Amide Molecules Research Articles

Size-Dependent Metamorphosis of Electron Binding Motif in Cluster Anions of Primary Amide Molecules

Electron binding motifs in cluster anions of primary amides, (acetamide)(n)(-) and (propionamide)(n)(-), were studied with photoelectron spectroscopy. For both the amides, two band series due to distinct isomeric species in the multipole-bound states were found in the low electron binding energy region (<~0.4 eV) of the photoelectron spectra at the excitation wavelength of 1064 nm. In the case of acetamide, the isomer of higher band peak energies is predominant for 6≤ n ≤ 8, but it vanishes completely for n ≥ 9 to be replaced with the lower energy isomer. The same spectral behavior was seen for propionamide exhibiting an exception at n = 7. The isomers appearing in the lower and higher energy sides were attributed to the straight and folded forms of ladder-like hydrogen bond network structures, respectively, on the basis of density functional calculations. In the folded forms, the excess electron is held in the space between two terminal amide molecules of the ladder-like networks. Referring to calculations of potential energy curves with respect to the folding coordinate of the ladder-like networks, it is inferred that the major isomer alternation between n = 8 and 9 originates from an increase of stiffness of the molecular ladders depending on the cluster sizes. In photoelectron spectra at the 355 nm excitation, the valence anion state having a band peak around 2.5 eV was observed to emerge with threshold sizes of n = 13 and 9 for acetamide and propionamide, respectively. Static and dynamical effects of alkyl groups on the electron binding motifs are discussed in comparison with the previous study on formamide cluster anions.

The effect of intermolecular hydrogen bonding on the planarity of amides

Ab initio and density functional theory (DFT) calculations on some model systems are presented to assess the extent to which intermolecular hydrogen bonding can affect the planarity of amide groups. Formamide and urea are examined as archetypes of planar and non-planar amides, respectively. DFT optimisations suggest that appropriately disposed hydrogen-bond donor or acceptor molecules can induce non-planarity in formamide, with OCNH dihedral angles deviating by up to ca. 20° from planarity. Ab initio energy calculations demonstrate that the energy required to deform an amide molecule from the preferred geometry of the isolated molecule is more than compensated by the stabilisation due to hydrogen bonding. Similarly, the NH(2) group in urea can be made effectively planar by the presence of appropriately positioned hydrogen-bond acceptors, whereas hydrogen-bond donors increase the non-planarity of the NH(2) group. Small clusters (a dimer, two trimers and a pentamer) extracted from the crystal structure of urea indicate that the crystal field acts to force planarity of the urea molecule; however, the interaction with nearest neighbours alone is insufficient to induce the molecule to become completely planar, and longer-range effects are required. Finally, the potential for intermolecular hydrogen bonding to induce non-planarity in a model of a peptide is explored. Inter alia, the insights obtained in the present work on the extent to which the geometry of amide groups may be deformed under the influence of intermolecular hydrogen bonding provide structural guidelines that can assist the interpretation of the geometries of such groups in structure determination from powder X-ray diffraction data.

Development and Validation of the EXAm Separation Process for Single Am Recycling

The EXAm process aims at recovering americium alone. The principle of the EXAm process is based on the extraction of americium together with some light lanthanides having close values of distribution coefficients in high nitric acidity, while curium and other lanthanides remain in the aqueous phase. The TEDGA amide molecule is added in the aqueous phase to increase Am/Cm and Am/heavy Ln selectivity, because of the preferential complexation of curium and heavy lanthanides by this diglycolamide. The Am is subsequently selectively stripped from the light lanthanides.The full approach aiming at validating this complex process is illustrated in this paper.

Hierarchically Organized Bimolecular Ladder Network Exhibiting Guided One-Dimensional Diffusion

The assembly and dynamics of a hierarchical, bimolecular network of sexiphenyl dicarbonitrile and N,N'-diphenyl oxalic amide molecules on the Ag(111) surface are studied by scanning tunneling microscopy at controlled temperature. The network formation is governed by a two-step protocol involving hierarchic interactions, including a novel carbonitrile-oxalic amide bonding motif. For temperatures exceeding ~70 K, more weakly bound sexiphenyl dicarbonitrile molecules carry out one-dimensional diffusion guided by the more stable substructure of the network held together by the carbonitrile-oxalic amide bonding motif. A theoretical investigation at the ab initio level confirms the different binding energies of the two coupling motifs and rationalizes the network formation and the diffusion pathway.

