Conformational landscapes of bimesogenic compounds and their implications for the formation of modulated nematic phases

The twist-bend phase (NTB) is most commonly observed in materials with a gross-bent shape: dimers; bent-cores; bent-oligomers. We had suggested previously that the bend-angle of such systems effectively dictates the relative thermal stability of the NTB phase. However, our earlier paper relied on the use of a single energy-minimum conformer and so failed to capture any information about flexibility and conformational distribution. In the present work, we revisit our hypothesis and examine a second set of dimers with varying linking groups and spacer composition. We have improved on our earlier work by studying the conformational landscape of each material, allowing average bend-angles to be determined as well as the conformer distribution. We observe that the stability of the NTB phase exhibits a strong dependence not only on the Boltzmann-weighted average bend-angle (rather than just a static conformer), but also on the distribution of conformers. To a lesser extent, the flexibility of the spacer appears important. Ultimately, this work satisfies both theoretical treatments and our initial experimental study and demonstrates the importance of molecular bend to the NTB phase

Signal transduction in a covalent post-assembly modification cascade

Natural reaction cascades control the movement of biomolecules between cellular compartments. Inspired by these systems, we report a synthetic reaction cascade employing post-assembly modification reactions to direct the partitioning of supramolecular complexes between phases. The system is composed of a self-assembled tetrazine-edged FeII8L12 cube and a maleimide-functionalized FeII4L6 tetrahedron. Norbornadiene (NBD) functions as the stimulus that triggers the cascade, beginning with the inverse-electron-demand Diels–Alder reaction of NBD with the tetrazine moieties of the cube. This reaction generates cyclopentadiene as a transient by-product, acting as a relay signal that subsequently undergoes a Diels–Alder reaction with the maleimide-functionalized tetrahedron. Cyclooctyne can selectively inhibit the cascade by outcompeting NBD as the initial trigger. Initiating the cascade with 2-octadecyl NBD leads to selective alkylation of the tetrahedron upon cascade completion. The increased lipophilicity of the C18-tagged tetrahedron drives this complex into a non-polar phase, allowing its isolation from the initially inseparable mixture of complexes

Strengthening of Reinforced Concrete Members in Bending by Externally Bonded Steel Plates - Design for Beam Shear and Plate Anchorage

Civil Engineering and Geoscience

New Synthetic Strategies and Disconnections in the Synthesis of Liquid Crystals Enabled by Photoredox Cross-Coupling Reactions

In this letter we describe the application of metallaphotoredox cross-electrophile couplings to the synthesis of liquid crystals using dual nickel and iridium catalysis. Given the proliferation of aryl and alkyl bromides in liquid crystal research we consider that the silyl-radical mediated cross coupling of alkyl bromide with an aryl bromide (to afford a direct alkyl-aryl bond) will become an extremely powerful tool in the synthesis of liquid crystalline materials, and we use this to synthesise several well-known materials (PCH32, 5CB, CB7CB and CB15) in a single synthetic step from inexpensive and commercially available building blocks. The metallaphotoredox decarboxylative sp3-sp2 cross-coupling of an aryl bromide with an alkyl carboxylic acid provides a complimentary method to form alkyl-aryl bonds, and we use this to successfully prepare trans PCH5 in a single synthetic step from commercially available building blocks. We also prepare novel methylene linked materials in a single synthetic step, one of which exhibit the topical TB phase

Interaction between flexure and shear on the debonding of RC beams retrofitted with compression face plates

© 2002 Multi-Science Publishing Steel and FRP plating reinforced concrete structures is increasingly being used for retrofitting. Plates can be bonded to any surface of a beam or slab, although it is common practice to adhesively bond plates to the tension faces. The addition of these tension face plates reduces the sectional ductility of the beam. Furthermore, these tension face plates are prone to premature debonding because the stress concentrations induced by these plates overlap with those induced by the tension reinforcing bars adjacent to the plate. Solutions to these two problems, which are the subject of this paper, consist of: adhesively bonding plates to the compression faces to counterbalance the tension face plates and, hence, improve the beam sectional ductility; and to extend the tension face plates, in continuous beams, past the points of contraflexure so that they terminate in a compression face. In this paper, eleven new tests on 340 mm deep beams are presented that show that compression face plates are less prone to debonding than tension face plates. </jats:p

Immunogenic properties of octasaccharide-protein conjugates derived from Klebsiella serotype 11 capsular polysaccharide.

The tetrasaccharide repeating unit of the capsular polysaccharide of Klebsiella serotype 11, K11PS, comprises the following sequence: [----3)-beta-D-GlcpA-(1----3)-alpha-D-Galp-(1----3)-beta-D-Glcp-(1 ----] with a 4,6-O-(1-carboxyethylidene)-alpha-D-galactopyranosyl residue linked to O-4 of the glucuronic acid residue. Octasaccharide (OS) derived from K11PS by bacteriophage phi 11-associated glycanase, was coupled to bovine serum albumin and to keyhole limpet hemocyanin. The immunogenicity of various antigens after intraperitoneal immunization was studied by measuring the levels of circulating antibodies. Injection of BALB/c mice with K11PS resulted in induction of 2-mercaptoethanol-sensitive immunoglobulin M antibodies. The responses observed in BALB/c nu/nu mice and in male (CBA/N X C3H/HeN)F1 mice indicate that K11PS is a thymus-independent type 2 antigen. Immunization of BALB/c mice with either OS-bovine serum albumin or OS-keyhole limpet hemocyanin resulted in the induction of circulating 2-mercaptoethanol-resistant immunoglobulin G antibodies. Results in BALB/c nu/nu mice indicate that the OS-protein conjugates are thymus-dependent antigens. Since the OS-keyhole limpet hemocyanin conjugate induced antibodies in both (CBA/N X C3H/HeN)F1 females and males, we propose to refer to this kind of antigen as a thymus-dependent type 1 antigen, whereas OS-bovine serum albumin, which evoked immunoglobulins in (CBA/N X C3H/HeN)F1 females only, can be referred to as a thymus-dependent type 2 antigen