Series Of Polyenes Research Articles

SUSCEPTIBILITY OF DIFFERENT REPRESENTATIVES OF THE GENUS CANDIDA TO ANTIMYCOTICS

Representatives of Candida.spp. demonstrate different susceptibility to azole compounds, which are widely used in the treatment of candidiasis. Due to the resistance to these compounds, C. glabrata remains in the body and, moreover, is able to multiply and increase its population. It quite often causes the development of nosocomial infections.
 The purpose of this study was to investigate the susceptibility of clinical strains of C. albicans and C. glabrata isolated from surgical patients to antifungal drugs.
 Materials and methods. We studied 5 clinical strains of C. albicans and 5 clinical strains of C. glabrata, taken from the patients of Thoracic and Vascular Surgery Units, V.M. Sklifosovskiy Poltava Regional Clinical Hospital.
 In order to assess the susceptibility of the studied clinical isolates to antimycotics, the method of two-fold serial dilutions (macrodilution) in liquid nutrient medium was used as the standard procedure according to the order of the Ministry of Public Health of Ukraine No. 167 dated April 05, 2007, on Approval of Guidelines “Assessment of Microbial Susceptibility to Antibacterial Drugs”. MIC was determined by the lowest concentration of the antifungal drug, which was able to suppress the visible growth of the studied microorganism culture. The presence of growth was assessed by inspecting the tubes in transmitted light compared to the “negative” control.
 To control the quality of evaluating susceptibility of microorganisms to antifungals, we used the reference strain Candida albicans CCM 885 taken from the Museum of Living Cultures of the Department of Microbiology, Virology and Immunology, UMSA. Testing of the control strain was carried out in accordance with the method described above in parallel with the study of clinical isolates. The findings obtained by evaluating the susceptibility (MIC) of the control strain were compared with the relevant parameters of its passport characteristics. If they match, the conditions of the experiment were considered as standard, and the results of evaluating sensitivity of clinical isolates obtained under these conditions were considered as reliable.
 To identify susceptibility of the genus Candida spp., natural anti-fungal agents of the polyene series (amphotericin B) and synthetic drugs of the azoles group (fluconazole, itraconazole) and pyrimidine derivatives (flucytosine) were used.
 Statistical analysis of the findings obtained was carried out using the standard software package "Microsoft Excel 2010". The presence of differences between the studied parameters was assessed by Student's t-test.
 Results and discussion. The study has demonstrated that the synthetic antifungal, flucytosine, has a low fungistatic effect on Candida spp. The presence of flucytosine inhibits the reproduction of the reference C. albicans strain at a concentration of 2 μg / ml. Along with it, clinical strains of yeast-like fungi of this genus were equally sensitive to flucytosine with a MIC of 3.2 ± 0.96 μ / ml. This indicates a low efficacy of this antimycotic for Candida spp.

The [formula omitted] state falls below [formula omitted] at carotenoid-relevant conjugation lengths

Spectroscopy of all-trans linear polyenes is characterized by a one-photon electronic transition to a bright S2 state and two-photon transition to a lower-lying dark S1 state. We apply ab initio quantum chemistry to distinguish additional diffuse dark singlet states. Building on a systematic implementation of CASSCF and DMRGSCF coupled to strongly-contracted NEVPT2, we report the excitation energies for a series of polyenes from butadiene to C16H18 at optimized S0, S1 and S2 geometries. Ionic/covalent state inversion within each manifold is identified at seven conjugated double bonds, making the Bu- a dark intermediate state at its optimized geometry and the Ag+ the S3 state at the S0 optimized geometry. The relevance of these results to the function of carotenoids in photosynthetic light harvesting is discussed.

