Carbon-13 nuclear magnetic resonance spectra of lignins

BIOCHEMICAL

Vol. 52, No. 4, 1973

CARBON-13

AND BIOPHYSICAL RESEARCH COMMUNICATIONS

NUCLEAR YiGNETIC

RESONANCE SPECTRA

OF LIGNINS H.-D.Liidemnnn Lehrstuhl

fiir

Regensburg,

Physik, D-84

Fachbereich

Regensburg,

Biologic,

Universitgt

UniversitatsstraBe

31

and H.Nimz Polymer-Institut

der D-75

Universitat

Karlsruhe,

Karlsruhe, Hertzstr.16

Germany Received

April

5, 1973

SUMMARY: From the 'SC-nmr spectra of a large number of dimeric and monomeric lignin model compounds the chemical shifts of the carbon atoms of the Ce-units in lignin with different substitution patterns were determined. The spectra of two lignins absorption peaks of the carbon-13 (beech and spruce) could be assigned by comparison (Table After

cellulose,

natural

units.

various

with

the

means

isolation

kinds

lignin.3

Based

structural this

paper

method

of

tution

of beech

propane

structure

which

the

results

"Ca-units"

high

thirty it

on the

dimeric

could

lignin

spectroscopy our

and spruce

chemical lignins.

bonds, From

and oligomeric

between of

connected

polymera

be shown that

exist

yields

of beech

13C-nmr

dimensional

from

are

three

of bonds

completing

polymeric

or by carbon-oxygen

about

scheme

abundant

by carbon-carbon

products

different

most

of p-hydroxy-phenyl

through

of

the

complicated

a cross-linked

degradation

In

' Its

one another

giving

is

consisting

product,

structural the

lignin

the

at

least

ten in

products

was recently was chosen

In

lignin

Ca-units

degradation

results

3).

a

proposed.4 as a physical

on the comparison

constiwith

BIOCHEMICAL

Vol. 52, No, 4,1973

'H-nmr

spectroscopy

advantages range

a twenty

sharpening

spruce In

order

to

get

the

were

solutions

gradually with

adding

agitation

crude

discrete by means

dures

or obtained

by lignin

'X-spectra

were

blocks

of 1000

transients

the

-CD,

Shift

values

to

of the the

quoted

RESULTL Figs.

1 and

beech

lignin,

lines

of the

2 show the respectively.

lignins,

by

(9:l)

solutions,

-,Dimeric

lignin

standard

mixtures

by means

9:l)

at

25.2

of

proce-

ppm).

are noise

of

The

acetone

(resp.

a Varian

XL-

in the

the

spectra

spectrometer (resp.

in

(9:l)

the

Fourier-

decoupled.

100

longis

was locked

-CDs-

as an internal

given

of the

MHz by the

accumulated

of dioxane). reference.

TMS scale.

AND DISCUSSION 13C-nmr In

the

ligninfrom

to the

to

water

solutions are

the

of 2oo/o W/W solutions

were

0.2

groups

TMS was added

mixer.

The resolution

+3 Hz (approximately

Bjijrkman.'

on alumina

of benzene

The protons

-term-averaging-mode.

to

taken

operating

-transform-technique.

to

and

degradation.

water,

spectrometer

-100-15

according

according

deuteroacetone/heavy

deuterodioxane/heavy

silvatica)

dioxane/water

of a vibro

were prepared

in

shift

(Fagus

precipitated

amounts

compounds

lignins

chemical

carbohydrates,

MWLs in

model

The

from

were

of the

convincing

decoupling.

prepared

MWLs free

-carbohydrate-complexes the

wider

(MWL) of beech

excelsa)

offers

AND METHODS

wood lignins (Picea

fold

by proton

MATERIALS Milled

5 'XC!-nmr

of lignins,

regarding

and line

AND BIOPHYSICAL RESEARCH COMMUNICATIONS

order

'%-spectra 1163

spectra to of

of

spruce

assign eighteen

the

and absorption dimeric

and

BIOCHEMICAL

Vol. 52, No. 4, 1973

12 IL 200

3

L

S-10

AND BIOPHYSICAL RESEARCH COMMUNICATIONS

11-16l7-222232L

25-30

,,,I,,,

I

31-3435

I,,, 100

150

36

@

@

37

I 50

I,

,

I 0

-6K

Fig.

1:

seven

'SC-nmr spectrum (R) = TMS.

monomeric

parison. shifts

From of

as tney

There

are

atoms the

in

from

with

aliphatic

in

the

to 105

and the

the

for

com-

chemical

and C-S)

atoms

of

the

sp2 carbon

other

groups

from

determined.

one covering

and the

methoxy

pat-

were

spectra, (C-a

88 and 20 ppm downfield

taken

(I-III),

ppm,

= aceton,

substitution

Cg-units

sp3 carbon

to C-y)

for

a ligninlike

the

(S)

were

values

andolefinic

160

lignin.

compounds the

regions

to C-6)

(C-l

saturated

between

atoms

two main

(C-a

model spectra

exist

ranging

chains

these

carbon

tern,

aromatic

lignin

of beech

covering

the

propane

with

chemical

side shifts

TMS.

