Ionic radon solutions

Radon is oxidized between -195 degrees and 25 degrees C by chlorine fluorides, bromine fluorides, iodine heptafluoride, and NiF(6)(2)- ion in hydrogen fluoride with the formation of stable solutions of radon fluoride. Electromigration studies show that the radon is present as a cation, possibly Rn(2)+ or RnF+, in several conducting solutions.     

Mitochondrial fusion intermediates revealed in vitro

The events that occur during the fusion of double-membraned mitochondria are unknown. As an essential step toward determining the mechanism of mitochondrial fusion, we have captured this event in vitro. Mitochondrial outer and inner membrane fusion events were separable and mechanistically distinct, but both required guanosine 5'-triphosphate hydrolysis. Homotypic trans interactions of the ancient outer transmembrane guanosine triphosphatase, Fzo1, were required to promote the fusion of mitochondrial outer membranes, whereas electrical potential was also required for fusion of inner membranes. Our conclusions provide fundamental insights into the molecular events driving mitochondrial fusion and advance our understanding of the evolution of mitochondrial fusion in eukaryotic cells.     

Iron-stabilized carbocations as intermediates for organic synthesis

Attachment of a transition metal moiety to an olefinic ligand presents the organic chemist with unequaled opportunities to control the regio- and stereospecificities of bond formation. Applications of cationic dienyliron-carbonyl complexes to a range of natural product syntheses have been developed. These applications show how the iron-carbonyl unit directs the regio- and stereochemistry of nucleophile addition. They also show that the iron-carbonyl unit can be used to stabilize otherwise inaccessible carbocations, thereby making them readily available as synthetic intermediates.     

Enols are common intermediates in hydrocarbon oxidation

Models for chemical mechanisms of hydrocarbon oxidation rely on spectrometric identification of molecular structures in flames. Carbonyl (keto) compounds are well-established combustion intermediates. However, their less-stable enol tautomers, bearing OH groups adjacent to carbon-carbon double bonds, are not included in standard models. We observed substantial quantities of two-, three-, and four-carbon enols by photoionization mass spectrometry of flames burning representative compounds from modern fuel blends. Concentration profiles demonstrate that enol flame chemistry cannot be accounted for purely by keto-enol tautomerization. Currently accepted hydrocarbon oxidation mechanisms will likely require revision to explain the formation and reactivity of these unexpected compounds.     

Ionic mobility in muscle cells

The diffusivities of ionic potassium, sodium, sulfate, and adenosine triphosphate inside a nmuscle cell are reduced by a factor of 2, relative to diffusivities in aqueous solution. The diffusion coefficients of nonelectrolytes are reduced by the same factor, showing that the diffusion of the ions is retarded by physical, rather than chemical, interactions. In contrast, the diffusivity of the calcium ion, which is taken up by the sarcoplasmic reticulum, is reduced fiftyfold.     

Divalent carbon intermediates: laser photolysis and spectroscopy

A brief review is given of the structures of an important class of reactive intermediates, divalent carbon species (carbenes). The electronic properties of carbenes force an unusual electronic character upon these species that, in turn, leads to intriguing physical and chemical properties. Because of the fleeting nature of carbenes, which are extraordinarily reactive, direct investigation of their structural and chemical behavior has presented a challenge to the experimentalist. The application of spectroscopic and ultrafast laser techniques has met this challenge. With the use of laser methods, along with conventional techniques, quantitative evaluation of the energetics, dynamics, and reactivities of a variety of carbenes has been possible.     

Water-inserted alpha-helical segments implicate reverse turns as folding intermediates

Information relevant to the folding and unfolding of alpha helices has been extracted from an analysis of protein structures. The alpha helices in protein crystal structures have been found to be hydrated, either externally by a water molecule hydrogen bonding to the backbone carbonyl oxygen atom, or internally by inserting into the helix hydrogen bond and forming a hydrogen-bonded bridge between the backbone carbonyl oxygen and the amide nitrogen atoms. The water-inserted alpha-helical segments display a variety of reverse-turn conformations, such as type III, type II, type I, and opened out, that can be considered as folding intermediates that are trapped in the folding-unfolding process of alpha helices. Since the alpha helix, most turns, and the extended beta strand occupy contiguous regions in the conformational space of phi, psi dihedral angles, a plausible pathway can be proposed for the folding-unfolding process of alpha helices in aqueous solution.     

