Phase stabilities solution phases

An example where the presence of a counterion makes a difference between the gas phase and solution phase pathways involves the intriguing carbanion produced on deprotonation of 1,3-dithiane at C-2. In solution, this species, almost invariably produced by reaction of the dithiane with butyllithium, is widely used as an acyl anion equivalent in synthetic chemistry. Its importance for the present work is that this is a configurationally stable lithiated species in solution the carbanion stays sp -hybridized, and the lithium prefers the equatorial position, even to the extent of driving a terr-butyl group on the same acidic C-2 carbanion to the axial position in the lithiocarbon species. The carbanion is thought to be stabilized primarily by orbital overlap with the C-S antibonding orbitals, as opposed to more conventional polar and 7t-resonance stabilization. ... 

The medium-film thickness is about 0.3-0.6 pm and generally offers the best compromise of sample capacity, retentivity, and phase stability. The phase ratio determines the capacity of the column and influences its retentivity of solutes. The phase ratio (j8) can be defined as the ratio of the inner column radius to that of the product of twice the stationary-phase film thickness or 0 = r/2df. We can now also use phase ratios to group film thicknesses and now say that thick-film columns have phase ratios of less than about 80. (In capillary SFC the typical stationary-phase film thicknesses are 0.1-0.3 pm.) The effective phase ratio can change in capillary SFC, depending on the characteristics of the stationary phase and the operating density [57]. The change in phase ratio can be attributable to a swelling of the stationary phase under certain SFC conditions. 

Diversity-Oriented Synthesis of Small Molecules Natural Product Inhibitors to Study Biological Function Nucleic Acid Synthesis, Key Reactions of Proteins Stmcture, Function and Stability Solution-Phase Synthesis of Biomolecules... 

Phenomena at Liquid Interfaces. The area of contact between two phases is called the interface three phases can have only aline of contact, and only a point of mutual contact is possible between four or more phases. Combinations of phases encountered in surfactant systems are L—G, L—L—G, L—S—G, L—S—S—G, L—L, L—L—L, L—S—S, L—L—S—S—G, L—S, L—L—S, and L—L—S—G, where G = gas, L = liquid, and S = solid. An example of an L—L—S—G system is an aqueous surfactant solution containing an emulsified oil, suspended soHd, and entrained air (see Emulsions Foams). This embodies several conditions common to practical surfactant systems. First, because the surface area of a phase iacreases as particle size decreases, the emulsion, suspension, and entrained gas each have large areas of contact with the surfactant solution. Next, because iaterfaces can only exist between two phases, analysis of phenomena ia the L—L—S—G system breaks down iato a series of analyses, ie, surfactant solution to the emulsion, soHd, and gas. It is also apparent that the surfactant must be stabilizing the system by preventing contact between the emulsified oil and dispersed soHd. FiaaHy, the dispersed phases are ia equiUbrium with each other through their common equiUbrium with the surfactant solution. 

Low temperatures can cause a phase separation in stabilized solutions in which case one phase can become deficient in stabilizer and subject to runaway reactions. Acrylic acid can crystallize out of stabilized solution, and subsequent thawing of these essentially pure acrylic acid crystals can initiate runaway reactions, often with severe consequences. Thawing of crystallized (frozen) materials needs to be accomplished using established procedures in thaw boxes or similar devices. If established procedures are not available, a safety review needs to be conducted and a procedure developed prior to thawing the material. 

There is an excellent correlation between these data and the gas-phase data, in terms both of the stability order and the energy differences between carbocations. A plot of the gas-phase hydride affinity versus the ionization enthalpy gives a line of slope 1.63 with a correlation coefficient of 0.973. This result is in agreement with the expectation that the gas-phase stability would be somewhat more sensitive to structure than the solution-phase stability. The energy gap between tertiary and secondary ions is about 17kcal/mol in the gas phase and about 9.5 kcal/mole in the SO2CIF solution. 

P-Fluonne or fluonne further removed from the cation center always inductively destabilizes carbocabons [115, 116] No simple p-fluoroalkyl cations have been observed in either the gas phase or solution, and unhke the cases of the other halogens, there is no evidence for formation of alkyl fltioronium ions (5) in solution [117, 118], although (CH3)2F is long-hved m the gas phase [119] The only P-fluonnated cations observed in solution are those that benefit from additional conjugativc stabilization, such as a-trifluoromethylbenzyl cations [112] and per-fluonnated allyl [120], cydopropenium [112], and tropylium [121] ions... 

G. Foumet, Order-disorder phenomena in solid solutions, in. Phase Stability in Metals and Alloys", P S. 

The development of nucleic acid-based therapeutics is not as straightforward as researchers had initially anticipated. Stability, toxicity, specificity, and delivery of the compounds continue to be challenging issues that need further optimization. In recent years, researchers have come up with intricate solutions that have greatly improved the efficacy of potential antisense, ribozyme, as well as RNAi-based therapeutics. Clinical trials for all these types of nucleic acid-based therapeutics are underway. So far, data from several trials and studies in animal models look promising, in particular, the therapies that trigger the RNAi pathway. However, history has shown that compounds that do well in phase I or phase II clinical trials may still fail in phase III. A striking example is the nonspecific suppression of angiogenesis by siRNA via toII-Iike receptor 3 (Kleinman et al. 2008). It will become clear in the near future which compounds will make it as a new class of antiviral therapeutics. 

As might be expected, the results from both theory and experiment suggest that the solution is more than a simple spectator, and can participate in the surface physicochemical processes in a number of important ways [Cao et al., 2005]. It is well established from physical organic chemistry that the presence of a protic or polar solvent can act to stabilize charged intermediates and transition states. Most C—H, O—H, C—O, and C—C bond breaking processes that occur at the vapor/metal interface are carried out homolytically, whereas, in the presence of aqueous media, the hetero-lytic pathways tend to become more prevalent. Aqueous systems also present the opportunity for rapid proton transfer through the solution phase, which opens up other options in terms of reaction and diffusion. 

Relatively few investigations involving palladium carbonyl clusters have been carried out, partly because palladium per se does not form stable, discrete homometallic carbonyl clusters at room temperature in either solid or solution states.114,917-922 Nevertheless, solution-phase palladium carbonyl complexes have been synthesized with other stabilizing ligands (e.g., phosphines),105,923 and carbon monoxide readily absorbs on palladium surfaces.924 Moreover, gas-phase [Pd3(CO)n]-anions (n = 1-6) have been generated and their binding energies determined via the collision-induced dissociation method.925... 

Since the first report on the ferrocene mediated oxidation of glucose by GOx [69], extensive solution-phase studies have been undertaken in an attempt to elucidate the factors controlling the mediator-enzyme interaction. Although the use of solution-phase mediators is not compatible with a membraneless biocatalytic fuel cell, such studies can help elucidate the relationship between enzyme structure, mediator size, structure and mobility, and mediation thermodynamics and kinetics. For example, comprehensive studies on ferrocene and its derivatives [70] and polypy-ridyl complexes of ruthenium and osmium [71, 72] as mediators of GOx have been undertaken. Ferrocenes have come to the fore as mediators to GOx, surpassing many others, because of factors such as their mediation efficiency, stability in the reduced form, pH independent redox potentials, ease of synthesis, and substitutional versatility. Ferrocenes are also of sufficiently small size to diffuse easily to the active site of GOx. However, solution phase mediation can only be used if the future biocatalytic fuel cell... 

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