Monitoring ssDNA Binding to the DnaB Helicase from Helicobacter pylori by Solid‐State NMR Spectroscopy

DnaB helicases are bacterial, ATP‐driven enzymes that unwind double‐stranded DNA during DNA replication. Herein, we study the sequential binding of the “non‐hydrolysable” ATP analogue AMP‐PNP and of single‐stranded (ss) DNA to the dodecameric DnaB helicase from Helicobacter pylori using solid‐state NMR. Phosphorus cross‐polarization experiments monitor the binding of AMP‐PNP and DNA to the helicase. ¹³C chemical‐shift perturbations (CSPs) are used to detect conformational changes in the protein upon binding. The helicase switches upon AMP‐PNP addition into a conformation apt for ssDNA binding, and AMP‐PNP is hydrolyzed and released upon binding of ssDNA. Our study sheds light on the conformational changes which are triggered by the interaction with AMP‐PNP and are needed for ssDNA binding of H. pylori DnaB in vitro. They also demonstrate the level of detail solid‐state NMR can provide for the characterization of protein–DNA interactions and the interplay with ATP or its analogues.     

Ascospiroketals A and B, unprecedented cycloethers from the marine-derived fungus Ascochyta salicorniae

Chemical investigation of the marine-derived fungus Ascochyta salicorniae led to the isolation of two novel natural products, ascospiroketals A (1) and B (2). From a biosynthetic standpoint, the compounds possess new ring systems. [structure: see text].     

Blank problems in trace analysis of diethylhexyl and dibutyl phthalate: investigation of the sources, tips and tricks

The analysis of phthalates, particularly that of di(2-ethylhexyl)phthalate (DEHP) and dibutyl phthalate (DBP), is notorious for blank problems. Methods and tools are listed to identify the sources and reduce the system contamination to below 1 pg DEHP and DBP or below 1 ng mL⁻¹ of sample solution. Once direct contact with phthalate-containing plastic articles is ruled out, the air is the major source, primarily via absorption to the surfaces of laboratory glass ware. A main improvement was achieved by cleaning solvents with aluminium oxide permanently left in the reservoirs. The data enables to estimate the contamination to be expected and to design methods keeping blanks below a critical threshold.     

Ion-neutral reactions in the ion source of a mixture of CO2/CH3OH, CO2/C2H5OH, and CO2/2-C3H7OH by packed capillary supercritical fluid chromatography-mass spectrometry (SFC-MS)

Ion neutral reactions in the gas phase in mixtures of ROH/CO(2), R = CH(3), C(2)H(5), and 2-C(3)H(7) were studied by supercritical fluid chromatography-mass spectrometry (SFC-MS). Three main reaction series were found for this system; ionization followed by alpha-cleavage, formation of clusters, and formation of protonated dialkyl ethers from the corresponding alcohol. The ion chemistries were similar for the three alcohols, but that of 2-propanol was somewhat more complex.     

Iterative tandem catalysis of secondary diols and diesters to chiral polyesters

The well-known dynamic kinetic resolution of secondary alcohols and esters was extended to secondary diols and diesters to afford chiral polyesters. This process is an example of iterative tandem catalysis (ITC), a polymerization method where the concurrent action of two fundamentally different catalysts is required to achieve chain growth. In order to procure chiral polyesters of high enantiomeric excess value (ee) and good molecular weight, the catalysts employed need to be complementary and compatible during the polymerization reaction. We here show that Shvo's catalyst and Novozym 435 fulfil these requirements. The optimal polymerization conditions of 1,1'-(1,3-phenylene) diethanol (1,3-diol) and diisopropyl adipate required 2 mol% Shvo's catalyst and 12 mg Novozym 435 per mmol alcohol group in the presence of 0.5 M 2,4-dimethyl-3-pentanol as the hydrogen donor. With these conditions, chiral polyesters were obtained with peak molecular weights up to 15 kDa, an ee value up to 99% and with 1-3 % ketone end groups. Also with the structural isomer, 1,4-diol, a chiral polyester was obtained, albeit with lower molecular weight (8.3 kDa) and slightly lower ee (94%). Aliphatic secondary diols also resulted in enantio-enriched polymers but at most an ee of 46 % was obtained with molecular weights in the range of 3.3-3.7 kDa. This low ee originates from the intrinsic low enantioselectivity of Novozym 435 for this type of secondary aliphatic diols. The results presented here show that ITC can be applied to procure chiral polyesters with good molecular weight and high ee from optically inactive AA-BB type monomers.     

Darstellung und Kristallstruktur von Rb4Br2O und Rb6Br4O

Syntheses and Crystal Structures of Rb₄Br₂O and Rb₆Br₄O In the quasi‐binary system RbBr/Rb₂O, the addition compounds Rb₄Br₂O and Rb₆Br₄O are obtained by solid state reaction of the boundary components RbBr and Rb₂O. Crystals of red‐orange Rb₄Br₂O as well as of orange Rb₆Br₄O decompose immediately when exposed to air. Rb₄Br₂O (Pearson code tI14, I4/mmm, a = 544.4(6) pm, c = 1725(2) pm, Z = 2, 175 symmetry independent reflections with I_o > 2σ(I), R₁= 0.0618) crystallizes in the anti K₂NiF₄ structure type; Rb₆Br₄O (Pearson code hR22, R3c, a = 1307.8(3) pm, c = 1646.6(5) pm, Z = 6, 630 symmetry independent reflections with I_o > 2σ(I), R₁ = 0.0759) in the anti K₄CdCl₆ structure type. Both structures contain characteristic ORb₆‐octahedra and can be understood as expanded perovskites, following the general systematics of alkaline metal oxide halides.     

Ferrocenyl‐Functionalised Molybdenum Imido Complexes: An Approach to Redox‐Tunable Olefin Polymerisation Catalysts

[(FcdippN)₂MoCl₂(DME)] ( 1 ) was used as starting material for the synthesis of the novel ferrocenyl‐functionalised complexes [(FcdippN)₂Mo(CH₂CMe₂Ph)₂] ( 2 ), [(FcdippN)₂Mo(OTf)₂(DME)] ( 3 ), and [(FcdippN)Mo(CHCMe₂Ph)(O^tBu)₂] ( 4 ) (Fcdipp = 4‐ferrocenyl‐2,6‐diisopropylphenyl). The crystal structure of 2 was determined. Electrochemical investigations by cyclic voltammetry suggest a communication of the ferrocenyl unit and the molybdenum centre in these compounds. The monoalkylation of [(DippN)₂MoCl₂(DME)] ( 5 ) to [(DippN)₂Mo(CH₂CMe₂Ph)Cl] ( 6 ) (Dipp = 2,6‐diisopropylphenyl) was achieved.