Acidic OH Research Articles

Dendritic polyamine architectures with lipophilic shells as nanocompartments for polar guest molecules: A comparative study of their transport behavior

AbstractDendritic core‐shell architectures were synthesized by simple melt reactions of polyethylenimine (PEI) with different fatty acids. These systems were investigated towards their ability to encapsulate various guest molecules. Parameters, such as the length of the attached alkyl chain, size of the polymer core, concentration of the core‐shell architecture in solution, pH, and nature of the guest molecule were investigated and compared. Guest molecules that bear anionic groups, such as carboxylate, phosphate, sulfonate, or acidic OH groups, as present in phenol units, are readily encapsulated and transferred from the aqueous phase to the organic phase because of multiple anionic–cationic interactions. Hyperbranched polymer architectures exhibit enhanced encapsulation properties when compared with their linear counterparts. In case of the hyperbranched system PEI25C16 amide higher transport capacities were observed at lower concentrations of the polymer, for example, 26 guest molecules at 10−5 mol L−1 versus 143 at 10−6 mol L−1, suggesting formation of larger aggregates. The aggregation behavior of these polar nanocompartments were investigated at different concentrations by AFM showing particle aggregates of typically 250 nm at a concentration of 10−5 M. The individual particle sizes in these aggregates are similar to the particle size at 10−6 M concentration, typically 4.0–5.5 nm (AFM height). This indicates that aggregate formation takes place at concentrations higher than 10−8 M and transport might be mediated by small aggregates rather than unimolecular particles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2287–2303, 2007

Isolation of Rhenium and ReOx Species within ZSM5 Channels and their Catalytic Function in the Activation of Alkanes and Alkanols

Synthesis protocols, structures, and reactivity of Re-oxo species grafted onto H-ZSM5, and their subsequent conversion to Re-clusters through contact with H2 or CH4 were studied by using Raman, infrared, and X-ray absorption spectroscopies. Reactivity measurements by using alkane and alkanol reactants were also examined. Sublimation of Re(2)O(7) at 723 K led to a stoichiometric exchange with each ReO(x) species replacing one proton. Raman features for Re(2)O(7) disappeared during thermal treatment and Raman bands assigned to distorted-tetrahedral Si-O(f)ReO(3)-Al (O(f): zeolite-lattice oxygen atoms) species emerged; infrared bands for acidic OH groups in H-ZSM5 weakened concurrently. X-ray absorption near-edge and fine-structure spectra detected the formation of distorted-tetrahedral Re7+-oxo species during thermal treatment of Re(2)O(7)/H-ZSM5 mixtures in air, and their subsequent reduction to Re(0) in H2 or CH4 to form encapsulated Re metal clusters similar in diameter (approximately 8 A) to the channel intersections in ZSM5. Si-O(f)ReO(3)-Al species in ReO(x)-ZSM5 catalyzed the oxidative conversion of C(2)H(5)OH to acetaldehyde, acetal, and ethyl acetate with very low selectivity to CO(x) (<1 %). Unprecedented turnover rates were exhibited at temperatures much lower than previously found for ReO(x)-based catalysts, and without deactivation or sublimation processes ubiquitous in crystalline Re7+ compounds at temperatures required for catalysis. Encapsulated Re metal clusters formed by the reduction of Si-O(f)ReO(3)-Al precursors led to CH4 pyrolysis and C(3)H(8) dehydrocyclodimerization rates (per Re) that are higher than those previously reported for zeolite-based catalysts. The rate of CH4 conversion to benzene, by using Re-ZSM5, was approximately 30 % higher than that of the best reported catalysts, based on encapsulated MoC(x) clusters, whereas C(2)H(4) and C6+ arene selectivities were similar. C(3)H(8) activity and selectivity of Re-ZSM5 was significantly higher than that of Ga-ZSM5, the best reported catalyst for these reactions. Reaction rates (per Re) were independent of the Re/Al(f) (Al(f): aluminum framework) ratio for both Re and ReO(x) species. This is consistent with the uniform character of the structures formed during grafting of the ReO(x) species through sublimation and their ability to retain their homogeneity even after their reduction to encapsulated Re-clusters.