Radialenes are minimally conjugated cyclic π-systems

ABSTRACTConjugation energy (CE) in benzene is larger than its aromatic stabilisation energy (ASE). A far-reaching conclusion offered by this work is that per π-electron, CE is energetically larger than aromaticity. If a diene has a doubly degenerate HOMO, then its Diels–Alder reaction will be kinetically faster than a similar diene with a nondegenerate HOMO. The topological conjugation energy (TCE) for the radialene, monocyclic, dendralene, and linear polyene series has quite different trends. Radialenes are minimally conjugated cyclic systems with the TCE/No. π-bond = 0.432 β; the members of the dendralene series approach this same value from smaller values with increasing size. With increasing size, the members of the monocyclic and linear polyene series have, respectively, decreasing and increasing TCE/No. π-bond values approaching 0.547 β. Topological resonance energy (TRE) for radialenes, dendralenes, and linear polyenes all have TRE = 0, and the TRE/π-electron for monocyclic polyenes has alternating declining values between antiaromatic (−0.3066 β, −0.07435 β, −0.03287 β, …) and aromatic (0.04543 β, 0.01594 β, 0.00807 β, …). For benzene, TRE/No. π-bond = 0.0909 β and TCE/No. π-bond = 0.576 β.

Novel dendritic polyenes for application to tailor-made thiol-ene photopolymers with excellent UV-curing performance

Abstract Two series of the dendritic polyenes of allyl-terminated and of norbornene-terminated types ( DAL( n ) and DNb( n ) , n = 4, 8, 16) were synthesized through simple terminal modification of polyol/polyacrylate dendrimers prepared in advance and in large scale by the alternate multi-addition (AMA) reaction. These dendrimers were mixed with conventional six-armed polythiol ( SH6 ) and photoinitiator ( Ir-369 ) to create novel dendritic thiol-ene UV-curable materials. In both DAL( n ) / SH6 and DNb( n ) / SH6 resins, the photosensitivity was markedly improved as the number of terminal ene units increased. The degree of shrinkages of the dendritic resin of DAL16 / SH6 due to photopolymerization was evaluated on the basis of specific gravity to be 3.2%, which is substantially lower than the degree of shrinkage of conventional UV-curable monomers. The multi-component systems comprising DAL16 , DAL4 , SH6 , and a photoinitiator were also investigated, where the smaller DAL4 served as an effective reactive diluent. The viscosity of the resins was adjustable from 16,000 to 3000 mPa s by the choice of appropriate mixing ratios between DAL16 and DAL4 , without significantly diminishing the performance characteristics of the UV-curable resins such as their photosensitivity and polymerization shrinkage. As a result, we obtained tailor-made UV-curable resins with excellent UV-curable performance using novel dendritic structuring of the component molecules.

Biosynthesis and genomic analysis of medium-chain hydrocarbon production by the endophytic fungal isolate Nigrograna mackinnonii E5202H.

An endophytic fungus was isolated that produces a series of volatile natural products, including terpenes and odd chain polyenes. Phylogenetic analysis of the isolate using five loci suggests that it is closely related to Nigrograna mackinnonii CBS 674.75. The main component of the polyene series was purified and identified as (3E,5E,7E)-nona-1,3,5,7-tetraene (NTE), a novel natural product. Non-oxygenated hydrocarbons of this chain length are uncommon and desirable as gasoline-surrogate biofuels. The biosynthetic pathway for NTE production was explored using metabolic labeling and gas chromatography time of flight mass spectometer (GCMS). Two-carbon incorporation (13)C acetate suggests that it is derived from a polyketide synthase (PKS) followed by decarboxylation. There are several known mechanisms for such decarboxylation, though none have been discovered in fungi. Towards identifying the PKS responsible for the production of NTE, the genome of N. mackinnonii E5202H (ATCC SD-6839) was sequenced and assembled. Of the 32 PKSs present in the genome, 17 are predicted to contain sufficient domains for the production of NTE. These results exemplify the capacity of endophytic fungi to produce novel natural products that may have many uses, such as biologically derived fuels and commodity chemicals.

