Sulfate‐Selective Recognition by Using Neutral Dipeptide Anion Receptors in Aqueous Solution

The synthesis of six small peptide anion receptors based on thiourea and squaramide recognition moieties is described. These new receptors bind to tetrahedral sulfate anions with remarkable affinity and selectivity in aqueous solution as shown by NMR spectroscopy. Molecular modelling suggests that selectivity is mediated by a hydrogen bond network incorporating the amide backbone protons in a manner similar to that found in the sulfate‐binding protein.     

Hybrid cyclic peptide-thiourea cryptands for anion recognition

Two cyclic peptide derived cryptands incorporating thioureas in the framework were synthesised as neutral anion receptors and bind acetate ions with high affinity and, in one case, good selectivity.     

An expanded neutral M4L6 cage that encapsulates four tetrahydrofuran molecules

A large 4,4'-biphenylene-spaced bis-β-diketone ligand is demonstrated to form a neutral tetrahedral M(4)L(6) metal-organic cage that encloses a volume of 844 ?(3) and encapsulates four tetrahydrofuran guest molecules.     

Liquid�Cliquid extraction studies with 4,4��-biphenylene-spaced bis-��-diketones

4,4??-biphenylene spaced lipophilic bis-??-diketone ligands of the type 4,4??-bis(RC(O)CH₂C(O))C₁₂H₈ (R = Pr, Ph, hexyl, octyl, nonyl) have been prepared and used for the liquid?Cliquid extraction of d-block metal ions. These ligands are expected to interact with divalent metal ions to form charge-neutral trinuclear metallocycles of type [M₃(L ³ )₃(solvent)] as has been demonstrated with the previously reported derivative of H₂ L ³ (R =  ^t Bu), the X-ray structure of which is reported. Liquid?Cliquid extraction studies were performed in a two-phase water/chloroform system employing a radiotracer technique for cobalt(II) and zinc(II). These experiments involved the systematic variation of ligand, metal and 4-ethylpyridine concentrations to probe the stoichiometries of the species extracted. Synergistic extraction was observed when 4-ethylpyridine was present with the ligand in the organic phase. Competitive extraction studies demonstrated the ligands are highly selective for copper(II) over cobalt(II), nickel(II), zinc(II) and cadmium(II).     

Synthesis of Nitro-Aryl Functionalised 4-Amino-1,8-Naphthalimides and Their Evaluation as Fluorescent Hypoxia Sensors

Fluorescent sensors are a vital research tool, enabling the study of intricate cellular processes in a sensitive manner. The design and synthesis of responsive and targeted probes is necessary to allow such processes to be interrogated in the cellular environment. This remains a challenge, and requires methods for functionalisation of fluorophores with multiple appendages for sensing and targeting groups. Methods to synthesise more structurally complex derivatives of fluorophores will expand their potential scope. Most known 4-amino-1,8-naphthalimides are only functionalised at imide and 4-positions, and structural modifications at additional positions will increase the breadth of their utility as responsive sensors. In this work, methods for the incorporation of a hypoxia sensing group to 4-amino-1,8-naphthalimide were evaluated. An intermediate was developed that allowed us to incorporate a sensing group, targeting group, and ICT donor to the naphthalimide core in a modular fashion. Synthetic strategies for attaching the hypoxia sensing group and how they affected the fluorescence of the naphthalimide were evaluated by photophysical characterisation and time-dependent density functional theory. An extracellular hypoxia probe was then rationally designed that could selectively image the hypoxic and necrotic region of tumour spheroids. Our results demonstrate the versatility of the naphthalimide scaffold and expand its utility. This approach to probe design will enable the flexible, efficient generation of selective, targeted fluorescent sensors for various biological purposes.     

Total synthesis of (+/-)-rhazinal,an alkaloidal spindle toxin from Kopsia teoi

The title alkaloid 1 and its B-nor-congener 3, both of which display potent and unusual anti-mitotic properties, have been synthesized in racemic form and characterised by single-crystal X-ray analysis.     

Laser wavelength measurements and the speed of light

Early determinations of the speed of light, based on astronomical observations or terrestrial time-of-flight experiments, were largely superseded in the 1940's by measurements of the frequency and wavelength of microwave radiation. The results were limited by the uncertainty in the wavelength measurements, and it was apparent that greater accuracy could be achieved by using radiation of shorter wavelength. It was, however, not until the development of lasers, and the nonlinear optical techniques made possible by their high output intensities, that frequency measurements could be extended towards the visible region of the spectrum.Stimulated by a demand for a more precise knowledge of the speed of light for application in space research, geodesy, and metrology, a new series of determinations has recently taken place. The measurements were made upon the radiations from a number of different stabilized-laser systems operating in the near infrared and visible spectral regions. Several different interferometric techniques were developed for the wavelength measurements. The results have led to a new recommended value for the speed of light, 299 792 458±1.2 m s^–1, and to the possibility of re-defining the unit of length.