Double Hook Perylene Diimide as a New Receptor for PAHs: An Experimental and Theoretical Study.

In a one-step reaction, we prepared a dibenzylamine perylene diimide derivative (PDI). Its double hook structure allows for self-association with a constant of Kd ∼108  M-1 determined by fluorescence. We confirmed its ability to bind PAHs using UV/Vis, fluorescence, and 1 H NMR titrations in CHCl3 . The complex formation signature in UV/vis is a new band at 567 nm. The calculated binding constants (Ka ∼104  M-1 ) follow the trend pyrene>perylene>phenanthrene>naphthalene>anthracene. Theoretical modeling of these systems using DFT ωB97X-D/6-311G(d,p) proved helpful in rationalizing the complex formation and the observed association trend. The distinctive signal in UV/vis is due to a charge transfer in the complex from orbitals in the guest to the host. SAPT(DFT) confirmed that the driving forces in the complex formation are exchange and dispersion (π-π interactions). Still, the recognition ability depends on the electrostatic component of the interaction, a minor fraction.

Interaction of aromatic compounds and anions with naphthylimide-dansylamide fluorescent dyad: Experimental evidence of aryl C-H π and aryl C-H anion contacts and DFT calculations.

In this work the interaction of halide anions and simple aromatic compounds with a bichromophoric fluorescent dyad derived from 1,8-naphthalimide (NAPIM) and 5-(dimethylamino)naphthalene-1-sulfonyl (DANS) was studied using electronic spectroscopy, 1H, and 19F NMR spectroscopy and quantum chemistry modeling (b3lyp/def2-TZVP). The NAPIM-DANS dyad interacts with electron-rich guests with binding constants in the range of 6×103 to 8×103M-1 in CHCl3. The formed complexes are stabilized through aryl C-H … anion and aryl C-H … π interactions.

Crystal structure of N,N'-bis[2-((benzyl){[5-(di-methyl-amino)naph-tha-len-1-yl]sulfonyl}amino)ethyl]naphthalene-1,8:4,5-tetracarboximide 1,2-di-chloro-benzene tris-olvate.

The asymmetric unit of the title compound, C56H50N6O8S2·3C6H4Cl2, contains two half-mol-ecules of the parent, A and B, which both have crystallographic inversion symmetry, together with three 2,3-di-chloro-benzene mol-ecules of solvation. Mol-ecules A and B are conformationally similar, with dihedral angles between the central naphthalenedi-imide ring and the peripheral naphthalene and benzyl rings of 2.43 (7), 81.87 (7)° (A) and 3.95 (7), 84.88 (7)° (B), respectively. The conformations are stabilized by the presence of intra-molecular π-π inter-actions between the naphthalene ring and the six-membered di-imide ring of the central naphthalenedi-imide moiety, with ring centroid-to-centroid distances of 3.5795 (8) Š(A) and 3.5640 (8) Š(B). In the crystal, C-H⋯O hydrogen bonds link the mol-ecules into infinite supra-molecular chains along the c axis. These chains are inter-connected through C-H⋯π and offset π-π inter-actions, generating supra-molecular nanotubes which are filled by 1,2-di-chloro-benzene mol-ecules.

Chiral Imidazolium-Functionalized Au Nanoparticles: Reversible Aggregation and Molecular Recognition.

Gold nanoparticles (AuNPs) stabilized by imidazolium salts derived from amino acids [glycine (1), rac-alanine (2), l-phenylalanine (3), and rac-methionine (4)] were prepared. The AuNPs were stabilized the most by 4, which kept the particles dispersed in water for months at pH > 5.5. These AuNPs exhibited a well-defined absorption band at 517 nm and had an average particle size of 11.21 ± 0.07 nm. The 4-AuNPs were reversibly aggregated by controlling the pH of the solution. Chiral R,R-4-AuNPs and S,S-4-AuNPs were synthesized, and the chiral environment on the nanoparticle surface was confirmed using circular dichroism; these nanoparticles exhibited a molecular recognition of chiral substrates. Furthermore, they showed potential for separating racemic mixtures when supported on a layered double hydroxide.

Crystal structure of 1,3-bis-(1,3-dioxoisoindolin-1-yl)urea dihydrate: a urea-based anion receptor.

The whole mol-ecule of the title compound, C17H10N4O5·2H2O, is generated by twofold rotation symmetry and it crystallized as a dihydrate. The planes of the phthalimide moieties and the urea unit are almost normal to one another, with a dihedral angle of 78.62 (9)°. In the crystal, mol-ecules are linked by N-H⋯O and O-H⋯O hydrogen bonds, forming a three-dimensional framework structure. The crystal packing also features C-H⋯O hydrogen bonds and slipped parallel π-π inter-actions [centroid-centroid distance = 3.6746 (15) Å] involving the benzene rings of neighbouring phthalimide moieties.

Streptomycin hydrazone derivatives: synthesis and molecular recognition in aqueous solution.

Five hydrazone derivatives of streptomycin were synthetized (D0h, D1ph, D2bt, D3dctf, D4ag) and characterized by IR, 1H and 13C NMR spectroscopy, mass spectrometry and elemental analysis. Protonation constants were determined by potentiometry for all derivatives. D1ph and D2bt derivatives were investigated as receptors of dicarboxylates and adenine nucleotides in aqueous solution by potentiometric and 1H NMR titrations. D1ph and D2bt derivatives have the highest affinity with AMP and ATP, respectively, which shows that electrostatic forces are not always the dominant factor in binding of streptomycin derivatives with nucleotides, but the conformational fit between them. Calculated structures at the DFT level of the D1ph derivative bonded with either AMP or ADP showed that the complexes are stabilized by the formation of multiple interactions with the receptors. The antibiotic activity of the derivatives was explored and compared with native streptomycin.

