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We design and synthesize four fused-ring electron acceptors based on 6,6,12,12-tetrakis(4-hexylphenyl)-indacenobis(dithieno[3,2-b;2',3'-d]thiophene) as the electron-rich unit and 1,1-dicyanomethylene-3-indanones with 0-2 fluorine substituents as the electron-deficient units. These four molecules exhibit broad (550-850 nm) and strong absorption with high extinction coefficients of (2.1-2.5) × 105 M-1 cm-1. Fluorine substitution downshifts the LUMO energy level, red-shifts the absorption spectrum, and enhances electron mobility. The polymer solar cells based on the fluorinated electron acceptors exhibit power conversion efficiencies as high as 11.5%, much higher than that of their nonfluorinated counterpart (7.7%). We investigate the effects of the fluorine atom number and position on electronic properties, charge transport, film morphology, and photovoltaic properties. [ABSTRACT FROM AUTHOR]

Molecular packing in organic single crystals greatly influences their charge transport properties but can hardly be predicted and designed because of the complex intermolecular interactions. In this work, we have realized systematic fine-tuning of the single-crystal molecular packing of five benzodifurandione-based oiigo(p-phenylenevinylene) (BDOPV)-based small molecules through incorporation of electronegative fluorine atoms on the BDOPV backbone. While these molecules all exhibit similar column stacking configurations in their single crystals, the intermolecular displacements and distances can be substantially modified by tuning of the amounts and/or the positions of the substituent fluorine atoms. Density functional theory calculations showed that the subtle differences in charge distribution or electrostatic potential induced by different fluorine substitutions play an important role in regulating the molecular packing of the BDOPV compounds. Consequently, the electronic couplings for electron transfer can vary from 71 meV in a slipped stack to 201 meV in a nearly cofacial antiparallel stack, leading to an increase in the electron mobility of the BDOPV derivatives from 2.6 to 12.6 cm2 V 1 s-1. The electron mobility of the five molecules did not show a good correlation with the LUMO levels, indicating that the distinct difference in charge transport properties is a result of the molecular packing. Our work not only provides a series of high-electron-mobility organic semiconductors but also demonstrates that fluorination is an effective approach for fine-tuning of single-crystal packing modes beyond simply lowering the molecular energy levels. [ABSTRACT FROM AUTHOR]

Fluorogenic probes, due to their often greater spatial and temporal sensitivity in comparison to permanently fluorescent small molecules, represent powerful tools to study protein localization and function in the context of living systems. Herein, we report fluorogenic probe 4, a 1,3,4-oxadiazole designed to bind selectively to transthyretin (TTR). Probe 4 comprises a fluorosulfate group not previously used in an environment-sensitive fluorophore. The fluorosulfate functional group does not react covalently with TTR on the time scale required for cellular imaging, but does red shift the emission maximum of probe 4 in comparison to its nonfluorosulfated analogue. We demonstrate that probe 4 is dark in aqueous buffers, whereas the TTR-4 complex exhibits a fluorescence emission maximum at 481 nm. The addition of probe 4 to living HEK293T cells allows efficient binding to and imaging of exogenous TTR within intracellular organelles, including the mitochondria and the endoplasmic reticulum. Furthermore, live Caenorhabditis elegans expressing human TTR transgenically and treated with probe 4 display TTR- 4 fluorescence in macrophage-like coelomocytes. An analogue of fluorosulfate probe 4 does react selectively with TTR without labeling the remainder of the cellular proteome. Studies on this analogue suggest that certain aryl fluorosulfates, due to their cell and organelle permeability and activatable reactivity, could be considered for the development of protein-selective covalent probes. [ABSTRACT FROM AUTHOR]

This Communication describes a successful olefin cross-metathesis with tetrafluoroethylene and its analogues. A key to the efficient catalytic cycle is interconversion between two thermodynamically stable, generally considered sluggish, Fischer carbenes. This newly demonstrated catalytic transformation enables easy and short-step synthesis of a new class of partially fluorinated olefins bearing plural fluorine atoms, which are particularly important and valuable compounds in organic synthesis and medicinal chemistry as well as the materials and polymer industries. [ABSTRACT FROM AUTHOR]

We explore the effect of fluorine doping on hydrophobicity of nanoporous silicon carbide-derived carbon (SiCDC), and investigate the underlying barriers for adsorption and diffusion of water vapor and C 0 2 in the fluorinated and nonfluorinated structures. We develop atomistic models of fluorine-doped SiCDC at three different levels of fluorination, based on a hybrid reverse Monte Carlo constructed model of SiCDC, and develop a novel first-principles force field for the simulation of adsorption and transport of water and C 0 2 in the fluorine-doped carbon materials. We demonstrate an apparent dual effect of fluorination, showing that while fluorination generates more hydrophilic carbon surfaces, they actually act as more hydrophobic structures due to enhanced energy barriers in the disordered network of microporous carbon. While an increase in adsorption energy and in water uptake is seen for fluorine-doped carbon, large internal free energy barriers as well as the results of MD simulations demonstrate that the increased adsorption is kinetically limited and not experimentally observable on practical time scales. We show that an increase in apparent hydrophobicity due to fluorination is mediated by larger free energy barriers arising from stronger binding of fluid molecules inside the pore network, as opposed to repulsion or steric hindrance to the diffusion of molecules through narrow pore entries. For carbon dioxide, adsorption enthalpies and activation energy barriers are both decreased on fluorination, indicating weakened solid--fluid binding energies in the fluorinated systems. [ABSTRACT FROM AUTHOR]

