Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Fluorine Compounds”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 577 records · Page 32Linked to original sources
PubMed2005

Stereoelectronic and steric effects in the collagen triple helix: toward a code for strand association.

Collagen is the most abundant protein in animals. The protein consists of a helix of three strands, each with sequence X-Y-Gly. Natural collagen is most stable when X is (2S)-proline (Pro) and Y is (2S,4R)-4-hydroxyproline (4R-Hyp). We had shown previously that triple helices in which X is (2S,4S)-4-fluoroproline (4S-Flp) or Y is (2S,4R)-4-fluoroproline (4R-Flp) display hyperstability. This hyperstability arises from stereoelectronic effects that preorganize the main-chain dihedral angles in the conformation found in the triple helix. Here, we report the synthesis of strands containing both 4S-Flp in the X-position and 4R-Flp in the Y-position. We find that these strands do not form a stable triple helix, presumably because of an unfavorable steric interaction between fluoro groups on adjacent strands. Density functional theory calculations indicate that (2S,3S)-3-fluoroproline (3S-Flp), like 4S-Flp, should preorganize the main chain properly for triple-helix formation but without a steric conflict. Synthetic strands containing 3S-Flp in the X-position and 4R-Flp in the Y-position do form a triple helix. This helix is, however, less stable than one with Pro in the X-position, presumably because of an unfavorable inductive effect that diminishes the strength of the interstrand 3S-FlpC=O...H-NGly hydrogen bond. Thus, other forces can counter the benefits derived from the proper preorganization. Although (Pro-Pro-Gly)7 and (4S-Flp-4R-Flp-Gly)7 do not form stable homotrimeric helices, mixtures of these two peptides form stable heterotrimeric helices containing one (Pro-Pro-Gly)7 strand and two (4S-Flp-4R-Flp-Gly)7 strands. This stoichiometry can be understood by considering the cross sections of the two possible heterotrimeric helices. This unexpected finding portends the development of a "code" for the self-assembly of determinate triple helices from two or three strands.

Animals↗
PubMed2004

Preparation and promotion of fruit growth in kiwifruit of fluorinated N-phenyl-N'-1,2,3-thiadiazol-5-yl ureas.

Seventeen phenyl-fluorinated analogues of thidiazuron [N-phenyl-N'-(1,2,3-thiadiazol-5-yl)urea, TDZ] have been prepared and characterized. The effects of each fluorinated urea on growth and quality of kiwifruits (Actinidia deliciosa) were evaluated by comparison with untreated (control) and TDZ-treated fruits. The results obtained showed a clear dependence of the growth-promoting activity of these fluorinated ureas on the pattern and degree of fluorine substitution in the phenyl ring. The most effective for promoting fruit growth was N-(2,3,5,6-tetrafluorophenyl)-N'-(1',2',3'-thiadiazol-5'-yl)urea at 25 ppm (at harvest, treated fruits were 58% heavier than untreated ones) followed by N-(3,5-difluorophenyl)-N'-(1',2',3'-thiadiazol-5'-yl)urea at 10 ppm (50%). Comparatively, TDZ-treated fruits were 31% (10 ppm) and 38% (25 ppm) heavier than untreated ones. The results also indicate that the effects of the more active phenyl-fluorinated ureas on some standard quality parameters of fruits, for example, percent of fruit dry matter content, soluble solids contents, total titratable acids, shape, and internal structure, are similar to those of TDZ. Quantitative structure-activity relationships have been derived for the fruit growth promoting activity of the phenyl-fluorinated analogues of TDZ.

Actinidia↗
PubMed1993

Syntheses of 2,5- and 2,6-difluoronorepinephrine, 2,5-difluoroepinephrine, and 2,6-difluorophenylephrine: effect of disubstitution with fluorine on adrenergic activity.

Synthetic routes to difluorinated analogs of the adrenergic agonists, norepinephrine (NE), epinephrine (E), and phenylephrine (PE) have been developed. The syntheses were based on elaboration of the ethanolamine side chains from the appropriately polyfunctionalized benzaldehydes. The benzaldehydes were prepared from precursor difluorinated benzenes by sequential regioselective lithiations and reaction with electrophiles to introduce hydroxyl and carboxaldehyde functionalities. Binding and functional assay data demonstrate that the 2,6-difluorinated analogs are relatively inactive at both alpha- and beta-adrenergic receptors. These results are consistent with earlier observations that 2-fluoro substitution of adrenergic agonists decreases alpha-adrenergic activity whereas 6-fluoro substitution decreases beta-adrenergic activity.