Atmospheric Chemistry of Linear Perfluorinated Aldehydes: Dissociation Kinetics of CnF2n+1CO Radicals

Linear perfluorinated aldehydes (PFALs, CnF2n+1CHO) are important intermediate species in the atmospheric oxidation pathway of many polyfluorinated compounds. PFALs can be further oxidized in the gas phase to give perfluorinated carboxylic acids (PFCAs, CnF2n+1C(O)OH, n = 6, 12) which have been detected in animal tissues and at low parts per billion levels in human blood sera. In this paper, we report ab initio quantum chemistry calculations of the decarbonylation kinetics of CnF2n+1CO radicals. Our results show that CnF2n+1CO radicals have a strong tendency to decompose to give CnF2n+1 and CO under atmospheric conditions: the Arrhenius activation energies for decarbonylation of CF3CO, C2F5CO, and C3F7CO obtained using PMP4/6-311++G(2d,p) are 8.8, 6.6, and 5.8 kcal/mol, respectively, each of which is about 5 kcal/mol lower than the barrier for the corresponding nonfluorinated radicals. The lowering of the barrier for decarbonylation of CnF2n+1CO relative to that of CnH2n+1CO is well explained by electron withdrawal by F atoms that serve to weaken the critical C-CO bond. These results have important implications for the atmospheric fate of PFALs and the atmospheric pathways to PFCAs. The main effect of decarbonylation of CnF2n+1CO is to decrease the molar yield of CnF2n+1C(O)OH; if 100% of the CnF2n+1CO decompose, the yield of CnF2n+1C(O)OH must be zero. There is considerable scope for additional experimental and theoretical studies.

Structure of Zirconium-Exchanged H-ZSM5 Prepared by Vapor Exchange of ZrCl4

Zr dimers (Zr2O32+) interacting with two exchange sites and uniform in structure were prepared by grafting anhydrous ZrCl4(g) onto H-ZSM5 followed by hydrolysis and dehydration. This method led to selective exchange, without concurrent formation of crystalline ZrO2 aggregates, ubiquitously formed via aqueous exchange because of the slow diffusion of aquo oxo-ions within small channels. ZrCl4(g) reacts with acidic OH groups to form HCl and ZrCl3+-ZSM5 species. This exchange stoichiometry was confirmed by the number of HCl molecules evolved during hydrolysis, a process that forms ZrO(OH)+ species. These species then dehydroxylate via condensation with vicinal ZrO(OH)+ to form (OZr−O−ZrO)2+ species interacting with two exchange sites and containing one bridging O-atom. This exchange process is consistent with the number of residual OH groups titrated by D2 and with the intensity of O−H infrared bands. X-ray diffraction, 27Al nuclear magnetic resonance, and infrared spectra showed that the exchange process did not influence zeolite crystallinity, led to Zr4+ introduction into the zeolite framework, or form residual Zr(OH)x species at exchange sites. Weak Raman bands in the 960−1030 cm-1 region, absent in crystalline ZrO2 and H-ZSM5, were detected upon exchange. The maximum attainable Zrdimer/Alf exchange ratios (0.6 ± 0.05) are consistent with Al radial structure distributions and with expected Al−Al distances required to anchor (OZr−O−ZrO)2+ species in ZSM-5 with a statistical distribution of Al atoms. ZrCl4 species in excess of this saturation stoichiometry formed monoclinic ZrO2, detectable in Raman spectra and X-ray diffraction patterns.

