Supramolecular recognition of nucleobases in the solid state

Zagrijavanjem fizičkih smjesa komplementarnih nukleobaza potaknuto je njihovo supramolekulsko prepoznavanje u čvrstom stanju. Dobiven je dosad nepoznati 1:1 kokristal 9- metilgvanina i 1-metilcitozina. Njegova je kristalna struktura riješena pomoću podataka dobivenih difrakcijom rentgenskog zračenja na polikristalnom uzorku. Molekule 9- metilgvanina i 1-metilcitozina povezane su Watson-Crickovim načinom povezivanja koje uključuje tri međumolekulske vodikove veze. Ovi rezultati mogu biti značajni jer predstavljaju alternativan put nastanka supramolekulskih struktura koje su bile preduvjet za daljnju biološku evoluciju.Supramolecular recognition of complementary nucleobases was thermally induced in the solid state. Novel 1:1 cocrystal between 9-methylguanine and 1-methylcytosine was obtained. The crystal structure of new cocrystal was elucidated using laboratory powder X-ray diffraction. Molecules of 9-methylguanine and 1-methylcytosine are held together by Watson-Crick hydrogen bonding motif that includes three intermolecule hydrogen bonds. It is considered that these findings could be relevant as they stress out an alternative route of occurance of supramolecular structures that were prerequisite for biological evolution

Mechanochemical Metathesis between AgNO3 and NaX (X = Cl, Br, I) and Ag2XNO3 Double-Salt Formation

Here we describe real-time, in situ monitoring of mechanochemical solid-state metathesis between silver nitrate and the entire series of sodium halides, on the basis of tandem powder X-ray diffraction and Raman spectroscopy monitoring. The mechanistic monitoring reveals that reactions of AgNO3 with NaX (X = Cl, Br, I) differ in reaction paths, with only the reaction with NaBr providing the NaNO3 and AgX products directly. The reaction with NaI revealed the presence of a novel, short-lived intermediate phase, while the reaction with NaCl progressed the slowest through the well-defined Ag2ClNO3 intermediate double salt. While the corresponding iodide and bromide double salts were not observed as intermediates, all three are readily prepared as pure compounds by milling equimolar mixtures of AgX and AgNO3. The in situ observation of reactive intermediates in these simple metathesis reactions reveals a surprising resemblance of reactions involving purely ionic components to those of molecular organic solids and cocrystals. This study demonstrates the potential of in situ reaction monitoring for mechanochemical reactions of ionic compounds as well as completes the application of these techniques to all major compound classes

In Situ Monitoring of the Mechanosynthesis of the Archetypal Metal–Organic Framework HKUST-1 : Effect of Liquid Additives on the Milling Reactivity

We have applied in situ monitoring of mechanochemical reactions by high-energy synchrotron powder X-ray diffraction to study the role of liquid additives on the mechanochemical synthesis of the archetypal metal–organic framework (MOF) HKUST-1, which was one of the first and is still among the most widely investigated MOF materials to be synthesized by solvent-free procedures. It is shown here how the kinetics and mechanisms of the mechanochemical synthesis of HKUST-1 can be influenced by milling conditions and additives, yielding on occasion two new and previously undetected intermediate phases containing a mononuclear copper core, and that finally rearrange to form the HKUST-1 architecture. On the basis of in situ data, we were able to tune and direct the milling reactions toward the formation of these intermediates, which were isolated and characterized by spectroscopic and structural means and their magnetic properties compared to those of HKUST-1. The results have shown that despite the relatively large breadth of analysis available for such widely investigated materials as HKUST-1, in situ monitoring of milling reactions can help in the detection and isolation of new materials and to establish efficient reaction conditions for the mechanochemical synthesis of porous MOFs

Solid-State Supramolecular Assembly of Salicylic Acid and 2-Pyridone, 3-Hydroxypyridine or 4-Pyridone

Mechanochemical milling of equimolar mixtures of salicylic acid with three hydroxy derivatives of pyridine provided three new phases. With 2-hydroxypyridine, which is in fact present as 2-pyridone, a discrete cocrystal supramolecular assembly is formed. 3-hydroxypyridine and salicylic acid formed a salt and an extended network of hydrogen bonds while the product of the reaction of 4-hydroxypyridine (present as 4-pyridone) and salicylic acid remained structurally uncharacterized. All three hydroxypyridines retain the tautomeric form as in their respective pure phases upon cocrystal formation. Where possible, reaction profiles have been extracted from in situ monitoring via Rietveld refinement to show direct product formation which could be well described using the first-order reaction rate law. This work is licensed under a Creative Commons Attribution 4.0 International License

Experimental and Theoretical Study of Selectivity in Mechanochemical Cocrystallization of Nicotinamide with Anthranilic and Salicylic Acid

Selectivity in mechanochemical cocrystal formation between nicotinamide and anthranilic acid or salicylic acid was studied using tandem in situ reaction monitoring by powder X-ray diffraction (PXRD) and Raman spectroscopy. Selectivity was probed by offering a competing cocrystal coformer to a previously prepared cocrystal or under competitive reaction conditions where all cocrystal coformers, in different stoichiometric ratios, were introduced together in the starting reaction mixture. Reaction paths were dependent on the starting mixture composition, and we find that the formation of intermediates and the final product can be predicted from solid-state ab initio calculations of relative energies of possible reaction mixtures. In some cases, the quantitative assessment revealed different reaction profiles derived from PXRD and Raman monitoring, directly indicating, for the first time, different mechanochemical reactivity on the molecular and the bulk crystalline level of the reaction mixture

Isotope Labeling Reveals Fast Atomic and Molecular Exchange in Mechanochemical Milling Reactions

Using tandem in situ monitoring and isotope-labeled solids, we reveal that mechanochemical ball-milling overcomes inherently slow solid-state diffusion through continuous comminution and growth of milled particles. This process occurs with or without a net chemical reaction and also occurs between solids and liquid additives that can be practically used for highly efficient deuterium labeling of solids. The presented findings reveal a fundamental aspect of milling reactions and also delineate a methodology that should be considered in the study of mechanochemical reaction mechanisms