Search results for "bond"
showing 10 items of 3527 documents
Vibrational spectroscopy of a tetraureidocalix[4]arene based molecular capsuleElectronic supplementary information (ESI) available: three tables cont…
2001
Structural models for self-assembled dimers composed of two urea calix[4]arenes which entrap benzene or cyclohexane are developed using Fourier transform infrared (FTIR) spectroscopy. Based on the host–guest ratio determined by 1H NMR spectroscopy in solution, and confirmed for the solid state by a thermogravimetric analysis, it is possible to prove by a comparison of the FTIR data of host, guest, complex and model compounds, that the capsule is held together by a cyclic array of weak and strong hydrogen bonds between the urea units attached at the wide rim of the calixarenes. The dimerization of the two urea units leads to a loss of symmetry, and an averaged C4 symmetrical arrangement is p…
Bis(6-thioxo-1,6-dihydropurinium) tetrachlorozincate(II).
2006
The title salt, (C(5)H(5)N(4)S)(2)[ZnCl(4)], consists of two 6-thioxo-1,6-dihydropurinium (6mpH(2)(+)) cations (A and B) and a tetrachlorozincate anion, which are held together by N-H...Cl and C-H...Cl interactions. There is an anion-pi interaction between one Cl atom of the [ZnCl(4)](-) anion and the pyrimidine ring of the 6mpH(2)(+)(B) cation. Intermolecular pi-pi stacking interactions allow 6mpH(2)(+)(A) cations to form antiparallel pairs. One interesting structural feature is the double N-H...N intermolecular hydrogen bonds between two 6mpH(2)(+)(A) cations. This kind of interaction, mimicking that of natural nucleobases, can be very valuable in designing new therapeutic purine derivati…
Hydrogen bond mediated intermolecular magnetic coupling in mononuclear high spin iron(iii) Schiff base complexes: synthesis, structure and magnetic s…
2020
The crystal structure and magnetic properties of two mononuclear iron(III) Schiff base complexes, [FeL1(NCS)2] (1), HL1 = 2-[1-[[2-[(2-aminoethyl)amino]ethyl]imino]ethyl]phenol and [FeL2(N3)Cl] (2), HL2 = 2-(-1-(2-(2-aminoethylamino)ethylimino)ethyl)-4-methylphenol are reported. Each complex contains a Fe(III) ion surrounded by a N3O Schiff base ligand and two NCS− ligands (in 1) or one N3− and one Cl− ligands (in 2). The magnetic properties can be well reproduced with zero field splittings in the high spin S = 5/2 Fe(III) ions and weak intermolecular Fe–Fe interactions mediated by hydrogen bonds. This intermolecular antiferromagnetic interaction has been validated by using DFT calculations…
Dimeric capsules of tetraurea calix[4]arenes. MD simulations and X-ray structure, a comparison
2002
The single crystal X-ray structure of a homodimer of a tetra(tolylurea) calix[4]arene including a tetraethylammonium cation as guest shows an expansion of the capsule and a distortion of its shape, in comparison to the structure of a similar dimer with an encapsulated benzene molecule. Thus, only 8 of 16 possible hydrogen bonds are present in the hydrogen bonded belt holding together the two hemispheres. The encapsulated cation is disordered over two equivalent positions with two methyl groups pointing to the equator, while two methyl groups pointing to the poles form CH–π interactions with the inner surfaces of the calixarene cavities. MD simulations are in agreement with the distorted X-r…
N-[1-(Silatran-1-yl)propyl]pentafluorobenzamide
2007
In the title compound {systematic name: N-[3-(5-aza-2,8,9-trioxa-1-silabicyclo[3.3.3]undecan-1-yl)propyl]pentafluorobenzamide}, C16H19F5N2O4Si, unexpected weak anion⋯π-type C=O⋯C(aromatic) interactions form a dimer [O⋯C distances of 3.096 (3) and 3.036 (3) A]. These dimers are further connected by a normal N—H⋯O hydrogen bond [2.955 (2) A], from the amide H atom to one of the silatrane O atoms. Also, four intermolecular contacts between CH groups and silatrane O and F atoms [3.101(3)–3.406 (3) A] are observed.