Y-FB-ya-CI:

II: OH The C-6)

III:

chemical

depend

on

shifts the

of

the

R'

= R2 = H

R'

= OCH,,

R'

= R2 = OCH3

R2 = H

aromatic

carbon

in

aromatic

substituents

1164

the

atoms ring,

(C-l

to

on the

BIOCHEMICAL

Vol. 52, No. 4, 1973

12

I

3

Fig.

2:

n-i6i7---22

s-10

is

Table

or not

1 it

has no influence

the to

ortho the

carbon

para shifted

methoxy

group

atoms

6 (-15

field

shift

is

the

of C-l even

C-2 (C-6,

downfield in

III

ppm),

effects

(-16

carbon

4 (-11

at the

2, 4, upfield smaller

the

atom

of

in

II,

that

shifts causes ppm)

ring

ppm).

in value,

phenolic

hydroxy

group

of both

meta-positions

an upfield

Similarly shifts

at

to

carbon

atoms

substituents

chemical

instead

when C-a is 1165

second

the

carbon

to and of

and a down-

to

are

an olefinic

C-6

are

When C-a of

of the

to +5 ppm)

The same effects

the

C-l

shifts (+2

shift

II.7

at C-a.

group

II

absorption

ppm),

relative

in

ppm)

(-11

the

and 2 (-7

and 6 move downfield (-6

= aceton,

methoxy

while

upfield ppm),

the

and C-4

ppm).

a carbonyl the

the

-8 ppm),

causes

(S)

1).

but

(+32

when altering

or a HCOR-group atoms

atoms

I,

of +33 ppm at C-5,

Smaller observed

to

position

C-3 is

(Table

I

w

lignin.

whether

chemical

relative

RESEARCH COMMUNICATIONS

31-3C3536

spruce

fact,

can be seen on the

and C-5))

(C-l

of

and on the

alkylated

From

25-30

'SC-nmr spectrum (R) = TMS;

C-a substituents group

AND BIOPHYSICAL

a HCOHcarbon

and that observed,

but

or a tertiary

BIOCHEMICAL

Vol. 52, No. 4, 1973

AND BIOPHYSICAL RESEARCH COMMUNICATIONS

Table 1: Chemical shifts and differences in chemical shifts of the aromatic carbon atoms (C-l to C-6) of the Cg-units (I-III) in ppm. For further details see text. a-HCOH(R)

C-u in: C9-unit

I

C-l

a-C=0

II

III

II

III

II

III

II

-4

+3 +I

+4

+3 +5

+I

+I

0

0

+5

-2 +5

+I +2

+2 0 +2

0 0 +3

+3 -1 0

+3 +5 0

134 105

-6 +2

c-3

116

148

149

c-4 c-5 C-6

158 116 128

147 116 120

136 149 105

2: Chemical shifts of the propylic (C-a to C-y) of the &-units (I-III) ty-pe

c-a

side in C-6

chain ppm. c-y

Ar-YH-YH-CH20H OH O-C-4'

(IV)

73

87

62

Ar-CH-CH-CH20H &H k-1'

0)

65

64

75

01)

88

54

65

CH-YHp (VII) &+ O-C-a '

87

55

72

40

47

73

YH-CH2011

O-C-4'

Ar-CH&c-,,

C-5'

Ar-CII2-$-YHp C-6 '

(VIII) o-c-y

'

Ar-YH-YH-C02R C-6' C-a'

(IX)

59

43

173

Ar-yH-CH2-CO2R c-p '

co

52

38

173

Ar-CH=CH-C02H

(XI >

146

116

170

154

132

195

131

127

63

(XIV)

195

83

64

on

192

Ar-CH-CH-CHO Ar-CH=CH-CH20H Ar-CO-CH-CH20H

(XII

>

(XIII)

b-C-4'

Ar-CHO

III

-3 +3

134 112

Ar-YH-

C-4-OR

-1

134 128

Structural

a-HC-C

+2

c-2

Table atoms

a-H&C

1166

carbon

0

Vol. 52, No. 4, 1973

Table

BIOCHEMICAL

3: Assignment of absorption Figs. 1 and 2.

AND BIOPHYSICAL RESEARCH COMMUNICATIONS

lines

+> Intensity beech spruce (1)

(2)

195.2 192.7 171.8

w

W

‘W

W VW

(3) (4)

162.0

m VW

(5) (6)

154.5 152.9

s VW

W

(7)

150.6

w

S

(8)

148.5

m

S

(9)

146.6

w

In

(10)

144.8

v-w

(11)

138.7

m

(12)

136.0

m

(13)

133.6

(14)

132.7

w w

m VW m m VW

(15)

130.2

w

W

(16) (17)

129.0 126.7

7JW

(18)

120.1

m

S

(79)

117.5

w

m

(20)

115.6

m

S

(21)

113.8

VW

W

(22)

112.0

m

S

(23)

107.1

(24)

105.1

(25)

88.1

VW

W

(26)

