Ultrafast Au(III)-Mediated Arylation of Cysteine.

Through mechanistic work and rational design, we have developed the fastest organometallic abiotic Cys bioconjugation. As a result, the developed organometallic Au(III) bioconjugation reagents enable selective labeling of Cys moieties down to picomolar concentrations and allow for the rapid construction of complex heterostructures from peptides, proteins, and oligonucleotides. This work showcases how organometallic chemistry can be interfaced with biomolecules and lead to a range of reactivities that are largely unmatched by classical organic chemistry tools.

Stimuli responsive asymmetric catalysis by triggered pseudo-enantiomeric proligand release.

Complex stimuli responsive systems are the basis for molecular machines and computing. A dual psuedo-enantiomer system was conceived, where the combination of two 'switch-on' asymmetric catalytic cycles could be selectively triggered to afford an enantioenriched product. Two pseudo-enantiomeric proligands were designed and synthesised for selective activation by fluoride and alkaline phosphatase. The proligands were firstly incorporated into single proligand systems, and then into a dual proligand system, where enantioselectivity of up to 98 : 2 was achieved in the reduction of prochiral ketone following external stimulation.

Pd(II)-Mediated C-H Activation for Cysteine Bioconjugation.

Selective bioconjugation remains a significant challenge for the synthetic chemist due to the stringent reaction conditions required by biomolecules coupled with their high degree of functionality. The current trailblazer of transition-metal mediated bioconjugation chemistry involves the use of Pd(II) complexes prepared via an oxidative addition process. Herein, the preparation of Pd(II) complexes for cysteine bioconjugation via a facile C-H activation process is reported. These complexes show bioconjugation efficiency competitive with what is seen in the current literature, with a user-friendly synthesis, common Pd(II) sources, and a more cost-effective ligand. Furthermore, these complexes need not be isolated, and still achieve high conversion efficiency and selectivity of a model peptide. These complexes also demonstrate the ability to selectively arylate a single surface cysteine residue on a model protein substrate, further demonstrating their utility.

Ratiometric Electrochemistry: Improving the Robustness, Reproducibility and Reliability of Biosensors.

Electrochemical biosensors are an increasingly attractive option for the development of a novel analyte detection method, especially when integration within a point-of-use device is the overall objective. In this context, accuracy and sensitivity are not compromised when working with opaque samples as the electrical readout signal can be directly read by a device without the need for any signal transduction. However, electrochemical detection can be susceptible to substantial signal drift and increased signal error. This is most apparent when analysing complex mixtures and when using small, single-use, screen-printed electrodes. Over recent years, analytical scientists have taken inspiration from self-referencing ratiometric fluorescence methods to counteract these problems and have begun to develop ratiometric electrochemical protocols to improve sensor accuracy and reliability. This review will provide coverage of key developments in ratiometric electrochemical (bio)sensors, highlighting innovative assay design, and the experiments performed that challenge assay robustness and reliability.

Ruthenium catalyzed remote C4-selective C-H functionalisation of carbazoles via σ-activation.

We report the C4-selective C-H alkylation of carbazole derivatives furnished with a pyrimidine directing group at N9. This was realized using ruthenium catalyzed σ-activation methodology, whereby C-H activation at C1 enables the interaction of this ruthenacycle, at the para position to the metal center, with tertiary alkyl radicals.

Ruthenium-catalysed σ-activation for remote meta-selective C-H functionalisation.

The search for selective C-H functionalisation has enabled some of the most elegant techniques in modern catalysis. Herein, we review the rapidly expanding field of ruthenium catalysed σ-activation as a tool in the selective meta-C-H functionalisation of arenes.

Ruthenium-Catalyzed para-Selective C-H Alkylation of Aniline Derivatives.

The para-selective C-H alkylation of aniline derivatives furnished with a pyrimidine auxiliary is herein reported. This reaction is proposed to take place via an N-H-activated cyclometalate formed in situ. Experimental and DFT mechanistic studies elucidate a dual role of the ruthenium catalyst. Here the ruthenium catalyst can undergo cyclometalation by N-H metalation (as opposed to C-H metalation in meta-selective processes) and form a redox active ruthenium species, to enable site-selective radical addition at the para position.

Ratiometric electrochemical detection of ß-galactosidase.

A novel ferrocene-based substrate for the ratiometric electrochemical detection of ß-galactosidase was designed and synthesised. It was demonstrated to be an excellent electrochemical substrate for ß-Gal detection with sensitivity as low as 0.1 U mL-1.

