Is There a “Most Chiral Tetrahedron”?

A degree of chirality is a function that purports to measure the amount of chirality of an object: it is equal for enantiomers, vanishes only for achiral or degenerate objects and is similarity invariant, dimensionless and normalisable to the interval [0,1]. For a tetrahedron of non-zero three-dimensional volume, achirality is synonymous with the presence of a mirror plane containing one edge and bisecting its opposite, and hence it is easy to design degree-of-chirality functions based on edge length that incorporate all constraints. It is shown that such functions can have largest maxima at widely different points in the tetrahedral shape space, and by incorporation of appropriate factors, the maxima can be pushed to any point in the space. Thus the phrase "most chiral tetrahedron" has no general meaning: any chiral tetrahedron is the most chiral for some legitimate choice of degree of chirality.     

CF3: An Electron‐Withdrawing Substituent for Aromatic Anion Acceptors? “Side‐On” versus “On‐Top” Binding of Halides

The ability of multiple CF₃‐substituted arenes to act as acceptors for anions is investigated. The results of quantum‐chemical calculations show that a high degree of trifluoromethyl substitution at the aromatic ring results in a positive quadrupole moment. However, depending on the polarizability of the anion and on the substitution at the arene, three different modes of interaction, namely Meisenheimer complex, side‐on hydrogen bonding, or anion–π interaction, can occur. Experimentally, the side‐on as well as a η²‐type π‐complex are observed in the crystal, whereas in solution only side‐on binding is found.     

Do Carbenes Have a “Hidden” Carbon(0) Character? Revisiting the Electronic Structure of 2,2′‐Bipyridyl Carbene

Density functional calculations predict that 2,2′‐bipyridyl carbenes have some degree of “hidden” carbon(0) character. This is supported by very high second proton affinity values and bond dissociation energies (BDEs) for the dissociation of one AuCl and one Ni(CO)₂ molecule from [(AuCl)₂(2,2′‐bipyridyl carbene)] and [{Ni(CO)₂}₂(2,2′‐bipyridyl carbene)]. An Arduengo type carbene also showed significant BDE values for gem‐dimetallation, thus indicating the possible existence of carbon(0) character. All of the dimetallated derivatives showed metallophilic interactions.     

Sialyl Lewisx: A “Pre‐Organized Water Oligomer”?

Organized and released: Sialyl Lewis(x) (sLe(x)) represents a "pre-organized water oligomer", that is, a surrogate for clustered water molecules attached to a scaffold. The impetus for sLe(x) binding to E-selectin is shown to be the high degree of pre-organization allowing an array of directed hydrogen bonds, and the entropic benefit of the release of water molecules from the large binding interface to bulk water (see picture).     

“What is KRI?” – R&D based on excellent tradition and innovation –

As far as KRI's clients were concerned, KRI's appeal was not only in having researchers who had a high level of expert knowledge, but it was also in the efficiency with which high risk jobs were conducted, and the speed of response time, especially when corporations made comparisons with their own in‐house labs. KRI, while being a facility for contract research, is also capable of becoming a profitable corporation, mostly thanks to the adoption of this system. KRI sincerely hopes to continue serving as a group made up of quality professionals who embrace a dream, and to contribute to society through its achievements. At the same time, the company strives to be sensitive to changing needs, and, of course, to conduct R&D and consulting activities which will ensure success for its clients.     

Catalytic Synthesis of Ammonia—A “Never‐Ending Story”?

Nitrogen atoms are essential for the function of biological molecules and thus are and important component of fertilizers and medicaments. Bonds to nitrogen also find nonbiological uses in dyes, explosives, and resins. The synthesis of all these materials requires ammonia as an activated nitrogen building block. This situation is true for natural processes and the chemical industry. Knowledge of the various techniques for the preparation of ammonia is thus of fundamental importance for chemistry. The Haber-Bosch synthesis was the first heterogeneous catalytic system employed in the chemical industry and is still in use today. Understanding the mechanism and the translation of the knowledge into technical perfection has become a fundamental criterion for scientific development in catalysis research.     

The Biosynthesis of Barbamide—A Radical Pathway for “Biohalogenation”?

A stereoselective chlorination of a methyl group and the preference of cleavage of nonactivated primary C−H bonds in one of the methyl groups with respect to a weaker tertiary C−H bond in the course of the biosynthesis of barbamide point to a surprising, new mechanism of “biohalogenation” (see schematic diagram).     

Could the “Janus‐like” properties of the halobenzene CX bond (XCl,Br) be leveraged to enhance molecular recognition?

The CX bond in halobenzenes (X?Cl, Br) exhibits a dual character, being electron‐deficient along the CX direction, and electron‐rich on its flanks. We sought to amplify both features by resorting to electron‐withdrawing and electron‐donating substituents, respectively. This was done by quantum chemistry (QC) computations in the recognition sites of three protein targets: farnesyl transferase, coagulation factor Xa, and the HIV‐1 integrase. In this context, some substituents, notably fluorine, CF₃, and NHCH₃, afforded significant overall gains in the binding energies as compared to the parent halobenzene, in the 2–5 kcal/mol range. In fact, we found that some di‐ and up to tetra‐substitutions enabled even larger gains than those they contribute separately owing to many‐body effects. Moreover, desolvation was also found to be a key contributor to the energy balances. As a consequence, some particular substituents, contributing to reduce the halobenzene dipole moment, accordingly reduced solvation: this factor acted in synergy with their enhancement of the intermolecular interaction energies along and around the CX bond. We could thus leverage the “Janus‐like” properties of such a bond and the fact that it can be tuned and possibly amplified by well‐chosen substituents. We propose a simple yet rigorous computational strategy resorting to QC to prescreen novel substituted halobenzenes. The QC results on the recognition sites then set benchmarks to validate polarizable molecular mechanics/dynamics approaches used to handle the entirety of the inhibitor‐protein complex. © 2014 Wiley Periodicals, Inc.     

Bis(4‐picoline‐κN)gold(I) dibromidoaurate(I) and bis(4‐picoline‐κN)gold(I) dichloridoaurate(I): space‐group ambiguity?

Bis(4‐picoline‐κN)gold(I) dibromidoaurate(I), [Au(C₆H₇N)₂][AuBr₂], (I), crystallizes in the monoclinic space group P2₁/n, with two half cations and one general anion in the asymmetric unit. The cations, located on centres of inversion, assemble to form chains parallel to the a axis, but there are no significant contacts between the cations. Cohesion is provided by flanking anions, which are connected to the cations by short Au...Au contacts and C—H...Br hydrogen bonds, and to each other by Br...Br contacts. The corresponding chloride derivative, [Au(C₆H₇N)₂][AuCl₂], (II), is isotypic. A previous structure determination of (II), reported in the space group P with very similar axis lengths to those of (I) [Lin et al. (2008). Inorg. Chem. 47 , 2543–2551], might be identical to the structure presented here, except that its γ angle of 88.79 (7)° seems to rule out a monoclinic cell. No phase transformation of (II) could be detected on the basis of data sets recorded at 100, 200 and 295 K.