Combined anticancer therapy with imidazoacridinone C-1305 and paclitaxel in human lung and colon cancer xenografts-Modulation of tumour angiogenesis

The acridanone derivative 5-dimethylaminopropylamino-8-hydroxytriazoloacridinone (C-1305) has been described as a potent inhibitor of cancer cell growth. Its mechanism of action in in vitro conditions was attributed, among others, to its ability to bind and stabilize the microtubule network and subsequently exhibit its tumour-suppressive effects in synergy with paclitaxel (PTX). Therefore, the objective of the present study was to analyse the effects of the combined treatment of C-1305 and PTX in vivo. In addition, considering the results of previous genomic analyses, particular attention was given to the effects of this treatment on tumour angiogenesis. Treatment with C-1305 revealed antitumor effect in A549 lung cancer cells, and combined treatment with PTX showed tendency to anticancer activity in HCT116 colon cancer xenografts. It also improved tumour blood perfusion in both tumour models. The plasma level of CCL2 was increased and that of PDGF was decreased after combined treatment with C-1305 and PTX. The experimental results showed that the levels of FGF1, TGF-β and Ang-4 decreased, whereas the levels of ERK1/2 and Akt phosphorylation increased in HCT116 tumour tissue following combined treatment with both drugs. The results of in vitro capillary-like structure formation assay demonstrated the inhibiting effect of C-1305 on this process. Although previous in vitro and in vivo studies suggested a positive effect of C-1305 on cancer cells, combined treatment of HCT116 human colon and A549 lung cancer cells with both PTX and C-1305 in vivo showed that the antitumor activity was restricted and associated with the modulation of tumour angiogenesis.

New luminometric method for quantification of biological sulfur nucleophiles with the participation of 9-cyano-10-methylacridinium salt

Biologically active compounds containing sulfhydryl groups (RSHs: N-acetyl-l-cysteine, d-penicillamine, glutathione and acetylthiocholine chloride) were used to develop a luminometric method for their quantification. The title substrate capable of chemiluminescence (CL) was isolated in a highly pure state as a chloride salt (99.9% using RP-HPLC) and identified using mass spectrometry (ESI Q-TOF) and ¹ H NMR spectroscopy. The cation included in the salt, 9-CMA⁺ , underwent oxidation in an alkaline environment containing RSHs by molecular oxygen, generating CL of various intensities, with no need for the use of hydrogen peroxide. The amount of produced light was linearly proportional to the content of investigated analytes in the system over the concentration range ~0.2-2 μM, with the detection limits in the range 0.19-1.73 μM. The mechanism of chemiluminogenic oxidation of 9-CMA⁺ in the presence of RSHs and molecular oxygen is proposed, using computational methods at the density-functional theory level. The presence of RSHs in an alkaline medium seems to be crucial to produce hydroperoxide anions (^- OOH), which initiate the 'light path' of 9-CMA⁺ transformations, ending with the excretion of electronically excited molecules of 10 methyl-acridan-9-one.

Utilizing Genome-Wide mRNA Profiling to Identify the Cytotoxic Chemotherapeutic Mechanism of Triazoloacridone C-1305 as Direct Microtubule Stabilization

Rational drug design and in vitro pharmacology profiling constitute the gold standard in drug development pipelines. Problems arise, however, because this process is often difficult due to limited information regarding the complete identification of a molecule’s biological activities. The increasing affordability of genome-wide next-generation technologies now provides an excellent opportunity to understand a compound’s diverse effects on gene regulation. Here, we used an unbiased approach in lung and colon cancer cell lines to identify the early transcriptomic signatures of C-1305 cytotoxicity that highlight the novel pathways responsible for its biological activity. Our results demonstrate that C-1305 promotes direct microtubule stabilization as a part of its mechanism of action that leads to apoptosis. Furthermore, we show that C-1305 promotes G2 cell cycle arrest by modulating gene expression. The results indicate that C-1305 is the first microtubule stabilizing agent that also is a topoisomerase II inhibitor. This study provides a novel approach and methodology for delineating the antitumor mechanisms of other putative anticancer drug candidates.