α-Halo carbonyls enable meta selective primary, secondary and tertiary C-H alkylations by ruthenium catalysis.

A catalytic meta selective C-H alkylation of arenes is described using a wide range of α-halo carbonyls as coupling partners. Previously unreported primary alkylations with high meta selectivity have been enabled by this methodology whereas using straight chain alkyl halides affords ortho substituted products. Mechanistic analysis reveals an activation pathway whereby cyclometalation with a ruthenium(ii) complex activates the substrate molecule and is responsible for the meta selectivity observed. A distinct second activation of the coupling partner allows site selective reaction between both components.

Ratiometric electrochemical detection of hydrogen peroxide and glucose.

Hydrogen peroxide (H2O2) detection is of high importance as it is a versatile (bio)marker whose detection can indicate the presence of explosives, enzyme activity and cell signalling pathways. Herein, we demonstrate the rapid and accurate ratiometric electrochemical detection of H2O2 using disposable screen-printed electrodes through a reaction-based indicator assay. Ferrocene derivatives equipped with self-immolative linkers and boronic acid ester moieties were synthesised and tested, and, through a thorough assay optimisation, the optimum probe showed good stability, sensitivity and selectivity towards H2O2. The optimised conditions were then applied to the indirect detection of glucose via an enzymatic assay, capable of distinguishing 10 µM from the background within minutes.

Use of the Hydantoin Directing Group in Ruthenium(II)-Catalyzed C-H Functionalization.

Ruthenium(II)-catalyzed C-H functionalization of N-arylhydantoins is herein described. The biologically relevant hydantoin (imidazolidinedione) heterocycle functions as a weakly coordinating directing group in a C-H alkenylation reaction. The reaction gave a wide scope of 23 examples with yields up to 94% in the green solvent 2-MeTHF. Functionalization of API nilutamide (antiandrogen) is also reported. The use of the succinimide heterocycle as a directing group is also demonstrated in modest yields.

Approaches towards molecular amplification for sensing.

Diagnostic assays that rely on molecular interactions have come a long way; from initial reversible detection systems towards irreversible reaction indicator-based methods. More recently, the emergence of innovative molecular amplification methodologies has revolutionised sensing, allowing diagnostic assays to achieve ultra-low limits of detection. There have been a significant number of molecular amplification approaches developed over recent years to accommodate the wide variety of analytes that require sensitive detection. To celebrate this achievement, this comprehensive critical review has been compiled to give a broad overview of the many different approaches used to attain amplification in sensing with an aim to inspire the next generation of diagnostic assays looking to achieve the ultimate detection limit. This review has been created with the focus on how each conceptually unique molecular amplification methodology achieves amplification, not just its sensitivity, while highlighting any key processes. Excluded are any references that were not found to contain an obvious molecular amplifier or amplification component, or that did not use an appropriate signal readout that could be incorporated into a sensing application. Additionally, methodologies where amplification is achieved through advances in instrumentation are also excluded. Depending upon the type of approach employed, amplification strategies are divided into four categories: target, label, signal or receptor amplification. More recent, more complex protocols combine a number of approaches and are therefore categorised by which amplification component described within was considered as the biggest advancement. The advantages and disadvantages of each methodology are discussed along with any limits of detection, if stated in the original article. Any subsequent use of the methodology within sensing or any other application is also mentioned to draw attention to its practicality. The importance of amplification within sensing is wholly emphasised while perspectives on the future direction of the field are also shared.

Community Sewage Sensors towards Evaluation of Drug Use Trends: Detection of Cocaine in Wastewater with DNA-Directed Immobilization Aptamer Sensors.

Illicit drug use has a global concern and effective monitoring and interventions are highly required to combat drug abuse. Wastewater-based epidemiology (WBE) is an innovative and cost-effective approach to evaluate community-wide drug use trends, compared to traditional population surveys. Here we report for the first time, a novel quantitative community sewage sensor (namely DNA-directed immobilization of aptamer sensors, DDIAS) for rapid and cost-effective estimation of cocaine use trends via WBE. Thiolated single-stranded DNA (ssDNA) probe was hybridized with aptamer ssDNA in solution, followed by co-immobilization with 6-mercapto-hexane onto the gold electrodes to control the surface density to effectively bind with cocaine. DDIAS was optimized to detect cocaine at as low as 10 nM with a dynamic range from 10 nM to 5 µM, which were further employed for the quantification of cocaine in wastewater samples collected from a wastewater treatment plant in seven consecutive days. The concentration pattern of the sampling week is comparable with that from mass spectrometry. Our results demonstrate that the developed DDIAS can be used as community sewage sensors for rapid and cost-effective evaluation of drug use trends, and potentially implemented as a powerful tool for on-site and real-time monitoring of wastewater by un-skilled personnel.