Animals↗
PubMed1991

Separation of alpha 1 adrenergic and N-methyl-D-aspartate antagonist activity in a series of ifenprodil compounds.

Ifenprodil (1) represents a new class of N-methyl-D-aspartate (NMDA) antagonist. This drug also possesses potent activity at several other brain receptors (most notably alpha 1 adrenergic receptors). We have prepared the enantiomers and diastereomers of ifenprodil along with a series of partial structures in order to explore the basic structure activity relations within this class of compounds. From this study, it is clear that alpha 1 adrenergic and NMDA receptor activities may be separated by selection of the threo relative stereochemistry. Examination of the optical isomers of threo-ifenprodil (2) reveals that no further improvement in receptor selectivity is gained from either antipode. Individual removal of most of the structural fragments from the ifenprodil molecule generally results in less active compounds although fluorinated derivative 9 with threo relative stereochemistry is somewhat more potent and substantially more selective for the NMDA receptor. Finally a minimum structure for activity in this series (14) has been identified. This stripped-down version of ifenprodil possesses nearly equivalent affinity for the NMDA receptor with no selectivity over alpha 1 adrenergic receptors.

Adrenergic alpha-Antagonists↗
PubMed1999

Conceptually new sulfone analogues of the hormone 1alpha, 25-dihydroxyvitamin D(3): synthesis and preliminary biological evaluation.

A conceptually new series of vitamin D(3)-like nonfluorinated and fluorinated 16-ene side chain tert-butyl sulfones 3-7 has been synthesized. Even though these novel C,D-ring side chain analogues of the hormone 1alpha,25-dihydroxyvitamin D(3) (1,1,25D(3)) lack a terminal OH group, thought previously to be essential for high biological activity, they are highly antiproliferative and, in several cases, transcriptionally active in vitro but desirably noncalcemic in vivo. The side chain sulfone group may be binding to the nVDR as a hydrogen-bond acceptor, in contrast to the hydrogen-bond donor function of the 25-OH group of natural 1,25D(3).

Animals↗
PubMed2002

An exceptional red shift of emission maxima upon fluorine substitution.

The effect of perfluorination on photophysical properties was investigated through synthesis and photophysical characterization of two isostructural donor-acceptor-donor dye molecules. The synthesis of two versatile fluorinated benzene compounds, 1,4-difluoro-2,5-diperfluorooctylbenzene (1) and 1,4-dibromo-2,5-difluoro-3,6-diperfluorooctylbenzene (2), is presented. The X-ray structure of 2 has been determined and shows that the perfluorinated octyl chains segregate from the benzene rings in the solid state, giving rise to a layered structure. The further synthesis through Suzuki coupling reactions using 4-formylbenzeneboronic acid with (2) and 1,4-dibromo-2,5-dioctylbenzene (3) gave, respectively, 1,4' '-diformyl-2',5'-difluoro-3',6'-diperfluorooctyl-p-terphenylene (4) and 1,4' '-diformyl-2',5'-dioctyl-p-terphenylene (5). The condensation of the dialdehydes 4 and 5 with 9,10-phenanthrenequinone and ammoniumbicarbonate in glacial acetic acid gave the dye molecules 1,4' '-bis(1H-phenanthro[9,10-d]imidazol-2-yl)-2',5'-difluoro-3',6'-diperfluorooctyl-p-terphenylene (6) and 1,4' '-bis(1H-phenanthro[9,10-d]imidazol-2-yl)-2',5'-dioctyl-p-terphenylene (7), respectively. The UV-vis spectra of the two molecules are nearly identical, whereas the fluorescence spectra are very different. Compound 7 shows blue fluorescence with little solvent dependence (lambda(emission) = 410 nm in THF, CH2Cl2, and hexane), whereas compound 6 shows a highly solvent-dependent emission wavelength (lambda(emission) = 583 nm in THF, lambda(emission) = 560 nm in CH2Cl2, and lambda(emission) = 450 nm in hexane). The fluorescence red shift of compound 6 in a series of solvents with different polarity is discussed using the Lippert-Mataga equation. Fluorescence lifetime and quantum yields were also determined. Ultraviolet photoelectron spectroscopy (UPS) was performed on thin films of compound 6 and 7 on a gold substrate. The observed ionization potential was 6.15 eV for 6 and 5.85 eV for 7" [correction].

