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Enhanced Molecular Dimension of a Humic Acid Induced by Photooxidation Catalyzed by Biomimetic Metalporphyrins
No full textRates of oxidative coupling of humic phenolic monomers catalyzed by a biomimetic iron-porphyrin
No full textOligomerization of Humic Phenolic Monomers by Oxidative Coupling under Biomimetic Catalysis
No full textThree humic phenolic monomers, catechol (CAT), caffeic
acid (CAFF), and p-coumaric acid (COUM), were subjected
to oxidative coupling catalyzed by biomimetic watersoluble
iron-porphyrin (Fe(TDCPPS)Cl) in either separate
or mixed solution, and the reaction products were
characterized by gas chromatography-mass spectrometry
(GC-MS) and electrospray-mass spectrometry (ESIMS).
The GC-MS analysis proved the formation of C-C
and C-O dimers, whereas the ESI-MS/MS analysis also
suggested trimerization for all the monomers and
tetramerization for CAT. On the basis of mass spectra,
molecular structures were assigned to the observed oligomers.
In the phenolic separate solutions, dimers represented
about 65%, 44%, and 30% of reaction products for CAT, CAFF,
and COUM, respectively, whereas trimers were from 4
to 5%. A relevant part of the products were unidentified
oligomers and several degradation compounds, mostly
aromatic aldehydes and alcohols and aromatic or aliphatic
carboxylic acids. When all three humic phenolic monomers
underwent the catalyzed coupling reaction in one mixed
solution, 14% of the reaction products were identified as
C-C dimers of CAT. Although no other C-O dimers of CAT,
nor any dimers of COUM and CAFF, could be identified,
some other structurally unknown oligomers were present
among the reaction products of the mixed solution.
However, no oligomers larger than tetramers were formed
in either separate or mixed solutions. This work indicates
the essential role of biomimetic metal-porphyrins in
catalyzing the oxidative coupling of humic phenolic monomers
in aqueous media, thereby promoting the polymerization
of natural organic matter
Molecular changes occurring during micro-oxygenation of an aglianico red wine as observed by NMR spectroscopy
No full textAggregation and disaggregation of humic supramolecular assemblies by NMR diffusion ordered spectroscopy (DOSY-NMR)
No full textDiffusion ordered nuclear magnetic resonance spectroscopy
(DOSY-NMR) was applied to a number of fulvic (FA) and humic
(HA) acids of different origin. Spectral separation achieved
by DOSY based on diffusion coefficients (D), and correlated to
molecular sizes by calibration standards, showed that
carbohydrates had the largest molecular size in FA, whereas
alkyl or aromatic components were the most slowly diffusing
moieties in HA. At increasing concentrations, these components
had invariably lower D values in DOSY spectra for all humic
samples, thereby indicating an aggregation into apparently larger
associations, whose increased hydrodynamic radius was
confirmed by viscosity measurements. When humic solutions
werebroughtfromalkalinetoacidicpH(3.6),componentsdiffusivity
detected by DOSY increased significantly, suggesting a
decreaseofaggregationandmolecularsize.Ageneralcomparison
of HA and FA molecular sizes was achieved by multivariate
statistical analysis. While a larger extent of aggregation and
disaggregation was observed for HA than for FA, no aggregation
wasdetected,undersimilar conditions, foratruemacropolymeric
standard. Such difference in diffusion between a polymeric
molecule and humic samples, is in line with the supramolecular
nature of humic matter. The possible formation of humic
micelles was also investigated by both changes of diffusivity
in DOSY spectra and shift of 1H NMR signals. Except for HA of
peat and soil origin, revealing a self-assembling in micellelike
structures at the 4 mg mL-1 concentration, no other humic
sample showed evidence of critical micelle concentration
(cmc) up to 20 mg mL-1. These results indicated that DOSYNMRspectroscopy
is a useful technique to evaluate components
of different molecular size in natural humic superstructures
Spectroscopic and conformational properties of size-fractions separated from a lignite humic acid
No full text
Evaluation of the factors affecting direct polarization solid state P-31-NMR spectroscopy of bulk soils
No full textEvaluation of the factors affecting direct polarization solid state 31P-NMR spectroscopy of bulk soils
No full textBinding of phenol and differently halogenated phenols to dissolved humic matter as measured by NMR spectroscopy
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