Thiamine Diphosphate Status and Dialysis-Related Losses in End-Stage Kidney Disease Patients Treated with Hemodialysis

Aim: (1) To describe the whole blood content of thiamine diphosphate (TDP), a biologically active form of vitamin B1 in end-stage kidney disease patients treated with hemodialysis (HD); (2) to establish the impact of a single HD procedure on TDP blood concentrations; and (3) to describe potential explanatory variables influencing TDP dialysis related losses, including dialysis prescription, vitamin B1 dietary intake and supplementation. Methods: Single-center, cross-sectional study in 50 clinically stable maintenance HD patients. The assessment of whole blood TDP with the High Performance Liquid Chromatography method, before and after a single, middle-week dialysis session and analysis of clinical and laboratory parameters potentially influencing TDP status Results: We report a significant difference in TDP levels before and after HD sessions - 42.5 (95% CI 38.7-46.2) μg/L and 23.6 (95% CI 18.9-28.2) μg/L, respectively (p = 0.000). The magnitude of intradialytic TDP changes is highly variable among individuals and is negatively associated only with the body weight of the patients (p < 0.013). Vitamin B1 dietary intake and supplementation do not influence whole blood TDP and dialysis-related loss of TDP. Conclusions: TDP, a bioactive compound of vitamin B1, is substantially lost during the HD procedure, and the magnitude of its loss is associated with the patient's body weight but it is not influenced by vitamin B1 dietary intake and standard supplementation dose.

The development of 1,3-diphenylisobenzofuran as a highly selective probe for the detection and quantitative determination of hydrogen peroxide

1,3-Diphenylisobenzofuran (DPBF) has been developed as a selective probe for the detection and quantitative determination of hydrogen peroxide in samples containing different reactive nitrogen and oxygen species (RNOS). DPBF is a fluorescent probe which, for almost 20 years, was believed to react in a highly specific manner toward some reactive oxygen species (ROS) such as singlet oxygen and hydroxy, alkyloxy or alkylperoxy radicals. Under the action of these individuals DPBF has been rapidly transformed to 1,2-dibenzoylbenzene (DBB). In order to check if DPBF can act as a unique indicator of the total amount of different RNOS, as well as oxidative stress caused by an overproduction of these individuals, a series of experiments was carried out, in which DPBF reacted with peroxynitrite anion, superoxide anion, hydrogen peroxide, hypochlorite anion, and anions commonly present under biological conditions, namely nitrite and nitrate. In all cases, except for hydrogen peroxide, the product of the reaction is DBB. Only under the action of H₂O₂ 9-hydroxyanthracen-10(9H)-one (oxanthrone) is formed. This product has been identified with the use of fluorescence spectroscopy, NMR spectroscopy, high performance liquid chromatography coupled with mass spectrometry, infrared spectroscopy, elemental analysis, and cyclic voltammetry (CV). A linear relationship was found between a decrease in the fluorescence intensity of DPBF and the concentration of hydrogen peroxide in the range of concentrations of 0.196-3.941 mM. DPBF responds to hydrogen peroxide in a very specific way with the limits of detection and quantitation of 88 and 122.8 μM, respectively. The kinetics of the reaction between DBBF and H₂O₂ was also studied.

A novel chemiluminescent immunoassay for detection of Toxoplasma gondii IgG in human sera

This study describes Toxoplasma gondii IgG chemiluminescent immunoassay (CLIA) based on the use of a novel immunochemical reagents in the form of the conjugates of original acridinium ester (AE) labels attached to antibodies and SAG2-GRA1-ROP1L chimeric antigen and shows that this test is useful for diagnostic purposes.

Flavonol-based fluorescent indicator for determination of β-glucosidase activity

A flavonol-based ESIPT fluorescence probe for evaluation of β-glucosidase activity was synthesized and tested for sensitivity to enzymatic cleavage at different conditions.

Structure, formation, thermodynamics and interactions in 9-carboxy-10-methylacridinium-based molecular systems

Comprehensive experimental and theoretical studies on the physicochemical features of crystals containing monomeric and homoconjugated forms of 9-carboxy-10-methylacridinium cations are presented.