Solvation Properties of Aliphatic Alcohol–Water and Fluorinated Alcohol–Water Solutions for Amide Molecules Studied by IR and NMR Techniques

Solvation properties of aliphatic alcohol–water and fluorinated alcohol–water solutions were probed by amide molecules as solutes using infrared (IR) and 1H and 13C NMR techniques. These include four alcohols: ethanol (EtOH), 2-propanol (2-PrOH), 2,2,2-trifluoroethanol (TFE), and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and three amides: N-methylformamide (NMF), N-methylacetamide (NMA) and N-methylpropionamide (NMP). The hydrogen bonds of the amide carbonyl oxygen with water are gradually weakened as the alcohol content increases. This decreases in the order of HFIP > TFE ≈ 2-PrOH > EtOH. In TFE– and HFIP–water solutions, the hydrogen bond between the amide amino hydrogen and water is also gradually broken with increasing xA. This trend is more notable in the order of NMP > NMA > NMF. The hydrophobic moieties of the amide methyl and ethyl groups are solvated by the fluoroalkyl groups of fluorinated alcohols due to the hydrophobic interaction among them. Thus, the steric hindrance generated by the solvated alkyl group of amides promotes the breaking of the hydrogen bonds between amide and water.

To Mix or Not To Mix: 2D Crystallization and Mixing Behavior of Saturated and Unsaturated Aliphatic Primary Amides

Physisorbed monolayers based on relatively weak noncovalent interactions can serve as excellent model systems for understanding crystallization of materials in reduced dimensionality. Here we employ a powerful combination of scanning tunneling microscopy (STM), differential scanning calorimetry (DSC), and computational modeling to reveal two-dimensional (2D) crystallization and mixing behavior of saturated and unsaturated (cis as well as trans) aliphatic primary amides. The foundation of the present work is laid by DSC measurements, which reveal characteristic adsorption and mixing behavior of aliphatic amides. These results are further supported by STM visualization of the adlayers. STM reveals, at submolecular resolution, the adsorption as well as the two-component 2D phase behavior of these molecules at the liquid-solid interface. The saturated and trans-unsaturated amides exhibit random mixing in view of their size and shape complementarity. Binary mixtures of saturated and cis-unsaturated amides, on the other hand, display unprecedented mixing behavior. The linear saturated and bent cis-unsaturated amide molecules are found to mix surprisingly better at the liquid-solid interface than might have been expected on account of the dissimilarity in their shapes. Strong, directional intermolecular hydrogen-bonding interactions as well as the relative stabilization energies of the adlayers are responsible for such unusual mixing behavior. Computational modeling provides additional insight into all the possible interactions in 2D assemblies and their impact on stabilization energies of the supramolecular networks. This study provides a model for understanding the effect of nanoscale cocrystallization on the thin film structure at interfaces and demonstrates the importance of molecular geometry and hydrogen bonding in determining the coadsorption behavior.

Unzipping the Dimer in Primary Amides by Cocrystallization with Sulfoxides

A systematic crystal engineering study was undertaken to investigate how different electronic substituents on the aromatic ring of primary aromatic amides impact the ability of the amide to cocrystallize with dibenzyl sulfoxide. Amides which cocrystallize with dibenzyl sulfoxide form 1:1 cocrystals containing a discrete N–H···O═S supramolecular synthon as well as the well-known C(4) amide chain. The combination of these two synthons gives rise to linear chains of amide molecules, with each amide molecule capped by one sulfoxide molecule. Thus, the R22(8) dimer typically seen for primary amides is no longer present in these cocrystals. The influence of electronic effects of substituents on the amide is similar to that observed for acids in cocrystals.

