The effects of different physical and chemical conditions on the decomposition and release of organic and inorganic P compound groups from the sediment of Lake Erken were investigated in a series of laboratory experiments. Conditions investigated were temperature, oxygen level, and the effects of additions of carbon substrate (glucose) and poison (formalin). The effects on the P compound groups were determined by measurements with 31P NMR before and after the experiments, as well as analysis of P in effluent water throughout the experiment. Phosphate analysis of the effluent water showed that oxygen level was the most influential in terms of release rates, with the sediments under anoxic conditions generally releasing more phosphate than the other treatments. 31P NMR showed that the various treatments did influence the P compound group composition of the sediment. In particular, the addition of glucose led to a decrease in orthophosphate and polyphosphate while the addition of formalin led to a decrease in phosphorus lipids, DNAphosphate and polyphosphate. Oxic conditions resulted in an increase in polyphosphates, and anoxic conditions in a decrease in these. Temperature did not seem to affect the composition significantly.
Being a major cause of eutrophication and subsequent loss of water quality, the turnover of phosphorus (P) in lake sediments is in need of deeper understanding. A major part of the flux of P to eutrophic lake sediments is organically bound or of biogenic origin. This P is incorporated in a poorly described mixture of autochthonous and allochthonous sediment and forms the primary storage of P available for recycling to the water column, thus regulating lake trophic status. To identify and quantify biogenic sediment P and assess its lability, we analyzed sediment cores from Lake Erken, Sweden, using traditional P fractionation, and in parallel, NaOH extracts were analyzed using 31P NMR. The surface sediments contain orthophosphates (ortho-P) and pyrophosphates (pyro-P), as well as phosphate mono- and diesters. The first group of compounds to disappear with increased sediment depth is pyrophosphate, followed by a steady decline of the different ester compounds. Estimated half-life times of these compound groups are about 10 yr for pyrophosphate and 2 decades for mono- and diesters. Probably, these compounds will be mineralized to ortho-P and is thus potentially available for recycling to the water column, supporting further growth of phytoplankton. In conclusion, 31P NMR is a useful tool to asses the bioavailability of certain P compound groups, and the combination with traditional fractionation techniques makes quantification possible.
A number of cyclopent[b]indol-1-ones as well as -3-ones have been synthesized, using a new methodology involving intramolecular ring closure of α,β-unsaturated acylindoles. In some cases 1,2,3,4-tetrahydrocarbazol-4-ones were obtained. This methodology was used in the syntheses of the indole alkaloid yuehchukene and the carbazole alkaloid analogue demethoxycarbazomycin B.
Thiol-functionalized cobalt porphyrins were used as a model system for investigating catalytic activity in homogeneous and heterogeneous oxidation catalysis. Self-assemble monolayers of thiol-functionalized cobalt porphyrins were prepared on a gold surface and served as heterogenous catalysts. These immoblilized molecules prevented the strong inactivation observed for their homogeneous congener. As a result, the turnover number per molecule in heterogeneous catalysis was at least 100 times higher than that of the corresponding homogeneous catalyst. It is atypical for a heterogenized catalyst to outperform its homogeneous congener. The properties of the molecular layers were characterized on the molecular level by means of X-ray photoelectorn spectroscopy (XPS) and scanning tunneling microscopy (STM). The results demonstrate that the performance of these biomimetic catalysts can be dramatically improved if the catalyst arangement can be controlled on the molecular level.
Peptidomimetics incorporating two amino acids 1 and 2 with a stiff stilbene chromophore have been screened by a computational study and compared to a previously investigated analog 3 with stilbene chromophore. The effect of E-Z isomerization of the chromophores on the conformational properties of the petidomimetics was assessed via the frequency of hydrogen bonding between the two peptide strands attached to either side of the chromophore. Substantial differences between the three amino acids were thus indicated, in line with the anticipated effect of chromophore rigidity variation.