Effective chemiluminogenic systems based on acridinium esters bearing substituents of various electronic and steric properties

A series of new acridinium esters, variously substituted in the benzene ring, have been investigated for the mechanism of light generation and ability to show chemiluminescence in various environments.

Phenyl acridine-9-carboxylate

The acridine ring system and the benzene ring in the title compound, C₂₀H₁₃NO₂, are oriented at a dihedral angle of 6.4 (2)°. The carboxyl group is twisted at an angle of 83.6 (2)° relative to the acridine skeleton. The mol­ecules in the crystal are arranged in stacks along the b axis, with two of the acridine rings involved in multiple π–π inter­actions [centroid–centroid distances in the range 3.536 (2)–3.894 (2) Å]. Stacks arranged parallel are linked via C—H⋯π inter­actions, forming layers in the ac plane that are in contact with adjacent, inversely oriented layers via other C—H⋯π inter­actions, giving rise to double layers. The inversely oriented double layers inter­act dispersively. The acridine units are parallel within the parallel-oriented stacks, but inclined at an angle of 79.6 (2)° in the inversely oriented stacks.

2,6-Dimethyl-phenyl acridine-9-carboxyl-ate

In the title compound, C₂₂H₁₇NO₂, the acridine ring system and the benzene ring are oriented at a dihedral angle of 37.7 (1)°. The carboxyl group is twisted at an angle of 67.7 (1)° relative to the acridine skeleton. In the crystal, mol­ecules are arranged in stacks along the b axis, with all of the acridine rings involved in multiple π–π inter­actions [centroid–centroid distances in the range 3.632 (2)–4.101 (2) Å]. The acridine moieties are parallel within the stacks, but inclined at an angle of 52.7 (1)° in adjacent stacks.

9-(2-Bromo-phen-oxy-carbon-yl)-10-methyl-acridinium trifluoro-methane-sulfonate

In the crystal structure of the title compound, C(21)H(15)BrNO(2) (+)·CF(3)SO(3) (-), adjacent cations are linked through C-Br⋯π and π-π contacts [centroid-centroid distance = 3.744 (2) Å], and neighbouring cations and anions via C-H⋯O, C-F⋯π and S-O⋯π inter-actions. The acridine and benzene ring systems are oriented at a dihedral angle of 18.7 (1)°. The carb-oxy group is twisted at an angle of 69.3 (1)° relative to the acridine skeleton. The mean planes of adjacent acridine moieties are either parallel or inclined at an angle of 27.8 (1)° in the lattice.

9-(3-Fluorophenoxycarbonyl)-10-methylacridinium trifluoromethanesulfonate monohydrate

In the crystal structure of the title mol­ecular salt, C₂₁H₁₅FNO₂⁺·CF₃SO₃⁻·H₂O, the cations form inversion dimers through π–π inter­actions between the acridine ring systems. These dimers are linked via C—H⋯O and C—F⋯π inter­actions to adjacent anions, and by C—H⋯π and C—F⋯π inter­actions to neighbouring cations. The water mol­ecule links two sites of the cation by C—H⋯O inter­actions and two adjacent anions by O—H⋯O hydrogen bonds. The mean planes of the acridine and benzene ring systems are oriented at a dihedral angle of 15.1 (1)°. The carboxyl group is twisted at an angle of 84.5 (1)° relative to the acridine skeleton. The mean planes of the acridine ring systems are parallel in the crystal.

9-(2,5-Dimethyl-phen-oxy-carbon-yl)-10-methyl-acridinium trifluoro-methane-sulfonate

In the title compound, C(23)H(20)NO(2) (+)·CF(3)SO(3) (-), the acridine ring system is oriented at a dihedral angle of 23.1 (1)° with respect to the benzene ring and the carboxyl group is twisted at an angle of 74.1 (1)° relative to the acridine skeleton. In the crystal, adjacent cations are linked through C-H⋯π inter-actions and neighboring cations and anions via weak C-H⋯O hydrogen bonds. The mean planes of adjacent acridine units are either parallel or inclined at angles of 15.0 (1), 26.9 (1) and 48.1 (1)° in the crystal structure.

