Synthesis and characterization of dithienylbenzobis(thiadiazole)-based low band-gap polymers for organic electronics

New donor-acceptor alternating conjugated polymers were synthesized and characterized. Among them, PCPBBT exhibited a band-gap of 1.01 eV and ambipolar characteristics with μ(h) = 7.1 × 10(-4) cm(2) V(-1) s(-1) and μ(e) = 3.3 × 10(-3) cm(2) V(-1) s(-1).     

Control of spins by ring deformation in a diiron(III)bisporphyrin: reversal of ClO4⁻ and CF3SO3⁻ ligand field strength in the magnetochemical series

The complete reversal of the ligand field strength of ClO(4)(-) and CF(3)SO(3)(-) in the magnetochemical series is observed in a diiron(III)bisporphyrin. While ClO(4)(-), as the axial ligand, gives a typical high-spin complex, just twisting the conformation of the porphyrin macrocycle gives properties of a pure intermediate-spin state with CF(3)SO(3)(-), although the axial ligand strengths suggest the reverse order of spin stabilization.     

Planar triazinium cations from VO(2+)-assisted ring cyclizations: a remarkably efficient thiazole species for nuclear staining, PDT and anaerobic photocleavage of DNA

Planar triazinium cationic species, from VO(2+)-assisted cyclization of 1-(2-thiazolylazo)-2-naphthol, shows efficient DNA intercalative binding, visible light-induced anaerobic plasmid DNA photocleavage activity and photocytotoxicity in HeLa and MCF-7 cancer cells by an apoptotic pathway with selective localization of the compound in the nucleus as evidenced from the nuclear staining and confocal imaging.     

Tunable emission of static excimer in a pyrene-modified polyamidoamine dendrimer aggregate through positive solvatochromism

Significant aggregation is observed in pyrene-modified zero- and first-generation polyamidoamine (PAMAM) dendrimers above their critical aggregation concentration (CAC, >10(-6) M). The pyrene units are attached to the dendrimer skeleton through imine bonds, which play a pivotal role in enhancing the aggregation propensity of the PAMAM dendrimers. Scanning electron microscopy studies suggest that pyrene-modified PAMAM dendrimers aggregate into doughnut-shaped assemblies. As a result of aggregation, the pyrene chromophores are pre-arranged in a face-to-face geometry in the ground state, and readily generate pyrene "static excimer" on photoexcitation. The static pyrene excimer emits with an unprecedented quantum yield of 0.62 ± 0.01 in dichloromethane, and also exhibits remarkable positive solvatochromism from 498 to 638 nm, which leads to the highest bathochromic shift for pyrene excimer emission in solution reported so far. Lippert-Mataga analysis of the system suggests that general and specific solvent effects play a crucial role in the positive solvatochromism exhibited by the system. Luminescence quenching studies on both monomer and aggregate systems were carried out in the presence of various metal ions, and the results imply that pyrene-modified PAMAM dendrimer can be utilized for selective detection of Hg ions in the presence of a wide variety of transition, alkali, and alkaline earth metal ions. This report presents the first dendrimer-based chromophoric system exhibiting positive solvatochromism over a range of 140 nm, and shows that pyrene-modified PAMAM dendrimers can be effectively utilized to generate wavelength-tunable emitting systems displaying bluish green, greenish yellow, and orange-red colors at room temperatures.     

Protonation of an Oxo‐Bridged Diiron Unit Gives Two Different Iron Centers: Synthesis and Structure of a New Class of Diiron(III)‐μ‐hydroxo Bisporphyrins and the Control of Spin States by Using Counterions

Reported herein is a hitherto unknown family of diiron(III)‐μ‐hydroxo bisporphyrins in which two different spin states of Fe are stabilized in a single molecular framework, although both cores have identical molecular structures. Protonation of the oxo‐bridged dimer ( 2 ) by using strong Brønsted acids, such as HI, HBF₄, and HClO₄, produce red μ‐hydroxo complexes with I₃^? ( 3 ), BF₄^? ( 4 ), and ClO₄^? ( 5 ) counterions, respectively. The X‐ray structure of the molecule reveals that the Fe? O bond length increases on going from the μ‐oxo to the hydroxo complex, whereas the Fe‐O(H)‐Fe unit becomes more bent, which results in the smallest known Fe‐O(H)‐Fe angles of 142.5(2) and 141.2(1)° for 3 and 5 , respectively. In contrast, the Fe‐O(H)‐Fe angle remains unaltered in 4 from the corresponding μ‐oxo complex. The close approach of two rings in a molecule results in unequal core deformations in 3 and 4 , whereas the cores are deformed almost equally but to a lesser extent in 5 . Although 3 was found to have nearly high‐spin and admixed intermediate Fe spin states in cores I and II, respectively, two admixed intermediate spin states were observed in 4 . Even though the cores have identical chemical structures, crucial bond parameters, such as the Fe? N_p, Fe? O, and Fe???Ct_p bond lengths and the ring deformations, are all different between the two Fe^III centers in 3 and 4 , which leads to an eventual stabilization of two different spin states of Fe in each molecule. In contrast, the two Fe centers in 5 are equivalent and assigned to high and intermediate spin states in the solid and solution states, respectively. The spin states are thus found to be dependent on the counterions and can also be reversibly interconverted. Upon protonation, the strong antiferromagnetic coupling in the μ‐oxo dimer (J, ?126.6 cm^?1) is attenuated to almost zero in the μ‐hydroxo complex with the I₃^? counterion, whereas the values of J are ?36 and ?42 cm^?1, respectively, for complexes with BF₄^? and ClO₄^? counterions.     

