Influence of chlorine and methyl substituents and their position on the antimicrobial activities and crystal structures of 4-methyl-1,6-diphenylpyrimidine-2(1H)-selenone derivatives

Derivatives of 4-methyl-1,6-diphenylpyrimidine-2(1H)-selenone show very strong antimicrobial activity. In order to extend the current knowledge about the features responsible for the biological activity, crystal structure analyses are presented for 4-methyl-1-(2-methylphenyl)-6-phenylpyrimidine-2(1H)-selenone (1), 4-methyl-1-(3-methylphenyl)-6-phenylpyrimidine-2(1H)-selenone (2), 4-methyl-1-(4-methylphenyl)-6-phenylpyrimidine-2(1H)-selenone (3) (all C18H16N2Se) and 1-(4-chlorophenyl)-4-methyl-6-phenylpyrimidine-2(1H)-selenone (4) (C17H13ClN2Se). Furthermore, the antibacterial and antifungal activities of these compounds were evaluated. All the presented derivatives crystallize in the space group P21/c with one molecule in the asymmetric unit. The molecular geometries differ slightly in the mutual orientation of the rings. The packing of molecules in the crystals is dominated by C—H...N and C—H...Se intermolecular interactions. Additionally, in the crystal structure of 4, C—H...Cl intermolecular interactions are observed. The introduction of a methyl or chlorine substituent improves the biological activity, while its position significantly affects biological activity only in case of the chlorine substituent.

Concise Chemoenzymatic Synthesis of Fasamycin A

<div>We report the development of a chemoenzymatic approach towards fasamycin A, a halogenated naphthacenoid that exhibits activities against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis. The synthesis was accomplished in a convergent manner: two fragments were combined together via Michael−Dieckmann condensation to afford a dimethylnaphthacenone system. Finally, an enzymatic halogenation was employed to introduce the requisite chlorine substituent of the natural product at a late stage.</div><div><br></div>

Concise Chemoenzymatic Synthesis of Fasamycin A

<div>We report the development of a chemoenzymatic approach towards fasamycin A, a halogenated naphthacenoid that exhibits activities against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis. The synthesis was accomplished in a convergent manner: two fragments were combined together via Michael−Dieckmann condensation to afford a dimethylnaphthacenone system. Finally, an enzymatic halogenation was employed to introduce the requisite chlorine substituent of the natural product at a late stage.</div><div><br></div>

ESTIMATION OF DEGRADATION POTENTIAL OF THE BACTERIAL DEGRADERS OF CHLORINE DERIVATIVES OF PHENOL OF THE INDUSTRIAL ECOTOPES IN UFA

The ability of eight natural isolates of the two ecotopes to separately use 2,5-dichlorophenol (2,5-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) as the sole source of carbon and energy were studied. Probably the chlorine substituent at the 5th position concerning the toxicity of the substrate is more important than its total amount because from the eight strains five used 2,4,6-TCP and only one used 2,5-DCP. No one of the studied strains did not show an antagonistic effect on other cultures. This indicates to the possibility of their combined use in technologies for the remediation of the environment from pollutants of a chloroaromatic nature.

The Influence of a Terminal Chlorine Substituent on the Kinetics and the Mechanism of the Solvolyses of n-Alkyl Chloroformates in Hydroxylic Solvents

A previous study of the effect of a 2-chloro substituent on the rates and the mechanisms of the solvolysis of ethyl chloroformate is extended to the effect of a 3-chloro substituent on the previously studied solvolysis of propyl chloroformate and to the effect of a 4-chloro substituent on the here reported rates of solvolysis of butyl chloroformate. In each comparison, the influence of the chloro substituent is shown to be nicely consistent with the proposal, largely based on the application of the extended Grunwald–Winstein equation, of an addition-elimination mechanism for solvolysis in the solvents of only modest solvent ionizing power, which changes over to an ionization mechanism for solvents of relatively high ionizing power and low nucleophilicity, such as aqueous fluoroalcohols with an appreciable fluoroalcohol content.

