Cooperativity of silanol defect chemistry in zeolites.

Deboronation treatment of zeolite B-SSZ-55 can generate vacancy defects consisting of four silanol groups (silanol nests). However, 1H solid-state NMR spectroscopy indicates the prevalence of two silanol groups (silanol dyads) instead of four silanol groups. Such silanol dyads must be formed by the silanol condensation of two silanol groups at the silanol nests. Yet, the exact mechanism of this condensation and detailed structure of the silanol defect are not known. Here, the structure and formation mechanism of silanol dyads in the SSZ-55 zeolite have been investigated by both cluster and periodic density functional theory calculations. The calculated 1H NMR chemical shifts agree with the experimental values, showing that the silanol dyads are indeed commonly present at the vacancies and the vacancy density plays a role in the relaxation of the zeolite framework. The nature (size) of the silanol clusters influences their acidity.

Hydrogen Bonds Dominate Brønsted Acid Sites in Zeolite SSZ-42: A Classification of Their Diversity.

The zeolite catalyst SSZ-42 shows a remarkable high abundance (≈80 %) of hydrogen-bonded Brønsted acid sites (BAS), which are deshielded from the 1 H chemical shift of unperturbed BAS at typically 4 ppm. This is due to their interaction with neighboring oxygen atoms in the zeolite framework when oxygen alignments are suitable. The classification and diversity of hydrogen bonding is assessed by DFT calculations, showing that oval-shaped 6-rings and 5-rings allow for a stronger hydrogen bond to oxygen atoms on the opposite ring side, yielding higher experimental chemical shifts (δ (1 H)=6.4 ppm), than circular 6-rings (δ(1 H)=5.2 ppm). Cage-like structures and intra-tetrahedral interactions can also form hydrogen bonds. The alignment of oxygen atoms is expected to impact their role in the stabilization of intermediates in catalytic reactions, such as surface alkoxy groups and possibly transition states.

Characterization of a Molecule Partially Confined at the Pore Mouth of a Zeotype.

We investigate the interaction between a molecule and a pore mouth-a critical step in adsorption processes-by characterizing the conformation of a macrocyclic calix[4]arene-TiIV complex, which is grafted on the external surface of a zeotype (*-SVY). X-ray absorption and 13 C{1 H} CPMAS NMR spectroscopies independently detect a unique conformation of this complex when it is grafted at crystallographically equivalent locations that lie at the interface of 7 Šhemispherical microporous cavities and the external surface. Electronic structure calculations support the presence of this unique conformation, and suggest that it is brought about by a specific orientation of the macrocycle that maximizes non-covalent interactions between calix[4]arene upper-rim tert-butyl substituents and the microporous-cavity walls. Our comparative study provides a rare "snapshot" of a molecule partially confined at a pore mouth, an essential intermediate for adsorption into micropores, and demonstrates how surrounding environment controls this confinement in a sensitive fashion.

A Stable Silanol Triad in the Zeolite Catalyst SSZ-70.

Nests of three silanol groups are located on the internal pore surface of calcined zeolite SSZ-70. 2D 1 H double/triple-quantum single-quantum correlation NMR experiments enable a rigorous identification of these silanol triad nests. They reveal a close proximity to the structure directing agent (SDA), that is, N,N'-diisobutyl imidazolium cations, in the as-synthesized material, in which the defects are negatively charged (silanol dyad plus one charged SiO- siloxy group) for charge balance. It is inferred that ring strain prevents the condensation of silanol groups upon calcination and removal of the SDA to avoid energetically unfavorable three-rings. In contrast, tetrad nests, created by boron extraction from B-SSZ-70 at various other locations, are not stable and silanol condensation occurs. Infrared spectroscopic investigations of adsorbed pyridine indicate an enhanced acidity of the silanol triads, suggesting important implications in catalysis.

Ultrastabilization of Zeolite†Y Transforms Brønsted-Brønsted Acid Pairs into Brønsted-Lewis Acid Pairs.