“Fluoro” refers to both fluorescent and fluorinated compounds. Despite the shared prefix, there are very few fluorescent molecules that are soluble in perfluorinated solvents. This paucity is surprising, given that optical microscopy is a ubiquitous technique throughout the physical sciences and the orthogonality of fluorous materials is a commonly exploited strategy in synthetic chemistry, materials science, and chemical biology. We have addressed this shortage by synthesizing a panel of “fluorofluorophores,” fluorescent molecules containing high weight percent fluorine with optical properties spanning the visible spectrum. We demonstrate the utility of these fluorofluorophores by preparing fluorescent perfluorocarbon nanoemulsions. [ABSTRACT FROM AUTHOR]

The synthesis of a pentadentate ligand with strategically designed fluorinated arene groups in the second coordination sphere of a nonheme iron center is reported. The oxidatively resistant fluorine substituents allow for the trapping and characterization of an FeIV ( O ) complex at —20 °C. Upon warming of the FeIV( O ) complex, an unprecedented arene C—F hydroxylation reaction occurs. Computational studies support the finding that substrate orientation is a critical factor in the observed reactivity. This work not only gives rare direct evidence for the participation of an FeIV( O ) species in arene hydroxylation but also provides the first example of a high-valent iron—oxo complex that mediates aromatic C— F hydroxylation. [ABSTRACT FROM AUTHOR]

An operationally simple protocol for the selective deoxyfluorination of structurally complex alcohols is presented. Several fluorinated derivatives of natural products and pharmaceuticals have been prepared to showcase the potential of the method for late-stage diversification and its functional group compatibility. A series of simple guidelines for predicting the selectivity in substrates with multiple alcohols is given. [ABSTRACT FROM AUTHOR]

On the basis of ¹H NMR spectroscopic analyses and single crystal X-ray crystal structural data, the ion-pair receptor 1, bearing a calix[4]pyrrole for anion binding and calix[4]arene crown-5 for cation recognition, was found to act as a receptor for both CsF and KF ion-pairs. Both substrates are bound strongly but via different binding modes and with different complexation dynamics. Specifically, exposure to KF in 10% CD3OD in CDCl3 leads first to complexation of the K+ cation by the calix[4]arene crown-5 moiety. As the relative concentration of KF increases, then the calix[4]pyrrole subunit binds the F- anion. Once bound, the K+ cation and the F- anion give rise to a stable 1:1 ion-pair complex that generally precipitates from solution. In contrast to what is seen with KF, the CsF ion-pair interacts with receptor 1 in two different modes in 10% CD3OD in CDCl3. In the first of these, the Cs+ cation interacts with the calix[4]arene crown-5 ring weakly. In the second interaction mode, which is thermodynamically more stable, the Cs+ cation and the counteranion, F-, are simultaneously bound to the receptor framework. Further proof that system 1 acts as a viable ion-pair receptor came from the finding that receptor 1 could extract KF from an aqueous phase into nitrobenzene, overcoming the high hydration energies of the K+ and F- ions. It was more effective in this regard than a 1:1 mixture of the constituent cation and anion receptors (4 and 5). [ABSTRACT FROM AUTHOR]

The symmetry of the hydrogen bond in hydrogen difluoromaleate monoanion is probed by X-ray crystallography and by the NMR method of isotopic perturbation in water, in two aprotic organic solvents, and in an isotropic liquid crystal. The X-ray crystal structure of potassium hydrogen difluoromaleate shows a remarkably short O-O distance of 2.41 Å and equal O-H distances of 1.206 Å, consistent with a strong and symmetric hydrogen bond. Incorporation of 18O into one carboxyl group allows investigation of the symmetry of the H-bond in solution by the method of isotopic perturbation. The 19F NMR spectra of the mono-18O-substituted monoanion in water, CD2Cl2, and CD3CN show an AB spin system, corresponding to fluorines in different environments. The difference is attributed to the perturbation of the acidity of a carboxylic acid by 18O, not to the mere presence of the 18O, because the mono-18O dianion shows equivalent fluorines. Therefore, it is concluded that the monoanion exists as an equilibrating pair of interconverting tautomers and not as a single symmetric structure not only in water but also in organic solvents. However, in the isotropic liquid crystal phase of 4-cyanophenyl 4-heptylbenzoate, tetrabutylammonium hydrogen difluoromaleate-18O shows equivalent fluorines, consistent with a single symmetric structure. These results support earlier studies, which suggested that the symmetry of hydrogen bonds can be determined by the local environment. [ABSTRACT FROM AUTHOR]

Control over faceting in nanocrystals (NCs) is pivotal for many applications, but most notably when investigating catalytic reactions which occur on the surfaces of nanostructures. Anatase titanium dioxide (TiO2) is one of the most studied photocatalysts, but the shape dependence of its activity has not yet been satisfactorily investigated and many questions still remain unanswered. We report the nonaqueous surfactant-assisted synthesis of highly uniform anatase TiO2 NCs with tailorable morphology in the 10-100 nm size regime, prepared through a seeded growth technique. Introduction of titanium(IV) fluoride (TiF4) preferentially exposes the {001} facet of anatase through in situ release of hydrofluoric acid (HF), allowing for the formation of uniform anatase NCs based on the truncated tetragonal bipyramidal geometry. A method is described to engineer the percentage of {001} and {101} facets through the choice of cosurfactant and titanium precursor. X-ray diffraction studies are performed in conjunction with simulation to determine an average NC dimension which correlates with results obtained using electron microscopy. In addition to altering the particle shape, the introduction of TiF4 into the synthesis results in TiO2 NCs that are blue in color and display a broad visible/NIR absorbance which peaks in the infrared (λmax ≈ 3400 nm). The blue color results from oxygen vacancies formed in the presence of fluorine, as indicated by electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) studies. The surfactants on the surface of the NCs are removed through a simple ligand exchange procedure, allowing the shape dependence of photocatalytic hydrogen evolution to be studied using monodisperse TiO2 NCs. Preliminary experiments on the photoreforming of methanol, employed as a model sacrificial agent, on platinized samples resulted in high volumes of evolved hydrogen (up to 2.1 mmol h-1 g-1) under simulated solar illumination. Remarkably, the data suggest that, under our experimental conditions, the {101} facets of anatase are more active than the {001}. [ABSTRACT FROM AUTHOR]

