Analysis of temperature programmed desorption (TPD) data for the characterisation of catalysts containing a distribution of adsorption sites

This paper discusses some methods of analysing TPD data for samples obeying first-order desorption kinetics and proposes several improvements to existing practice. The methods apply in the case when the Arrhenius parameters A and E for each site are independent of coverage, and thus are normally suitable for the characterisation of porous solids. An improved implementation of the condensation approximation method is proposed to gain an initial estimate of the adsorption site distribution. Further, a variation of the method is proposed that can be used when A is a function of E. The initial estimate of the distribution can be used to analyse data obtained by an interrupted TPD experiment, in which heating is halted at a specified temperature. This method provides a reliable method of determining the parameter A for a peak in the distribution. Finally, regularisation procedures for obtaining physically sensible distributions from "noisy" TPD data are discussed. It is shown that a penalty function based on the square of the second derivative of the distribution is normally most suitable for analysing TPD data, at least in the case when the L-curve method is used to select the regularisation parameter.     

TiO<Subscript>2</Subscript>-assisted photodegradation of pharmaceuticals — a review

Pharmaceutical compounds have been detected in the environment and potentially arise from the discharge of excreted and improperly disposed medication from sewage treatment facilities. In order to minimize environmental exposure of pharmaceutical residues, a potential technique to remove pharmaceuticals from water is the use of an advanced oxidation process (AOP) involving titanium dioxide (TiO₂) photocatalysis. To evaluate the extent UV/TiO₂ processes have been studied for pharmaceutical degradation, a literature search using the keywords ‘titanium dioxide’, ‘photocatalysis’, ‘advanced oxidation processes’, ‘pharmaceuticals’ and ‘degradation’ were used in the ISI Web of Knowledge TM, Scopus TM and ScienceDirect TM databases up to and including articles published on 23 November 2011. The degradation rates of pharmaceuticals under UV/TiO₂ treatment were dependent on type and amount of TiO₂ loading, pharmaceutical concentration, the presence of electron acceptors and pH. Complete mineralization under particular experimental conditions were reported for some pharmaceuticals; however, some experiments reported evolution of toxic intermediates during the photocatalytic process. It is concluded that the UV/TiO₂ system is potentially a feasible wastewater treatment process, but careful consideration of the treatment time, the loading and the type of TiO₂ (doped vs. undoped) used for a particular pharmaceutical is necessary for a successful application (198 words).      

Heterologous expression in Saccharopolyspora erythraea of a pentaketide synthase derived from the spinosyn polyketide synthase

A truncated version of the spinosyn polyketide synthase comprising the loading module and the first four extension modules fused to the erythromycin thioesterase domain was expressed in Saccharopolyspora erythraea. A novel pentaketide lactone product was isolated, identifying cryptic steps of spinosyn biosynthesis and indicating the potential of this approach for the biosynthetic engineering of spinosyn analogues. A pathway for the formation of the tetracyclic spinosyn aglycone is proposed.     

The electronic structure of heteroaromatic molecules; non-empirical calculations and photoelectron spectra for the isomeric-thiazoles and -thiadiazoles

The He(I) and MgKα photoelectron spectra are reported for the isomeric thiazoles, and He(I) spectra for the isomeric-thiadiazoles. Marked fine structure is apparent on some of the spectra. Comparison with the earlier spectra for thiophen and the azoles, and with ab initio calculations for the seven compounds, has led to assignment of the spectra. The calculations suggest that 1,3,4-thiadiazole is less aromatic than the other title compounds. As expected, the role of the 3d_s orbitals is found to be that of polarisation functions for all of the compounds, but inclusion of these orbitals leads to much better agreement with the observed dipole moments, both in magnitude and direction.     

The coordination chemistry of 2,2′-oxydibenzoic acid, 2,2′-thiobenzoic acid, 3,3′-oxydipropionic acid and 3,3′-thiodipropionic acid with selected first row transition metal ions

Summary Solid metal complexes of the title ligands are described. The largest range is prepared with 2,2-oxydibenzoic acid, namely Zn^IIL · 1.5 H₂O, Cu^IIL · H₂O, Co^IIL · H₂O, Fe^IIIL · (OH) and Fe^IIIL · (OH) · H₂O where L denotes the ligand dianion. Zinc(II) and copper(II) complexes of the other ligands are prepared for comparison and these have, generally, the stoichiometry ML · xH₂O (0.5 x 1.5; M = Cu or Zn).The i.r. spectra are discussed and antiferromagnetic behaviour is noted for the copper(II) and iron(III) complexes. Magnetic properties are investigated over the 80–300 K range in several cases. Reflectance (u.v./visible) spectroscopy and Mössbauer spectroscopy have been used, where appropriate, in association with the magnetic data and i.r. data to suggest that the metal is located in a distorted MO₆ environment involving unsymmetrically bidentate carboxylate groups and -aquo or -hydroxo groups.     

Preparation and structural analysis of (±)‐cis‐ethyl 2‐sulfanylidenedecahydro‐1,6‐naphthyridine‐6‐carboxylate and (±)‐trans‐ethyl 2‐oxooctahydro‐1H‐pyrrolo[3,2‐c]pyridine‐5‐carboxylate

Bicycle ring closure on a mixture of (4aS,8aR)‐ and (4aR,8aS)‐ethyl 2‐oxodecahydro‐1,6‐naphthyridine‐6‐carboxylate, followed by conversion of the separated cis and trans isomers to the corresponding thioamide derivatives, gave (4aSR,8aRS)‐ethyl 2‐sulfanylidenedecahydro‐1,6‐naphthyridine‐6‐carboxylate, C₁₁H₁₈N₂O₂S. Structural analysis of this thioamide revealed a structure with two crystallographically independent conformers per asymmetric unit (Z′ = 2). The reciprocal bicycle ring closure on (3aRS,7aRS)‐ethyl 2‐oxooctahydro‐1H‐pyrrolo[3,2‐c]pyridine‐5‐carboxylate, C₁₀H₁₆N₂O₃, was also accomplished in good overall yield. Here the five‐membered ring is disordered over two positions, so that both enantiomers are represented in the asymmetric unit. The compounds act as key intermediates towards the synthesis of potential new polycyclic medicinal chemical structures.     

Engineered biosynthesis of hybrid macrolide polyketides containing D-angolosamine and D-mycaminose moieties

The glycosylation of natural product scaffolds with highly modified deoxysugars is often essential for their biological activity, being responsible for specific contacts to molecular targets and significantly affecting their pharmacokinetic properties. In order to provide tools for the targeted alteration of natural product glycosylation patterns, significant strides have been made to understand the biosynthesis of activated deoxysugars and their transfer. We report here efforts towards the production of plasmid-borne biosynthetic gene cassettes capable of producing TDP-activated forms of D-mycaminose, D-angolosamine and D-desosamine. We additionally describe the transfer of these deoxysugars to macrolide aglycones using the glycosyl transferases EryCIII, TylMII and AngMII, which display usefully broad substrate tolerance.     

A simple and efficient synthesis of optically pure 4-alkylisoxazolidin-4-ols

The reaction between N-hydroxyphthalimide and optically pure epichlorohydrin followed by addition of methanol represents a straightforward procedure for the synthesis of isoxazolidin-4-ols in high enantiomeric purity. Under the same conditions, the reaction of glycidyl arenesulfonates can lead to different products depending on the nature of the sulfonate. This property allowed the synthesis of both enantiomers of 4-methylisoxazolidin-4-ol from the same chiral epoxide starting material.