Excited State Equilibrium Induced Lifetime Extension in a Dinuclear Platinum(II) Complex

Covalently linking two square planar platinum­(II) centers using two pyrazolate bridging ligands allows the filled d<i>z</i>² orbitals on each Pt center to overlap, producing a Pt–Pt σ interaction and new low energy dσ* → π* metalmetal-to-ligand charge transfer (MMLCT) transitions terminating on an appropriate π-acceptor ligand such as 2-phenylpyridine (ppy). In an effort to extend the lifetime of the associated MMLCT excited state, we decided to append piperidinyl naphthalimide (PNI) chromophores to the 2-phenylpyridine charge transfer ligands. This structural modification introduces low-lying PNI-based triplet states serving as long-lived triplet population reservoirs, thermally capable of repopulating the charge transfer state at room temperature (RT), thereby extending its excited state lifetime. Specifically, [Pt­(PNI-ppy)­(μ-Ph₂pz)]₂ (<b>1</b>), where PNI-ppy is <i>N</i>-(2-phenylpyridine)-4-(1-piperidinyl)­naphthalene-1,8-dicarboximide and Ph₂pz is 3,5-diphenylpyrazolate, was synthesized and structurally characterized. The static and dynamic photophysical behavior of <b>1</b> was directly compared to the MMLCT complex [Pt­(ppy)­(μ-Ph₂pz)]₂ (<b>2</b>), lacking the PNI substituents, as well as the naked PNI-ppy ligand <b>3</b>, intended to independently model the MMLCT and NI excited state properties, respectively. Ultimately, experimental evidence for the presence of both the ³PNI and ³MMLCT excited states in <b>1</b> were revealed at RT in nanosecond transient absorbance and time-resolved photoluminescence spectroscopy, respectively. Temperature-dependent transient absorption spectroscopy permitted the extraction of an energy gap of 1740 cm^–1 between the MMLCT and PNI triplet states in <b>1</b> along with the time constants associated with the interconversions between the various excited states resident on this complex chromophore, ultimately decaying back to the ground state with a time constant of 65 μs at RT

Excited-State Processes of Cyclometalated Platinum(II) Charge-Transfer Dimers Bridged by Hydroxypyridines

A series of four anti-disposed dinuclear platinum­(II) complexes featuring metal–metal-to-ligand charge-transfer (MMLCT) excited states, bridged by either 2-hydroxy-6-methylpyridine or 2-hydroxy-6-phenylpyridine and cyclometalated with 7,8-benzoquinoline or 2-phenylpyridine, are presented. The 2-hydroxypyridine bridging ligands control intramolecular d⁸–d⁸ metal–metal σ interactions, affecting the frontier orbitals’ electronic structure, resulting in marked changes to the ground- and excited-state properties of these complexes. Three of these molecules possess reversible one-electron oxidations in cyclic voltammetry experiments as a result of strong intramolecular metallophilic interactions. In this series of molecules, X-ray crystallography revealed Pt–Pt distances ranging between 2.815 and 2.878 Å; the former represents the shortest reported metal–metal distance for platinum­(II) dimers possessing low-energy MMLCT transitions. All four molecules reported here display visible absorption bands beyond 500 nm and feature MMLCT-based red photoluminescence (PL) above 700 nm at room temperature with high PL quantum yields (up to 4%) and long excited-state lifetimes (up to 341 ns). The latter were recorded using both transient PL and transient absorption experiments that self-consistently yielded quantitatively identical excited-state lifetimes. The energy-gap law was successfully applied to this series of chromophores, documenting this behavior for the first time in molecules possessing MMLCT excited states. The combined data illustrate that entirely new classes of MMLCT chromophores can be envisioned using bridging pyridyl hydroxides in cooperation with various C^N cyclometalates to achieve photophysical properties suitable for excited-state electron- and energy-transfer chemistry

DNA Binding, amelioration of oxidative stress, and molecular docking study of Zn(II) metal complex of a new Schiff base ligand

<p>A new Schiff base ligand, H₂L, and its Zn(II) complex were prepared and characterized by different analytical and spectroscopic techniques. The elemental analysis results suggest the stoichiometry of the complex to be 1:1. The molar conductance study shows the non-electrolytic nature of the complex. Infrared spectra reveal that the metal ion is coordinated in tetradentate fashion which was further confirmed by NMR study. The synthesized complex was found to interact with CT-DNA quite efficiently. The DNA binding study of the complex was explored by UV–vis and viscosity measurement. Fluorescence titration studies and the experimental results suggest that the complex might bind to DNA via an intercalative mode. The <i>in silico</i> target prediction and molecular docking experiments confirm that, apart from high interaction potentiality with nucleotides, the complex has possible implications in carcinogenesis, too.</p

A Quest for miRNA Bio-Marker: A Track Back Approach from Gingivo Buccal Cancer to Two Different Types of Precancers

