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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
481

Synthesis, Conformation and Glycosidic Bond Stabilities of Septanoside Sugars

Dey, Supriya January 2014 (has links) (PDF)
Seven-membered cyclic sugars, namely, septanoses and septanosides, are less commonly known sugar homologues. Synthesis of septanoses arise an interest due to their configurational and conformational features and the attendant possibilities to explore their chemical and biological properties. Septanosides derivatives, mostly, deoxy-septanosides were synthesized, by many synthetic methodologies, such as, Knoevengal condensation, ring-closing metathesis, Bayer-Villeger oxidation and ring-expansion of 1,2-cyclopropanted glycals as key steps. Apart from septanosyl monosaccharides, septanoside containing di- and tri-saccharides were also performed using glycosylation and ring expansions. Another area of sustained interest is the studies of the stabilities of glycosidic bonds. Acid- and enzyme-catalyzed hydrolysis of glycosidic bond were investigated intensely in the case of pyranosides and furanosides. The explanation of the hydrolysis of such stereomeric sugars were rationalized on the basis of stereoelectronic effects, such as, (i) antiperiplanarity; (ii) synperiplanarity of lone-pair of electrons involed in the hydrolysis process; (iii) steric effects; (iv) field and hyperconjugative effects; (v) conformational effects; (vi) disarming torsional effects and (vii) substituent effects. Chapter 1 of the thesis describes a survey of (i) synthesis of deoxy-septanosides and septanoside-containing di-and tri-saccharides and (ii) acid-catalyzed hydrolysis of glycopyranosides. In a programme, it was desired to identify a new methodology for the synthesis of 2-deoxy-2-C-septanosides. Synthesis of various septanosides from 2-hydroxy glycals, namely, oxyglycals, involves intermediates, such as, vinyl halide (III) and diketone (IV) (Scheme 1). These intermediates were identified as precursors for the synthesis of desired 2-deoxy-2-C-septanosides. Scheme 1 reactions, namely, Heck, Suzuki and Sonogashira reaction for the formation of hither-to unknown septanoside, branching out at C-2. Heck coupling and Suzuki coupling reaction of bromo-oxepine was performed using activated alkenes, acrylates and substituted boronic acid, respectively, in presence of Pd(OAc)2, to furnish 2-deoxy-2-C-alkyl/aryl septanoside derivatives (Scheme 2). Scheme 2 2-deoxy-2-C-alkynyl septanoside derivatives (Scheme 3). Scheme 3 BnO OOMe BnO OOMePd(PPh3)2Cl2,CuIBr BnO R BnO DMF:THF:Et3N(3:2:1)BnO OBn 98 oC, 72 h BnO OBn R=Ph,SiMe3,C6H13 One of the 2-deoxy-2-C-alkyl septanoside derivative was converted to the corresponding protecting-group free 2-deoxy-2-C-alkyl septanoside, using hydrogenolysis (Pd/C, H2) and NaBH4-mediated reduction. Chapter 2 presents details of the synthesis of 2-deoxy-2-C-alkyl/aryl/alkynyl septanoside derivatives from a bromo-oxepine. Continuing the efforts to extend the ring-opening of oxyglycal derived gem-dihalo-1,2¬cyclopropanted sugar, a Lewis acid-catalyzed ring-opening was considered important. The presence of an additional substituent in C-2 of oxyglycal switches reactivity as compared to glycals. For example, ring-opening of glycal derived gem-dihalo-1,2-cyclopropane generates 2-C-branched pyranoside, whereas corresponding oxyglycal generates oxepines even when both the reactions were performed under a mild basic condition, illustrating a sufficient reactivity difference between a glycal and an oxyglycal. Thus, ring-opening reaction of gem-dichloro-1,2-cyclopropanted oxyglycal in the presence of a Lewis acid, hither-to unknown, was examined. In this event, it was found that ring-opening reaction led to chloro-oxepine derivatives in the presence of AgOAc, using alcohol as nucleophiles. Primary, secondary, unsaturated and aromatic alcohols were used in the ring-opening reaction. The ring-opening reaction was stereoselective and only α-anomer was obtained in a good yield in each case (Scheme 5). The counter-anion also reacted in an instance, so as to furnish O-acetyl chloro-oxepine during the ring-opening reaction. Scheme 5 The course of the reaction in the absence of alcohol led to afford only the O-acetyl chloro-oxepine (Scheme 6). Scheme 6 It became pertinent to compare the result this work with that of AgOAc-catalyzed ring-opening of glycal derived gem-dihalo-1,2-cyclopropanated sugar, which led to C-furanoside derivative, as reported by Harvey and co-workers. The sequence of reactions involved were protonation of the endo-cyclic oxygen, followed by ring-opening to generate resonance stabilized allylic ion, which rearranged to C-furanoside. In contrast, oxyglycal derived gem-dihalo-1,2-cyclopropane studied herein led to chloro-oxepine exclusively, without subsequent rearrangement. Ring-opening of glucal derived gem-dihalo-1,2-cyclopropanated sugars, followed by cyclization to C-furanoside were likely to have occurred, due to isomerisation of less-substituted endo-cyclic double bond at C2-C3 of oxepine to C1-C2 unsaturated vinyl ether. Such a reaction was related closely to the acid-catalyzed rearrangement in less-substituted oxepine systems. On the other hand, gem-dichloro-1,2¬cyclopropanated oxyglycal derived chloro-oxepine did not undergo such an isomerisation, possibly due to unsaturation being present at highly substituted