Iodo- and bromodifluoromethylated compounds are important synthetic intermediates and halogen-bond acceptors. However, direct introduction of -CF2I and -CF2Br groups through nucleophilic addition is particularly challenging because of the high tendency of decomposition of CF2Br- and CF2I- to difluorocarbene. In this work, we have developed a formal nucleophilic iodo- and bromodifluoromethylation for carbonyl compounds. The key strategy of the method is the halogenation of in situ-generated sulfinate intermediates from the Julia-Kocienski reaction to change the reaction pathway from the traditional olefination to alkylation. Interesting halogen-π interactions between the halocarbon and aromatic donors were observed in the crystal structures of the products. The method could also be extended to the introduction of other fluorinated groups, such as -CFClBr, -CFClI, -CFBr2, and -CFMeI, which opens up new avenues for the synthesis of a wide range of useful fluorinated products. [ABSTRACT FROM AUTHOR]

We address the recent debate surrounding the ability of 2,4-difluorotoluene (F), a low-polarity mimic of thymine (T), to form a hydrogen-bonded complex with adenine in DNA. The hydrogen bonding ability of F has been characterized as small to zero in various experimental studies, and moderate to small in computational studies. However, recent X-ray crystallographic studies of difluorotoluene in DNA/RNA have indicated, based on interatomic distances, possible hydrogen bonding interactions between F and natural bases in nucleic acid duplexes and in a DNA polymerase active site. Since F is widely used to measure electrostatic contributions to pairing and replication, it is important to quantify the impact of this isostere on DNA stability. Here, we studied the pairing stability and selectivity of this compound and a closely related variant, dichlorotoluene deoxyriboside (L), in DNA, using both experimental and computational approaches. We measured the thermodynamics of duplex formation in three sequence contexts and with all possible pairing partners by thermal melting studies using the van't Hoff approach, and for selected cases by isothermal titration calorimetry (ITC). Experimental results showed that internal F-A pairing in DNA is destabilizing by 3.8 kcal/mol (van't Hoff, 37 °C) as compared with T-A pairing. At the end of a duplex, base-base interactions are considerably smaller; however, the net F-A interaction remains repulsive while T-A pairing is attractive. As for selectivity, F is found to be slightly selective for adenine over C, G, T by 0.5 kcal mol, as compared with thymine's selectivity of 2.4 kcal/mol. Interestingly, dichlorotoluene in DNA is slightly less destabilizing and slightly more selective than F, despite the lack of strongly electronegative fluorine atoms. Experimental data were complemented by computational results, evaluated at the M06-2X/6-31+G(d) and MP2/cc-pVTZ levels of theory. These computations suggest that the pairing energy of F to A is 28% of that of T-A, and most of this interaction does not arise from the F…HN interaction, but rather from the CH…N interaction. The nucleobase analogue shows no inherent selectivity for adenine over other bases, and L-A pairing energies are slightly weaker than for F-A. Overall, the results are consistent with a small favorable noncovalent interaction of F with A offset by a large desolvation cost for the polar partner. We discuss the findings in light of recent structural studies and of DNA replication experiments involving these analogues. [ABSTRACT FROM AUTHOR]

Two protocols for the nickel-catalyzed cross-coupling of aryl fluorides with aryl boronic esters have been developed. The first employs metal fluoride cocatalysts, such as ZrF4 and TiF4, which enable Suzuki-Miyaura reactions of aryl fluorides bearing electron-withdrawing (ketones, esters, and CF3), aryl and alkenyl groups as well as those comprising fused aromatic rings, such as fluoronaphthalenes and fluoroquinolines. The second protocol employs aryl fluorides bearing ortho-directing groups, which facilitate the difficult C-F bond activation process via cyclometalation. N-heterocycles, such as pyridines, quinolines, pyrazoles, and oxazolines, can successfully promote cross-coupling with an array of organoboronic esters. A study into the substituent effects with respect to both coupling components has provided fundamental insights into the mechanism of the nickel-catalyzed cross-coupling of aryl fluorides. [ABSTRACT FROM AUTHOR]