<div><p>Deregulation of miRNA expression may contribute to tumorigenesis and other patho-physiology associated with cancer. Using TLDA, expression of 762 miRNAs was checked in 18 pairs of gingivo buccal cancer-adjacent control tissues. Expression of significantly deregulated miRNAs was further validated in cancer and examined in two types of precancer (leukoplakia and lichen planus) tissues by primer-specific TaqMan assays. Biological implications of these miRNAs were assessed bioinformatically. Expression of <i>hsa-miR-1293, hsa-miR-31, hsa-miR-31*</i> and <i>hsa-miR-7</i> were significantly up-regulated and those of <i>hsa-miR-206, hsa-miR-204</i> and <i>hsa-miR-133a</i> were significantly down-regulated in all cancer samples. Expression of only <i>hsa-miR</i>-31 was significantly up-regulated in leukoplakia but none in lichen planus samples. Analysis of expression heterogeneity divided 18 cancer samples into clusters of 13 and 5 samples and revealed that expression of 30 miRNAs (including the above-mentioned 7 miRNAs), was significantly deregulated in the cluster of 13 samples. From database mining and pathway analysis it was observed that these miRNAs can significantly target many of the genes present in different cancer related pathways such as “proteoglycans in cancer”, <i>PI3K-AKT</i> etc. which play important roles in expression of different molecular features of cancer. Expression of <i>hsa-miR-31</i> was significantly up-regulated in both cancer and leukoplakia tissues and, thus, may be one of the molecular markers of leukoplakia which may progress to gingivo-buccal cancer.</p></div

A Quest for miRNA Bio-Marker: A Track Back Approach from Gingivo Buccal Cancer to Two Different Types of Precancers - Figure 3

<p><b>A: Manhattan plot of p-values for 520 miRNAs from the cluster of 13 samples.</b> The plot of relative location of 520 miRNAs (along the horizontal axis) across the human chromosome and their corresponding –log₁₀ transformed p-value (along the vertical axis). Benjamini-Hochberg corrected P-value cut off was 0.00298 (Horizontal line in the middle of figure). <b>B: Heat map diagram of ΔΔCt values of 30 miRNAs</b>. Expression of these miRNAs was significantly deregulated in the cluster of 13 samples. Each row represents a miRNA and each column represents a sample. Sky-blue colored cells stand for failed assay (i.e.no data in those cells). Red and green colors signify up- and down-regulation of expression, respectively. Heat map was constructed using Heatmap 2 of R's “gplot” package. <b>C: Highly correlated expression of miR-411* and miR-411</b>.</p

Reported targets associated with 7 miRNAs significantly deregulated in 18 cancer samples.

@<p>: Up-regulation of expression of miRNAs.</p>$<p>: Down regulation of expression of miRNAs.</p>∧<p>Benjamini-Hochberg corrected p-value cut off at 5% level: 6.5E⁻⁰⁴.</p><p><b>ΔΔCt</b> =  ΔCt _{of a gene in cancer tissue} - ΔCt _{of that gene in control tissue}.</p>#<p>; Expression of <i>has-miR-1</i> is not significantly deregulated and shown for comparison only.</p><p>MN- Mouth Neoplasm, HN- Head and Neck Cancer, SCC- Squamous Cell Carcinoma, LN- Laryngeal Neoplasm, EN- Esophageal Neoplasm, OLP-Oral Leukoplakia, <i>GCN1L1</i>- general control of amino-acid synthesis 1-like 1.</p

Demography of 18 leukoplakia patients.

<p><b>*</b>All except two (LK5 & LK9) patients had tobacco habits.</p

Demography of 12 lichen planus patients.

<p>*2 out of 12 (Patient LP1 and LP6) patients had tobacco habits.</p

Demography of 18 cancer patients and their tumor differentiation status.

<p><b>*</b>All patients had tobacco habits;</p>@<p>Mx: metastasis status not known.</p

Tunable Excited-State Properties and Dynamics as a Function of Pt–Pt Distance in Pyrazolate-Bridged Pt(II) Dimers

The influence of molecular structure on excited-state properties and dynamics of a series of cyclometalated platinum dimers was investigated through a combined experimental and theoretical approach using femtosecond transient absorption (fs TA) spectroscopy and density functional theory (DFT) calculations. The molecules have the general formula [Pt­(ppy)­(μ-R₂pz)]₂, where ppy = 2-phenylpyridine, pz = pyrazolate, and R = H, Me, Ph, or ^tBu, and are strongly photoluminescent at room temperature. The distance between the platinum centers in this A-frame geometry can be varied depending on the steric bulk of the bridging pyrazolate ligands that exert structural constraints and compress the Pt–Pt distance. At large Pt–Pt distances there is little interaction between the subunits, and the chromophore behaves similar to a monomer with excited states described as mixtures of ligand-centered and metal-to-ligand charge transfer (LC/MLCT) transitions. When the Pt­(II) centers are brought closer together with bulky bridging ligands, they interact through their d_<i>z</i>² orbitals and the S₁ and T₁ states are best characterized as metal–metal-to-ligand charge transfer (MMLCT) in character. The results of the femtoseconds TA experiments reveal that intersystem crossing (ISC) occurs on ultrafast time scales (τ_S1 < 200 fs), while there are two relaxation processes occurring within the triplet manifold, τ₁ = 0.5–3.2 ps and τ₂ = 20–70 ps; the longer time constants correspond to the presence of bulkier bridging ligands. DFT calculations illustrate that the Pt–Pt distances further contract in the T₁ ³MMLCT states; therefore, slower relaxation may be related to a larger structural reorganization. Subsequent investigations using faster time resolution are planned to measure the ISC process as well as to identify any potential coherent interaction(s) between the platinum centers that may occur