Journal Article↗
PubMed2005

Crossing conventional boundaries in half a century of research.

An overview of the research of the Olah group over five decades--ranging from synthetic reagents and methods to mechanistic-structural studies to new hydrocarbon chemistry and the development of methanol based fuels and hydrocarbon synthesis--is presented.

Acids↗
PubMed2006

Synthesis of 3-fluoroazetidines.

N-(Alkylidene or 1-arylmethylidene)-2-propenylamines were regiospecifically functionalized to novel N-(alkylidene or 1-arylmethylidene)-3-bromo-2-fluoropropylamines, which were proven to be excellent precursors for 3-fluoroazetidines.

Azetidines↗
PubMed2005

Membrane-derived fluorinated radicals detected by electron spin resonance in UV-irradiated Nafion and Dow ionomers: effect of counterions and H2O2.

Electron spin resonance (ESR) spectroscopy was used to detect and identify radicals formed by UV irradiation of Nafion and Dow perfluorinated membranes partially or fully neutralized by Cu(II), Fe(II), and Fe(III). This method allowed the monitoring of ESR signals from the paramagnetic counterions together with the appearance of membrane-derived radical species. The most surprising aspect of this study was the formation of membrane-derived radical species only in the neutralized membranes, and even in the absence of H2O2 in the case of Nafion/Cu(II) and Nafion/Fe(III). In Nafion/Cu(II), ESR spectra from radicals exhibiting hyperfine interactions with three equivalent 19F nuclei (the "quartet") and with four equivalent 19F nuclei (the "quintet") were detected. In Nafion/Fe(II) exposed to H2O2 solutions, the formation of Fe(III) was detected. Upon UV irradiation, strong signals from the chain-end radical ROCF2CF2* were detected first, followed by the appearance, upon annealing above 200 K, of the quartet signal observed in Nafion/Cu(II). In subsequent experiments with Nafion and Dow membranes neutralized by Fe(III), the ROCF2CF2* radicals were formed even in the absence of H2O2, indicating that the role of H2O2 is oxidation of Fe(II) to Fe(III); moreover, in these systems small amounts of the chain-end radicals were detected even without UV irradiation. This result validates the method used to form the radicals: the role of UV irradiation is to accelerate the formation of a signal that is produced, albeit slowly, even in the dark, and possibly during fuel cell operation. The major conclusion is that cations are involved in degradation processes; the point of attack appears to be at or near the pendant chain of the ionomer. Therefore when studying membrane stability, it is important to consider not only the formation of oxygen radicals, such as HO*, HOO*, and O2*-, that can attack the membrane but also the specific reactivity of counterions.

Copper↗
PubMed2006

Fluorosurfactants at structural extremes: adsorption and aggregation.

Fluorosurfactants with several structural modifications have been synthesized, and the air/water interface and bulk aggregation properties investigated. The compounds were fluorinated ethylene oxide (EO) nonionics where the number and position of the hydrophilic group(s) has been radically altered to generate linear, bolaform, and Y-shaped analogues. A noticeable structure-interfacial packing relationship was observed via both tensiometric measurements and neutron reflection studies: the limiting molecular areas, a(cmc), and surface excesses, gamma(cmc), are strongly dependent on the number and position of the EO headgroups. Differing bulk aqueous properties were also observed. Small-angle neutron scattering shows an evolution of micelle structure from cylindrical to disk-like aggregates on changing from Y-shaped to bolaform molecular structure.

Journal Article↗
PubMed2006

Stable superhydrophobic polybenzoxazine surfaces over a wide pH range.

In this study, we report on a simple two-step casting process designed to create a stable superhydrophobic surface. This method possesses the advantages of being both simple and inexpensive as well as utilizing non-fluorine-containing compounds. Most interestingly, we found that the as-prepared surface possesses superhydrophobic properties not only for pure water but also for corrosive water under both acidic and basic conditions. Furthermore, the superhydrophobic polybenzoxazine surfaces had excellent environmental stability with regard to both heating and organic solvent treatment in terms of the contact angle to water.

Journal Article↗
PubMed2000

A novel and efficient synthesis of 3-fluorooxindoles from indoles mediated by Selectfluor.

