Amide Dimers Research Articles

Chiral calixarenes derived from resorcinol. Part 3: Functionalization of octaester derivatives with chiral amines and amino alcohols

A new type of chiral calixresorcarene is described. The formation of both enantiomers of 3 and 4 is controlled by the chiral amines and amino alcohols used for the reaction. Formation of the dimers of these compounds in the gas phase and in solution was observed using the LSIMS and ESI-MS methods. Formation of amide dimers of the derivative 3 in chloroform was confirmed by fluorescence spectroscopy.

Synthesis and Structure of a New Lithium Amide Ligand Precursor: A Tridentate Nitrogen-Based Donor Set of the Formula N(SiMe(2)CH(2)NMe(2))(2). Synthesis and Structure of the Group 4 Amides MCl(3)[N(SiMe(2)CH(2)NMe(2))(2)] (M = Ti, Zr, Hf).

The new lithium amide LiN(SiMe(2)CH(2)NMe(2))(2) was prepared by reaction of NH(3) with the corresponding silylamine Me(2)NSiMe(2)CH(2)NMe(2) followed by addition of butyllithium. This lithium derivative exists as a dimer in the solid state wherein the two lithium ions are bridged by the two amido units with the amine arms of each unit bonded to opposite lithium centers in an overall pseudo D(2) structure; however, in solution, a fluxional process serves to interconvert the enantiomeric forms of the dimer unit. The coordination chemistry of the lithium amide dimer has been investigated; reaction with a series of group 4 starting halides, MCl(4), leads to the corresponding complexes MCl(3)[N(SiMe(2)CH(2)NMe(2))(2)], where M = Ti, Zr, and Hf. The structures of these starting trihalides in solution and in the solid state are presented.

Amide backbone modifications for antisense oligonucleotides carrying potential intercalating substituents: Influence on the thermodynamic stability of the corresponding duplexes with RNA- and DNA- complements

Abstract The synthesis of the amide dimers 3–5 carrying a potential intercalating substituent on the nitrogen atom of the backbone is presented, together with the incorporation of these modifications into oligonucleotides, the resulting melting temperatures (Tm's) of the corresponding duplexes with RNA- and DNA- complements, and a summary of molecular modeling studies.

A rhodium(I) amide dimer: Synthesis, structural characterisation and preliminary reactivity studies

Abstract A rhodium(I) amide complex was synthesised, isolated and crystallographically characterised: this is the first reported molecular structure of a dimeric rhodium amide complex.

Transfer of molecular property tensors in cartesian coordinates: A new algorithm for simulation of vibrational spectra

A direct transfer of Cartesian molecular force fields FF and electric property tensors is tested on model systems and compared to transfer in internal coordinates with an aim to improve simulation of vibrational spectra for larger molecules. This Cartesian transformation can be implemented easily and offers greater flexibility in practical computations. It can be also applied for transfer of anharmonic derivatives. The results for model calculations of the force field and vibrational frequencies for N-methylacetamide show that our method removes errors associated with numerical artifacts caused by nonlinearity of the otherwise required Cartesian to internal coordinate transformation. For determination of IR absorption and vibrational circular dichroism intensities, atomic polar and axial tensors were also transferred in the Cartesian representation. For the latter, which are dependent upon the magnetic dipole operator, a distributed origin gauge is used to avoid an origin dependence. Comparison of the results of transferring ab initio FF and intensity parameters from an amide dimer fragment onto a tripeptide with those from a conventionally determined tripeptide FF document some limitations of the transfer method and its possible applications in the vibrational spectroscopy. Finally, application to determination of the FF and spectra for helical heptapeptide are presented and compared to experimental results. Q 1997 by John Wiley & Sons, Inc.

