Kooperativer Bibliotheksverbund

Berlin Brandenburg

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  • American Chemical Society (CrossRef)  (309)
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  • 1
    Language: English
    In: Journal of the American Chemical Society, 19 January 2011, Vol.133(2), pp.167-9
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 2
    Language: English
    In: Journal of the American Chemical Society, 03 April 2013, Vol.135(13), pp.5062-7
    Description: We investigated salt interactions with butyramide as a simple mimic of cation interactions with protein backbones. The experiments were performed in aqueous metal chloride solutions using two spectroscopic techniques. In the first, which provided information about contact pair formation, the response of the amide I band to the nature and concentration of salt was monitored in bulk aqueous solutions via attenuated total reflection Fourier transform infrared spectroscopy. It was found that molar concentrations of well-hydrated metal cations (Ca(2+), Mg(2+), Li(+)) led to the rise of a peak assigned to metal cation-bound amides (1645 cm(-1)) and a decrease in the peak associated with purely water-bound amides (1620 cm(-1)). In a complementary set of experiments, the effect of cation identity and concentration was investigated at the air/butyramide/water interface via vibrational sum frequency spectroscopy. In these studies, metal ion-amide binding led to the ordering of the adjacent water layer. Such experiments were sensitive to the interfacial partitioning of cations in either a contact pair with the amide or as a solvent separated pair. In both experiments, the ordering of the interactions of the cations was: Ca(2+) 〉 Mg(2+) 〉 Li(+) 〉 Na(+) ≈ K(+). This is a direct cationic Hofmeister series. Even for Ca(2+), however, the apparent equilibrium dissociation constant of the cation with the amide carbonyl oxygen was no tighter than ∼8.5 M. For Na(+) and K(+), no evidence was found for any binding. As such, the interactions of metal cations with amides are far weaker than the analogous binding of weakly hydrated anions.
    Keywords: Amides -- Chemistry ; Water -- Chemistry
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 3
    Language: English
    In: Journal of the American Chemical Society, 20 June 2012, Vol.134(24), pp.10039-46
    Description: The specific binding sites of Hofmeister ions with an uncharged 600-residue elastin-like polypeptide, (VPGVG)(120), were elucidated using a combination of NMR and thermodynamic measurements along with molecular dynamics simulations. It was found that the large soft anions such as SCN(-) and I(-) interact with the polypeptide backbone via a hybrid binding site that consists of the amide nitrogen and the adjacent α-carbon. The hydrocarbon groups at these sites bear a slight positive charge, which enhances anion binding without disrupting specific hydrogen bonds to water molecules. The hydrophobic side chains do not contribute significantly to anion binding or the corresponding salting-in behavior of the biopolymer. Cl(-) binds far more weakly to the amide nitrogen/α-carbon binding site, while SO(4)(2-) is repelled from both the backbone and hydrophobic side chains of the polypeptide. The Na(+) counterions are also repelled from the polypeptide. The identification of these molecular-level binding sites provides new insights into the mechanism of peptide-anion interactions.
    Keywords: Ions -- Chemistry ; Peptides -- Chemistry
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 4
    Language: English
    In: The journal of physical chemistry. A, 11 August 2011, Vol.115(31), pp.8731-42
    Description: A new method is presented to describe deformations of an N-membered planar ring (N-ring) molecule in terms of deformation vectors that can be expressed by a set of 2N-3 deformation amplitudes and phase angles. The deformation coordinates are directly derived from the normal vibrational modes of the N-ring and referenced to a regular polygon (N-gon) of unit length. They extend the conceptual approach of the Cremer-Pople puckering coordinates (J. Am. Chem. Soc. 1975, 97, 1354) to the planar ring and make it possible to calculate, e.g., a planar ring of special deformation on a Jahn-Teller surface. It is demonstrated that the 2N-3 deformation parameters are perfectly suited to describe the pseudorotation of a bond through the ring as it is found in cyclic Jahn-Teller systems. In general, an N-membered planar ring can undergo N-2 different bond pseudorotations provided the energetics of such a process is feasible. The Jahn-Teller distortions observed in ring compounds correspond either directly to the basic pseudorotation modes or to linear combinations of them. Any deformed ring molecule can be characterized in terms of the new ring deformation coordinates, which help to identify specific electronic effects. The usefulness of the ring deformation coordinates is demonstrated by calculating the Jahn-Teller surfaces for bond pseudorotation in the case of the cyclopropyl radical cation and cyclobutadiene as well as the ring deformation surfaces of disulfur dinitride and its dianion employing multireference averaged quadratic coupled cluster (MR-AQCC) theory, equation-of-motion coupled cluster theory in form of EOMIP-CCSD, and single determinant coupled cluster theory in form of CCSD(T).