C2-C3 carbons (Scheme 7). Thus, the presence of an additional oxy-substituent at C-2 in oxyglycal derived cyclopropane derivative plays a major role to control the reactivity, as compared to glycal derived cyclopropane derivatives. Scheme 7 without undergoing further reactions, was confirmed further by the following reactions: (i) RuCl3¬NaIO4 mediated oxidation; (ii) NaBH4 reduction and (iii) Pd/C mediated hydrogenolysis (Scheme 8). Scheme 8 1,2-cyclopropane to exclusive formation of chloro-oxepine in the presence of AgOAc. It was planned further to synthesize a 1,7-linked-α-D-diseptanoside, through the oxyglycal route. Ring-opening of oxyglycal derived gem-dihalo-1,2-cyclopropanated derivative with 6¬hydroxy glycal led to 1,7-α-linked disaccharide unit. The following reactions were performed in order to synthesize 1,7-linked-α-diseptanoside 2: (i) cyclopropanation of the glycal double bond; (ii) ring opening of the gem-dihalo cyclopropane; (iii) RuO4 mediated oxidation; (iv) NaBH4 reduction and (v) hydrogenolysis using Pd/C, H2 (Scheme 9). Similar methodology was used for the synthesis of monoseptanoside, namely, n-pentyl-D-glycero-D-galacto-septanoside. Scheme 9 1 Oxyglycal route was also used for the synthesis of 2-chloro-2-deoxy septanoside 3, using hydrogenolysis (Pd/C, H2) and NaBH4 mediated reduction of chloro-oxepine (Scheme 10). Scheme 10 A kinetic study of the hydrolytic stabilities of mono-and diseptanoside was undertaken using an acid-catalysis, in a subsequent investigation. In the course of studies, it was observed that glycosidic bond in the reducing-end hydrolyzed twice faster than that at the non-reducing end, whereas glycosidic bond in monosaccharide 1 hydrolyzed 1.5 times faster than of reducing-end glycosidic bond in diseptanoside 2. Further, it was found that the replacement of the C-2 hydroxyl group by a chloride group reduced the rate of hydrolysis (Table 1). Table 1. First order rate constants and thermodynamic parameters for the acid-catalyzed hydrolysis of glycosidic bond in septanosides 1, 2 and 3. Compound Rate of hydrolysis ΔH# ΔS# ΔG# (kobs) (104 s-1) (kcal/mol) (cal/mol K) (kcal/mol) 35 oC 45 oC 85 oC 90 oC a non-reducing end of 2. A computational study was conducted, in order to gain further insight into the hydrolysis, using B3LYP/6-311G* level theory in the Gaussian 09 program packages. Calculations using the PCM solvent model with water as the solvent showed that the orientation of hydroxylmethyl group plays an important role. In the case of 1, the gg conformer was calculated stable by 2.12 kcal/mol, as compared, to tg-conformer. In the gg conformation, the optimal positioning of the dipole C7-O7 stabilized the oxo-carbonium ion in the transition state (Figure 1). Also, hydroxyl group at C4 stabilized the transition state, through non-covalent interaction (Figure 1). The transition state for the hydrolysis of 1 was found to present activation barrier (∆G#) of 19.9 kcal/mol, which was in good agreement with value for 1 (∆G# = 23.26 kcal/mol), as calculated from Erying plot (Table 1). On the other hand, inductive effect of the chloride group, as well as, the tg-orientation of the hydroxymethyl group appeared to contribute to the slower rate of the hydrolysis. Figure 1. gg- and tg-conformations in the ground state of 1. Chapter 4 describes synthesis of 1,7-linked-α-D-diseptanoside, 2-chloro-2-deoxy septanoside and their acid-catalyzed hydrolysis studies. Solid-state and solution phase conformation of septanosides are rare at present even when solid-state structures of pyranoside and furanosides are known commonly, that provide rich information of covalent and non-covalent interactions. In this context, single crystal X-ray structural analysis of septanosides, namely, n-pentyl-2-chloro-2-deoxy-α-D-manno-sept-3-uloside 4 and p-bromo phenyl 4,5,7-tri-O-benzyl-β-D-glycero-D-talo-septanoside 5 were analyzed. It was observed that the solid-state structure of 4 adopted twist-chair conformation, namely, 5,6TC3,4, whereas 5 adopted O,1TC2,3 conformation (Figure 2). An analysis of non-covalent interactions revealed that a dense network of O−H···O and C−H···O stabilized the crystal lattice of 4, whereas O−H···O and C−H···π stabilized the crystal lattice of 5. Chapter 5 describes the detailed analysis of X-ray crystal structure of two septanoside derivatives including non-covalent interactions responsible for the stabilization of crystal lattice. Figure 2. ORTEP of 4 and 5 with displacement ellipsoids, at a 10 % and 50 % probability level. In summary, the thesis established the following major results: (i) synthesis of 2-deoxy-2-C¬alkyl/aryl septanoside from a bromo-oxepine, using organometallic C-C bond forming reactions; (ii) the ring-opening reaction of oxyglycal derived gem-dihalo-1,2-cyclopropane in the presence of AgOAc and the effect of additional C-2 oxy-substituent in the reactivity, in comparison to glycal; (iii) an oxyglycal route for the synthesis of 1,7-linked-α-D-diseptanoside, 2-chloro-2-deoxy septanoside and their acid-catalyzed hydrolysis studies and (iv) solid-state X-ray crystal structural analysis and computational analysis of the conformation and non-covalent interactions associated with the stabilization of crystal lattice. Overall, the studies presented in the thesis provide a new insight into the synthesis, acid-catalyzed hydrolysis and solid-state structural analysis of septanoside derivatives.
482

