Structural and thermodynamic properties and intermolecular interactions in aqueous and acetonitrile solutions of aprotic amides

The structural and thermodynamic properties are calculated for mixtures of aprotic amides with water and acetonitrile. The simulation approach is used to identify the specific and nonspecific components of the total energy of intermolecular interactions, which are used to calculate the corresponding contributions to the enthalpy of mixing. The negative enthalpies of mixing in the aqueous mixtures are found to be caused not by heterocomponent specific interactions, but by nonspecific ones. The difference in the structural and thermodynamic properties of the aqueous and nonaqueous mixtures of aprotic amides is shown to be largely due to the behavior of the hydrogen bond network of water and the packing of the resulting solutions.     

Thermodynamic characteristics of self-associated aminoalcohols

Thermodynamic characteristics of aminoalcohols self-associated by hydrogen bonds have been calculated. Specific and nonspecific components of the total energy of intermolecular interactions have been determined within the model approach. Main goal of this work is the search of thermodynamic characteristics of the liquid-phase systems effectively reflecting both features of intermolecular interactions, and structural changes of individual aminoalcohols. It is established that the most part of the studied aminoalcohols belongs to solvents with H-bonds networks in which there is an intensifying of nonspecific interactions with the temperature rise, and to solvents with chained self-association where the contribution of these interactions practically do not depend on temperature. The aminoalcohols obtained by the substitution of nitrogen atom protons of monoethanolamine by alkyl radicals belong to group of solvents similar aprotic ones at which nonspecific interactions are weakened with the temperature rise. The reasons of it have been discussed by comparison of the data with results for diols, oxyethylated glycols, monoalcohols, and aprotic amides obtained by us earlier.     

Thermodynamic characteristics of self-associated solvents

The thermodynamic characteristics of solvents differing by the type of molecular self-assembly through the hydrogen bonds were considered. In the framework of a model approach specific and nonspecific components of the total energy of intermolecular interaction were identified. The solvents with hydrogen bond network are found to belong to a class of liquids, where the strength of non-specific interactions increases with increasing temperature, while in the solvents with a chain of self-association contribution of these interactions is virtually independent of temperature. For this reason, the effect of increasing temperature on the internal pressure and its temperature coefficient were found to be different in these groups of solvents.     

Thermodynamic Study of Oxyethylated Glycols and Their Mixtures with Tertiary Carboxamides

The contributions into the total energy of intermolecular interactions in oxyethylated ethylene glycol derivatives were estimated in terms of a model approach that uses inner pressure as a measure of nonspecific interactions in a liquid. Increased number of ether groups in ethylene glycols increases the nonspecific contribution and decreases specific contributions. Unlike diethylene glycol, triethylene glycol and tetraethylene glycol contain H-bond networks in the range 298.15–308.15 K. The enthalpies of mixing of tertiary amides with tetraethylene glycol were measured and compared with those for ethylene glycol, diethylene glycol, and triethylene glycol. The effect of the structural and thermodynamic properties of the components on the integral and differential thermochemical characteristics of mixtures of glycols with N,N-disubstituted amides was discussed.     

Self-assembly driven by an aromatic primary amide motif

Primary amides are unique supramolecular synthons possessing two hydrogen donors and two hydrogen acceptors. By interacting in a complementary fashion, primary amides reliably generate two-dimensional hydrogen bonded networks that differ from conventional hydrogen bonded structures such as carboxylic acid dimers or one-dimensional secondary amide chains. This feature permits the design of sophisticated supramolecular assemblies based on primary amides (especially aromatic amides). Several interesting crystal structures have been constructed utilizing primary amides, although such structures have been applied only in the field of crystal engineering because the networks strongly favor crystallization. Expansion of the applications of primary amides to liquid crystals and self-assembly in solution requires an appropriate balance between primary amide-based hydrogen bonding and other noncovalent interactions. This perspective article reviews the key hydrogen bonding properties of primary amides determined from crystal structure studies, and a variety of supramolecular assemblies involving primary amides are discussed. A new strategy for overcoming crystallinity and solubility issues is proposed, involving introduction of a trifluoromethyl group at the ortho position of the aromatic primary amide. Such substitutions produce highly processable primary amides, while maintaining the two-dimensional hydrogen bonded network. Examples of self-assembly using 2-trifluoromethylbenzamide demonstrate its usefulness in self-assembly.     

Structural thermodynamic parameters and intermolecular interactions in aqueous solutions of secondary amides

Structural thermodynamic parameters are calculated for aqueous solutions of secondary amides of carboxylic acids. Specific and nonspecific contributions to the total energy of intermolecular interactions are determined and the boundaries of concentration regions for a various structural organization of solutions are found.     

Structural and thermodynamic parameters and intermolecular interactions in aqueous dialkylacetamides

The structural and thermodynamic parameters of aqueous dimethylacetamide and diethylacetamide have been calculated; the specific and nonspecific components of the total energy of intermolecular interactions have been determined. As alkyl radicals increase in size, the concentration regions with different structural organizations of solutions undergo transformation.     

