Thermal Alteration in Adsorption Sites over SAPO-34 Zeolite.

Zeolites have found tremendous applications in the chemical industry. However, the dynamic nature of their active sites under the flow of adsorbate molecules for adsorption and catalysis is unclear, especially in operando conditions, which could be different from the as-synthesized structures. In the present study, we report a structural transformation of the adsorptive active sites in SAPO-34 zeolite by using acetone as a probe molecule under various temperatures. The combination of solid-state nuclear magnetic resonance, in situ variable-temperature synchrotron X-ray diffraction, and in situ diffuse-reflectance infrared Fourier-transform spectroscopy allow a clear identification and quantification that the chemisorption of acetone can convert the classical Brønsted acid site adsorption mode to an induced Frustrated Lewis Pairs adsorption mode at increasing temperatures. Such facile conversion is also supported by the calculations of ab-initio molecular-dynamics simulations. This work sheds new light on the importance of the dynamic structural alteration of active sites in zeolites with adsorbates at elevated temperatures.

Induced Active Sites by Adsorbate in Zeotype Materials.

There has been a long debate on how and where active sites are created for molecular adsorption and catalysis in zeolites, which underpin many important industrial applications. It is well accepted that Lewis acidic sites (LASs) and basic sites (LBSs) as active sites in pristine zeolites are generally believed to be the extra-framework Al species and residue anion (OH-) species formed at fixed crystallographic positions after their synthesis. However, the dynamic interactions of adsorbates/reactants with pristine zeotype materials to "create" sites during real conditions remain largely unexplored. Herein, direct experimental observation of the establishment of induced active sites in silicoaluminophosphate (SAPO) by an adsorbate is for the first time made, which contradicts the traditional view of the fixed active sites in zeotype materials. Evidence shows that an induced frustrated Lewis pair (FLP, three-coordinated framework Al as LAS and SiO (H) as LBS) can be transiently favored for heterolytic molecular binding/reactions of competitive polar adsorbates due to their ineffective orbital overlap in the rigid framework. High-resolution magic-angle-spinning solid-state NMR, synchrotron X-ray diffraction, neutron powder diffraction, in situ diffuse reflectance infrared Fourier transform spectroscopy, and ab initio molecular dynamics demonstrate the transformation of a typical Brønsted acid site (Al(OH)Si) in SAPO zeolites to new induced FLP structure for hetereolytic binding upon adsorption of a strong polar adsorbate. Our unprecedented finding opens up a new avenue to understanding the dynamic establishment of active sites for adsorption or chemical reactions under molecular bombardment of zeolitic structures.

Direct Visualization of Substitutional Li Doping in Supported Pt Nanoparticles and Their Ultra-selective Catalytic Hydrogenation Performance.

It has only recently been established that doping light elements (lithium, boron, and carbon) into supported transition metals can fill interstitial sites, which can be observed by the expanded unit cell. As an example, interstitial lithium (int Li) can block H filling octahedral interstices of palladium metal lattice, which improves partial hydrogenation of alkynes to alkenes under hydrogen. In contrast, herein, we report int Li is not found in the case of Pt/C. Instead, we observe for the first time a direct 'substitution' of Pt with substitutional lithium (sub Li) in alternating atomic columns using scanning transmission electron microscopy-annular dark field (STEM-ADF). This ordered substitutional doping results in a contraction of the unit cell as shown by high-quality synchrotron X-ray diffraction (SXRD). The electron donation of d-band of Pt without higher orbital hybridizations by sub Li offers an alternative way for ultra-selectivity in catalytic hydrogenation of carbonyl compounds by suppressing the facile CO bond breakage that would form alcohols.

Characterisation of oxygen defects and nitrogen impurities in TiO2 photocatalysts using variable-temperature X-ray powder diffraction.

TiO2-based powder materials have been widely studied as efficient photocatalysts for water splitting due to their low cost, photo-responsivity, earthly abundance, chemical and thermal stability, etc. In particular, the recent breakthrough of nitrogen-doped TiO2, which enhances the presence of structural defects and dopant impurities at elevated temperatures, exhibits an impressive visible-light absorption for photocatalytic activity. Although their electronic and optical properties have been extensively studied, the structure-activity relationship and photocatalytic mechanism remain ambiguous. Herein, we report an in-depth structural study of rutile, anatase and mixed phases (commercial P25) with and without nitrogen-doping by variable-temperature synchrotron X-ray powder diffraction. We report that an unusual anisotropic thermal expansion of the anatase phase can reveal the intimate relationship between sub-surface oxygen vacancies, nitrogen-doping level and photocatalytic activity. For highly doped anatase, a new cubic titanium oxynitride phase is also identified which provides important information on the fundamental shift in absorption wavelength, leading to excellent photocatalysis using visible light.

Interstitial and substitutional light elements in transition metals for heterogeneous catalysis.

The addition of foreign element dopants to monometallic nanoparticle catalysts is of great importance in industrial applications. Both substitutional and interstitial doping of pure metallic phases can give profound effects such as altering electronic and transport properties, lattice parameters, phase transitions, and consequently various physicochemical properties. For transition metal catalysts, this often leads to changes in catalytic activity and selectivity. This article provides an overview of the recent developments regarding the catalytic properties and characterisation of such systems. In particular, the structure-activity relationship for a number of important chemical reactions is summarised and the future prospects of this area are also explored.