    Keywords: Chemistry;
    ISSN: 10895639
    E-ISSN: 1520-5215
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  • 5
    Language: English
    In: The journal of physical chemistry. A, 05 April 2012, Vol.116(13), pp.3481-6
    Description: Based on the normalized elimination of the small component relativistic formalism, a new approach to the calculation of hyperfine structure parameters of paramagnetic molecules is developed and implemented. The new method is tested in the calculation of the isotropic hyperfine structure constant for a series of open-shell molecules containing mercury. The results of calculations carried out in connection with ab initio methods of increasing complexity demonstrate the high accuracy of the formalism developed. In view of its computational simplicity, the new approach provides the basis for an efficient and accurate calculation of the HFS parameters of large molecules.
    Keywords: Chemistry;
    ISSN: 10895639
    E-ISSN: 1520-5215
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  • 6
    Language: English
    In: The journal of physical chemistry. A, 10 September 2015, Vol.119(36), pp.9541-56
    Description: Bond anomalies have been investigated for a set of 53 molecules with either N-F, Ti-P, Cr-H, Pb-C, or Pb-F bonds for which reverse rather than inverse bond length-bond strength relationships have been previously claimed. The intrinsic strength of each bond investigated was determined utilizing the associated local stretching force constant obtained at the CCSD(T)/aug-cc-pVTZ level of theory. For the metal containing molecules, LC-ωPBE calculations with the aug-cc-pVTZ (Cr, Pb) and the 6-31++G(d,p) basis set (Ti) were carried out. For bonds containing a metal atom, any bond anomaly could not be confirmed. Previously reported results were due to ill-defined bond strength descriptors or lacking accuracy. In the case of the fluoro amines, methyl fluoro amines, and the fluoro amine oxides, direct or hidden bond anomalies were detected, which result from two or more opposing electronic effects: a dominant bond shortening effect due to electron withdrawal and a bond weakening due to lone pair repulsion or hybridization defects. Bond anomalies can be disguised by a complex interplay of electronic effects. These hidden bond anomalies could be identified in this work for the fluoro amine chalcogenides.
    Keywords: Chemistry;
    ISSN: 10895639
    E-ISSN: 1520-5215
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  • 7
    Language: English
    In: The journal of physical chemistry. A, 12 September 2013, Vol.117(36), pp.8981-95
    Description: Increasing the effective electronegativity of two atoms forming a triple bond can increase the strength of the latter. The strongest bonds found in chemistry involve protonated species of hydrogen cyanide, carbon monoxide, and dinitrogen. CCSD(T)/CBS (complete basis set) and G4 calculations reveal that bond dissociation energies are misleading strength descriptors. The strength of the bond is assessed via the local stretching force constants, which suggest relative bond strength orders (RBSO) between 2.9 and 3.4 for heavy atom bonding (relative to the CO bond strength in methanol (RBSO = 1) and formaldehyde (RBSO = 2)) in [HCNH](+)((1)Σ(+)), [HCO](+)((1)Σ(+)), [HNN](+)((1)Σ(+)), and [HNNH](2+)((1)Σg(+)). The increase in strength is caused by protonation, which increases the electronegativity of the heavy atom and thereby decreases the energy of the bonding AB orbitals (A, B: C, N, O). A similar effect can be achieved by ionization of a nonbonding or antibonding electron in CO or NO. The strongest bond with a RBSO value of 3.38 is found for [HNNH](2+) using scaled CCSD(T)/CBS frequencies determined for CCSD(T)/CBS geometries. Less strong is the NN bond in [FNNH](2+) and [FNNF](2+).
