THE EFFECTS OF LIQUID HOLDING ON NEAR-UV(300–400 nm) IRRADIATED ESCHERICHIA COLI STRAINS DIFFERING IN NEAR AND FAR-UV RADIATION SENSITIVITY

Abstract— Stationary phase cells from four Escherichia coli strains differing in near- (nur vs. nur ₊) and far-UV (recAl vs. recA₊) radiation sensitivity were subjected to near-UV radiation (NUV) in 0.85% saline. Although the NUV-irradiated cultures yielded increased colony numbers following 24 h of liquid holding (LH), a fluctuation test for each experiment showed that the observed increases were not due to recovery but were in fact due to cell multiplication. The decline in viability observed after NUV with liquid holding using the fluctuation test was equivalent in strains RT2, 3 and 4 while the decline observed with RT1 was less marked. The discrepancy between LH involving cell densities of 10₈-10₉ and 1–4 cells/m/ can be resolved by assuming that with dense cell suspensions, NUV-induced membrane damage leads to leakage or lysis, supplying sufficient nutrients to allow growth of undamaged, surviving cells.     

13C-NMR. Spectroscopy of Naturally Occuring Substances. XLII. Conformational analysis of quebrachamine-like indole alkaloids and related substances

The ¹³C shifts of 16α- and 16β-substituted derivatives of quebrachamine, 14,15-dehydroquebrachamine, cleavamine, 15,20α-dihydrocleavamine and 15,20β-dihydrocleavamine are determined and correlated with possible conformations of these tetracycles. The method of analysis of the C(16) configuration of these compounds, which emanated from this study, is used for the determination of the configuration of the site of coupling of vindoline and cleavamine β-chloroindolenine.     

Crystal structure of supramolecular complexes formed by 18-crown-6 andcis-anti-cis-dicyclohexano-18-crown-6 (host) with 3,4-diaminofurazane (guest)

An X-ray—diffraction study is reported for two molecular complexes containing 3,4-diamino-1,2,5-oxadiazole as guest (G) with 18-crown-6 (18-C-6) andcis-anti-cis-dicyclohexano-18-crown-6 (DCH-6B) as host. Both complexes are of the polymeric-chain structure with the guest molecule bridging two crown neighbours. ComplexI: [18-C-6*G*H₂O], 111, monoclinic,P2₁/n,a=8.171(1),b=15.042(2),c=16.209(6) Å, =101.15(2)°, finalR-factor 0.068. ComplexII: [DCH-6B*G], 11, monoclinicC2/c,a=21.212(4),b=9.380(2),c=13.049(3) Å, =108.61(3)°, finalR 0.047.     

Synthesis of substituted imidazoles via organocatalysis

A one-pot synthesis of substituted imidazoles is described. The cornerstone of this methodology involves the thiazolium-catalyzed addition of an aldehyde to an acyl imine to generate the corresponding alpha-ketoamide in situ followed by ring closure to the imidazole in a one-pot sequence. The extension of this methodology to the one-pot synthesis of substituted oxazoles and thiazoles is also described. [reaction: see text]     

Synthesis, X-ray diffraction analysis and NMR studies of (Z)-2-methyl-3-triphenylstannyl-3-pentene-2-ol

The synthesis of (Z)-2-methyl-3-triphenylstannyl-3-pentene-2-ol and its characterization by an X-ray diffraction study and multinuclear NMR are reported. The tin atom exhibits a distorted tetrahedral SnC₄ geometry with the four Sn---C bond distances experimentally equivalent. The slight distortion from the ideal tetrahedral geometry is because of the presence of a weak intramolecular HO → Sn interaction of 3.012(3) Å which produces a loose four-membered ring. The title compound was characterized in solution by ¹H, ¹³C and ¹¹⁹Sn NMR, and the persistence of the weak intramolecular HO → Sn coordination in solution was revealed by ¹³C and ¹¹⁹Sn secondary isotope multiplet of partially labelled entities (SIMPLE-NMR) experiments.     

Bis-substituted benzo-15-crown-5 ethers as ion carriers in potassium ion-selective electrodes

Lipophilic bis-substituted ester and ether derivatives of benzo-15-crown-5 have been synthesised. The correlation between the structure and potentiometric ion-selectivity has been studied in PVC membrane ion-selective electrodes. An ion-selective potassium sensitive electrode based on 4,5-bis (biphenyloxymethyl)benzo-15-crown-5 exhibited the best electrode properties. The detection limit was loga _K = -5.4; logK _K,Na ^ppot = -3.5. The effect of the lipophilicity of neutral carriers upon electrode performance has been also discussed.     

