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See detailStructure of triplex DNA in the gas phase.
Arcella, Annalisa; Portella, Guillem; Ruiz, Maria Luz et al

in Journal of the American Chemical Society (2012), 134(15), 6596-606

Extensive (more than 90 microseconds) molecular dynamics simulations complemented with ion-mobility mass spectrometry experiments have been used to characterize the conformational ensemble of DNA ... [more ▼]

Extensive (more than 90 microseconds) molecular dynamics simulations complemented with ion-mobility mass spectrometry experiments have been used to characterize the conformational ensemble of DNA triplexes in the gas phase. Our results suggest that the ensemble of DNA triplex structures in the gas phase is well-defined over the experimental time scale, with the three strands tightly bound, and for the most abundant charge states it samples conformations only slightly more compact than the solution structure. The degree of structural alteration is however very significant, mimicking that found in duplex and much larger than that suggested for G-quadruplexes. Our data strongly supports that the gas phase triplex maintains an excellent memory of the solution structure, well-preserved helicity, and a significant number of native contacts. Once again, a linear, flexible, and charged polymer as DNA surprises us for its ability to retain three-dimensional structure in the absence of solvent. Results argue against the generally assumed roles of the different physical interactions (solvent screening of phosphate repulsion, hydrophobic effect, and solvation of accessible polar groups) in modulating the stability of DNA structures. [less ▲]

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See detailSynthesis of Modified Peptidoglycan Precursor Analogues for the Inhibition of Glycosyltransferase.
Dumbre, S; Derouaux, Adeline ULg; Lescrinier, E et al

in Journal of the American Chemical Society (2012)

The peptidoglycan glycosyltransferases (GTs) are essential enzymes that catalyze the polymerization of glycan chains of the bacterial cell wall from lipid II and thus constitute a validated antibacterial ... [more ▼]

The peptidoglycan glycosyltransferases (GTs) are essential enzymes that catalyze the polymerization of glycan chains of the bacterial cell wall from lipid II and thus constitute a validated antibacterial target. Their enzymatic cavity is composed of a donor site for the growing glycan chain (where the inhibitor moenomycin binds) and an acceptor site for lipid II substrate. In order to find lead inhibitors able to fill this large active site, we have synthesized a series of substrate analogues of lipid I and lipid II with variations in the lipid, the pyrophosphate, and the peptide moieties and evaluated their biological effect on the GT activity of E. coli PBP1b and their antibacterial potential. We found several compounds able to inhibit the GT activity in vitro and cause growth defect in Bacillus subtilis . The more active was C16-phosphoglycerate-MurNAc-(l-Ala-d-Glu)-GlcNAc, which also showed antibacterial activity. These molecules are promising leads for the design of new antibacterial GT inhibitors. [less ▲]

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See detailHighly Efficient Separation of Actinide from Lanthanide by a Phenanthroline-Derived Bis-triazine Ligand
Lewis, Frank W.; Harwood, Laurence M.; Hudson, Michael J. et al

in Journal of the American Chemical Society (2011), 133

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See detailUnexpected tricovalent binding mode of boronic acids within the active site of a penicillin binding protein.
Zervosen, Astrid ULg; Herman, Raphaël ULg; Kerff, Frédéric ULg et al

in Journal of the American Chemical Society (2011)

Boronic acids bearing appropriate side chains are good inhibitors of serine amidohydrolases. The boron usually adopts a tetrahedral conformation, bound to the nucleophilic serine of the active site and ... [more ▼]

