Theoretical investigation of the conformations of the methylamide of N-acetyl-L-phenylalanine

Russian Chemical Bulletin -     

Theoretical and experimental study of the vibrational spectrum of N-acetyl-L-alanine

The energies, vibrational frequencies and IR intensities of cis- and trans-N-acetyl-L-alanine (NAAL) are computed using the density functional theory (B3LYP) combined with the 6-311G(d, p) basis set. The trans conformer is characterized by an intramolecular NH ... O hydrogen bond leading to the formation of a five-membered ring and is by 23 kJ mol(-1) more stable than the cis conformer. The difference between the vibrational frequencies and IR intensities computed for the two conformers is discussed. The IR spectra at different temperatures and the Raman spectra of solid NAAL and its deuterated counterpart are investigated and discussed. The frequencies of the v(OH) vibration and the isotopic ratio suggest the formation of short OH ... O hydrogen bonds in the solid state. The NH group seems also to be involved in a weak hydrogen bond.     

Theoretical conformational analysis of the methylamide of N-acetyl-L-alanyl-L-prolyl-L-alanine. II

Summary 1. Spatial forms of Ac-L-Ala-L-Pro-L-Ala-NHMe with trans peptide bonds are the most preferred. Elongation of the peptide chain promotes the stabilization of the trans configuration of the tertiary amide group.2. In the structure of the compound investigated, the dominating role is played by the interaction of the neighboring residues.3. Of the six types of conformations of X-Pro-Y observed in proteins, the first four belong to the preferred forms of the Ac-L-Ala-L-Pro-L-Ala-NHMe molecule.M. M. Shemyakin Institute of Bioorganic Chemistry, Academy of Science of the USSR. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 626–630, September–October, 1975.     

An investigation of the conformational states of the methylamide of N-acetyl-L-histidine

Summary 1. All the conformational states of the methylamide of N-acetyl-L-histidine have been calculated.2. It has been shown that in the case of the tautomer of the imidazole ring with a hydrogen atom on the atom, form R of the main chain is preferred, and in the tautomer with the proton on and also in the protonated state of the side chain B forms are preferred.3. The conformational equilibrium is displaced in the direction of form I.M. M. Shemyakin Institute of Biochemistry, Academy of Sciences of the USSR, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 371–378, May–June, 1976.     

Theoretical investigation of the Anti-Parkinson drug rasagiline and its salts: conformations and infrared spectra

The conformational analysis of rasagiline [N-propargyl-1(R)-aminoindan] was performed by the density functional theory (DFT) B3LYP method using the 6–31++G (d,p) basis set. A single point energy calculations based on the B3LYP optimized geometries were also performed at MP2/6-31++G (d, p) level. The vibrational frequencies of the most stable conformer of rasagiline was calculated at the B3LYP level and vibrational assignments were made for normal modes on the basis of scaled quantum mechanical force field (SQM) method. The influence of mesylate and ethanedisulfonate salts on the geometry of rasagiline free base and its normal modes are also discussed.      

Theoretical studies on the conformations of selenamides

Ab initio HF/6-31+G*, MP2/6-31+G*, B3LYP/6-31+G* level calculations have been performed on HSe-NH₂ to estimate the Se-N rotational barriers and N-inversion barriers. Two conformers have been found withsyn andanti arrangement of the NH₂ hydrogens with respect to Se-H bond. The N inversion barriers in selenamide are 1.65, 2.47, 1.93 kcal/mol and the Se-N rotational barriers are 6.58, 6.56 and 6.12 kcal/mol respectively at HF/6-31+G*, MP2/6-31+G* and B3LYP/6-31+G* levels respectively. The n_N →Σ *_Se-H negative hyperconjugation is found to be responsible for the higher rotational barriers.     

Theoretical investigation of the EPR hyperfine coupling constants in amino derivatives

The HFCCs of the radical cations of a series of amines have been determined at different levels of approximation including the CISD, QCISD, and CCSD ab initio correlated methods and density functional theory approaches employing the B3LYP, PBE0, BHandHLYP, TPSS, and BLYP exchange-correlation functionals. Although quantitative differences with respect to experimental data have been noticed, these are mostly systematic within a given class of N and H atoms. As a consequence, these different levels of theory are reliable in most cases to account for the substituent and structure effects on the HFCCs of amines. Linear regression fits have then been performed to reach quantitative agreement between the theoretical and experimental values. This has finally been substantiated by considering the EPR signal of the recently synthesized radical cations of two derivatives of [10-(4-aminophenyl)-9-anthryl]aniline as well as in confirming a recent assignment of the EPR signal of n-propylamine.     

含B-N相互作用偶氮苯强荧光材料光电性质的理论研究

本文基于增大光谱发光强度的结构修饰方法,采用理论计算方法研究了结构修饰后分子的电子性质、光谱性质以及电荷传输性质的变化.计算结果表明,-N(CH3)2取代、-N(CH3)2和-Br组合取代有助于吸收/发射光谱发光强度的提高.与母体分子相比,-N(CH3)2和-Br取代位置不同或取代数量不同可以引起最高占据分子轨道能量(EHOMO)、最低空分子轨道能量(ELUMO)和能隙(Eg=ELUMO-EHOMO)发生明显变化,从而有效调节了最大吸收波长(λabs)和最大发射波长(λem),从理论角度设计了一系列蓝光和绿光材料.重组能计算显示,除了GM-1和GM-6,其余分子可以作为有机电致发光材料(OLEDs)中的空穴传输材料,GM-1和GM-7可以作为双极性电荷传输材料.     

Theoretical investigation of the coexistence of α and β-nitric acid trihydrates (NAT) molecular conformations

In this letter we document the possibility of the existence of a second molecular configuration for nitric acid trihydrates. Density functional theory (DFT) methods have been used for studying the nitric acid trihydrates α and β-NAT conformations, their spectroscopic and thermodynamics properties and dipole moments have been calculated. This study describes the gas–solid phase transition of the NAT and provides two possible pathways for the molecular structure transformation between α and β-NAT.     

Theoretical investigation of the reducing capacity of sodium borohydride and sodium acetoxyborohydride derivatives

The reducing capacity of sodium borohydride and its acetoxy derivatives was studied. Density functional theory using four different functionals were used to investigate the enthalpies, charges and molecular structures of four distinct reactions associated with hydride release. The theoretical results in the gas phase reinforce the experimental observations that the acetoxyborohydride derivative reducing capacities are a consequence of both the inductive electron-withdrawing ability of the acetoxy group and the steric bulk surrounding the BH bond. The electron acceptor effect of the acetoxy group provided a linear relation between the boron GAPT charges and the enthalpy necessary to remove the hydride from sodium borohydride, justifying the smaller or even nonexistent reductor capacity of more substituted borohydrides.     

Theoretical investigation on the impact sensitivity of tetrazole derivatives and their metal salts

The relative orders of impact sensitivity of tetrazole derivatives and their metal salts are investigated by examining the activation energy for forming azide in the process of thermal decomposition based on PM3-SCF-MO calculations. It is found that there is a parallel relationship between the activation energy and the sensitivity and a good linear relationship between the experimental impact sensitivity of metal salts of tetrazole and the reaction activation energy. It is shown that treating the metal salts of the tetrazole derivatives as the metal derivatives of tetrazole is meaningful.