to dating of cellulose Luigi Campanella

Transcription

1 Sensoristic approach to dating of cellulose Luigi Campanella

2 Pagina 2

3 Effect of ageing g on cellulose molecule 1) Acidification cat (COOH groups) 2) Oxidation (CO groups) 3) Hydrolysis (fragmentation) 4) Methylation (CH 3 groups) 5) Self reaction (sites for CO-NH bonds) (intramolecular) 1,2 meaningly depending on environmental conditions 3,4,5 meaningly depending on time Pagina 3

4 Acidification Protein Immobilising power CO-NH binding applied to enzymes (catalysts not reagents) multiplying effect (by the final product of the catalysed reaction) Pagina 4

5 Enzymatic biosensoristic test (carboxylation degree assessment) The enzymatic immobilization method involves the formation of amide bonds between carboxyl groups (formed after cellulose degradation) and amino groups in the protein component of the glucose oxidase enzyme by means of a chemical bond using carbodiimide which acts as an actual bridge: Pagina 5

6 Enzymatic activity variation is related to the formed carboxylic group number. The amperometric transducer measures the consumption of dissolved oxygen produced by the enzymatic reaction: β glucose oxidase 2 + H 2O gluconic acid H 2O 2 glucose + O + O 2 ) Concentration of oxy ygen in solution (ppm Δppm O 2 (proportional to enzymatic activity) addition of substrate (glucose) Consumption of oxygen catalyzed by glucose oxidase time (min) Pagina 6

7 Biosensor scheme Sample Immobilised enzyme Trasducer (Clark electrode) Signal Computer (treatment of data) Pagina 7

8 Experimental Samples Cellulose water washed circular disks (ideal shape) diameter 8 mm weight ~ 10 mg Pagina 8

9 Artificial ageing of cellulose l samples Veterometer QUV Weathering Tester - Model QUV/Spray Q - Panel LAB - Products T=45 C λ = 310 nm H = 58% Pagina 9

10 Original profiles i i 400 h 300 h t t Pagina 10

11 Calibration (dated linen samples) ormalised No Pagina 11

12 y = (2.8 ± 0,1) 10-3 X+ (4.3 ± 0,1) Δy = 0,5 Δx = 160 y Pagina 12

13 Paper samples normal lised Δppm mo 2 y Pagina 13

14 y = (1,0 ± 0,3) 10-2 ± (3.5 ± 0,5) Δy = 0,5 Δx = 50 Pagina 14

15 Dating of an unknown wood sample needs calibration with dated samples of the same kind of wood Pagina 15

16 Wood species Straight line equation r 2 Chestnut Y = x Cherry wood Y = x Walnut Y = x Olive wood Y = x Pinewood Y =0407x x Pagina 16

17 Fragmentation vs age Photosensor Pagina 17

18 Titanium dioxide photosensor Titanium dioxide, TiO 2, photoactivated at 350 nm acts as photocatalyst of degradation. When TiO 2 absorbs light having an energy 3.2 ev (band gap energy of titaniumi anatase), electrons and holes are formed in the conductivity and valence bands, respectively: TiO 2 ( hν TiO2 e + h ) TiO2( e cb + hvb) Pagina 18

19 Main mechanism of photodegradation begins with radical production: OH as result of OH - or H 2 O oxidation by trapped holes O._ 2 as a result of oxygen reduction from photogenerated electrons These radicals react with cellulose and degrade it to: (CO 2 + H 2 O + mineral acids) During this process ph decreases due to the acid production. Pagina 19

20 The 350 nm UV photoactivated TiO 2 acts also as a ph indicator. It therefore allows measurement of the time needed to reach the acidification corresponding to the production of CO 2 due to the degradation of the cellulose. Pagina 20

21 Diagnostic index P = Δ t stio 2 Δt = delay time s TiO2 = curve slope s of the increasing TiO 2 potential versus irradiation time s TiO2. (rate of acidification) Δt Pagina 21

22 No influence of from emicellulose % deg tempo (h) artificial ageing time (h) Pagina 22

23 Environmental persistance of not written natural aged paper Diagnostic index values for dated paper samples V) nv (min2 /mv P en Natural ageing time (years) birth year Pagina 23

24 Methylation Enzymatic test + GC-MS Pagina 24

25 SAMT: s-adenosylmethionine-transmethylase SAM: s-adenosylmethionine; THFA: tetrahydrofolic acid cellulosic material SAMT + SAM +THFA cellulosic l demethylated t d material + adenosine + omocisteine Pagina 25

26 Mass spectra of differently methylated (on ageing) cellulosie samples Pagina 26

27 Possible metabolic pathivay Pagina 27

28 SAMT Method calibration (adesion determined by HPLC) Date wood Samples Age Produced adenosine μmol/g 10-3 σ A7 750 d.c. 8,4 4 ± 1,0 M d.c 4,3 7 ± 0,5 T dc d.c 44 4,4 3 ±05 0,5 T d.c 2,1 1 ± 0,4 T d.c 2,3 5 ± 0,4 A d.c 3,2 1 ± 0,6 M d.c 2,8 3 ± 0,5 LCF 1972 d.c 0,5 5 ± 0,5 Pagina 28

29 SAMT method on dated linen samples No ornalised Adenosi ample) ne (nmol/g sa y Pagina 29

30 y = (6.9 ± 1,0) 10-3 X - (1.0 ± 0,1) Δy = 1 ppm Δx = 150 year Pagina 30