Post-irradiation identification of papaya (Carica papaya L.) fruit

Impact of radiation processing on the volatile essential oil profile of papaya (Carica papaya) was investigated. Gamma-radiation processing resulted in the appearance of a new peak in the GLC profile that was identified as phenol. The observed dose dependent increase in phenol content suggested possible use of this compound as a marker for radiation processed papaya.     

Conformational polymorphism in bicalutamide: a quantum chemical study

Bicalutamide is an anti-neoplastic drug widely used for the treatment of prostate cancer and it exhibits conformational polymorphism. Three crystal structures of bicalutamide are reported as racemic mixtures, two of which are polymorphs. In addition, three co-crystals are also reported—two with organic coformers and one with adrenoreceptor (the macromolecular target). All the reported structures show significant conformational differences. Quantum chemical B3LYP/6-31+G(d,p) analysis has been carried out to understand the interplay of intra- and intermolecular interactions leading to the conformational preferences in this molecule. The difference between the two polymorphic forms has been traced to the C5–S8–C11–C12 torsional angle. Inside the cavity of androgen receptor, a completely different conformation is found but it does not correspond to any local minima on the potential energy surface of the drug. A relatively rigid torsional angle C11–C12–C15–N17 is also expected due to a strong five-membered ring intramolecular hydrogen bond (H–O13–C12–C15–O16), which has been reported to be desirable; quantum chemical analysis revealed that this rigidity is of the order of 11 kcal/mol. Ab initio calculations demonstrate that polymorphs and polymorphic co-crystals differ in the extent of intra- and intermolecular hydrogen bonding interactions. The strength of the intermolecular interactions associated with these structures is analyzed in terms of energy release due to dimerization.     

Influence of water on anharmonicity, stability, and vibrational energy distribution of hydrogen-bonded adducts in atmospheric reactions: case study of the OH + isoprene reaction intermediate using ab initio molecular dynamics

The effect of water on the stability and vibrational states of a hydroxy-isoprene adduct is probed through the introduction of 1-15 water molecules. It is found that when a static nuclear harmonic approximation is invoked there is a substantial red-shift of the alcohol O-H stretch (of the order of 800 cm(-1)) as a result of introduction of water. When potential energy surface sampling and associated anharmonicities are introduced through finite temperature ab initio dynamics, this hydroxy-isoprene OH stretch strongly couples with all the water vibrational modes as well as the hydroxy-isoprene OH bend modes. A new computational technique is introduced to probe the coupling between these modes. The method involves a two-dimensional, time-frequency analysis of the finite temperature vibrational properties. Such an analysis not only provides information about the modes that are coupled as a result of finite-temperature analysis, but also the temporal evolution of such coupling.     

Chiroptical spectroscopy of surfactants

Three different chiroptical spectroscopic methods, namely, optical rotation, electronic circular dichroism (ECD), and vibrational circular dichroism (VCD) have been evaluated for studying the aggregation of sodium dodecylsulfate (SDS), an achiral surfactant, using garcinia acid disodium salt (GADNa) as a chiral probe. The specific rotation and ECD of GADNa are found to be altered by the aggregation of SDS, suggesting for the first time that achiral surfactants can be characterized with chiroptical spectroscopy using appropriate chiral probes. In addition, a chiral compound, fluorenyl methyloxy carbonyl l-leucine sodium salt (FLNa) is found for the first time to behave as a surfactant in water, with 205 ?(2) surface area per molecule at the air-water interface, critical micelle concentration (CMC) of 0.18 M, and Gibbs energy of micellization of -14 kJ/mol. The specific rotation of FLNa in water is found to increase with concentration beyond CMC, suggesting the formation of chiral aggregates. Different conformations of FLNa amenable to micellization have been identified using quantum chemical conformational analysis and their specific rotations calculated. The formation of lamellar aggregates of FLNa in water is suggested to be the cause for increase in specific rotation with concentration beyond CMC.     

Remarkable photocytotoxicity of curcumin in HeLa cells in visible light and arresting its degradation on oxovanadium(IV) complex formation

Curcumin (Hcur) as a cellular imaging and PDT agent shows remarkable photocytotoxicity in HeLa cells in visible light of 400-700 nm giving IC(50) = 8.2 ± 0.2 μM and its degradation is arrested on formation of photocytotoxic dipyridophenazine (dppz) complex [VO(cur)(dppz)Cl] (IC(50) = 3.3 ± 0.4 μM), while both are less toxic in the dark.