Fluorescence spectroscopic study of hypericin-photosensitized oxidation of low-density lipoproteins

By means of UV-VIS absorption and fluorescence spectroscopy, we demonstrate that the photosensitizer hypericin (Hyp) interacts nonspecifically with low-density lipoproteins (LDL), most probably with the lipid fraction of LDL. The molar ratio of monomeric Hyp binding to nonoxidized LDL and mildly oxidized LDL is 30:1. Increasing the Hyp concentration further leads to the formation of Hyp aggregates inside the LDL molecule. We also demonstrate that photoactivated Hyp oxidizes LDL in a light dose and excitation wavelength dependent manner. The level of oxidation of LDL depends on the amount of Hyp inside the LDL molecule. The maximum of the photosensitized oxidation of the LDL by Hyp is achieved for a 30:1 molar ratio, which corresponds to the maximum concentration of monomeric form of Hyp in LDL.     

A procedure for finding first integrals of mechanical systems with gauge-variant Lagrangians

In this paper a procedure is given for finding first integrals of non-conservative mechanical systems in which the Lagrangian is gauge-variant under infinitesimal transformations as functions of time, position and generalized velocities. The procedure is founded on the generalized Noetherian theorem. The existence of first integrals depends on the existence of solutions of the system of partial differential equations. Two examples are analyzed in detail using this theory. The considerations are based on mechanical systems but the results obtained can be used on all problems in physics, engineering and mathematics for which one can construct an action integral in Hamilton's sense.     

A note on the disturbed equations of motion in the non-holonomic coordinates

Summary The aim of this article is to establish the disturbed equations of motion in the non-holonomic coordinates. The governing differential equations of non disturbed motion are the Hamel-Boltzman equations. The disturbed equations obtained in this article can be used for consideration in holonomic and non-holonomic dynamics systems. Entrata in Redazione 1'8 maggio 1972.     

Contribution to error estimate

The error estimate of an approximate solution to a nonlinear ordinary differential equations of the second order is obtained. The differential equation is subject to either two-point boundary conditions or initial conditions. The independent variable interval may be finite or infinite. The theory is applied to five problems.     

Evidence for a single hydrogen molecule connected by an atomic chain

Stable, single-molecule conducting-bridge configurations are typically identified from peak structures in a conductance histogram. In previous work on Pt with H2 at cryogenic temperatures it has been shown that a peak near 1G0 identifies a single-molecule Pt-H2-Pt bridge. The histogram shows an additional structure with lower conductance that has not been identified. Here, we show that it is likely due to a hydrogen decorated Pt chain in contact with the H2 molecular bridge.     

Phenolic content and antioxidant properties of soybean (Glycine max (L.) Merr.) seeds

The contents and antioxidant ability of various classes of phenolic compounds present in the seeds of twenty soybean hybrids were evaluated. Total phenolics, tannins and proanthocyanidins were determined spectrophotometrically, after extraction of seeds with 70% aqueous acetone. In addition, the flavonoid contents were determined. The antioxidant activity of aqueous acetone extracts was evaluated by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity assay. The highest contents of total phenolics were found in Serbian cultivar 1511 and Chinese cultivar LN92-7369, which also displayed the highest total antioxidant activity. Conversely, genotypes poor in phenolics also showed low levels of DPPH-radical scavenging activity. The results suggested that besides protein and oil contents, the phenolic contents should be also considered as an important characteristic feature of soybean seeds, and as a potential selection criterion for antioxidant activity in soybean.     

Synthesis of a 2-benzocymantrenylpyridine and further mechanistic insights

The synthesis of a new benzocymantrene derivative containing an appended pyridyl moiety was attempted by reacting a lithioindenylpyridine with (CO)₅MnBr. The reaction led to the formation of small amounts of the targeted benzocymantrene, which was subsequently characterized by structural X-ray diffraction analysis. Alternative treatment of the same ligand with (η¹-benzyl)pentacarbonylmanganese led to the formation of a five-membered manganacycle resulting from the C-H bond activation at the five-membered ring of the indenyl group. To rationalize the origin of the poor yield in the benzocymantrene derivative a complete study of the reaction profile was carried out by means of a state-of-the-art DFT-D2 method. The theory indicated that the main difficulty in producing the targeted benzocymantrene stems from the relatively high activation energy barrier necessary to convert a (η¹-indenyl)Mn(CO)₅ intermediate into a (η³-indenyl)Mn(CO)₄ transient species.     

