99Tc NMR as a promising technique for structural investigation of biomolecules: theoretical studies on the solvent and thermal effects of phenylbenzothiazole complex

Exploring EPR Parameters of 187Re Complexes for Designing New MRI Probes: From the Gas Phase to Solution and a Model Protein Environment

Breast cancer is one of the major types of cancer around the world, and early diagnosis is essential for successful treatment. New contrast agents (CAs), with reduced toxicology, are needed to improve diagnosis. One of the most promising Magnetic Resonance Imaging (MRI) CA is based on rhenium conjugated with a benzothiazole derivate (ReABT). In this sense, DFT has been used to evaluate the best methodology for calculating the hyperfine coupling constant (Aiso) of ReABT. Then, a thermodynamic analysis was performed to confirm the stability of the complex. Furthermore, a docking study of ReABT at the enzyme PI3K active site and Aiso calculations of ReABT in the enzyme environment were carried out. The best methodology for the Aiso calculation of ReABT was using the M06L functional, SARC-ZORA-TZVP (for Re) and TZVP (for all other atoms) basis set, relativistic Hamiltonian, and the CPCM solvation model with water as the solvent which confirm that the relativistic effects are important for calculating the Aiso values. In addition, thermodynamic analysis indicates that ReABT presents a higher stability and a lower toxicity than Gd-based CAs. The docking studies point out that ReABT interacts with amino acids residues of alanine, aspartate, and lysine from the PI3K active site. Considering the enzyme environment, Aiso values decrease significantly. These findings indicate that the CA candidate ReABT could be a good candidate for a new contrast agent.

Computational Prediction of Tc-99 NMR Chemical Shifts in Technetium Complexes with Radiopharmaceutical Applications

The Tc-99m nucleus is the most used nuclide in radiopharmaceuticals designed for imaging diagnosis. The metal can exist in nine distinct oxidation states and forms distinct coordination complexes with a variety of chelating agents and geometries. These complexes are usually characterized through Tc-99 NMR that is very sensitive to the Tc coordination sphere. Therefore, predicting Tc-99 NMR might be useful to assist experimentalists in structural characterization. In the present study, we propose three computational protocols for predicting Tc-99 NMR chemical shifts based on density functional theory calculations using relativistic and nonrelativistic Hamiltonians: the relativistic Model 1, the nonrelativistic Model 2, and the empirical nonrelativistic Model 3. In Models 2 and 3, the NMR-DKH basis set was used for all atoms, including the Tc, for which it was developed here. All models were applied for a set of 41 Tc-complexes with metal oxidation states 0, I, and V, for which the Tc-99 chemical shift was available experimentally. The mean absolute deviation and the mean relative deviation were 67 ppm and 4.8% (Model 1), 92 ppm and 6.2% (Model 2), and 65 ppm and 4.9% (Model 3), respectively. Last, the effect of the explicit solvent was evaluated for the [TcO₂(en)₂]⁺─Tc(V) complex. The calculated results for the Tc-99 NMR chemical shift at SO-ZORA-SSB-D/TZ2P-ZORA/COSMO//TPSS/def2-SVP/IEF-PCM(UFF) show that the inclusion of 14 water molecules (first solvation shell) together with the implicit solvation model leads to an absolute deviation of only 7 ppm (0.3%) from the experimental value, indicating that the solvent effects play a key role in predicting Tc-99 NMR.

Insights into the value of statistical models, solvent, and relativistic effects for investigating Re complexes of 2-(4'-aminophenyl)benzothiazole: a potential spectroscopic probe