1H and 13C NMR spectra, structure and physicochemical features of phenyl acridine-9-carboxylates and 10-methyl-9-(phenoxycarbonyl)acridinium trifluoromethanesulphonates--alkyl substituted in the phenyl fragment

The 1H and 13C NMR spectra of twelve phenyl acridine-9-carboxylates--alkyl-substituted in the phenyl fragment--and their 10-methyl-9-(phenoxycarbonyl)acridinium salts dissolved in CD3CN, CD3OD, CDCl3 and DMSO-d6 were recorded in order to examine the influence of the structure of these compounds and the properties of the solvents on chemical shifts and 1H-(1)H coupling constants. Experimental data were compared with 1H and 13C chemical shifts predicted at the GIAO/DFT level of theory for DFT(B3LYP)/6-31G** optimised geometries of molecules, as well as with values of 1H chemical shifts and 1H-(1)H coupling constants, estimated using ACD/HNMR database software to ensure that the assignment was correct. To investigate the relations between chemical shifts and selected structural or physicochemical characteristics of the target compounds, the values of several of these parameters were determined at the DFT or HF levels of theory. The HOMO and LUMO energies obtained at the HF level yielded the ionisation potentials and electron affinities of molecules. The DFT method provided atomic partial charges, dipole moments, LCAO coefficients of pz LUMO of selected C atoms, and angles reflecting characteristic structural features of the compounds. It was found that the experimentally determined 1H and 13C chemical shifts of certain atoms relate to the predicted dipole moments, the angles between the acridine and phenyl moieties, and the LCAO coefficients of the pz LUMO of the C atoms believed to participate in the initial step of the oxidation of the target compounds. The spectral and physicochemical characteristics of the target compounds were investigated in the context of their chemiluminogenic ability.

9-Phenyl-10H-acridinium trifluoromethanesulfonate

In the crystal structure of the title compound, C₁₉H₁₄N⁺·CF₃SO₃⁻, the cations are linked to each other by very weak C—H⋯π inter­actions, while the cations and anions are connected by N—H⋯O, C—H⋯O and S—O⋯π inter­actions. The acridine ring system and the phenyl ring are oriented at an angle of 80.1 (1)° with respect to each other. The mean planes of adjacent acridine units are either parallel or inclined at an angle of 35.6 (1)°. The trifluoro­methane­sulfonate anions are disordered over two positions; the site occupancy factors are 0.591 (8) and 0.409 (8).

9-(2,6-Dimethyl-phen-oxy-carbon-yl)-10-methyl-acridinium trifluoro-methane-sulfonate

In the crystal structure of the title compound, C₂₃H₂₀NO₂⁺·CF₃SO₃⁻, adjacent cations are linked through a network of C—H⋯π and π–π inter­actions, and neighboring cations and anions via C—H⋯O inter­actions. The acridine and benzene ring systems are oriented at a dihedral angle of 31.4 (1)°. The carboxyl group is twisted at an angle of 66.3 (1)° relative to the acridine skeleton. The mean planes of the adjacent acridine moieties are parallel in the crystal structure.

9-(4-Chloro-phen-oxy-carbon-yl)-10-methyl-acridinium trifluoro-methane-sulfonate

In the crystal of the title compound, C₂₁H₁₅ClNO₂⁺·CF₃SO₃⁻, adjacent cations are linked through C—H⋯π and π–π inter­actions [centroid–centroid distance = 3.987 (2) Å], and neighboring cations and anions via C—H⋯O and C—F⋯π inter­actions. The acridine ring system and benzene ring are oriented at a dihedral angle of 1.0 (1)° while the carboxyl group is twisted at an angle of 85.0 (1)° relative to the acridine skeleton. The mean planes of adjacent acridine units are either parallel or inclined at an angle of 78.2 (1)° in the crystal structure.