π-Extended and six-coordinate iron(II) complexes: structures, magnetic properties, and the electrochemical synthesis of a conducting iron(II) metallopolymer

Herein, we describe the preparation of three new bidentate π-extended derivatives of the ligand N-phenyl-2-pyridinalimine (ppi) containing a 3-thienyl (4) substituent at position 4 of the aniline ring or 2-thienyl (6) or phenyl (2) substituents at each of the 2,5 positions of the aniline rings. Three iron(2+) complexes (7-9) containing these ligands were prepared by combining two equivalents each of 2, 4, or 6 with Fe(NCS)(2), and the resulting neutral, six-coordinate complexes were fully characterized, including with single crystal X-ray diffraction experiments in the case of complexes 7 and 9. Variable temperature magnetic susceptibility and Mo?ssbauer experiments confirm the presence of spin-crossover in complexes 7 and 8, and the unusual solid state variable temperature magnetic properties of complex 9 likely result from crystal packing forces. Electropolymerization of the 2,5-dithienyl-substituted complex (9) produces a conducting and electrochromic metallopolymer film (poly-9).     

Structural and magnetic properties of homoleptic iron(III) complexes containing N-(8-quinolyl)-salicylaldimine [Fe(Qsal)2]+X− {X = I or (Qsal)FeCl3}

The structural properties of two homoleptic iron(III) complexes containing N-(8-quinolyl)-salicylaldimine (qsalH) are reported on the basis of two single-crystal X-ray diffraction experiments. The complexes are shown to share the general formula [Fe(qsal)₂]⁺X^? {X = I (1) or (qsal)FeCl₃ (2)} and include one new complex 2 and one previously reported complex 1 for which structural details were until now unknown. Variable-temperature magnetic susceptibility measurements on both samples indicate the nature of the spin state of the metal ion, which is low-spin for 1 and high-spin for 2. Mössbauer spectra are recorded for 1 at 293 and 5.6 K and indicate unusual temperature-dependent behaviour, which corroborates an earlier report.     

The Thermochemistry of London Dispersion-Driven Transition Metal Reactions: Getting the ‘Right Answer for the Right Reason’

Reliable thermochemical measurements and theoretical predictions for reactions involving large transition metal complexes in which long-range intramolecular London dispersion interactions contribute significantly to their stabilization are still a challenge, particularly for reactions in solution. As an illustrative and chemically important example, two reactions are investigated where a large dipalladium complex is quenched by bulky phosphane ligands (triphenylphosphane and tricyclohexylphosphane). Reaction enthalpies and Gibbs free energies were measured by isotherm titration calorimetry (ITC) and theoretically ‘back-corrected’ to yield 0 K gas-phase reaction energies (ΔE). It is shown that the Gibbs free solvation energy calculated with continuum models represents the largest source of error in theoretical thermochemistry protocols. The (‘back-corrected’) experimental reaction energies were used to benchmark (dispersion-corrected) density functional and wave function theory methods. Particularly, we investigated whether the atom-pairwise D3 dispersion correction is also accurate for transition metal chemistry, and how accurately recently developed local coupled-cluster methods describe the important long-range electron correlation contributions. Both, modern dispersion-corrected density functions (e.g., PW6B95-D3(BJ) or B3LYP-NL), as well as the now possible DLPNO-CCSD(T) calculations, are within the ‘experimental’ gas phase reference value. The remaining uncertainties of 2–3 kcal mol⁻¹ can be essentially attributed to the solvation models. Hence, the future for accurate theoretical thermochemistry of large transition metal reactions in solution is very promising.