The chemistry of phosphines in constrained, well-defined microenvironments

Developments in the confinement of phosphines within micro- or nano-environments are explored. Phosphines are ubiquitous across metal coordination chemistry and underpin some of the most famous homogeneous transition metal catalysts. Constraining phosphines within confined environments influences not only their behaviour but also that of their metal complexes. Notable examples include the use of metal–organic frameworks (MOFs) or metal–organic cages (MOCs) to support phosphines which demonstrate how the microenvironment within such constructs leads to reactivity modification. The development of phosphine confinement is explored and parallels are drawn with related constrained macrocyclic systems and mechanically interlocked molecules. The review concludes by identifying areas that remain a challenge and those that will provide new avenues for research

Physisorption controls the conformation and density of states of an adsorbed porphyrin

Conformational changes caused by adsorption can dramatically affect a molecule’s properties. Despite extensive study, however, the exact mechanisms underpinning conformational switching are often unclear. Here we show that the conformation of a prototypical flexible molecule, the freebase tetra(4-bromophenyl) porphyrin, adsorbed on Cu(111), depends critically on its precise adsorption site and that, remarkably, large conformational changes are dominated by van der Waals interactions between the molecule and the substrate surface. A combination of scanning probe microscopy, single-molecule manipulation, DFT with dispersion density functional theory, and molecular dynamics simulations show that van der Waals forces drive significant distortions of the molecular architecture so that the porphyrin can adopt one of two low-energy conformations. We find that adsorption driven by van der Waals forces alone is capable of causing large shifts in the molecular density of states, despite the apparent absence of chemical interactions. These findings highlight the essential role that van der Waals forces play in determining key molecular properties

Simulated structure and imaging of NTCDI on Si(1 1 1)-7 × 7 : a combined STM, NC-AFM and DFT study

The adsorption of naphthalene tetracarboxylic diimide (NTCDI) on Si(1 1 1)-7 × 7 is investigated through a combination of scanning tunnelling microscopy (STM), noncontact atomic force microscopy (NC-AFM) and density functional theory (DFT) calculations. We show that NTCDI adopts multiple planar adsorption geometries on the Si(1 1 1)-7 × 7 surface which can be imaged with intramolecular bond resolution using NC-AFM. DFT calculations reveal adsorption is dominated by covalent bond formation between the molecular oxygen atoms and the surface silicon adatoms. The chemisorption of the molecule is found to induce subtle distortions to the molecular structure, which are observed in NC-AFM images

Research Output From University-Industry Collaborative Projects

We study collaborative and noncollaborative projects that are supported by government grants. First, we propose a theoretical framework to analyze optimal decisions in these projects. Second, we test our hypotheses with a unique data set containing academic publications and research funds for all academics at the major university engineering departments in the United Kingdom. We find that the type of the project (measured by its level of appliedness) increases the type of both the university and firm partners. Also, the quality of the project (number and impact of the publications) increases with the quality of the researcher and firm, and with the affinity in the partners' preferences. The collaboration with firms increases the quality of the project only when the firms' characteristics make them valuable partners

A novel compartment, the 'subqpical stem' of the aerial hyphae, is the location of a sigN-dependent, developmentally distinct transcription in Streptomyces coelicolor.

Streptomyces coelicolor has nine SigB-like RNA polymerase sigma factors, several of them implicated in morphological differentiation and/or responses to different stresses. One of the nine, SigN, is the focus of this article. A constructed sigN null mutant was delayed in development and exhibited a bald phenotype when grown on minimal medium containing glucose as carbon source. One of two distinct sigN promoters, sigNP1, was active only during growth on solid medium, when its activation coincided with aerial hyphae formation. Transcription from sigNP1 was readily detected in several whi mutants (interrupted in morphogenesis of aerial mycelium into spores), but was absent from all bld mutants tested, suggesting that sigNP1 activity was restricted to the aerial hyphae. It also depended on sigN, thus sigN was autoregulated. Mutational and transcription studies revealed no functional significance to the location of sigN next to sigF, encoding another SigB-like sigma factor. We identified another potential SigN target, nepA, encoding a putative small secreted protein. Transcription of nepA originated from a single, aerial hyphae-specific and sigN-dependent promoter. While in vitro run-off transcription using purified SigN on the Bacillus subtilis ctc promoter confirmed that SigN is an RNA polymerase sigma factor, SigN failed to initiate transcription from sigNP1 and from the nepA promoter in vitro. Additional in vivo data indicated that further nepA upstream sequences, which are likely to bind a potential activator, are required for successful transcription. Using a nepA–egfp transcriptional fusion we located nepA transcription to a novel compartment, the ‘subapical stem’ of the aerial hyphae. We suggest that this newly recognized compartment defines an interface between the aerial and vegetative parts of the Streptomyces colony and might also be involved in communication between these two compartments

Thermoelectric properties of the bismuth telluride nanowires in the constant-relaxation-time approximation

