Search results for "solution"

Exchange Coupling in Cyano-Bridged Homodinuclear Cu(II) and Ni(II) Complexes:  Synthesis, Structure, Magnetism, and Density Functional Theoretical St…

2001

The synthesis and structural characterization of several new cyano-bridged copper(II) and nickel(II) homodinuclear complexes is presented. The measure of magnetic properties for these complexes is complemented with a computational study of the exchange coupling for several model structures representing this family of compounds. The influence of several factors on the coupling constant has been examined, coordination position occupied by the bridging ligand, distortions of the coordination environment, and relative disposition of the cyanide ion with respect to the M-M vector. Comparison of experimental and calculated coupling constants allows for the rationalization of the most relevant fea…

Conformation of the galactose ring adopted in solution and in crystalline form as determined by experimental and DFT 1H NMR and single-crystal X-ray …

2003

The solution-state conformations of various galactose derivatives were determined by comparison of the experimental (1)H-(1)H vicinal coupling constants to those calculated using density functional theory (DFT) at the B3LYP/cc-pVTZ//B3LYP/6-31G(d,p) level of theory. The agreement between the experimental and calculated vicinal coupling constants for 1,2:3,4-di-O-isopropylidene-alpha-d-galactopyranose was good, thereby confirming an (O)S(2) skew conformation for it and its derivatives on the basis of their similar observed couplings. Single-crystal X-ray analysis of 1,2:3,4-di-O-isopropylidene-6-O-(3,4,6-tri-O-acetyl-2-deoxy-2-N-phthalimido-beta-d-glucopyranosyl)-alpha-d-galactopyranose and …

13C nuclear magnetic resonance study of some phosphinolipids: Assignments and conformational studies

1989

13C chemical shifts and 31P, 13C spin-spin coupling constants are reported for six model phosphinates and eight synthetic phosphinolipids. The complex spectra of the synthetic phosphinolipids could be assigned from increments and couplings derived from the model compounds. Based on these investigations the 3J(PC) couplings of 7–15 Hz indicate a preferential trans orientation of the respective head-group carbon relative to the phosphorus. This behaviour is similar to that of natural phosphatidylcholine lipids.

Non-Markovian master equation for the XX central spin model

2008

The non-Markovian correlated projection operator technique is applied to the model of a central spin coupled to a spin bath through non uniform XX Heisenberg coupling. The second order results of the Nakajima-Zwanzig and of the time-convolutionless methods are compared with the exact solution considering a fully polarized initial bath state.

Force probe simulations using a hybrid scheme with virtual sites.

2017

Hybrid simulations, in which a part of the system is treated with atomistic resolution and the remainder is represented on a coarse-grained level, allow for fast sampling while using the accuracy of atomistic force fields. We apply a hybrid scheme to study the mechanical unfolding and refolding of a molecular complex using force probe molecular dynamics (FPMD) simulations. The degrees of freedom of the solvent molecules are treated in a coarse-grained manner while atomistic resolution is retained for the solute. The coupling between the solvent and the solute is provided using virtual sites. We test two different common coarse-graining procedures, the iterative Boltzmann inversion method an…

Serial versus parallel columns using isocratic elution: a comparison of multi-column approaches in mono-dimensional liquid chromatography.

2015

Abstract When a new separation problem is faced with high-performance liquid chromatography (HPLC), the analysis is addressed conventionally with a single column, trying to find out a single experimental condition aimed to resolve all compounds. However, in practice, the system selectivity may be insufficient to achieve full resolution. When a separation fails, the usual practice consists of introducing drastic changes in the chromatographic system (e.g. use of another column, solvent or pH). An alternative solution is taking benefit of the combined separation capability of two or more columns, which can be attained in multiple ways, such as diverse modalities of two-dimensional HPLC, or mo…

Existence and multiplicity of periodic solutions for second order Hamiltonian systems depending on a parameter

2013

The existence of at least one nontrivial periodic solution for a class of second order Hamiltonian systems depending on a parameter is obtained, under an algebraic condition on the nonlinearity G and without requiring any asymptotic behavior neither at zero nor at infinity. The existence is still deduced in the particular case when G is subquadratic at zero. Finally, two multiplicity results are proved if G, in addition, is required to fulfill some different Ambrosetti-Rabinowitz type superquadratic conditions at infinity. The approach is fully variational. © Heldermann Verlag.

Multiple solutions for a Sturm-Liouville problem with mixed boundary conditions

2010

How “African” Is the African Peace and Security Architecture? Conceptual and Practical Constraints of Regional Security Cooperation in Africa

2012

ABSTRACT With the creation of the African Peace and Security Architecture in 2004, African states were aiming to assume the primary responsibility for peace and security on the continent and establish a structure to assemble the necessary financial and military means. However, despite the constant evocation of “African ownership,” it is non-African actors that call the tune and can define and drive African security. Based on a detailed juxtaposition of rhetoric and empirical evidence, this paper argues that significant conceptual and practical problems constrain the “Africanization” of African security and that it appears increasingly unlikely that the continent's states will be able to ach…

Investigating the cryopreservation of nodal explants of Lithodora rosmarinifolia (Ten.) Johnst., a rare, endemic Mediterranean species

2012

In this study, we investigated the possibility of using the droplet-vitrification technique for cryopreserving nodal segments of in vitro plantlets of the endangered plant species Lithodora rosmarinifolia. Among the three vitrification solutions tested, only solutions B1, containing (w/v) 50 % glycerol and 50 % sucrose, and B3, containing 40 % glycerol and 40 % sucrose, were able to induce cryotolerance in nodal explants, resulting in intermediate survival and recovery after cryopreservation. A three-step vitrification protocol, including an additional dehydration treatment with half-strength vitrification solution for 30 min before the treatment with full-strength vitrification solution, d…