Crystal Structures and Thermal Behavior of Isostructural Bis(dibenzyldimethylammonium) Tetrachlorometallate [M = Mn(II), Co(II), Ni(II) and Zn(II)] S…
2007
Five isostructural bis(dibenzyldimethylammonium) tetrachlorometallate solvate complexes [M = Mn(II), Co(II), Ni(II) or Zn(II)] were crystallized from acetonitrile and/or methanol solutions. The crystal structures are compared to those of the analogous, isostructural copper compounds (X = Cl or Br) reported earlier. The complexes crystallize in the monoclinic space group P21/n with Z = 4, and unit cell dimensions of a ≈ 14.1, b ≈ 16.1, c ≈ 15.7 °A and β ≈ 108 - 109°. The asymmetric unit of these compounds contains one MCl4 2− anion, two Bz2Me2N+ cations in theW-conformation and one half of a disordered solvent molecule (acetonitrile or methanol). The geometry of the MCl4 2− anion is close to…
The black female slave takes literary revenge: Female gothic motifs against slavery in Hannah Crafts’s "The Bondwoman’s Narrative"
2015
The Bondwoman’s Narrative is a novel that functions as a story made up from Hannah Crafts’s experiences as a bondwoman and thus merges fact and fiction giving a thoroughly new account of slavery both committed to reality and fiction. Following and taking over the Gothic literary genre that spread in Europe as a reaction toward the Romantic spirit, Crafts uses it to denounce the degrading slavery system and, mainly, to scathingly attack the patriarchal roots that stigmatize black women as the ultimate victims. It is my contention that Hannah Crafts uses the female Gothic literary devices both to attack slavery and also to stand as a proper (African) American citizen capable of relating to th…
Taylor on Solidarity
2009
After characterizing Taylor’s general approach to the problems of solidarity, we distinguish and reconstruct three contexts of solidarity in which this approach is developed: the civic, the socio-economic, and the moral. We argue that Taylor’s distinctive move in each of these contexts of solidarity is to claim that the relationship at stake poses normatively justified demands, which are motivationally demanding, but insufficiently motivating on their own. On Taylor’s conception, we need some understanding of extra motivational sources which explain why people do (or would) live up to the exacting demands. Taylor accepts that our self-understanding as members of either particular communiti…
Effect of saliva contamination on bracket failure with a self-etching primer: A prospective controlled clinical trial
2010
Introduction The aim of this study was to evaluate in vivo the effect of saliva contamination at different stages of the bonding procedure on the bond failure rate and the adhesive remaining on teeth after debonding brackets bonded with a hydrophilic self-etching primer (Transbond Plus self-etching primer [TSEP], 3M Unitek, Monrovia, Calif). Methods This was a prospective controlled clinical trial. The sample consisted of 46 patients with similar treatment plans and mechanotherapies. Stainless steel brackets (n = 531) were bonded with TSEP. The patients were divided into 2 groups: contamination with saliva before TSEP application and contamination with saliva after TSEP application. In both…
Effect of cyclic loading on fracture strength and microleakage of a quartz fiber dowel with different adhesive, cement and resin core material combin…
2010
Background: This study evaluated the performance of different adhesive-cement-core combinations coupled with quartz fiber dowels after cyclic loading and fracture strength tests and assessed the microleakage using dye penetration method. Methods: Forty maxillary canines (n=10 per group) were restored with fiber dowels (Quartz fiber DT Light Post) and four adhesive-cement-core material combinations [(Group 1: All-Bond 2+C&B (root) / All-Bond 2+Biscore (core); Group 2: All-Bond 2+Bisfil 2B (root) / All-Bond 2+Bisfil 2B (core); Group 3: Scotchbond 1+RelyX ARC (root) / Scotchbond 1+Supreme (core); Group 4: RelyX Unicem (root) / Scotchbond 1+Filtek Supreme (core)]. The specimens were initially c…