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LIGNIN STRUCTURE OF ACACIA AND EUCALYPTUS SPECIES AND ITS RELATION TO DELIGNIFICATION
Deded S. Nawawi
a,b
, Wasrin Syaii
a
, Takuya Akiyama
b
, Tomoya Yokoyama
b
,Yuji Matsumoto
b1
a
Department of Forest Products, Faculty of Forestry, Bogor Agricultural University IPB, Bogor, Indonesia
b
Wood Chemistry Laboratory, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
1
amatsumomail.ecc.u-tokyo.ac.jp
ABSTRACT
Lignin structure of 15 acacia woods and 13 eucalyptus woods were analyzed and the relationships between lignin structure and lignin reactivity were examined. Generally hardwood lignins are different
from softwood lignins by the presence of syringyl type aromatic nuclei. In addition, there are wide varieties in the structure and amount of hardwood lignins depending on wood species, environment
of growing site, portion in the wood, portion in the cell wall, and so on. We have shown that the wide variety of lignin structure and amount can be sorted out by taking the syringylguaiacyl ratio as an index.
Furthermore, we have also shown that lignin structure can be quantitatively related to the chemical
reactivity such as deligniication during chemical pulping by taking the syringylguaiacyl ratio as an index. In this report, we review our recent achievements about the quantitative relationships between
lignin structure and reactivity .
Keywords: lignin; structure; deligniication; pulp; aromatic; stereo structure
Lignin Aromatic Structures and b-O-4 Structures
Generally, hardwood lignin contains syringyl nuclei and guaiacyl nuclei as aromatic ring types Fig.1. Syringylguaiacyl ratio is a very important structural characteristics of lignin and greatly different each
other depending on the difference of wood species, position in the wood, environment of growing site, portion in a cell wall, and so on.
C O
OCH
3
C CH
2
OH O
OCH
3
H H
OH C
O OCH
3
C CH
2
OH O
OCH
3
H HO
H
erythro β-O-4 structure
threo β-O-4 structure
O OCH
3
O OCH
3
H
3
CO
syringyl guaiacyl
aromatic ring type side-chain stereo structure
OH OCH
3
O OCH
3
C
non-phenolic phenolic
aromatic ring type
Fig. 1 Important Chemical Characteristics of Lignin from the Point of Reactivity Another important difference of aromatic structure is phenolic or non-phenolic. Although the
difference of whether guaiacyl or syringyl doesn’t change the reaction mechanism, it greatly affects the reactivity. On the other hand, difference of whether phenolic or non-phenolic sometimes results in the
different reaction mechanism. As a most important structure in lignin, b-O-4 structure is present in both hardwood and softwood lignins. This structure has two stereo isomers, erythro and threo at its side-chain
Fig. 1. All of these differences affect the reactivity of lignin. Therefore, if lignin structure is different, the pulping performance can be greatly different.
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General Tendency of Lignin Chemical Structure
Based on the analysis of 21 wood species, Akiyama et al. 2005 reported that the general tendency of lignin chemical structure can be visualized by taking syringylguaiacyl ratio as an index. General
tendency was as following: the higher the syringylguaiacyl ratio, the higher the erythrothreo ratio of
b-O-4 side chain stereo structure, the higher the proportion of b-O-4 structure, the higher the proportion of non-condensed structure, the lower the lignin content, and so on. These general tendency can be seen
not only among different wood species, but also in different portions of the same wood. For example, Akiyama et al. 2003 demonstrated that the tension part of reaction wood can be characterized by
higher syringylguaiacyl ratio, higher erythrothreo ratio, higher proportion of b-O-4 structure, and, lower lignin content compared with the compression part by the analysis of samples obtained from the
different portion within the same wood disc of yellow poplar stem which was standing on the slope before harvest. Later, Nawawi et al. applied the same analysis to various type of reaction wood samples
and conirmed the same tendency Nawawi et al. 2016A, B. The relation can be recognized not only in the wide range of wood species but also in the same group
of trees in which the structural difference is rather small. If the structural difference is small, it will be dificult to establish a correlation between two structural factors. However, Nawawi et al. 2016C
successfully demonstrated that the general tendency can be well recognized among the same group of trees, such as genus Acacia and genus Eucalyptus Table 1.
