Charge-Transfer Complexes in Kraft Lignin Part 2: Contribution to Color

Furman, Gary S.; Lonsky, Werner F. W.

doi:10.1080/02773818808070679

Cited by 17 publications

(10 citation statements)

References 3 publications

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“…These results are broadly consistent with the charge transfer model previously proposed for the optical properties of HS and CDOM (12,13) and lignins (13,24). This model predicts that elimination of electron acceptor groups or moieties (quinoid, aromatic ketone, or carbonyl moieties in other structures) by NaBH 4 reduction will lead to the preferential loss of long-wavelength absorption due to the elimination of the lower energy charge transfer transitions (12,13; Figures 1-4).…”

Section: Discussionsupporting

confidence: 90%

Optical Properties of Humic Substances and CDOM: Effects of Borohydride Reduction

Vecchio

Golanoski

et al. 2010

Environ. Sci. Technol.

148

261

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Treatment of Suwanee River humic (SRHA) and fulvic (SRFA) acids, a commercial lignin (LAC), and a series of solid phase extracts (C18) from the Middle Atlantic Bight (MAB extracts) with sodium borohydride (NaBH(4)), a selective reductant of carbonyl-containing compounds including quinones and aromatic ketones, produces a preferential loss of visible absorption (> or = 50% for SRFA) and substantially enhanced, blue-shifted fluorescence emission (2- to 3-fold increase). Comparison of the results with those obtained from a series of model quinones and hydroquinones demonstrates that these spectral changes cannot be assigned directly to the absorption and emission of visible light by quinones/hydroquinones. Instead, these results are consistent with a charge transfer model in which the visible absorption is due primarily to charge transfer transitions arising among hydroxy- (methoxy-) aromatic donors and carbonyl-containing acceptors. Unlike most of the model hydroquinones, the changes in optical properties of the natural samples following NaBH(4) reduction were largely irreversible in the presence of air and following addition of a Cu(2+) catalyst, providing tentative evidence that aromatic ketones (or other similar carbonyl-containing structures) may play a more important role than quinones in the optical properties of these materials.

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Section: Discussionsupporting

confidence: 90%

Optical Properties of Humic Substances and CDOM: Effects of Borohydride Reduction

Vecchio

Golanoski

et al. 2010

Environ. Sci. Technol.

148

261

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“…22,42 Although the longer wavelength, visible absorption (>400 nm) still cannot be explained directly from either lignin derivatives or CRAM corresponding to these low mass (<600 Da) compounds, aggregation could facilitate charge transfer interactions between electron acceptors (e.g., aromatic ketones/aldehydes and quinones) and donors (e.g., alkoxy aromatics), both of which are known to be present within lignin derivatives. 21,25,43 Indeed, previous work 32,34 has indicated that the electrospray ionization process may cause disaggregation of high molecular weight species. The view that humic substances are composed primarily of aggregates of relatively low molecular weight components 44,45 is compatible with a model in which intramolecular charge transfer interactions between lignin-derived molecules of these aggregates give rise to the unique absorption and emission properties of these materials.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Selective Mass Labeling for Linking the Optical Properties of Chromophoric Dissolved Organic Matter to Structure and Composition via Ultrahigh Resolution Electrospray Ionization Mass Spectrometry

Baluha

Blough

Vecchio

2013

Environ. Sci. Technol.

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The mass spectra acquired by ESI FT-ICR MS of untreated, borohydride-reduced, and borodeuteride-reduced samples of Suwannee River fulvic acid (SRFA) and a C18 extract from the upper Delaware Bay were compared to one another. Treatment of these samples with sodium borodeuteride was shown to produce unique mass labels for species which contain one or two ketone/aldehyde moieties. Approximately 30% of all identified peaks in the two samples were shown to comprise ketone/aldehyde-containing species. The molecular formulas of the majority of these species had O/C and H/C molar ratios typically attributed to lignin-derived compounds and/or carboxylic rich alicyclic molecules (CRAM). However, the significant loss of UV-vis absorption following reduction supports a lignin-based origin for the optical (and photochemical) properties of these samples. The mass-labeling method described and tested herein shows great promise as a means to further characterize the structure and composition of complex natural samples, especially in terms of identifying specific subsets of chemical species that contribute significantly to the optical and photochemical properties of such samples.

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“…These interactions are capable of producing new, lower energy, optical CT transitions 85,124,126 arising from short-range contacts between hydroxy-/methoxy-aromatic electron donors and carbonyl-containing electron acceptors. 74,85,89,127,128 The CT model thus proposes that the long-wavelength absorption and emission in the near-UV and visible results primarily from intramolecular CT complexes between hydroxy-/methoxy-aromatic electron donors and carbonyl-containing electron acceptors formed through the partial oxidation of lignin precursors. 74,85,89,127,128 Within lignin, electron donors could include phenols and/or methoxylated phenols, while acceptors could include quinones and/or (aromatic) ketones/aldehydes.…”

Section: Structural Basis Of Absorption/emission Spectramentioning

confidence: 99%

The importance of charge-transfer interactions in determining chromophoric dissolved organic matter (CDOM) optical and photochemical properties

Sharpless

Blough

2014

Environ. Sci.: Processes Impacts

279

412

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Absorption of sunlight by chromophoric dissolved natural organic matter (CDOM) is environmentally significant because it controls photic zone depth and causes photochemistry that affects elemental cycling and contaminant fate. Both the optics (absorbance and fluorescence) and photochemistry of CDOM display unusual properties that cannot easily be ascribed to a superposition of individual chromophores. These include (i) broad, unstructured absorbance that decreases monotonically well into the visible and near IR, (ii) fluorescence emission spectra that all fall into a single envelope regardless of the excitation wavelength, and (iii) photobleaching and photochemical quantum yields that decrease monotonically with increasing wavelength. In contrast to a simple superposition model, these phenomena and others can be reasonably well explained by a physical model in which charge-transfer interactions between electron donating and accepting chromophores within the CDOM control the optical and photophysical properties. This review summarizes current understanding of the processes underlying CDOM photophysics and photochemistry as well as their physical basis.

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Charge-Transfer Complexes in Kraft Lignin Part 2: Contribution to Color

Cited by 17 publications

References 3 publications

Optical Properties of Humic Substances and CDOM: Effects of Borohydride Reduction

Optical Properties of Humic Substances and CDOM: Effects of Borohydride Reduction

Selective Mass Labeling for Linking the Optical Properties of Chromophoric Dissolved Organic Matter to Structure and Composition via Ultrahigh Resolution Electrospray Ionization Mass Spectrometry

The importance of charge-transfer interactions in determining chromophoric dissolved organic matter (CDOM) optical and photochemical properties

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