    Keywords: Chemistry;
    ISSN: 10895639
    E-ISSN: 1520-5215
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  • 8
    Language: English
    In: Inorganic chemistry, 06 January 2014, Vol.53(1), pp.478-95
    Description: Tolman's electronic parameter (TEP) derived from the A1-symmetrical CO stretching frequency of nickel-phosphine-tricarbonyl complexes, R3PNi(CO)3, is brought to a new, improved level by replacing normal with local vibrational frequencies. CO normal vibrational frequencies are always flawed by mode-mode coupling especially with metal-carbon stretching modes, which leads to coupling frequencies as large as 100 cm(-1) and can become even larger when the transition metal and the number of ligands is changed. Local TEP (LTEP) values, being based on local CO stretching force constants rather than normal mode frequencies, no longer suffer from mode coupling and mass effects. For 42 nickel complexes of the type LNi(CO)3, it is shown that LTEP values provide a different ordering of ligand electronic effects as previously suggested by TEP and CEP values. The general applicability of the LTEP concept is demonstrated.
    Keywords: Chemistry;
    ISSN: 00201669
    E-ISSN: 1520-510X
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  • 9
    Language: English
    In: Journal of the American Chemical Society, 09 May 2012, Vol.134(18), pp.7773-9
    Description: Phosphatidylserine (PS) embedded within supported lipid bilayers was found to bind Cu(2+) from solution with extraordinarily high affinity. In fact, the equilibrium dissociation constant was in the femtomolar range. The resulting complex formed in a 1:2 Cu(2+)-to-PS ratio and quenches a broad spectrum of lipid-bound fluorophores in a reversible and pH-dependent fashion. At acidic pH values, the fluorophores were almost completely unquenched, while at basic pH values significant quenching (85-90%) was observed. The pH at which the transition occurred was dependent on the PS concentration and ranged from approximately pH 5 to 8. The quenching kinetics was slow at low Cu(2+) concentrations and basic pH values (up to several hours), while the unquenching reaction was orders of magnitude more rapid upon lowering the pH. This was consistent with diffusion-limited complex formation at basic pH but rapid dissociation under acidic conditions. The tight binding of Cu(2+) to PS may have physiological consequences under certain circumstances.
    Keywords: Copper -- Metabolism ; Lipid Bilayers -- Metabolism ; Phosphatidylserines -- Metabolism
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 10
    Language: English
    In: Analytical chemistry, 21 July 2015, Vol.87(14), pp.7163-70
    Description: Herein, we developed a new separation-based detection method that is capable of simultaneously identifying multiple competitively binding proteins for the same ligand on supported lipid bilayers (SLBs). This strategy used unlabeled target analyte proteins that bind to fluorescently tagged, lipid-conjugated ligands within the SLB. The protein-ligand binding complexes were then focused under an applied potential to different locations within the SLB based on each protein's size and charge. Both protein identity and relative surface concentration information could be obtained, simultaneously. Specifically, the competitive binding of streptavidin and goat anti-biotin for biotin-conjugated lipids was explored. It was found that streptavidin could inhibit the binding of goat anti-biotin antibodies for biotin-cap-1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl)(biotin-cap-NBD-PE) lipids and that streptavidin more effectively outcompeted the anti-biotin antibody at lower protein concentrations. Also, modulating the chemical composition of the membrane helped control the ultimate focusing position and separation of the streptavidin-bound biotin, anti-biotin-bound biotin, and free biotin-conjugated lipid bands. The assay developed herein provides a simple and convenient strategy for simultaneously monitoring target analytes that bind to the identical ligand and may ultimately be useful in developing assays that help overcome problems associated with cross-reactivity.
    Keywords: Binding, Competitive ; Antibodies -- Analysis ; Lipid Bilayers -- Chemistry ; Streptavidin -- Analysis
    ISSN: 00032700
    E-ISSN: 1520-6882
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