Mechanistic insights into a gas–solid reaction in molecular crystals: the role of hydrogen bonding

Reactions in (molecular) organic crystalline solids have been shown to be important for exerting control that is unattainable over chemical transformations in solution. Such control has also been achieved for reactions within metal– organic cages. In these examples, the reactants are already in place within the crystals following the original crystal growth. The post-synthetic modification of metal–organic frameworks (MOFs and indeed reactions and catalysis within MOFs have been recently demonstrated; in these cases the reactants enter the crystals through permanent channels. Another growing area of interest within molecular solid-state chemistry is synthesis by mechanical co-grinding of solid reactants—often referred to as mechanochemistry. Finally, in a small number of reported examples, molecules also have been shown to enter nonporous crystals directly from the gas or vapor phase, but in only a few of these examples does a change in covalent bonding result, which indicates that a reaction occurs within the nonporous crystals. It is this latter type of highly uncommon reaction that is the focus of the present study.

The surface geometry of carbon monoxide and oxygen co-adsorbed on Ni{111}

Low energy electron diffraction (LEED) structure determinations have been performed for the p(2 x 2) structures of pure oxygen and oxygen co-adsorbed with CO on Ni{111}. Optimisation of the non-geometric parameters led to very good agreement between experimental and theoretical IV-curves and hence to a high accuracy in the structural parameters. In agreement with earlier work atomic oxygen is found to adsorb on fee sites in both structures. In the co-adsorbed phase CO occupies atop sites. The positions of the substrate atoms are almost identical, within 0.02 Angstrom, in both structures, implying that the interaction with oxygen dominates the arrangement of Ni atoms at the surface.

A phosphorus analogue of Bis(eta(4)-cyclobutadiene)iron(0)

Iron is a pivotal element in organometallic chemistry, enabling fundamental insights with high-impact applications.[1] Ferrocene derivatives have countless uses,[2] and the recent advances in iron catalysis are equally impressive.[3]

Direct observation of time-resolved polymorphic states in the self-assembly of end-capped heptapeptides

Amyloid fibrils resulting from uncontrolled peptide aggregation are associated with several neurodegenerative diseases. Their polymorphism depends on a number of factors including pH, ionic strength, electrostatic interactions, hydrophobic interactions, hydrogen bonding, aromatic stacking interactions, and chirality. Understanding the mechanism of amyloid fibril formation can improve strategies towards the prevention of fibrillation processes and enable a wide range of potential applications in nanotemplating and nanotechnology.

Oligomeric pseudorotaxanes adopting infinite-chain lattice superstructures

Above a critical chain length, where oligomers contain five or more recognition units, apparently infinite donor–acceptor polypseudorotaxanes are formed in the solid state. X-ray crystallographic analyses of three different examples have shown that although the oligomeric chains are undoubtedly discrete and monodisperse, they nevertheless appear to be infinite in the crystal.

Liquid AP-UV-MALDI enables stable ion yields of multiply charged peptide and protein ions for sensitive analysis by mass spectrometry

In biological mass spectrometry (MS), two ionization techniques are predominantly employed for the analysis of larger biomolecules, such as polypeptides. These are nano-electrospray ionization [1, 2] (nanoESI) and matrix-assisted laser desorption/ionization [3, 4] (MALDI). Both techniques are considered to be “soft”, allowing the desorption and ionization of intact molecular analyte species and thus their successful mass-spectrometric analysis. One of the main differences between these two ionization techniques lies in their ability to produce multiply charged ions. MALDI typically generates singly charged peptide ions whereas nanoESI easily provides multiply charged ions, even for peptides as low as 1000 Da in mass. The production of highly charged ions is desirable as this allows the use of mass analyzers, such as ion traps (including orbitraps) and hybrid quadrupole instruments, which typically offer only a limited m/z range (< 2000–4000). It also enables more informative fragmentation spectra using techniques such as collisioninduced dissociation (CID) and electron capture/transfer dissociation (ECD/ETD) in combination with tandem MS (MS/MS). [5, 6] Thus, there is a clear advantage of using ESI in research areas where peptide sequencing, or in general, the structural elucidation of biomolecules by MS/MS is required. Nonetheless, MALDI with its higher tolerance to contaminants and additives, ease-of-operation, potential for highspeed and automated sample preparation and analysis as well as its MS imaging capabilities makes it an ionization technique that can cover bioanalytical areas for which ESI is less suitable. [7, 8] If these strengths could be combined with the analytical power of multiply charged ions, new instrumental configurations and large-scale proteomic analyses based on MALDI MS(/MS) would become feasible.