Cancer affects a major part of the worldwide population, and, to minimize deaths, the diagnosis in the early stages of the disease is fundamental. Thus, to improve diagnosis and treatment new potential spectroscopic probes are crucial. Benzothiazole derivates present antitumor properties and are highly selective and interact strongly with the enzyme phosphoinositide 3-kinase (PI3K), which was associated with cell proliferation and breast cancer cells. In this paper, the rhenium shielding tensors (¹⁸⁷Re(σ)) and hydrogen and carbon chemical shifts (¹H(δ) and ¹³C(δ)) of the Re(CO)₃(NNO) complex conjugated with 2-(4'-aminophenyl)benzothiazole (ReABT) were evaluated. A statistical HCA model was used to analyze the best DFT protocol to compute σ and δ values and to evaluate the relativistic effects, both in the basis set and Hamiltonian as well as the functionals M06L or PBE0. The best protocol was applied to obtain ¹⁸⁷Re(σ) of the ReABT complex in different environments (gas phase, solution, and in the active site of the PI3K enzyme). The results point out that ¹⁸⁷Re(σ) values of the ReABT complex change significantly when the complex is docked in the PI3K enzyme.

Exploring electronic, structural and dynamics parameters of phenylbenzothiazole complexes with Mn2+, Cu2+ and Zn2+ for designing new magnetic resonance imaging (MRI) probes: congruence between computation and spectroscopic data

Cancer is one of the leading causes of human death worldwide, being one of the most serious problems faced by mankind. For the diagnosis, Magnetic Resonance Imaging (MRI), through effective contrast agents (Cas), has greatly helped in the diagnosis at the initial stages. However, it is necessary to include new compounds more effective and selective for cancer diagnosis. The complexes with Mn²⁺, Cu²⁺ and Zn²⁺ have received great attention due to their applications as CAs for MRI. Those materials can shorten the T₂ and T₂* transverse relaxation times. Thus, the representative structures for hyperfine coupling constants (HFCCs) were selected from docking results by frequency of occupancy calculations. From the Multivariate Analysis to obtain the PCA graphs in the choice of a representative conformations. it is possible to notice that the variable energy does not present a high correlation with the other variables, and structural factors, such as the spatial positions of the metal atoms, seem to be important in the reactivity of the complexes. Structural factors, such as the spatial positions of the metal atoms, seem to be important in the reactivity of the complexes. Theoretical findings suggest that the compounds are capable of increasing the A_iso values of the water molecules, but the complex [Zn(H₂O)(NNO)] shows a greater influence, being more sensitive to the Electron paramagnetic resonance parameters than the complexes [CuCl(H₂O)NNO] and [MnCl₂(H₂O)(NNO)] with the explicit solvent and the enzyme. MRI contrast agents have generated various problems due to their high toxicity. In this perspective, this compound may be a promising alternative for transporting the CAs into diseased tissue.Communicated by Ramaswamy H. Sarma.

Hybrid Materials Based on Magnetic Iron Oxides with Benzothiazole Derivatives: A Plausible Potential Spectroscopy Probe

Rare diseases affect a small part of the population, and the most affected are children. Because of the low availability of patients for testing, the pharmaceutical industry cannot develop drugs for the diagnosis of many of these orphan diseases. In this sense, the use of benzothiazole compounds that are highly selective and can act as spectroscopy probes, especially the compound 2-(4'-aminophenyl)benzothiazole (ABT), has been highlighted. This article reports the design of potential contrast agents based on ABT and iron to develop a new material with an efficient mechanism to raise the relaxation rate, facilitating diagnosis. The ABT/δ-FeOOH hybrid material was prepared by grafting (N-(4'-aminophenyl) benzothiazole-2-bromoacetamide) on the surface of the iron oxyhydroxide particles. FTIR spectra confirmed the material formations of the hybrid material ABT/δ-FeOOH. SEM analysis checked the covering of nanoflakes' surfaces in relation to the morphology of the samples. The theoretical calculations test a better binding mode of compound with iron oxyhydroxide. Theoretical findings show the radical capture mechanism in the stabilization of this new material. In this context, Fe³⁺ ions are an electron acceptor from the organic phase.

