Search results for "bonding"
showing 10 items of 996 documents
Cationic Cyclopentadienyl Phenylenediamido Titanium Species Generated by Reaction of TiCpR[1,2-C6H4(NCH2t-Bu)2]R (CpR = η5-C5H5, η5-C5Me5; R = CH3, C…
2006
The reaction of TiCpR[1,2-C6H4(NNp)2]R with the Lewis acid B(C6F5)3 in noncoordinating solvent affords the new zwitterionic species TiCpR[1,2-C6H4(NNp)2)][μ-RB(C6F5)3]. When the reaction is performed in dichloromethane, the [μ-RB(C6F5)3]- anion is displaced by solvent molecules, giving ionic products in which the anion is not coordinated. The cyclopentadienyl zwitterionic complexes TiCp[1,2-C6H4(NNp)2)[μ-RB(C6F5)3] decompose via ligand scrambling between boron and titanium to give the neutral titanium complex TiCp[1,2-C6H4(NNp)2](C6F5) along with the byproduct RB(C6F5)2. In contrast, the pentamethylcyclopentadienyl analogues TiCp*[1,2-C6H4(NNp)2][μ-RB(C6F5)3] evolve through C−H activation t…
Sheets of alternating chirality in the structure of a novel iron(III) complex with a cyclic oxamide ligand
1998
An organic–metalloorganic analogue of the inorganic clay minerals has been obtained from the cyclization of N,N′-bis(ethoxalyl)phenylenediamine in basic medium in the presence of iron(III) ions leading to formation of a cyclic oxamide ligand (L). The combination of intramolecular (covalent) interactions between metal and ligand and intermolecular (noncovalent) ionic interactions creates a novel layered compound with an intriguing crystal structure (shown on the right).
Excitation-Wavelength-Dependent Photocycle Initiation Dynamics Resolve Heterogeneity in the Photoactive Yellow Protein from Halorhodospira halophila
2018
Photoactive yellow proteins (PYPs) make up a diverse class of blue-light-absorbing bacterial photoreceptors. Electronic excitation of the p-coumaric acid chromophore covalently bound within PYP results in triphasic quenching kinetics; however, the molecular basis of this behavior remains unresolved. Here we explore this question by examining the excitation-wavelength dependence of the photodynamics of the PYP from Halorhodospira halophila via a combined experimental and computational approach. The fluorescence quantum yield, steady-state fluorescence emission maximum, and cryotrapping spectra are demonstrated to depend on excitation wavelength. We also compare the femtosecond photodynamics …
Light-Induced Protein-Matrix Uncoupling and Protein Relaxation in Dry Samples of Trehalose-Coated MbCO at Room Temperature
2005
In humid samples of trehalose-coated carboxy-myoglobin (MbCO), thermally driven conformational relaxation takes place after photodissociation of the carbon monoxide (CO) molecule at room temperature. In such samples, because of the extreme viscosity of the external matrix, photodissociated CO cannot diffuse out of the protein and explores the whole (proximal and distal side) heme pocket, experiencing averaged protein heme pocket structures, as a result of the presence of Brownian motions. At variance, in very dry samples, a lower portion of the photodissociated CO diffuses from the distal to the proximal heme pocket side probing in nonaveraged structures. We revisit here the flash photolysi…
Photoactivation of Drosophila melanogaster cryptochrome through sequential conformational transitions
2019
Time-resolved x-ray scattering reveals light-induced signal transduction in insect cryptochromes.
COMPUTER AIDED ENGINEERING OF SOLID BONDING PHENOMENA
2014
Joining is a fundamental technological process in manufacturing used to create a single piece from two or more parts. Welding is still today one of the most popular joining techniques used in manufacturing allowing a permanent junction. Traditional welding processes are based on the melting of the materials to be joined. In this way, several defects may arise because of solidification problems, joints deformation due to elevated residual stress and metallurgical integrity of the joints (intermetallic, porosities, etc). As an example, some aluminum alloys present considerable problems the junction is carried out by traditional fusion welding methods. During the melting process, in fact, the …
On the chemiluminescence emission of luminol: protic and aprotic solvents and encapsulation to improve the properties in aqueous solution.
2020
Luminol is a popular molecule that is currently gaining further interest due to its potential role for non-invasive cancer treatments. Design of more efficient derivatives in this context would benefit from a clear knowledge on the origin of the distinct intensity and spectroscopic properties in protic and aprotic solvents observed experimentally, which are still not rationalized. By efficiently combining molecular dynamics, quantum methodologies based on density functional theory and multiconfigurational quantum chemistry and hybrid approaches, and developing herein a computational approach for accurately determining "molar negative extinction (or gain) coefficients of emission", we firstl…
Coordination networks incorporating halogen-bond donor sites and azobenzene groups
2016
Two Zn coordination networks, {[Zn(1)(Py)2]2(2-propanol)}n (3) and {[Zn(1)2(Bipy)2](DMF)2}n (4), incorporating halogen-bond (XB) donor sites and azobenzene groups have been synthesized and fully characterized. Obtaining 3 and 4 confirms that it is possible to use a ligand wherein its coordination bond acceptor sites and XB donor sites are on the same molecular scaffold (i.e., an aromatic ring) without interfering with each other. We demonstrate that XBs play a fundamental role in the architectures and properties of the obtained coordination networks. In 3, XBs promote the formation of 2D supramolecular layers, which, by overlapping each other, allow the incorporation of 2-propanol as a gues…
Zn(II)-coordination and fluorescence studies of a new polyazamacrocycle incorporating 1H-pyrazole and naphthalene units.
2010
The synthesis and Zn(2+) coordination properties of a new macrocycle (L1) obtained by dipodal (2 + 2) condensation of the polyamine 3-(naphthalen-2-ylmethyl)pentane-1,5-diamine with 1H-pyrazole-3,5-dicarbaldehyde are reported. pH-metric studies show that L1 bears five measurable protonation steps in the 2.0-11.0 pH range. Fluorescence emission studies indicate that the removal of the first proton from the H(5)L1(5+) species leads to a significant decrease in the emission due to a photoinduced electron transfer process. Addition of Zn(2+) promotes a boat-like conformation that approaches both fluorophores and facilitates the formation of an excimer which reaches its highest emission for a 1 …
Guest exchange in dimeric capsules formed by tetra-urea calix[4]arenes
2008
Ten tetra-urea calix[4]arene derivatives with different ether residues (methyl, pentyl, benzyl, all combinations of methyl and pentyl, 1,3-dibenzyl-2,4-dipentyl), including also the tetrahydroxy compound and the 1,3-dipentyl ether, were synthesised. Their urea groups were substituted with a lipophilic residue to ensure sufficient solubility in cyclohexane. Thus, kinetics for the exchange of the included guest (benzene) against the solvent (cyclohexane) could be followed by 1H NMR spectroscopy. The apparent first order rate constants decrease with increasing size of the ether residues from methyl to benzyl by more than three orders of magnitude. This can be understood by a decreasing flexibi…