphyrin moiety to the respective Mo center in 1, 2, and 5. Electrochemical studies showed that the reduction potentials of the acceptor Mo centers in a newly synthesized pyridyl derivative (2; E(1/2)[Mo(I/0)] = approximately -1.4 V vs Ag/AgCl) and previously reported phenoxy- (1; E(1/2)[Mo(II/I)] = approximately -0.3 V vs Ag/AgCl) and amido- (3; E(1/2)[Mo(II/I)] = approximately -0.82 V vs Ag/AgCl) derivatives were varied over a wide range. Thus, studies with these complexes permitted us to correlate the probable effect of this potential gradient on the electron-transfer dynamics. Time-resolved absorption studies, following excitation at the Soret band of the porphyrin fragment in complexes 1, 2, and 5, established that forward electron transfer took place biexponentially from both S2 and S1 states of the porphyrin center to the Mo moiety with time constants 150-250 fs and 8-20 ps, respectively. In the case of MoL*(NO)ClX (where X is pyridine derivative 2), the high reduction potential for the MoI/0 couple allowed electron transfer solely from the S2 state of the porphyrin center. Time constants for the charge recombination process for all complexes were found to be 150-300 ps. Further, electrochemical and EPR studies with the trichromophoric complexes (3 and 4) revealed that the orthogonal orientation of the peripheral phenoxy/pyridyl rings negated the possibility of any electronic interaction between two paramagnetic Mo centers in the ground state and thereby the spin exchange, which otherwise was observed for related Mo complexes when two Mo centers are separated by a polyene system with comparable or larger separation distances.

Femtosecond Time-Resolved Transient Absorption Spectroscopy of Xanthophylls

Xanthophylls are a major class of photosynthetic pigments that participate in an adaptation mechanism by which higher plants protect themselves from high light stress. In the present work, an ultrafast time-resolved spectroscopic investigation of all the major xanthophyll pigments from spinach has been performed. The molecules are zeaxanthin, lutein, violaxanthin, and neoxanthin. beta-Carotene was also studied. The experimental data reveal the inherent spectral properties and ultrafast dynamics including the S(1) state lifetimes of each of the pigments. In conjunction with quantum mechanical computations the results address the molecular features of xanthophylls that control the formation and decay of the S* state in solution. The findings provide compelling evidence that S* is an excited state with a conformational geometry twisted relative to the ground state. The data indicate that S* is formed via a branched pathway from higher excited singlet states and that its yield depends critically on the presence of beta-ionylidene rings in the polyene system of pi-electron conjugated double bonds. The data are expected to be beneficial to researchers employing ultrafast time-resolved spectroscopic methods to investigate the mechanisms of both energy transfer and nonphotochemical quenching in higher plant preparations.