Correction: Time-resolved infra-red studies of photo-excited porphyrins in the presence of nucleic acids and in HeLa tumour cells: insights into binding site and electron transfer dynamics.

Correction for 'Time-resolved infra-red studies of photo-excited porphyrins in the presence of nucleic acids and in HeLa tumour cells: insights into binding site and electron transfer dynamics' by Páraic M. Keane et al., Phys. Chem. Chem. Phys., 2022, 24, 27524-27531, https://doi.org/10.1039/D2CP04604K.

Time-resolved infra-red studies of photo-excited porphyrins in the presence of nucleic acids and in HeLa tumour cells: insights into binding site and electron transfer dynamics.

Cationic porphyrins based on the 5,10,15,20-meso-(tetrakis-4-N-methylpyridyl) core (TMPyP4) have been studied extensively over many years due to their strong interactions with a variety of nucleic acid structures, and their potential use as photodynamic therapeutic agents and telomerase inhibitors. In this paper, the interactions of metal-free TMPyP4 and Pt(II)TMPyP4 with guanine-containing nucleic acids are studied for the first time using time-resolved infrared spectroscopy (TRIR). In D2O solution (where the metal-free form exists as D2TMPyP4) both compounds yielded similar TRIR spectra (between 1450-1750 cm-1) following pulsed laser excitation in their Soret B-absorption bands. Density functional theory calculations reveal that vibrations centred on the methylpyridinium groups are responsible for the dominant feature at ca. 1640 cm-1. TRIR spectra of D2TMPyP4 or PtTMPyP4 in the presence of guanosine 5'-monophosphate (GMP), double-stranded {d(GC)5}2 or {d(CGCAAATTTGCG)}2 contain negative-going signals, 'bleaches', indicative of binding close to guanine. TRIR signals for D2TMPyP4 or PtTMPyP bound to the quadruplex-forming cMYC sequence {d(TAGGGAGGG)}2T indicate that binding occurs on the stacked guanines. For D2TMPyP4 bound to guanine-containing systems, the TRIR signal at ca. 1640 cm-1 decays on the picosecond timescale, consistent with electron transfer from guanine to the singlet excited state of D2TMPyP4, although IR marker bands for the reduced porphyrin/oxidised guanine were not observed. When PtTMPyP is incorporated into HeLa tumour cells, TRIR studies show protein binding with time-dependent ps/ns changes in the amide absorptions demonstrating TRIR's potential for studying light-activated molecular processes not only with nucleic acids in solution but also in biological cells.

The influence of loops on the binding of the [Ru(phen)2dppz]2+ light-switch compound to i-motif DNA structures revealed by time-resolved spectroscopy.

Ultrafast time resolved infrared (TRIR) is used to report on the binding site of the "light-switch" complex [Ru(phen)2(dppz)]2+1 to i-motif structures in solution. Detailed information is provided due to perturbation of the local base vibrations by a 'Stark-like' effect which is used to establish the contribution of thymine base loop interactions to the binding site of 1 in this increasingly relevant DNA structure.

Caught in the Loop: Binding of the [Ru(phen)2 (dppz)]2+ Light-Switch Compound to Quadruplex DNA in Solution Informed by Time-Resolved Infrared Spectroscopy.

Ultrafast time-resolved infrared (TRIR) is used to report on the binding site of the [Ru(phen)2 (dppz)]2+ "light-switch" complex with both bimolecular (Oxytricha nova telomere) and intramolecular (human telomere) guanine-quadruplex structures in both K+ and Na+ containing solutions. TRIR permits the simultaneous monitoring both of the "dark" and "bright" states of the complex and of the quadruplex nucleobase bases, the latter via a Stark effect induced by the excited state of the complex. These data are used to establish the contribution of guanine base stacking and loop interactions to the binding site of this biologically relevant DNA structure in solution. A particularly striking observation is the strong thymine signal observed for the Na+ form of the human telomere sequence, which is expected to be in the anti-parallel conformation.

Investigation of the Cellular Destination of Fluorescently Labeled Carbon Nanohorns in Cultured Cells.

The high surface area, facile functionalization, and biocompatibility of carbon nanohorns (CNHs) make them attractive for many applications, including drug delivery. The cellular destination of nanomaterials dictates both the therapeutic application and the potential toxicity. Identifying the uptake mechanism is challenging as several endocytic pathways have been identified that facilitate cellular entry. Here, the cellular uptake of fluorescently labeled CNHs was assessed by utilizing quantitative cell-based assays to determine the factors influencing how internalization occurs and the destinations they reach in HeLa cells. Cell viability assays suggest that about 80% of the cells remained viable even at the highest concentration of 20 µg/mL exposure to CNHs. Uptake studies revealed that when pulse-chase conditions were applied, CNHs were seen to be localized both at the cell periphery and in a juxtanuclear pattern inside HeLa cells, in the latter case colocalizing with the lysosomal marker LAMP1. RNA interference studies, using a panel of RNA tools to individually deplete key molecules associated with the endocytic machinery, failed to block the internalization of CNHs into cells, suggesting that multiple mechanisms of endocytosis are used by this particle type.