Boronic acids bearing appropriate side chains are good inhibitors of serine amidohydrolases. The boron usually adopts a tetrahedral conformation, bound to the nucleophilic serine of the active site and mimicking the transition state of the enzymatic reaction. We have solved the structures of complexes of a penicillin-binding protein, the DD-peptidase from Actinomadura sp. R39, with four amidomethylboronic acids (2,6 dimethoxybenzamidomethylboronic acid, phenylacetamidomethylboronic acid, 2-chlorobenzamidomethylboronic acid, and 2-nitrobenzamidomethylboronic acid) and the pinacol ester derived from phenylacetamidomethylboronic acid. We found that, in each case, the boron forms a tricovalent adduct with Ogamma of Ser49, Ser298, and the terminal amine group of Lys410, three key residues involved in the catalytic mechanism of penicillin-binding proteins. This represents the first tricovalent enzyme-inhibitor adducts observed by crystallography. In two of the five R39-boronate structures, the boronic acid is found as a tricovalent adduct in two monomers of the asymmetric unit and as a monocovalent adduct with the active serine in the two remaining monomers of the asymmetric unit. Formation of the tricovalent complex from a classical monocovalent complex may involve rotation around the Ser49 Calpha-Cbeta bond to place the boron in a position to interact with Ser298 and Lys410, and a twisting of the side chain amide such that its carbonyl oxygen is able to hydrogen bond to the oxyanion hole NH of Thr413. Biphasic kinetics were observed in three of the five cases and details of the reaction between R39 and 2,6-dimethoxybenzamidomethylboronic acid were studied. Observation of biphasic kinetics was not, however, thought to be correlated to formation of tricovalent complexes, assuming that the latter do form in solution. Based on the crystallographic and kinetic results, a reaction scheme for this unexpected inhibition by boronic acids is proposed. [less ▲]

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See detailSelective Binding of O2 over N2 in a Redox-Active Metal-Organic Framework with Open Iron(II) Coordination Sites
Bloch, Eric; Murray, Leslie; Queen, Wendy et al

in Journal of the American Chemical Society (2011), 133

The air-free reaction of FeCl2 and H4dobdc (dobdc4- = 2,5-dioxido-1,4- benzenedicarboxylate) in a mixture of DMF and methanol affords Fe2(dobdc), a metal-organic framework isostructural to M2(dobdc) (M ... [more ▼]

The air-free reaction of FeCl2 and H4dobdc (dobdc4- = 2,5-dioxido-1,4- benzenedicarboxylate) in a mixture of DMF and methanol affords Fe2(dobdc), a metal-organic framework isostructural to M2(dobdc) (M = Mg2+, Mn2+, Co2+, Ni2+, Zn2+). The desolvated form of this material has a BET surface area of 1360 m2/g and features 1-D hexagonal pores lined with coordinatively unsaturated Fe2+ cations. O2 adsorption isotherms indicate Fe2(dobdc) irreversibly binds oxygen at 298 K at a capacity over 0.10 mass fraction, corresponding to the adsorption of one O2 molecule per two framework Fe2+ cations. Remarkably, O2 uptake is reversible and the capacity increases two-fold to 0.19 mass fraction at 211 K. Powder neutron diffraction and IR spectroscopy indicate that in both scenarios O2 is coordinated side-on to the iron centers as superoxide at low temperatures and peroxide at room temperature, an observation that is confirmed by Mössbauer spectroscopy. Ideal adsorbed solution theory calculations reveal that Fe2(dobdc) is a promising material for the separation of O2 from air at temperatures well above those currently used in industrial settings. [less ▲]

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See detailPopulation of nonnative States of lysozyme variants drives amyloid fibril formation.
Buell, Alexander K.; Dhulesia, Anne; Mossuto, Maria F. et al

in Journal of the American Chemical Society (2011), 133(20), 7737-43

The propensity of protein molecules to self-assemble into highly ordered, fibrillar aggregates lies at the heart of understanding many disorders ranging from Alzheimer's disease to systemic lysozyme ... [more ▼]