Bisporphyrin molecular tweezers with an enediyne (1) or a stiff stilbene (2) photoswitchable spacer are proposed as systems for modulation of bitopic binding to diamine guests via E/Z photoisomerization. The photoisomerization has been monitored by UV-Vis and 1H NMR spectroscopy and occurs without side reactions such as Bergman cyclization. Possible applications are rationalized in terms of competitive binding involving monoamine/diamine mixtures, and are supported by conformational analysis of the envisioned host-guest complexes. Binding dynamics for conformationally flexible guests show significantly different performance of aliphatic 1,w-diamine guests with varying N-N distance.
Stereocontrolledp alladium(I1)-catalyzed1 ,4-chloro-and 1,4-acetoxylactonizations o f conjugated cyclic dienes have been developed to give stereodefined fused lactones. The stereochemistry of the 1,4- acetoxylactonization was controlled by the ligand on the metal catalyst, and in this way either a cisor truns-acetoxylactonization was obtained. This dual stereoselectivity is explained by a stereocontrolled acetate attack (trans or cis, respectively) on the allyl group in the catalytic (π-allyl)- palladium intermediate. To further strengthen the mechanism the intermediate (π-ally1)palladium complex was isolated and fully characterized. A stereospecific synthesis of cis- and truns-2-[6- (benzyloxy)-2,4-heptadien-l-yllacetic a cid (cis- and truns-9) followed by stereoselective Pd(I1)- catalyzed chloro- and acetoxylactonization in acetonelacetic acid resulted in highly functionalized fused lactones with control of the relative stereochemistry at four different carbons.
Evidence for a coordination of p-benzoquinone to palladium in [4-acetoxy-η3-(1,2,3)-cyclohexenyl]-palladium(II) complexes was provided by changes of the 1H NMR chemical shift values of the π-allyl protons and a decrease of the spin-lattice relaxation time constant for the p-benzoquinone protons.
The intermediate (π-allyl)palladium(benzoquinone) complexes previously postulated in palladium-catalyzed 1,4-oxidations of 1,3-dienes were detected by NMR spectroscopy.
The mediator system palladium(II)–hydroquinone was shown to catalyse the anodic oxidation of cyclohexa-1,3-diene in acetic acid to produce selectively either trans- or cis-1,4-diacetoxycyclohex-2-ene (1) depending on the conditions.
The 1H and 13C NMR spectra of 9-hydroxyphenalenone (1) and 9-hydroxy-2-methylphenalenone (2) have been completely assigned. Primary and secondary deuterium isotope effects were determined in three solvents (chloroform, acetone and dimethyl sulphoxide), including the effect of temperature on the secondary isotope effects. Both negative and large long-range secondary isotope effects were found for both 1 and 2. The average secondary isotope effects for corresponding carbons follow the same sign and magnitude pattern in both compounds.
A microwave-enhanced, rapid and efficient homogeneous-phase version of the Sonogashira reaction is presented. It has been applied to the coupling of aryl iodides, bromides, triflates, and aryl chloride, as well as pyridine and thiophene derivatives with trimethylsilylacetylene. Excellent yields (80−95%) for substrates containing a large variety of substituents in different positions are obtained in 5−25 min.
A method for assignment of the relative stereochemistry in acyclic pi-allyl)palladium complexes by H-1 NMR H-H coupling constants has been developed. It is based on the introduction of nitrogen chelating ligands of the bipyridyl type into the complexes. The analytical suitability of several other types of nitrogen chelating ligands has also been investigated. A model for rationalization of the observed relation between stereochemistry and spectral parameters is proposed. Introduction of the chelating ligand also affects the syn,anti equilibrium of the complexes. Isomer ratios depend upon the relative stereochemistry of the side chain as well as on the chelating ligand.
The reaction of 2-thio-pyridine N-oxide, 2-amino-, 2-hydroxy, 2-thio-, and 4-thiopyridine with butyl glycidyl ether was investigated as a model system for the functionalization of 2,3-epoxypropyl activated agarose. Unambiguous structural assignment of the products was provided by selective INEPT and nuclear Overhauser difference spectra. All reactions were shown to give only one of the possible regioisomers. Further conclusions regarding the structure of the agarose derivatives were drawn from IR spectra.
