Consecutive two-photon absorption of azulene in solution utilizing dye lasers

We report a spectroscopic study of consecutive two-photon absorption of azulene excited in the range 32800–42000 cm^?1, which provides information concerning the cross sections for the S₁ → S₃ and the S₁ → S₄ transitions.     

Multiphysics of Tribocontacts

The complex processes involved in the dry friction between two bodies are not yet fully understood. Towards an improved understanding of the associated tribological phenomena, the authors combine their skills and expertise in the respective fields of tribological experimentation, modeling, and simulation, as well as topological and chemical surface analyses. The aim of this research is more accurate predictions of the tribological behavior of minimal friction material mixtures. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Orthogonal Cysteine Protection Enables Homogeneous Multi-Drug Antibody–Drug Conjugates

A strategy for the preparation of homogeneous antibody–drug conjugates (ADCs) containing multiple payloads has been developed. This approach utilizes sequential unmasking of cysteine residues with orthogonal protection to enable site-specific conjugation of each drug. In addition, because the approach utilizes conjugation to native antibody cysteine residues, it is widely applicable and enables high drug loading for improved ADC potency. To highlight the benefits of ADC dual drug delivery, this strategy was applied to the preparation of ADCs containing two classes of auristatin drug-linkers that have differing physiochemical properties and exert complementary anti-cancer activities. Dual-auristatin ADCs imparted activity in cell line and xenograft models that are refractory to ADCs comprised of the individual auristatin components. This work presents a facile method for construction of potent dual-drug ADCs and demonstrates how delivery of multiple cytotoxic warheads can lead to improved ADC activities. Lastly, we anticipate that the conditions utilized herein for orthogonal cysteine unmasking are not restricted to ADCs and can be broadly utilized for site-specific protein modification.     

Kinetic Destabilization of Metal–Metal Single Bonds: Isolation of a Pentacoordinate Manganese(0) Monoradical

The 17e⁻ monoradical [Mn(CO)₅] is widely recognized as an unstable organometallic transient and is known to dimerize rapidly with the formation of a Mn Mn single bond. As a result of this instability, isolable analogues of [Mn(CO)₅] have remained elusive. Herein, we show that two sterically encumbering isocyanide ligands can destabilize the Mn Mn bond leading to the formation of the isolable, manganese(0) monoradical [Mn(CO)₃(CNAr^Dipp2)₂] (Ar^Dipp2=2,6‐(2,6‐(iPr)₂C₆H₃)₂C₆H₃). The persistence of [Mn(CO)₃(CNAr^Dipp2)₂] has allowed for new insights into nitrosoarene spin‐trapping studies of [Mn(CO)₅].     

Structure–property relationships of blended polysaccharide and protein biomaterials in ionic liquid

Cellulose and silk blended biomaterial films were regenerated from ionic liquid solution and investigated to characterize and understand the effect of inter- and intra-molecular interactions upon the morphology and thermal properties. The blended films were dissolved in 1-allyl-3-methylimidazolium chloride ionic liquid, coagulated and regenerated with water. Various characterization techniques were implemented to characterize structural, morphological and thermal properties: FTIR, SEM, TGA, DSC and X-ray scattering. The results showed that the cellulose microcrystalline structure and β-sheets from the silk can be disrupted by inter- and intra-molecular hydrogen bonds forming intermediate semicrystalline or amorphous structures. The SEM showed morphological effects of such interactions that cause varying thermal degradation and glass transition temperature. The X-ray scattering confirms such findings at the molecular level, demonstrating that the cellulose microfibril diameter decreases as the silk content increases. It also shows that the β-sheets size increases as the cellulose content increases. These various techniques provide evidence that suggest the hydrogen bonds between the β-sheets and the glucose units in the cellulose chains control the thermal and structural properties of the blended films, changing the morphology and physicochemical properties.     

Sulfur Pentafluoride is a Preferred Reagent Cation for Negative Electron Transfer Dissociation