The propensity of protein molecules to self-assemble into highly ordered, fibrillar aggregates lies at the heart of understanding many disorders ranging from Alzheimer's disease to systemic lysozyme amyloidosis. In this paper we use highly accurate kinetic measurements of amyloid fibril growth in combination with spectroscopic tools to quantify the effect of modifications in solution conditions and in the amino acid sequence of human lysozyme on its propensity to form amyloid fibrils under acidic conditions. We elucidate and quantify the correlation between the rate of amyloid growth and the population of nonnative states, and we show that changes in amyloidogenicity are almost entirely due to alterations in the stability of the native state, while other regions of the global free-energy surface remain largely unmodified. These results provide insight into the complex dynamics of a macromolecule on a multidimensional energy landscape and point the way for a better understanding of amyloid diseases. [less ▲]

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See detailDynamics Characterization of Fully Hydrated Bacterial Cell Walls by Solid-State NMR: Evidence for Cooperative Binding of Metal Ions
Kern, Thomas; Giffard, Mathilde; Hediger, Sabine et al

in Journal of the American Chemical Society (2010), 132

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See detailLocal Cooperativity in an Amyloidogenic State of Human Lysozyme Observed at Atomic Resolution.
Dhulesia, A.; Cremades, N.; Kumita, J. R. et al

in Journal of the American Chemical Society (2010)

The partial unfolding of human lysozyme underlies its conversion from the soluble state into amyloid fibrils observed in a fatal hereditary form of systemic amyloidosis. To understand the molecular ... [more ▼]

The partial unfolding of human lysozyme underlies its conversion from the soluble state into amyloid fibrils observed in a fatal hereditary form of systemic amyloidosis. To understand the molecular origins of the disease, it is critical to characterize the structural and physicochemical properties of the amyloidogenic states of the protein. Here we provide a high-resolution view of the unfolding process at low pH for three different lysozyme variants, the wild-type protein and the mutants I56T and I59T, which show variable stabilities and propensities to aggregate in vitro. Using a range of biophysical techniques that includes differential scanning calorimetry and nuclear magnetic resonance spectroscopy, we demonstrate that thermal unfolding under amyloidogenic solution conditions involves a cooperative loss of native tertiary structure, followed by progressive unfolding of a compact, molten globule-like denatured state ensemble as the temperature is increased. The width of the temperature window over which the denatured ensemble progressively unfolds correlates with the relative amyloidogenicity and stability of these variants, and the region of lysozyme that unfolds first maps to that which forms the core of the amyloid fibrils formed under similar conditions. Together, these results present a coherent picture at atomic resolution of the initial events underlying amyloid formation by a globular protein. [less ▲]

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See detailElectrospray Mass Spectrometry of Telomeric RNA (TERRA) Reveals the Formation of Stable Multimeric G-Quadruplex Structures
Collie, Gavin W.; Parkinson, Gary N.; Neidle, Stephen et al

in Journal of the American Chemical Society (2010), 132(27), 93289334

We report on the self-assembled structures formed by 12-mer, 22-mer, and 45-mer telomeric RNA (telRNA/TERRA) sequences compared to their DNA analogues, as studied by electrospray mass spectrometry ... [more ▼]

We report on the self-assembled structures formed by 12-mer, 22-mer, and 45-mer telomeric RNA (telRNA/TERRA) sequences compared to their DNA analogues, as studied by electrospray mass spectrometry, circular dichroism, and thermal denaturation. The major difference between telomeric RNA and DNA sequences is the ability of telomeric RNA to form higher-order dimeric assemblies, initiated by cation-mediated stacking of two parallel G-quadruplex subunits. The 5′-5′ stacking had been observed recently by NMR for the r(GGGUUAGGGU) 10-mer (Martadinata, H.; Phan, A. T. J. Am. Chem. Soc. 2009, 131, 2570); the present work shows that stacking also occurs for the 22-mer containing four G-tracts and for the 45-mer containing eight G-tracts, suggesting a general structural feature of telomeric RNA. The importance of kinetic effects in multimer formation, unfolding, and structural rearrangements is also highlighted. [less ▲]