10-Methyl-9-[2-(propan-2-yl)phenoxy-carbonyl]-acridinium trifluoro-methane-sulfonate

In the crystal of the title compound, C₂₄H₂₂NO₂⁺·CF₃SO₃⁻, adjacent cations and anions are connected through C—H⋯O, C—H⋯F and S–O⋯π inter­actions, while neighboring cations via π–π inter­actions [centroid–centroid distance = 3.962 (2) Å]. The acridine and benzene ring systems are oriented at a dihedral angle of 14.6 (1)°. The carboxyl group is twisted at an angle of 87.6 (1)° relative to the acridine skeleton. The mean planes of adjacent acridine units are parallel or inclined at an angle of 13.4 (1)° in the crystal structure.

9-(4-Fluoro-phen-oxy-carbon-yl)-10-methyl-acridinium trifluoro-methane-sulfonate

In the crystal structure of the title compound, C(21)H(15)FNO(2) (+)·CF(3)SO(3) (-), the cations form inversion dimers through C-H⋯O, C-F⋯π and π-π inter-actions. These dimers are further linked by π-π inter-actions. The cations and anions are connected through C-H⋯O, C-F⋯π and S-O⋯π inter-actions. The acridine and benzene ring systems are oriented at a dihedral angle of 74.1 (1)°. The carboxyl-ate group is twisted at an angle of 4.4 (1)° relative to the acridine skeleton. The mean planes of the adjacent acridine moieties are parallel or inclined at an angle of 55.4 (1)° in the crystal structure.

9-Benzyl-10-methylacridinium trifluoromethanesulfonate

In the crystal structure of the title compound, C₂₁H₁₈N⁺·CF₃OS₃⁻, the cations form inversion dimers through π–π inter­actions between the acridine ring systems. These dimers are further linked by C—H⋯π inter­actions. The cations and anions are connected by C—H⋯O, C—F⋯π and S—O⋯π inter­actions. The acridine and benzene ring systems are oriented at a dihedral angle of 76.8 (1)°with respect to each other. The acridine moieties are either parallel or inclined at an angle of 62.4 (1)° in the crystal structure.

9-(4-Bromo-phenoxy-carbon-yl)-10-methyl-acridinium trifluoro-methane-sulfonate

In the crystal structure of the title compound, C(21)H(15)BrNO(2) (+)·CF(3)SO(3) (-), the cations form inversion dimers through π-π inter-actions between the acridine ring systems. These dimers are further linked by C-H⋯π and C-Br⋯π inter-actions. The cations and anions are connected by multidirectional C-H⋯O and C-F⋯π inter-actions. The acridine and benzene ring systems are oriented at 10.8 (1)°. The carboxyl group is twisted at an angle of 85.2 (1)° relative to the acridine skeleton. The mean planes of adjacent acridine units are parallel or almost parallel [inclined at an angle of 1.4 (1)°] in the crystal structure.

9-(4-Methyl-phenoxy-carbon-yl)-10-methyl-acridinium trifluoro-methane-sulfonate

In the crystal structure of the title compound, C₂₂H₁₈NO₂⁺·CF₃SO₃⁻, adjacent cations are linked through C—H⋯π and π–π inter­actions, and the cations and anions are connected by C—H⋯O and C—F⋯π inter­actions. The acridine and benzene ring systems are oriented at a dihedral angle of 3.0 (1)°. The carboxyl group is twisted at an angle of 83.1 (1)° relative to the acridine skeleton. The mean planes of adjacent acridine units are parallel or inclined at an angle of 75.2 (1)° in the crystal structure.

Vibrational spectra of phenyl acridine-9-carboxylates and their 10-methylated cations: A theoretical and experimental study

Infrared spectra of phenyl acridine-9-carboxylates and their 10-methylated cationic derivatives were recorded and discussed. Experimental data were compared with theoretically predicted transitions at the DFT level of theory (using the B3LYP functional and 6-31G** basis set) for optimized geometries of molecules. Substitution influences the values of the wavenumbers of characteristic stretching and bending modes, i.e. those corresponding to ester groups and fragments of molecules containing a heterocyclic nitrogen atom. The experimentally determined transitions of selected groups of atoms correlate well with the theoretically predicted values. Interdependences among some theoretically derived physicochemical features of the compounds and IR frequencies of selected bands are also discussed.

