## 3 Results and Discussion
### Determination of the Composition and Thermal Behavior of Solid State Samples  
The co-crystallization efficiency and thermal behavior of the tested solid products were evaluated by combining information from the TG and DSC technology. Moreover, the DSC data for the raw standard molecular components and solid samples **1-4** were analyzed in order to observe the changes in the melting points caused by supramolecular complexation. TG and DSC traces for caffeic and protocatechuric complexes **1-4** and for the starting co-partners are presented in Figures 2 and 3, respectively.  
The obtained thermal results showed that CFA and PCA formed supramolecular complexes with both NA and INA, as evidenced by the different courses of their thermal plots against the thermal curves received for raw co-formers. The caffeic-nicotinamide, caffeic-ionicotinamide, protocatechuric-nicotinamide and protocatechuric-isonicotinamide complexes exhibited unique characteristic endothermic events on the calorimetric profiles at 103 \({}^{\circ}\)C (**1**),  
Figure 1: Chemical structures of supramolecular compounds **1–4**.  
161 \({}^{\circ}\)C (2), 189 \({}^{\circ}\)C (3) and 196 \({}^{\circ}\)C (4), respectively, which was different from the pure CFA, PCA, NA and INA melting points (220 \({}^{\circ}\)C (196-237 \({}^{\circ}\)C [22]), 203 \({}^{\circ}\)C (202-204 \({}^{\circ}\)C [23]), 131 \({}^{\circ}\)C (126-128 \({}^{\circ}\)C [24]) and 159 \({}^{\circ}\)C [25] (157 \({}^{\circ}\)C [26]), respectively). The occurrence of a single peak for a melting point represents the homogeneous phase in each case.  
Figure 3: TG-DSC thermal plots for associations **3** and **4** in comparison to parent molecular species in the range of 30–650 \({}^{\circ}\)C.  
Figure 2: TG-DSC thermal curves for materials **1** and **2** as well as starting entities between 30 and 650 \({}^{\circ}\)C.  
The initial course of the TG plot revealed weight loss of 5.71% only for adduct **1**, which corresponded to one molecule of water per molecule of caffeic acid and nicotinamide (expected value: 5.62%). The presence of one water molecule was consistent with the previously determined crystal structure of a CFANAM\(\cdot\)H\({}_{2}\)O complex [27] co-crystallized from an ethanol/water mixture with a founded mass loss of 5.33%. The water removal was also visible on the DSC curve as the first detectable endothermic jump between 60 and 130 \({}^{\circ}\)C. The presence of two distinct peak tops at 83 \({}^{\circ}\)C and 103 \({}^{\circ}\)C arising from the same endothermic effect suggested water releasing concurrently with the melting of the analyzed sample. The TG curves of compounds **2-4** did not show any weight loss before the corresponding melting point, indicating that no solvent molecules were bound to or adsorbed into the solids. In the case of materials **2-4**, the endothermic melting process accompanied the exothermic destruction of organic units, which took place at approximately 630 \({}^{\circ}\)C for both caffe adducts or 550 \({}^{\circ}\)C (**3**) and 530 \({}^{\circ}\)C (**4**) for the protocatechic assemblies. The degradation of organic species connected with the heat release was clearly visible as exothermic effects, with the strongest maxima situated at 582 \({}^{\circ}\)C (**1**), 562 \({}^{\circ}\)C (**2**), 447 \({}^{\circ}\)C (**3**) and 436 \({}^{\circ}\)C (**4**). All co-crystallization products decomposed completely, as reflected by the 100% weight loss seen for the TG traces.