The 13C NMR spectra of several indole derivatives have been completely assigned by reverse detected one-bond and long-range CH correlation spectra (HMQC) and by selective INEPT experiments. The resolution and sensitivity of the two techniques are discussed. As a result, the literature assignments for the previously known compounds have been revised.
After correlation of the majority of signals by COSY and one-bond heteronuclear correlation, the complete assignment of the 1H and 13C NMR spectra of the macrolide antibiotic venturicidin A required the application of long-range CH coupling information. This was accessible by the COLOC-S and selective INEPT experiments, and the sensitivity of these experiments is discussed. Steric information was obtained from a NOESY spectrum, and the solution structure compared with that in the crystal.
A series of pyrroles functionalized in the 3-position with p-dimethoxybenzene via various linkers (CH2, CH2CH2, CH=CH, C≡C) has been synthesized. Their electronic properties have been deduced from 1H NMR, 13C NMR, and UV–vis spectra to detect possible interactions between the two aromatic subunits. The extent of conjugation between the subunits is largely controlled by the nature of the linker, with the largest conjugation found with the trans-ethene linker and the weakest with the aliphatic linkers. DFT calculations revealed substantial changes in the HOMO–LUMO gap that correlated with the extent of conjugation found experimentally. The results of this work are expected to open up for use of the investigated compounds as components of redox-active materials in sustainable, organic electrical energy storage devices.
The unsaturated alcohol (1) is readily cyclised to the hydroxytetrahydrofuran (3) by means of thallium(III), whereas its congener (4) has been found to give (7) as the product of a novel, stereoelectronically controlled, fragmentation; the scope of the tandem electrophilic cyclisation/solvolysis is discussed; the structure of (7) has been determined by X-ray crystallography.
Conjugated dienes were transformed to synthetically useful 3,4-epoxy-3-nitro-1-alkenes via a nitroselenation-oxidation sequence.
Conjugated dienes were transformed to synthetically useful 3,4-epoxy-3-nitroalkenes via a nitroselenation-oxidation sequence.
Phosphorus (P) compounds in three different lake surface sediments were extracted by sequential P extraction and identified by P-31 nuclear magnetic resonance (P-31 NMR) spectroscopy. The extraction procedure primarily discriminates between inorganic P-binding sites but most extraction steps also contained P not reacting (nrP) with the molybdenum complex during P analyses. In all three lakes, the nrP dominated in the NaOH extracts. Nonreactive P from the dystrophic lake was dominated by potentially recalcitrant P groups such as orthophosphate monoesters, while the nrP in the two more productive lakes also contained polyphosphates, pyrophosphate, and organic P groups such as P lipids and DNA-P that may be important in remineralization and recycling to the water column. In addition, polyphosphates showed substantial dynamics in settling seston. The Humic-P pools (P associated with humic acids) showed strong signals of orthophosphate monoesters in all three lakes, which supported the assumption that P-containing humic compounds are indeed recovered in this fraction, although other organic P forms are also present. Thus, in addition to expanding the understanding of which organic P forms that are present in lake sediments, the P-31 NMR technique also demonstrated that the chemical extraction procedure may provide some quantification of recalcitrant versus labile organic P forms.
The effects of aluminum (A1) treatment on sediment composition of carbon (C), nitrogen (N) and phosphorus (P) were investigated in sediment representing pre- and post-treatment years in the Danish Lake Sönderby. 31P NMR spectroscopy analysis of EDTA-NaOH extracts revealed six functional P groups. Direct effects of the A1 treatment were reflected in the othophosphate profile revealing increased amounts of A1-P in the sediment layers representing the post-treatment period, as well as changes in organic P groups due to precipitation of phytoplankton and bacteria at the time of A1 additon. Furthermore, changes in phytoplankton community structure and lowered production due to the A1 treatment resulted in decreased concentrations of sediment organic P groups and total C. Exponential regressions were used to describe the diagensisi of C, N, and P in the sediment. From these regressions , half-life degradation times and C, N, and P burial rates were determined.