Detection of Chemical Weapon Agents Using Spectroscopic Probes: A Computational Study

Organophosphorus compounds are organic compounds widely employed in agriculture as well as in chemical weapons. The use in agriculture is due to their insecticidal properties. However, in chemical warfare, the use of organophosphorus is associated with acetylcholinesterase inhibition, which promotes the cholinergic syndromes. In this line, the fast detection of this class of compound is crucial for the determination of environmental exposure. This improved detection will naturally allow for more prompt courses of treatment depending on the contaminant findings. In this perspective, the dipyrrinone oxime (1) was employed for the detection of organophosphorus compounds that are employed as nerve agents, such as cyclosarin, sarin, soman, diethyl chlorophosphate, diisopropylfluorophosphate, 2-(dimethylamino)ethyl N,N-dimethylphosphoramidofluoridate, O-ethyl-S-[2-(diethylamino)ethyl]methylphosphonothioate, O-ethyl-S-[2(diisopropylamino)ethyl] methylphosphonothioate, and O,O-diethyl-S-[2-(diethylamino)ethyl] phosphorothioate, through fluorescent emission. The thermodynamics and kinetic parameters as well as spectroscopic properties of the complexes formed for 1 and all organophosphorus compounds previously cited were investigated by means of theoretical calculations. From our findings, only the diethyl chlorophosphate, 2-(dimethylamino)ethyl N,N-dimethylphosphoramidofluoridate, and O,O-diethyl-S-[2-(diethylamino)ethyl] phosphorothioate emitted fluorescence in the hexane, toluene, chloroform, dichloromethane, methanol, acetonitrile, water, and dimethyl sulfoxide solvents. The study of the absorption wavelength with the most polar solvent showed higher values compared to apolar solvents. In the same solvent, for instance, soman in hexane showed the lowest absorption wavelength value, 324.5 nm, and DCP the highest value, 330.8 nm. This behavior was observed in other tested solvents. The thermodynamic parameters indicate negative Gibbs free energy (ΔG) values for the O-ethyl-S-[2(diisopropylamino)ethyl] methylphosphonothioate with 1 reaction. On the other hand, the sarin and cyclosarin revealed the lowest Gibbs free energy (ΔG‡) values, being kinetically favorable and presenting more reactivity.

First Attempts of the Use of 195Pt NMR of Phenylbenzothiazole Complexes as Spectroscopic Technique for the Cancer Diagnosis

Platinum complexes have been studied for cancer treatment for several decades. Furthermore, another important platinum characteristic is related to its chemical shifts, in which some studies have shown that the ¹⁹⁵Pt chemical shifts are very sensitive to the environment, coordination sphere, and oxidation state. Based on this relevant feature, Pt complexes can be proposed as potential probes for NMR spectroscopy, as the chemical shifts values will be different in different tissues (healthy and damaged) Therefore, in this paper, the main goal was to investigate the behavior of Pt chemical shifts in the different environments. Calculations were carried out in vacuum, implicit solvent, and inside the active site of P13K enzyme, which is related with breast cancer, using the density functional theory (DFT) method. Moreover, the investigation of platinum complexes with a selective moiety can contribute to early cancer diagnosis. Accordingly, the Pt complexes selected for this study presented a selective moiety, the 2-(4′aminophenyl)benzothiazole derivative. More specifically, two Pt complexes were used herein: One containing chlorine ligands and one containing water in place of chlorine. Some studies have shown that platinum complexes coordinated to chlorine atoms may suffer hydrolyses inside the cell due to the low chloride ion concentration. Thus, the same calculations were performed for both complexes. The results showed that both complexes presented different chemical shift values in the different proposed environments. Therefore, this paper shows that platinum complexes can be a potential probe in biological systems, and they should be studied not only for cancer treatment, but also for diagnosis.

Probing long-range spin-spin coupling constants in 2-halo-substituted cyclohexanones and cyclohexanethiones: The role of solvent and stereoelectronic effects