Nature of Local Interactions at cisPro-Aro Peptide Sequences in Proteins : Evidences for van der Waals type Interactions. Design and Synthesis of Novel Covalent Surrogates for the Peptide Hydrogen Bond

Gupta, Sunil K January 2016 (has links) (PDF)
This thesis titled, “Nature of Local Interactions at cisPro-Aro Peptide Sequences in Proteins: Evidences for van der Waals type Interactions. Design and Synthesis of Novel Covalent Surrogates for the Peptide Hydrogen Bond”, describes two important studies. The first is to gain a thorough understanding of the nature of interactions that govern cisPro stability at Pro-Aro sequences, which described in the first four chapters. The final chapter describes the synthesis of novel 4-carbon covalent surrogates for the peptide H-bonding interaction. Chapter 1: Local Interactions Governing cisPro Stability: Refining the Model Peptides Chapter 1 Section A: Understanding the role of inter-side chain CH•••Aro interaction in cis-trans isomerization at Pro-Aro and Aro-Pro Sequences. This chapter is divided into two sections. In the first section an exhaustive overview of earlier investigations into the nature of local interactions at Xaa-cisPro-Aro and Aro-cisPro-Xaa peptide sequences, by various groups, are discussed. Most studies have found evidence for the close assemblage between side chains of residues flanking cisPro motifs, when at least one of them is an aromatic group. An electronic C-H•••π nature has been proposed for these assemblies and they are proposed to influence the cisPro stability. We highlight those features in these studies that indicate that these interactions are not always electronically tunable, are insensitive to presence of strong chaotropes in the solvent and occur at protein sequences lacking Pro or cisPro; all of which contradict the electronic C-H•••π model for these inter-side chain assemblages and their perceived influence on cisPro stability. Chapter 1 Section B: Investigation of the Nature of H Xaa•••Aro interaction at Xaa-Pro-Pro-Phe-sequences In Section B, we design and synthesize Pro-Aro containing short peptide models to investigate the nature of local C-H•••Aro interactions in them. We synthesize a series of homologous Pro-Pro-Aro containing peptides (modeled based on earlier studies) and investigate the relative populations of its four Xaa-Pro rotamers using extensive 1D and 2D NMR techniques including TOCSY, HSQC and ROESY. We find several drawbacks that make this a relatively deficient model. Firstly, their relative populations of the rotamers (the most important data for current investigation) cannot be determined with high fidelity as they are dependent on the solvent polarity, solute concentration and chemical shift degeneracy of crucial NMR signals for the rotamers. Importantly, the populations of a few rotamers are influenced by strong 13-membered ring backbone H-bonds. Notably, some of the cisPro rotamers do not even contain the inter-side chain assembly, whose nature is under investigation. Design of novel models – unconstrained by H-bonds We design the Acyl-Pro-Pro-Aro-OMe peptides that lack the possibility of forming the 13-membered ring H-bonded structures. Thorough 1D and 2D NMR analyses of these models reveal that strong Type VI β-turn type 10-membered ring H-bonds are formed in the rotamers of these models – hence precluding their applications for current study. Interestingly, the relative rotamer populations are strongly influenced by solvent polarity and are entirely different from those of the corresponding C-terminal amide models. We further discover that the Pro-Pro-Aro motif is not essential to express the inter-side chain interactions – Ala-Pro-Aro are sufficient. Formation of the 10-membered H-bonding interactions, however, are not precluded. Chapter 2: Design and Synthesis of Acyl-Pro-Phe-OMe: Novel models to investigate the role of HαXaa•••Aro interactions on Xaa-cisPro-Aro stability. Chapter 2 Section A: Design, Synthesis and Conformational Analysis of Ibu-Pro-Phe-OMe Chapter 2 is divided into two sections. In Section A, we replace the amino acid at the N-terminal of the putative Pro residue with simple isosteric isobutyryl group, the resulting minimalist dipeptide model shows the exclusive influence of desired inter-side chain interactions in the cisPro rotamer. Solvent polarity and temperature coefficient studies reveal that absence of any intramolecular H-bonding or Oπ* interactions in it. 1D and 2D NMR analyses clearly indicate the close proximity between the side chains of Ibu and Phe exclusively in the cisPro rotamer. The Kc/t value decreases upon mutation of Phe to Ala. All these features favor the Ibu-Pro-Phe-OMe as an ideal minimalistic model for investigating the nature of Ibu•••Ph assemblages in the cisPro rotamer. Chapter 2 Section B: Investigation of CH•••Aro /Alp•••Alp interactions in Ibu-cisPro-Xaa-OMe In Section B, the 1D and 2D NMR analyses of the complete set of the aliphatic and aromatic analogues Ibu-Pro-Xaa-OMe were investigated. DMSO-d6 was found to be the best solvent for mimicking both the folded and the unfolded local environments of these short peptide sequences. The HαIbu•••Aro assemblage is observed in Aro analogues, but cannot be electronically tuned. The aliphatic analogues also surprisingly contain the HαIbu•••Alp interactions! The Kc/t values (cisPro %) increase in the aliphatic analogues too, where the aliphatic side chain is long. Increase in cisPro stability is not due to ring current effects or intramolecular H-bonds or Oπ* interactions. It seems to be due to van der Waals type interactions between the involved side chains, either of which need not be aromatic in nature. Chapter 3: Nature of Inter-Side Chain Interactions at Acyl-cisPro-Aro Sequences: Evidence for van der Waals Interactions Chapter 3 Section A: Investigation of nature of inter-side chain interactions in R-CO-cisPro-Phe-OMe Chapter 3 has two sections. Section A describes the systematic design and synthesis of Acyl-Pro-Phe-OMe homologues where first the steric bulk and hence the surface area of the aliphatic side chain of the acyl group is varied. Interaction of the phenyl ring of Phe seems to occur with the Cα-Cβ σ-bond of the acyl group. Branching at either Cα or Cβ seems to destabilize the cisPro rotamer. Aliphatic•••Aromatic interactions overwhelm the cisPro rotamer population to be greater than that of transPro. In the analogues where the acidity of the acyl Cα-H bond is increased, the Kc/t does not increase correspondingly. The Δδ(trans-cis) ppm shifts of HαAcyl protons are dependent exclusively on its acidity rather than on the Kc/t values. In carbamyl-Pro, which entirely lack the HαAcyl proton, the Kc/t values are significantly high and improve as the aliphatic