Protonation of kanamycin A: detailing of thermodynamics and protonation sites assignment.

Protonation of an aminoglycoside antibiotic kanamycin A sulfate was studied by potentiometric titrations at variable ionic strength, sulfate concentration and temperature. From these results the association constants of differently protonated forms of kanamycin A with sulfate and enthalpy changes for protonation of each amino group were determined. The protonation of all amino groups of kanamycin A is exothermic, but the protonation enthalpy does not correlate with basicity as in a case of simple polyamines. The sites of stepwise protonation of kanamycin A have been assigned by analysis of (1)H-(13)C-HSQC spectra at variable pH in D(2)O. Plots of chemical shifts for each H and C atom of kanamycin A vs. pH were fitted to the theoretical equation relating them to pK(a) values of ionogenic groups and it was observed that changes in chemical shifts of all atoms in ring C were controlled by ionization of a single amino group with pK(a) 7.98, in ring B by ionization of two amino groups with pK(a) 6.61 and 8.54, but in ring A all atoms felt ionization of one group with pK(a) 9.19 and some atoms felt ionization of a second group with pK(a) 6.51, which therefore should belong to amino group at C3 in ring B positioned closer to the ring A while higher pK(a) 8.54 can be assigned to the group at C1. This resolves the previously existed uncertainty in assignment of protonation sites in rings B and C.

Macrocyclic diorganotin complexes of gamma-amino acid dithiocarbamates as hosts for ion-pair recognition.

The dimethyl-, di-n-butyl-, and diphenyltin(IV) dithiocarbamate (dtc) complexes [{R2Sn(L-dtc)}x] 1-7 (1, L = L1, R = Me; 2, L = L1, R = n-Bu; 3, L = L2, R = Me, x = infinity; 4, L = L2, R = n-Bu; 5, L = L3, R = Me, x = 2; 6, L = L3, R = n-Bu, x = 2; 7, L = L3, R = Ph, x = 2) have been prepared from a series of secondary amino acid (AA) homologues as starting materials: N-benzylglycine (alpha-AA derivative = L1), N-benzyl-3-aminopropionic acid (beta-AA derivative = L2), and N-benzyl-4-aminobutyric acid (gamma-AA derivative = L3). The resulting compounds have been characterized by elemental analysis, mass spectrometry, IR and NMR ((1)H, (13)C, and (119)Sn) spectroscopy, thermogravimetric analysis, and X-ray crystallography, showing that in all complexes both functional groups of the heteroleptic ligands are coordinated to the tin atoms. By X-ray diffraction analysis, it could be shown that [{Me2Sn(L2-dtc)}x] (3) is polymeric in the solid state, while the complexes derived from L3 (5-7) have dinuclear 18-membered macrocyclic structures of the composition [{R2Sn(L3-dtc)}2]. For the remaining compounds, it could not be established with certainty whether the structures are macrocyclic or polymeric. A theoretical investigation at the B3LYP/SBKJC(d,p) level of theory indicated that the alpha-AA-dtc complexes might have trinuclear macrocyclic structures. The macrocyclic complexes 5-7 have a double-calix-shaped conformation with two cavities large enough for the inclusion of aliphatic and aromatic guest molecules. They are self-complementary for the formation of supramolecuar synthons that give rise to 1D molecular arrangements in the solid state. Preliminary recognition experiments with tetrabutylammonium acetate have shown that the [{R2Sn(L3-dtc)}2] macrocycles 6 and 7 might interact simultaneously with anions (AcO(-)), which coordinate to the tin atoms, and organic cations (TBA(+)), which accommodate within the hydrophobic cavity (ion-pair recognition).

Boron macrocycles having a calix-like shape. Synthesis, characterization, X-ray analysis, and inclusion properties.

The syntheses, structure, and inclusion properties of trinuclear boron compounds having a calix-like shape are described. The compounds have been obtained via self-assembly reactions between salicylaldehyde derivatives and 3-aminophenylboronic acid, whereby the formation of three N --> B coordination bonds favored the oligomerization. The products have high melting points (>370 degrees C), are stable to moisture, and have good solubility in organic solvents; the latter property is useful for host-guest recognition experiments. The structural analysis by X-ray diffraction revealed that diverse conformations are possible because of the presence of two different units of aromatic rims. A cone-cone (double-cone) conformation is observed for three of these compounds, while the remaining one has a cone-partial cone conformation. An analysis of the molecular packing showed that the molecules are stacked in columns in two different orientations in relation to the organization of the macrocycles when referred to the N-B bonds. The inclusion properties toward primary amines and ammonium chlorides were analyzed by titration experiments and monitored by UV spectroscopy, whereby association constants on the order of 10(2)-10(3) M(-1) were determined.

Recognition of alpha-amino acid derivatives by N,N'-dibenzylated S,S-(+)-tetrandrine.

Complexation of free and N-acetylated alpha-amino acid anions (Gly, Ala, Phe) and some structurally related guests by a dicationic cyclophane-type N,N'-dibenzylated chiral derivative of a bisisoquinoline macrocyclic alkaloid S,S-(+)-tetrandrine (DBT) has been studied by (1)H-NMR titrations in D(2)O. In contrast to other macrocyclic hosts like cyclodextrins and calixarenes, DBT shows highest affinity and large enantioselectivity (K(S)/K(R) >/=10) toward smaller N-acetylalanine and binds larger phenylalanine derivatives more weakly and non-selectively. With 1,2,3,4-tetrahydroisoquinoline-3-carboxylate, a rigid analog of phenylalanine, binding again becomes enantioselective with K(S)/K(R)= 3.8. The binding specificity of DBT is rationalized on the basis of molecular mechanics calculations.