Negative mode proteome analysis offers access to unique portions of the proteome and several acidic post-translational modifications; however, traditional collision-based fragmentation methods fail to reliably provide sequence information for peptide anions. Negative electron transfer dissociation (NETD), on the other hand, can sequence precursor anions in a high-throughput manner. Similar to other ion–ion methods, NETD is most efficient with peptides of higher charge state because of the increased electrostatic interaction between reacting molecules. Here we demonstrate that NETD performance for lower charge state precursors can be improved by altering the reagent cation. Specifically, the recombination energy of the NETD reaction—largely dictated by the ionization energy (IE) of the reagent cation—can affect the extent of fragmentation. We compare the NETD reagent cations of C₁₆H₁₀ ^●+ (IE?=?7.9 eV) and SF₅ ^●+ (IE?=?9.6 eV) on a set of standard peptides, concluding that SF₅ ^●+ yields greater sequence ion generation. Subsequent proteome-scale nLC-MS/MS experiments comparing C₁₆H₁₀ ^●+ and SF₅ ^●+ further supported this outcome: analyses using SF₅ ^●+ yielded 4637 peptide spectral matches (PSMs) and 2900 unique peptides, whereas C₁₆H₁₀ ^●+ produced 3563 PSMs and 2231 peptides. The substantive gain in identification power with SF₅ ^●+ was largely driven by improved identification of doubly deprotonated precursors, indicating that increased NETD recombination energy can increase product ion yield for low charge density precursors. This work demonstrates that SF₅ ^●+ is a viable, if not favorable, reagent cation for NETD, and provides improved fragmentation over the commonly used fluoranthene reagent.

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A Sharp Thermal Transition of Fast Aromatic‐Ring Dynamics in Ubiquitin

Aromatic amino acid side chains have a rich role within proteins and are often central to their structure and function. Suitable isotopic‐labelling strategies enable studies of sub‐nanosecond aromatic‐ring dynamics using solution NMR relaxation methods. Surprisingly, it was found that the three aromatic side chains in human ubiquitin show a sharp thermal dynamical transition at approximately 312 K. Hydrostatic pressure has little effect on the low‐temperature behavior, but somewhat decreases the amplitude of motion in the high‐temperature regime. Therefore, below the transition temperature, ring motion is largely librational. Above this temperature, a complete ring‐rotation process that is fully consistent with a continuous diffusion not requiring the transient creation of a large activated free volume occurs. Molecular dynamics simulations qualitatively corroborate this view and reinforce the notion that the dynamical character of the protein interior has much more liquid‐alkane‐like properties than previously appreciated.     

Quasi-co-local subgroups of abelian groups

Let {0}≠K be a subgroup of the abelian group G. In [J. Buckner, M. Dugas, Co-local subgroups of abelian groups, in: Abelian Groups, Rings, Modules, and Homological Algebra, in: Lect. Notes Pure and Appl. Math., vol. 249, Chapman & Hall/CRC, Boca Raton, FL, 2006, pp. 29-37], K was called a co-local (cl) subgroup of G if is naturally isomorphic to . We generalize this notion to the quasi-category of abelian groups and call the subgroup K≠{0} of G a quasi-co-local (qcl) subgroup of G if is naturally isomorphic to . We show that qcl subgroups behave quite differently from cl subgroups. For example, while cl subgroups K are pure in G, i.e. G/K is torsion-free if G is torsion-free, any reduced torsion group T can be the torsion subgroup t(G/K) of G/K where G is torsion-free and K is a qcl subgroup of G.     

Picosecond time resolved photoluminescence spectroscopy of a tetracene film on highly oriented pyrolytic graphite: dynamical relaxation, trap emission, and superradiance

A detailed time resolved investigation of the photoluminescence of a thin tetracene film deposited on highly oriented pyrolytic graphite is presented. In agreement with Lim et al. [Phys. Rev. Lett. 92, 107402 (2004)], we find strong evidence for superradiance: an increase of the relative intensity of the pure electronic transition with respect to the vibronic sideband and a concomitant decrease of the radiative lifetime from 10 to 1.83 ns upon cooling from 300 to 4 K. For lower temperatures, a redshift (approximately 200 cm(-1)) of the free exciton is observed. Previously, this shift was attributed to a structural phase transition. Our time resolved spectra reveal that the spectral shift is related to a dynamical relaxation process which occurs within the first 50 ps.     

Synthesis of beta-functionalized porphyrins via palladium-catalyzed carbon-heteroatom bond formations: expedient entry into beta-chiral porphyrins

A procedure was developed for the preparation of beta-monobromo-tetraphenylporphyrin (BrTPP) in a greatly improved yield from the selective bromination of tetraphenylporphyrin (TPP) by NBS. BrTPP was successfully employed as a versatile synthon for convenient synthesis of a wide range of beta-monofunctionalized porphyrins with various heteroatom functionalities via palladium-mediated carbon-heteroatom bond formations. Examples include beta-amino, -amido, -oxo, and -mercaptoporphyrins from reactions with amines, amides, alcohols, and thiols, respectively. Applying the synthetic approach to chiral amides, beta-chiral porphyrins were effectively constructed.