Size-tunable fluorescent dendrimersomes via aggregation-induced emission

Tetraphenylethylene-functionalized amphiphilic Janus dendrimers of up to third generation are synthesized. Their self-assembly has been studied under kinetic and thermodynamic control. By varying the dendrimer generation number and the self-assembly...

Decoding the Reaction Mechanism of the Cyclocondensation of Ethyl acetate 2-oxo-2-(4-oxo-4H-pyrido [1.2-a] pyrimidin-3-yl) polyazaheterocycle and Ethylenediamine using Bond Evolution Theory

The bonding evolution theory has been used to investigate the flow of electron density along the reaction pathways of ethyl acetate 2-oxo-2-(4-oxo-4H-pyrido [1.2-a] pyrimidin-3-yl) polyazaheterocycle (1) and ethylenediamine (2). This reaction has three channels (1-3) and each one takes place via three or four steps. DFT results reveal that channel 2, which goes through imine intermediate is by far the most favorable one, and the main product 3 is more stable than 4 and 5, showing that this reaction is under kinetic and thermodynamic control, in clear agreement with the experimental outcomes. The BET analysis allows identifying unambiguously the main chemical events happening along channel 2. For this reaction channel, the mechanism along the first step (TS2-a) is described by a series of four structural stability domains (SSDs), while five SSDs are required for the second (TS2-b) and the third (TS2-c) one. The first step can be summarized as follow, the appearance of V(N1,C6) basin illustrating the formation of N1-C6 bond (SSD-II), the splitting of N1-H1 bond, followed by the restoration of the nitrogen N1 lone pair (SSD-III), and finally, the formation of the last O1-H1 bond (SSD-IV). For the second step, the formation of hydroxide ion is noted, consequent of the disappearance of V(C6,O7) basin, the transformation of C6-N1 single bond into double one (SSD-IV). Finally, the appearance of V(O7,H2) basin leading to the elimination of water molecule within the last domain. Overall, for the three reaction steps, the formation of the N-C bond appears always before the O-H one.

Kinetic and Thermodynamic Control in Rare Earth Cyamelurates Synthesis

If various compounds exist in the metal cation – C6N7O33– – H2O system, the synthesis temperature can affect the isolation of a particular product. Low temperatures favor the release of metastable kinetic products, and high temperatures, on the contrary, of thermodynamic ones. It is found that several structural types exist in the row of rare-earth cyamelurates. Room temperature synthesis leads to the formation of [Ln(H2O)7C6N7O3] (Ln=Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er), an increase in temperature yields thermodynamically more stable [Ln(H2O)4C6N7O3]n·nH2O (Ln=Y, Ho, Er, Tm, Yb, Lu) and [Ln(H2O)5C6N7O3]n (Ln = Pr, Nd). The change in the synthesis temperature did not affect the structures of Sm, Eu, Gd, Tb, Dy cyamelurates, as well as the structure of lanthanum cyamelurate [La(H2O)6C6N7O3]·H2O.In synthesized at increased temperature [Ln(H2O)4C6N7O3]n·nH2O and [Ln(H2O)5C6N7O3]n cyamelurates polymeric chains exist due to the fact that the cyamelurate anion acts as a bridging ligand. Kinetically trapped Y, Pr, Nd, Ho, Er cyamelurates, in contrast, consist of individual complex molecules [Ln(H2O)7C6N7O3]. Probably, steric difficulties caused a decrease in the coordination number of Y, Ho, Er from 9 to 8 in the thermodynamic product. The coordination number of Pr and Nd remains equal to 9 in both types of compounds.

Pyrophosphate and Irreversibility in Evolution, or why PPi Is Not an Energy Currency and why Nature Chose Triphosphates

The possible evolutionary significance of pyrophosphate (PPi) has been discussed since the early 1960s. Lipmann suggested that PPi could have been an ancient currency or a possible environmental source of metabolic energy at origins, while Kornberg proposed that PPi vectorializes metabolism because ubiquitous pyrophosphatases render PPi forming reactions kinetically irreversible. To test those ideas, we investigated the reactions that consume phosphoanhydride bonds among the 402 reactions of the universal biosynthetic core that generates amino acids, nucleotides, and cofactors from H2, CO2, and NH3. We find that 36% of the core’s phosphoanhydride hydrolyzing reactions generate PPi, while no reactions use PPi as an energy currency. The polymerization reactions that generate ~80% of cell mass – protein, RNA, and DNA synthesis – all generate PPi, while none use PPi as an energy source. In typical prokaryotic cells, aminoacyl tRNA synthetases (AARS) underlie ~80% of PPi production. We show that the irreversibility of the AARS reaction is a kinetic, not a thermodynamic effect. The data indicate that PPi is not an ancient energy currency and probably never was. Instead, PPi hydrolysis is an ancient mechanism that imparts irreversibility, as Kornberg suggested, functioning like a ratchet’s pawl to vectorialize the life process toward growth. The two anhydride bonds in nucleoside triphosphates offer ATP-cleaving enzymes an option to impart either thermodynamic control (Pi formation) or kinetic control (PPi formation) upon reactions. This dual capacity explains why nature chose the triphosphate moiety of ATP as biochemistry’s universal energy currency.