Podcasts about nabh4

Williamson Ether Synthesis, NaBH4 reduction, NMR

This thesis focuses on the experimental and theoretical investigation of small molecules containing phosphorus, nitrogen and sulfur. The first part of this work presents synthesis and characterisation of molecules bearing a P-N-N-group: N,N´,N´-[tris(trimethylsilyl)]-hydrazino-diphenylphosphane, (TMS)2N-(TMS)N-PPh2, and N,N´,N´-[tris(trimethylsilyl)]-hydrazino-phenyl(chloro)phosphane, (TMS)2N-(TMS)N-P(Cl)Ph, were obtained in the reaction of bis-[lithiumtris(trimethylsilyl)hydrazide] with PhnPCl3 - n (n = 1, 2). The structure and bonding of both species are discussed on the basis of experimentally observed (X-ray, Raman, NMR, and MS) and theoretically obtained data (B3LYP/6-31G(d,p), NBO analysis). Oxidation with sulfur and selenium results in the formation of (TMS)2N-(TMS)N-P(S)-Ph2, (TMS)2N-(TMS)N-P(Se)Ph2, (TMS)2N-(TMS)N-P(S)Ph(Cl) and (TMS)2N-(TMS)N-P(Se)Ph(Cl). Moreover, the thermal decomposition of N,N´,N´-[tris(trimethylsilyl)]hydrazine-dichlorophosphane, (TMS)2N-(TMS)N-PCl2 and the reaction with magnesium have been investigated. The formation and molecular structure of the novel MgCl2(THF)2* 2Mg[(TMS)NP(O)2N(TMS)2](THF) salt containing the hitherto unknown (TMS)NP-(O)2N(TMS)22- anion are discussed. DFT calculations (B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d,p)) are used to evaluate the bonding, ground-state structures, and energy landscape for the different isomers of (TMS)2N-(TMS)N-PCl2: the thermodynamics and kinetics of the successive elimination of chlorotrimethylsilane (TMS-Cl) resulting in the formation of covalent azide analogues such as TMS-PNN or TMS-NNP are discussed. While investigating the reaction of (TMS)2N-(TMS)N-PCl2 with Lewis acides a galliumtrichloride-adduct of 4-bis[trimethylsilylamino]-1,2,4,3,5-triazadiphosphole was discovered. This hitherto unknown triazadiphosphole represents one of the few examples of a five-membered ring-molecule containing only phosphorus and nitrogen. This ring system was unequivocally characterized by X-Ray, Raman, NMR and MS analysis. Furthermore the Staudinger-type reaction of N,N´,N´-[tris(trimethylsilyl)]-hydrazino-diphenylphosphane with SP(N3)3 and and C3N12 in different stoichiometries were investigated. It is possible to substitute only one azide group in SP(N3)3 and up to two azide groups in C3N12 with (TMS)2N-(TMS)N-PPh2, resulting in the expected products. Upon heating of a solution of (TMS)2N-(TMS)N-PPh2 and SP(N3)3 a new eight-membered ring containing phosphorus and nitrogen in alternating order was obtained. The molecule contains a long pnicogene-chain (eleven atoms in total, three phosphorus- and eight nitrogen-atoms). The reactions of (NSCl)3 and NSCl2- with AgX salts (X = CN, SCN, OCN), as well as the reaction of (NSCl)3 with [PPh4]X (X = CN, SCN, OCN) and HgX (X = CN, SCN) have been investigated in a combined experimental and theoretical study. Additionally, the reaction of NSCl2- salts with hydride-transferring-agents like NaBH4 or NaBH3CN was studied. The thermodynamics as well as structure and bonding of the formation of NSX, NSX2- and NSXY- (X, Y = Cl, H, CN, SCN, OCN) have been studied. Unfortunately the preparation of these species did not suceed. The substitution of sulfur by selenium with SeO2, as reported by Rawson, was investigated on the salts of NSCl2- and S2N3+. These reactions resulted polymeric products and selenium; the formation of a nitrogen-selenium-species could not be confirmed.

The mechanism of formation of the formyl group of chlorophyll b has long been obscure but, in this paper, the origin of the 7-formyl-group oxygen of chlorophyll b in higher plants was determined by greening etiolated maize leaves, excised from dark-grown plants, by illumination under white light in the presence of either H218O or 18O2 and examining the newly synthesized chlorophylls by mass spectroscopy. To minimize the possible loss of 18O label from the 7-formyl substituent by reversible formation of chlorophyll b-71-gem-diol (hydrate) with unlabelled water in the cell, the formyl group was reduced to a hydroxymethyl group during extraction with methanol containing NaBH4: chlorophyll a remained unchanged during this rapid reductive extraction process. Mass spectra of chlorophyll a and [7-hydroxymethyl]-chlorophyll b extracted from leaves greened in the presence of either H218O or 18O2 revealed that 18O was incorporated only from molecular oxygen but into both chlorophylls: the mass spectra were consistent with molecular oxygen providing an oxygen atom not only for incorporation into the 7-formyl group of chlorophyll b but also for the well-documented incorporation into the 131-oxo group of both chlorophylls a and b [see Walker, C. J., Mansfield, K. E., Smith, K. M. & Castelfranco, P. A. (1989) Biochem. J. 257, 599–602]. The incorporation of isotope led to as much as 77% enrichment of the 131-oxo group of chlorophyll a: assuming identical incorporation into the 131 oxygen of chlorophyll b, then enrichment of the 7-formyl oxygen was as much as 93%. Isotope dilution by re-incorporation of photosynthetically produced oxygen from unlabelled water was negligible as shown by a greening experiment in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The high enrichment using 18O2, and the absence of labelling by H218O, unequivocally demonstrates that molecular oxygen is the sole precursor of the 7-formyl oxygen of chlorophyll b in higher plants and strongly suggests a single pathway for the formation of the chlorophyll b formyl group involving the participation of an oxygenase-type enzyme.

The reaction of several plant chlorophyll-protein complexes with NaBH4 has been studied by absorption spectroscopy. In all the complexes studied, chlorophyll b is more reactive than Chi a, due to preferential reaction of its formyl substituent at C-7. The complexes also show large variations in reactivity towards NaBH4 and the order of reactivity is: LHCI > PSII complex > LHCII > PSI > P700 (investigated as a component of PSI). Differential pools of the same type of chlorophyll have been observed in several complexes. Parallel work was undertaken on the reactivity of micellar complexes of chlorophyll a and of chlorophyll b with NaBH4 to study the effect of aggregation state on this reactivity. In these complexes, both chlorophyll a and b show large variations in reactivity in the order monomer > oligomer > polymer with chlorophyll b generally being more reactive than chlorophyll a. It is concluded that aggregation decreases the reactivity of chlorophylls towards NaBH4 in vitro, and may similarly decrease reactivity in naturally-occurring chlorophyll-protein complexes.