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See detailSlow Magnetic Relaxation in a Series of Non-Heme Trigonal Pyramidal Iron(II) Pyrrolide Complexes
Harmann, Hill E; Harris, T David; Freedman, Danna E et al

in Journal of the American Chemical Society (2010), 132

We present a family of novel non-heme trigonal pyramidal iron(II) complexes supported by tris(pyrrolyl-α-methyl)amine ligands of the form [M(solv)n][(tpaR)Fe] (M = Na, R = tert-butyl (1), phenyl (4); M ... [more ▼]

We present a family of novel non-heme trigonal pyramidal iron(II) complexes supported by tris(pyrrolyl-α-methyl)amine ligands of the form [M(solv)n][(tpaR)Fe] (M = Na, R = tert-butyl (1), phenyl (4); M = K, R = mesityl (2), 2,4,6-triisopropylphenyl (3), 2,6-difluorophenyl (5)) and their characterization by X-ray crystallography, cyclic voltammetry, and Mössbauer spectroscopy. Expanding on the initial discovery of slow magnetic relaxation in the recently reported mesityl derivative 2, we report the static and dynamic magnetic properties of a homologous series of high-spin mononuclear iron(II) complexes that exhibit this intriguing behavior. Magnetization experiments reveal large, negative zero-field splitting parameters of D = −48, −40, −36, −26 and −6.2 cm−1 for 1-5, respectively. In the case of 2,6-difluorophenyl 5, high-field EPR experiments provide an independent determination of the zero-field splitting parameters (D = −4.397(9)) that are in reasonable agreement with the magnetization data. Ac susceptibility measurements indicate field-dependent, thermally-activated spin reversal barriers in complexes 1, 2 and 4 of Ueff = 60, 42 and 25 cm−1, respectively. In the case of 1, this value constitutes the highest spin-reversal barrier observed for a mononuclear transition metal complex, a property that has broad implications for the design of molecules that can potentially store and process magnetic information. [less ▲]

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See detailStructural basis of the inhibition of class A beta-lactamases and penicillin-binding proteins by 6-beta-iodopenicillanate
Sauvage, Eric ULg; Zervosen, Astrid ULg; Dive, Georges ULg et al

in Journal of the American Chemical Society (2009), 131(42), 15262-15269

6-Beta-halogenopenicillanates are powerful, irreversible inhibitors of various beta-lactamases and penicillin-binding proteins. Upon acylation of these enzymes, the inhibitors are thought to undergo a ... [more ▼]

6-Beta-halogenopenicillanates are powerful, irreversible inhibitors of various beta-lactamases and penicillin-binding proteins. Upon acylation of these enzymes, the inhibitors are thought to undergo a structural rearrangement associated with the departure of the iodide and formation of a dihydrothiazine ring, but, to date, no structural evidence has proven this. 6-Beta-iodopenicillanic acid (BIP) is shown here to be an active antibiotic against various bacterial strains and an effective inhibitor of the class A beta-lactamase of Bacillus subtilis BS3 (BS3) and the D,D-peptidase of Actinomadura R39 (R39). Crystals of BS3 and of R39 were soaked with a solution of BIP and their structures solved at 1.65 and 2.2 A, respectively. The beta-lactam and the thiazolidine rings of BIP are indeed found to be fused into a dihydrothiazine ring that can adopt two stable conformations at these active sites. The rearranged BIP is observed in one conformation in the BS3 active site and in two monomers of the asymmetric unit of R39, and is observed in the other conformation in the other two monomers of the asymmetric unit of R39. The BS3 structure reveals a new mode of carboxylate interaction with a class A beta-lactamase active site that should be of interest in future inhibitor design. [less ▲]

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See detailToward the characterization of peptidoglycan structure and protein-peptidoglycan interactions by solid-state NMR spectroscopy.
Kern, Thomas; Hediger, Sabine; Muller, Patrick et al

in Journal of the American Chemical Society (2008), 130(17), 5618-9

Solid-state NMR spectroscopy is applied to intact peptidoglycan sacculi of the Gram-negative bacterium Escherichia coli. High-quality solid-state NMR spectra allow atom-resolved investigation of the ... [more ▼]