Shape and location of multiple charge carriers in linear π-electron systems

We have performed a quantum-mechanical study of a series of neutral polyenes, their multiply charged ions, and related ionic polymethines with a closed electron shell, using different methods/basis with/without electron correlations. The study shows that a multiple injection of charge carriers into a collective system of π-electrons causes a formation of distinctive electron levels in the energy gap along with a simultaneous regular gap shift in accordance to the number of injected carriers. Each charge generates its own solitonic electron density alternation wave on adjacent carbon atoms, as well as similar bond length and valence angle alternation waves. Established regularities in charge distribution and variations of bond lengths and valence angles may be used in the molecular design of organic semiconducting materials. © 2013 Wiley Periodicals, Inc.

On the relationship between bond-length alternation and many-electron self-interaction error

Predicting accurate bond-length alternations (BLAs) in long conjugated molecular chains has been a major challenge for electronic-structure theory for many decades. While Hartree-Fock (HF) overestimates BLA significantly, second-order perturbation theory and commonly used density functional theory (DFT) approaches typically underestimate it. Here, we discuss how this failure is related to the many-electron self-interaction error (MSIE), which is inherent to both HF and DFT approaches. We use tuned long-range corrected hybrids to minimize the MSIE for a series of polyenes. The key result is that the minimization of the MSIE alone does not yield accurate BLAs. On the other hand, if the range-separation parameter is tuned to yield accurate BLAs, we obtain a significant MSIE that grows with chain length. Our findings demonstrate that reducing the MSIE is one but not the only important aspect necessary to obtain accurate BLAs from density functional theory.

Solitonic waves in polyene dications and principles of charge carrier localization in π-conjugated organic materials

The quantum-chemical investigations by ab initio method (restricted Hartree–Fock/6-31G**) have been performed for a series of unsubstituted, monosubstituted, and disubstituted neutral polyenes and their double charged cations. The waves of charge alternation (characterized by the difference in the electron densities at the nearest carbon atoms or Δq function) and bond length alternation (characterized by the lengths difference of the nearest carbon–carbon bonds or Δl function) are reported. Comparisons are made with the corresponding monocationic polymethine molecules. We found that ionization by two electrons results in formation of two solitonic waves of charge alternation, rather than superposition of two overlapping solitonic waves into one. These waves behave similar to two independent elastic particles, which do not penetrate into each other despite the special confinement by the length of chromophore π-system. In monosubstituted polyene dication, Δq and Δl functions contain two waves each; however, only one wave is mobile and sensitive to a change of the chemical nature of the terminal group, whereas the second wave remains practically unchanged. The introduction of one oxymethyl or phenyl terminal groups leads to a relatively small shift of the mobile wave from the center to a direction of the terminal group. The effect of the amino or tropilium terminal groups is much more pronounced and leads to a shift of the mobile wave to the end of the molecule. In disubstituted polyene dication, both solitonic waves become mobile and shift symmetrically to both ends. The general principles of the charge localization described in this study may be used in molecular design and fine-tuning of the charge transport properties in plastic photovoltaics and other organic semiconducting materials. © 2012 Wiley Periodicals, Inc.

Hyphenation of a thermobalance to soft single photon ionisation mass spectrometry for evolved gas analysis in thermogravimetry (TG-EGA)

Abstract The potential of hyphenating thermogravimetry (TG) and soft photo ionisation mass spectrometry (EBEL-SPI-MS) for fundamental and applied research and material analysis has been demonstrated by a newly developed TG-SPI quadrupole MS coupling (TG-SPI-QMS). Thermal decomposition of three common plastics, polyethylene (PE), polystyrene (PS) and polyvinylchloride (PVC) has been studied. While the decomposition of PE and PS in inert atmosphere takes place in a one step process (main mass loss at about 490 and 420 °C, respectively), PVC decomposes in a two step mechanism. The organic signature of the PE decomposition shows homologous series of alkenes and polyenes, while PS is forming mainly styrene mono- and oligomers. In the PVC decomposition, firstly hydrogen chloride (HCl) is eliminated in a hydro-dechlorination reaction (1st mass loss step: 285–305 °C), this is accompanied by the emission of the carbon skeletons of small aromatics (predominately benzene and naphthalene). In the second step (2nd ma...

