The orthosomycin family of antibiotics-II : The13C NMR spectra of flambamycin and its derivatives

The important features of the ¹³C NMR spectra of flambamycin (1a) and its degradation products (22–12) are discussed, and assignments are made. The general use of ¹³C NMR spectroscopy for structural investigations of the orthosomycin family of antibiotics is summarised.     

Influence of Polydispersity on Adsorption of Nanoparticles

The adsorption of polydisperse, interacting nanoparticles is studied experimentally and discussed in terms of the random sequential adsorption model. Two kinds of polystyrene particles with different size variation (41+/-6 and 107+/-5 nm) were used in adsorption experiments at or close to saturation. The dried monolayer particle films were analyzed with scanning electron microscopy. Selective adsorption of smaller particles resulted in altered size distributions on the surface compared to that in solution. Varying the ionic strength was seen to influence the effective polydispersity of the particles. With increasing salt concentration there was a relative increase in the adsorption of smaller particles, resulting in a large shift toward smaller particle sizes in the size distribution on the surface. Polydispersity gave a slight increase in coverage at high salt concentrations and a decrease in the ordering of the particles on the surface. Copyright 2001 Academic Press.     

Keto complexes from the oxidation of η6-xanthene or thioxanthene-η5-cyclopentadienyliron cation and some reactions of the fluorenone and xanthone complexes

Ligand exchange between xanthene and ferrocene gave the η⁶-xanthene-η⁵-cyclopentadienyliron cation which was oxidized in situ with KMnO₄ to give the η⁶-xanthone-η⁵-cyclopentadienyliron cation (III). Similar oxidation of the η⁶-thioxanthene-η⁶-cyclopentadienyliron cation gave a mixture of the thioxanthone complex IV and the corresponding complexed sulfone V. III and the η⁶-fluorenone-η⁵-cyclopentadienyliron cation (VI) were utilized as reactants in the synthesis of new complexes via reactions with a number of reagents. Stereospecific exo-addition to give complexed endo-alcohols were observed in the reaction of III with NaBH₄, NaBD₄ or CH₃Li, and in the reaction of VI with CH₃Li, the anion of acetonitrile, the anion of nitromethane or the phenylacetylide anion. Ring opening reactions to give complexed o,o′-disubstituted benzophenones were observed when III was treated with the anion of acetonitrile, the anion of nitromethane, methylamine, cyclohexylamine, benzylamine or pyrrolidine.     

Fluorimetric assay of ergotamine

Studies on the fluorescence properties of ergotamine in water at various pH values, and in several organic solvents are described. An assay procedure for ergotamine, based on its intense fluorescence in ethanol, is presented. Extraction of ergotamine into benzene from basic aqueous solution is followed by transfer of the extract to ethanol for fluorescence determination. The plot of fluorescence intensity vs. concentration is linear up to 5 μg ml^?1, and the assay has a limit of detection of 0.002 μg ml^?1. Reproducibility data at the 2.5-μg ml^?1 level are given.     

ORGANIZATION OF PIGMENT-PROTEIN COMPLEXES INTO MACRODOMAINS IN THE THYLAKOID MEMBRANES OF WILD-TYPE and CHLOROPHYLL fo-LESS MUTANT OF BARLEY AS REVEALED BY CIRCULAR DICHROISM

The organization of pigment-protein complexes into large chiral macrodomains was investigated in wild-type and chlorophyll b-less mutant thylakoid membranes of barley. The variations in the anomalous circular dichroism bands and in the angular-dependence of circular intensity differential scattering showed that in wild-type chloroplasts, the formation of macrodomains was governed by interactions of the light-harvesting chlorophyll alb complexes (LHCII). Two external factors could be identified which regulate the parameters of the anomalous circular dichroism signal: (i) electrostatic screening by divalent cations under conditions that favor membrane stacking and (ii) the osmotic pressure of the medium, which is suggested to affect the lateral interactions between complexes and influence the packing-density of particles. These two factors governed preferentially the negative and the positive anomalous circular dichroism signals, respectively. In the chlorina f-2 mutant thylakoid membranes, deficient in most chlorophyll b binding proteins, the formation of macrodomains which gave rise to the anomalous circular dichroism signals was still regulated by these same external factors. However, in the absence of major LHCII polypeptides the formation of macrodomains was apparently mediated by other complexes having weaker interaction capabilities. As a consequence, the size of the macrodomains under comparable conditions appeared smaller in the mutant than in the wild-type thylakoid membranes. Circular dichroism is a valuable probe for examining the long-range interactions between pigment-protein complexes which participate in the formation and stabilization of membrane ultrastruc-ture. A functional role of macrodomains in long-range energy migration processes is proposed.     

NETROPSIN: INTERACTION WITH ULTRAVIOLET IRRADIATED DNA

Abstract—Ultraviolet irradiation of double-stranded DNA reduces the circular dichroism (i < 300 nm) induced when the basic peptide antibiotic netropsin (Nt) is added to DNA subsequent to thc irradiation compared to the CD induced by the same concentrations of Nt added to unirradiated DNA. Nt is known to bind to A T base pairs in duplex DNA but will not bind to single-stranded DNA. The reduction in the maximum induced CD observed with saturating concentrations of Nt is a linear function of the concentration of pyrimidine dimers which. along with other dinucleotide photoproducts. form short disrupted regions in duplex DNA. The decrease in the CD of Nt bound to irradiated DNA could be due to elimination of potential Nt sites in the vicinity of a dimer. reduction in the average magnitude of the CD of Nt bound near a dimer or various combinations of these effects. In addition there is a reduction in the average binding constant for Nt bound to irradiated DNA compared to unirradiated DNA suggesting that formation of dinucleotide photoproducts either tends to preferentially eliminate the tighter binding sites or that tighter sites are converted to weaker ones. A simple model suggests that no more than one-third to one-half of the pyrimidine dimcrs formed in DNA completely eliminate a Nt site.     