Solid-state NMR spectroscopy is applied to intact peptidoglycan sacculi of the Gram-negative bacterium Escherichia coli. High-quality solid-state NMR spectra allow atom-resolved investigation of the peptidoglycan structure and dynamics as well as the study of protein-peptidoglycan interactions. [less ▲]

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See detailG-Quadruplex DNA Assemblies: Loop Length, Cation Identity, and Multimer Formation
Smargiasso, Nicolas ULg; Rosu, Frédéric ULg; Hsia, Wei et al

in Journal of the American Chemical Society (2008), 130(31), 10208-10216

G-rich DNA sequences are able to fold into structures called G-quadruplexes. To obtain general trends in the influence of loop length on the structure and stability of G-quadruplex structures, we studied ... [more ▼]

G-rich DNA sequences are able to fold into structures called G-quadruplexes. To obtain general trends in the influence of loop length on the structure and stability of G-quadruplex structures, we studied oligodeoxynucleotides with random bases in the loops. Sequences studied are dGGGWiGGGWjGGGWkGGG, with W = thymine or adenine with equal probability, and i, j, and k comprised between 1 and 4. All were studied by circular dichroism, native gel electrophoresis, UV-monitored thermal denaturation, and electrospray mass spectrometry, in the presence of 150 mM potassium, sodium, or ammonium cations. Parallel conformations are favored by sequences with short loops, but we also found that sequences with short loops form very stable multimeric quadruplexes, even at low strand concentration. Mass spectrometry reveals the formation of dimers and trimers. When the loop length increases, preferred quadruplex conformations tend to be more intramolecular and antiparallel. The nature of the cation also has an influence on the adopted structures, with K+ inducing more parallel multimers than NH4+ and Na+. Structural possibilities are discussed for the new quadruplex higher-order assemblies. [less ▲]

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See detailInfrared Signature of DNA G-Quadruplexes in the Gas Phase
Gabelica, Valérie ULg; Rosu, Frédéric ULg; De Pauw, Edwin ULg et al

in Journal of the American Chemical Society (2008), 130(6), 1810-1

DNA oligonucleotide ions forming G-quadruplex structures were studied in the gas phase using IRMPD spectroscopy. Data interpretation on these large biomolecule ions was made using carefully chosen control ... [more ▼]

DNA oligonucleotide ions forming G-quadruplex structures were studied in the gas phase using IRMPD spectroscopy. Data interpretation on these large biomolecule ions was made using carefully chosen control experiments. The major finding is a fingerprint of hydrogen bonding in the gas phase in the guanine C6=O6 stretching mode, that allows probing the conservation of G-quartets in the gas phase. The experiments demonstrate the conservation of G-quadruplex hydrogen bonds in the human telomeric sequence d(TTAGGG)4. [less ▲]

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See detailOne-step polymer grafting from silicon nitride SPM probes: From isolated chains to brush regime
Gabriel, Sabine ULg; Jérôme, Christine ULg; Jérôme, Robert ULg et al

in Journal of the American Chemical Society (2007), 129(27), 8410

We show that a reactive polymer can be directly grafted from commercial Si3Nx SPM tips, without any intermediate layer. The conditions can be chosen to achieve either an isolated mushroom regime, with ... [more ▼]

We show that a reactive polymer can be directly grafted from commercial Si3Nx SPM tips, without any intermediate layer. The conditions can be chosen to achieve either an isolated mushroom regime, with only one or a few chains accessible at the tip apex, or a brush regime. [less ▲]

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See detailBase-dependent electron photodetachment from negatively charged DNA strands upon 260-nm laser irradiation
Gabelica, Valérie ULg; Rosu, Frédéric ULg; Tabarin, Thibault et al

in Journal of the American Chemical Society (2007), 129(15), 4706-4713

DNA multiply charged anions stored in a quadrupole ion trap undergo one-photon electron ejection (oxidation) when subjected to laser irradiation at 260 nm (4.77 eV). Electron photodetachment is likely a ... [more ▼]

