# Silicon Compounds in Sponges
## 4 Results and Discussion
### Infrared (IR) Absorption Spectra  
IR spectra of all studied sponge samples (Figure 12) are united by the presence of absorption bands characteristic of deposited silicon dioxide: 3289-3399 \(\
u\) (O-H), 1630-1660 8 (O-H), 1090-1099 \(\
u_{\rm as}\) (_Si-O-Si_), 953-964 8 (_Si-OH_), 797-799 8 (_Si-O-Si_), 465-471 8 (_Si-O-Si_) [12; 13; 14]. At the same time, several differences are observed in the spectra, according to which the samples can be divided into two groups.  
The first group includes samples 4, 5, and 6. A feature of their IR spectra is the presence of absorption bands in the region close to the absorption bands of petroleum jelly: \(\sim\)1480 \(\delta_{\rm as}\) (_CH\({}_{3}\)_), 8 (_CH\({}_{2}\)_) and -1420 cm \(\delta_{\rm s}\) (_CH\({}_{3}\)_), as well as bands at 876-878 and 856-88 cm\({}^{-1}\), characteristic of vibrations of the _Si-C_ bond, for example, in the _Si-CH\({}_{2}\)_ and _Si-CH\({}_{3}\)_ groups [15; 16; 17].  
The second group includes samples of sponges 1, 2, 3, 7, 8, 9, the IR spectra of which in the range of 400-4000 cm\({}^{-1}\) are practically identical to the spectrum of deposited amorphous _SiO\({}_{2}\)_-_H\({}_{2}\)_O_, as in [12; 13; 14]. Apparently, this is due to the low content of organic matter relative to the silica skeleton.  
The IR spectrum of the freshwater sponge _Lubomirska bicalensis_ (sample 9) is distinguished separately. A set of absorption bands 3289 \(\
u\) (N-H), 1660 \(\delta\) (N-H) and 1537 \(\delta\) (N-H) + \(\
u\) (C-N) (the \"Amide II\" band is a position characteristic of primary amides [15]) allows us to speak unambiguously about the high content of peptides.  
Thus, the analysis of IR spectra allows us to conclude that the sponges of the first group (4-6) contain silica (_SiO\({}_{2}\)_), partially bound to the organic matrix, while the silica skeleton of the sponges of the second group (1-3, 7-9) practically does not differ from the precipitated _SiO\({}_{2}\)_. At the same time, a high content of peptides is identified in the spectrum of a freshwater sponge.  
\begin{table}
\begin{tabular}{c c c} \hline
**Sample No** & **Sample Status** & **Composition of the Crystal Phase** \\ \hline
1 (_Schulzeviella gigas_) & Amorphous & \\ \hline
2 (_Sericoloplmus sp._) & Amorphous & \\ \hline
3 (_Asconema setubaltense_) & & Halite (_NaCl_), magnesian calcite \\  & & (_Mg\({}_{0.1}\)CaO\({}_{0.9}\)CO\({}_{3}\)_) \\ \hline
4 (_Euplectella aspergillus_) & Amorphous-crystalline & Tridymite (_SiO\({}_{2}\)_), quartz (_SiO\({}_{2}\)_), aragonite \\  & & (_CaCO\({}_{3}\)_), calcite (_CaCO\({}_{3}\)_), magnesian calcite \\  & & (_Mg\({}_{0.129}\)CaO\({}_{0.871}\)CO\({}_{3}\)_), zinc oxide (_ZnO_) \\ \hline
5 (_Euplectella suberia_) & & Calcite (_CaCO\({}_{3}\)_), magnesian calcite \\  & & (_Mg\({}_{0.129}\)CaO\({}_{0.871}\)CO\({}_{3}\)_), arcognite (_CaCO\({}_{3}\)_) \\ \hline
6 (_Dactylolxyx sp._) & & Calcite (_CaCO\({}_{3}\)_), magnesian calcite \\  & & (_Mg\({}_{0.06}\)CaO\({}_{0.94}\)CO\({}_{3}\)_), arcognite (_CaCO\({}_{3}\)_) \\ \hline
7 (_Sarostegia oculata_) & Amorphous & \\ \hline
8 (_Farrea sp._) & Amorphous-crystalline & quartz (_SiO\({}_{2}\)_) \\ \hline
9 (_Lubomirska bicalensis_) & Amorphous & \\ \hline \end{tabular}
\end{table}
Table 3: Results of X-ray phase analysis.