86.8

s

W

(27)

w

m

(28)

85.8 81-83

w

VW

m

w

m VW

m vs

w

W

(29)

75.0

(30)

73.3

vs

s

(31)

63.8 61.3

m vs

m

(32) (33)

56.3

vs

(34) (35) (36)

54.5 52.3 46.8

VW VW

(37)

20.8

m

+)Intensity:

w

VW

S

vs W

VW VW w=weak,

in

the

lignin

spectra

of

Assignment a-C=0 in XIV, y-CHO in XII a-CHO in XV O-C=0 in aliphatic esters C-4 in I (alkylated at C-4) C-3 and C-5 in III (alkylated at C-4) C-a in XII C-4 in II with a-C=0 C-4 in II (alkylated), C-i; in II (a-C=O) C-3 in II, C-3, C-5 in III, C-l in biphenyls C-4 in II, C-a in XI C-4' in VI C-4 and C-l in III (alkylated) C-l in II (aikylated), C-4 in III C-l in I-III C-B in XII C-l with C-a in HC=C or HC-C (= C-l' in V) C-2 and C-6 in I C-8 in XIII C-6 in II C-6' in VI C-5 in II, C-3 and C-5 in I, C-8 in XI C-2 in II (with a-C=O, a-HC-C) C-2 in II C-Z and C-6 in III (with a-C=O, a-HC-C) C-2 and C-6 in III C-a in VI C-p in IV, C-a in VII (syringaresinol-type) C-a in VII (pinoresinol-type) C-8 in XIV C-y in V C-a in IV, C-y in VII and VIII C-a and C-8 in V, C-y in XIII and XIV C-y in IV OCH, C-8 in VI and VII C-a in X C-P in VIII acetoxy-CH3 m=medium,s=strong, vw=very weak, vs=very strong 1167

Vol. 52, No. 4, 1973

carbon

atom

hydroxy about

(cf.

group

in

The C-R,

in

II

Table

patterns,

the

for

which

data

spectra

is

lignin

(Fig.

spruce

to C-2 the

II

of

(cf.

last

the

Table

strong

carbon

lignin

two lignin

atoms

C-d,

between

the

absorption

peak

105 ppm (24)

in

the

(Fig.

2).

As this

absorption

units in

(III)

spruce

spectroscopy

distinguishing

between

at

spectrum

missing

j3C-nmr

of Figs.

difference

completely

units

assignment

3.

is

such

substitution

spectra

which

and C-S 0-f syringyl of

chain

2.

at 107 ppm (23)

lignin

for

to

shi.X

1 and 2 a preliminary

in

in

very

Therefore

method

relative

side

Table

of Tables

I),

absence

ted.

in

lines

the

a shoulder

phenclic

a weak downfield

on typical

characteristic

with

of

of the depend

proposed

The most

causes

of the

C-i+ and C-l,

listed

37 absorption

and 2 is

- Alkyiation

mainly

shifts

are

From

1).

AND BIOPHYSICAL RESEARCH COMMUNICATIONS

1).

chemical

and C-y,

for

Table

+3 ppm both

column

1

BIOCHEMICAL

in

two lignin

of beech in

the

peak lignin

spectrum is

assigned

(cf.

Table

lignin

is

offers

an outstanding

hardwood

clearly

indica-

and softwood

iignins. The rather ppm (2) groups

weak but

indicate

at least

to be present

absorption

peak

lignin,

which should

atoms,

possibly the

beech

(37)

in

lignin. research

in

at is

171.8

assigned

be regarded

result

from

lignin. beech

distinct

Further

both

and will

lignins

ppm (3) to

in

spectrum ester

ester the

of lignin later. 1168

carbonyl 3).

The

of beech

carbonyl

carbon it

could

contaminating line

by substances '3C-nmr

192.7

and

because

groups

absorption

of

Table

some caution,

polyuronic

be published

the

aliphatic

with

(1)

types (cf.

may be caused

details

at 195.2

two different

Similarly lignin

peaks

spectra

at

20.8

ppm

other

than

are

under

3),

Vol. 52, No. 4, 1973

BIOCHEMICAL

AND BIOPHYSICAL RESEARCH COMMUNICATIONS

REFERENCES K.V.Sarkanen and C.H.Ludwig, "Lignins, Occurrence, Formation, Structure,and Reactions", WiLey-Interscience, New York - London - Sydney - Toronto 1977. "Constitution and Biosynthesis 2. K.Preudenberg and A.C.Neish, Berlin - Heidelberg - New York of Lignin, Springer-Verlag,

1.

1968.

3. H.Nim:z and K.Das, Chem. Ber. 104, 2359 (1971). 4. H.Nim,z, TapDi, in press. 5. C.H.Ludwig, B.J.Nist, and J.L.McCarthy, J.Amer. Chem. 86, 1186, 1196 (1964). 6. A.BjGrkman, Svensk Papperstidn. 59, 477 (1956). 7. For comparison see: P.C.Lauterbur, J.Amer. Chem. Sot. 3, 1846 (1961).

1169

Sot.