an experimental research

Due to difficulties associated with measuring expectations and observing random coordination devices, the models that posit the idea that business cycles being driven by expectations are hard to test empirically. The paper proposes an experiment to capture features of an expectation driven business cycles model and investigate whether such cycles arise in an experimental setting. Externalities, uncertainty and an extrinsic random variable to mimic the crucial features of the model are introduced. The results provide preliminary support for the hypothesis that given the right incentives for coordination, expectations-driven cycles do occur

Synthesis and reactivity of rare earth and alkaline earth metal complexes

One of the aspects of our research group is developing new ligands, for instance -SiH containing alkyl, amide ligands and oxazoline based scorpionate type ligands for the synthesis of their rare earth metal, alkali earth metal and transition metal complexes which are used as catalyst precursors for organic transformation reactions. Rare earth complexes of tris(dimethylsilyl)methyl ligand have been developed by our research group. In this thesis a new alkyl ligand is accessed by replacing one dimethylsilyl moiety with a phenyl group. The -SiH functionalized benzyl ligand HC(SiHMe2)2Ph is synthesized by reductive coupling of HCBr2Ph and SiHMe2Cl and the anion of the ligand [C(SiHMe2)2Ph]– is obtained by deprotonation of HC(SiHMe2)2Ph with KCH2Ph. An alternate route is introduced to obtain the same -SiH functionalized benzyl anion [C(SiHMe2)2Ph]– by reaction of KOtBu and (Me2HSi)3CPh which reacts via C–Si cleavage. LnI3·THFn and three equivalents of this carbanion combine to provide homoleptic tris(alkyl)lanthanide compounds Ln{C(SiHMe2)2Ph}3 (Ln = La, Ce, Pr, Nd) containing secondary metal-ligand interactions. Rare earth compounds of –N(SiHMe2)tBu ligand have been synthesized by our research group. A new amide ligand is accessed by introducing an aryl group to the tertbutyl position, and this ligand is the amide version of the new alkyl ligand reported in this thesis. Further, addition of substituents on the aryl group allows to vary the steric properties of the new ligand series. Three new hydridosilazido ligands, –N(SiHMe2)Aryl (Aryl = Ph, 2,6-C6Me2H3 (dmp), 2,6-C6iPr2H3 (dipp)) and their homoleptic rare earth complexes Ln{N(SiHMe2)Aryl}3(THF)n (Ln = Sc, Y, Lu; Aryl = Ph, n = 2; Aryl = dmp, n = 1; Aryl = dipp, n = 0) are synthesized. NMR, IR and X-ray diffraction studies of the complexes show that Ln{N(SiHMe2)Ph}3(THF)2 contain only classical Si–H interactions with the metal center. Y{N(SiHMe2)dmp}3THF and Lu{N(SiHMe2)dmp}3THF contain three and two bridging Si–H interactions respectively. Three secondary Ln↼HSi interactions and one agostic CH bond per molecule are observed for planar Ln{N(SiHMe2)dipp}3 complexes. Further, the reaction of Ln{N(SiHMe2)dipp}3 with ketones provides the hydrosilylated product by inserting the C=O in bridging Ln↼H-Si rather than inserting into the Y–N bond or enolate formation. The insertion reaction is postulated to occur via an associative mechanism. Ln{N(SiHMe2)dipp}3 undergo β-SiH abstraction by Lewis acids, such as B(C6F5)3. The reaction of Ln{N(SiHMe2)dipp}3 and one equivalent of B(C6F5)3 provides the cationic species Ln{κ2-N(dipp)SiMe2N(SiHMe2)dipp}{N(SiHMe2)dipp}HB(C6F5)3. The decomposition of that compound provides (Me2Si–Ndipp)2 and a rare earth adduct. A second order rate law is obtained for the decomposition of the cationic complex. Tris(oxazolinyl)boratomagnesium alkyls (ToMMgR) have been developed by our research group and tested in various catalytic reactions for instance hydroboration and dehydrocoupling. In this thesis kinetic studies of the stoichiometric reaction between ToMMgR and HBpin are performed for comparison with other sigma bond metathesis type reactions. The reaction of ToMMgMe or ToMMgnPr with HBpin was too fast even at –78 °C to measure using NMR and IR kinetics. In contrast, ToMMgBn reacts with HBpin or DBpin more slowly at room temperature, and kinetic studies revealed a bimolecular rate law. The activation parameters obtained for the reaction of ToMMgBn with HBpin and DBpin are ΔH‡ = 13.08(0.02) kcal mol-1, ΔS‡ = –29.09(0.05) cal mol-1 K-1 and ΔH‡ 11.86(0.05) kcal mol-1, ΔS‡ = –33.44(0.15) cal mol-1 K-1 respectively. This study shows a kinetic isotope effect of 1.35 at 55 °C and it appears to be increased with increasing the temperature. The mechanistic investigations show that B-H/B-D bond cleavage is involved in the rate-determining step

Homoleptic organolanthanide compounds supported by the bis(dimethylsilyl)benzyl ligand