Photophysical Studies on the Interaction of Formamide and Alkyl Substituted Amides with Photoinduced Electron Transfer (PET) Based Acridinedione Dyes in Water

Interaction of photoinduced electron transfer (PET) based acridinedione dye (ADR 1) with amides like formamide, acetamide and dimethylformamide (DMF) were investigated by fluorescence spectral techniques. A fluorescence enhancement accompanied with a blue shift in the emission maximum was observed on the addition of amides to ADR 1 dye, which possess C(6)H(4)(p-OCH(3)) in the 9th position of the basic acridinedione ring. The extent of fluorescence enhancement and the blue shift in the emission maximum of ADR 1 dye is of the order of DMF > acetamide > formamide. DMF, which is more hydrophobic and less polar, results in a higher extent of fluorescence enhancement and a larger shift in the emission maximum towards the blue region. On the addition of amides, the ADR 1 dye prefers to orient towards a more hydrophobic phase surrounded by more number of amide molecules. The fluorescence enhancement of ADR 1 dye is attributed to the suppression of PET process occurring through space. The influence of the hydrophobic nature and the polarity of the amides on the excited state properties of acridinedione dyes are elucidated by steady-state and time resolved fluorescence measurements.

Dependence of the solution and transfer enthalpies of DL-α-alanyl-DL-α-asparagine on the composition of water-amide binary solvents at 298.15 K

Solution enthalpies of DL-α-alanyl-DL-α-asparagine (AlaAsn) in water-formamide, water-N-methylformamide, water-N,N-dimethylformamide, and water-N,N-dimethylacetamide mixtures were measured in the range of amide mole fractions x 2 = 0–0.3. The standard enthalpies of solution (Δsol H°) and transfer (Δtr H°) of AlaAsn from water to the binary solvent and enthalpy coefficients of pair-wise interactions (h xy ) of AlaAsn with amide molecules were calculated. The influence of the composition of the water-organic mixture on the enthalpy characteristics of AlaAsn is discussed. It is shown that the enthalpy characteristics of solution and transfer of AlaAsn are related to the structure of amides.

ChemInform Abstract: Synthesis of Amides from Esters and Amines with Liberation of H2 under Neutral Conditions.

AbstractThe acyl and the alkoxo part of a symmetrical ester forms with secondary or primary amines two amide molecules in the presence of the dearomatized ruthenium—pincer catalyst RUT.

The crystal structures and melting point properties of isonicotinamide cocrystals with alkanediacids HO2C(CH2)n−2CO2H n = 7–9

The tunability of physiochemical properties of crystalline materials through controlled cocrystal formulation is an aim for both the pharmaceutical industry and crystal engineers. In this paper we report that the melting point alternation behaviour of odd and even alkanedicarboxylic acids is mimicked in a set of cocrystals in which isonicotinamide is combined in a 1 : 1 stoichiometry with pimelic acid, suberic acid and azelaic acid. All three structures contain hydrogen bonded chains of alternating acid and amide molecules between which acid–pyridine and acid–amide synthons are formed. Both isonicotinamide : pimelic acid and isonicotinamide : azelaic acid form structures in which the acid moiety adopts a twisted alkyl backbone conformation similar to that observed in the pure odd alkanediacid materials. The isonicotinamide : suberic acid cocrystal differs from the others reported here retaining both the elevated melting point and the planar acid conformation displayed by even alkanediacid materials in this series.

Rapid Carbon‐11 Radiolabelling for PET Using Microfluidics

Labels all around: A gas–liquid microfluidic reactor is used for the first time to efficiently perform [11C]carbon monoxide carbonylation reactions for the preparation of 11C-radiolabelled amide molecules within a short timeframe (<15 min; see scheme).

Computing Relative Free Energies of Solvation using Single Reference Thermodynamic Integration Augmented with Hamiltonian Replica Exchange.