surface on the alkoxy group increases. Introduction of benzyloxy carbamyl group at Pro renders almost the same Kc/t values as that of ethyloxy carbamate. All these data contradict the C-H•••π interaction model and strongly support a van der Waals type interaction between the Acyl (preceding cisPro) group’s Xα-Yβ σ-bond and the Aro or Alp side chains (succeeding cisPro). Chapter 3 Section B: Evidence for the Van der Waals nature of Inter Side Chain (Acyl•••S.C.Aro/Alp) interactions- Determination of Interactions energies In Section B, a thorough investigation of both aliphatic•••aliphatic and aliphatic•••aromatic interactions on the background of homologous Acyl-Pro-Aro/Alp-OMe peptide models is undertaken. These models uniquely allow the delineation of contribution of the van der Waals interactions and the ring current effects to the cis/trans isomerization in these peptides. We see that the energy of the van der Waals component of these aliphatic•••aliphatic and aliphatic…aromatic interactions increase linearly with increase in Kc/t, in both DMSO-d6 and D2O. On other hand, energy from the ring current effects largely remains invariant. The Acyl•••Aro/Alp interactions are not hydrophobic and are facilitated by conformational effects. Chapter 4: Crystallographic evidence for van der Waals interaction-mediated stabilization of cisPro conformers Chapter 4 Section A: Systematic crystallization and crystal structure analyses of homologous Xaa-cisPro-Alp and Xaa-cisPro-Aro rotamers: Evidence for van der Waals interactions Chapter 4 has two sections, both of which present crystallographic evidence for the van der Waals nature of the Xaa•••Aro interactions at Xaa-cisPro-Aro sequences. Section A describes the unique crystal structures of five of the Acyl-Pro-Alp-OMe analogues that have been synthesized in the current study. All of them remarkably crystallize with two features: 1) the Acyl-Pro peptide bond adopts the cisPro rotamer in all; and 2) the aliphatic side chains of the acyl group and the Alp side chain are involved in van der Waals type interactions. The cisPro rotamers of even the bulkiest motifs, namely Ibu-Pro-Val-OMe, Piv-Pro-Ile-OMe and Piv-Pro-Leu-OMe crystallize, stabilized by van der Waals packing between aliphatic groups of the acyl and the Leu/Ile/Val side chains. Where the side chains are not long enough to make sub-van der Waals contacts with each other, their acyl C′-Cα σ-bond rotations are restricted due to Oσ* interactions involving the charge on the acyl carbonyl O. Where this occurs, the short space between the acyl and Alp side chains are filled in by aliphatic groups from neighbouring molecules at sub van der Waals distances. The Pro, Alp and χ1(Alp) dihedral angles are restricted to narrow range of values, irrespective of the length of Alp side chain, indicating that this backbone conformation is a conformational minimum when i+3i backbone H-bond is removed, with Pro at the i+1st position. This is further substantiated in Piv-Pro-Gly-OMe, which crystallizes in trans-Pro form, but still adopts similar backbone dihedral angles in spite of lacking any Alp side chain for interactions with the acyl group. Three of the Acyl-Pro-Aro-OMe models also crystallize in cisPro rotamer forms – both exhibit van der Waals type contacts between the Acyl group and backbone of Phe, rather than the aromatic ring of Phe. The phenyl ring of Phe may or may not form intramolecular Ph•••Pro inter-side chain contacts – which is not a pre-requisite for cisPro stabilization. No C-H••• interactions are observed anywhere in these peptides – van der Waals type contacts alone predominate in all cases. There are no abnormal distortions in bond angles or lengths even in the most sterically hindered cases, signifying that the conformations of these cisPro rotamers involving aliphatic•••aliphatic type contacts are natural minima. Chapter 4 Section B: Mining the PDB for Statistical Evidence of van der Waals interactions Section B of chapter 4 describes the data mining and statistical analyses of Xaa-cisPro-Phe, Xaa-cisPro-Val and Xaa-cisProLeu sequences in the PDB. The PEARL program was used to mine the PDB data. The overall frequency of 5.3% for appearance of cisPro among all Xaa-Pro peptide bonds, improves when Xaa is Phe or Tyr. However, several anomalies highlight the need for refining the analyses set to only those sequences where the side chains of Xaa and Aro/Alp face each other. In this refined set, clearly, inter side chain Xaa•••Alp/Aro contacts take precedence over even Aro•••Pro interactions at Aro-cisPro sequences (where Xaa is Aro). The Phe and the Leu side chains induce similar conformational effects on the preceding Xaa-Pro backbone. So does Val. Strong aliphatic•••aliphatic inter side chain contacts at van der Waals distances are observed to flank cisPro in several proteins. Substitution at the Cα of Xaa governs the proximity of the approaching side chain of Alp / Aro residue. The Cα-H of Xaa steers away from the Aro side chain at Xaa-Pro-Phe sequences, as the Aro group gets closer to it – implying the absence of ordered C-H••• contacts between them. There is consistent parallel alignment between Cα-Cβ -bond of Xaa and the C -C bond of the approaching side chain of Alp or Aro group – clearly highlighting the presence of van der Waals type interactions between them. All these evidences clearly point towards the van der Waals nature of local interactions at cisPro-Aro/Alp peptide sequences. Chapter 5: A novel 4-carbon covalent surrogate model for peptide H-Bond Chapter 5 describes the design and synthesis of novel 4-carbon covalent surrogates for the peptide H-bond (HBS). These surrogates would allow the unique constraining of two peptide strands in their extended conformations. The covalent HBS contain four orthogonal functional groups for independent extension at all of the four ends – similar to an endogenous inter-strand peptide H-bond. The synthesis of the surrogate is achieved by directly using natural chiral amino acid derivatives, beginning from amino alcohols obtained from reduction of desired amino acids. Suitably N-protected alcohols undergo oxidation to aldehyde followed by Grignard addition of allyl magnesium bromide, TBDMS protection of the homoallylic alcohol and reductive ozonolysis of the olefin to get a primary alcohol which is subject to Fukuyama-Mitsunobu reaction with desire protected peptide. The residue preferences that produce strongest inter-strand H-bonds were explored. The designed 4-carbon covalent HBS was incorporated using this methodology in a Gramicidin-S analogue, its first structural mimic containing only a single turn motif. This HBS model will have wide applications for constraining peptides in a number of secondary structures.
483

