presentazione cerm 19-04-2007

7/28/2019 Presentazione CERM 19-04-2007

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SOLID STATE NMR SPECTROSCOPY APPLIED TONATURAL ORGANIC MATTER AND

ENVIRONMENTAL SAMPLES

Pellegrino Conte

Dipartimento di Ingegneria e Tecnologie Agro-Forestali,Universit degli Studi di Palermo

Contact: [email protected]


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Definition of Natural Organic Matter (NOM)

The decomposition of plant, animaland microbial material in soil andwater produces a variety of complex

organic molecules, collectively callednatural organic matter. Thesecompounds play many importantroles in the environment.


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Roles of Natural Organic Matter (NOM)

NOM is ubiquitous in soils, watersand sediments.

In agriculture, NOM is importantbecause of its positive effects onthe structure, water retentionand nutrient properties of soils.


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NOM also interacts with metal ionsand minerals to form complexes ofwidely differing chemical andbiological nature.

Solubility, mobility and toxicity ofmany trace metals are stronglycorrelated with the concentration of

natural organic matter in soil andwater.


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NOM interacts with organicpollutants (i.e. polycyclic aromatic

hydrocarbons, PAH) to reduce theirenvironmental availability and toxicity


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Natural organic matter createsproblems for the water supplyindustry. It is required its removal inorder to minimize water color andeliminate formation of potentiallyharmful chemical byproducts as aresult of chlorination.

Through a process called "bio-fouling," natural organic matter is

also a major culprit in degrading theperformance of membrane filtrationsystems used for water purificationand desalination.


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Models for studying NOM complexity


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Nature of Natural Organic Matter (NOM)

Persistent and universal naturalorganic matter molecules are in theenvironment, they are littleunderstood.

Natural organic matter has no uniquestructure or composition, cannot becrystallized and is extremely difficultto characterize.

Structure proposed by Flaig (1960)

Structure proposed by Stevenson (1982)

Structureproposed byStein (1997)

Structure proposed bySchulten (1993)


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Nature of Natural Organic Matter (NOM)

Natural Organic Matter is a complexmixture of several different self-

aggregatingcompounds formingsupramolecular aggregates.

The size of each molecular systemwithin NOM does not exceed 2000Da.

The new view (by Piccolo, 2001)

Weak dispersive forcesare mainlyinvolved in the conformationalstabilization of NOM

Saccharides

Peptides

Alkyl chains

Aromatic systems

Cations


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Importance of NMR in characterizing NOM

Solid state NMR(CPMAS 13C-NMR)

Liquid state NMR(13C-NMR)


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Liquid state 13C-NMR vs Solid state 13C-NMR spectroscopy


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Hydrophobic core

Hydrophilic moiety

Water


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Conformational analysis of NOM fractions


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High performance size exclusion profile


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ppm (t2)

-200-1000100200300400

=

CH

CH

CH

T

CTHT

T

HT

CT

HT

TItI

)(1

exp1)(

exp)(

1)(1

1

1

1

0


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TCH: 1. fast local motionshigh TCH

values;2. high amount of protonslow TCHvalues

T1(H):proton spin lattice in therotating frame; fast local motionsshorterT1(H) values. High protonconcentrationfaster spin diffusionwith shorter T

1(H) values.


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Quantitative assessment of CPMAS 13C-NMR spectroscopy


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What does it mean?

(ppm)

-40-20020406080100120140160180200220240

Content of a chemical groupI

i/I

ix 100


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1H 90 pulse

Hartman-Hahn condition

Contact time

Spin diffusion


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Measurement of1

H90 pulse

via CP

via1

H


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Precise measurement of1H 90 pulse by application of a 4 x 90 CP pulse sequence


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Spectra acquired with:

1H 90 pulse calibrated on Gly

1

H 90 pulse calibrated on Glyand 4 x 90 CP sequence1H 90 pulse calibrated with 4 x90 CP sequence


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Samples 1H 90 pulse (s) by

DD (Inversion

Recoverymeasurement)

4 x 90 CP sequence

SDS 3.12 2.83

CMC 3.02 2.83

HMB 3.06 2.83

pepsin 3.11 2.80

HA1 3.17 2.90

FA1 3.12 2.88

UM1 3.04 2.80

HA2 2.96 2.80

HA3 2.98 2.84HA4 3.05 2.84

Between 2 and 6% of signalrecovery is obtained when aquantitative evaluation of CPMAS 13C-NMR spectra isdone after application of thecorrect 1H 90 pulse.


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The Hartmann-Hahn Condition

SSIIBB 11 =

SI=


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The rotor spin rate is directly related to thestrength of the dipolar interactions


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Rotor spinning rate: 5kHz


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Cross polarization

Cross polarization

with RAMP on 1H

Cross polarizationwith RAMP on 13C


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Effect of spin diffusion (Standard molecules)

SO4-

12

34

56

78

910

1112

OH

O

OHO

CH3

12

34

5

6

78

9

10

CH3

CH3

CH3

CH3

CH3

CH3

Hexamethylbenzene (HMB)

Sodium dodecylsulphonate (SDS)

Ferulic Acid

12

3

4

5

O

OH

O

6

OH

O

CH27 O

O

O

*

*

n

Carboxymethylcellulose sodium salt (CMC)


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Standards Humic substances


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Solid state NMR in the differentiation of NOM of different origin


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Solid state NMR in the analyses of bulk soils


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A Chinese soil

An Italian soil

An Australian soil


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CONCLUSIONS

1. Solid state NMR spectroscopy is a very powerful tool to analyzehardly soluble natural organic matter

2. It is the only way to obtain quantitative information on the chemicalnature of NOM

3. It provides information on the chemical nature of organic matterdirectly in bulk soils

4. It can be used to study the interactions between NOM and theinorganic moieties of soils as well as the interactions withenvironmental pollutants

5. Further applications are still possible such as solid state 31P-NMR(for the analyses of phosphorous cycle in the environment), 27Al-and29Si-NMR (for the understanding of amorphous clay minerals)

presentazione cerm 19-04-2007

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