Two pairs of Brønsted acid sites have been identified in H,Na-Y zeolite, located in the supercage and in the sodalite cage, which upon ultrastabilization (dealumination) are transformed into pairs of Brønsted and Lewis acid sites. This mild postsynthetic modification step is an important process for converting this material into an active catalyst for large-scale commercial reactions. Pairing structures and their transformations have been investigated using 1 H double-quantum NMR spectroscopy experiments for dehydrated zeolite, H,Na-Y, and its ultrastabilized form, H,Na-USY. This approach enables the detection of pairs of Brønsted and Lewis acid sites with unprecedented 1 H resolution and distinguishing them from isolated acid sites. The dealumination is also detected by static 27 Al solid-state NMR experiments.

Outer-Sphere Control of Catalysis on Surfaces: A Comparative Study of Ti(IV) Single-Sites Grafted on Amorphous versus Crystalline Silicates for Alkene Epoxidation.

The effect of outer-sphere environment on alkene epoxidation catalysis using an organic hydroperoxide oxidant is demonstrated for calix[4]arene-TiIV single-sites grafted on amorphous vs crystalline delaminated zeotype (UCB-4) silicates as supports. A chelating calix[4]arene macrocyclic ligand helps enforce a constant TiIV inner-sphere, as characterized by UV-visible and X-ray absorption spectroscopies, thus enabling the rigorous comparison of outer-sphere environments across different siliceous supports. These outer-sphere environments are characterized by solid-state 1H NMR spectroscopy to comprise proximally organized silanols confined within 12 membered-ring cups in crystalline UCB-4, and are responsible for up to 5-fold enhancements in rates of epoxidation by TiIV centers.

Defect Models of As-Made High-Silica Zeolites: Clusters of Hydrogen-Bonds and Their Interaction with the Organic Structure-Directing Agents Determined from 1 H Double and Triple Quantum NMR Spectroscopy.

Internal defect SiOH and SiO- groups evolve during the structure formation of high-Si zeolites in the presence of a cationic organic structure-directing agent (SDA). These negatively charged defects do not completely disappear upon calcination. Herein we investigate the clustering of defect groups and their location within the pore walls of four zeolites. ZSM-12, ZSM-5, and SSZ-74 have three clustered SiOH groups which are hydrogen-bonded to SiO- , whereas SSZ-24 has only two. These defects interact with the structure-directing quaternary ammonium ions preferably close to the charge center, unless steric shielding is present. The framework topologies of ZSM-12, ZSM-5, and SSZ-24 have connected six-rings where the organics interact with the defects. It is suggested that these six-ring patterns form connectivity defects. SSZ-74 is unique, it does not contain an extended six-ring motif, so vacancy defects form instead.

Solid state NMR of porous materials : zeolites and related materials.

Solid state NMR spectroscopy applied to the science of crystalline micro- and mesoporous silica materials over the past 10 years is reviewed. A survey is provided of framework structure and connectivity analyses from chemical shift effects of various elements in zeolites including heteroatom substitutions, framework defects and pentacoordinated silicon for zeolites containing fluoride ions. New developments in the field of NMR crystallography are included. Spatial host-guest ordering and confinement effects of zeolite-sorbate complexes are outlined, with special emphasis on NMR applications utilizing the heteronuclear dipolar interaction. The characterization of zeolite acid sites and in situ NMR on catalytic conversions is also included. Finally, the motion of extra-framework cations is investigated in two tutorial cases of sodium hopping in sodalite and cancrinite.

Two-dimensional pH mapping of release kinetics of silica-encapsulated drugs.