Regioselective H/D exchange of propane on Zn/H-MFI zeolite

The hydrogen exchange for propane-d 8 adsorbed on zeolite Zn/H-MFI has been studied by1H MAS NMR spectroscopy in situ within the temperature range of 420–490 K. Kinetic measurements of the H/D exchange between the acidic hydroxyl groups of the zeolite and the adsorbed deuterated propane molecules show that only methyl groups of the alkane are involved in the exchange. Two mechanisms are proposed to rationalize the regioselectivity of the exchange: (i) propane dehydrogenation on Zn-sites followed by protonation of propene by acidic OH groups in accordance to the Markovnikov’s rule and abstraction of deuteride ion from another propane molecule; (ii) the reversible heterolytic dissociative adsorption of propane to form Zn-propyl species and acidic OH groups.

Synthesis of poly(sebacic anhydride)-indomethacin controlled release composites via supercritical carbon dioxide assisted impregnation

Poly(sebacic anhydride), PSA and indomethacin drug composite (DC) formulations were prepared using supercritical CO 2 (sc-CO 2) aided mixing. The effect of the experimental temperature and sebacic acid purity on the physical properties of PSA–indomethacin DCs was investigated using a range of analytical techniques. The nature of the PSA–indomethacin interaction in composites after processing in sc-CO 2 under various conditions was investigated using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and powder X-ray diffraction (XRD) methods, respectively. The results indicate that processing at 130 °C of a 4:1 (w/w) ratio PSA–indomethacin mixture, renders the indomethacin amorphous and dispersed within the polymer matrix. The primary interaction between PSA and indomethacin appears to be hydrogen bonding between the carboxylic acid OH of indomethacin and the carbonyl group of PSA. In vitro dissolution studies revealed that the processed composites exhibit a substantially enhanced dissolution rate compared to the physical mixtures. Also, through the control of experimental conditions, the initial burst effect of the drug release was largely alleviated. Instead, the erosion of PSA (zero order degradation) became the dominant factor in controlling the drug release rate.

Concentration and acid strength of hydroxyl groups in zeolites La,Na-X and La,Na-Y with different lanthanum exchange degrees studied by solid-state NMR spectroscopy

1H MAS NMR spectroscopy was applied for a quantitative investigation of the concentration of hydroxyl groups on lanthanum-exchanged zeolites X and Y as a function of the dehydration temperature. A maximum concentration of Brønsted acidic bridging OH groups (SiOHAl) was reached upon dehydration of zeolites La,Na-X and La,Na-Y at 423 K. Further raise of the dehydration temperature leads to the recombination of the above-mentioned hydroxyl groups, while the dealumination of the framework is negligible. The maximum number of bridging OH groups formed on zeolites La,Na-X and La,Na-Y correlates well with the lanthanum exchange degree. By adsorption of deuterated acetonitrile as a probe molecule, an increase of the acid strength of bridging OH groups in lanthanum-exchanged zeolites X and Y was found. This finding is explained by the polarizing effect of multivalent lanthanum cations, which leads to a withdrawal of electrons from the O–H bonds of Brønsted acid sites in lanthanum-exchanged zeolites with a high concentration of these extra-framework cations.

Synthesis and evaluation of prodrugs for anti-angiogenic pyrrolylmethylidenyl oxindoles

Potential prodrugs of inhibitors of VEGF-induced angiogenesis have been investigated. The prodrug systems studied were the 4-nitrobenzyl, 2-nitrophenylacetyl and 3-methyl-3-(3,6-dimethylbenzo-1,4-quinon-2-yl)butanoyl groups, readily attached to acidic OH or NH groups in drug molecules, and released upon bioreductive activation. The anti-angiogenic compounds studied were the pyrrolylmethylidenyl oxindole SU5416 (semaxanib) and its novel 6-hydroxy derivative. The potentially pro-anti-angiogenic compounds were assayed for their ability to block VEGF-induced angiogenesis in HUVECS in comparison to the free agents.