Efficient protocols for the syntheses of well-defined, solvent-free cations of the large alkaline-earth (Ae) metals (Ca, Sr, Ba) and their smaller Zn and Mg analogues have been designed. The reaction of 2,4-di-tert-butyl-6-(morpholinomethyl)phenol ({LO1}H), 2-{ [bis(2- methoxyethyl)amino]methyl}-4,6-di-tert-butylphenol ({LO2}H), 2-[( 1, 4,7,10-tetraoxa-13-azacyclopentadecan-13-yl)methyl]-4,6-di-tert-butylphenol ({LO3}H), and 2-{(1,4,7, 10-tetraoxa- 13-azacyclo-pentadecan-13-yl)rnethy1]-1,1,1,3,3,3-hexafluoropropan-2-ol ({RO3}H) with [H(OEt2)2]+ [H2N{B(C6F5)3}2]- readily afforded the doubly acidic pro-ligands [{LO1}HH]+[X]- (1), [{LO2}HH]+[X]-(2), [{LO3}HH]+[X]- (3), and [{RO3}HH]+[X]- (4) ({x] = [H2N{B(C6F5)3}2]). The addition of 2 to Ca[N(SiMe3)2]2-(THF)2 and Sr[N(SiMe3)2]2(THF)2 yielded [{LO2}Ca(THF)0.5]+[X] (5) and [{LO2}Sr(THF)]0.5[X]- (6), respectively. Alternatively, S could also be prepared upon treatment of {LO2}CaN(SiMe3)2 (7) with {H(OEt2)2]+[X]-. Complexes [{LO3}M]+[X]- (M = Zn, 8; Mg, 9; Ca, 10; Sr, 11; Ba, 12) and [{RO3}M]+[X] (M = Zn, 13; Mg, 14; Ca, 15; Sr, 16; Ba, 17) were synthesized in high yields (70-90%) by reaction of 3 or 4 with the neutral precursors M[N(SiMe3)i]2(THF)x (M = Zn, Mg, x = 0; M = Ca, Sr, Ba, x = 2). All compounds were fully characterized by spectroscopic methods, and the solid-sate structures of compounds 1, 3, 7, 8, 13, 14, { 1S}4 3CD2Cl2, {16}4 · 3CD2Cl2, and {{ 17}4 · EtOH}· ·3CD2Cl2 were determined by X-ray diffraction crystallography. Whereas the complexes are monomeric in the case of Zn and Mg, they form bimetallic cations in the case of Ca, Sr and Ba; there is no contact between the metal and the weakly coordinating anion. In all metal complexes, the multidentate ligand is K6-coordinated to the metal. Strong intramolecular M … F secondary interactions between the metal and F atoms from the ancillary ligands are observed in the structures of {15}4·3CD2Cl2, {16}4·3CD2Cl2, and { { 17}4·EtOH}·3CD2Cl2·VT19F {1H} NMR provided no direct evidence that these interactions are maintained in solution; nevertheless, significant Ae … F energies of stabilization of 25-26 (Ca, Ba) and 40 kcal· mol-1 (Sr) were calculated by NBO analysis on DFT-optimized structures. The identity and integrity of the cationic complexes are preserved in solution in the presence of an excess of alcohol (BnOH, iPrOH) or L-lactide (L-LA). Efficient binary catalytic systems for the immortal ring-opening polymerization of L-LA (up to 3000 equiv) are produced upon addition of an excess (5-so equiv) of external protic nucleophilic agents (BnOH, iPrOH) to 8-12 or 13-17. PLLAS with Mn up to 35000 g·mol-1 were produced in a very controlled fashion (Mw/Mn ≈ 1.10-1.20) and without epimerization. In each series of catalysts, the following order of catalytic activity was established: Mg « Zn < Ca < Sr « Ba; also, Ae complexes supported by the aryloxide ligand are more active than their parents supported by the fluorinated alkoxide ancillary, possibly owing to the presence of Ae …. F interactions in the latter case. The rate law -d[L-LA]/dt = kp · [L-LA]1.0. [16]1.0·[BnOH]1.0 was established by NMR kinetic investigations, with the corresponding activation parameters ΔH= 14.8(5) kcal·mol-1 and ΔS = -7.6(2.0) cal·K-1 · mol-1. DFT calculations indicated that the observed order of catalytic activity matches an increase of the L-LA coordination energy onto the cationic metal centers with parallel decrease of the positive metal charge. [ABSTRACT FROM AUTHOR]

Versatile, safe, shelf-stable, and easy-to-handle fluorinating agents are strongly desired in both academic and industrial arenas, since fluorinated compounds have attracted considerable interest in many areas, such as drug discovery, due to the unique effects of fluorine atoms when incorporated into molecules. This article describes the synthesis, properties, and reactivity of many substituted and thermally stable phenylsulfur trifluorides, in particular, 4-tert-butyl-2,6-dimethylpheflylsulfur trifluoride (Fluolead, 1k), as a crystalline solid having surprisingly high stability on contact with water and superior utility as a deoxofluorinating agent compared to current reagents, such as DAST and its analogues. The roles of substiuents on 1k in thermal and hydrolytic stability, fluorination reactivity, and the high-yield fluorination mechanism it undergoes have been clarified. In addition to fluorinations of alcohols, aldehydes, and enolizable ketones, 1k smoothly converts non-enolizable carbonyls to CF2 groups, and carboxylic groups to CF3 groups, in high yields. 1k also converts C(=S) and CH3SC(=S)O groups to CF2 and CF3O groups, respectively, in high yields. In addition, 1k effects highly stereoselective deoxofluoro-arylsulfinylation of diols and amino alcohols to give fluoroalkyl arylsulfinates and arylsulfinamides, with complete inversion of configuration at fluorine and the simultaneous, selective formation of one conformational isomer at the sulfoxide sulfur atom. Considering the unique and diverse properties, relative safety, and ease of handling of 1k in addition to its convenient synthesis, it is expected to find considerable use as a novel fluorinating agent in both academic and industrial arenas. [ABSTRACT FROM AUTHOR]

