α-Domination

AbstractLet G=(V,E) be any graph with n vertices, m edges and no isolated vertices. For some α with 0<α⩽1 and a set S⊆V, we say that S is α-dominating if for all v∈V−S,|N(v)∩S|⩾α|N(v)|. The size of a smallest such S is called the α-domination number and is denoted by γα(G). In this paper, we introduce α-domination, discuss bounds for γ1/2(G) for the King's graph, and give bounds for γα(G) for a general α, 0<α⩽1. Furthermore, we show that the problem of deciding whether γα(G)⩽k is NP-complete

Gas-phase complexes of Ni2+ and Ca2+ with deprotonated histidylhistidine (HisHis): A model case for polyhistidyl-metal binding motifs

In the complex formed between the calcium cation (Ca2+) and a deprotonated HisHis dipeptide, the complex adopts a charge solvation (CS) structure. Ca2+, a weak binding main group metal cation, interacts with the oxygens of the peptide carbonyl moiety and the deprotonated C-terminus. In contrast, the much stronger binding Ni2+ cation deprotonates the peptide nitrogen and induces an iminolate (Im) ligand structure in the [Ni(HisHis-H)]+ complex ion. The combination of infrared multiple-photon dissociation (IRMPD) spectroscopy and quantum chemistry evidence these two representative binding motifs. The iminolate coordination pattern identified and characterized in the [Ni(HisHis-H)]+ complex serves as a model case for nickel complexes of poly-histidyl-domains and is thereby also of interest to better understand the fundamentals of immobilized metal ion affinity chromatography as well as of Ni co-factor chemistry in enzymology

The Business Model: Recent Developments and Future Research

This article provides a broad and multifaceted review of the received literature on business models in which the authors examine the business model concept through multiple subject-matter lenses. The review reveals that scholars do not agree on what a business model is and that the literature is developing largely in silos, according to the phenomena of interest of the respective researchers. However, the authors also found emerging common themes among scholars of business models. Specifically, (1) the business model is emerging as a new unit of analysis; (2) business models emphasize a system-level, holistic approach to explaining how firms “do business”; (3) firm activities play an important role in the various conceptualizations of business models that have been proposed; and (4) business models seek to explain how value is created, not just how it is captured. These emerging themes could serve as catalysts for a more unified study of business models

The site of cr+ attachment to gas-phase aniline from infrared spectroscopy

Contains fulltext : 98897.pdf (publisher's version ) (Open Access

Cationized phenylalanine conformations characterized by IRMPD and computation for singly and doubly charged ions

Electrospray ionization produces phenylalanine (Phe) complexes of the alkali metal ion series, plus Ag+ and Ba2+. Infrared multiple photon dissociation (IRMPD) spectroscopy using the FELIX free electron laser light source is used to characterize the conformations of the ions, in conjunction with density functional theory (DFT) calculations giving thermochemical information and computed infrared spectra for likely candidate conformations. For complexes of small, singly charged ions (Li+, Na+, K+ and Ag+) a single tridentate, charge-solvated conformational theme (N/O/Ring) binding amino nitrogen, carbonyl oxygen and the aromatic ring to the metal ion accounts for all the observations. The larger alkalis Rb+ and Cs+ show clear spectroscopic evidence of mixed populations, containing substantial fractions of both tridentate and also bidentate chelation. For Rb+ the bidentate fraction is assigned as the (O/Ring) chelation pattern, while for Cs+ a mixture of (O/Ring) and (O/O) chelation patterns seems likely. All of the smaller ions with high positive charge density have a clear preference for cation-pi interaction with the side-chain aromatic ring, but for the larger ions Rb+ and particularly Cs+ this interaction becomes sufficiently weak to allow conformations having the metal ion remote from the pi system. The Ba2+ complex is unique in showing clear evidence of a major fraction of salt-bridge (zwitterionic) ions along with charge-solvated conformations. Plots of the frequency shifts of the two highly perturbed ligand vibrational modes (C=O stretch and NH2 frustrated inversion) give good linear correlations with the binding energy of the metal to the ligand

How does a small peptide choose how to bind a metal ion? Irmpd and computational survey of cs versus iminol binding preferences

Item does not contain fulltex

Encapsulation of metal cations by the PhePhe ligand: a cation-pi ion cage

Structures and binding thermochemistry are investigated for protonated PhePhe and for complexes of PhePhe with the alkaline-earth ions Ba2+ and Ca2+, the alkali-metal ions Li+, Na+, K+, and Cs+, and the transition-metal ion Ag+. The two neighboring aromatic side chains open the possibility of a novel encapsulation motif of the metal ion in a double cation−π configuration, which is found to be realized for the alkaline-earth complexes and, in a variant form, for the Ag+ complex. Experimentally, complexes are formed by electrospray ionization, trapped in an FT-ICR mass spectrometer, and characterized by infrared multiple photon dissociation (IRMPD) spectroscopy using the free electron laser FELIX. Interpretation is assisted by thermochemical and IR spectral calculations using density functional theory (DFT). The IRMPD spectrum of protonated PhePhe is reproduced with good fidelity by the calculated spectrum of the most stable conformation, although the additional presence of the secondmost stable conformation is not excluded. All metal-ion complexes have charge-solvated binding modes, with zwitterion (salt bridge) forms being much less stable. The amide oxygen always coordinates to the metal ion, as well as at least one phenyl ring (cation−π interaction). At least one additional chelation site is always occupied, which may be either the amino nitrogen or the carboxy carbonyl oxygen. The alkaline-earth complexes prefer a highly compact caged structure with both phenyl rings providing cation−π stabilization in a "sandwich" configuration (OORR chelation). The alkali-metal complexes prefer open-cage structures with only one cation−π interaction, except perhaps Cs+ . The Ag+ complex shows a unique preference for the closed-cage amino-bound NORR structure. Ligand-driven perturbations of normal-mode frequencies are generally found to correlate linearly with metal-ion binding energy