Table 1. List of wood samples examined in this study
Sample Wood species
Sample Wood species
Genus Acacia Genus Eucalyptus
1 Acacia auriculiformis
16 Eucalyptus camaldulensis A
2 Acacia hybrid A
1
17 Eucalyptus camaldulensis B
3 Acacia hybrid B
1
18 Eucalyptus deglupta
4 Acacia hybrid C
1
19 Eucalyptus dunii
5 Acacia hybrid D
1
20 Eucalyptus globulus A
6 Acacia hybrid E
1
21 Eucalyptus globulus B
7 Acacia hybrid F
1
22 Eucalyptus grandis A
8 Acacia mangium A
23 Eucalyptus grandis B
9 Acacia mangium B
24 Eucalyptus grandis C
10 Acacia mangium C-1
2
25 Eucalyptus hybrid
3
11 Acacia mangium C-2
2
26 Eucalyptus nitens
12 Acacia mangium D
27 Eucalyptus saligna
13 Acacia mangium E
28 Eucalyptus urophylla
14 Acacia mangium F
15 Acacia meransii
Same wood species with different alphabets are from different growing area.
1
: Hybrid of Acacia mangium and Acacia auriculiformis with different mother trees
2
: Same species from the same plantation area but C-1 was 8 years and C-2 was 12 years old
3
: Hybrid of Eucalyptus camaldulensis and Eucalyptus deglupta
For example, Fig. 2 shows the relation between lignin content and syringylguaiacyl ratio. Here, the ratio between syringyl and guaiacyl is expressed as syringyl ratio proportion of syringyl among the total
of syringyl and guaiacyl. It is clearly shown that lignin content is signiicantly related to the syringyl ratio within each genus.
Among the general tendency of lignin chemical structure, the correlation between the syringyl guaiacyl ratio and
erythrothreo ratio of b-O-4 side-chain stereo structure is very high and this relation is quite important from the point of chemical reactivity of lignin as will be seen in the following sections.
This correlation was irst established by Akiyama et al. 2005 for 21 wood species 15 hardwoods and 6 softwoods and later we have demonstrated that all the native lignins it this correlation. Fig. 3 shows
the correlation between the syringylguaiacyl ratio and erythrothreo ratio when they are expressed as
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erythro ratio proportion of erythro and syringyl ratio, respectively. In this igure, the correlation found
for 21 wood species by Akiyama et al. 2005 and that found for genus Acacia and genus Eucalyptus by Nawawi et al. 2016C are expressed together. Since softwood has no syringyl nucleus, the erythro ratio
is exactly 0.5, which means the amount of erythro and threo b-O-4 structure is equal.
Fig. 2 Relationship between lignin content and s
yringyl ratio. Acacia Eucalyptus syringyl ratio = syringylsyringyl+guaiacyl
Fig. 3 Correlation between erythro ratio of b-O-4 structure and syringyl ratio.
Acacia
Eucalyptus ○ 21 wood species by Akiyama et al. 2005
erythro ratio = erythroerythro+threo
Structure-Reactivity Relationships of Lignin
During alkali pulping including kraft pulping, the most important reaction is the cleavage of non- phenolic b-O-4 structure shown in Fig. 4. In this mechanism, ionized a-hydroxyl group nucleophilically
attacks the b-carbon from the backside of b-O-4 ether resulting in the cleavage of this linkage.
Fig. 4 Alkaline cleavage of non-phenolic b-O-4 structure Considering the presence of 2 types of aromatic structures syringyl and guaiacyl and 2 types of
side-chain stereo structures erythro and threo, basically 8 types of b-O-4 structures are possibly present in lignin. In Fig. 5, structures of model compounds which represent these 8 types of b-O-4 structures
are shown. The number below each structure is the alkali cleavage rate constant obtained by the alkali treatment under 160 ºC at 2 molar NaOH concentration.
Since softwood lignin has only guaiacyl type aromatic nucleus, there are only two types of b-O-4 erythro and threo of GG, Fig. 5 in softwood. The ratio between erythro and threo of softwood lignin is
exactly 1:1. On the other hand, hardwood lignin has totally 8 types of b-O-4 erythro and threo of GS, SG, SS in addition to GG, Fig. 5. Proportion between GG, GS, SG and SS can be different in different
lignins depending on the ratio between syringyl and guaiacyl of the lignin.