Structural thermodynamic characteristics and intermolecular interactions in aqueous solutions of hexamethylphosphorotriamide

Structural thermodynamic parameters of aqueous solutions of hexamethylphosphorotriamide are calculated. They are discussed together with previously obtained data on aqueous solutions of disubstituted amides of carboxylic acids. The specific and non-specific components of the total energy of intermolecular interactions are determined. The boundaries of concentration regions with different structural organizations of solutions are found, and the preferential solvation parameters of solution components are estimated.     

Structural-thermodynamic characteristics and intermolecular interactions in mixtures of strongly associated solvents with aprotic amides

Thermodynamic characteristics of mixtures of aprotic amides with water and organic solvents with hydrogen bond networks are calculated. Within a model approach the specific and non-specific components of the total energy of the intermolecular interaction are determined, based on which the corresponding contributions to the enthalpies of component mixing are calculated. It is found that negative enthalpies of mixing in the mixtures under study are due to non-specific interactions rather than heterocomponent specific ones. It is shown that the difference in the structural-thermodynamic characteristics of aqueous and nonaqueous mixtures of aprotic amides is mainly caused by packing features of solutions and the behavior of hydrogen bond networks of water and organic solvents.     

Amide–Amide Hydrogen Bonding. Semirubin Amides

Summary. Semirubins are analogs for one-half of the bilirubin structure and capable of intramolecular hydrogen bonding. Semirubin amides of ammonia and primary amines are also capable of intramolecular hydrogen bonding. From a combination of spectroscopic methods (¹H NMR, NOE, and VPO), the primary amide is found to engage very effectively in intramolecular hydrogen bonding. The secondary and tertiary amides engage in both intramolecular (i) and intermolecular (ii) hydrogen bonding: N-methyl (i, monomer + ii, dimer), N-tert-butyl (ii, dimer), N,N-diethyl (i, monomer + ii, dimer). With an oxo-group at C(10), all of the amides are monomeric and most engage in intramolecular hydrogen bonding.     

Amide–Amide Hydrogen Bonding. Semirubin Amides

Semirubins are analogs for one-half of the bilirubin structure and capable of intramolecular hydrogen bonding. Semirubin amides of ammonia and primary amines are also capable of intramolecular hydrogen bonding. From a combination of spectroscopic methods (¹H NMR, NOE, and VPO), the primary amide is found to engage very effectively in intramolecular hydrogen bonding. The secondary and tertiary amides engage in both intramolecular (i) and intermolecular (ii) hydrogen bonding: N-methyl (i, monomer + ii, dimer), N-tert-butyl (ii, dimer), N,N-diethyl (i, monomer + ii, dimer). With an oxo-group at C(10), all of the amides are monomeric and most engage in intramolecular hydrogen bonding.     

Structral and thermodynamic characteristics and intermolecular interactions in aqueous solutions of diols

The structural and thermodynamic characteristics of aqueous solutions of ethanediol, 1,2-and 1,3-propanediols, and 1,2-and 1,4-butanediols were calculated over the whole range of the compositions of the mixtures. The specific and nonspecific components of the total energy of intermolecular interactions were determined. The boundaries of the concentration regions with different structural organizations of solutions were established, and the parameters of preferable solvation of the solution components were evaluated.     

Homochiral and heterochiral coordination polymers and networks of silver(I)

The self-assembly of racemic and enantiopure binaphthylbis(amidopyridyl) ligands 1,1'-C(20)H(12){NHC(O)-4-C(5)H(4)N}(2), 1, and 1,1'-C(20)H(12){NHC(O)-3-C(5)H(4)N}(2), 2, with silver(I) salts (AgX; X = CF(3)CO(2), CF(3)SO(3), NO(3)) to form extended metal-containing arrays is described. It is shown that the self-assembly with racemic ligands can lead to homochiral or heterochiral polymers, through self-recognition or self-discrimination of the ligand units. The primary polymeric materials adopt helical conformations (secondary structure), and they undergo further self-assembly to form sheets or networks (tertiary structure). These secondary and tertiary structures are controlled through secondary bonding interactions between pairs of silver(I) centers, between silver cations and counteranions, or through hydrogen bonding involving amide NH groups. The self-assembly of the enantiopure ligand R-1 with silver trifluoroacetate gave a remarkable three-dimensional chiral, knitted network composed of polymer chains in four different supramolecular isomeric forms.     

Thermodynamic characteristics of water-N-methylpyrrolidone mixtures and intermolecular interactions in them

Thermodynamic characteristics of water-N-methylpyrrolidone mixtures in the range 298.15–338.15 K were calculated from the data obtained in our previous studies and by other authors. The specific and nonspecific terms of the total energy of intermolecular interaction were determined within the framework of a model approach using the internal pressure as a measure of nonspecific interactions in a liquid. The parameters obtained indicate that, with an increase in the N-methylpyrrolidone concentration, the three-dimensional network of hydrogen bonds in water undergoes transformations and is broken. For the solutions differ in the type of intercomponent association and structural organization the boundaries of concentration ranges were determined.     