Synthesis of 4-Chloro-1,3-Diazobenzene Bent-Cores Liquid Crystal and Characterizations of Its Mesogenic Behaviors and Photosensitivity

<p></p><p>Azobenzene-based bent-core liquid crystals demonstrate a variety of mesomorphic behaviours and photochromic properties which are desirable for optical switching. In this study, a novel compound <b>4c</b> was synthesised by adding azo functional groups and chlorine substituent to the central bent-core. The structure, mesogenic properties, and photosensitivity of <b>4c</b> was characterised by fourier-transform infrared spectroscopy (FTIR), ¹H and ¹³C nuclear magnetic resonance (NMR), mass spectrometry (MS), differential scanning calorimetry (DSC), polarised optical microscopy (POM), and ultraviolet–visible spectroscopy (UV-Vis). The experimental results show that <b>4c</b> exhibited a broad temperature window of nematic phase (63.8 °C), rapid <i>trans – cis</i> photoisomerisation in seconds, and high <i>cis</i> fraction of 0.81. At room temperature, <b>4c </b>dissolved in ethyl acetate can reach photostationary state in 10 seconds. At 95 °C, nematic <b>4c</b> became isotropic under UV irradiation in 3 seconds and can be restored to be nematic under natural visible light in 5 seconds. Quantum mechanics calculations confirm that using azos instead of esters as the central linkages can effectively reduce the molecular dipole moment and enhance the overall molecular polarisabilities, which promotes favourable mesogenic and photonic behaviours. This study provides novel synthesis route and synergistic approach to advance the design of azobenzene bent-core liquid crystals.</p><p></p>

Synthesis of 4-Chloro-1,3-Diazobenzene Bent-Cores Liquid Crystal and Characterizations of Its Mesogenic Behaviors and Photosensitivity

<p></p><p>Azobenzene-based bent-core liquid crystals demonstrate a variety of mesomorphic behaviours and photochromic properties which are desirable for optical switching. In this study, a novel compound <b>4c</b> was synthesised by adding azo functional groups and chlorine substituent to the central bent-core. The structure, mesogenic properties, and photosensitivity of <b>4c</b> was characterised by fourier-transform infrared spectroscopy (FTIR), ¹H and ¹³C nuclear magnetic resonance (NMR), mass spectrometry (MS), differential scanning calorimetry (DSC), polarised optical microscopy (POM), and ultraviolet–visible spectroscopy (UV-Vis). The experimental results show that <b>4c</b> exhibited a broad temperature window of nematic phase (63.8 °C), rapid <i>trans – cis</i> photoisomerisation in seconds, and high <i>cis</i> fraction of 0.81. At room temperature, <b>4c </b>dissolved in ethyl acetate can reach photostationary state in 10 seconds. At 95 °C, nematic <b>4c</b> became isotropic under UV irradiation in 3 seconds and can be restored to be nematic under natural visible light in 5 seconds. Quantum mechanics calculations confirm that using azos instead of esters as the central linkages can effectively reduce the molecular dipole moment and enhance the overall molecular polarisabilities, which promotes favourable mesogenic and photonic behaviours. This study provides novel synthesis route and synergistic approach to advance the design of azobenzene bent-core liquid crystals.</p><p></p>

Structural Evidence of Photoisomerization Pathways in Fluorescent Proteins

<p>Double-bond photoisomerization in molecules such as the green fluorescent protein (GFP) chromophore can occur either via a volume-demanding one-bond-flip pathway or via a volume-conserving hula-twist pathway. Understanding the factors that determine the pathway of photoisomerization would inform the rational design of photoswitchable GFPs as improved tools for super-resolution microscopy. In this communication, we reveal the photoisomerization pathway of a photoswitchable GFP, rsEGFP2, by solving crystal structures of <i>cis</i> and <i>trans</i> rsEGFP2 containing a monochlorinated chromophore. The position of the chlorine substituent in the <i>trans</i> state breaks the symmetry of the phenolate ring of the chromophore and allows us to distinguish the two pathways. Surprisingly, we find that the pathway depends on the arrangement of protein monomers within the crystal lattice: in a looser packing, the one-bond-flip occurs, whereas in a tighter packing (7% smaller unit cell size), the hula-twist occurs.</p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p> <p> </p>

Structural Evidence of Photoisomerization Pathways in Fluorescent Proteins

<p>Double-bond photoisomerization in molecules such as the green fluorescent protein (GFP) chromophore can occur either via a volume-demanding one-bond-flip pathway or via a volume-conserving hula-twist pathway. Understanding the factors that determine the pathway of photoisomerization would inform the rational design of photoswitchable GFPs as improved tools for super-resolution microscopy. In this communication, we reveal the photoisomerization pathway of a photoswitchable GFP, rsEGFP2, by solving crystal structures of <i>cis</i> and <i>trans</i> rsEGFP2 containing a monochlorinated chromophore. The position of the chlorine substituent in the <i>trans</i> state breaks the symmetry of the phenolate ring of the chromophore and allows us to distinguish the two pathways. Surprisingly, we find that the pathway depends on the arrangement of protein monomers within the crystal lattice: in a looser packing, the one-bond-flip occurs, whereas in a tighter packing (7% smaller unit cell size), the hula-twist occurs.</p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p> <p> </p>