Evidence for a monomeric structure of nonribosomal Peptide synthetases

Nonribosomal peptide synthetases (NRPS) are multimodular biocatalysts that bacteria and fungi use to assemble many complex peptides with broad biological activities. The same modular enzymatic assembly line principles are found in fatty acid synthases (FAS), polyketide synthases (PKS), and most recently in hybrid NRPS/PKS multienzymes. FAS as well as PKS are known to function as homodimeric enzyme complexes, raising the question of whether NRPS may also act as homodimers. To test this hypothesis, biophysical methods (size exclusion chromatography, analytical equilibrium ultracentrifugation, and chemical crosslinking) and biochemical methods (two-affinity-tag-system and complementation studies with enzymes being inactivated in different catalytic domains) were applied to NRPS subunits from the gramicidin S (GrsA-ATE), tyrocidine (TycB(1)-CAT and TycB(2-3)-AT.CATE), and enterobactin (EntF-CATTe) biosynthetic systems. These methods had revealed the dimeric structure of FAS and PKS previously, but all three NRPS systems investigated are functionally active as monomers.     

Electron impact and chemical ionization mass spectra of some unsaturated anomeric C-glycosides

Electron impact mass spectra at 70 eV electron energy and chemical ionization mass spectra with ammonia as the reagent gas are reported for certain unsaturated C-glycosides. Comparisons are made between the mass spectra of anomeric pairs of these glycosides.     

Syntheses,structure, and photoluminescence properties of the 1-dimensional chain compounds [(TPA)(2)Au][Au(CN)(2)] and (TPA)AuCl (TPA = 1,3,5-triaza-7-phosphaadamantane)

The structures and temperature-dependent photoluminescence properties of the one-dimensional compounds [(TPA)(2)Au][Au(CN)(2)], 1, and (TPA)AuCl, 2, are reported. An extended linear chain with weak Au.Au interactions along the c-axis is evident in the structure of 1, and a helical chain with a pitch of 3.271 A is seen for 2. The intrachain Au...Au separation is 3.457(1) and 3.396(2) A in 1 and 2, respectively. As a result of this weak Au...Au interaction, the physical properties of these compounds are anisotropic. Scanning electron microscopy (SEM) studies indicate that single crystals of both compounds are noninsulating. Single crystals of 1 do not luminesce visibly, but grinding the crystals finely initiates a strong green emission under UV irradiation at room temperature. Further interesting optical properties include the dependence of the emission profile of the powder on the exciting wavelength and luminescence thermochromism. When excited at wavelengths < 360 nm, the powder exhibits a blue emission at 425 nm while excitation with longer wavelengths leads to a green emission near 500 nm. While the green emission dominates at ambient temperature, cooling to cryogenic temperatures leads to the dominance of the blue emission. Fibers of 2 are luminescent at 78 K with an emission band centered at 580 nm. Compound 1 crystallizes in the orthorhombic space group Cccm (No. 66), with Z = 2, a = 6.011(1) A, b = 23.877(6) A, c = 6.914(1) A, V = 992.3(3) A(3), and R = 0.0337. Compound 2 crystallizes in the trigonal space group R3 (No. 148), with Z = 18, a = 22.587(2) A, b = 22.587(2) A, c = 9.814(2) A, V = 4336 A(3), and R = 0.0283.     

Physical,chemical and biological studies on transition metal complexes of chelating tridentate ligand

Summary The interaction of 1-benzoin-4-phenylthiosemicarbazone (H₂ BPS) with some transition metal ions has been investigated. The ligand can function as a tridentate chelating agent, giving M(HBPS)₂ and M(BPS). Potentiometric studies proved that the mechanism of chelation is based on hydrogen ion liberation. Spectral studies in solution show that the ligand could be used for the microdetermination of Cu^IIions. On the basis of magnetic and spectral data, an octahedral structure is proposed for the Co^II and Ni^II complexes and a square-planar structure for the Cu^II complex. The corrosion inhibition of aluminium in Cl₃CCO₂H using H₂BPS is studied. The electrical conductivity of H₂BPS and of its complexes have been measured. The ligand shows an activation energy in the range of semiconducting materials. The antimicrobial activity of all compounds has also been demonstrated.     