Reactivity of these 8 types of b-O-4 structures can be summarized as following: 1. erythro isomer is always more reactive than threo isomer when the aromatic composition is the same
2. substitution of guaiacyl with syringyl nucleus at any position results in the increase of reactivity 3. the effect of substitution from guaiacyl to syringyl is greater when etherifying guaiacyl is
substituted than when guaiacyl in the carbon main skeleton is substituted. It is very important to note that syringyl ratio could be higher than 0.8 in some wood species Fig.
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3. Since the proportion of erythro b-O-4 becomes higher when the syringyl ratio is higher, erythro type of SS can be predominant b-O-4 structure in these wood species. In softwood lignin, half of b-O-
4 structure is threo GG type, while majority of b-O-4 structure is erythro SS type in these hardwood species. The alkali cleavage rate constant of the former type is 16.7 and that of latter is as high as 217.
By this comparison, it is easily predicted that hardwood lignin with higher proportion of syringyl nuclei is much more easily degraded during alkali pulping process such as kraft pulping than softwood lignin
or hardwood lignin with lower syringyl proportion Shimizu et al. 2012, 2013, 2015.
Fig. 5 Model compounds of 8 types of non-phenolic b-O-4 structures and their alkali cleavage reaction rate constant in 2 molar aqueous NaOH under 160 ºC.
S: syringyl, G: guaiacyl Shimizu et al., 2012
Pulping Result
In the previous section, it was predicted that hardwood with higher proportion of syringyl is easily deligniied from the point of chemical reactivity of non-phenolic b-O-4 structures. One more factor
which beneits the woods with higher syringyl proportion is the lower lignin content of such woods. Nawawi et al.
conirmed this prediction by subjecting wood species belonging to genus acacia and eucalyptus to kraft pulping Nawawi et al. 2016C. Fig. 6 clearly shows that woods with higher syringyl
ratio needs less alkali charge to reach kappa 19.
Fig. 6 Relationship between syringyl ratio
and deligniication. Acacia Eucalyptus
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References
1. Akiyama, T., Matsumoto, Y., Okuyama, T., Meshitsuka, G. Phytochemistry 64, 1157–1162 2003
2. Akiyama, T., Goto, H., Nawawi, D.S., Syaii, W., Matsumoto, Y., Meshitsuka, G. Holzforschung,
593, 276-281 2005 3.
Nawawi, D.S, Syaii, W., Akiyama, T., Matsumoto, Y. Holzforschung 707:593-602. 2016A 4.
Nawawi, D.S., Akiyama, T., Syaii, W., Matsumoto, Y. 2016. Holzforschung Holz.2016.0100: Accepted 12-Aug-2016. 2016B
5. Nawawi, D.S., Syaii, W., Tomoda, I., Uchida, Y., Akiyama, T., Yokoyama, T., Matsumoto, Y.
Submitted to Journal Wood Chemistry and Technology. 2016C 6.
Shimizu, S., Yokoyama, T., Akiyama, T., Matsumoto, Y. J. Agric. Food Chem., 60, 6471−6476 2012
7. Shimizu, S., Posoknistakul, P., Yokoyama, T., Matsumoto, Y. BioResources, 8 3, 4312-4322 2013
8. Shimizu, S., Yokoyama, T., Matsumoto, Y. J. Wood Sci., 61 5, 529-536 2015
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A NOVEL PAPER-BASED SENSOR FOR COLORIMETRIC AND FLUORESCENT DETECTION OF COPPER IONS IN WATER
Yinchao Xu
a1
, Toshiharu Enomae
b2
a
Research fellow of Japan Society for the Promotion of Science; Graduate School of Life and Environmental Sciences, University of Tsukuba, Tennodai 1-1-1, Tsukuba, Ibaraki, 305-8572, Japan
b
Faculty of Life and Environmental Sciences, University of Tsukuba, Tennodai 1-1-1, Tsukuba, Ibaraki, 305- 8572, Japan
1
xuyinchaopaperscience.org
2
tenomae.com
ABSTRACT
In this research, we have developed a user-friendly, low-cost, sensitive and ion-species-selective paper-based sensor to inspect drinking and industrial water for excessive levels of copper ions. The
paper-based sensor was simply fabricated by printing an anthraquinone derivative acetone solution onto ilter paper. In the colorimetric detection, by 10 min immersion in a 5 mL test water sample, the paper-
based sensor was proven to be feasible to indicate a Cu
2+
concentration of as low as 2 ppm, through the visible colour change from yellow to light purple. In the instrumental luorescence detection, the linear
relationship was successfully obtained between the resulting surface luorescence intensity of the paper- based sensor and Cu