What does it cost to be green? : An empirical investigation of the European green bond market

Söderström, Gustaf, Pettersson, Anton January 2020 (has links)
The green bond market offers investors the opportunity to take an explicit focus on sustainable investment projects. However, it is yet to be determined whether this novel asset class offers attractive yields compared to non-green bonds. To address this question, we study European green bonds and how they diverge from conventional bonds in terms of yields. Using a dataset of 88 matched pairs of European green bonds between 2015 and 2019, we document a significant negative green bond premium of -12 bps on average in the secondary market. The green bond premium is defined as the yield differential between a green and a conventional bond while controlling for liquidity. The results suggest that European investors accept a lower financial return in exchange for receiving non-pecuniary benefits and thus challenging the assumptions of classical asset pricing models. Furthermore, we use a matching method and two-step regression to control for liquidity and identify the determinants of the green bond premium. The results show that the negative green bond premium is less pronounced for lower-rated bonds. Moreover, we find support for variations in the green bond premium across different business sectors. Government-related green bonds experience a greater negative green bond premium than green bonds related to financials and industrial corporates.
484

LCA for Green Bonds : Utilisation of Life Cycle Assessment in the context of green bond financed projects / LCA för gröna obligationer : Användning av livscykelanalys i samband med projekt som finansieras med gröna obligationer