Semiexperimental Equilibrium Structure for the C6 Backbone of cis-1,3,5-Hexatriene; Structural Evidence for Greater π-Electron Delocalization with Increasing Chain Length in Polyenes

Twenty-five microwave lines were observed for cis-1,3,5-hexatriene (0.05 D dipole moment) and a smaller number for its three (13)C isotopomers in natural abundance. Ground-state rotational constants were fitted for all four species to a Watson-type rotational Hamiltonian for an asymmetric top (kappa = -0.9768). Vibration-rotation (alpha) constants were predicted with a B3LYP/cc-pVTZ model and used to adjust the ground-state rotational constants to equilibrium rotational constants. The small inertial defect for cis-hexatriene shows that the molecule is planar, despite significant H-H repulsion. The substitution method was applied to the equilibrium rotational constants to give a semiexperimental equilibrium structure for the C(6) backbone. This structure and one predicted with the B3LYP/cc-pVTZ model show structural evidence for increased pi-electron delocalization in comparison with butadiene, the first member of the polyene series.

Resonance Energies of Vinylcarbenes

The stabilization energy provided by resonance in singlet and triplet vinylcarbenes is evaluated using density functional and G3 theory, without symmetry restriction. Structural and charge change upon rotation are reviewed with singlet vinylcarbene exhibiting a larger barrier (1s-TS-1s-E), 5.49 (7.10) kcal/mol, than triplet (1t-TS-1t-E), 4.06 (4.54) kcal/mol. The changes in charge upon rotation for singlet vinylcarbene are consistent with a simple resonance picture for the ground state, whereas there is insignificant charge change for the triplet. Difficulties of the rotational analysis are avoided by evaluating the inductive stabilization difference between ethyl and vinyl in isodesmic equation 1. This inductive difference was determined by comparing the energy change for hydrogen loss for polyene series 2 (n double bonds) with polyene series 3 (n double bonds), which are combined in isodesmic equation 4. The effect of the ultimate vinyl group in equation 2 is restricted to inductive interaction by holding its pi-system so it is orthogonal to the remaining pi-system. Extrapolation of plots of the inductive difference (Delta inductive) revealed for equation 4 versus a through-bond inductive attenuation of 1.75(-2n) to n = 0 provides a Delta inductive for singlet vinylcarbene of -4.52 kcal/mol (R = 0.995) at B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) + ZPE at B3LYP/6-31G(d) and -4.16 (R = 0.993) at the G3(MP2)//B3LYP level. Correcting for Delta inductive in eq 1, the resonance energy of singlet vinylcarbene is 9.2 (8.9) kcal/mol. An analogous analysis of triplet vinylcarbene suggests that inductive effects are 0-1 kcal/mol, which leads to a resonance energy of 11-14 kcal/mol.

Hydroformylation of Monoterpenic Polyenes: Effect of the Conjugation of Double Bonds on Reactivity

Rhodium-catalyzed hydroformylation of a series of monoterpenic polyenes, i.e., myrcene (1), α-terpinene (2), γ-terpinene (3), terpinolene (4), and limonene (5), was studied in the presence of various monophosphines. Effects of reaction variables, such as the ligand to rhodium ratio, ligand basicity, and partial pressures of reacting gases were evaluated for each reactive substrate. The hydroformylation of conjugated olefins 1 and 2 results in two main aldehydes in each case with excellent combined selectivities and can be performed under mild conditions (80 °C, 80 atm) using a large excess of PPh3 (P/Rh = 20−40). The hydroformylation of 1 follows the trends opposite to those usually observed with simple olefins: the increase in the concentration of the phosphorus ligand, ligand basicity, and pressure of both hydrogen and CO strongly accelerates the reaction showing that the most critical step is a conversion of η3-allylrhodium intermediates into much more reactive η1-complexes. The hydroformylation of 2 does not seem to occur through the formation of η3-complexes and at low P/Rh ratios and in systems with more bulky ligands than PPh3, such as PBz3 and PCy3, is strongly complicated by the hydrogenation of the substrate. Nonconjugated olefins 3 and 4 show an extremely low reactivity toward hydroformylation under similar conditions, whereas in substrate 5, only a terminal exocyclic double bond reacts with rhodium to give a corresponding aldehyde in near quantitative yield. Thus, the endocyclic double bond in p-menthane dienes 2−5 can be hydroformylated at a reasonable rate under relatively mild conditions only if it is conjugated with another double bond. All obtained aldehydes have a pleasant scent and can be useful as components of synthetic fragrances.