10-Methyl-9-phenoxy-carbonyl-acridinium trifluoro-methane-sulfonate monohydrate

In the crystal structure of the title compound, C₂₁H₁₆NO₂⁺·CF₃SO₃⁻·H₂O, the anions and the water mol­ecules are linked by O—H⋯O inter­actions, while the cations form inversion dimers through π–π inter­actions between acridine ring systems. These dimers are linked by C—H⋯O and C—F⋯π inter­actions to adjacent anions, and by C—H⋯π inter­actions to neighboring cations. The water mol­ecule links two H atoms of the cation by C—H⋯O inter­actions and two adjacent anions by O—H⋯O inter­actions. The acridine and benzene ring systems are oriented at 15.6 (1)°. The carboxyl group is twisted at an angle of 77.0 (1)° relative to the acridine skeleton. The mean planes of the adjacent acridine units are either parallel or inclined at an angle of 18.4 (1)°.

9-(2-Ethyl-phenoxy-carbon-yl)-10-methyl-acridinium trifluoro-methane-sulfonate

In the crystal structure of the title compound, C₂₃H₂₀NO₂⁺·CF₃SO₃⁻, the cations form inversion dimers through π–π inter­actions between the acridine ring systems. These dimers are further linked by C—H⋯π inter­actions. The cations and anions are connected by C—H⋯O and C—F⋯π inter­actions. The acridine and benzene ring systems are oriented at a dihedral angle of 20.8 (1)°. The carboxyl group is twisted at an angle of 66.2 (1)° relative to the acridine skeleton. The mean planes of adjacent acridine units are parallel in the lattice.

2-Meth-oxy-9-phenoxy-acridine

The mol-ecules in the crystal structure of the title compound, C(20)H(15)NO(2), form inversion dimers connected through the C-H⋯N and π-π inter-actions. These dimers are further linked by C-H⋯π inter-actions. The meth-oxy group is nearly coplanar with the acridine ring system [dihedral angle = 4.5 (1)°], whereas the phen-oxy fragment is nearly perpendicular to it [dihedral angle = 85.0 (1)°]. The mean planes of the acridine ring systems are either parallel or inclined at angles of 14.3 (1), 65.4 (1) and 67.3 (1)° in the crystal.

9-Chloro-2,4-dimethoxyacridinium trifluoromethanesulfonate

In the mol­ecular structure of the title compound, C₁₅H₁₃ClNO₂⁺·CF₃SO₃⁻, the meth­oxy groups are nearly coplanar with the acridine ring system, making dihedral angles of 0.4 (2) and 5.1 (2)°. Multidirectional π–π contacts between acridine units are observed in the crystal structure. N—H⋯O and C—H⋯O hydrogen bonds link cations and anions, forming a layer structure.

9-[(2,6-Dimethoxyphenoxy)carbonyl]-10-methylacridinium trifluoromethanesulfonate

In the crystal structure of the title compound, C₂₃H₂₀NO₄⁺·CF₃SO₃⁻, the cations are linked through C—H⋯O, C—H⋯π and π–π inter­actions [centroid-centroid distances = 3.641 (2) and 3.885 (2) Å]. The cation and the anion are held together by C—H⋯O and S—O⋯π inter­actions. The acridine ring system and the benzene ring in the cation are oriented at a dihedral angle of 8.7 (1)°. The carb­oxy group is twisted at an angle of 83.2 (1)° relative to the acridine skeleton.

9-(Biphenyl-4-yl-oxycarbon-yl)-10-methyl-acridinium trifluoro-methane-sulfonate

In the crystal structure of the title compound, C₂₇H₂₀NO₂⁺·CF₃SO₃⁻, the cations form inversion dimers through π–π inter­actions between the acridine ring systems [centroid-centroid distances = 3.668 (2)–3.994 (2) Å]. These dimers are further linked by C—H⋯O and C—H⋯π inter­actions. The cation and the anion are connected by C—H⋯O inter­actions. The mean plane of the acridine ring system makes dihedral angles of 10.6 (1) and 82.5 (1)°, respectively, with the adjacent phenyl ring and the carb­oxy group. The two phenyl rings of the biphenyl group are oriented at 42.9 (1)°.