This paper introduces an efficient single-topology variant of Thermodynamic Integration (TI) for computing relative transformation free energies in a series of molecules with respect to a single reference state. The presented TI variant that we refer to as Single-Reference TI (SR-TI) combines well-established molecular simulation methodologies into a practical computational tool. Augmented with Hamiltonian Replica Exchange (HREX), the SR-TI variant can deliver enhanced sampling in select degrees of freedom. The utility of the SR-TI variant is demonstrated in calculations of relative solvation free energies for a series of benzene derivatives with increasing complexity. Noteworthy, the SR-TI variant with the HREX option provides converged results in a challenging case of an amide molecule with a high (13-15 kcal/mol) barrier for internal cis/trans interconversion using simulation times of only 1 to 4 ns.

Study of static permittivity and hydrogen bonded structures in amide–alcohol mixed solvents

Relative static permittivity of the binary mixtures of amides (formamide (FA), N-methylformamide (NMF), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA)) with alcohols (ethyl alcohol (EA) and ethylene glycol (EG)) over the entire composition range have been investigated at 1 MHz and 30 °C. The concentration-dependent relative permittivity increment and the excess permittivity of these binary mixtures reveal that the strength of heterogeneous H-bonded molecular interactions, the dipolar ordering and the molar ratio of stable adduct of amides with EA and EG are influenced by number of hydroxyl groups of the alcohol molecules and the type of substitution in amide molecules.

Temperature dependent static dielectric constant and viscosity behaviour of glycerol–amide binary mixtures: Characterization of dominant complex structures in dielectric polarization and viscous flow processes

The static dielectric constant and viscosity of the binary mixtures of glycerol (Gly) with N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) were measured over the entire composition range at temperatures 288.15, 303.15, 318.15 and 333.15 K. The concentration dependent non-linear behaviour of the measured thermodynamical parameters revealed the formation of hydrogen bond interactions between glycerol and amide molecules with a variety of complexes. The excess dielectric constant and excess viscosity were determined and analyzed for the confirmation of the composition of dominant complex species. Results inferred that the dielectric polarization in both the Gly–DMF and Gly–DMA mixtures is governed by 1:1 complex species with enhanced dipolar ordering at all the investigated temperatures. The complex species of 3Gly:DMF and 2Gly:DMA facilitates the viscous flow process in Gly–DMF and Gly–DMA mixtures, respectively and the density of these species is strongly influenced by the change in temperature. Arrhenius type behaviour of viscosity against the reciprocal of temperature was used to determine the apparent activation energy of the viscous flow. The electric-field-induced increment of the Helmholtz free energy and the entropy were determined from the temperature dependence of the static dielectric constant and its derivative of the binary mixtures. Results were discussed to assess the volume effect of DMF and DMA molecules on hydrogen bonding interactions with glycerol molecules in order to confirm the structural conformations of these mixed solvents.

Crystalline Structures of Alkylamide Monolayers Adsorbed on the Surface of Graphite

Synchrotron X-ray and neutron diffraction have been used to determine the two-dimensional crystalline structures of alkylamides adsorbed on graphite at submonolayer coverage. The calculated structures show that the plane of the carbon backbone of the amide molecules is parallel to the graphite substrate. The molecules form hydrogen-bonded dimers, and adjacent dimers form additional hydrogen bonds yielding extended chains. By presenting data from a number of members of the homologous series, we have identified that these chains pack in different arrangements depending on the number of carbons in the amide molecule. The amide monolayers are found to be very stable relative to other closely related alkyl species, a feature which is attributed to the extensive hydrogen bonding present in these systems. The characteristics of the hydrogen bonds have been determined and are found to be in close agreement with those present in the bulk materials.

Studies of heterogeneous interactions between N-acetyl- N′-methyl- l-α-amino acid amides and urea molecules in water at 298.15 K

The enthalpies of solution of N-acetyl- N′-methyl- l-α-threoninamide, N-acetyl- N′-methyl- l-α-tyrosinamide, N-acetyl- N′-methyl- l-α-histidinamide, N-acetyl- N′-methyl- l-α-tryptophanamide have been measured in water and in aqueous urea solutions at 298.15 K. The mixing enthalpies of aqueous urea solution with aqueous N-acetyl- N′-methyl- l-α-valinamide solution and their respective enthalpies of dilution by water have been determined at 298.15 K. The experimental results were used to obtain the enthalpic coefficients of the interaction between amino acid amides and urea molecules in water based on McMillan–Mayer's model. The values of the interaction parameters were interpreted in terms of the hydrophobic or hydrophilic properties of the amino acid radicals in the examined amide molecules and the influence on their interactions with a urea molecule in water.