Ammann, Cedric January 2024 (has links)
Green bonds are a growing and popular financial product that aims to channel capital towards environmentally friendly projects and promote sustainable development. Despite some efforts to increase credibility, the lack of standardization, for example in the reporting of environmental impacts, is still a problem in the green bond market. Life Cycle Assessment (LCA) as a tool to address these problems has been investigated by only a few studies, giving reason to further investigate its utilisation in the context of green bond-financed projects. This study investigated the use of LCA as a suitable tool to assess the eligibility and environmental impacts of projects financed through green bonds. The method included a document analysis of three common green bond standards to investigate the current use of LCA and life cycle thinking (LCT) based methods in the context of green bonds. Additionally, four green bond-financed projects were analysed to determine whether LCA is a suitable tool to assess their eligibility and report their environmental impacts with regard to providing relevant results in relation to criteria from the European Green Bond Standard (EUGBS). Furthermore, methodological challenges that can occur when conducting an LCA on the projects were investigated.   The results showed that LCA and LCT based methodologies are already in use by common green bond standards. However, they mainly occur in the criteria that determine whether a project is eligible or not to receive financing. Regarding the impact reporting no binding re-quirements exists for bond issuers to use LCA or LCT based methodologies. According to the results LCA is capable of reporting many relevant environmental impacts of the different pro-jects. However, different impacts were identified which are not covered by LCIA methods, which can limit the suitability of LCA as a method for impact reporting. This includes especially local impacts on the projects which are not covered by an LCA and would therefore be missed in the reporting. Various methodological challenges were identified when conducting an LCA on the projects, including allocation, system boundary, life cycle inventory, time span, data challenges, and challenges in the selection of functional units, which can impact LCA results and the comparison among projects. The results stress the necessity of future research on impact reporting and also for setting binding requirements for the impact reporting of green bonds. / Gröna obligationer är en växande och populär finansiell produkt som syftar till att kanalisera kapital till miljövänliga projekt och främja en hållbar utveckling. Trots vissa ansträngningar för att öka trovärdigheten är bristen på standardisering, till exempel när det gäller rapportering av miljöpåverkan, fortfarande ett problem på marknaden för gröna obligationer. Livscykelanalys (LCA) som ett verktyg för att hantera dessa problem har endast undersökts i ett fåtal studier, vilket ger anledning att ytterligare undersöka dess användning i samband med projekt finansi-erade med gröna obligationer. I denna studie undersöktes användningen av LCA som ett lämp-ligt verktyg för att bedöma stödberättigande och miljöpåverkan av projekt som finansieras ge-nom gröna obligationer. Metoden omfattade en dokumentanalys av tre vanliga standarder för gröna obligationer för att undersöka den nuvarande användningen av LCA och livscykeltän-kande (LCT) baserade metoder i samband med gröna obligationer. Dessutom analyserades fyra projekt som finansierats med gröna obligationer för att avgöra om LCA är ett lämpligt verktyg för att bedöma deras berättigande och rapportera deras miljöpåverkan med avseende på att tillhandahålla relevanta resultat i förhållande till kriterierna i European Green Bond Stan-dard (EUGBS). Vidare undersöktes metodologiska utmaningar som kan uppstå när man ge-nomför en LCA på projekten.   Resultaten visade att LCA- och LCT-baserade metoder redan används i gemensamma stan-darder för gröna obligationer. De förekommer dock främst i de kriterier som avgör om ett pro-jekt är berättigat eller inte att erhålla finansiering. När det gäller konsekvensrapportering finns det inga bindande krav på att obligationsemittenter ska använda LCA- eller LCT-baserade metoder. Enligt resultaten kan LCA rapportera många relevanta miljökonsekvenser av de olika projekten. Dock identifierades olika effekter som inte täcks av LCIA-metoder, vilket kan be-gränsa lämpligheten av LCA som metod för rapportering av effekter. Detta omfattar särskilt lokala effekter på projekten som inte omfattas av en LCA och som därför skulle missas i rap-porteringen. Olika metodologiska utmaningar identifierades när man genomförde en LCA för projekten, inklusive allokering, systemgränser, livscykelinventering, tidsspann, datautma-ningar och utmaningar i valet av funktionella enheter, vilket kan påverka LCA-resultaten och jämförelsen mellan projekt. Resultaten understryker behovet av framtida forskning om konse-kvensrapportering och även av att fastställa bindande krav för konsekvensrapportering av gröna obligationer.
485

How liquid and efficient are Botswana Bond Markets?

Sebate, Matlhogonolo Victor 12 1900 (has links)
Thesis (MDevF (Business Management))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: The importance of market microstructure in determining the success of a bond market in allocating financial resources depends on the degree to which the microstructure elements like liquidity, efficiency and volatility have been designed to determine the proper price at which matching of demand and supply in an efficient and effective manner is done. This research project analyzes some of the fundamental microstructure elements responsible for the current state of the Botswana bond market. The Botswana bond market is still in its infant stage hence there is little information on trades, which contributes to the liquidity problem. The purpose of the study was to investigate the liquidity and efficiency in Botswana’s bond market. The study also sought to compare the behaviour of the Botswana bond market to those of South Africa and further indicate what is behind the bond market emergence. Houweling, Mentink and Vorst‘s (2003) measure was used, in addition to a combination of simple regression and latent models. In the test of efficiency, a static model has been employed. Overall, it is established that the corporate bond market is less efficient and is illiquid. Furthermore, it is revealed that Botswana is still lagging behind South Africa when it comes to the level of development of the corporate bond market.
486

Calculations of Reaction Mechanisms and Entropic Effects in Enzyme Catalysis

Kazemi, Masoud January 2017 (has links)
Ground state destabilization is a hypothesis to explain enzyme catalysis. The most popular interpretation of it is the entropic effect, which states that enzymes accelerate biochemical reactions by bringing the reactants to a favorable position and orientation and the entropy cost of this is compensated by enthalpy of binding. Once the enzyme-substrate complex is formed, the reaction could proceed with negligible entropy cost. Deamination of cytidine catalyzed by E.coli cytidine deaminase appears to agree with this hypothesis. In this reaction, the chemical transformation occurs with a negligible entropy cost and the initial binding occurs with a large entropy penalty that is comparable to the entropic cost of the uncatalyzed reaction. Our calculations revealed that this reaction occurs with different mechanisms in the cytidine deaminase and water. The uncatalyzed reaction involves a concerted mechanism and the entropy cost of this reaction appears to be dominated by the reacting fragments and first solvation shell. The catalyzed reaction occurs via a stepwise mechanism in which a hydroxide ion acts as the nucleophile. In the active site, the entropy cost of hydroxide ion formation is eliminated due to pre-organization of the active site. Hence, the entropic effect in this reaction is due to a pre-organized active site rather than ground state destabilization. In the second part of this thesis, we investigated peptide bond formation and peptidyl-tRNA hydrolysis at the peptidyl transferase center of the ribosome. Peptidyl-tRNA hydrolysis occurs by nucleophilic attack of a water molecule on the ester carbon of peptidyl-tRNA. Our calculations showed that this reaction proceeds via a base catalyzed mechanism where the A76 O2’ is the general base and activates the nucleophilic water. Peptide bond formation occurs by nucleophilic attack of the α-amino group of aminoacyl-tRNA on the ester carbon of peptidyl-tRNA. For this reaction we investigated two mechanisms: i) the previously proposed proton shuttle mechanism which involves a zwitterionic tetrahedral intermediate, and ii) a general base mechanism that proceeds via a negatively charged tetrahedral intermediate. Although both mechanisms resulted in reasonable activation energies, only the proton shuttle mechanism found to be consistent with the pH dependence of peptide bond formation.
487

