Applications of enzymes to the preparation of optically active compounds

The introduction to this thesis is in the form of a review entitled 'Aspects of Selectivity in Lipase Catalysed Biotransformations'. Each of the most widely used lipases have been discussed. The reactions of each lipase have been extensively reviewed with the aim of establishing whether any trends have appeared in the characteristics of compounds accepted as substrates. The remaining chapters cover five unrelated studies in areas of resolutions of chiral compounds using biotransformations. In Chapter 2 the resolution of a P-blocker precursor was attempted via lipase-catalysed hydrolysis. l-Chloro-2- hydroxy-3[4(2-acetoxyethyl) phenoxy] propane was obtained in high enantiomeric excess from hydrolysis of the corresponding butyrate ester with lipases from Mucor or Rhizopus sp. Yields were low however, owing to enzyme inhibition by the butyric acid byproduct. In Chapter 3 the resolution of methyl 3-hydroxy-4-(p- chlorophenylthio)-butanoate was carried out. Hydrolysis of the corresponding butanoate ester with lipase P gave the R enantiomer of the desired compound in high enantiomeric excess. Transesterification of the racemic alcohol with vinyl acetate, again catalysed by lipase P, furnished the opposite enantiomer in 62%ee. Chapter 4 is concerned with the resolution of a chiral acid, namely 3-methyl-4-oxo-4(4-aminobenzyl) butanoic acid. This was attempted by hydrolysis of an ester using pig liver esterase and various lipases and via microbial reduction of the corresponding unsaturated compound. The reactions were all found to be non-stereoselective. Chapters 5 and 6 discuss novel methods for the enzymatic resolution of ketones. The enantioselective enzymatic hydrolysis of oxime esters is discussed in Chapter 5. The resulting optically enriched oximes may readily be cleaved to the ketones. This method was unsuccessful in the resolution of the 2-methyl- and 2,6- dimethylcyclohexanones. A low enantiomeric excess was achieved in the resolution of norcamphor, and attempts to improve this using a purified enzyme and by variation of the ester chain were unsuccessful. However, this represents the first example of the indirect enzymatic resolution of ketones. In Chapter 6 the enantioselective hydrolysis of enol acetates of three ketones was attempted. This method of resolution was unsuccessful in the resolution of 2-methyl and 2,6- dimethylcyclohexanones. In the case of norcamphor the ketone was obtained in low enantiomeric excess

Hyperfeatures - multilevel local coding for visual recognition

International audienceHistograms of local appearance descriptors are a popular representation for visual recognition. They are highly discriminant and have good resistance to local occlusions and to geometric and photometric variations, but they are not able to exploit spatial co-occurrence statistics at scales larger than their local input patches. We present a new multilevel visual representation, ‘hyperfeatures', that is designed to remedy this. The starting point is the familiar notion that to detect object parts, in practice it often suffices to detect co-occurrences of more local object fragments – a process that can be formalized as comparison (e.g. vector quantization) of image patches against a codebook of known fragments, followed by local aggregation of the resulting codebook membership vectors to detect co-occurrences. This process converts local collections of image descriptor vectors into somewhat less local histogram vectors – higher-level but spatially coarser descriptors. We observe that as the output is again a local descriptor vector, the process can be iterated, and that doing so captures and codes ever larger assemblies of object parts and increasingly abstract or ‘semantic' image properties. We formulate the hyperfeatures model and study its performance under several different image coding methods including clustering based Vector Quantization, Gaussian Mixtures, and combinations of these with Latent Dirichlet Allocation. We find that the resulting high-level features provide improved performance in several object image and texture image classification tasks

Practical Application of Methanol-Mediated Mutualistic Symbiosis between Methylobacterium Species and a Roof Greening Moss, Racomitrium japonicum

Bryophytes, or mosses, are considered the most maintenance-free materials for roof greening. Racomitrium species are most often used due to their high tolerance to desiccation. Because they grow slowly, a technology for forcing their growth is desired. We succeeded in the efficient production of R. japonicum in liquid culture. The structure of the microbial community is crucial to stabilize the culture. A culture-independent technique revealed that the cultures contain methylotrophic bacteria. Using yeast cells that fluoresce in the presence of methanol, methanol emission from the moss was confirmed, suggesting that it is an important carbon and energy source for the bacteria. We isolated Methylobacterium species from the liquid culture and studied their characteristics. The isolates were able to strongly promote the growth of some mosses including R. japonicum and seed plants, but the plant-microbe combination was important, since growth promotion was not uniform across species. One of the isolates, strain 22A, was cultivated with R. japonicum in liquid culture and in a field experiment, resulting in strong growth promotion. Mutualistic symbiosis can thus be utilized for industrial moss production

How Can Selection of Biologically Inspired Features Improve the Performance of a Robust Object Recognition Model?

Humans can effectively and swiftly recognize objects in complex natural scenes. This outstanding ability has motivated many computational object recognition models. Most of these models try to emulate the behavior of this remarkable system. The human visual system hierarchically recognizes objects in several processing stages. Along these stages a set of features with increasing complexity is extracted by different parts of visual system. Elementary features like bars and edges are processed in earlier levels of visual pathway and as far as one goes upper in this pathway more complex features will be spotted. It is an important interrogation in the field of visual processing to see which features of an object are selected and represented by the visual cortex. To address this issue, we extended a hierarchical model, which is motivated by biology, for different object recognition tasks. In this model, a set of object parts, named patches, extracted in the intermediate stages. These object parts are used for training procedure in the model and have an important role in object recognition. These patches are selected indiscriminately from different positions of an image and this can lead to the extraction of non-discriminating patches which eventually may reduce the performance. In the proposed model we used an evolutionary algorithm approach to select a set of informative patches. Our reported results indicate that these patches are more informative than usual random patches. We demonstrate the strength of the proposed model on a range of object recognition tasks. The proposed model outperforms the original model in diverse object recognition tasks. It can be seen from the experiments that selected features are generally particular parts of target images. Our results suggest that selected features which are parts of target objects provide an efficient set for robust object recognition

Stable Carbon and Nitrogen Isotopes in a Peat Profile Are Influenced by Early Stage Diagenesis and Changes in Atmospheric CO2 and N Deposition

In this study, we test whether the δ13C and δ15N in a peat profile are, respectively, linked to the recent dilution of atmospheric δ13CO2 caused by increased fossil fuel combustion and changes in atmospheric δ15N deposition. We analysed bulk peat and Sphagnum fuscum branch C and N concentrations and bulk peat, S. fuscum branch and Andromeda polifolia leaf δ13C and δ15N from a 30-cm hummock-like peat profile from an Aapa mire in northern Finland. Statistically significant correlations were found between the dilution of atmospheric δ13CO2 and bulk peat δ13C, as well as between historically increasing wet N deposition and bulk peat δ15N. However, these correlations may be affected by early stage kinetic fractionation during decomposition and possibly other processes. We conclude that bulk peat stable carbon and nitrogen isotope ratios may reflect the dilution of atmospheric δ13CO2 and the changes in δ15N deposition, but probably also reflect the effects of early stage kinetic fractionation during diagenesis. This needs to be taken into account when interpreting palaeodata. There is a need for further studies of δ15N profiles in sufficiently old dated cores from sites with different rates of decomposition: These would facilitate more reliable separation of depositional δ15N from patterns caused by other processes