What you thought you already knew about the bending motion of triatomic molecules

The bending vibrations of linear, quasilinear, and bent molecules are qualitatively different phenomena. Each of these cases has been fully described by quantum mechanical formulations in the last half century, but important two-dimensional aspects of all three cases as well as the relationship between the three types of bending behavior remain difficult to visualize. Simple two-dimensional figures can help to provide an introduction to basic spatial and mathematical aspects of the bending problem.     

High resolution TDL spectroscopy of the Ar-CH4 complex

The spectrum of the weakly bound complex Ar-CH4 in the 7 microm region was discovered, analysed, and compared with a spectrum, predicted from ab initio calculations. The measurements were made by probing a supersonic gas expansion with a tunable diode laser (TDL). Several bands of Ar-CH4 associated with different ro-vibrational transitions of the v4 vibration of CH4 were recorded and analysed in a spectral region from 1295 to 1330 cm(-1). In particular the following transitions were studied: j = 1 <-- 0 (at 1311 cm(-1)) reported in Pak et al. [Z. Naturforsch. 53 (1998) 725], j = 0 <-- 1 (at 1301 cm(-1)), j = 2 <-- 1 (at 1316 cm(-1)), and j = 3 <-- 2 transitions (at 1322 cm(-1)). Here, j denotes the angular momentum of the methane unit inside the complex. Analysis of the recently recorded j = 1 <-- 1 transitions at about 1306 cm(-1) in the region of methane Q(1) is in progress. The experimental results are compared with ab initio calculations. The close agreement between observed and ab initio spectra is convincingly demonstrated with respect to the gross spectral features, including many details of the spectra.     

Detection of the microwave spectrum of tricarbon oxide sulphide,C3OS

The microwave spectrum of tricarbon oxide sulphide (3-thioxo-1,2-propadiene-1-one), OCCCS, is shown to be that of a linear molecule with B_o = 1413.898 MHz and D_o = 0.046 kHz. The dipole moment was determined to be 0.634 debye. As a five-atomic linear molecule C₃OS has three degenerate bending modes, ν₅, ν₆, and ν₇. The l-type doubling constant for each of these modes was determined, and the vibrational frequencies have been estimated from these values and from relative intensity measurements.     

A precise study of the rotational spectrum of formaldehyde H2CO, H2CO, H2CO, H2CO

The rotational spectra of formaldehyde, H₂¹²C¹⁶O and its isotopic species H₂¹³C¹⁶O, H₂¹²C¹⁸O, and H₂¹³C¹⁸O have been investigated in the ground vibrational state in the frequency region between 8 and 460 GHz. For most cases in which measurements of the a-type R- and Q-branch transitions already existed the accuracy of the line position has been improved to about 10 kHz. For H₂¹²C¹⁶O and H₂¹³C¹⁶O a large number of ΔK_a = ±2 transitions were measured with similar accuracy. These new data when combined with all other available data and appropriate weightings lead to a set of ground state parameters which for the first time are compatible with infrared and ultraviolet data. The rotational constants (and 3σ standard deviations) obtained using Watson's A-reduced Hamiltonian are:

Full-size image

     

Deorphaning the Macromolecular Targets of the Natural Anticancer Compound Doliculide

The cyclodepsipeptide doliculide is a marine natural product with strong actin‐polymerizing and anticancer activities. Evidence for doliculide acting as a potent and subtype‐selective antagonist of prostanoid E receptor 3 (EP3) is presented. Computational target prediction suggested that this membrane receptor is a likely macromolecular target and enabled immediate in vitro validation. This proof‐of‐concept study demonstrates the in silico deorphanization of phenotypic screening hits as a viable concept for future natural‐product‐inspired chemical biology and drug discovery efforts.     

Scaffold diversity of natural products: inspiration for combinatorial library design

Natural products contain scaffold structures that can be systematically exploited for the design of combinatorial compound libraries with druglike properties. We review approaches for scaffold identification, and compare properties and pharmacophoric features of drugs and natural products. In particular, an application of the self-organizing map technique is presented for natural product-derived compound and library design.