The Thermodynamic Influence of Trapped Water Molecules on a Protein–Ligand Interaction

Water molecules doing time : Atomic‐resolution crystal structures of the PPIase domain of cyclophilin G, alone and in complex with cyclosporin A, and together with MD simulations and calorimetry, reveal how trapped water molecules influence the thermodynamic profile of a protein–ligand interaction.

     

Effect of peracylation of beta-cyclodextrin on the molecular structure and on the formation of inclusion complexes: an X-ray study.

The molecular structures of peracylated beta-cyclodextrins (CDs)--heptakis(2,3,6-tri-O-acetyl)-beta-CD (TA), heptakis(2,3,6-tri-O-propanoyl)-beta-CD (TP), and heptakis(2,3,6-tri-O-butanoyl)-beta-CD (TB)--have been determined by single crystal X-ray structure analysis. Due to the lack of O2...O3' hydrogen bonds between adjacent glucose units of the peracylated CDs, the macrocycles are elliptically distorted into nonplanar boat-shaped structures. The glucose units are tilted with respect to the O4 plane to relieve steric hindrance between adjacent acyl chains. In TB, all glucose units adopt the common (4)C(1)-chair conformation and one butanoyl chain intramolecularly penetrates the cavity, whereas, in TA and TP, one glucose unit each occurs in (O)S(2)-skew-boat conformation and one acyl chain closes the O6 side like a lid. In each of the three homologous molecules the intramolecular self-inclusion and lidlike orientation of acyl chains forces the associated O5-C5-C6-O6 torsion angle into a trans-conformation never observed before for unsubstituted CD; the inclusion behavior of TA, TP, and TB in solution has been studied by circular dichroism spectroscopy with the drug molsidomine and several organic compounds. No inclusion complexes are formed, which is attributed to the intramolecular closure of the molecular cavity by one of the acyl chains.     

Cyanphosphorverbindungen. IX. Cyanidabbau von weißem Phosphor zu Dicyanphosphiden und die Dicyanphosphid-Struktur

Cyanophosphorus Compounds. IX. Breakdown of White Phosphorus by Cyanide Yielding Dicyanophosphides and Dicyanophosphide Structure White phosphorus is degraded by strong enough anionic nucleophiles X^? with more or less disproportionation. With crown ether alkali, ammonium or phosphonium cyanides, X^? = CN^?, selectively the corresponding dicyanophosphide, P(CN)₂^?, is formed and a polyphosphide, preferentially P₁₅^?. [18] Crown-6-KP(CN)₂ is also obtained from the reaction of P(CN)₃, KF, and crown ether. In the crystal of this salt the dicyanophosphide anions (bent at phosphorus by an angle of 95°) coordinate with both nitrogen ends towards (different) cations. The PC distance (168 pm on the average) is as short as in phosphaalkenes. δ¹³C and J_PC of P(CN)₂^? fit well into a correlation with the charge density at phosphorus generally valid for cyanophosphorus compounds.