Ammonia IRMS-TPD measurements and DFT calculation on acidic hydroxyl groups in CHA-type zeolites

Brønsted acidity of H-chabazite (CHA) zeolites (Si : Al(2) = 4.2) was investigated by means of ammonia infrared-mass spectrometry/temperature-programmed desorption (IRMS-TPD) methods and density functional calculations. Four IR bands were observed at 3644, 3616, 3575 and 3538 cm(-1), and they were ascribable to the acidic OH groups on four nonequivalent oxygen sites in the CHA structure. The absorption band at 3538 cm(-1) was attributed to the O(4)H in the 6-membered ring (MR), and ammonia adsorption energy (DeltaU) of this OH group was the lowest among the 4 kinds of OH groups. The other 3 bands were assigned to the acidic OH groups in 8MR. It was observed that the DeltaU in 8 and 6MR were 131 (+/-3) and 101 kJ mol(-1), respectively. On the other hand, the density functional theory (DFT) calculations within periodic boundary conditions yielded the adsorption energies on these OH groups in 8 and 6MR to be ca. 130 and 110 kJ mol(-1), respectively, in good agreement with the experimentally-observed values.

Self-assembly of fullerene-rich nanostructures with a stannoxane core

Fullerene derivatives bearing a carboxylic acid function undergo self-assembly with n-butylstannonic acid (nBuSn(O)OH) to produce fullerene-rich nanostructures with a stannoxane core in almost quantitative yields.

Nature, Structure and Strength of the Acidic Sites of Amorphous Silica Alumina: An IR and NMR Study

IR spectroscopy of probe molecules (pyridine, 2,6-dimethylpyridine, and CO) as well as high-resolution solid state NMR and especially double-resonance experiments give a new insight into the acidic sites of amorphous silica alumina (ASA). ASA samples are heterogeneous compounds that contain a silica alumina mixed phase as well as aluminum clusters and pure silica zones. The distribution of various forms depends both on the preparation method and on the Si/Al ratio. Formation of mixed phase leads to the creation of acidic hydroxyl groups of various strength, up to that present in dealuminated HY zeolite. Detailed spectroscopic analyses show that these acidic OH groups correspond to the silanol groups located in close vicinity to an Al atom in tetrahedral environment. The strength of the acidity of the OH species of ASA could be modified both by the location of the vicinal Al atom on the surface or in the bulk and by the number of aluminum atoms in the vicinity of silanol group. Cogelification of high silica-containing ASA appears as the best mean to prepare homogeneous amorphous aluminosilicate, which exhibits the strongest Brønsted acidity.

Quantitative Measurement of the Brönsted Acid Sites in Solid Acids: Toward a Single-Site Design of Mo-Modified ZSM-5 Zeolite

On the basis of our previous H/D exchange studies devoted to the quantification of the number of Brönsted acid sites in solid acids, we report here an innovative approach to determine both the amount and the localization of Mo atoms inside the Mo/ZSM-5 catalyst, commonly used for the methane dehydroaromatization reaction. The influence of Mo introduction in the MFI framework was studied by means of BET, X-ray diffraction, 27Al magic angle spinning NMR, NH3 temperature-programmed desorption, and H/D isotopic exchange techniques. A dependence was found between the decrease of acidic OH groups and the Mo content. Depending on the Si/Al ratio of the zeolite, i.e., the proximity of two Brönsted acid sites, the Mo atoms substitute a different number of OH groups. Consequently, a chemical structure was proposed to describe the geometry of the Mo complex in the channels of the ZSM-5 zeolite.

Atmospheric Chemistry ofN-methyl Perfluorobutane Sulfonamidoethanol, C4F9SO2N(CH3)CH2CH2OH: Kinetics and Mechanism of Reaction with OH

