Integrated biological and chemical characterisation of a pair of leonardesque canal lock gates

Abstract

The Museo Nazionale della Scienza e della Tecnologia "Leonardo da Vinci" in Milan is exposing two pairs of canal lock gates, used to control the water flow in Milan canal system, whose design appears in the Leonardo's Codex Atlanticus. The wood present in the gates has been deeply characterised by mean of a multidisciplinary investigation involving i) DNA barcoding of wood fragments; ii) microbial community characterisation, and iii) chemical analyses. DNA barcoding revealed that two fragments of the gates belonged to wood species widely used in the middle age: Fagus sylvatica and Picea abies. The chemical characterisations were based on the use of ionic liquid as dissolving medium in order to analyse the entire cell wall material by means of Gel Permeation Chromatography (GPC) and 2D-NMR-HSQC techniques. This multidisciplinary analytical approach was able to highlight the complex nature of the degradation occurred during the gate operation (XVI-XVIII centuries): an intricate interplay between microbial populations (i.e. Shewanella), inorganic factors (i.e. iron from nails), physical factors and the lignocellulosic material.

Fig 1. Images of the two canal lock gates.

Numbers and points represent the sampling points for the chemical and biological analyses.

Fig 2. The integrated characterisation approach performed in this work and in [1]*.

Fig 3. Taxonomic classification of bacterial communities associated to wood samples 11, 14 and 16 at Genus level.

“Other Genera” groups genera that were less abundant than 1% in all samples.

Fig 4. FT-IR spectra (range 1800–700 cm^-1) for wood samples 1, 10, 13, 11, 6 and 12 along with the main band assignments (in letter) reported in Table 2.

Fig 5. Gel Permeation Chromatography (GPC-UV) profiles (benzoylated on the left at 240 nm, acetylated on the right at 280 nm) for the 1, 10, 13, 11, 6 and 12 woods samples.

Y-scale in A.U. normalized.

Fig 6. 2D-HSQC-NMR spectra of acetylated wood samples (1, 10, 11, 13, 6, 12).

At the bottom, the main aliphatic and aromatic lignin and polysaccharide structures are reported: A) β-O-4 alkyl-aryl ethers; S’) oxidized syringyl units bearing a carbonyl at Cα; S) syringyl units; G) guaiacyl units; OCH₃ methoxy group; X_n) xylan units of hemicelluloses; C_n) anydroglucopyranose units of cellulose.

Fig 7. MWC (%), GPC data output (M_p in mol/g for benzoylated BZ and acetylated AC profiles), integration ratio C₁/OCH₃ and X₅/OCH₃ from HSQC spectra, intensity ratio 1505/1030 cm^-1 from FT-IR spectra, and SEM images for the archaeological samples 1, 10, 13, 11, 6 and 12.

* Analysed in [1].