Long-range fluorine-proton coupling in 1,2,4-triazole derivatives

Several 1,2,4-triazole derivatives containing a 2-fluorophenyl substituent at either the 3- or 5-position and a methyl group at the 4-position were synthesized. These derivatives exhibit long-range ¹⁹F-¹H and ¹⁹F-¹³C through-space coupling in their ¹H and ¹³C nmr spectra between the fluorine and the 4-methyl group. The close spatial proximity of these nuclei was confirmed by X-ray analysis and by fluorine irradiated proton observe ({¹⁹F}-¹H) NOE difference spectroscopy.     

Crystallographic and bioinformatic studies on restriction endonucleases: inference of evolutionary relationships in the "midnight zone" of homology

Type II restriction endonucleases (ENases) cleave DNA with remarkable sequence specificity. Their discovery in 1970 and studies on molecular genetics and biochemistry carried out over the past four decades laid foundations for recombinant DNA techniques. Today, restriction enzymes are indispensable tools in molecular biology and molecular medicine and a paradigm for proteins that specifically interact with DNA as well as a challenging target for protein engineering. The sequence-structure-function relationships for these proteins are therefore of central interest in biotechnology. However, among numerous ENase sequences, only a few exhibit statistically significant similarity in pairwise comparisons, which was initially interpreted as evidence for the lack of common origin. Nevertheless, X-ray crystallographic studies of seemingly dissimilar type II ENases demonstrated that they share a common structural core and metal-binding/catalytic site, arguing for extreme divergence rather than independent evolution. A similar nuclease domain has been also identified in various enzymes implicated in DNA repair and recombination. Ironically, following the series of crystallographic studies suggesting homology of all type II ENases, bioinformatic studies provided evidence that some restriction enzymes are in fact diverged members of unrelated nuclease superfamilies: Nuc, HNH and GIY-YIG. Hence, the restriction enzymes as a whole, represent a group of functionally similar proteins, which evolved on multiple occasions and subsequently diverged into the "midnight zone" of homology, where common origins within particular groups can be inferred only from structure-guided comparisons. The structure-guided approaches used for this purpose include: identification of functionally important residues using superposition of atomic coordinates, alignment of sequence profiles enhanced by secondary structures, fold recognition, and homology modeling. This review covers recent results of comparative analyses of restriction enzymes from the four currently known superfamilies of nucleases with distinct folds, using crystallographic and bioinformatic methods, with the emphasis on theoretical predictions and their experimental validation by site-directed mutagenesis and biochemical analyses of the mutants.     

Synthesis and properties of water-soluble gold colloids covalently derivatized with neutral polymer monolayers

Citrate-capped gold nanoparticles as well as planar gold surfaces can be efficiently grafted with a covalently attached polymer monolayer a few nanometers thick, by simple contact of the metal surface with dilute aqueous solutions of hydrophilic polymers that are end-capped with disulfide moieties, as shown by UV/vis absorption, dynamic light scattering, and surface plasmon resonance studies. The hydrophilic polymer-coated gold colloids can be freeze-dried and stored as powders that can be subsequently dissolved to yield stable aqueous dispersions, even at very large concentrations. They allow for applying filtrations, gel permeation chromatography, or centrifugation. They do not suffer from undesirable nonspecific adsorption of proteins while allowing the diffusion of small species within the hydrogel surface coating. In addition, specific properties of the original hydrophilic polymers are retained such as a lower critical solution temperature. The latter feature could be useful to enhance optical responses of functionalized gold surfaces toward interaction with various substrates.     

2,3‐Difluoro‐4‐formyl­phenyl­boronic acid

The mol­ecule of the title compound, 2,3‐F₂‐4‐(CHO)C₆H₂B(OH)₂ or C₇H₅BF₂O₃, contains a formyl group coplanar with the benzene ring. The boronic acid group is twisted with respect to the benzene ring plane. The mol­ecules are organized into infinite chains via inter­molecular O—H⋯O hydrogen bonds. These chains are additionally connected via strong O—H⋯O hydrogen bonds, producing a folded layer structure perpendicular to the a axis. These layers are paired due to B⋯F inter­actions.