Le corps en jeu dans le théâtre anglais contemporain (1983-2010) : Edward Bond, Howard Barker, Martin Crimp et Sarah Kane / The body at play : The body and its representation in contemporary English theatre (1983-2010) : Edward Bond, Howard Barker, Martin Crimp and Sarah Kane

Obis, Eleonore 21 November 2011 (has links)
Le théâtre est le lieu d’un rapport privilégié au corps, dans la co-présence du corps de l’acteur et du corps du spectateur au moment de la représentation théâtrale. Il est l’arène privilégiée où s’observe l’impact des bouleversements qui ont modifié les codes de la représentation au cours du vingtième siècle. Le théâtre anglais contemporain attire les regards sur le spectacle d’un corps souffrant, exhibé, violenté (théâtre In-yer-face, théâtre de la Catastrophe) et dans le même temps propose la représentation d’un corps spectral dans un théâtre influencé par Beckett. Ces deux tendances – corps spectacle et corps spectral – sont les signes visibles d’une crise de la représentation du corps et de la déconstruction du sujet. Les auteurs que nous avons choisis pour cette étude (Edward Bond, Howard Barker, Martin Crimp et Sarah Kane) se sont imposés comme les figures de proue d’un théâtre non-naturaliste, poétique et subversif, qui font du corps le pilier de leurs esthétiques. Notre étude se présente comme une anatomie du « corps esthétique » (Roland Barthes) dans une perspective comparatiste des dramaturgies abordées. Elle explore le rôle du corps dans tous les domaines de la représentation : Comment le texte construit-il le corps ? Comment le corps envahit-il le texte ? Quelles sont les stratégies mises en œuvre pour représenter le corps dans le passage de la page au plateau ? Quelle est la place du corps de l’acteur ? du corps du spectateur ? Parce que « le » corps n’existe pas, les théâtres du corps en jeu ne cessent d’affirmer le potentiel illimité du corps en exposant la labilité du corps du personnage, de l’acteur et du spectateur. / The theatre is a privileged site to understand the body, because of the copresence of the body of the actor and that of the spectator during the representation. It is the privileged arena where we can observe the consequences of the upheavals that changed the conventions in representation in the course of the twentieth century. English contemporary theatre attracts our attention both to the spectacle of a suffering body, which is also exposed and violated (In-yer-face theatre, the theatre of Catastrophe) and that of a spectral body, in a theatre influenced by Beckett. These two trends – the body as spectacle and the spectral body – are the visible signs of a crisis in the representation of the body and the deconstruction of the subject. The authors chosen for this study (Edward Bond, Howard Barker, Martin Crimp and Sarah Kane) are the figureheads of a non-naturalistic, poetic and subversive theatre. The body is at the core of their aesthetics. Our contention is to develop an anatomy of the “aesthetic body” (Roland Barthes) with a comparative approach of the works, and to investigate the role of the body in all the different fields of representation: How does the text create a body? How does the body invade the text? What are the strategies at stake to represent the body in the translation from page to stage? How is the body of the actor used? How is the spectator’s body affected? Because it seems there is no such thing as “the” body, the theatres of the “body-at-play” try to reassess the limitless potential of the body, to deliver it from all constraints, and to expose the lability of the character’s body, as well as the actor’s and the spectator’s.
488

"Distribuição de tensões em testes de cisalhamento e micro-cisalhamento mediante análise de elementos finitos" / A finite element stress analysis of shear and micro-shear bond strength tests