Electronic structure of bismuth telluride nanowires with the growth directions [110] and [015] is studied in the framework of anisotropic effective mass method using the parabolic band approximation. The components of the electron and hole effective mass tensor for six valleys are calculated for both growth directions. For a square nanowire, in the temperature range from 77 K to 500 K, the dependence of the Seebeck coefficient, the electron thermal and electrical conductivity as well as the figure of merit ZT on the nanowire thickness and on the excess hole concentration are investigated in the constant-relaxation-time approximation. The carrier confinement is shown to play essential role for square nanowires with thickness less than 30 nm. The confinement decreases both the carrier concentration and the thermal conductivity but increases the maximum value of Seebeck coefficient in contrast to the excess holes (impurities). The confinement effect is stronger for the direction [015] than for the direction [110] due to the carrier mass difference for these directions. The carrier confinement increases maximum value of ZT and shifts it towards high temperatures. For the p-type bismuth telluride nanowires with growth direction [110], the maximum value of the figure of merit is equal to 1.3, 1.6, and 2.8, correspondingly, at temperatures 310 K, 390 K, 480 K and the nanowire thicknesses 30 nm, 15 nm, and 7 nm. At the room temperature, the figure of merit equals 1.2, 1.3, and 1.7, respectively.Comment: 13 pages, 7 figures, 2 tables, typos added, added references for sections 2-

Photochemistry of framework-supported M(diimine)(CO)₃X complexes in 3D Lithium-Carboxylate metal−organic frameworks: monitoring the effect of framework cations

The structures and photochemical behaviour of two new metal-organic frameworks are reported. Reaction of Re(2,2ʹ-bipyʹ-5,5ʹ-dicarboxylic acid)(CO)₃Cl or Mn(2,2ʹ-bipyʹ-5,5ʹ- dicarboxylic acid)(CO)₃Br with either LiCl or LiBr, respectively, produces single crystals of {Li₂(DMF)₂[(2,2ʹ-bipyʹ-5,5ʹ-dicarboxylate)Re(CO)₃Cl]}n (ReLi) or {Li₂(DMF)₂[(2,2ʹ-bipyʹ- 5,5ʹ-dicarboxylate)Mn(CO)₃Br]}n (MnLi). The structures formed by the two MOFs comprise one-dimensional chains of carboxylate-bridged Li(I) cations that are cross-linked by units of Re(2,2ʹ-bipyʹ-5,5ʹ-dicarboxylate)(CO)₃Cl (ReLi) or Mn(2,2ʹ-bipyʹ-5,5ʹ- dicarboxylate)(CO)₃Br (MnLi). The photophysical and photochemical behaviour of both ReLi and MnLi are probed. The rhenium-containing MOF, ReLi, exhibits luminescence and the excited state behaviour, as established by time-resolved infra-red measurements, are closer in behaviour to that of unsubstituted [Re(bipy)(CO)₃Cl] rather than a related MOF where the Li(I) cations are replaced by Mn(II) cations. These observations are further supported by DFT calculations. Upon excitation MnLi forms a dicarbonyl species which rapidly recombines with the dissociated CO, in a fashion consistent with the majority of the photoejected CO not escaping the MOF channels

Mechanically interlocked molecular handcuffs

The field of mechanically interlocked molecules that employ a handcuff component are reviewed. The variety of rotaxane and catenane structures that use the handcuff motif to interlock different components are discussed and a new nomenclature, distilling diverse terminologies to a single approach, is proposed. By unifying the interpretation of this class of molecules we identify new opportunities for employing this structural unit for new architectures

Order, disorder, and metalation of tetraphenylporphyrin (2H-TPP) on Au(111)

A thermally induced order–disorder transition of tetraphenylporphyrin (2H-TPP) on Au(111) is characterised by scanning probe microscopy and X-ray photoelectron spectroscopy-based techniques. We observed that a transition from an ordered close-packed phase to a disordered diffuse phase is correlated with an on-surface cyclodehydrogenation reaction, and that additional heating of this diffuse phase gives rise to a single distinct nitrogen environment indicative of the formation of a Au–TPP species

Broken symmetry and the variation of critical properties in the phase behaviour of supramolecular rhombus tilings

The degree of randomness, or partial order, present in two-dimensional supramolecular arrays of isophthalate tetracarboxylic acids is shown to vary due to subtle chemical changes such as the choice of solvent or small differences in molecular dimensions. This variation may be quantified using an order parameter and reveals a novel phase behaviour including random tiling with varying critical properties as well as ordered phases dominated by either parallel or non-parallel alignment of neighbouring molecules, consistent with long-standing theoretical studies. The balance between order and randomness is driven by small differences in the intermolecular interaction energies, which we show, using numerical simulations, can be related to the measured order parameter. Significant variations occur even when the energy difference is much less than the thermal energy highlighting the delicate balance between entropic and energetic effects in complex self-assembly processes