The reaction of 1 equiv of the disilenide Tip2Si=Si(Tip)Li (5; Tip = 2,4,6-iPr3C6H2) with para-substituted phenyl iodides, 4-X-Phl, transfers the Tip2Si=Si(Tip) moiety with elimination of lithium iodide to yield the laterally functionalized disilenes Tip2Si=Si(Tip)(4-X-Ph) [X = H (6a), F (6b), Cl (6c), Br (6d), I (6e)]. The UV-vis absorptions of 6a-d suggest a linear correlation with electronic Hammett parameters. In addition, X-ray structural analyses of 6a-d verified the theoretically predicted linear dependence of the Si=Si bond length and trans-bent angles. The p-bromophenyl-substituted disilene 6d undergoes a metal-halogen exchange reaction to give 6f (X = Li), which was trapped with Me3SiCI to afford 6g (X = SiMe3). In the case of simple phenyl halides PhX without additional functionality, the reaction with 5 proceeded smoothly for X = Br, but phenyl chlorides and fluorides did not react at room temperature even after one week, hinting at an SN2-type aromatic substitution mechanism. Reactions of p- and m- diiodobenzene with 5 afford the corresponding phenylene-bridged tetrasiladienes p-7 and m-7. While red p.7 (λmax = 508 nm) exhibits efficient conjugation of the two Si=Si bonds with the phenylene linker, the conjugation in yellow m-7 (λmax = 449 nm) is much less effective. Electrochemical studies of m-7 and p-7 as well as density functional theory calculations and electron paramagnetic resonance studies of their respective radical anions provided further support for the notion of conjugation. [ABSTRACT FROM AUTHOR]

We report the selective activation of carbon-fluorine bonds in trifluoroethylene using the diiridium complex [Ir2(CH3)(CO)2(dppm)2][OTf] (1). Coordination of trifluoroethylene in a bridging position between the two metals in 1 results in facile fluoride ion loss in three different ways. Attack by strong fluorophiles such as Me3SiOTf and HOTf results in F- removal from one of the geminal fluorines to give the cis-difluorovinyl-bridged product [Ir2(CH3)(OTf)(CO)2(μ-κ¹:η²-C(F)=CFH)(dppm)2][OTf]. A second activation can also be accomplished by addition of excess Me3SiOTf to give the fluorovinylidene-bridged product [Ir2(CH3)(OTf)(CO)2(μ-C2FH)(dppm)2][OTf]2. Interestingly, activation of the trifluoroethylene-bridged precursor by water also occurs, yielding [Ir2(CH3)(CO)2(κ¹-C(H)=CF2)(μ-OH)(dppm)2][OTf], in which the lone vicinal fluorine is removed, leaving a geminal arrangement of fluorines in the product. A [1,2]-fluoride shift can also be induced in the trifluoroethylene-bridged precursor upon the addition of CO to give the 2,2,2-trifluoroethylidene-bridged product [Ir2(CH3)(CO)3(μ-C(H)CF3)(dppm)2][CF3SO3]. Addition of hydrogen to the cis-difluorovinyl-bndged product results in the quantitative elimination of cis-difluoroethylene, while its reaction with CO yields a mixture of cis-difluoropropene and 2,3-difluoropropene by reductive elimination of the methyl and difluorovinyl groups with an accompanying isomerization in the case of the second product. Finally, protonation of the 2,2,2-trifluoroethylidene-bridged product liberates 1,1,1 -trifluoroethane, in which one hydrogen (H+) is from the acid while the other hydrogen (H-) is derived from activation of the methyl group. [ABSTRACT FROM AUTHOR]

Polyphenylsilsesquioxane [PhSiO1.5]n (PPS) and polyvinylsilsesquioxane [vinyISiO1.5]n (PVS) are polymeric byproducts of the syntheses of the related T8 octamers [PhSiO1.5]5 and [vinylSiO1.5]8. Here we demonstrate that random-structured PPS and PVS rearrange in the presence of catalytic amounts of Bu4N+F- in THF to form mixed-functionality polyhedral T10 and T12 silsesquioxane (SQ) cages in 80-90% yields. Through control of the initial ratio of starting materials, we can statistically tailor the average values for x for the vinylxPh10-xT10 and vinylxPh12-xT12 products. Metathetical coupling of x ≈ 2 vinyl cages with 4-bromostyrene produces SOs with an average of two 4-bromostyrenyl substituents. These products can be reacted via Heck coupling with vinylSi(OEt)3 to produce SOs with vinylSi(OEt)3 end-caps. Alternately, Heck coupling with the originally produced x ≈ 2 vinyl SOs leads to "beads on a chain" SQ oligomers joined by conjugated organic tethers. The functionalized T10 and T12 cages, metathesis, and Heck compounds were characterized by standard analytical methods (MALDI-TOF MS, ¹H and 13C NMR spectroscopy, TGA, and GPC). MALDI confirms the elaboration of the cages after each synthetic step, and GPC verifies the presence of higher molecular weight SO oligomers. TGA shows that all of these compounds are thermally stable in air (>300 °C). The UV-vis absorption and emission behavior of the Heck oligomers reveals exceptional red-shifts (≥60 nm) compared to the vinylSi(OEt)3 end-capped model compounds, suggesting electronic interactions through the SQ silica cores. Such phenomena may imply 3-D conjugation through the cores themselves. [ABSTRACT FROM AUTHOR]

The conformations of three 2',3'-difluoro uridine nucleosides were studied by X-ray crystallography, NMR spectroscopy, and ab initio calculations in an attempt to define the roles that the two vicinal fluorine atoms play in the puckering preferences of the furanose ring. Two of the compounds examined contained fluorine atoms in either the arabino or xylo dispositions at C2' and C3' of a 2',3'-dideoxyuridine system. The third compound also incorporated fluorine atoms in the xylo configuration on the furanose ring but was substituted with a 6-azauracil base in place of uracil. A battery of NMR experiments in D[sub2]O solution was used to identify conformational preferences primarily from coupling constant and NOE data. Both [sup1]H and [sup19]F NMR data were used to ascertain the preferred sugar pucker of the furanose ring through the use of the program PSEUROT. Compound-dependent parameters used in the PSEUROT calculations were newly derived from complete sets of conformations calculated from high-level ab initio methods. The solution and theoretical data were compared to the conformations of each molecule in the solid state. It was shown that both gauche and antiperiplanar effects may be operative to maintain a pseudodiaxial arrangement of the C2' and C3' vicinal fluorine atoms. These data, along with previously reported data by us and others concerning monofluorinated nucleoside conformations, were used to propose a model of how fluorine influences different aspects of nucleoside conformations. [ABSTRACT FROM AUTHOR]