Polymer therapeutics designed for a combination therapy of hormone-dependent cancer

Designer drug: A polymer therapeutic was designed for a combination therapy of breast cancer. N-(2-Hydroxypropyl)methacrylamide was used as the model polymer platform to prepare a unimolecular polymer conjugate (see picture, radius of gyration: 12.8 nm) that combines an endocrine (the aromatase inhibitor aminoglutethimide, blue) and a chemotherapeutic agent (the anthraxcycline antibiotic doxorubicin, red).

Insights into the molecular architecture of a peptide nanotube using FTIR and solid-state NMR spectroscopic measurements on an aligned sample

The self-assembly of proteins and peptides into b-sheet-rich amyloid fibers is a process that has gained notoriety because of its association with human diseases and disorders. Spontaneous self-assembly of peptides into nonfibrillar supramolecular structures can also provide a versatile and convenient mechanism for the bottom-up design of biocompatible materials with functional properties favoring a wide range of practical applications.[1] One subset of these fascinating and potentially useful nanoscale constructions are the peptide nanotubes, elongated cylindrical structures with a hollow center bounded by a thin wall of peptide molecules.[2] A formidable challenge in optimizing and harnessing the properties of nanotube assemblies is to gain atomistic insight into their architecture, and to elucidate precisely how the tubular morphology is constructed from the peptide building blocks. Some of these fine details have been elucidated recently with the use of magic-angle-spinning (MAS) solidstate NMR (SSNMR) spectroscopy.[3] MAS SSNMR measurements of chemical shifts and through-space interatomic distances provide constraints on peptide conformation (e.g., b-strands and turns) and quaternary packing. We describe here a new application of a straightforward SSNMR technique which, when combined with FTIR spectroscopy, reports quantitatively on the orientation of the peptide molecules within the nanotube structure, thereby providing an additional structural constraint not accessible to MAS SSNMR.

AP-UV-MALDI mit flüssigen Matrizes: stabile Ionenausbeuten von mehrfach geladenen Peptid- und Proteinionen für die empfindliche Massenspektrometrie

In der biologischen Massenspektrometrie (MS) werden überwiegend zwei Ionisationstechniken für die Analyse von grçßeren Biomolekfürlen wie Polypeptiden eingesetzt. Dies sind die Nano-Elektrospray-Ionisation[1,2] (nanoESI) und die matrixunterstfürtzte Laserdesorption/-ionisation[3, 4] (MALDI). Beide Techniken werden als „sanft“ bezeichnet, weil sie die Desorption und Ionisation von intakten Analytmolekfürlen und damit ihre erfolgreiche massenspektrometrische Analyse erlauben. Einer der wichtigsten Unterschiede zwischen diesen beiden Ionisationstechniken liegt in ihrer F�higkeit, mehrfach geladene Ionen zu erzeugen. MALDI erzeugt typischerweise einfach geladene Peptidionen, w�hrend nano- ESI leicht mehrfach geladene Ionen produziert, sogar für Peptide mit einer Masse von weniger als 1000 Da. Die Erzeugung von hoch geladenen Ionen ist wünschenswert, da dies die Verwendung von Massenanalysatoren wie Ionenfallen (inkl. Orbitraps) und Hybrid-Quadrupolinstrumenten ermçglicht, die typischerweise nur einen begrenzten m/z- Bereich (<2000–4000) bieten. Hohe Ladungszust�nde ermçglichen auch die Aufnahme von informativeren Fragmentionenspektren, wenn Methoden wie die kollisionsinduzierte Dissoziation (CID), die Elektroneneinfang-Dissoziation (ECD) und die Elektronentransfer-Dissoziation (ETD) in Kombination mit der Tandem-MS (MS/MS) verwendet werden.

Switchable amplification of vibrational circular dichroism as a probe of local chiral structure

A new method to detect the vibrational circular dichroism (VCD) of a localized part of a chiral molecular system is reported. A local VCD amplifier was implemented, and the distance dependence of the amplification was investigated in a series of peptides. The results indicate a characteristic distance of 2.0±0.3 bonds, which suggests that the amplification is a localized phenomenon. The amplifier can be covalently coupled to a specific part of a molecule, and can be switched ON and OFF electrochemically. By subtracting the VCD spectra obtained when the amplifier is in the ON and OFF states, the VCD of the local environment of the amplifier can be separated from the total VCD spectrum. Switchable local VCD amplification thus makes it possible to “zoom in” on a specific part of a chiral molecule.