Halogen bonds as a tool in the design of high energetic materials: evidence from crystal structures and quantum chemical calculations

Positive electrostatic potential over the central area of the molecular surface is one of the main characteristics of high energetic materials (HEM) that determines their sensitivity towards detonation. The influence...

How aromatic system size affects the sensitivities of highly energetic molecules?

DFT calculations showed that with the increase of the aromatic system size, values of positive electrostatic potential above the central areas of energetic molecules decrease, leading to the decrease in the sensitivities towards detonation.

Can the sensitivity of energetic materials be tuned by using hydrogen bonds? Another look at the role of hydrogen bonding in the design of high energetic compounds.

Strongly positive electrostatic potential in the central areas of molecules of the energetic materials is one of the most important factors that determine the sensitivity of these molecules towards detonation....

Heparin Blocks the Inhibition of Tissue Kallikrein 1 by Kallistatin through Electrostatic Repulsion

Kallistatin, also known as SERPINA4, has been implicated in the regulation of blood pressure and angiogenesis, due to its specific inhibition of tissue kallikrein 1 (KLK1) and/or by its heparin binding ability. The binding of heparin on kallistatin has been shown to block the inhibition of KLK1 by kallistatin but the detailed molecular mechanism underlying this blockade is unclear. Here we solved the crystal structures of human kallistatin and its complex with heparin at 1.9 and 1.8 Å resolution, respectively. The structures show that kallistatin has a conserved serpin fold and undergoes typical stressed-to-relaxed conformational changes upon reactive loop cleavage. Structural analysis and mutagenesis studies show that the heparin binding site of kallistatin is located on a surface with positive electrostatic potential near a unique protruded 310 helix between helix H and strand 2 of β-sheet C. Heparin binding on this site would prevent KLK1 from docking onto kallistatin due to the electrostatic repulsion between heparin and the negatively charged surface of KLK1, thus blocking the inhibition of KLK1 by kallistatin. Replacement of the acidic exosite 1 residues of KLK1 with basic amino acids as in thrombin resulted in accelerated inhibition. Taken together, these data indicate that heparin controls the specificity of kallistatin, such that kinin generation by KLK1 within the microcirculation will be locally protected by the binding of kallistatin to the heparin-like glycosaminoglycans of the endothelium.

Specific Recognition of Methanol Using a Symmetric Tetramethylcucurbit[6]uril-Based Porous Supramolecular Assembly Incorporating Adsorbed Dyes

A symmetric tetramethylcucurbit[6]uril-based porous supramolecular assembly was prepared in an aqueous H2SO4 solution (5M). The driving force for the formation of this assembly is mainly the outer surface interaction of Q[n], which includes the ion-dipole interaction of SO42− anions and the positive electrostatic potential of the outer surface of the symmetric tetramethylcucurbit[6]uril (TMeQ[6]), the dipole-dipole interactions between the positive electrostatic potential of the outer surface of TMeQ[6] and portal carbonyl oxygens of TMeQ[6], and the hydrogen bonding between lattice water molecules and portal carbonyl oxygen atoms in TMeQ[6]. The TMeQ[6]-based porous supramolecular assembly exhibits the characteristics of absorbed fluorophore guests (FGs), such as dyes and polycyclic compounds with different fluorescence characteristics. Moreover, the resulting luminescent assemblies (FG@As) can respond to certain volatile organic compounds; in particular, the luminescent assemblies of rhodamine B or pyrene display a unique fluorescence enhancement in response to methanol.

σ-Holes vs. Buildups of Electronic Density on the Extensions of Bonds to Halogen Atoms

Our discussion focuses upon three possible features that a bonded halogen atom may exhibit on its outer side, on the extension of the bond. These are (1) a region of lower electronic density (a σ-hole) accompanied by a positive electrostatic potential with a local maximum, (2) a region of lower electronic density (a σ-hole) accompanied by a negative electrostatic potential that also has a local maximum, and (3) a buildup of electronic density accompanied by a negative electrostatic potential that has a local minimum. In the last case, there is no σ-hole. We show that for diatomic halides and halogen-substituted hydrides, the signs and magnitudes of these maxima and minima can be expressed quite well in terms of the differences in the electronegativities of the halogen atoms and their bonding partners, and the polarizabilities of both. We suggest that the buildup of electronic density and absence of a σ-hole on the extension of the bond to the halogen may be an operational indication of ionicity.

Theoretical insights into the π-hole interactions in the complexes containing triphosphorus hydride (P3H3) and its derivatives

The π-hole of triphosphorus hydride (P3H3) and its derivativesZ3X3(Z= P, As;X= H, F, Cl, Br) was discovered and analyzed. MP2/aug-cc-pVDZ calculations were performed on the π-hole interactions in the HCN...Z3X3complexes and the mutual influence between π-hole interactions and the hydrogen bond in the HCN...HCN...Z3X3and HCN...Z3X3...HCN complexes studied. The π-hole interaction belongs to the typical closed-shell noncovalent interaction. The linear relationship was found between the most positive electrostatic potential of the π-hole (VS,max) and the interaction energy. Moreover, theVS,maxof the π-hole was also found to be linearly correlated to the electrostatic energy term, indicating the important contribution of the electrostatic energy term to the π-hole interaction. There is positive cooperativity between the π-hole interaction and the hydrogen bond in the termolecular complexes. The π-hole interaction has a greater influence on the hydrogen bond thanvice versa. The mutual enhancing effect between the π-hole interaction and the hydrogen bond in the HCN...HCN...Z3X3complexes is greater than that in the HCN...Z3X3...HCN complexes.

The σ-hole revisited

A covalently-bonded atom typically has a region of lower electronic density, a “σ-hole,” on the side of the atom opposite to the bond, approximately along its extension. There is often a positive electrostatic potential (strongest shown in red) associated with a σ-hole, although it may deviate from the extension of the bond.

Optimisation of LS54/Dx Aqueous Two Phase System Conditions for Cutinase Recovery

Aqueous two phase system comprising Dehypon® LS 54 and K4484 Dextrin® was selected for recovery of cutinase enzyme. Parameters such as pH, system composition and type of salt as an additive, influenced the protein partitioning behaviour and optimisation of these parameters become necessary to be done in the design of primary recovery process of ATPS. The cutinase partitioning experiments were carried out with 30% of cutinase solution added to LS 54/Dx system. Results showed that cutinase enzyme preferred to partition into LS 54 rich-phase at pH 8.0 and the affinity of cutinase into top phase was observed higher with the increment of system compositions, which represented by tie line length (TLL). Furthermore, the addition of 50mM salts such as K2SO4 and KCl into LS 54/Dx system has led to raise partition coefficient of cutinase, kcut to 2.2 and 1.95 fold, respectively. The dependence of kcut on various additives such as (NH4)2SO4, Na2SO4 and K2SO4 at the same concentration, suggested that the addition of selected ions could enhance positive electrostatic potential which could attract more cutinase to partition into LS54 rich phase. As conclusion, the best conditions obtained for cutinase partitioning were pH8.0, TLL = 23% and Na2SO4 = 50mM, from which the maximum kcut of 2.83 with improved recovery of cutinase in top phase up to 79% can be achieved.