The methylene blue, N-methylquinolinium tetrafluoroborate, and pyrylium-cation-sensitized photooxygenations of 5H, 7H-dibenzo[b,g] [1,5]dithiocin, 1, and 1,5-dithiacyclooctane, 2, have been investigated. The methylene blue sensitized reactions exhibit all of the characteristics of a singlet oxygen reaction including isotope effects for the formation of a hydroperoxysulfonium ylide and the ability of 1 and 2 to quench the time-resolved emission of singlet oxygen at 1270 nm. The product compositions in the N-methylquinolinium tetrafluoroborate and pyrylium-cation-sensitized reactions are dramatically different and are both different from that anticipated for the participation of singlet oxygen. This argues for different reaction mechanisms for all three sensitizers. However, both the quinolinium and pyrylium-cation-sensitized reactions display all of the characteristics of electron-transfer-initiated photooxygenations. Both sensitizers were quenched at nearly diffusion-limited rates by 1 and 2. Laser flash photolysis of mixtures of either sensitizer and 1 or 2 resulted in direct observation of the reduced sensitizer and the sulfide radical cation. In addition, electron-transfer reactions involving both sensitizers were shown to be exergonic. These results are consistent with the previously proposed outer sphere electron-transfer mechanism for N-methylquinolinium tetrafluoroborate and were used to argue for a new inner sphere mechanism for the pyrylium cation reactions. [ABSTRACT FROM AUTHOR]

By measuring excited state and charge dynamics in blends of an alternating polyfluorene copolymer and fullerene derivative over nine orders in time and two orders in light intensity, we have monitored the light-induced processes from ultrafast charge photogeneration to much slower decay of charges by recombination. We find that at low light intensities relevant to solar cell operation relatively fast (~30 ns) geminate recombination is the dominating charge decay process, while nongeminate recombination has a negligible contribution. The conclusion of our work is that under solar illumination conditions geminate recombination of charges may be directly competing with efficient charge collection in polymer/fullerene solar cells. [ABSTRACT FROM AUTHOR]

Convergent synthetic routes for the preparation of hitherto unknown fluorene-p-xylene oligomers (containing up to 10 fluorene moieties) from readily available starting materials are described. The conformationally adaptable monomeric receptor (which is made of a pair of fluorene and one p-xylene ring, i.e., Zi) undergoes a simple C-C bond rotation in the presence of silver cations to produce a π-prismand-like receptor which binds a single silver cation with remarkable efficiency (i.e., K ≈ 150 00 M-1). The data on ¹H NMR spectroscopic titrations with Ag+ together with the density functional theory and AM1 calculations allows us to establish that various oligomers of Zi (i.e., Z2-Z9) also undergo ready folding into the structures that contain multiple π-prismand-like receptor sites in the presence of silver cations. The multiple cavities in Z3-Z9 accommodate a single silver cation per cavity with efficiency similar to that of Z1. [ABSTRACT FROM AUTHOR]

19F NMR is a powerful tool for monitoring protein conformational changes and interactions; however, the inability to site-specifically introduce fluorine labels into proteins of biological interest severely limits its applicability. Using methods for genetically directing incorporation of unnatural amino acids, we have inserted trifluoromethyl-L-phenylalanine (tfm-Phe) into proteins in vivo at TAG nonsense codons with high translational efficiency and fidelity. The binding of substrates, inhibitors, and cofactors, as well as reactions in enzymes, were studied by selective introduction of tfm-Phe and subsequent monitoring of the 19F NMR chemical shifts. Subtle protein conformational changes were detected near the active site and at long distances (25 Å). 19F signal sensitivity and resolution was also sufficient to differentiate protein environments in vivo. Since there has been interest in using 19F-labeled proteins in solid-state membrane protein studies, folding studies, and in vivo studies, this general method for genetically incorporating a 19F-label into proteins of any size in Escherichia coli should have broad application beyond that of monitoring protein conformational changes. [ABSTRACT FROM AUTHOR]

Treatment of 1,8-bis(diphenylhydroxymethyl)naphthalene with a mixture of [HBF4]aq and (CF3CO)2O affords the corresponding dication, 1 ,8-bis(diphenylmethylium)naphthalenediyl (12+), which was isolated as the [BF4]- salt. This dication has been fully characterized, and its structure has been studied computationally. The 13C NMR resonance of the methylium centers appears at 207.7 ppm. As indicated by an X-ray single-crystal analysis, the vicinal methylium centers are separated by 3.112(4) Å. Dication (12+) reacts with fluoride to afford [1-F]+ which has been isolated as the [BF4]- salt. The fluorine atom of [1-F]+ is connected to one of the former methylium centers through a typical C-F bond of 1.424(2) Å and forms a long interaction of 2.444(2) Å with the other methylium center. While the structure of [1-F]+ can be largely accounted for by considering a simple methylium formulation, density functional calculations followed by an Atom In Molecuies analysis as well as a calculation of the Boys localized orbitals indicate that the long C-F interaction of 2.444(2) Å corresponds to a dative bond. Hence, formulation of [1-F]+ as an unsymmetrical fluoronium must also be considered. As indicated by ¹H NMR spectroscopy, the structure of this ion is fluxional; the fluorine atom oscillates between the former methylium centers with apparent activation parameters of ΔH† = 52(±3) kJ mol-1 and ΔS† = -18(±9) J K-1 mol-1 as derived from line shape analysis. This dynamic process, which has also been studied theoretically by B3LYP density functional theory and Møller-Plesset second-order perturbation theory methods, involves symmetrical fluoronium ions as low-energy transition states. [ABSTRACT FROM AUTHOR]