Ruthenium-Catalyzed O- to S-Alkyl Migration: A Pseudoreversible Barton-McCombie Pathway.

A practical ruthenium-catalyzed O- to S-alkyl migration affords structurally diverse thiooxazolidinones in excellent yields. Our studies suggest this catalytic transformation proceeds through a pseudoreversible radical pathway drawing mechanistic parallels to the classic Barton-McCombie reaction.

Catalytic meta-selective C-H functionalization to construct quaternary carbon centres.

A catalytic meta-selective C-H functionalization of 2-phenylpyridines using a range of tertiary halides is described. The protocol is simple to perform and uses commercially available reagents to construct challenging quaternary carbon centres in a regioselective manner. Preliminary studies suggest the C-H functionalization proceeds through a radical process directed via a remote σ-activation.

Trans-selective rhodium catalysed conjugate addition of organoboron reagents to dihydropyranones.

The selective synthesis of 2,6-trans-tetrahydropyran derivatives employing the rhodium catalysed addition of organoboron reagents to dihydropyranone templates, derived from a zinc-catalysed hetero-Diels-Alder reaction, is reported. The addition of both arylboronic acids and potassium alkenyltrifluoroborates have been accomplished in high yields using commercially-available [Rh(cod)(OH)]2 catalyst. The selective formation of the 2,6-trans-tetrahydropyran stereoisomer is consistent with a mechanism involving alkene association and carbometalation on the less hindered face of the dihydropyranone.

A novel DNA biosensor using a ferrocenyl intercalator applied to the potential detection of human population biomarkers in wastewater.

A new label-free electrochemical DNA (E-DNA) biosensor using a custom synthesized ferrocenyl (Fc) double-stranded DNA intercalator as a redox marker is presented. Single-stranded DNA (ssDNA) was co-immobilized on gold electrodes with 6-mecarpto-hexanol to control the surface density of the ssDNA probe, and hybridized with complementary DNA. The binding of the Fc intercalator to dsDNA was measured by differential pulse voltammetry. This new biosensor was optimized to allow the detection of single base pair mismatched sequences, able to detect as low as 10 pM target ssDNA with a dynamic range from 10 pM to 100 nM. DNA extracted from wastewater was analyzed by quantitative polymerase chain reaction targeting human-specific mitochondrial DNA (mtDNA). The aim of this approach is to enable the analysis of population biomarkers in wastewater for the evaluation of public health using wastewater-based epidemiology (WBE). The E-DNA biosensor was employed to detect human-specific mtDNA from wastewater before and after PCR amplification. The results demonstrate the feasibility of detecting human DNA biomarkers in wastewater using the developed biosensor, which may allow the further development of DNA population biomarkers for public health using WBE.

A novel immobilization strategy for electrochemical detection of cancer biomarkers: DNA-directed immobilization of aptamer sensors for sensitive detection of prostate specific antigens.

We report on a novel strategy for DNA aptamer immobilization to develop sensitive electrochemical detection of a protein biomarker, with prostate specific antigen (PSA) as a case biomarker. Thiolated single-stranded DNA (ssDNA) was co-immobilized with 3-mercapto-1-propanol on gold electrodes, and used as a scaffold for DNA aptamer attachment through hybridization of the aptamer overhang (so-called "DNA-directed immobilization aptamer sensors", DDIAS). In the approach, the complementary DNA aptamer against PSA was assembled by the probe ssDNA onto the electrode to detect PSA; or the probe ssDNA directly hybridized with a complementary DNA aptamer/PSA complex following their pre-incubation in solution, so-called 'on-chip' and 'in-solution' methods, respectively. A double stranded DNA intercalator with a ferrocenyl (Fc) redox marker was synthesized to evaluate the feasibility of the strategy. The results demonstrate that the 'in-solution' method offers a favourable medium (in a homogeneous solution) for the binding between the aptamer and PSA, which shows to be more efficient than the 'on-chip' approach. DDIAS shows promising analytical performance under optimized conditions, with a limit of detection in the range of fM and low non-specific adsorption.

Ratiometric electrochemical detection of alkaline phosphatase.

A novel ferrocene-derived substrate for the ratiometric electrochemical detection of alkaline phosphatase (ALP) was designed and synthesised. It was demonstrated to be an excellent electrochemical substrate for the ALP-labelled enzyme-linked immunosorbent assay (ELISA).