DNA multiply charged anions stored in a quadrupole ion trap undergo one-photon electron ejection (oxidation) when subjected to laser irradiation at 260 nm (4.77 eV). Electron photodetachment is likely a fast process, given that photodetachment is able to compete with internal conversion or radiative relaxation to the ground state. The DNA [6-mer](3-) ions studied here show a marked sequence dependence of electron photodetachment yield. Remarkably, the photodetachment yield (dG(6) > dA(6) > dC(6) > dT(6)) is inversely correlated with the base ionization potentials (G < A < C < T). Sequences with guanine runs show increased photodetachment yield as the number of guanine increases, in line with the fact that positive holes are the most stable in guanine runs. This correlation between photodetachment yield and the stability of the base radical may be explained by tunneling of the electron through the repulsive Coulomb barrier. Theoretical calculations on dinucleotide monophosphates show that the HOMO and HOMO-1 orbitals are localized on the bases. The wavelength dependence of electron detachment yield was studied for dG(6)(3-). Maximum electron photodetachment is observed in the wavelength range corresponding to base absorption (260-270 nm). This demonstrates the feasibility of gas-phase UV spectroscopy on large DNA anions. The calculations and the wavelength dependence suggest that the electron photodetachment is initiated at the bases and not at the phosphates. This also indicates that, although direct photodetachment could also occur, autodetachment from excited states, presumably corresponding to base excitation, is the dominant process at 260 nm. Excited-state dynamics of large DNA strands still remains largely unexplored, and photo-oxidation studies on trapped DNA multiply charged anions can help in bridging the gap between gas-phase studies on isolated bases or base pairs and solution-phase studies on full DNA strands. [less ▲]

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See detailStabilization and structure of telomeric and c-myc region intramolecular G-quadruplexes: The role of central cations and small planar ligands
Gabelica, Valérie ULg; Baker, Erin Shammel; Teulade-Fichou, Marie-Paule et al

in Journal of the American Chemical Society (2007), 129(4), 895-904

A promising approach for anticancer strategies is the stabilization of telomeric DNA into a G-quadruplex structure. To explore the intrinsic stabilization of folded G-quadruplexes, we combined ... [more ▼]

A promising approach for anticancer strategies is the stabilization of telomeric DNA into a G-quadruplex structure. To explore the intrinsic stabilization of folded G-quadruplexes, we combined electrospray ionization mass spectrometry, ion mobility spectrometry, and molecular modeling studies to study different DNA sequences known to form quadruplexes. Two telomeric DNA sequences of different lengths and two DNA sequences derived from the NHE III1 region of the c-myc oncogene (Pu22 and Pu27) were studied. NH4+ and the ligands PIPER, TMPyP4, and the three quinacridines MMQ1, MMQ3, and BOQ1 were complexed with the DNA sequences to determine their effect on the stability of the G-quadruplexes. Our results demonstrate that G-quadruplex intramolecular folds are stabilized by NH4+ cations and the ligands listed. Furthermore, the ligands can be classified according to their ability to stabilize the quadruplexes and end stacking is shown to be the dominant mode for ligand attachment. In all cases our solvent-free experimental observations and theoretical modeling reveal structures that are highly relevant to the solution-phase structures. [less ▲]

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See detailDesign of DNA minor groove binding diamidines that recognize GC base pair sequences: a dimeric-hinge interaction motif.
Munde, Manoj; Ismail, Mohamed A; Arafa, Reem et al

in Journal of the American Chemical Society (2007), 129(44), 13732-43

The classical model of DNA minor groove binding compounds is that they should have a crescent shape that closely fits the helical twist of the groove. Several compounds with relatively linear shape and ... [more ▼]

