Blue-shifting H-bonded (C-D···O) complexes between CDCl and CHHCO, (CH)CO, and CH(CH)CO, and red-shifting H-bonded (C-D···S) complexes between CDCl with (CH)S and (CH)S have been identified by Fourier transform infrared spectroscopy in the gas phase at room temperature. With increasing partial pressure of the components, a new band appears in the C-D stretching region of the vibrational spectra. The intensity of this band decreases with an increase in temperature at constant pressure, which provides the basis for identification of the H-bonded bands in the spectrum. The C-D stretching frequency of CDCl is blue-shifted by +7.1, +4, and +3.2 cm upon complexation with CHHCO, (CH)CO, and CH(CH)CO, respectively, and red-shifted by -14 and -19.2 cm upon complexation with (CH)S and (CH)S, respectively. By using quantum chemical calculations at the MP2/6-311++G** level, we predict the geometry, electronic structural parameters, binding energy, and spectral shift of H-bonded complexes between CDCl and two series of compounds named RCOR' (HCO, CHHCO, (CH)CO, and CH(CH)CO) and RSR' (HS, CHHS, (CH)S, and (CH)S) series. The calculated and observed spectral shifts follow the same trends. With an increase in basicity of the H-bond acceptor, the C-D bond length increases, force constant decreases, and the frequency shifts to the red from the blue. The potential energy scans of the above complexes are done, which show that electrostatic attraction between electropositive D and electron-rich O/S causes bond elongation and red shift, and the electronic and nuclear repulsions lead to bond contraction and blue shifts. The dominance of the two opposing forces at the equilibrium geometry of the complex determines the nature of the shift, which changes both in magnitude and in direction with the basicity of the hydrogen-bond acceptor.

Acetic acid CH3C(O)OH plays an important role in the acidity of the troposphere. The reactions of Criegee intermediates with CH3C(O)OH have been proposed to be a potential source of secondary...

Blue-shifting H-bonded complexes between CHCl 3 and CH/D 3 CN have been identified by Fourier transform infrared spectroscopy in the gas phase at room temperature. The change in FTIR peak intensity of the mixture of the two components as a function of temperature and composition provides the basis for identification of the H-bonded band in the infrared spectrum. On complex formation with CH 3 CN and CD 3 CN, the C−H stretching frequency of CHCl 3 shifts to the blue by +8.7 and +8.6 cm −1 , respectively. The molecular electrostatic potential calculation at the MP2/6-311++G** level has been used to arrive at the geometry of the complex. It has been reported in the literature that CHCl 3 and CH/D 3 CN form red-shifting H-bonded complex in Ar matrix. The red shifting has been verified by doing ab initio calculations in the presence of Ar atoms, which has been attributed to the matrix effect at low temperature. The interaction of Ar with CH 3 CN makes the CH 3 CN more basic and as a result it becomes better hydrogen bond acceptor and causes red shift. The potential energy scans and NBO analysis of the Cl 3 CH•••NCCH 3 complex have been compared with those of F 3 CH•••NCCH 3 and Cl 3 CH•••NH 3 complexes. The change in electron density of the CHCl 3 as a function of C−H•••N distance shows that the approach of CH 3 CN to CHCl 3 induces a shift in electron density from the H atom to the Cl atoms of CHCl 3 which leads to C−H bond contraction and blue shifting of C−H stretching frequency. However, in the complex Cl 3 CH•••NH 3 , where frequency shift to the red is reported, charge transfer and electrostatic interaction dominate.

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To artificially expand the genetic information system and to realize artificial life, it is necessary to discover new functional DNA bases that can form stable duplex DNA and participate in error-free replication. It is recently proposed that the 2-amino-imidazo[1,2- a]-1,3,5-triazin-4(8 H)one (P) and 6-amino-5-nitro-2(1 H)-pyridone (Z) would form a base pair complex, which is more stable than that of the normal G-C base pair and would produce an unperturbed duplex DNA. Here, by using quantum chemical calculations in aqueous medium, it is shown that the P and Z molecules can be modified with the help of electron-withdrawing and -donating substituents mainly found in B-DNA to generate new bases that can produce even more stable base pairs. Among the various bases studied, P3, P4, Z3, and Z5 are found to produce base pairs, which are about 2-15 kcal/mol more stable than the P-Z base pair. It is further shown that these base pairs can be stacked onto the G-C and A-T base pairs to produce stable dimers. The consecutive stacking of these base pairs is found to yield even more stable dimers. The influence of charge penetration effects and backbone atoms in stabilizing these dimers are also discussed. It is thus proposed that the P3, P4, Z3, and Z5 would form promiscuous artificial genetic information system and can be used for different biological applications. However, the evaluations of the dynamical effects of these bases in DNA-containing several nucleotides and the efficacy of DNA polymerases to replicate these bases would provide more insights.