The encapsulation of pharmaceutical drug molecules in silica gels during the sol-gel synthesis and their kinetic release profile in aqueous solutions were systematically investigated in dependence of synthesis pH(S) and extraction pH(E) values. Six pH values in the range from 1 to 6 were chosen in a 6 × 6 two-dimensional matrix to screen the first-order initial dissolution rate constant and the total amount of released drug. Characteristic differences are discovered in such two-dimensional pH mapping profiles for the molecules with different ionization behavior and they are explained by surface imprinting and encapsulation processes. Remarkably, these encapsulations must occur either in the particles of the sol solutions or during the rapid liquid-solid transition of the spray-drying process employed in this study. This pH mapping method is suggested as a novel tool to probe noncovalent imprinting and encapsulation processes in sol-gel-derived materials with embedded guest molecules.

Microheterogeneity in phenyl group modified inorganic/organic hybrid gels after aerosol drying or slow solvent evaporation.

Sol-gel systems were prepared by co-hydrolysis and co-condensation of tetraethoxysilane (TEOS) and phenyltriethoxysilane (PhTES). The sols were transferred into silica gels by Evaporation Induced Self-Assembly (EISA) or Aerosol Assisted Self-Assembly (AASA) using a laboratory spray-dryer. The structural properties such as porosity and homogeneity/microheterogeneity of these different systems are compared by N(2) sorption measurements, thermal analysis (TG, DTG and DTA), (29)Si MAS NMR and (29)Si{(1)H} CP MAS NMR. The cross polarization of the AASA gels can be described with the conventional I-S dynamics of a homogeneous proton spin bath. The EISA gels are heterogeneous, and the I-I(*)-S model, or a bimodal I-S model, was employed for the simulation of CP dynamics. Microheterogeneities are observed by (1)H-(29)Si cross polarization on an EISA sample, whereas rapid drying (AASA) transfers the corresponding sol into homogeneous xerogels. The EISA gels are microporous after calcination at 923 K, and the AASA gels are dense.

Non-covalent interactions of a drug molecule encapsulated in a hybrid silica gel.

The drug molecule Propranolol has been encapsulated by a sol-gel process in an organic-inorganic hybrid matrix by in-situ self-assembly; the 2D HETCOR solid state NMR spectroscopy provides direct proof of the intimate spatial relationship between the host matrix and guest drug molecules.

Anion-promoted cation motion and conduction in zeolites.

The motion of sodium cations in sodalite and cancrinite has been investigated by force field calculations, solid-state NMR, and impedance spectroscopy. Special emphasis is dedicated to the influence of anions on sodium mobilities. Local cation motion is promoted when they interact with anions. However, not all systems with high local mobilities exhibit good ion conductivities, as cooperativity of the motion appears to be an important factor, as well. The activation barrier for local sodium motion (calculations) and long-range transport (dc conductivities) is lowered in sodalite when halogenide anions, Cl(-), Br(-), or I(-), are present. The activation barriers increase with increasing size of the anion and decreasing coordination in the transition state. On the basis of (23)Na solid-state NMR data, all the sodium ions in the dense sodalite structure are rather rigid up to 470 K. All the cations in chromate sodalite, and Na(+) in the small cancrinite epsilon-cages without anion interactions, show a restricted local motion at higher temperatures. There is a selective high local motion of Na(+) in the neighborhood of chromate anions in the more open channel system of cancrinite. These results suggest that sodium migration can be enhanced, at least locally, in open channel systems by anion interactions. A dynamics coupling between anion reorientation and cation mobility was not observed.

Pleural empyema associated with Gemella morbillorum: report of a case and review of the literature.

Gemella morbillorum, a microaerophilic Gram-positive coccus, is a natural inhabitant of the human oropharyngeal, gastrointestinal and urogenital flora. However, it is an infrequently isolated organism and a rare cause of pulmonary or pleural infections. We report on a 26-y-old male subject with a past medical history of epilepsy and intravenous drug abuse, who presented with imminent sepsis and respiratory failure. Computed tomography of the thorax revealed a pleuropulmonary consolidation of the left lower lobe, and ultrasound guided thoracentesis resulted in aspiration of pus. Microbiological analysis revealed Gemella morbillorum in the pleural fluid. Thoracic drainage and antibiotic therapy resulted in full recovery. We discuss previous cases of pleuropulmonary infections due to Gemella morbillorum and review the available literature of this rare occurrence.