4-Meth-oxy-N-phenyl-aniline

In the mol-ecule of the title compound, C(13)H(13)NO, the two benzene rings are oriented at a dihedral angle of 59.9 (2)°. In the crystal structure, the benzene rings of neighbouring mol-ecules are oriented nearly parallel or perpendicular, making dihedral angles of 2.8 (2) and 79.5 (2)°, respectively. The crystal structure is stabilized by a network of C-H⋯π and N-H⋯π inter-actions.

Spectral features of substituted 9-(phenoxycarbonyl)-acridines and their protonated and methylated cation derivatives

The long-wavelength absorption of eight 9-(phenoxycarbonyl)-acridines and the 10-H-9-(phenoxycarbonyl)-acridinium and 10-methyl-9-(phenoxycarbonyl)-acridinium cations derived from them, substituted with an alkyl or trifluoroalkyl group at the benzene ring, occurs above 300 nm as the superposition of four bands. Three of these bands occupy comparable positions (expressed in nm) in all the compounds; the fourth one, however, changes position, appearing in neutral molecules as a long-wavelength shoulder below 400 nm, but in cations as an almost separate band above 400 nm. The weak fluorescence resulting from excitation within the long-wavelength absorption band is red-shifted relative to absorption, such that Stokes shifts are similar for both neutral molecules and cations. Stokes shifts tend to increase with the orientational polarisability of a medium. Computations predict that long-wavelength electronic transitions are accompanied by structural changes in molecules. They also indicate that such transitions are followed by roughly uniform electron density changes in whole molecules accompanied by small changes in their dipole moments, which accounts for the weak absorption in the long-wavelength region. The predicted radiative and non-radiative deactivation rate constants suggest the occurrence of efficient spin-orbital coupling in the molecules investigated, which is the cause of the relatively low fluorescence quantum yields. Apart from the cognitive significance of these investigations, the results demonstrate that absorption of radiation by 10-methyl-9-(phenoxycarbonyl)-acridinium cations above 400 nm may influence their chemiluminescence output.

10-Methyl-9-(2-nitro-phenoxy-carbon-yl)acridinium trifluoro-methane-sulfonate

The crystal structure of the title compound, C(21)H(15)N(2)O(4) (+)·CF(3)O(3)S(-), is stabilized by C-H⋯O and C-H⋯F hydrogen bonds, by C-F⋯π, N-O⋯π and S-O⋯π inter-actions, and by O⋯O [2.70 (4) Å] and O⋯F [2.85 (1) or 2.92 (1) Å] contacts; π-π interactions are also present. In the packing of the mol-ecules, acridine units are either parallel or inclined at an angle of 12.5 (1)°. The nitrophenoxycarbonyl unit is disordered over two position; the site occupancy factors are 0.89 and 0.11.

9-(2,6-Difluorophenoxycarbonyl)-10-methylacridinium trifluoromethanesulfonate and its precursor 2,6-difluorophenyl acridine-9-carboxylate: C-H...O, C-F...pi, S-O...pi and pi-pi stacking interactions

The title compounds, C21H14F2NO2+.CF3SO3-, (I), and C20H11F2NO2, (II), form monoclinic and triclinic crystals, respectively. Adjacent cations of (I) are oriented in a ;head-to-tail' manner and are linked to one another via networks of C-H...O, C-F...pi, S-O...pi and multidirectional pi-pi interactions. Adjacent molecules of (II) are also arranged in a ;head-to-tail' manner and are linked via networks of C-H...O and multidirectional pi-pi interactions. The mean planes of the acridine moieties lie parallel in the lattices of both compounds. The benzene rings are also parallel. However, the acridine and difluorophenyl rings are mutually oriented at an angle of 17.3 (2) degrees in (I) and 5.8 (2) degrees in (II). This mutual orientation in various phenyl acridine-9-carboxylates and related compounds is strongly influenced by the nature of the substituents on the phenyl fragment.