2+
concentration. Based on this linear relationship, more accurate concentrations are available. In addition, the high selectivity of the paper-based sensor ensured applications to detect
practical contaminated water samples. Keywords: copper ion detection, inkjet printing, paper-based sensor
Introduction
Heavy metals, commonly deined as metals with densities higher than 5 gm
3
[1], exist naturally in the environment. However, in past decades, heavy metals have caused serious environmental pollution,
originating from industrial efluents and, more recently, metal ions leached from soil by acid rain.[2] As heavy metals form complexes with nitrogen, sulfur, and oxygen ligands in biosystems, excessive
concentrations of heavy metals are harmful, or even deadly, to human and animals.[3] Copper, one of the most abundant and fundamental trace elements, can adopt distinct redox states, oxidized CuII or
reduced CuI, allowing the metal to play a pivotal role in cell physiology as a catalytic cofactor in the redox chemistry of enzymes, mitochondrial respiration, iron absorption, free radical scavenging, and
elastin cross-linking.[4] In contrast, excessive concentrations of copper cause oxidative stress and related symptoms, which can lead to diabetes and many neurodegenerative disorders, such as Alzheimer’s
disease[5], and Menkes disease[6], and Wilson disease[7].
Conventionally, inductively coupled plasma–optical emission spectroscopy ICP–OES is the most common and sensitive method used to determine metal ion concentrations [8].However, it is an expensive
and laborious analytical method, limited to high-demand laboratory research analysis and, thus, inaccessible to nonprofessionals. To explore other analytical approaches, published alternative methods
are mostly based on colorimetric analysis and luorescence spectroscopy, combining modiied dyes, synthesized organic compounds, or nanomaterials to achieve highly selective and sensitive detection.
Mahapatra et al . developed a colorimetric and turn-off luorimetric sensor for Cu
2+
detection using a synthesized triphenylamine-based indolylmethane derivative [9]. Liu et al. developed a colorimetric
Cu
2+
sensor using DNA-functionalized gold nanoparticles [10]. Chen et al . developed a luorescence
sensor for Cu
2+
detection using synthesized highly-luorescent glutathione-capped gold nanoparticles [11]. Maity et al. [12] used thiourea-salicylaldehyde to realize visible and near-IR sensing of Cu
2+
based on the coordination reaction.Many more effective synthesized chemicals and methods have also been
proposed and developed, all showing remarkable sensing selectivity and sensitivity. However, these approaches are still costly and limit the methods to laboratory use as an alternative to ICP–OES.
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Therefore, the development of a high-performance, user-friendly method to detect heavy metal ions, such as Cu
2+
, in water is in strong demand, and would allow nonprofessionals to determine water safety, especially in Third World countries. Herein, we proposed and developed a simple low-cost method,
using inkjet printing technology to fabricate a paper-based copper ion sensor for both qualitative and quantitative detection. A commercial anthraquinone dye and common ilter paper were used as the
main chemical and substrate, respectively, for sensor fabrication. Consequently, the developed paper- based sensor can realize both qualitative detection of Cu
2+
in water and quantitative detection based on luorescence spectroscopy for high ion species selectivity and sensitivity.
Experimental 2.1 Materials
An anthraquinone derivative Sigma-Aldrich and ilter paper No. 1, Advantec were used as the sensing dye and substrate of the sensor, respectively. Metal nitrate salts, including sodium, potassium,
calcium, ferric, cobalt, cadmium, manganese, mercury, lead, nickel, zinc, and silver nitrates Japanese Industrial Standard [JIS] special grade, Wako Pure Chemical, were used in the experiment to evaluate
interference by metal ions other than Cu
2+
. Copper standard solution Cu 100, Wako Pure Chemical was used to calibrate Cu
2+
concentrations measured by ICP–OES Optima-7300DV, PerkinElmer, USA and the paper-based sensor.
2.2 Fabrication