Earlier studies with 2-bromocyclohexanone demonstrated a measurable long-range coupling constant (⁴ J_H2,H6 ) for the equatorial conformer, although ⁴ J_H2,H4 and ⁴ J_H4,H6 were not observed; as a consequence, it is inferred that the carbonyl group plays an important role particularly due to hyperconjugative interactions σ_C2H2 →π*_C═O and σ_C6H6 →π*_C═O. In the present study, NBO analysis and coupling constant calculations were performed to cyclohexanone and cyclohexanethione alpha substituted with F, Cl, and Br, aiming to evaluate the halogen effect and acceptor character of the π* orbital on the long-range coupling pathway. The σ_C2H2 →π*_C1═Y and σ_C6H6 →π*_C1═Y (Y═O and S) hyperconjugative interactions for the equatorial conformer indeed contribute for the ⁴ J_H2,H6 transmission mechanism_. Surprisingly, the ⁴ J_H2,H6 value is higher for the carbonyl compounds, although the interactions σ_C2H2 →π*_C═Y and σ_C6H6 →π*_C═Y are more efficient for the thiocarbonyl compounds. Accordingly, the Fermi contact (FC) contribution for the thiocarbonyl compounds decays deeper than in ketones, thus reducing more the ⁴ J_H2,H6 values. Moreover, both π_C═S →σ*_C─X and π_C═S →σ*_C─H interactions seem to be stronger in thiocarbonyl than in carbonylic compounds. The implicit solvent effect (DMSO and water) on the coupling constant values was negligible when compared with the gas phase. On the other hand, an explicit solvent effect was found and ⁴ J_H2,H6 for the thiocarbonyl compounds appeared to be more sensitive than for the cyclohexanones.

Synthesis and Biocompatibility Studies of New Iminodiacetic Acid Derivatives

BACKGROUND

Iminodiacetic acid (IDA) derivatives can be used as ligands to form complexes with technetium, with potential application as hepatobiliary diagnostic agents. The aim of this study was to synthesize five novel IDA derivatives and to compare their effects on plasma haemostasis with clinically approved ligands for technetium complexation.

METHODS

The influence of synthesized IDA derivatives on plasma haemostasis was evaluated spectrophotometrically by clot formation and lysis test (CL-test), coagulation assay, Prothrombin Time and Activated Partial Tromboplastin Time. The effects of the tested compounds on erythrocytes were assessed using haemolysis assays, microscopy and flow cytometry studies.

RESULTS

Despite their significant influence on the kinetic parameters of the process of clot formation and fibrinolysis, the tested ligands, at potential diagnostic concentrations, did not alter the overall potential of clot formation and lysis (CLAUC). At potential diagnostic concentrations (0.4 μmol/mL) all the tested compounds showed no adverse effects on the membranes of RBCs (Red Blood Cells).

CONCLUSION

IDA derivatives with methoxy substituents in aromatic ring, exert multidirectional effects on plasma haemostasis and should be considered safe as their significant impacts were mostly observed at 4 μmol/mL, which is about 10-fold higher than the theoretical plasma concentrations of these compounds.

Exploring EPR Parameters of 99Tc Complexes for Designing New MRI Probes: Coordination Environment, Solvent, and Thermal Effects on the Spectroscopic Properties

We have evaluated the solvent and thermal effects on spectroscopic parameters of 99Tc complexes coordinated to explicit water molecules. Molecular dynamics simulations were performed followed by hyperfine coupling constant calculations (Aiso). Our results show a significant increase of Aiso, which demonstrates that the studied compounds can be promising contrast agents in MRI.

Quantum chemistry calculations of technetium and rhenium compounds with application in radiopharmacy: review

Quantum chemistry calculations are a powerful tool in the development of new ^99mTc and ^186/188Re radiopharmaceuticals.

Excited-State Proton Transfer Can Tune the Color of Protein Fluorescent Markers

We show by quantum mechanical/molecular mechanical (QM/MM) simulations that phenylbenzothiazoles undergoing an excited-state proton transfer (ESPT) can be used to probe protein binding sites. For 2-(2'-hydroxy-4'-aminophenyl)benzothiazole (HABT) bound to a tyrosine kinase, the absolute and relative intensities of the fluorescence bands arising from the enol and keto forms are found to be strongly dependent on the active-site conformation. The emission properties are tuned by hydrogen-bonding interactions of HABT with the neighboring amino acid T766 and with active-site water. The use of ESPT tuners opens the possibility of creating two-color fluorescent markers for protein binding sites, with potential applications in the detection of mutations in cancer cell lines.