Benzene, probe molecule

The binding behaviour of benzene can be extrapolated to many other aromatic compounds such as naphthalene and benzene derivativesInterestingly, a large number of probe molecules contain aromatic rings and many of them will prefer the outer regions of micelles, whereas in bilayer systems, the same molecules prefer the interior of the aggregate ". Qearly these probes cannot be used to determine polarity of the micellar interior or the extent of water penetration therein . 

The acidity probes discussed above are the most commonly used. However, the use of many different probes has been reported in the literature. This list includes nitriles, alkanes, amines, water, di-hydrogen, deuterium, isotopically labeled molecules, benzene, etc. Probe molecules can also be used to measure basicity on zeohtes. In this case, weakly acidic molecules such as CO2, pyrrole, acetic acid and halogenated light paraffins have been used. Space does not permit discussion of these in any detail, but information about these probes and their applications can be found in the following references [87, 127-130]. 

To fully characterize and categorize the solute selectivities of GC stationary phases, Rohrschneider and McRe5molds pioneered one of the earliest characterization methods [5,6]. The Rohrschneider-McReynolds system is the oldest and widely accepted stationary phase classification systems that is based on the retention of five probe molecules namely, benzene, bufanol, 2-penfanone, nifropropane, and pyridine. Each probe molecule is used to represenf a disfincf or a combination of interactions with the stationary phase. Benzene measures dispersive interactions with weak proton acceptor properties butanol measures dipolar interactions with both proton donor and proton acceptor capabilities 2-pentanone measures dipolar interactions with proton acceptor but not proton donor capabilities nitropropane measures weak dipolar interactions and pyridine measures weak dipolar interactions with strong proton acceptor but not proton donor capabilities. 

This experiment introduces the use of a probe molecule to explore the microenvironment within a micelle. The results in this case show the environment to be quite wet, but this observation alone does not tell us where either the benzene or the water is. Any one of the... 

The coordinative and/or dissociative adsorption of various probe molecules has been used to characterize the surface properties of Ti02) which finds applications as a catalyst, photocatalyst, and sensor. Among the molecules used as probes, we mention CO (37, 38, 563-576), C02 (563, 565, 577), NO (578,579), water (580,581), pyridine (582,583), ammonia (584,585), alcohols (586, 587), ethers (including perfluoroethers) (588), ozone (589), nitrogen oxide (590), dioxygen (591), formic acid (592-594), benzene (584), benzoic acid (595), and chromyl chloride (596). 

The transport and adsorption properties of hydrocarbons on microporous zeolites have been of practical interest due to the important properties of zeolites as shape-selective adsorbents and catalysts. The system of benzene adsorbed on synthetic faujasite-type zeolites has been thoroughly studied because benzene is an ideal probe molecule and the related role of aromatics in zeolitic catalysts for alkylation and cracking reactions. For instance, its mobility and thermodynamic properties have been studied by conventional diffusion 1-6) and adsorption 7-9) techniques. Moreover, the adsorbate-zeolite interactions and related motion and location of the adsorbate molecules within the zeolite cavities have been investigated by theoretical calculations 10-15) and by various spectroscopic methods such as UV (16, 17), IR 17-23), neutron 24-27), Raman 28), and NMR 29-39). 

Solution calorimetry of the molecular probes pyrrole, A-methylpyrrole, benzene, and toluene in 35 solvents has been used by Catalan el al. to determine a solvent HBA basicity scale, ranging from the gas phase to HMPT [31a]. Analogously, a solvent HBD acidity scale was derived calorimetrically using A-methylimidazole and A-methylpyrrole as probe molecules in 3 6 solvents, ranging from the gas phase to 2,2,2-trifluoroethanol [31b]. 

The roughness of the silica surface could introduce the steric hindrance of the surface accessibility similar to the effect of the micropores. In the discussion above, we assume the ideal tubular geometry of the silica surface. The use of different probe molecules for the BET measurement of silica surface area (such as N2, Ar, Kr, benzene, etc.) leads to significant difference in the surface area values for the same silica sample. It was suggested that silica surfaces possess the property of fractals [16] this essentially means that molecules of different size will see a different surface area. 

Finally, dynamic structure-based pharmacophore models can be derived through a method first described by Carlson et al that uses multiple conformations of the target protein, which are obtained either by molecular dynamics simulation or by the use of multiple experimentally determined conformations. The binding sites of the respective snapshots are flooded with small molecular probes (e.g., methanol for hydrogen-bond interactions and benzene for aromatic hydrophobic interactions) and while the protein structure is held rigid the probe molecules are subjected to a low-temperature Monte Carlo minimization where they undergo multiple, simultaneous gas-phase... 

Probe Molecule Reaction. Two probe molecules, cumene and 1, 3, 5-triisopropylbenzene were chosen to study the active sites on the zeolite. Triisopropyl-benzene molecule is too bulky to penetrate into intracrystalline micro pore of MFI type zeolite, thus the cracking reaction takes place only on the external surface of the... 