Charge Transport Properties of Molecular Junctions Built from Dithiol Polyenes

We present a study of the charge transmission behavior of a series of dithiol polyenes in the context of molecular junctions. Using the Landauer theory and zero voltage approximation the Green’s functions of the inserted molecules are calculated from a fully ab initio wave function based procedure. Various possibilities in approximating the correlation space are explored and quantitatively evaluated. Our results show that the transmission behavior of a molecular junction is not a monotonic function of the length of the employed molecule. Moreover, we introduce the analytic solution of a suitable model system to countercheck the ab initio results and find a remarkable degree of correspondence.

Novel Linear and Cyclic Polyenes with Dramatic Aggregation-Induced Enhancements in Photoresponsiveness

ABSTRACT A series of new linear and cyclic polyenes including siloles, butadienes, cyclcobutenes, fulvenes, and 4H-pyrans are designed and synthesized. When molecularly dissolved in common organic solvents, all the polyenes are practically nonemissive. Addition of poor solvents induces the polyenes to cluster into nanoaggregates, which turns the emission of the polyenes “on” and boosts their luminescence efficiencies dramatically (hence “aggregation-induced emission” or AIE). The emission color ranges from blue to red, depending on the chromophoric structures. Polyene nanoparticles on TLC plates show bright blue fluorescence which switches off reversibly in an atmosphere of volatile organic compounds. Addition of poor solvents to solution of cyclic polyenes bearing cholsteryl moieties leads to polarized green and anisotropic red emissions dependant on the solvent ratios. The different emissions may be caused by different packing patterns of the polyene crystals under different conditions.

A Numerical Simulation of Nonadiabatic Electron Excitation in the Strong Field Regime: Linear Polyenes

Time-dependent Hartree-Fock theory has been used to study of the electronic optical response of a series of linear polyenes in strong laser fields. Ethylene, butadiene, and hexatriene have been calculated with 6-31G(d,p) in the presence of a field corresponding to 8.75 x 10(13) W/cm2 and 760 nm. Time evolution of the electron population indicates not only the pi electrons, but also lower lying valence electrons are involved in electronic response. When the field is aligned with the long axis of the molecule, Löwdin population analysis shows large charges at each end of the molecule. For ethylene, the instantaneous dipole moment followed the field adiabatically, but for hexatriene, nonadiabatic effects were very pronounced. For constant intensity, the nonadiabatic effects in the charge distribution, instantaneous dipole, and orbital populations increased nonlinearly with the length of the polyene. These calculations elucidate the mechanism of the strong field nonadiabatic electron excitation of polyatomic molecules leading to their eventual ionization and fragmentation. The described computational methods are a viable tool for studying the complex processes in multielectron atomic and molecular systems in strong laser fields.

Syntheses and spectroscopic and quadratic nonlinear optical properties of extended dipolar complexes with ruthenium(II) ammine electron donor and N-methylpyridinium acceptor groups.

