Synthesis and evaluation of a desymmetrised synthetic lectin:An approach to carbohydrate receptors with improved versatility

A new design for carbohydrate receptors features unmatched apolar surfaces, and could lead to selectivities for a broader range of substrates.</p

Enantioselective carbohydrate recognition by synthetic lectins in water

These chiral “synthetic lectins” are the first to discriminate between carbohydrate enantiomers, and also show unprecedented affinities for monosaccharide substrates.</p

The bright future of unconventional s/p-hole interactions

[eng] Non-covalent interactions play a crucial role in (supramolecular) chemistry and much of biology. Supramolecular forces can indeed determine the structure and function of a host- guest system. Many sensors, for example, rely on reversible bonding with the analyte. Natural machineries also often have a significant non-covalent component (e.g. protein folding, recognition) and rational interference in such 'living' devices can have pharmacological implications. For the rational design/ tweaking of supramolecular systems it is helpful to know what supramolecular synthons are available and to understand the forces that make these synthons stick to one another. In this review we focus on s-hole and p-hole interactions. A s- or phole can be seen as positive electrostatic potential on unpopulated s* or p(*) orbitals, which are thus capable of interacting with some electron dense region. A s-hole is typically located along the vector of a covalent bond such as X H or X Hlg (X=any atom, Hlg=halogen), which are respectively known as hydrogen and halogen bond donors. Only recently it has become clear that s-holes can also be found along a covalent bond with chalcogen (X Ch), pnictogen (X Pn) and tetrel (X Tr) atoms. Interactions with these synthons are named chalcogen, pnigtogen and tetrel interactions. A p-hole is typically located perpendicular to the molecular framework of diatomic p-systems such as carbonyls, or conjugated p-systems such as hexafluorobenzene. Anion-p and lone-pair-p interactions are examples of named p-hole interactions between conjugated p-systems and anions or lone-pair electrons respectively. While the above nomenclature indicates the distinct chemical identity of the supramolecular synthon acting as Lewis acid, it is worth stressing that the underlying physics is very similar. This implies that interactions that are now not so well-established might turn out to be equally useful as conventional hydrogen and halogen bonds. In summary, we describe the physical nature of s- and p-hole interactions, present a selection of inquiries that utilise s- and p-holes, and give an overview of analyses of structural databases (CSD/PDB) that demonstrate how prevalent these interactions already are in solid-state structure

Influence of ring size on the strength of carbon bonding complexes between anions and perfluorocycloalkanes

[eng] In this paper we combine high level theoretical calculations (RI-MP2/def2-TZVP) with Cambridge Structural Database (CSD) analysis to demonstrate the importance of carbon bonding in cyclobutane rings. The higher ability of four-membered rings to interact with electron rich molecules is rationalized using several computational tools, including molecular electrostatic potential surfaces, energetic and geometric features of the complexes and ''atoms in molecules'' analysis. We have found that the solid state architectures of several X-ray structures, retrieved from the CSD searches, strongly support the theoretical calculations. In particular, carbon bonding interactions are quite common in nitro-substituted cubanes

Non-covalent sp3 carbon bonding with ArCF3 is analogous to CH-pi interactions.

[eng] A combined CSD and ab initio study reveals that the interaction between the sp3 C-atom in para-substituted ArCF3 and electron rich atoms is weak (o5 kcal mol 1), somewhat directional, and thus comparable to CH-p interactions

Small cycloalkane 1,1',2,2'-tetracyano structures are highly directional non-covalent carbon-bond donors

[eng] High-level calculations (RI-MP2/def2-TZVP) disclosed that the s-hole in between two C atoms of cycloalkane X2C CX2 structures (X=F, CN) is increasingly exposed with decreasing ring size. The interacting energy of complexes of F , HO , N C , and H2CO with cyclopropane and cyclobutane X2C CX2 derivatives was calculated. For X=F, these energies are small to positive, while for X=CN they are all negative, ranging from 6.8 to 42.3 kcal mol 1. These finding are corroborated by a thorough statistical survey of the Cambridge Structural Database (CSD). No clear evidence could be found in support of non-covalent carbon bonding between electron-rich atoms (El.R.) and F2C CF2 structures. In marked contrast, El.R.···(CN)2C C(CN)2 interactions are abundant and highly directional. Based on these findings, the hydrophobic electrophilic bowl formed by 1,1',2,2'-tetracyano cyclopropane or cyclobutane derivatives is proposed as a new and synthetically accessible supramolecular synthon

Mechanistic Study of the L₂Pd-Catalyzed Reduction of Nitrobenzene with CO in Methanol: Comparative Study between Diphosphane and 1,10-Phenanthroline Complexes

The catalytic activity of Pd^II compounds supported by 1,10-phenanthroline (phen) or the bidentate diarylphosphane ligand L4X has been studied in the reaction of nitrobenzene with CO in methanol. Both systems are ∼70% selective for azoxybenzene and azobenzene but also produce carbonylation products (methyl phenyl carbamate (MPC) and <i>N,N’</i>-diphenylurea (DPU)) and hydrogenation products (aniline and DPU). The Pd^II(L4X) system also produces methanol oxidation products (dimethyl carbonate, dimethyl oxalate, water). Upon the addition of a catalytic amount of acid, the coupling reaction is suppressed in favor of either the carbonylation reaction (for Pd^II(phen)) or of both the carbonylation and hydrogenation reaction (for Pd^II(L4X)). The palladacycle L₂PdC­(O)­N­(Ph)­OC­(O) (<b>C7</b>) and palladium–imido species L₂PdNPh (<b>C3</b>) were considered as possible carbonylation product-releasing species, where L₂ is phen or the diphosphane ligands L4X and L3X. A ligand exchange experiment of phen-<b>C7</b> with L4X and L3X, ESI-MS analysis of L3X-<b>C7</b> and phen-<b>C7</b>, and a DFT study of nitrobenzene deoxygenation intermediates to L₂PdNPh all suggest that <b>C7</b> is not the major product-releasing intermediate; all data suggest that the barrier for <b>C7</b> decarbonylation (−CO) is lower than that for decarboxylation (−CO₂). <b>C7</b> is thus thought to be part of an “NPh reservoir” consisting of palladacycles that are mutually accessible through carbonylation/decarbonylation. Under <i>acidic conditions</i> the decarboxylation barrier is lowered; for phen-<b>C7</b> apparently to the point where decarboxylative alcoholysis is favored relative to decarbonylation, but for L4X-<b>C7</b> the decarbonylation barrier still seems lowest due to the destabilizing effect that this bulkier ligand has on such palladacycles. It is thus concluded that the L₂PdNPh complex <b>C3</b> is the prime “NPh” product-releasing intermediate and only under acidic conditions and in an alcoholic environment may <b>C7</b>for phenanthrolinebecome the predominant carbamate product releasing intermediate

π‑Hole Interactions Involving Nitro Compounds: Directionality of Nitrate Esters

The MEPs of a variety of nitro compounds (R–NO₂) suggest the existence of a π-hole with a potential of up to +54 kcal/mol in <b>10</b> (R = CF₃). Several of these nitro compounds were considered as partners for anions (F^–, Cl^–, NC^–) and the electron rich molecules acetonitrile and dimethyl ether. In most cases a π-hole complex was obtained with calculated binding energies of up to 20 kcal/mol with anions and 5 kcal/mol with the neural molecules. A thorough analysis of the CSD revealed that nitrate esters are highly directional π-holes in the solid state, for at least sp² O atoms. This was further illustrated by highlighting several crystal structures where more than 0.2 Å van der Waals overlap was observed between the N atom of the nitrate ester and an electron rich atom like oxygen