Simulating electron spin resonance spectra of nitroxide spin labels from molecular dynamics and stochastic trajectories

Simulating electron spin resonance spectra of nitroxide spin labels from motional models is necessary for the quantitative analysis of experimental spectra. We present a framework for modeling the spin label dynamics by using trajectories such as those from molecular dynamics (MD) simulations combined with stochastic treatment of the global protein tumbling. This is achieved in the time domain after two efficient numerical integrators are developed: One for the quantal dynamics of the spins and the other for the classical rotational diffusion. For the quantal dynamics, we propagate the relevant part of the spin density matrix in Hilbert space. For the diffusional tumbling, we work with quaternions, which enables the treatment of anisotropic diffusion in a potential expanded as a sum of spherical harmonics. Time-averaging arguments are invoked to bridge the gap between the smaller time step of the MD trajectories and the larger time steps appropriate for the rotational diffusion and/or quantal spin dynamics.     

Cyclotomic Gaudin Models: Construction and Bethe Ansatz

To any finite-dimensional simple Lie algebra \({\mathfrak{g}}\) and automorphism \({\sigma: \mathfrak{g}\to \mathfrak{g}}\) we associate a cyclotomic Gaudin algebra. This is a large commutative subalgebra of \({U(\mathfrak{g})^{\otimes N}}\) generated by a hierarchy of cyclotomic Gaudin Hamiltonians. It reduces to the Gaudin algebra in the special case \({\sigma ={\rm id}}\).     

Almost One Bit Violation for the Additivity of the Minimum Output Entropy

In a previous paper, we proved that, in the appropriate asymptotic regime, the limit of the collection of possible eigenvalues of output states of a random quantum channel is a deterministic, compact set K_k,t. We also showed that the set K_k,t is obtained, up to an intersection, as the unit ball of the dual of a free compression norm. In this paper, we identify the maximum of \({\ell^p}\) norms on the set K_k,t and prove that the maximum is attained on a vector of shape (a, b, . . . , b) where a > b. In particular, we compute the precise limit value of the minimum output entropy of a single random quantum channel. As a corollary, we show that for any \({\varepsilon > 0}\), it is possible to obtain a violation for the additivity of the minimum output entropy for an output dimension as low as 183, and that for appropriate choice of parameters, the violation can be as large as \({\log 2 -\varepsilon}\). Conversely, our result implies that, with probability one in the limit, one does not obtain a violation of additivity using conjugate random quantum channels and the Bell state, in dimension 182 and less.     

Copolymerization of 2,3,4,5,6‐Pentafluorostyrene and Methacrylic Acid by Nitroxide‐Mediated Polymerization: The Importance of Reactivity Ratios

Amphiphilic block copolymers of 2,3,4,5,6‐pentafluorostyrene (PFS) and methacrylic acid (MAA) are synthesized via nitroxide‐mediated polymerization (NMP). It is established that to obtain a controlled copolymerization a minimum of 40 mol% of PFS is required, which is significantly greater than other copolymerization systems such as using 4.5–8 mol% styrene or 1 mol% of 9‐(4‐vinylbenzyl)‐9H‐carbazole to control the copolymerization of methacrylates. It is surmised that this lack of control is due to the reactivity ratios that favor the addition of MAA rather than PFS (r_PFS = 0.14, r_MAA = 6.97). However this reactivity ratio pair suggests that a one‐shot delayed injection approach can be utilized to synthesize almost pure block copolymers in one pot. Therefore, poly(PFS)‐b‐(PFS‐ran‐MAA) block copolymers are synthesized by a one‐shot delayed addition of MAA. While the concentration of irreversibly terminated chains is evident these results suggest a promising route to the synthesis of fluorinated amphiphilic block copolymers by NMP.