The classical model of DNA minor groove binding compounds is that they should have a crescent shape that closely fits the helical twist of the groove. Several compounds with relatively linear shape and large dihedral twist, however, have been found recently to bind strongly to the minor groove. These observations raise the question of how far the curvature requirement could be relaxed. As an initial step in experimental analysis of this question, a linear triphenyl diamidine, DB1111, and a series of nitrogen tricyclic analogues were prepared. The goal with the heterocycles is to design GC binding selectivity into heterocyclic compounds that can get into cells and exert biological effects. The compounds have a zero radius of curvature from amidine carbon to amidine carbon but a significant dihedral twist across the tricyclic and amidine-ring junctions. They would not be expected to bind well to the DNA minor groove by shape-matching criteria. Detailed DNase I footprinting studies of the sequence specificity of this set of diamidines indicated that a pyrimidine heterocyclic derivative, DB1242, binds specifically to a GC-rich sequence, -GCTCG-. It binds to the GC sequence more strongly than to the usual AT recognition sequences for curved minor groove agents. Other similar derivatives did not exhibit the GC specificity. Biosensor-surface plasmon resonance and isothermal titration calorimetry experiments indicate that DB1242 binds to the GC sequence as a highly cooperative stacked dimer. Circular dichroism results indicate that the compound binds in the minor groove. Molecular modeling studies support a minor groove complex and provide an inter-compound and compound-DNA hydrogen-bonding rational for the unusual GC binding specificity and the requirement for a pyrimidine heterocycle. This compound represents a new direction in the development of DNA sequence-specific agents, and it is the first non-polyamide, synthetic compound to specifically recognize a DNA sequence with a majority of GC base pairs. [less ▲]

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See detailCrystal structure of BRL 42715, C6-(N1-methyl-1,2,3-triazolylmethylene)penem, in complex with Enterobacter cloacae 908R beta-lactamase: evidence for a stereoselective mechanism from docking studies.
Michaux, Catherine; Charlier, Paulette ULg; Frère, Jean-Marie ULg et al

in Journal of the American Chemical Society (2005), 127(10), 3262-3

BRL 42715, C6-(N1-methyl-1,2,3-triazolylmethylene)penem, is an active-site-directed inactivator of bacterial beta-lactamases. The crystal structure of Enterobacter cloacae 908R class C beta-lactamase in ... [more ▼]

BRL 42715, C6-(N1-methyl-1,2,3-triazolylmethylene)penem, is an active-site-directed inactivator of bacterial beta-lactamases. The crystal structure of Enterobacter cloacae 908R class C beta-lactamase in complex with BRL 42715, docking, and energy minimization studies explain stereoselectivity of the binding of C6-(heterocyclic methylene)penems against class C beta-lactamase. [less ▲]

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See detailReversible chemical patterning on stimuli-responsive polymer film: Environment-responsive lithography
Ionov, Leonid; Minko, Sergiy; Stamm, Manfred et al

in Journal of the American Chemical Society (2003), 125(27), 8302-8306

We report on a novel type of chemical patterning based on thin stimuli-responsive polymer films. The basic concept is the permanent storage (writing) of a pattern, which is reversibly developed and erased ... [more ▼]

We report on a novel type of chemical patterning based on thin stimuli-responsive polymer films. The basic concept is the permanent storage (writing) of a pattern, which is reversibly developed and erased upon exposure to appropriate environment, e.g., solvent, pH, and temperature. The smart surface is fabricated from the mixed brush of poly(2-vinylpyridine) and polyisoprene. The mixed brush demonstrates switching behavior upon exposure to different solvents. Cross-linking of polyisoprene via illumination through a photomask results in formation of patterns with suppressed switching. Due to the contrast in switching between illuminated and dark areas, exposure of the smart surface to different solvents causes either reversible formation or erasing of chemical contrast between the illuminated and dark areas. Thus, the pattern surface can very locally attract colloidal particles or can be wetted by water only upon exposure to the special solvent which introduces the contrast between the illuminated and dark areas. Appearance of the patterns indicates particular environment and can be used for local switching of adsorption. [less ▲]

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