Search results for "Fluorides"

Supramolecular chirality and symmetry breaking of fluoride complexes of achiral foldamers

2017

Aromatic oligoamide foldamers containing a central pyridine-2,6-dicarbonyl motif are partially preorganized to favor the binding of fluoride anions. In the solid state, the foldamer-fluoride complexes form achiral, polar and chiral crystal structures depending on the chemical structure of the foldamer. One of the six foldamers studied here, a C2v symmetrical foldamer (1), formed repeatedly chiral crystal structures when crystallized with tetra-butylammonium fluoride, showing supramolecular bulk chirality and symmetry breaking in crystallization.

The (2-phenyl-2-trimethylsilyl)ethyl-(PTMSEL)-linker in the synthesis of glycopeptide partial structures of complex cell surface glycoproteins.

2003

The (2-phenyl-2-trimethylsilyl)ethyl-(PTMSEL) linker represents a novel fluoride-sensitive anchor for the solid-phase synthesis of protected peptides and glycopeptides. Its cleavage is achieved under almost neutral conditions using tetrabutylammonium fluoride trihydrate in dichloromethane thus allowing the construction of complex molecules sensitive to basic and acidic media commonly required for the cleavage of standard linker systems. The advantages of the PTMSEL linker are demonstrated in the synthesis of glycopeptides from the liver intestine (LI)-cadherin and the mucin MUC1, bearing carbohydrate moieties such as N-linked chitobiose or O-linked sialyl-T(N)-residues. The synthesis of the…

Topical Fluoride for Preventing Dental Caries in Children and Adolescents

2012

The use of topically applied fluoride has been widely researched as a means to reduce the risk of dental caries in conjunction with other treatment modalities (mechanical oral hygiene, dietary control, antimicrobial intervention, pit and fissure sealants). There is overwhelming evidence that reports not only the significance and importance of the use of fluoride as a caries-preventive agent, but also how safe fluoride application is when used appropriately, particularly in higher risk individuals and populations. This paper reviews the caries-protective benefits of topical fluoride application in children and adolescents, with an emphasis on the clinical efficacy and safety of the vehicles …

NMR Spectroscopic Evidence for the Intermediacy of XeF3– in XeF2/F– Exchange, Attempted Syntheses and Thermochemistry of XeF3– Salts, and Theoretical…

2010

The existence of the trifluoroxenate(II) anion, XeF3−, had been postulated in a prior NMR study of the exchange between fluoride ion and XeF2 in CH3CN solution. The enthalpy of activation for this exchange, ΔH⧧, has now been determined by use of single selective inversion 19F NMR spectroscopy to be 74.1 ± 5.0 kJ mol−1 (0.18 M) and 56.9 ± 6.7 kJ mol−1 (0.36 M) for equimolar amounts of [N(CH3)4][F] and XeF2 in CH3CN solvent. Although the XeF3− anion has been observed in the gas phase, attempts to prepare the Cs+ and N(CH3)4+ salts of XeF3− have been unsuccessful, and are attributed to the low fluoride ion affinity of XeF2 and fluoride ion solvation in CH3CN solution. The XeF3− anion would rep…

Community water fluoridation and caries prevention: a critical review.

2006

The aim of this paper was to critically review the current role of community water fluoridation in preventing dental caries. Original articles and reviews published in English language from January 2001 to June 2006 were selected through MEDLINE database. Other sources were taken from the references of the selected papers. For the past 50 years community water fluoridation has been considered the milestone of caries prevention and as one of the major public health measures of the 20th century. However, it is now accepted that the primary cariostatic action of fluoride occurs after tooth eruption. Moreover, the caries reduction directly attributable to water fluoridation have declined in the…

Effects of retinotoxic drugs on rats heterozygotic for recessive retinitis pigmentosa

1971

One-pot cross-enyne metathesis (CEYM)-Diels-Alder reaction of gem-difluoropropargylic alkynes.

2013

Propargylic difluorides 1 were used as starting substrates in a combination of cross-enyne metathesis and Diels–Alder reactions. Thus, the reaction of 1 with ethylene in the presence of 2nd generation Hoveyda–Grubbs catalyst generates a diene moiety which in situ reacts with a wide variety of dienophiles giving rise to a small family of new fluorinated carbo- and heterocyclic derivatives in moderate to good yields. This is a complementary protocol to the one previously described by our research group, which involved the use of 1,7-octadiene as an internal source of ethylene.

Spectroscopie des hexafluorures à nombre impair d'électrons

1995

From a theoretical point of view, a tensorial formalism adapted to the study of molecules or octahedral ions with a half-integer angular momentum has been developed for the first time. We have used here the method of projective representations, more consistent than that of double groups. A complete set of coupling coefficients and formulas, as well as the corresponding computing programs have been elaborated. This has firstly allowed to write a simple model describing the vibronic structure of colored hexafluorides. Then, somme applications of this formalism to the study of rovibronic couplings of XY6 molecules in a fourfold degenerate electronic state have been considered, especially conce…