Relative rate methods were used to measure the gas-phase reaction of N-methyl perfluorobutane sulfonamidoethanol (NMeFBSE) with OH radicals, giving k(OH + NMeFBSE) = (5.8 +/- 0.8) x 10(-12) cm3 molecule(-1) s(-1) in 750 Torr of air diluent at 296 K. The atmospheric lifetime of NMeFBSE is determined by reaction with OH radicals and is approximately 2 days. Degradation products were identified by in situ FTIR spectroscopy and offline GC-MS and LC-MS/MS analysis. The primary carbonyl product C4F9SO2N(CH3)CH2CHO, N-methyl perfluorobutane sulfonamide (C4F9SO2NH(CH3)), perfluorobutanoic acid (C3F7C(O)OH), perfluoropropanoic acid (C2F5C(O)OH), trifluoroacetic acid (CF3C(O)OH), carbonyl fluoride (COF2), and perfluorobutane sulfonic acid (C4F9SO3H) were identified as products. A mechanism involving the addition of OH to the sulfone double bond was proposed to explain the production of perfluorobutane sulfonic acid and perfluorinated carboxylic acids in yields of 1 and 10%, respectively. The gas-phase N-dealkylation product, N-methyl perfluorobutane sulfonamide (NMeFBSA), has an atmospheric lifetime (>20 days) which is much longer than that of the parent compound, NMeFBSE. Accordingly,the production of NMeFBSA exposes a mechanism by which NMeFBSE may contribute to the burden of perfluorinated contamination in remote locations despite its relatively short atmospheric lifetime. Using the atmospheric fate of NMeFBSE as a guide, it appears that anthropogenic production of N-methyl perfluorooctane sulfonamidoethanol (NMeFOSE) contributes to the ubiquity of perfluoroalkyl sulfonate and carboxylate compounds in the environment.

Hydroxy- and Mercaptopyridine Pincer Platinum and Palladium Complexes Generated by Silver-Free Halide Abstraction

A silver-free route has been employed for the synthesis of a number of Pd and Pt complexes supported by an NCN "pincer" ligand (NCN = [2,6-(Me2NCH2)2C6H3]-) via halide abstraction. This was achieved by the use of o-, m-, and p-hydroxypyridines or o- and p-mercaptopyridines in basic ethanol solutions. The acidic OH or SH protons are removed to generate the formally anionic ligands. X-ray crystal structure determination of these complexes shows that the bonding of the substituted pyridine ligands occurs exclusively through the pyridine N for hydroxypyridines and exclusively through the thiol S in mercaptopyridines. In the hydroxypyridine case, the ortho and para isomers tautomerize to generate pyridone structures with a covalent M-N bond, whereas the m-hydroxypyridine complex, which is unable to tautomerize, is found to still be bound through the pyridine N but in a zwitterionic structure. The mercaptopyridine complexes are the first reported examples of pincer-ligated Pd and Pt thiolate species. The pyridine ligands can be quantitatively exchanged for chloride by reaction with excess NH4Cl, a potentially useful chemical switch for ligation/decomplexation of this ligand type.

Enhanced Photocatalytic Activity of Zeolite‐Encapsulated TiO2 Clusters by Complexation with Organic Additives and N‐Doping

In the literature it was found that titanium oxide clusters of a few metal atoms encapsulated inside the micropores of zeolite Y exhibit large blue shifts in the Ti-O ligand-to-metal charge-transfer band as compared to non-encapsulated bulk titanium dioxide particles. This blue shift of the Ti-O absorption band is believed to have a negative effect on the photocatalytic activity of zeolite-encapsulated TiO2. We report here on circumventing this problem and increasing visible-light absorption by means of a red shift of the absorption band caused by addition of some organic molecular modifiers containing acidic OH groups that can strongly bind with titanol groups TiOH. In the studied series of zeolite-encapsulated TiO2 samples, the red shift of the optical spectrum follows the order: catechol > 4-aminobenzoic acid > benzoic acid. Also N-doping of zeolite-encapsulated TiO2 clusters by thermal treatment with urea leads to a red shift of the TiO2 absorption band that depends on the annealing and hydration conditions. By comparison to the degradation of phenol in aqueous solution, we have demonstrated that these changes in the absorption spectrum on addition of the organic modifier are also reflected in the photocatalytic activity of the samples; a greater increase in photocatalytic activity (about 30%) was observed for the additive catechol.

