Diazadioxa[8]circulenes: Planar Antiaromatic Cyclooctatetraenes

In this paper we describe a new class of antiaromatic planar cyclooctatetraenes: the diazadioxa[8]circulenes. The synthesis was achieved by means of a new acid‐mediated oxidative dimerization of 3,6‐dihydroxycarbazoles to yield the diazadioxa[8]circulenes in high yields. The synthetic protocol appears to be general, and is a one‐pot transformation in which two C? C bonds and two C? O bonds are formed with the loss of two molecules of water. We also present a detailed characterization of the optical and electrochemical properties of this new class of stable planar cyclooctatetraenes. The properties of the diazadioxa[8]circulenes are compared with the properties of isoelectronic tetraoxa[8]circulenes and azatrioxa[8]circulenes. We discuss the antiaromatic nature of the planar central cyclooctatetraene moiety. The antiaromatic nature of the planar cyclooctatetraenes was studied by using computational methods (NICS calculations), and these calculations reveal that the central eight‐membered ring has antiaromatic character.     

Internal Rotation of the Acetyl Methyl Group in Methyl Alkyl Ketones: The Microwave Spectrum of Octan-2-one

Methyl n-alkyl ketones form a class of molecules with interesting internal dynamics in the gas-phase. They contain two methyl groups undergoing internal rotations, the acetyl methyl group and the methyl group at the end of the alkyl chain. The torsional barrier of the acetyl methyl group is of special importance, since it allows for the discrimination of the conformational structures. As part of the series, the microwave spectrum of octan-2-one was recorded in the frequency range from 2 to 40 GHz, revealing two conformers, one with C₁ and one with C_s symmetry. The barriers to internal rotation of the acetyl methyl group were determined to be 233.340(28) cm⁻¹ and 185.3490(81) cm⁻¹, respectively, confirming the link between conformations and barrier heights already established for other methyl alkyl ketones. Extensive comparisons to molecules in the literature were carried out, and a small overview of general trends and rules concerning the acetyl methyl torsion is given. For the hexyl methyl group, the barrier height is 973.17(60) cm⁻¹ for the C₁ conformer and 979.62(69) cm⁻¹ for the C_s conformer.     

The phase shift method applied to cross grating moiré measurements

The automatic evaluation of the grating deformation in a moiré image is greatly enhanced by the phase shift method. Based on three or more local grey values of a related number of phase shifted moiré patterns, the local displacement of a deformed grating against a reference grating, and hence the total displacement in one direction, is calculated. In this paper an extension to cross gratings is presented yielding a two- dimensional displacement field.     

Current trends in finite-time thermodynamics

The cornerstone of finite-time thermodynamics is all about the price of haste and how to minimize it. Reversible processes may be ultimately efficient, but they are unrealistically slow. In all situations-chemical, mechanical, economical-we pay extra to get the job done quickly. Finite-time thermodynamics can be used to develop methods to limit that extra expenditure, be it in energy, entropy production, money, or something entirely different. Finite-time thermodynamics also includes methods to calculate the optimal path or mode of operation to achieve this minimal expenditure. The concept is to place the system of interest in contact with a time-varying environment which will coax the system along the desired path, much like guiding a horse along by waving a carrot in front of it.     

Physiological role of phnP-specified phosphoribosyl cyclic phosphodiesterase in catabolism of organophosphonic acids by the carbon-phosphorus lyase pathway

In Escherichia coli , internalization and catabolism of organophosphonicacids are governed by the 14-cistron phnCDEFGHIJKLMNOP operon. The phnP gene product was previously shown to encode a phosphodiesterase with unusual specificity toward ribonucleoside 2',3'-cyclic phosphates. Furthermore, phnP displays shared synteny with phnN across bacterial phn operons. Here the role of PhnP was examined by (31)P NMR spectrometry on the culture supernatants of E. coli phn mutants grown in the presence of alkylphosphonic acid or phosphite. The addition of any of these alkylphosphonic acids or phosphite resulted in the accumulation of α-D-ribosyl 1,2-cyclic phosphate and α-D-ribosyl 1-alkylphosphonate in a phnP mutant strain. Additionally, α-D-ribosyl 1-ethylphosphonate was observed to accumulate in a phnJ mutant strain when it was fed ethylphosphonic acid. Purified PhnP was shown to regiospecifically convert α-D-ribosyl 1,2-cyclic phosphate to α-D-ribosyl 1-phosphate. Radiolabeling studies revealed that 5-phospho-α-D-ribosyl 1,2-cyclic phosphate also accumulates in a phnP mutant. This compound was synthesized and shown to be regiospecifically converted by PhnP to α-D-ribosyl 1,5-bisphosphate. It is also shown that organophosphonate catabolism is dependent on the synthesis of 5-phospho-α-D-ribosyl 1-diphosphate, suggesting that this phosphoribosyl donor is used to initiate the carbon-phosphorus (CP) lyase pathway. The results show that 5-phospho-α-D-ribosyl 1,2-cyclic phosphate is an intermediate of organophosphonic acid catabolism, and it is proposed that this compound derives from C-P bond cleavage of 5-phospho-α-D-ribosyl 1-alkylphosphonates by CP lyase.     

Stimulated Raman scattering microscopy by spectral focusing and fiber-generated soliton as Stokes pulse

We demonstrate stimulated Raman microscopy with broadband pump and Stokes pulses, using spectral focusing to attain spectral resolution and to rapidly acquire spectra within a spectral window determined by the bandwidth of the pulses. As the Stokes pulse, we use the redshifted soliton generated in a photonic crystal fiber, which allows for simple shifting of the accessible spectral window.     

Sensing the Molecular Structures of Hexan-2-one by Internal Rotation and Microwave Spectroscopy

Using two molecular jet Fourier transform spectrometers, the microwave spectrum of hexan-2-one, also called methyl n-butyl ketone, was recorded in the frequency range from 2 to 40 GHz. Three conformers were assigned and fine splittings caused by the internal rotations of the two terminal methyl groups were analyzed. For the acetyl methyl group CH₃ COC₃H₆CH₃, the torsional barrier is 186.9198(50) cm⁻¹, 233.5913(97) cm⁻¹, and 182.2481(25) cm⁻¹ for the three observed conformers, respectively. The value of this parameter could be linked to the structure of the individual conformer, which enabled us to create a rule for predicting the barrier height of the acetyl methyl torsion in ketones. The very small splittings arising from the internal rotation of the butyl methyl group CH₃COC₃H₆ CH₃ could be resolved as well, yielding the respective torsional barriers of 979.99(88) cm⁻¹, 1016.30(77) cm⁻¹, and 961.9(32) cm⁻¹.     

Fractional decay of quantum dots in real photonic crystals

We show that fractional decay may be observable in experiments using quantum dots and photonic crystals with parameters that are currently achievable. We focus on the case of inverse opal photonic crystals and locate the position in the crystal where the effect is most pronounced. Furthermore, we quantify the influence of absorptive loss and show that it is a limiting but not prohibitive effect.