Bronchoscopy-guided topical hemostatic tamponade therapy for the management of life-threatening hemoptysis.

STUDY OBJECTIVES: Massive hemoptysis is a life-threatening condition. Therapeutic strategies such as interventional angiography, surgery, and/or bronchoscopy have been applied in the clinical setting with variable results. We investigated the efficacy of bronchoscopy-guided topical hemostatic tamponade therapy (THT) using oxidized regenerated cellulose (ORC) mesh in the management of life-threatening hemoptysis. DESIGN: Seventy-six consecutive patients underwent emergency bronchoscopy for massive hemoptysis. Fifty-seven patients (75%) had persistent endobronchial bleeding despite bronchoscopic wedging technique, cold saline solution lavage, and instillation of regional vasoconstrictors. These patients subsequently underwent THT according to the same procedure. SETTING: Teaching hospital, bronchoscopy unit of a 300-bed tertiary pulmonary referral center. RESULTS: THT with ORC was successfully performed on 56 of 57 patients (98%) with an immediate arrest of hemoptysis. All patients successfully treated with THT remained free of hemoptysis for the first 48 h. None required intensive care support or immediate surgery. Mean procedure time (+/- SD) of THT was 11.5 +/- 4.2 min. Recurrence of hemoptysis that was characterized as being mild (< 30 mL) to moderate (30 to 100 mL) developed in six patients (10.5%) 3 to 6 days after THT. Post-obstructive pneumonia developed in five subjects (9%) after endoscopic THT. A subgroup of patients (n = 14) underwent bronchoscopic follow-up 4 weeks after discharge. The ORC mesh was absorbed in all of these patients without signs of foreign body reaction. CONCLUSIONS: Endobronchial THT using ORC is a safe and practicable technique in the management of life-threatening hemoptysis with a high success and a relatively low complication rate.

ITQ-12: a new microporous silica polymorph potentially useful for light hydrocarbon separations.

The new synthetic form of microporous crystalline silica, denoted as ITQ-12, shows a high potential for the separation of propane and propene from its mixtures.

A case of primary tularemic pneumonia presenting with necrotizing mediastinal and hilar lymph nodes.

Tularemia is an unusual disease caused by the gram-negative coccobacillus Francisella tularensis. The clinical features of the disease depend on the route of inoculation. Ulceroglandular and typhoidal forms have been recognized as occurring in tularemia, however primary or secondary pneumonic infections have also been reported. Symptoms, laboratory markers and radiological features are non-specific in tularemic pneumonia. Diagnosis is made on clinical grounds and evidence of elevated agglutinating antibodies to F. tularensis (> 1:128). We report a case of primary tularemic pneumonia presenting with pulmonary infiltrates and necrotizing mediastinal and hilar lymph nodes in an otherwise healthy subject from a non-endemic area. Diagnosis of tularemia was obtained serologically, and antibiotic therapy with doxycycline and streptomycin resolved symptoms and radiological abnormalities. We suggest that tularemia should be considered in the differential diagnosis of pneumonia with mediastinal and/or hilar lymphadenopathy.

Evidence for Selective Association of Tetrahedral BO4 Units with Na+ and of Trigonal BO3 Units with H+ in Dehydrated Zeolite B-ZSM-5 from Solid-State NMR Spectroscopy.

Conclusive proof has now been obtained for the selective association of trigonal BO3 and tetrahedral BO4 units with H+ and Na+ ions, respectively, in B-ZSM-5 zeolites (the interactions are depicted in the picture). This was achieved with a combination of 11 B{23 Na}, 11 B{1 H}, and 1 H{11 B} rotational echo double resonance (REDOR) NMR spectroscopic experiments.