[reaction: see text] Treatment of several 3-substituted indoles, including derivatives of tryptophan and serotonin, with commercially available Selectfluor in acetonitrile/water furnished 3-substituted 3-fluorooxindoles in good to high yields. Since 3-fluorooxindoles obtained are sterically similar to both oxindoles and 3-hydroxyoxindoles, they should be useful as probes for investigating the enzymatic mechanism of indole biosynthesis and metabolism.

Diazonium Compounds↗
PubMed2004

Macrophage-mediated endothelial inflammatory responses to airborne particulates: impact of particulate physicochemical properties.

Epidemiological studies have implicated a role for airborne particulates of <2.5 microm diameter in the development/exacerbation of chronic cardiopulmonary disease; however, specific pathogenic mechanisms and the etiological significance of particle physicochemical properties remain unresolved. Using a microporous aluminosilicate zeolite Y as a manifold, we have synthesized 1 microm particulates of pure carbon (C), carbon-iron (C/Fe), and carbon-iron/fluoro-aluminum silicate (C-Fe/F-Al-Si). We have used these particulates, as well as coal fly ash (CFA) and diesel exhaust particulates (DEP), to test the hypotheses that human macrophages treated with particulates elaborate proinflammatory cytokines in quantities sufficient to induce endothelial adhesion molecule expression and that macrophage responses to particulate exposure vary as a function of particulate physicochemical properties. Human monocyte-derived macrophages (Mø) were exposed for 24 h to sublethal concentrations of particulates, at which time phagocytosis was evident from optical microscopy. Human arterial, microvascular, or venous endothelial cells (EC) were treated with clarified supernatants recovered from Mø cultures, stained with fluorescein-conjugated mononclonal antibodies specific for endothelial adhesion molecules intercellular adhesion molecule-1, vascular cell adhesion molecule-1, or E-selectin, and assayed by fluorescence flow cytometry. Data generated by these experiments demonstrate that while supernatants of Mø exposed to CFA and C particulates are relatively ineffective, supernatants from DEP, C/Fe, or C-Fe/F-Al-Si strongly induced adhesion molecule expression on EC, responses which were completely attenuated by antibody with blocking specificity for tumor necrosis factor alpha. Because the only difference between C and C/Fe particulates is the presence of surface iron on C/Fe, these findings suggest particulate-induced oxidative stress as a contributing factor in Mø activation and implicate redox active iron as a major determinant of particulate bioreactivity.

Air Pollutants↗
PubMed2004

Synthesis of 4,4-difluoroglycosides using ring-closing metathesis.

4-Deoxy-4,4-difluoro-glycosides have been synthesised for the first time via a direct sequence involving ring-closing metathesis and indium-mediated difluoroallylation with 1-bromo-1,1-difluoropropene in water. Two protecting group strategies were explored, one to allow protection of the primary C-6 hydroxyl group throughout the sequence, while the second was intended to allow deprotection after RCM and before dihydroxylation. The benzyl ether could be used in the first role, and pivaloyl is effective in the second. Dihydroxylations were highly stereoselective and controlled by the orientation of the glycosidic C-O bond.

Fluorine Compounds↗
PubMed2004

Effect of protonation and hydrogen bonding on the fluorescent properties and exciplex formation of N-(4-pyridyl)-1,2-naphthalimide.

The effects of fluorinated hydroxy compounds and naphthalene on the fluorescence of N-(4-pyridyl)-1,2-naphthalimide (PyNI) have been studied in toluene. The interaction of the pyridyl moiety of PyNI with hexafluoro-2-propanol (HFIP) gave rise to a hydrogen-bonded complex, whereas a more stable, hydrogen-bonded ion pair was formed with trifluoroacetic acid (TFA). Time-resolved fluorescence measurements demonstrate that hydrogen bonding with HFIP is a reversible process, even in the excited state, and revealed the rate constants of the various energy dissipation processes. The fluorescence yield enhancement of about one order of magnitude upon the 1 : 1 binding of PyNI to HFIP or TFA is primarily attributed to the deceleration of the internal conversion, and the fluorescence proved to be the dominant deactivation pathway of the singlet excited complexes. Both PyNI and its TFA complex produced fluorescent exciplexes with naphthalene. Protonation of PyNI markedly decreases the energy of the exciplex, leading to faster radiationless energy dissipation as well as to slow dissociation into an excited PyNI-TFA complex and ground-state naphthalene.

Journal Article↗