Ion Mobility Mass Spectrometry Measures the Conformational Landscape of p27 and its Domains and how this is Modulated upon Interaction with Cdk2/cyclin A

Intrinsically disordered proteins have been reported to undergo disorder‐to‐order transitions upon binding to their partners in the cell. The extent of the ordering upon binding and the lack of order prior to binding is difficult to visualize with classical structure determination methods. Binding of p27 to the Cdk2/cyclin A complex is accompanied by partial folding of p27 in the KID domain, with the retention of dynamic behavior for function, particularly in the C‐terminal half of the protein. Herein, native ion mobility mass spectrometry (IM‐MS) is employed to measure the intrinsic dynamic properties of p27, both in isolation and within the trimeric complex with Cdk2/cyclin A. The trimeric Cdk2/cyclin A/p27‐KID complex possesses significant structural heterogeneity compared to Cdk2/cyclin A. These findings support the formation of a fuzzy complex in which both the N‐ and C‐termini of p27 interact with Cdk2/cyclin A in multiple, closely associated states.     

Minimally corrected partial atomic charges for non-covalent electrostatic interactions

We develop a new scheme for determining molecular partial atomic charges (PACs) with external electrostatic potential (ESP) closely mimicking that of the molecule. The PACs are the ‘minimal corrections’ to a reference set of PACs necessary for reproducing exactly the tensor components of the Cartesian zero-, first- and second- molecular electrostatic multipoles. We evaluate the quality of ESP reproduction when ‘minimally correcting’ (MC) Mulliken, Hirshfeld or iterative-Hirshfeld reference PACs. In all these cases, the MC-PACs significantly improve the ESP while preserving the reference PACs’ invariance under the molecular symmetry operations. When iterative-Hirshfeld PACs are used as reference, the MC-PACs yield ESPs of comparable quality to those of the ChElPG charge fitting method.     

Experimental and theoretical studies of the basicity and proton affinity of SiF4 and the structure of SiF4H+

A combined experimental and theoretical approach has been employed to establish the basicity and proton affinity of SiF₄ and the structure of SiF₄H⁺. The kinetics and energetics for the transfer of a proton between SiF₄, N₂, and Xe have been explored experimentally in helium at 0.35±0.02 torr and 297±3 K with a selected-ion flow tube apparatus. The results of equilibrium constant measurements are reported that provide a basicity and proton affinity for SiF₄ at 297±3 K of 111.4±1.0 and 117.7±1.2 kcal mol^?1, respectively. These values are more than 2.5 kcal mol^?1 lower than currently recommended values. The basicity order was determined to be GB(Xe)>GB(SiF₄)>GB(N₂), while the proton-affinity order was shown to be PA(Xe)>PA(N₂)>PA (SiF₄). Ab initio molecular orbital computations at MP4SDTQ(fc)/6-311++G(3df,3pd) using geometries from B3LYP/6-31+G(d,p) indicate a value for PA(SiF₄)=118.7 kcal mol^?1 that is in good agreement with experiment. Also, the most stable structure of SiF₄H⁺ is shown to correspond to a core SiF ₃ ⁺ cation solvated by HF with a binding energy of 43. 9 kcal mol^?1. Support for this structure is found in separate SIFT collision induced dissociation (CID) measurements that indicate exclusive loss of HF.     

Studies into the Early Degradation Stages of Cellulose by Different Iron Gall Ink Components

Selective fluorescence labelling of oxidized cellulose functionalities followed by GPC-MALLS was used to get a deeper insight into ink-induced degradation processes. As the method is very sensitive towards oxidation and molecular weight changes, slight variations at the very beginning of aging processes, e.g. during ink corrosion of cellulose, can be studied. Five different ink modifications were applied on model papers and underwent mild accelerated aging at 55 °C and cycling humidity (7 days) followed by a short period of static humid aging at 80 °C (2 days). Pure ink constituents like tannic acid or iron sulphate do not result in the same degree of oxidation or chain scission as complete inks. Balanced ink degrades paper more than single compounds, but less than unbalanced inks. Interestingly, some degradation occurs already during or shortly after the application process of unbalanced inks on paper. It could be demonstrated that this oxidation proceeded in a rather high Mw area, while the subsequent aging steps affected predominantly regions of shorter cellulose chains.     

THM PyGC–MS of wood fragment and vegetable fibre forensic samples

Wood fragments and vegetable fibres were investigated using thermally assisted hydrolysis and methylation with pyrolysis gas chromatography–mass spectrometry (THM PyGC–MS). Multiple ion chromatography was used to decrease the interference from cellulosic peaks, and to obtain greater resolution between the lignin peaks. Forty-four wood samples were analysed using THM PyGC–MS. The wood fragments were able to be differentiated into angiosperms (hardwoods) and gymnosperms (softwoods) using principle component analysis (PCA), hierarchical cluster analysis (HCA), and the ratio of syringyl to guaiacyl lignin fragments (S/G ratio). PCA and HCA also differentiated several Monterey pine samples from the rest of the gymnosperms, primarily by the presence of β-pinene, an extractive compound. Other gymnosperm species and the individual angiosperm species were unable to be differentiated. A pilot study investigating the use of THM PyGC–MS for the analysis of vegetable fibres in forensic science found that the fibre types tended to group into two clusters, with one containing cotton, hemp and linen; and the other consisting of hessian, sisal, jute and coir. The seagrass sample was able to be differentiated from both groups. These groups were well separated using PCA, HCA and by the ratio of cinnamyl phenolic derivatives to guaiacyl lignin derivatives (C/G ratio). Some grouping of each fibre type was evident within each cluster, however the separation between the clusters was insufficient to differentiate them using these statistical techniques. THM PyGC–MS of vegetable fibres showed some potential for future use in forensic science.     

Sensitized Lanthanide‐Ion Luminescence with Aryl‐Substituted N‐(2‐Nitrophenyl)acetamide‐Derived Chromophores

The syntheses of the two tetraazamacrocyclic ligands L1 and L2 bearing a [(methoxy‐2‐nitrophenyl)amino]carbonyl chromophore, i.e., an N‐(methoxy‐2‐nitrophenyl)acetamide moiety, together with their corresponding lanthanide‐ion complexes are described. A combined spectroscopic (UV/VIS, ¹H‐NMR), structural (X‐ray), and theoretical (DFT) investigation revealed that the absorption properties of the chromophores were dictated by the extent of electronic delocalisation, which in turn was determined by the position of the MeO substituent at the aromatic ring. X‐Ray crystallographic studies showed that when attached to the macrocycle, both isomeric forms of the N‐(methoxy‐2‐nitrophenyl)acetamide unit can participate in coordination, via the C?O, to an encapsulated potassium cation. Luminescence measurements confirmed that such a binding mode also exists in solution for the corresponding lanthanide complexes (q ca. ≤1), with the para‐MeO derivative allowing longer wavelength sensitization (λ_ex 330 nm).