Dielectric constant and molecular association in binary mixtures of N,N-dimethylethanolamine with alcohols and amides

The hydrogen-bond molecular interactions and molar ratio of stable adduct in binary mixtures of N,N-dimethylethanolamine with alcohols (ethyl alcohol, ethylene glycol, glycerol) and amides (formamide, N,N-dimethylformamide, N,N-dimethylacetamide) have been investigated over the entire concentration range at 30 °C by dielectric measurements. The effect of molecular size, number of hydroxyl groups of alcohols molecules and the extent of substitution in amide molecules on the hydrogen-bond molecular interactions in amine–alcohols and amine–amides binary mixtures were determined using the concentration dependent values of the excess dielectric constant. Results confirm that N,N-dimethylethanolamine form expressive hydrogen-bond interactions with alcohols and behave weakly with N,N-dimethylformamide and N,N-dimethylacetamide, but these interactions are very strong with formamide.

環境応答型芳香族アミド化合物の構造変換と動的制御

The three–dimensional structure and the dynamic behavior of a molecule is important issue for regulating the molecular function or biological activity. Recently the development of functional molecular devices that undergo reversible conformational interconversion between two or more stable states when exposed to an external stimulus, such as light, electricity or a chemical reaction, has received much attention. In our investigations on the cis conformational preference of aromatic N–methylated amides, we found several aromatic amides altered the stable conformations depending on the external stimulus. Namely, 3,5–bis (dimethylamino) –N–methylacetanilide (6) existed in cis form in CD2Cl2, while the addition of TFA–d caused the conformational alteration into trans form. Similarly, N– (2,5–dihydroxyphenyl) –N–phenylacetanilide (8) and N–phenylbenzohydroxamic acid (12) changed the amide conformation by redox reaction or solvent properties, respectively. N–Methylated pyridylamide also showed unique conformational properties. The stable conformation of the diamide 16 is solvent–dependent, and the acceptor number of the solvent seems to be significant. These pyridylamides and the oligomers changed the conformation by addition of acid. Further, we demonstrated the conformational change of the amide molecules could be detected by fluorescence spectra. These properties of the aromatic amides would be applied to the molecular switch or fluorescent sensors towards some external stimulus.

Preparation of polypropylene–clay nanocomposites by the co‐intercalation of modified polypropylene and short‐chain amide molecules

AbstractThe effect of short‐chain amide (AM) molecules on the intercalation of montmorillonite clay has been investigated by the melt blending of polypropylene (PP) with clay in the presence of AM molecules such as 13‐cis‐docosenamide (erucamide). Polypropylene–clay nanocomposites (PPCNs) were prepared by the co‐intercalation of maleic anhydride grafted polypropylene (PP–MA) and an AM compound. The resulting nanocomposite structures were characterized with X‐ray diffraction (XRD) and transmission electron microscopy, whereas the thermal characterization of the PPCNs was conducted by thermogravimetric analysis. XRD results showed that the AM molecules intercalated into clay galleries and increased the interlayer spacing, a result confirmed by surface energy (contact angle) and melt flow index measurements. This additive allowed the formation of an intercalated nanocomposite structure, but an exfoliated PPCN structure was also formed with the use of AM with a PP–MA‐based compatibilizer. A new preparation method for PPCNs was, therefore, developed by the co‐intercalation of AM and PP–MA; this resulted in a significantly improved degree of intercalation and dispersion. The enhanced thermal stability of PPCN, relative to pure PP, further demonstrated the improved clay dispersion in the nanocomposite structures prepared by this method. A possible mechanism for the co‐intercalation of AM and PP–MA into the clay galleries is proposed, based on hydrogen bonding between these additives and the silicate layers. Consideration is also given to possible chemical reactions and physical interactions in this rather complex system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009