A DFT study of the structures of pyruvic acid isomers and their decarboxylation

Pyruvic acid and its isomers, including the enol tautomers and enantiomeric lactone structures, have been investigated at the B3LYP/6-311 + + G(3df,3pd) level, and it is found that a keto form with trans C(methyl)C(keto)C(acid)O(hydroxyl) and cis C(keto)C(acid)OH, and with one methyl hydrogen in a synperiplanar position with respect to the keto oxygen, is the most stable. This agrees with previous theoretical and experimental determinations. However, no minimum corresponding to protonated pyruvate could be located, although previous semiempirical calculations had found such structures. Decarboxylation by different possible routes was then studied. It was found that the direct formation of acetaldehyde, the most stable of the resulting C2H4O isomers, via a four-center-like transition state is the most feasible, although there is a high activation barrier of 70 kcal mol(-1). In contrast to semiempirical calculations, it is found that no hydroxyethylidene-carbon dioxide complex exists as a product, and no transition state leading to the dissociation to hydroxethylidene could be located.

Reaction pathways of ethane oxidative and non-oxidative dehydrogenation on γ-Al 2O 3 studied by temperature-programmed reaction (TP-reaction)

In this work, the reactions of ethane and ethene in an oxidizing and non-oxidizing atmosphere over γ-alumina were investigated under temperature-programmed conditions, in an attempt to estimate the possible contribution and functionality of the support in the reaction pathway of ethane ODH over MoO 3/Al 2O 3 catalysts. The results indicate that alumina contributes to the primary deep oxidation and dehydrogenation routes of ethane to CO x and coke respectively, which proceed effectively over the acidic OH groups and the Al 3+–O 2− acidic centers. On the contrary, the formation of ethylene seems to be coupled to the presence of redox sites on the catalytic surface and requires the presence of the molybdena phase. Moreover, the redox sites of the MoO x species were found to unselectively activate the further overoxidation of the olefin to carbon oxides. Therefore, Al 2O 3 catalyzes the unselective primary oxidation of ethane to carbon oxides, whereas the molybdena phase is involved in the selective oxidative dehydrogenation (ODH) of ethane to ethene and the secondary overoxidation of ethene to CO x .

Novel catalytic systems containing n-BuSn(O)OH for the transesterification of dimethyl carbonate and phenol

Novel catalytic systems containing n-butylstannonic acid ( n-BuSn(O)OH) were used to synthesize methyl phenyl carbonate (MPC) and diphenyl carbonate (DPC) by the transesterification of dimethyl carbonate (DMC) with phenol in atmospheric conditions. The catalytic system consisting of n-BuSn(O)OH and cuprous iodide (CuI) had the highest activity for the transesterification. When the reaction was carried out between 150 and 180 °C, with a molar ratio of n-BuSn(O)OH to CuI of 1:1, a catalyst amount 0.005 (molar ratio to DMC), a reaction time 10 h, a molar ratio of DMC to phenol of 2:1, a dropping time of DMC 6 h, the conversion of phenol was 67.2%, and the selectivity of MPC and DPC was 40.2 and 59.6%, respectively. Upon comparison of the activities of Cu 2O, CuX (X = Cl, Br, I) and the catalytic system being composed of n-BuSn(O)OH and Cu 2O/CuX, it was found that Cu 2O and CuX were excellent promoters, and the stronger was the anion electronegativity in the promoter, the weaker was the promoting catalysis of the promoter.