Preparation of polymer gold nanoparticle composites with tunable plasmon coupling and their application as SERS substrates.

The controlled surface functionalisation of polystyrene beads (200 nm) with a lipoic acid derivative is used to assemble composites with between 4 to 20% loadings of citrate stabilised gold nanoparticles (13 nm-30 nm), which exhibit variable optical properties arising from interactions of the nanoparticle surface plasmon resonance (SPR). The decrease in average interparticle distance at higher loadings results in a red-shift in the SPR wavelength, which is well described by a universal ruler equation. The composite particles are shown to act as good SERS substrates for the standard analyte 4-mercaptophenol. The direct assessment of the SERS activity for individual composite particles solution is achieved by Raman optical tweezer measurements on 5.3 µm composite particles. These measurements show an increase in performance with increasing AuNP size. Importantly, the SERS activity of the individual particles compares well with the bulk measurements of samples deposited on a surface, indicating that the SERS activity arises primarily from the composite and not due to composite-composite interactions. In both studies the optimum SERS response is obtained with 30 nm AuNPs.

Carbon nanohorn modified platinum electrodes for improved immobilisation of enzyme in the design of glutamate biosensors.

Electrochemical enzymatic biosensors are the subject of research due to their potential for in vivo monitoring of glutamate, which is a key neurotransmitter whose concentration is related to healthy brain function. This study reports the use of biocompatible oxidised carbon nanohorns (o-CNH) with a high surface area, to enhance the immobilization of glutamate oxidase (GluOx) for improved biosensor performance. Two families of biosensors were designed to interact with the anionic GluOx. Family-1 consists of covalently functionalised o-CNH possessing hydrazide (HYZ) and amine (PEG-NH2) terminated surfaces and Family-2 comprised non-covalently functionalised o-CNH with different loadings of polyethyleneimine (PEI) to form a cationic hybrid. Amperometric detection of H2O2 formed by enzymatic oxidation of glutamate revealed a good performance from all designs with the most improved performance by the PEI hybrid systems. The best response was from a o-CNH : PEI ratio of 1 : 10 mg mL-1, which yielded a glutamate calibration plateau, JMAX, of 55 ± 9 µA cm-2 and sensitivity of 111 ± 34 µA mM-1 cm-2. The low KM of 0.31 ± 0.05 mM indicated the retention of the enzyme function, and a limit of detection of 0.02 ± 0.004 µM and a response time of 0.88 ± 0.13 s was determined. The results demonstrate the high sensitivity of these biosensors and their potential for future use for the detection of glutamate in vivo.

Multimodal Microscopy Distinguishes Extracellular Aggregation and Cellular Uptake of Single-Walled Carbon Nanohorns.

The low toxicity, high surface area, and ease of functionalisation of carbon nanohorns (CNH) makes them attractive systems for cellular imaging, diagnostics and therapeutics. However, challenges remain for the biomedical translation of these and other nanomaterials. A significant task is tuning the surface chemistry to achieve optimal cellular interactions. Herein, we combine real-time fluorescent imaging of nanoparticle cellular uptake and real-time differential interference contrast (DIC) imaging of extracellular media to monitor a) nanoparticle/nanoparticle and b) nanoparticle/cell interactions for CNHs covalently modified with an OFF/ON near-IR dye, the fluorescence of which is switched OFF in extracellular environments and triggered upon cellular internalisation. CHN samples modified with different loadings of the hydrophobic dye are taken as a simple model of drug-loaded nanoparticle systems. The punctate fluorescence suggests the CNHs are delivered to lysosomes and other vesicles of the endocytic pathway. DIC imaging highlights the competition that exists for many particle types, between extracellular aggregation and cellular internalization, the efficiency of which would be dependent upon the amount of fluorophore loading. The results of this study illustrate how complementary real-time imaging methods together with physicochemical characterisation can be used to address the challenges involved in optimising nanoparticle/cell interactions for biomedical applications.

Long-Lived Excited-State Dynamics of i-Motif Structures Probed by Time-Resolved Infrared Spectroscopy.

UV-generated excited states of cytosine (C) nucleobases are precursors to mutagenic photoproduct formation. The i-motif formed from C-rich sequences is known to exhibit high yields of long-lived excited states following UV absorption. Here the excited states of several i-motif structures have been characterized following 267 nm laser excitation using time-resolved infrared spectroscopy (TRIR). All structures possess a long-lived excited state of ∼300 ps and notably in some cases decays greater than 1 ns are observed. These unusually long-lived lifetimes are attributed to the interdigitated DNA structure which prevents direct base stacking overlap.

Study of picosecond processes of an intercalated dipyridophenazine Cr(III) complex bound to defined sequence DNAs using transient absorption and time-resolved infrared methods.

Picosecond transient absorption (TA) and time-resolved infrared (TRIR) measurements of rac-[Cr(phen)2(dppz)](3+) () intercalated into double-stranded guanine-containing DNA reveal that the excited state is very rapidly quenched. As no evidence was found for the transient electron transfer products, it is proposed that the back electron transfer reaction must be even faster (<3 ps).