In this paper, we describe the extremely unusual optical properties of Ru(II)-based electron donor-acceptor (D-A) polyene and some closely related chromophores. For three different polyene series, the intense, visible d-->pi* metal-to-ligand charge-transfer bands unexpectedly blue-shift as the number of E-ethylene units (n) increases from 1 to 3, and the static first hyperpolarizabilities beta(0) determined via hyper-Rayleigh scattering and Stark spectroscopy maximize at n = 2, in marked contrast to other known D-A polyenes in which beta(0) increases steadily with n. Time-dependent density-functional theory and finite field calculations verify these empirical trends, which arise from the orbital structures of the complexes. This study illustrates that transition metal-based nonlinear optical chromophores can show very different behavior when compared with their more thoroughly studied purely organic counterparts.

Approximate Calculations of Ionization Potential in Electronic Cluster Models

A simple formulation of generalized Koopmans' theorem is suggested for multiconfigurational wave functions. In a coupled cluster approximation (CCD variant), π-electron estimates have been obtained for the first ionization potential in a series of linear polyenes and polyacenes. The calculated data satisfactorily reproduce the electron correlation effects characteristic of the ionized states of molecules.

Origin of transition dipole-moment polarizability and hyperpolarizability in hydrazones

The origin of transition dipole-moment polarizability and hyperpolarizability in organic materials was investigated using electroabsorption (EA) spectroscopy. It is well established that the following three nonlinear optical properties can be derived from the analysis of EA spectrum; (1) the transition dipole-moment polarizability and hyperpolarizability $(D$ factor), (2) the change of polarizability upon photoexcitation $(\ensuremath{\Delta}\ensuremath{\alpha}),$ and (3) the change of static dipole moment upon photoexcitation $(\ensuremath{\Delta}\ensuremath{\mu}).$ We prepared hydrazones derived from a series of biological polyenes to investigate the physical meaning of the D factor. The hydrazones derived here have two features; (1) they are polar carotenoid analogs with a large third-order nonlinear polarizability, and (2) they have two transition dipoles nearly collinear with the molecular axis. The number of conjugated $\mathrm{C}=\mathrm{C}$ bonds was systematically varied and then the relationship between their structures and nonlinear optical properties of the molecules was investigated. We found that the D factor was the main contributor to the EA spectra of the present set of hydrazones and it had a nearly constant value regardless of the lengths of polyene fragments investigated. Based on the sum rule of the transition dipole moments, the D factor was attributed to charge transfer between the neighboring transition dipoles in the excited states. We conclude that the presence of more than two transition dipole moments in one molecule and the intramolecular charge transfer between them, are necessary for the D factor to be predominant in the nonlinear optical process of organic materials.

Modeling vibronic spectra and excited states of polyenes with a parametric method

The structural-dynamic models of excited states and vibronic structure of absorption spectra of linear polyenes (R-(CH=CH)n-R, R=H, CH3, n=4, 5, 7) are calculated using the parametric method of the theory of vibronic spectra of such molecules. Good agreement is obtained between the calculated and experimental spectra. It is shown that the system of parameters of the method for the polyenes has a high degree of transferability in the series of related polyenes. The constructed models adequately reflect the real structure of the molecules in excited states and allow one to predict quantitatively the fine vibrational structure of the spectra, including relatively weak effects related to the methyl substitution. The dynamic of structural changes of the molecules upon their excitation is studied in the series of polyenes.

Simulation of time-resolved vibronic spectra and the possibility of analyzing molecules with similar spectral properties

The possibility of using time-resolved vibronic spectroscopy for spectral analysis of mixtures of chemical compounds with similar optical properties, when traditional methods (based on stedy-state spectra) are inefficient, is demonstrated by using the method of computer simulation. The analysis is carried out by the example of molecules of a series of polyenes (butadiene, hexadiene, octatetraene, decapentaene, and decatetraene), their various cis-and trans-rotational isomers, and phenyl-substituted polyenes. Ranges of relative concentrations of molecules similar in their spectral properties, where reliable interpretation of time-resolved spectra of mixtures and both qualitative and quantitative analyses are possible, are determined. The use of computer simulation methods for optimizing full-scale experiments in femtosecond spectroscopy is shown to hold much promise.