Surface Characterization of the Stabilized Catalyst by Probe Molecule Reaction. HZSM-5 obtained from PQ Zeolite was chosen to study the mechanism of stabilization in light naphtha aromatization. The reactions of both molecules were carried out over stabilized and unstabilized HZSM-5. We assumed first order kinetics with respect to each reactant concentration and first order decay of each reaction, and calculated initial rate constants. Figure 6 shows the initial rate constants of cumene cracking and triisopropyl-benzene cracking over the stabilized and the unstabilized catalysts. 

In contrast to n-paraffins, which exhibit no or only a slight C NMR CSA, aromatics or hydrocarbons with double or triple bonds show a much larger anisotropy. Therefore, benzene (57) and 2-butyne 14) were chosen as suitable probe molecules to study molecular motions by C NMR lineshape analysis. Theoretical lineshapes for different motional states of benzene and 2-butyne molecules are depicted in Figs. 3 and 4. The proton-decoupled C NMR spectra were recorded by means of the homemade NMR spectrometer UDRIS (University of Leipzig) and a BRUKER MSL 400 (Central Institute of Physical Chemistry, Berlin) at frequencies of 22.6 and 100.6 MHz (9,14,57). 

With this sample both methanol and dichloromethane give reversible isotherms and the same micropore volume. A much smaller micropore volume is given by benzene indicating that almost 40% of the pores or pore entrances are of size between that of dichloromethane and benzene. On the other hand, only a relatively small amount of low pressure hysteresis is present on the benzene isotherm indicatii that the remaining pores and pore entrances are significantly larger than the benzene molecule. A more complete characterisation of this sample would require the use of a larger probe molecule, such as neopentane. 

In many cases multiple probe molecules are used in order to deduce the existence of acid strength distributions. For example, the heterogeneity of the acid sites in H-ZSM-5 was studied by monitoring the adsorption of a series of weak electron donor molecules, such as hexane, fluorobenzene, chlorobenzene, benzene, toluene, p-xylene, and ethylene, to the acid sites. The frequency shift of the acidic OH group was taken as a... 

The expression (68) was applied [44] to the interpretation of the effect of electrolyte on the stability of a photoinduced charge-separated states of such probe molecules as p-aminonitrobiphenyl and p-aminonitroterphenyl in solution of different tetrabutulammonium salts in nonpolar solvents such as benzene (e - 2.28) and toluene (e = 2.38). According to the experimen-... 

R spectroscopy is one of the most useful techniques for the characterization of zeolitie materials. It provides information on the nature of OH-groups in the materials and on the framework vibrations. Even more useful is the IR analysis of adsorbed species. Basic probe molecules, such as pyridine, ammonia, or benzene, allow the analysis of acidic sites. CO adsorbed at low temperature also helps to analyze acidic sites, but can also be used for the analysis of noble metal particles in zeolites. 

Since carbon molecular sieves are amorphous materials, the dimensions of their pore structures must be measured phenomenologically by the adsorption of small probe molecules with different critical dimensions. There is insufficient long range order to utilize standard x-Ray diffraction methods for characterization. The earliest reports of molecular sieving carbons dealt primarily with coals and charcoals. Sorption of helium, water, methanol, n-hexane, and benzene was measured and related to the porosity of the carbon. Pore-sizes were estimated to be two to six angstroms (3-6). In a classic paper P.H. Emmett described methods for tailoring the adsorptive properties and pore size distributions of carbon Whetlerites. 

Specific Component of the Surface Free Energy of Heat-Treated Silicas. Specific interaction capacities of heat-treated silicas, that is, their ability to interact with polar molecules, were examined with chloroform (Lewis acid probe) and toluene and benzene (amphoteric molecules). Figure 2 provides examples of the evolution of the specific interaction parameter Zsp of the different silicas with chloroform as a probe. 

Three TS-1 zeolites were prepared by three different methods. In order to determine that all of them are "well manufactured", DRX, IR, SEM and DRS were used. The jointly use of probe molecules (H2O2 eind CeH6) and DRS allowed us to detect differences in the population of the named "closed" and "open" Ti" sites and in their geometries in the three zeolites. These differences lead to distinct catalytic behavior when these solids are tested in the oxidation of benzene with H2O2. 

Studies on local viscosity effects can be carried out using a free probe molecule, such as naphthacene, in polymer solution. Thus poly(styrene) in benzene solution has been studied with this probe at a concentration of 10 mole S,. Two stepwise increases In local viscosity at polymer concentrations of 20 to 30% and 60 to 70% were taken as indications of internal structure in the polymer solution at these concentrations (4). Similar studies were carried out on melts of n-paraffin homologues and poly(ethylene) at 150°C. The local viscosity increased with increasing molecular weight in the low molecular-weight range, but reached a plateau at around MW 2000. 

---