Synthesis of new triphenodithiazine- and indolocarbazolediones of biological interest

Tetrabromo-p-benzoquinone reacted with excess aromatic amines to give 2,5-dirylamino-3,6-dibromo-p-benzoquinones. The latter molecules on heating with sodium sulfide in alcohol in the presence of air gave triphenodithiazinediones. Heating with copper powder in nitrobenzene transformed these compounds into the respective indolocarbazolediones. Comparative antimicrobial and antifungal activities of the studied compounds were determined and discussed.     

Die Oxydationswirkung von Natrium-1,2-naphthochinon-4-sulfonat

Zusammenfassung Die Reaktionen von Natrium-1,2-naphthochino-4-sulfonat mit -Aminosäuren, primären aliphatischen Aminen, Dicarbonsäuren, aliphatischen -Hydroxysäuren und primären Alkoholen werden beschrieben. In allen diesen Fällen reagiert Natrium-1,2-naphtochinon-4-sulfonat als Oxydationsmittel und wird zu dem entsprechenden Diphenol reduziert.     

Allylsilane‐Modified Amino Acids from the Claisen Rearrangement

The Claisen rearrangement of the N‐protected, silylated allyl glycinates 11 and 12 led to the formation of allyl/silyl‐functionalized amino acids 13 and 14 in yields up to 80%. The diastereoisomer ratio varied from 2 : 1 to 29 : 1 for 11mb , and from 2 : 1 to 46 : 1 (syn/anti) for 12mb , depending on reaction conditions, as shown by X‐ray crystallographic analysis of 14mb . The relationship between the size of the alkyl groups on the chlorosilane reagent (Me₂R″SiCl, R″=Cl, Me, t‐Bu, Ph) used as an enolate trap and the observed stereoselectivity was investigated in the case of the Ireland–Claisen variant. Me₃SiCl gave the best results. However, the size of the alkyl groups on the silylated ester (Me₂R″Si, R=Me, t‐Bu, Ph, i‐Pr) did not exert a significant effect on the diastereoselectivity or yield of the rearrangement.     

Potentiometric Membrane Sensor for Determination of Saccharin

A potentiometric poly(vinyl chloride) membrane sensor for determination of saccharin is described. It is based on the use of Aliquat 336S-saccharinateion-pair as an electroactive material in plasticized PVC membranes with o-nitrophenyloctylether or dioctylphthalate. The sensor is conditioned for at least two days in 0.1 mol L⁻¹ sodium saccharinate before use. It exhibits fast, stable and Nernstian response for saccharinate ions over the concentration range of 1.0 × 10⁻¹–5.0 × 10⁻⁵ mol L⁻¹ and pH range of 4.5–11. The sensor is used for determination of saccharin in some dosage forms. Results with an average recovery of 101% and a mean standard deviation of 0.2% are obtained which is compared favourably with data obtained using the British pharmacopoeia method. The sensor shows reasonable selectivity towards saccharin in presence of many anions and natural sweeteners.     

Non-covalent assemblies of negatively charged boronated porphyrins with different cationic moieties

A unique approach to non-covalent electron and energy transfer is described that is based on the formation of salt bridges between oppositely charged porphyrin units. A new class of electrostatically linked dimeric and pentameric porphyrins was synthesized by interaction of novel anionic boron containing porphyrins such as 5-(benzamidodecahydro-closo-dodecaborate)-10,15,20-triphenylporphyrin (N1) and meso-tetrakis-benzamidodecahydro-closo-dodecaborate)porphyrin (N2) and a variety of cationic meso-tetraarylporphyrin units. A bipyridine linked dimer (N1 · bpy · N1) was also prepared by employing N,N′-dimethyl-4,4′-bipyridinium (bpy) as a spacer between two mono-anionic species. A quinone-porphyrin dyad was also prepared for electron or energy transfer demonstration. All the synthesized assemblies were characterized by NMR, IR, UV-Vis, and mass spectroscopy. Significant spectral changes occurred in the absorption spectra of these non-covalent porphyrin assemblies compared to those of the reference monomers, indicating the presence of electronic interaction between the adjacent porphyrin units. Resonance light scattering was also used to study the formation of these assemblies in solution.     

Enaminones in heterocyclic synthesis: Synthesis and chemical reactivity of 3‐anilino‐1‐substituted‐2‐propene‐1‐ one

The 3‐anilinoenones 3a,b were prepared from the corresponding 3‐dimemyl‐aminopropenones. The reactivity of 3a,b towards a variety of carbon and nitrogen nucleophiles as well as naphthoquinones is reported.