Primary Phosphines Studied by Gas-Phase Electron Diffraction and Quantum Chemical Calculations. Are They Different from Amines?

Noble-Eddy, Robert; Masters, Sarah L.; Rankin, David W. H.; Wann, Derek A.; Robertson, Heather E.; Khater, Brahim; Guillemin, Jean‐Claude

doi:10.1021/ic901018s

Cited by 15 publications

(18 citation statements)

References 63 publications

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“…Although few aryl–As rotational barriers are known, in general, aryl–X rotational barriers decrease as the atomic radius of X increases . The rotational barriers calculated for aryl–P bonds are low (1–3.74 kcal·mol –1 depending on aryl substituent), suggesting that the As–aryl rotational barrier in ReAsH is accessible at room temperature, with a substantial number of molecules (15.6%–0.2%, assuming a Boltzmann distribution of states) populating even the least favorable rotamer. , But more importantly, the rotationally restricted model predicts that the lifetime of the ReAsH-EDT 2 excited state will be shorter than that of ReAsH bound to a protein where little or no rotation (and thus little or no quenching) can occur. Although the excited-state lifetime of ReAsH-EDT 2 has not been reported, the reported excited-state lifetimes of FlAsH bound to the α 2A adrenergic receptor or the peptide FLNCCPGCCMEP are between 4 and 5 ns. , …”

Section: Resultsmentioning

confidence: 99%

Rotamer-Restricted Fluorogenicity of the Bis-Arsenical ReAsH

Walker¹,

Rablen

Schepartz³

2016

J. Am. Chem. Soc.

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Fluorogenic dyes such as FlAsH and ReAsH are used widely to localize, monitor, and characterize proteins and their assemblies in live cells. These bis-arsenical dyes can become fluorescent when bound to a protein containing four proximal Cys thiols – a tetracysteine (Cys4) motif. Yet the mechanism by which bis-arsenicals become fluorescent upon binding a Cys4 motif is unknown, and this nescience limits more widespread application. Here we probe the origins of ReAsH fluorogenicity using computational techniques. Our results support a model in which ReAsH fluorescence depends on the relative orientation of the aryl chromophore and the appended arsenic chelate; the fluorescence is rotamer-restricted. Our results do not support a mechanism in which fluorogenicity arises from the relief of ring strain. The calculations identify those As-aryl rotamers that support fluorescence and those that do not and correlate well with experiment. The rotamer-restricted model we propose is supported further by biophysical studies: the excited state fluorescence lifetime of a complex between ReAsH and a high affinity Cys4 motif is longer than that of ReAsH-EDT2, and the fluorescence intensity of ReAsH-EDT2 increases in solvents of increasing viscosity. By providing a higher resolution view of the structural basis for fluorogenicity, these results provide a clear strategy for the design of more selective bis-arsenicals and better-optimized protein targets, with a concomitant improvement in the ability to characterize previously invisible protein conformational changes and assemblies in live cells.

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Section: Resultsmentioning

confidence: 99%

Rotamer-Restricted Fluorogenicity of the Bis-Arsenical ReAsH

Walker¹,

Rablen

Schepartz³

2016

J. Am. Chem. Soc.

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“…In principle this effect could be between the phosphorus lone pair and the aromatic system, or simply within the aromatic system itself, or both. In considering this, we take into account the following: (1) conjugation of the phosphino group and aromatic rings has been a most contentious issue in the literature [15,[46][47][48][49]; (2) both 1-naphthyl and 2-naphthyl substitution lead to a similar stabilization, whereas a conjugative effect to the lone pair might be expected to show a difference; (3) there appears to be no simple relationship between the basicity of the phosphine (as defined in terms of its effect on transition metal-bound carbonyls) and its airstability, which would again imply that the phosphorus 'lone pair' is not involved in the factors imparting the air-stability; (4) a higher oxidation potential of the phosphine seems to correlate with greater air-stability; (5) PES studies [46][47][48] have To understand this issue in more detail we have undertaken molecular modeling studies of many relevant primary phosphines [50]. The geometry optimizations of each of the phosphines were performed in the gas phase at the DFT level of theory using the B3LYP functional with a 6-31G * basis set, as employed in the Spartan '06 Essential edition from Wavefunction, Inc.…”

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confidence: 99%

The Primary Phosphine Renaissance

Higham¹

2011

Phosphorus Compounds

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Primary phosphines are renowned for being toxic, volatile, pyrophoric compounds which have to be handled under an inert atmosphere due to their ease of air-oxidation. Thus despite numerous potential applications, they remain underutilized precursors in synthetic chemistry. Only a small number of air-stable primary phosphines are known, and their stability is either attributable to high steric hindrance about the phosphino group or the underlying factors are as yet undetermined. This work is an account of the recent studies carried out by our research group and presents a new family of air-stable chiral primary phosphines (R)-5 and (S)-6 based on the binaphthyl backbone. The stabilization is a result of p-conjugation and is discussed with reference to naphthyl-and phenyl-based analogues. Computational studies based on the DFT B3LYP/6-31G* level of theory suggests significant p-conjugation or sufficient heteroatom presence dislocates the phosphorus away from the HOMO of the ground state and raises the energy of the HOMO in the associated radical cation, with a threshold of stability emerging. Novel phosphonites, phospholanes and bis(hydroxymethyl)phosphines were synthesized from (R)-5 and (S)-6 and tested in the catalytic asymmetric hydrosilylation of styrene.

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“…rP-C i was determined to be 187.4(4) pm, fitting with the P-C bond length in gauche-iso-propylphosphine P(iPr)H 2 [187.7(1) pm]. 29 Even this P-C bond length shows no influence of the electron-withdrawing effect from the chlorine atoms on the silicon atom when compared with P(iPr) Cl 2 [184.7 (13) pm]. 28 It has been previously reported for P(tBu) 2 (SiCl 3 ) 7 and P(tBu)(SiCl 3 ) 2 11 that the angles at the phosphorus atom are all smaller than tetrahedral (∼109.5°), caused by the influence of the high p-orbital contribution to these bonds.…”

Section: Discussionmentioning

confidence: 99%

“…A sample of iso-propyl(tert-butyl)(trichlorosilyl)phosphine (1) was synthesised by W.-W. du Mont (Braunschweig, Germany). 7 The purity of the sample was checked by 1 H NMR, 29 Si NMR, and 31 P NMR spectroscopy.…”

Section: Synthesismentioning

confidence: 99%