Interaction of fisetin with human serum albumin by fluorescence, circular dichroism spectroscopy and DFT calculations: binding parameters and conformational changes

The interaction between fisetin, an antioxidant and neuroprotective flavonoid, and human serum albumin (HSA) is investigated by means of fluorescence (steady-state, synchronous, time-resolved) and circular dichroism (CD) spectroscopy. The formation of a 1:1 complex with a constant of about 10⁵ M⁻¹ was evidenced. Förster's resonance energy transfer and competitive binding with site markers warfarin and ibuprofen were considered and discussed. Changes in the CD band of HSA indicate a decrease in the α-helix content upon binding. An induced CD signal for bound fisetin was observed and rationalized in terms of density functional theory calculations.     

Thermochemical and structural study of a dibenzocycloheptane cyanoenamine

The crystalline and gas phase enthalpy of formation of 5-cyano-7H-dibenzo-[a,c]-cyclohepten-6-amine (1) (142.0 ± 11.6 and 264 ± 20 kJ mol^?1, respectively) are reported. The sublimation enthalpy at T = 298.15 K for this compound was evaluated by combining the fusion enthalpy from DSC measurements adjusted to 298 K with estimated vaporization enthalpy. The experimental enthalpy of formation is discussed in relationship with values calculated at the G3(MP2)//B3LYP level of quantum chemical theory and by means of group additivity. The crystal structure of this compound was determined by X-ray crystallography and shown to exist entirely in the cyanoenamine form 1, i.e. not the tautomeric α-cyanoimine 2.     

Thermochemistry and quantum chemical calculations of two dibenzocycloalkane nitriles

The energies of combustion and fusion of 5-cyano-5H-dibenzo[a,d]cycloheptene (1) and (5E,11E)-dibenzo[a,e]cyclooctene-5,11-dicarbonitrile (2) were measured by means of microbomb calorimetry and DSC, respectively. The derived enthalpies of formation in solid state are 320 ± 18 for nitrile 1 and 470 ± 31 kJ mol⁻¹ for nitrile 2, respectively. The experimental enthalpies of formation are discussed in relationship with values calculated at the G3(MP2)//B3LYP level of quantum chemical theory, by means of group additivity and isodesmic reactions. The two nitriles are not stabilized by dibenzoannelation.     

Surface-enhanced Raman effect in ultra-thin CuPc films employing periodic silver nanostructures

In order to investigate the interaction of organic molecules with metals by means of Raman spectroscopy, special substrates were designed which combine interference and surface-enhancement mechanisms. Triangular shaped silver nanostructures with an angle bisector and a height of about 80 nm were prepared by nanosphere lithography on silicon substrates with a 100-nm oxide layer. Utilizing these substrates the dependence of the Raman signal intensity on the thickness of copper phthalocyanine (CuPc) was studied in the range from few percentages of a monolayer coverage up to 80 nm using an in situ setup. At an excitation in resonance with the plasmons of the nanostructures (2.6 eV) an increase of the signal was observed during film growth. Contrary to that, excitation at 1.92 eV in resonance with the CuPc absorption band leads to a strongly enhanced Raman signal for submonolayer coverage which hardly changes with the CuPc film thickness in the ultra-low coverage regime.     

Rate coefficients for the gas‐phase reactions of OH radicals with methylbutenols at 298 K

The relative‐rate method has been used to determine the rate coefficients for the reactions of OH radicals with three C₅ biogenic alcohols, 2‐methyl‐3‐buten‐2‐ol (k₁), 3‐methyl‐3‐buten‐1‐ol (k₂), and 3‐methyl‐2‐buten‐1‐ol (k₃), in the gas phase. OH radicals were produced by the photolysis of CH₃ONO in the presence of NO. Di‐n‐butyl ether and propene were used as the reference compounds. The absolute rate coefficients obtained with the two reference compounds agreed well with each other. The O₃ and O‐atom reactions with the target alcohols were confirmed to have a negligible contribution to their total losses by using two kinds of light sources with different relative rates of CH₃ONO and NO₂ photolysis. The absolute rate coefficients were obtained as the weighted mean values for the two reference compound systems and were k₁ = (6.6 ± 0.5) × 10^?11, k₂ = (9.7 ± 0.7) × 10^?11, and k₃ = (1.5 ± 0.1) × 10^?10 cm³ molecule^?1 s^?1 at 298 ± 2 K and 760 torr of air. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 379–385 2004