9-(2,6-dichlorophenoxycarbonyl)-10-methylacridinium trifluoromethanesulfonate and its precursor 2,6-dichlorophenyl acridine-9-carboxylate

The title compounds, C21H14Cl2NO2+.CF3O3S-, (I), and C20H11Cl2NO2, (II), form triclinic crystals. Adjacent cations of (I) are oriented either parallel or antiparallel; in the latter case, they are related by a centre of symmetry. Together with the CF3SO3- anions, the antiparallel-oriented cations of (I) form layers in which the molecules are linked via a network of C-H...O and pi-pi interactions (between the benzene rings). These layers, in turn, are linked via a network of multidirectional pi-pi interactions between the acridine rings, and the whole lattice is stabilized by electrostatic interactions between ions. Adjacent molecules of (II) are oriented either parallel or antiparallel; in the latter case, they are related by a centre of symmetry. Parallel-oriented molecules are arranged in chains stabilized via C-H...Cl interactions. These chains are oriented either parallel or antiparallel and are stabilized, in the latter case, via multidirectional pi-pi interactions and more generally via dispersive interactions. Acridine and independent benzene moieties lie parallel in the lattices of (I) and (II), and are mutually oriented at an angle of 33.4 (2) degrees in (I) and 9.3 (2) degrees in (II).

9-(2-Chloroethylamino)acridine monohydrate and its precursor 9-phenoxyacridine

The title compounds, C15H13ClN2.H2O, (I), and C19H13NO, (II), form monoclinic crystals. Arranged in a 'head-to-tail' manner, the molecules of the amine form (I) lie along the b axis in layers that are linked by a network of hydrogen bonds involving the endocyclic N atom, the H atom at the exocyclic N atom and all the atoms of the solvent water molecule. Molecules of (II), with the phenoxy group nearly perpendicular to the acridine moiety, are arranged in pairs related by a center of symmetry and stabilized via two C-H...N contacts; the latter are linked via a network of further C-H...N contacts and non-specific dispersive interactions.

2-Ethylphenyl acridine-9-carboxylate and 2,5-dimethylphenyl acridine-9-carboxylate

The title compounds, 2-ethylphenyl acridine-9-carboxylate, C22H17NO2, (I), and 2,5-dimethylphenyl acridine-9-carboxylate, C22H17NO2, (II), form triclinic and monoclinic crystals, respectively. Related by a centre of symmetry, adjacent molecules of (I) are linked in the lattice via a network of C-H...pi and non-specific dispersive interactions. As a result, acridine moieties and independent phenyl moieties of (I) are parallel in the lattice. The molecules of (II), arranged in a 'head-to-tail' manner and related by a centre of symmetry, form pairs stabilized via C-H...pi interactions. These are linked in the crystal via dispersive interactions. Acridine and independent phenyl moieties lie parallel within the pairs, while adjacent pairs are perpendicular, forming a herring-bone pattern.

9-(Trichloroacetylimino)acridine monohydrate

The title compound, alternatively called N-acridin-9(10H)-ylidene-2,2,2-trichloroacetamide monohydrate, C(15)H(9)Cl(3)N(2)O.H(2)O, crystallizes in space group P2(1)/c with Z = 4. The acridine moieties are arranged in layers, tilted at an angle of 15.20 (4) degrees relative to the ac plane, while adjacent molecules pack in a head-to-tail manner. Acridine and water molecules form columns along the b axis held in place by a network of hydrogen bonds, which is the major factor stabilizing the lattice. The acridine molecule exhibits structural features of both the amino and imino forms, which could be due to the presence of the strong electronegative trichloroacetyl substituent at the exocyclic N atom.

2-Methylphenyl 2-methoxyacridine-9-carboxylate

The title compound, C(22)H(17)NO(3), crystallizes in the monoclinic space group P2(1)/c with four molecules per unit cell. The molecules are arranged in centrosymmetric pairs, joined via the C and attached H atoms in the meta position relative to the methoxy group. These pairs are bonded in the crystalline phase as a result of non-specific dispersive interactions, and through a network of C-H...O interactions involving the non-bonded O atom of the carboxy group and, to some extent, the O atom of the methoxy group. The methoxy substituent lies in the plane of the almost planar acridine moiety and is directed towards the phenyl ester group. The phenyl ester group itself is twisted by 35.9 (5) degrees relative to the mean plane of the acridine moiety.