A β-SiH functionalized benzyl anion [C(SiHMe2)2Ph]− is obtained by deprotonation of HC(SiHMe2)2Ph with KCH2Ph or by reaction of KOtBu and (Me2HSi)3CPh; LnI3(THF)n and three equivalents of this carbanion combine to provide homoleptic tris(alkyl)lanthanide compounds Ln{C(SiHMe2)2Ph}3 (Ln = La, Ce, Pr, Nd) containing secondary metal–ligand interactions

Direct 17O Dynamic Nuclear Polarization of Single-Site Heterogeneous Catalysts

We utilize direct 17O DNP for the characterization of non-protonated oxygens in heterogeneous catalysts. The optimal sample preparation and population transfer approach for 17O direct DNP experiments performed on silica surfaces are determined and applied to the characterization of Zr- and Y-based mesoporous silica-supported single-site catalysts

β-SiH-Containing Tris(silazido) Rare-Earth Complexes as Homogeneous and Grafted Single-Site Catalyst Precursors for Hydroamination

A series of homoleptic rare-earth silazido compounds and their silica-grafted derivatives were prepared to compare spectroscopic and catalytic features under homogeneous and interfacial conditions. Trivalent tris(silazido) compounds Ln{N(SiHMe2)tBu}3 (Ln = Sc (1), Y (2), Lu (3)) are prepared in high yield by salt metathesis reactions. Solution-phase and solid-state characterization of 1–3 by NMR and IR spectroscopy and X-ray diffraction reveals Ln↼H–Si interactions. These features are retained in solvent-coordinated 2·Et2O, 2·THF, and 3·THF. The change in spectroscopic features characterizing the secondary interactions (νSiH, 1JSiH) from the unactivated SiH in the silazane HN(SiHMe2)tBu follows the trend 3 \u3e 2 \u3e 1 ≈ 2·Et2O \u3e 2·THF ≈ 3·THF. Ligand lability follows the same pattern, with Et2O readily dissociating from 2·Et2O while THF is displaced only during surface grafting reactions. 1 and 2·THF graft onto mesoporous silica nanoparticles (MSN) to give Ln{N(SiHMe2)tBu}n@MSN (Ln = Sc (1@MSN), Y (2@MSN)) along with THF and protonated silazido as HN(SiHMe2)tBu and H2NtBu. The surface species are characterized by multinuclear and multidimensional solid-state (SS) NMR spectroscopic techniques, as well as diffuse reflectance FTIR, elemental analysis, and reaction stoichiometry. A key 1JSiH SSNMR measurement reveals that the grafted sites most closely resemble Ln·THF adducts, suggesting that siloxane coordination occurs in grafted compounds. These species catalyze the hydroamination/bicyclization of aminodialkenes, and both solution-phase and interfacial conditions provide the bicyclized product with equivalent cis:trans ratios. Similar diastereoselectivities mediated by catalytic sites under the two conditions suggest similar effective environments

Effectiveness of commonly used high level disinfectants on bacteria responsible for hospital acquired infections in Sri Jayewardenepura General Hospital, Sri Lanka

Introduction: Hospital-acquired infections (HAIs) cause high morbidity and mortality in patients throughout the world. Nosocomial pathogens can be transmitted through contaminated instruments and surfaces. Disinfectants play a crucial role in preventing HAIs. This study focuses on two high level disinfectants designated ‘disinfectant 1’ which contains primarily peracetic acid and ‘disinfectant 2’ which contains primarily didecyldimethylammonium chloride.Objective: To determine the effectiveness of commonly used high level disinfectants on bacteria responsible for causing HAIs in Sri Jayewardenepura General Hospital, Sri Lanka (SJGH), on different surfaces.Method: Data of the Infection Prevention and Control (IPC) unit of SJGH was traced back to identify bacteria causing HAIs from 1st January to 31st July 2018. This experimental study was conducted for disinfectant 1 and 2 according to the quantitative carrier test (European Standard EN 14561:2006). Disinfectants were tested at three different concentrations on glass, stainless steel and rexine surfaces against the commonest three bacteria responsible for causing HAIs in SJGH.Results: Coliforms, Acinetobacter species and Staphylococcus aureus were the three most common bacteria responsible for causing HAIs in SGJH. Surgical site infections were the predominant type of HAI and Intensive Care Units (ICUs) were identified as having the highest prevalence of HAIs. Both high level disinfectants achieved a Microbicidal Effect (ME) value of 5 as per ‘clean disinfectants’ in manufacturer recommended dilutions and passed the test against Escherichia coli, Acinetobacter spp. and S. aureus under both clean and dirty condition on all three tested surfaces. However, bacterial colonies of all 3 test organisms were detected after both disinfectant 1 and 2 use . Effect of disinfectant 1 was poor in manufacturer recommended concentrations on glass, stainless steel and rexine surfaces. ME of disinfectant 2 was considerably higher when compared to disinfectant 1.Conclusion: Although the manufacturer stated test standard was achieved for both disinfectants, the presence of residual bacteria after high level disinfectant use on different surfaces is not acceptable.</p