In Situ 1H and 13C MAS NMR Kinetic Study of the Mechanism of H/D Exchange for Propane on Zeolite H−ZSM-5

The kinetics of hydrogen (H/D) exchange between Brønsted acid sites of zeolite H-ZSM-5 and variously deuterated propanes (propane-d(8), propane-1,1,1,3,3,3-d(6), propane-2,2-d(2)) have been monitored in situ by (1)H MAS NMR spectroscopy within the temperature range of 503-556 K. The contribution of intramolecular hydrogen transfer to the H/D exchange in the adsorbed propane was estimated by monitoring the kinetics of (13)C-labeled carbon scrambling in propane-2-(13)C in situ with (13)C MAS NMR at 543-573 K. Possible mechanisms of the exchange have been verified on the basis of the analysis of the variation of protium concentration in both the methyl and the methylene groups of propane in dependence of the reaction time. The main route of the exchange consists of a direct exchange of the acidic OH groups of the zeolite with either the methyl groups or the methylene group presumably with a pentacoordinated carbonium ion intermediate. The assumption that the intramolecular H scrambling between the methyl groups and the methylene group of propane via carbenium-ion-type intermediates is the fastest process among the other possible routes does not account for the experimental kinetics of H/D exchange for propanes with different initial contents and locations of deuterium in a propane molecule. The rate constant (k(3)) for intramolecular H/D exchange between the methyl and the methylene groups is 4-5 times lower compared to those of the direct exchange of both the methyl (k(1)) and the methylene (k(2)) groups with Brønsted acid sites of the zeolite, the k(1) being ca. 1.5 times higher than k(2). At lower temperature (473 K), the exchange is slower, and the expected difference between k(1) and k(2) is more essential, k(1) = 3k(2). This accounts for earlier observed regioselectivity of the exchange for propane on H-ZSM-5 at 473 K. Faster direct exchange with the methyl groups compared to that with the methylene groups was attributed to a possible, more spatial accessibility of the methyl groups for the exchange. Similar activation energies for H and C scramblings with a 2 times more rapid rate of H scrambling was rationalization by the proceeding of these two processes through an isopropyl cation intermediate, as in classical carbenium ion chemistry.

An investigation of the acid properties of UL-ZSM-5 by FTIR of adsorbed 2,6-ditertbutylpyridine and aromatic transalkylation test reaction

The surface acidity of semicrystalline zeolitic mesoporous UL-ZSM-5 aluminosilicate materials of different degree of crystallinity (UL-zeolites were introduced recently in our laboratory [D. Trong On, S. Kaliaguine, Nanoporous Materials—Science and Engineering, Imperial College Press, 2005; D. Trong On, S. Kaliaguine, Angew. Chem. Int. Ed. 40 (2001) 3248; A. Ungureanu, D. Trong On, E. Dumitriu, S. Kaliaguine, Appl. Catal. A: Gen. 254 (2003) 203]) has been investigated by means of FTIR spectroscopy of adsorbed 2,6-ditertbutylpyridine (DTBPy) and the test reaction of transalkylation of toluene with 1,3,5-trimethylbenzene. FTIR experiments and catalytic tests allowed also characterizing the surface acidity of the starting amorphous mesostructured aluminosilicate precursor and the external acid sites of crystalline ZSM-5 zeolite. The results indicated that most of the Brönsted acidic OHs accessible to DTBPy molecules are terminal on the mesopore surfaces of both UL-ZSM-5 materials and mesostructured aluminosilicate and also on the external surface of ZSM-5. These sites, which are responsible for the O H stretching band near 3745 cm −1, are of medium strength. Their density correlated well with the external surface area. On the other hand, bridging Si OH Al sites generating O H stretching band at 3612 cm −1 and conferring the medium-strong Brönsted acidity of UL-ZSM-5 and ZSM-5 are located predominantly in the micropores of the zeolitic ZSM-5 phase and thus not accessible to bulky DTBPy. Just like the external surface of ZSM-5, the mesoporous surface of UL-ZSM-5 carries a small fraction of bridging Brönsted acid sites which are likely located in the pore mouth region of their ZSM-5 zeolitic phase. The catalytic activity of the distinct aluminosilicate materials under study as well as the selectivity towards the different reactions involved in the transalkylation process has been found to strongly depend on the nature, density, strength and accessibility of the characteristic Brönsted acid sites.