Calciphylaxis with a protracted course in a patient with end-stage renal failure.

Calciphylaxis is a rare condition with a high mortality involving mural calcification of small vessels and occurring primarily in patients with end-stage renal disease. Most cases are characterized by rapid progression of tender subcutaneous nodules or cutaneous plaques to epidermal necrosis, with death in the majority of cases occurring from sepsis. The condition is still poorly understood and the pathogenesis not known. We report a case of calciphylaxis following an unusually benign course. Our patient was a 63-year-old Chinese woman with end-stage renal failure undergoing peritoneal dialysis who presented with itchy pruriginous rashes on her limbs and trunk with subsequent development of eschars and ulceration. Biopsy confirmed the presence of calcification within vessel walls in the subcutis. She was managed conservatively and refused a parathyroidectomy. Surprisingly, her disease did not worsen but remained stable. She died from an acute myocardial infarction 5 months after presenting to our clinic.

Squamous cell carcinoma and Bowen's disease of the skin in Singapore.

INTRODUCTION: Non-melanoma skin cancer is one of the commonest cancers in Singapore and worldwide. The aim of our study was to evaluate the demographic and clinicopathological patterns of squamous cell carcinoma (SCC) and Bowen's disease (BD) of the skin, in order to better understand the characteristics of these tumours in our population. MATERIALS AND METHODS: Histologically proven cases of SCC and BD seen at our centre between 2002 and 2003 were retrospectively analysed according to age, sex, race, predisposing factors such as immunosuppression and ultraviolet therapy, site and size of tumour, histological differentiation and subtype, and treatment method. RESULTS: A total of 161 patients were studied--81 with SCC, 68 with BD, and 12 with both tumours. There were 199 tumours in total--105 SCC and 94 BD. For both SCC and BD, males outnumbered females (ratio of 2.4:1 and 1.5:1 respectively); patient age averaged 72.9 years and 66.8 years respectively; and Chinese were the majority race. The mean duration to presentation was 21.2 months for SCC compared with 39.9 months for BD, and common symptoms were itch, pain and bleeding for both. The mean tumour size was 19.0 mm and 18.5 mm, and the commonest site was the head and neck for both. CONCLUSIONS: SCC and BD show rather similar patient characteristics, with a predominance among males, having a predilection for the head and neck region, and with a tendency towards slow growth. As incidences increase worldwide, it is important for healthcare providers to be adept at recognising and managing nonmelanoma skin cancers.

Retrospective review of the correlation of symptoms, signs and microscopy with the diagnosis of Chlamydia trachomatis in men.

We have investigated the correlation of symptoms, signs and microscopy on the detection of Chlamydia trachomatis infection in men attending our clinic. One hundred and eleven men diagnosed with chlamydia over an 11-month period in our clinic were reviewed. Of these, 70 (63%) were symptomatic and 41 (37%) were asymptomatic. 84% (59/70) of symptomatic and 51% (21/41) of asymptomatic patients met the UK clinical criteria for diagnosis of non-gonococcal urethritis (NGU) and received treatment appropriate for chlamydia and NGU at their initial clinic visit. Our findings show that 19% (21/111) of men with Chlamydia trachomatis infection would leave the clinic untreated if a urethral smear preparation was not performed on those who were clinically asymptomatic at presentation. We feel that this is a sufficient argument to warrant continuing the current practice of testing asymptomatic men attending GUM clinics for NGU.

T-cell receptor-gamma gene analysis in evolving to advancing cutaneous T-cell lymphoma.

The diagnosis of cutaneous T-cell lymphoma is often a challenge for the dermatopathologist. Early stages can mimic inflammatory dermatoses. Our aim was to explore the applicability of a standard T-cell receptor-gamma polymerase chain reaction in various subtypes of cutaneous T-cell lymphomas. Ninety-six biopsy specimens from 38 patients were selected. These included 72 specimens of mycosis fungoides, 12 specimens of non-mycosis fungoides T-cell lymphomas, and 12 specimens in which histology was non-specific or equivocal in patients who were later diagnosed to have lymphoma. T-cell clones were detected in 53 of 72 specimens of mycosis fungoides and eight of 12 specimens of non-mycosis fungoides lymphomas. Of the 72 specimens of mycosis fungoides, T-cell clones were detected in eight of 10 specimens of mycosis fungoides-associated follicular mucinosis and pigmented purpura-like mycosis fungoides. Four specimens from the 12 prediagnostic for cutaneous T-cell lymphomas showed presence of T-cell clones, identical to subsequent clones detected when lymphoma was fully established. In specimens where histology is not diagnostic and T-cell receptor-gamma gene analysis is positive, patients should be followed up closely. T-cell receptor-gamma gene analysis is a useful adjunct to histological diagnosis of early stage and variant types of mycosis fungoides.

Juvenile elastoma: a forme fruste of the Buschke-Ollendorff syndrome?

We describe an Asian child with juvenile elastoma who presented to us at 9 years of age with flesh-coloured nodules on his thigh. Histologically, H&E sections were normal, but elastin stains showed collections of increased and thickened elastic fibres consistent with juvenile elastoma. Radiological examination did not demonstrate osteopoikilosis. However, we postulate that he may represent a forme fruste of the Buschke-Ollendorff syndrome or early presentation prior to the subsequent development of osteopoikilosis.