C-H...F hydrogen bonding: the origin of the self-assemblies of bis(2,2'-difluoro-1,3,2-dioxaborine)

The effect of the molecular structure on the self-assembly of specially designed two-core 1,3,2-dioxaborines has been studied with various techniques. It was found that the molecules spontaneously adsorbed on HOPG surfaces and self-organized into well-ordered two-dimensional (2D) monolayers. The structural details of the 2D assemblies were investigated by scanning tunneling microscopy (STM). From X-ray analysis of the corresponding three-dimensional (3D) crystal and from theoretical calculation, we were able to reveal the driving force behind the specific self-assembly. The C-H...F hydrogen bonding between the ortho carbon of the phenyl ring and the fluorine of the BF2 group plays an important role in the formation of the adlayers. The different electron affinities and geometries of the molecules affect the intermolecular interactions which further lead to different properties in the bulk materials.     

Structural and thermodynamic parameters and intermolecular interactions in aqueous formic acid amides

The structural and thermodynamic characteristics of aqueous solutions of formamide, N-methylformamide, N,N-dimethylformamide, and N,N-diethylformamide were calculated. The specific and nonspecific components of the total energy of intermolecular interactions were determined. The limits of the concentration regions with differently arranged structures of solutions were established, and the preferable solvation parameters of the solution components were evaluated.     

Development of carbohydrate-based scaffolds for restricted presentation of recognition groups. Extension to divalent ligands and implications for the structure of dimerized receptors

The solution structure of glycosyl amides has been studied by using NMR. A strong preference is displayed by tertiary aromatic glycosyl amides for E-anti structures in contrast with secondary aromatic glycosyl amides where Z-anti structures predominate. The structural diversity displayed by these classes of molecules would seem to be important as the directional properties of the aromatic ring, or groups attached to the aromatic ring, would be determined by choosing to have either a secondary or tertiary amide at the anomeric center and could be considered when designing bioactive molecules with carbohydrate scaffolds. The structural analysis was also carried out for related divalent secondary and tertiary glycosyl amides and these compounds display preferences similar to that of the monovalent compounds. The constrained divalent compounds have potential for promoting formation of clusters that will have restricted structure and thus have potential for novel studies of mechanisms of action of multivalent ligands. Possible applications of such compounds would be as scaffolds for the design and synthesis of ligands that will facilitate protein-protein or other receptor-receptor interactions. The affinity of restricted divalent (or higher order) ligands, designed to bind to proteins that recognize carbohydrates which would facilitate clustering and concomitantly promote protein-protein interactions, may be significantly higher than monovalent counterparts or multivalent ligands without these properties. This may be useful as a new approach in the development of therapeutics based on carbohydrates.     

Molecular Recognition within a Self-Assembled Cylindrical Host

A change in geometry is necessary on entry into the capsule: a supramolecular associate approximately 1.8 nm long (see schematic representation), which consists of two halves stabilized by hydrogen bonds, influences the intra- and intermolecular interactions of the guest molecules encapsulated. Thus tertiary amides and anilides such as 1 , which exist in solution preferably as E rotamers, are fixed in the Z conformation inside the capsule for steric reasons.     

A direct comparison of one- and two-component dendritic self-assembled materials: elucidating molecular recognition pathways

This paper compares and contrasts, for the first time, one- and two-component gelation systems that are direct structural analogues and draws conclusions about the molecular recognition pathways that underpin fibrillar self-assembly. The new one-component systems comprise l-lysine-based dendritic headgroups covalently connected to an aliphatic diamine spacer chain via an amide bond. One-component gelators with different generations of headgroup (from first to third generation) and different length spacer chains are reported. The self-assembly of these dendrimers in toluene was elucidated using thermal measurements, circular dichroism (CD) and NMR spectroscopies, scanning electron microscopy (SEM), and small-angle X-ray scattering (SAXS). The observations are compared with previous results for the analogous two-component gelation system in which the dendritic headgroups are bound to the aliphatic spacer chain noncovalently via acid-amine interactions. The one-component system is inherently a more effective gelator, partly as a consequence of the additional covalent amide groups that provide a new hydrogen bonding molecular recognition pathway, whereas the two-component analogue relies solely on intermolecular hydrogen bond interactions between the chiral dendritic headgroups. Furthermore, because these amide groups are important in the assembly process for the one-component system, the chiral information preset in the dendritic headgroups is not always transcribed into the nanoscale assembly, whereas for the two-component system, fiber formation is always accompanied by chiral ordering because the molecular recognition pathway is completely dependent on hydrogen bond interactions between well-organized chiral dendritic headgroups.