2D Correlation Spectroscopy (2DCoS) Analysis of Temperature-Dependent FTIR-ATR Spectra in Branched Polyethyleneimine/TEMPO-Oxidized Cellulose Nano-Fiber Xerogels

Abstract

Fourier transform infrared spectroscopy in attenuated total reflectance geometry (FTIR-ATR), combined with a 2D correlation analysis, was here employed to investigate temperature-induced spectral changes occurring in a particular type of novel cellulosic-based nano-material prepared using 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) oxidized and ultra-sonicated cellulose nano-fibers (TOUS-CNFs) as three-dimensional scaffolds, and branched polyethyleneimine (bPEI) as cross-linking agent. The aim was to highlight the complex sequential events involving the different functional groups of the polymeric network, as well as to gain insight into the interplay between the amount of bPEI and the resulting sponge-like material, upon increasing temperature. In this framework, synchronous and asynchronous 2D spectra were computed and analyzed in three wavenumber regions (900–1200 cm−1, 1500–1700 cm−1 and 2680–3780 cm−1), where specific vibrational modes of the cellulosic structure fall, and over a T-range between 250 K and 340 K. A step-by-step evolution of the different arrangements of the polymer functional groups was proposed, with particular regard to how the cooperativity degree of inter- and intramolecular hydrogen bonds (HBs) changes upon heating. Information acquired can be useful, in principle, in order to develop a next-generation, T-sensitive novel material to be used for water remediation applications or for drug-delivery nano-vectors.

Temperature-Dependent Dynamical Evolution in Coum/SBE-β-CD Inclusion Complexes Revealed by Two-Dimensional FTIR Correlation Spectroscopy (2D-COS)

“…First of all, as can be noted from both Figure 3 c,d and Figure 4 , two completely different pattern/trends for the inclusion complex and physical mixture can be recognized. The presence of sharper correlation peaks in the 2DAM of the Coum/SBE-β-CD inclusion complex ( Figure 3 c) with respect to those observed in the corresponding physical mixture ( Figure 3 d) supports the presence of constrained nano-geometries in the Coum/SBE-β-CD complexed structure [ 47 ], resulting in high-localized correlations upon thermal stimulus. The asynchronous 2D correlation slice at (see Figure 4 ) shows strong negative-correlations with modes at ~1008 cm −1 , ~1020 cm −1 , ~1080 cm −1 and ~1152 cm −1 (black arrow in Figure 4 ).…”

“…The aforementioned progression reveals that temperature affects the dipole moment developed by terminal/outer units of the SBE-β-CD rims first. In fact, being the material characterized by reduced degrees of freedom as a consequence of the complexation of Coum within the SBE-β-CD nano-cavities, external functional groups of the host molecule, not strongly influenced by the establishment of host-guest interactions, “feel” temperature easier and sooner with respect to less mobile inner groups (i.e., C–O, C–O–C and C–H) [ 47 ]. Furthermore, the observation of less-intense negative-correlations with modes at ~1260 cm −1 and ~1305 cm −1 (green arrows in Figure 4 ), respectively associated with the C–O and C–O–C stretching vibrations of Coum, testifies that the aforementioned modes experience modifications, due to thermal motion, lastly in the proposed chronological progression.…”

Bacterial Cellulose/Tomato Puree Edible Films as Moisture Barrier Structures in Multicomponent Foods

“…The C–O–C stretching at 1161 cm −1 is ascribed to β(1,4)-glycosidic linkages in cellulose [ 25 ] and the presence of esters in palm olein [ 26 ]. There are other bands related to cellulose, including the C–O–C asymmetric stretching of the cellulose rings [ 27 ], C–H rocking at the β-glycosidic linkage at 893 cm −1 [ 28 ], and the O–H out-of-phase bending at 667 cm −1 [ 29 ]. Some bands are related to vegetable oils (including palm olein), such as the ones at 2920 and 2853 cm −1 corresponding to the symmetric and asymmetric stretching of aliphatic CH 2 groups, the C=O stretching band of ester carbonyl groups of triglycerides at 1743 cm −1 , and the bending vibration of CH 2 and CH 3 aliphatic groups at 1462 cm −1 [ 30 ].…”

Pd-Loaded Cellulose NanoSponge as a Heterogeneous Catalyst for Suzuki–Miyaura Coupling Reactions

“…Further optimization of pristine formulations by addition of citric acid (CA) allowed the nanostructure to have higher mechanical resistance [ 25 ] and to better fix bPEI, improving the eco-safety [ 26 , 27 , 28 , 29 ] and the sustainability [ 30 ] of the material. More recently, the nanoporosity of the material was revealed by small-angle neutron scattering (SANS) investigation [ 31 ] and by FTIR-ATR analysis of the H-bond network, which evidenced water nanoconfinement in the nanostructure [ 32 , 33 ].…”