Chemistry and chemical intermediates in supersonic free jet expansions

Short-lived intermediates often play key roles in determining the course of chemical reactions. Recently the combination of sophisticated laser techniques and supersonic free jet expansions has offered new insight into the structure and reactivity of such intermediates. Because of their extremely reactive nature the intermediates are produced in situ in the expansion. The free jet expansion provides cooling of the intermediates to very low temperatures, so that even complex organic free radicals and molecular ions can be identified and characterized. Radical-radical reactions and ionic cluster formation likewise proceed in the expansion and can be monitored by laser spectroscopy.     

离子液体中芳基吡唑醚的合成

在离子液体中进行了芳基吡唑酮与卤代衍生物反应合成一系列芳基吡唑醚的试验研究。结果表明,该方法具有反应条件温和、低毒、时间短、产率高、离子液体可以循环使用的优点。     

Rhodopsin: responses from transient intermediates formed during its bleaching

Fast electrical responses elicited from the transient intermediates in the bleaching of rhodopsin have been investigated in the retina of the albino rat. In the experiments we used two-flash stimuli triggered sequentially with a continuously variable time delay between them. At room temperature the potential is biphasic in wave-form. The dominant, corneal-positive component is preceded by a small, corneal-negative component. Cooling the retina to about 0 degrees C suppresses the positive component and isolates the faster, negative component. Experiments with color filters show that these two components display different spectral sensitivities and, hence, suggest that each of them is produced by a different photoproduct of bleaching.     

Porphyrin-heme pathway: regulation by intermediates in bile acid synthesis

Dihydroxycoprostane and trihydroxycoprostane, intermediates in normal bile acid synthesis in the liver, enhanced the rate of porphyrin synthesis in cultured liver cells by induction of delta-aminolevulinate synthetase, the rate-limiting enzyme for this pathway. Other 5beta-cholestane derivatives and cholest-5-ene derivatives were ineffective. The selectivity of the induction may indicate that the above-mentioned coprostanes have a physiological role in porphyrin synthesis.     

Stabilization of labile carbonyl addition intermediates by a synthetic receptor

Products of unfavorable chemical equilibria are not readily observed because their high energy and increased reactivity result in low concentrations. Biological macromolecules use binding forces to access unfavorable equilibria and stabilize reactive intermediates by isolating them from the medium. In a similar vein, we describe here a synthetic receptor that allows direct observation of labile tetrahedral intermediates: hemiaminals formed in the reaction of an aldehyde carbonyl group with amines. The receptor encapsulates alkyl-substituted primary amines, then orients them toward a covalently tethered aldehyde function. The hemiaminal intermediates appear at high concentration, confined from the bulk solution and observable at ambient temperature by conventional nuclear magnetic resonance spectroscopy.     

Ionic mechanism of cholinergic inhibition in molluscan neurons

Acetylcholine, the inhibitory transmitter to the so-called H-neurons of molluscs, produces its effect by increasing the permeability of the subsynaptic membrane to chloride ions. The change in permeability gives rise to a net influx of this anion, which hyperpolarizes the neuron. The presence of an outward pump of chloride ions is postulated to account for the required electrochemical gradient. The participation of potassium ions in this inhibitory phenomenon was not detected.     

一种离子型磁性液体的制备与性质

采用了一种新方法制备出了经ZnCl2表面调制处理的γ-Fe2O3磁性纳米微粗,并用这种微粒合成了稳定的磁性液体.利用透射电子显微镜(TEM)对该微粒进行了形态观察与粒径分析,并与未经表面调制处理的γ-Fe2O3纳米微粒进行了对比研究.利用粘度计测量了磁性液体的粘度.利用振动样品磁强计(VSM)对调制处理过的及未调制处理的纳米微粒和磁性液体的磁化性质进行了表征.实验结果表明,经ZnCl2表面调制处理过的微粒近似球形,粒径比γ-Fe2O3纳米微粒大,比饱和磁化强度比γ-Fe2O3纳米微粒小.粘度随质量分数的增大呈现非单调变化.该制备磁性液体的方法与Massart法相比,减少了处理步骤,制备方法更为简洁.