ACTION SPECTRA FOR KILLING NON-DIVIDING NORMAL HUMAN AND XERODERMA PIGMENTOSUM CELLS

Abstract— Non-dividing human cells degenerate and eventually detach from a culture vessel surface when exposed to UV light. Action spectra for this kind of cell inactivation were determined using eight monochromatic wavelengths from 240 to 313 nm and both a normal DNA excision-repair-proficient strain and a repair-deficient Xeroderma pigmentosum (XP12BE) strain. The action spectra for both strains have similar shapes with a broad peak between 254 and 280 nm followed by a steep decline at wavelengths greater than 280 nm. The relative action spectra are similar to those for inactivation of reproductive capacity and pyrimidine dimer formation in rodent cells suggesting that the critical target and critical damage for inactivation of non-dividing human cells is DNA and damage to DNA, respectively. Normal repair-proficient cells are 5–7 times more resistant at all wavelengths, based on a comparison of D_o values, than repair-deficient XP12BE cells, supporting the conclusion that the inactivating damage at all wavelengths is to DNA.     

Ferroelectric liquid crystals induced by dopants with axially chiral 2,2'-spirobiindan-1,1'-dione cores

The axially chiral dopants (R)-5,5'-, 5,6'-, and 6,6'-diheptyloxy-2,2'-spirobiindan-1,1'-dione ((R)-2, -3, and -4) were synthesized in optically pure form, and their absolute configurations were assigned by the exciton chirality method using circular dichroism spectroscopy. These new compounds were doped in four achiral liquid crystal hosts to give chiral smectic C* (SmC*) phases with spontaneous polarizations (Ps) that vary with the core structure of the host. The spontaneous polarization induced by the 5,5'-dialkoxy derivative (R)-2 is uniformly positive, whereas that induced by the 6,6'-dialkoxy derivative (R)-4 is uniformly negative and shows a different trend in host dependence. Polarization power (delta(p)) values range from +21 nC/cm2 for (R)-2 in 2',3'-difluoro-4-heptyl-4' '-nonyl-p-terphenyl (DFT) to -1037 nC/cm2 for (R)-4 in 4-(4'-heptyl[1,1'-biphen]-4-yl)-1-hexylcyclohexanecarbonitrile (NCB76). The unsymmetrical dopant (R)-3 behaves like a hybrid of the two symmetrical isomers, with lower absolute values of delta(p), on average, and varying signs of Ps. 2H NMR spectra of the doped mixtures using racemic mixtures of 2-4 with -OCD2C6H13 side-chains, in combination with phase diagrams, show that relatively minor changes in the dopant structure, that is, moving the alkoxy side-chains from the 5,5' to the 6,6' positions of the spirobiindandione core, have profound effects on dopant-host compatibility, and on the propensity of the dopant to exert chiral perturbations in the host environment. The variations in sign and magnitude of delta(p) as a function of alkoxy group positions are rationalized based on an analysis of zigzag conformations that conform to the binding site of the SmC host according to the Boulder model.     

PHOTOPHYSICS AND PHOTOCHEMISTRY OF PHOTOREACTIVATION

Abstract— Photoreactivating enzyme (PRE) monomerizes cyclobutyl pyrimidine dimers formed in DNA by UV light ( Λ < 300 nm). The enzyme requires near UV and visible wavelengths (300 < Λ < 600 nm) for activity. Possible mechanisms of action of the PRE are suggested by non-enzymatic processes in which pyrimidine dimers are monomerized by UV and visible light. Two such non-enzymatic processes are (a) photolysis of dimers resulting from direct absorption of UV, and (b) sensitized monomerization involving charge transfer complexes. Several lines of evidence suggest that the mechanism of action of the PRE more closely resembles (b) than (a). Recent experiments on the PRE from E. coli reveal the presence of new long wavelength absorption which may indicate the presence of a ground state complex. The known ability of PRE to monomerize dimers of thymine, cytosine and uracil suggests that the carbonyl groups at 2 position of the pyrimidine ring may be important in the interaction between enzyme and dimer.     

VACUUM ULTRAVIOLET CIRCULAR DICHROISM OF DOUBLE STRANDED NUCLEIC ACIDS

The vacuum ultraviolet (VUV) circular dichroism (CD) of double stranded DNA and RNA is greater in amplitude than the CD of these molecules for wavelengths longer than 200 nm. The amplitude of the VUV-CD depends on the base composition of DNA, with guanine-cytosine base pairs contributing more intensity than adenine-thymine base pairs. The shape and amplitude of the VUV-CO are better indicators of nucleic acid conformation (A, B or Z) than are those of the longer wavelength CD. We illustrate the unique features of VUV-CD with specific examples. In the presence of Cs⁺ and ethanol, VUV-CD reveals that poly(dA-dC)poly(dG-dT) forms a right handed double helix despite the inversion of the longer wavelength CD, which usually is used as a benchmark for the left-handed form. The greater magnitude of the VUV-CD of DNA and RNA compared to longer wavelengths means that the VUV-CD is less susceptible to distortion by the induced CD of UV-absorbing ligands like mitomycin C and N-2-acetylaminofluorene.