     

Redox-driven intramolecular anion translocation between a metal centre and a hydrogen-bond-donating compartment

Dicationic ligands incorporating two 2,2'-bipyridine units and two imidazolium moieties, [1](2+) and [2](2+), form stable chelate complexes with Cu(II) and Cu(I) in acetonitrile solution. Each Cu(II) complex binds two X(-) ions according to two stepwise equilibria, the first involving the Cu(II) centre and the second involving the bis-imidazolium compartment. Cu(I) complexes are able to host only one NO(3)(-) ion in the bis-imidazolium cavity, while other anions induce demetallation. Thus, in the presence of one equivalent of NO(3)(-), the Cu(II)/Cu(I) redox change makes the anion translocate quickly and reversibly from one binding site to the other within the [Cu(II,I)(1)](4+/3+) system, as demonstrated by cyclic voltammetry and controlled-potential electrolysis experiments.     

Aminoborylene complexes of group 6 elements and iron: a synthetic, structural, and quantum chemical study

Transition-metal-borylene complexes of the type [(OC)(5)M=BR] {M=Cr, Mo, W; R=N(SiMe(3))(2), 1a-3a, Si(SiMe(3))(3), 4a} and [(OC)(4)Fe=B=N(SiMe(3))(2)] (8) were prepared by salt elimination reactions. Synthesis of the latter complex was accompanied by the formation of substantial amounts of an unusual dinuclear iron complex [Fe(2){mu-C(2)O(2)(BN(SiMe(3))(2))}(2)(CO)(6)] (9). The aminoborylene complexes of Group 6 metals were converted to trans-[(Cy(3)P)(CO)(4)M=B=N(SiMe(3))(2)] (5a-7a) by irradiation in the presence of PCy(3). Structural and spectroscopic parameters were discussed with respect to the trans-effect of the borylene ligand and the degree of M-B d(pi)-p(pi)-backbonding. Computational studies were performed on Group 6-borylene complexes. The population and topological analyses as well as the molecular orbital composition are consistent with the presence of both sigma-and pi-type interactions. There are, however, indications that the d(pi)-p(pi)-backbonding in the silylborylene complex is significantly more pronounced than in the aminoborylene complexes.     

Chemical end-grafting of homogeneous polystyrene monolayers on mica and silica surfaces

Homogeneous polystyrene monolayers covalently end-attached on mica and silica surfaces were obtained using a "graft to" methodology. The grafting was achieved via nucleophilic substitution between silanol groups (Si-OH) containing surface and monochlorosilyl terminated polystyrene (PS). Different parameters, such as surface activation, grafting reaction time, polymer concentration, nature of solvent, and presence of catalyst, were investigated to determine the optimal conditions for creating very homogeneous and stable polymer monolayers. Ellipsometry, atomic force microscopy (AFM), surface forces apparatus (SFA), and contact angle measurements were used to characterize the polymer-grafted layers. An efficient plasma activation procedure was established to create a maximum number of silanol groups on mica surfaces without increasing the surface roughness. Surface reactivity was investigated by grafting trimethylchlorosilane (TMS) on OH-activated mica and silica. The maximum TMS surface coverage on activated mica is similar to that observed for silica. The stability of covalently attached TMS and PS layers in toluene and water were investigated. Both grafted layers (TMS and PS) partially detached from the mica and silica surfaces when immersed in water. Hydrolysis of the siloxane bond between the monochlorosilyl groups and the surface is the most probable cause of layer degrafting. The degrafting was much slower with the long PS polymer chains, compared to the small TMS molecules, which may act as a protective layer against hydrolysis.     

Synthesis of polyphosphodiesters by ring‐opening polymerization of cyclic phosphates bearing allyl phosphoester protecting groups

The allyl phosphoester group is shown to be a protecting group for the synthesis of anionic polyphosphodiesters. Our strategy relies on the synthesis of a cyclic phosphate monomer bearing a pendant allyl phosphoester group, its easy purification by fractional distillation, its organocatalyzed ring‐opening polymerization by 1,8‐diazobicyclo[5.4.0]undec‐7‐ene (DBU) and 1‐[3,5‐bis(trifluoromethyl)phenyl]‐3‐cyclohexyl‐thiourea (TU). Finally, the deprotection of the allyl phosphoester group is carried out by reaction with sodium benzenethiolate in the absence of any detectable degradation. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2642–2648