Fluorine-like lines

The stability of peptides is generally increased when natural amino acids are substituted by fluorinated analogs (e.g., tri- or hexafluoroleucine, hexafluorova-line). Such stabilization augments with the number of hexafluoroleucine residues introduced [77]. Native-like structure was preserved, but the peptides had a more structured backbone and less fluid hydrophobic core. Substitution of four leucine residues by trifluoroleucines in the leucine zipper peptide GCN4-p1d led to a substantial gain in thermal stability and resistance to chemical denaturation of the... 

Carbon-hydrogen bonds, such as those in hydrocarbons like methane and ethane, have dissociation energies close to 400 kj-mol whereas single bonds between carbon and fluorine have dissociation energies close to 500 kj-mol-1. The greater strength of a carbon-fluorine bond helps to explain why fluorocarbon polymers are very resistant to chemical attack. They are used to construct valves for corrosive gases and to line the interiors of chemical reactors. 

Count the total number of valence electrons Xenon has 8, each fluorine has 7, and 1 is subtracted to account for the positive charge, giving a total of 42. Then, decide on the probable connections between atoms, and draw a line for each bond. In the case of XeF5 +, it s likely that the five fluorines are bonded to xenon, a fifth-row atom. 

AgF with PdP4 in BrF3/BrF5 at 90 °C followed by fluorination with p2 at 250 °C gave a product the powder pattern of which showed the rhombohedral-like pattern of AgPtFe obtained in (a) together with some weak lines of an unidentified phase. 

A second important mechanism for fluorine spin-lattice and spin-spin relaxation is produced by the chemical shielding anisotropy (CSA) [13, 14, 21, 71]. The magnetic field experienced by a nuclear spin depends on both the electronic structure of the molecule and how easily the electrons can move in the molecular orientations. In addition, the CSA depends on how the molecule is oriented in the magnetic field. Like spin-spin and dipole-dipole interactions, the CSA of small, rapidly tumbling molecules will be an averaged value (the chemical shift). However, these tumbling motions cause fluctuations of the local magnetic field that lead to relaxation. Also slower reorientation, or an environment that restricts the molecular motion, will result in broader lines due to CSA. 

Perhaps the most likely immediate commercial application of carbonyl fluoride, however, arises from its spectroscopic properties. Irradiation of mixtures of COF, and H, (or D,), over a wide pressure range and at ambient temperature, with the multiline output of a continuous wave CO, laser, results in the generation of excited state HF (DF) which lases [1387]. Energy transfer from the R, line (970 cm" ) of CO, (which is close in energy to the c, band of COF,) causes the dissociation of the COF, to CO and two excited state fluorine atoms which subsequentiy react with the dihydrogen (or dideuterium). However, COF, itself has been found to effect rapid vibrational de-excitation of HF [239], an observation that suggests that the COF,/H, route to the HF laser may be of limited practicality. 

The high-intensity continuum source offers a number of advantages over narrow line sources. Secondary lines (nomesonance lines) can be used in order to reduce sensitivity, thereby avoiding dilntions. All spectral lines are available, including lines for which no HCL or EDL sources are available, such as fluorine and chlorine. In addition, molecular absorptions, such as those of diatomic fragments like CS or PO, can be used to measure sulfur and phosphorus (Huang et al.)... 

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