The First Structurally Characterized Monolithio Aluminum Amide Dimer

Herein is reported the first synthesis and structural characterization of a monolithio aluminum amide dimer: [Me2AlNLi(THF)2Ph]2. It is prepared by deprotonation of the corresponding neutral dimeric species [Me2AlNHPh]2 with tBuLi in THF in 78% yield. Characterization data include 1H and 13C NMR, elemental analysis, and a single crystal X-ray analysis. The crystal structure demonstrates that the lithium atoms are still associated with the molecule. The spectroscopic and structural data indicate that there is not a significant degree of π bonding between the Al and N atoms.

Complementary hydrogen bonding in diamides: a study on the influence of remote substituents using density functional theory

Density functional calculations using gradient corrected functionals have been used to explore the factors which determine the strength of the intermolecular interaction in cyclic systems formed by complementary hydrogen bonding between amides. Optimised structures and interaction energies are presented for the simplest amide dimer, diformamide, and the results are compared with experimental and ab initio results available in the literature. Full optimisations are also performed on hydrogen bonded molecular pairs formed from the N-substituted derivatives of formamide, N-methylformamide (NMF) and N-formylformamide (NFF). The total interaction energy is found to decrease in the order NMF·NMF > NFF·NMF > NFF·NFF, the difference between successive pairs being approximately 10 kJ mol–1 in each case. The origin of this trend is traced to electrostatic repulsions between the spectator carbonyl groups in NFF and the carbonyl groups involved in the cyclic hydrogen bonded array.

Comparison of two amides as backbone replacement of the phosphodiester linkage in oligodeoxynucleotides

The two isomeric amide modifications 1 and 2 show similar effects on the melting temperature of RNA/DNA duplexes, when they replace the natural phosphodiester linkage in the DNA strand. The synthesis of the amide dimer 1 is presented.

ChemInform Abstract: SOME REACTIONS OF O,O‐DIPHENYLPHOSPHORYL AZIDE

AbstractDas Titelazid (I) liefert beim Erhitzen in Dioxan‐Wasser (IIa) das Hydrogen‐ phosphat (IIIa) und mit Butanol (IIb) den Butylester (IIIb).

Some reactions of O,O-diphenylphosphoryl azide

Diphenylphosphoryl azide, in contrast to N,N?-disubstituted phosphorodiamidic azides, undergoes nucleophilic displacement of the azido group by reaction with water, butanol, ammonia, and amines. Possible mechanisms for the conversion of diphenyl-phosphoryl azide into urethanes and amides are briefly discussed. Pyrolysis of N,N?- dicyclohexylphosphorodiamidic azide gave the phosphenimidic amide dimer.

Improved calculation of the n-pi rotational strength in polypeptides.

Previous calculations of the nπ* rotational strength in the α helix using the Kirkwood theory as extended by Moffitt and Tinoco have led to results which are of the right order of magnitude and correct sign but too small by a factor of 6–8. It is possible that contributions neglected by the Kirkwood approach, e.g., charge-transfer transitions, are important in the α helix. A molecular-orbital treatment of an amide dimer indicates that mixing of the nπ* and charge-transfer states makes a negligible contribution to the nπ* rotational strength in the α helix. However, when two modifications are made in previous Kirkwood-type treatments, the calculated rotational strength is found to be about − 0.2 debye bohr magnetons (D·μB), in good agreement with experiment. In addition, the calculated exciton splitting for the ππ* transition agrees better with experiment than do previous theoretical values. The modifications are (a) a more consistent choice of permanent and transition monopole positions, and (b) solution of a secular determinant for the mixing of the nπ* and ππ* excited states, rather than using first-order perturbation with zero-order wavefunctions. Analyses of experimental circular-dichroism (CD) curves as sums of Gaussians have led to ππ* rotational strengths appreciably smaller than theoretically calculated ones. We show here that this discrepancy may be due to failure to include a non-Gaussian term predicted by theory. Using reasonable band positions and widths, theoretical CD curves agree reasonably well with experimental curves. It is also pointed out that the exact shape of the CD curve is very sensitive to the band frequencies and widths. Therefore, observed variations in the shape may result from rather subtle changes in these parameters.