Solution conformations about the metal-carbon bond of the secondary fluoroalkyl ligands in iridium complexes [IrCp*(PMe3)(RF)X] [Cp* = C5Me5 RF = CF(CF3)2, X = I (1), CH3 (2); RF = CF(CF3)- (CF2CF3), X = I (4), CH3 (5)] have been determined using 19F{¹H} HOESY techniques. The molecules adopt the staggered conformation with the tertiary fluorine in the more hindered sector between the PMe3 and X ligands, with CF3 (and CF2CF3) substituents lying in the less hindered regions between PMe3 and Cp* or X and Cp*. In molecules containing the CF(CF3)2 ligand, these conformations are identical to those adopted in the solid state. For compound 4, containing the CF(CF3)(CF2CF3) ligand, two diastereomers are observed in solution. Solution conformations and relative stereocenter configuration assignments have been obtained using 19F{¹H} HOESY and correlated with the X-ray structure for the major diastereomer of 4, which has the (Slr, Sc) or (Rlr, Rc) configuration. Relative stereocenter configurations of analogue 5, for which no suitable crystals could be obtained, were assigned using 19F{¹H} HOESY and proved to be different from 4, with 5 preferring the (Slr, Rc) or (Rlr, Sc) configuration. [ABSTRACT FROM AUTHOR]

Cp*2ZrH2 (1*) (Cp* = pentamethylcyclopentadienyl) reacts with perfluoropropene (2) to give Cp*2- ZrHF (3*) and hydrodefluorinated products under very mild conditions. Initial C-F bond activation occurs selectively at the vinylic terminal position of the olefin to exchange fluorine for hydrogen. Subsequent hydrodefluorination leads to the formation of the n-propylhydride complex Cp*2ZrH(CH2CH2CH3, which can be cleaved with dihydrogen to give propane and 1*. A theoretical study of the reaction of Cp2ZrH2 (Cp = cyclopentadienyl) and CF2=CF(CF3) has been undertaken. Several mechanisms have been examined in detail using DFT(B3PW91) calculations and are discussed for this H/F exchange: (a) internal olefin insertion/β-fluoride elimination, (b) external olefin insertion/β-fluoride elimination, and (c) F/H metathesis from either an inside or outside approach. Of these, the first case is found to be energetically preferred. Selective defluorination at the terminal carbon has been shown to be favored over defluorination at the substituted and allylic carbons. [ABSTRACT FROM AUTHOR]

Fluoride complexation of element 104, rutherfordium (Rf), produced in the 248Cm(18O,5n)261Rf reaction has been studied by anion-exchange chromatography on an atom-at-a-time scale. The anion-exchange chromatographic behavior of Rf was investigated in 1.9-13.9 M hydrofluoric acid together with those of the group-4 elements Zr and Hf produced in the 18O-induced reactions on Ge and Gd targets, respectively. It was found that the adsorption behavior of Rf on anion-exchange resin is quite different from those of Zr and Hf, suggesting the influence of relativistic effects on the fluoride complexation of Rf. [ABSTRACT FROM AUTHOR]

Photodissociation of both fluorobenzene and d[sub 5]-fluorobenzene at 193 nm under collision-free conditions has been studied in separate experiments using multimass ion imaging techniques. HF and DF eliminations were found to be the major dissociation channels. Small amounts of photofragments, C[sub 6]H[sub 4]F and C[sub 6]D[sub 4]F, corresponding to H and D atom eliminations were also observed. Dissociation rate and fragment translational energy distribution suggest that HF (DF) and H (D) atom elimination reactions occur in the ground electronic state. The potential energy surface obtained from ab initio calculations indicates that the four-center reaction in the ground electronic state is the major dissociation mechanism for the HF and DF eliminations. A comparison with photodissociation of benzene has been made. [ABSTRACT FROM AUTHOR]

(E)-2'-Fluoromethylene-2'-deoxycitidine-5'-diphosphate (FMCDP) is a potent time-dependent inactivator of the enzyme Ribonucleotide Reductase, which operates by destructing an essential tyrosil radical and performing a covalent addition to an active site residue. Considerable effort to elucidate the inhibition mechanism has been undertaken in recent years, and some insights have been obtained. Although a mechanistic proposal has been put forward, based on a general paradigm of inhibition of RNR by 2' substituted substrate analogues, details about the mechanism have remained elusive. Namely, the exact residue that adds to the inhibitor is still not identified, although mutagenesis experiments suggest that it should correspond to the E441 residue. In this work, we performed an extensive theoretical exploration of the potential energy surface of a model system representing the active site of RNR with FMCDP, using Density Functional Theory. This study establishes the detailed mechanism of inhibition, which is considerably different from the one proposed earlier. The proposed mechanism is fully consistent with available experimental data. Energetic results reveal unambiguously that the residue adding to the inhibitor is a cysteine, most probably C439, and exclude the possibility of the addition of E441. However, the E441 residue is shown to be essential for inhibition, catalyzing both the major and minor inhibition pathways, in agreement with mutagenesis results. It is shown also that the major mode of inactivation mimics the early stages of the natural substrate pathway. [ABSTRACT FROM AUTHOR]

Investigates the synthesis and characterization of highly selective fluoride receptor and its binding properties. Use of Monte Carlo free energy perturbation technique and Poisson calculations; Effect of water on the calculated free energies of binding; Electrostatic interactions that the fluoride gains by sitting lower in the phenolic activity of the receptor.