Placido, Eliane 23 June 2006 (has links)
Os objetivos deste estudo foram comparar, através de análise de elementos finitos, a distribuição de tensões em modelos que representam arranjos experimentais nor-malmente utilizados em testes de cisalhamento e micro-cisalhamento, verificar a tendência de variar o local de início e o modo de fratura em função de mudanças nos parâmetros dos ensaios e analisar a influência de dois modos de fixação do substrato sobre a concentração de tensões. Os modelos bidimensionais em estado plano de deformações representaram o compósito (híbrido ou flow) aderido à dentina através de uma camada de adesivo de 50 μm. Duas condições de fixação da dentina foram estabelecidas: na primeira (mais rígida), os deslocamentos foram restritos em todas as direções nos nós das arestas que representam as três superfícies livres de adesão e na segunda, a restrição foi colocada apenas na parte posterior da dentina. Foi aplicado um carregamento pontual a várias distâncias da interface dentina-adesivo, de modo a obter um tensão nominal constante de 4MPa. Foram analisadas as tensões máximas de tração e cisalhamento, a distribuição das tensões ao longo dos nós da interface dentina-adesivo e os vetores de tensão máxima principal, como indicativos do local de início e o provável modo de fratura. A distribuição de tensões ao longo da interface aderida foi sempre não uniforme e apresentou picos muito ele-vados em todos os casos, o que conduz a pensar que os valores de resistência nominal não são representativos da máxima tensão suportada no momento da fratura. A tensão de tração predominou sobre a de cisalhamento. O módulo de elasticidade do compósito aderido, a espessura relativa da camada de adesivo e a distância de aplicação da carga influenciam a concentração de tensões e devem ser padroniza-dos. Para o teste de micro-cisalhamento, a camada de adesivo relativamente mais espessa e o uso do compósito com baixo módulo de elasticidade propiciaram a in-tensificação das tensões. O ensaio de cisalhamento parece mais suscetível que o de micro-cisalhamento para que o início da ruptura ocorra no substrato, pois o ponto de maior concentração de tensões localizou-se na dentina em alguns casos e verifica-se pequena diferença de módulo entre os maiores vetores localizados no adesivo e na dentina de base. O teste de micro-cisalhamento, embora mais favorável a que as fraturas se iniciem no adesivo, concentra muito a tensão, especialmente com a utili-zação de resinas do tipo flow, o que o torna menos representativo da máxima tensão que o espécime realmente resistiu no momento da fratura. / The objectives of this study were to compare the stress distribution in finite element models that represented experimental designs commonly used for shear and micro-shear bond strength testing, to verify the tendency to vary the location and mode of fracture as a consequence of changes in the studied parameters, and to analyze the influence of two substrate restriction conditions on stress concentration. Bi-dimensional plane strain models represented a composite (hybrid or flow) bonded to dentin through a 50 μm adhesive layer. Two dentin restriction conditions were estab-lished: in the first (more rigid), movements were restricted in all directions on the nodes located in the dentin surface edges free of adhesion, and in the second, re-striction was imposed only to the posterior dentin surface. Concentrated loading was applied at several distances from the dentin-adhesive interface so as to obtain con-stant nominal bond strength of 4MPa. Maximum tensile and shear stress values, stress distribution along the dentin-adhesive interfacial nodes and the principal maximum stress vectors as indicative of the most probable location and mode of frac-ture were analyzed. Stress distribution along bonded interfaces was always non-uniform and presented very high stress peaks for all cases. This led to the assump-tion that nominal bond strength values are non-representative of the maximum stress supported at fracture. Tensile stresses were always predominant over shear stresses. The composite elastic modulus, relative adhesive layer thickness and different load application distances influenced stress concentration and should be stan-dardized. For micro-shear tests, the relatively thicker adhesive layer and use of a low modulus composite propitiated stress intensification. The shear test seems to be more susceptible than micro-shear to fracture initiation in the substrate, once the point of highest stress concentration was in some cases located in dentin, and small modulus difference was verified between the greatest stress vectors located both on the adhesive and dentin base. Although more favorable to fracture initiation in the adhesive, the micro-shear test design highly concentrated stresses, especially when flow composite was modeled, hence it might be less representative of the maximum stress the specimen resisted at fracture.
489

Three essays on insurance asset liability management. / CUHK electronic theses & dissertations collection / ProQuest dissertations and theses

January 2008 (has links)
The key objective of insurance company on money management is asset liability management, as policy asset is solely for paying policy liability. It is true whether it is in case of life insurance, general insurance, or reinsurance. The difficulty of achieving such objective is that the exact cash flow and the exact duration of policy liability are unknown ex ante that requires the asset manager's a good quantitative, financial skill. What is worse is that the variations of cash flow and duration can be huge that is demanding on the asset manager's quantitative, financial skill. Quantitative problem is difficult but qualitative problem can be even more difficult. The specialist problem in insurance industry, which is also known as agency problem in information economics, is notorious. It is because a specialist may no longer work for the insurance company when the long term liability is due and the existing liability portfolio is always composed of myriad policies liability. / The purpose of this thesis is to try to provide solutions to three critical problems in insurance industry. (1) China is the most booming country for insurance at the moment. So, it is selected for discussing about the most difficult problem in modern finance---specialist problem. A structural approach is devised in this thesis to solve such problem. The solution can be generalized to all countries. (2) As many people argue about that modern finance is inapplicable to emerging market, such as China, especially when there are capital account and currency controls, the bond market of China is selected to provide evidence that modern finance is applicable to emerging market even both the capital account and the currency of the country are controlled by the government. (3) The last part of this thesis provides a breakthrough solution to price insurer default option, an embedded option, in insurance company using observable credit default swap price, as the traditional approach needs statistical assumption that is subjective. / Li, Wing Ping Desmond. / Adviser: Frank Youhua Chen. / Source: Dissertation Abstracts International, Volume: 70-06, Section: A, page: 2169. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 64-65). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest dissertations and theses, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.
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Alternativní formy finančního řešení rizikovosti / Alternative way of financial risk transfer

Müller, Michal January 2010 (has links)
This diploma thesis deals with a considerable innovation of modern finance, insurance securitization. For better understanding of this concept it is important to consider insurance securitization in a broader context of financial securitization, which is presented in the first chapter. In the second part of this work the factors which have led to the development of insurance securitization are mentioned. Then there is a short comparison of insurance securitization with financial securitization and description of various secured products with discussing their positive and negative aspects. Finally, the thesis is concluded with some thoughts regarding the near future of insurance securitization. The aim of this diploma thesis is to evaluate using of insurance securitization as an alternative way of transfer risk, analyze its weaknesses and propose possible solutions.

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