Valence shell electronically excited states of norbornadiene and quadricyclane.

The absolute photoabsorption cross sections of norbornadiene (NBD) and quadricyclane (QC), two isomers with chemical formula C7H8 that are attracting much interest for solar energy storage applications, have been measured from threshold up to 10.8 eV using the Fourier transform spectrometer at the SOLEIL synchrotron radiation facility. The absorption spectrum of NBD exhibits some sharp structure associated with transitions into Rydberg states, superimposed on several broad bands attributable to valence excitations. Sharp structure, although less pronounced, also appears in the absorption spectrum of QC. Assignments have been proposed for some of the absorption bands using calculated vertical transition energies and oscillator strengths for the electronically excited states of NBD and QC. Natural transition orbitals indicate that some of the electronically excited states in NBD have a mixed Rydberg/valence character, whereas the first ten excited singlet states in QC are all predominantly Rydberg in the vertical region. In NBD, a comparison between the vibrational structure observed in the experimental 11B1-11A1 (3sa1 ← 5b1) band and that predicted by Franck-Condon and Herzberg-Teller modeling has necessitated a revision of the band origin and of the vibrational assignments proposed previously. Similar comparisons have encouraged a revision of the adiabatic first ionization energy of NBD. Simulations of the vibrational structure due to excitation from the 5b2 orbital in QC into 3p and 3d Rydberg states have allowed tentative assignments to be proposed for the complex structure observed in the absorption bands between ∼5.4 and 7.0 eV.

Biomechanical assessment of an alternative method of staple fixation for anchoring the Bone Patellar Tendon Bone graft to the tibia.

INTRODUCTION: The Anterior cruciate ligament (ACL) is the most commonly injured ligament around the knee and is best reconstructed with a biological graft. For ideal graft fixation, there should be sufficient initial strength to avoid failure of fixation and sufficient stiffness to restore the stability of the knee and to avoid gradual loosening in the post-operative period.When considering fixation of Bone Patellar Tendon Bone (BPTB) grafts to the tibia, the interference screw is considered to be the gold standard. As an alternative, we have used of staples and stainless steel (SS) wire to anchor the BPTB graft to the tibia and femur. The aim of this study was to assess the biomechanical efficacy of this fixation technique for anchoring the BPTB graft to the proximal tibia. We used a bovine model to compare three fixation techniques -interference screw, braided polyester sutures tied to a screw post and SS wire tied to a staple. MATERIALS AND METHODS: Fifteen fresh bovine knees specimens were used for the study. The patella was fixed to a load cell and the construct was pre-tensioned to 40N to allow for creep of the tendon. The BPTB graft was fixed to the tibia using the three fixation techniques - the interference screw, polyester suture tied to a post, and SS wire anchored to a staple. After fixation, the graft was subjected to a single load to failure test, and the forces generated were recorded. The ultimate failure load (the pullout strength), stiffness, and mode of failure were noted. RESULTS: In the single load-to-failure biomechanical testing, the ultimate failure load and stiffness for Staple with SS wire were 726.40N and 61.9N/mm respectively. For the screw post and polyester suture, it was 733.20N and 53.22N/mm, and for Interference screw - 594.00N and 79.50 N/mm respectively. There was no statistically significant difference in the stiffness or ultimate failure load between the three fixation techniques. The graft fixation using interference screws failed at the bone- tunnel interface by slippage of the bone block from the tunnel in all 5 specimens. In all 5 of the specimens fixed with polyester suture and the screw post, the fixation failed when the polyester suture snapped. When the SS wire and staple construct was stressed, the graft failed as the SS wire cut through the graft in 4 specimens, and in the fifth construct, the knot over the staple unraveled as the load was applied. CONCLUSION: The biomechanical properties of BPTB graft fixation with SS wire tied to a staple is similar to that of other fixation devices like the interference screw and suture post. This technique provides a simple, yet effective fixation for the graft - but needs further clinical assessment.

Evaluation of cell toxicity and DNA and protein binding of green synthesized silver nanoparticles.

Silver nanoparticles (AgNPs) were prepared by GREEN chemistry relying on the reduction of AgNO3 by phytochemicals present in black tea extract. AgNPs were fully characterized by transmission electron microscopy (TEM), ultraviolet-visible spectroscopy ((UV-vis)), X-ray diffraction (XRD) and energy dispersive absorption spectroscopy (EDS). The synthesized AgNPs induced a decrease of the cell viability in a dose-dependent manner with a low IC50 (0.5 ±â€¯0.1 µM) for an ovarian carcinoma cell line (A2780) compared to primary human fibroblasts (IC50 5.0 ±â€¯0.1 µM). The DNA binding capability of CT (calf thymus) DNA was investigated using electronic absorption and fluorescence spectroscopies, circular dichroism and viscosity titration methods. Additionally, the AgNPs strongly quench the intrinsic fluorescence of BSA, as determined by synchronous fluorescence spectra.

Structural, magnetic, electrochemical, catalytic, DNA binding and cleavage studies of new macrocyclic binuclear copper(II) complexes.

The macrocyclic symmetrical and a series of unsymmetrical binuclear copper(II) complexes have been synthesized by using mononuclear complex [CuL] [3,3'-((1E,7E)-3,6-dioxa-2,7-diazaocta-1,7-diene-1,8-diyl)bis(3-formyl-5-methyl-2-diolato)copper(II)]. Another compartment of the [CuL] have been condensed with various diamines like 1,2-bis(aminooxy)ethane (L(1)), 1,2-diamino ethane(L(2a)), 1,3-diamino propane(L(2b)), 1,4-diamino butane(L(2c)), 1,2-diamino benzene(L(2d)), 1,8-diamino naphthalene(L(2e)) and characterized by elemental, spectroscopic, and X-ray crystallographic methods. The influence of the coordination geometry and the ring size of the binucleating ligands on the electronic, redox, magnetic, catecholase activity, DNA binding and cleavage properties have been studied. The molecular structures of the symmetrical binuclear complex [Cu(2)L(1)(H(2)O)(2)](ClO(4))(2) (1) and unsymmetrical binuclear complex [Cu(2)L(2b)(ClO(4))(H(2)O)]ClO(4) (2b) were determined by X-ray crystallography. Both of them were discrete binuclear species in which each Cu(II) ions are in distorted square pyramid. The Cu...Cu distances vary from 3.0308 (2b) to 3.0361 A (1). Electrochemical studies evidenced that two quasi-reversible one electron-transfer reduction waves (E(pc)(1)) -0.91 to -1.01 V, (E(pc)(2)) -1.26 to -1.55 V) for binuclear complexes are obtained in the cathodic region. Cryomagnetic investigation of the binuclear complexes reveals a weak antiferromagnetic spin exchange interaction between the Cu(II) ions within the complexes (-2J=104.4-127.5 cm(-1)). The initial rate (V(in)) for the oxidation of 3,5-di-tert-butylcatechol to o-quinone by the binuclear Cu(II)complexes are in the range 3.6 x 10(-5) to 7.3 x 10(-5)Ms(-1). The binuclear Cu(II) complexes are avid binders to calf thymus DNA. The complexes display significant oxidative cleavage of circular plasmid pBR322 DNA in the presence of mercaptoethanol using the singlet oxygen as a reactive species. The aromatic diamine condensed macrocyclic ligands of copper(II) complexes display better DNA interaction and significant chemical nuclease activity than the aliphatic diamine condensed macrocyclic Cu(II) complexes.