Explores the structure and electronic properties of the complexes formed by several perfluoroaromatic compounds with a number of anions. Use of density functional theory and ab initio methods; Interaction of anions with the pi-bond of the aromatic compounds; Scheme used in partitioning the interaction energies.

Examines the crystal structures of BrF[sub 4+25] and IF[sub 4+26,27] and the vibrational spectra of the CIF[sub 4+], BrF[sub 4+] and IF[sub 4+] cations [sup 22,28] and of the isoelectronic SF[sub 4], SeF[sub 4], and TeF[sub 4] molecules. Effects of fluorine bridging on the structure and vibrational spectra of ions; Method for modeling the bridging.

Explores the relative contributions of electric fields and short-range electronic interactions to fluorine shielding of 6-fluorotryptophan residues contained in the enzyme dihydrofolate reductase Escherichia coli. Binary and ternary complexes of the enzyme; Important role for short-range electronic interactions in determining fluorine shielding changes.

Part VIII. Calculates the nuclear spin--spin coupling constants for a set of compounds related structurally to 1,8-difluoronaphthalene. Use of 19fluorine nuclear magnetic resonance spectroscopy; Analysis of fluorine-fluorine distances using molecular orbital calculations; Details on exponential and linear relationships and extent of overlap interaction.

Studies the impact of bridgehead fluorine substitution on the solution- and solid-state properties of functionalized adamantanes in the preparation of fluoroadamantane. Strategies for the synthesis of fluoroadamantane; Physiochemical parameters of fluoroadamantanes.

Evaluates the synthesis, isomerization and structural characterization of bis(4-nitrophynyl)tetrafluorosulfuranes. Hypervalent sulfur fluorides as structural building blocks for functional organic materials; Novel catalytic process in the isomerization of cis isomer to the pure trans isomer.

Applies a simple solid-liquid extraction procedure over fluorous reverse-phase silica gel for light fluorous synthesis. Separation of tagged and untagged products; Organic substrates; Tagged amino acids on nitrogen; Coupling of resulting acids; Use of two-stage filtration; Isolation of yield products for purity.

Presents a study which investigated the binding of fluorolumazines to the 1-MDa capsid of lumazine synthase by nuclear magnetic resonance. Results and discussion; Experimental procedures.

Examines the four-electron photochemistry of dirhodium fluorophosphine complexes. Photoreaction of singly bonded dirhodium(II) complex, Rh2(dfpma)3Br4, where dfpma=bis(diflurophosphine)methylamine, CH3N(PF2)2; Oxidation-reduction reactions of electronically excited transition metal complexes.

Demonstrates the synthesis and characterization of the IOFb2- dianion, an XoF5E series. Structural characterization by vibrational spectroscopy; IOF52- dianion as a stable cesium salt; Pseudo-pentagonal bipyrimidal main group species incorporating five equatorial fluorine ligands and one doubly bonded oxygen ligand and one sterically active free valence pair.

Examines the structure of xenon fluorine (XeF6) and of compounds isoelectronic with it. Models for the chemical bond in XeF6 and related molecules; Results of the quantum chemical calculations; Comparison of all electron calculations with calculations in an effective core potential; Factors that determine the preference of XeF6 for an octahedron structure.

Presents carbon-13 MAS-nuclear magnetic resonance (NMR) and x-ray diffraction experiments on solid fluorobullvalene. Crystallization of the compound in the orthorhombic space group Pnam with four symmetry related molecules per unit cell; Crystal structure of fluorobullvalene; MAS spectra in the solid state.

Studies the properties of multiply-charged hexafluorometallates. Vibrational frequencies; Factors affecting the discrepancies of vibrational frequencies; Basic set trends.

Determines the fluorine kinetic isotope effects using the accelerator-produced short-lived radionuclide 18F in combination with natural 19F. Investigation of the solvent dependence of the leaving group F KIE for the nucleophilic aromatic substitution reaction of 2,4-dinitrofluorobenzene with piperidine.

Presents an experimental determination of the structure of HF-BF3 by pulsed nozzle Fourier transform microwave spectroscopy. Re-investigation of the complex by ab initio theory; Rotational specturm analysis; Structure analysis; Indications that a complex which is weakly bound in nature; Indications that the intermolcular B-F distance is shorter than the sum of van der Waals radii.

Reports results of a 13C-labeling experiment to test whether fluorine migration happens during the decomposition of ionized (CH3)2CFCH2OPh to yield ionized phenol in the gas phase. SCF computations showing a bridged, three-member cyclic transition state; Electronic bombardment flow experiments; Mass spectrometric results.

Reports on the determination of the geometric structure of fluorine nitrate by gas electron diffraction and a harmonic force field derived from matrix spectra of various isotopic species. Vibrational spectra; Normal coordinate analysis; Gas-phase structure; Theoretical calculations; Planar structure of fluorine nitrate.

Describes the synthesis and structure of two dinuclear anionic complexes from the dark garnet fluoroaryl compound. Quinone-like bridging ligands; Pt-Pt bond lengths; Comparison of crystal structure; Comparison of reactivity.

Determines the infrared vibrational spectra and mutual ligand interactions in the hydrogen-substituted main group hexafluorides HPF5- and HSF5. Synthesis of N(CH3)4HPF5- salt; Ab initio electric structure theory calculations; Comparison of internal stretching force constants; Existence of cis-effect; Hypervalent bonding scheme.