Iron oxide nanoparticles with a variable size and an iron oxidation state for imaging applications

Magnetite nanoparticles in the size range of 3.2-7.5 nm were synthesized with high yields under variable reaction conditions using high temperature hydrolysis of the precursor iron(II) and iron(III) chelated alkoxide complexes in surfactant-free diethylene glycol solutions. The average sizes of the particles were adjusted by changing the reaction temperature and time, and by using sequential growth technique. Reaction products formed as shelf-stable colloids. In order to obtain γ‑iron(III) oxide particles in the same range of sizes, diethylene glycol colloids of magnetite were oxygenated at room temperature. As-obtained colloids were characterized by DLS; powdery products obtained by coagulating them with oleic acid, were characterized by TEM, XRD, TGA, FTIR and magnetic measurements. In order to evaluate the potential of these particles for biomedical imaging, 1H NMR r1 and r2 relaxivity measurements were performed in diethylene glycol (for OH and CH2-protons) and in water. The results have shown the decrease in r2/r1 ratio with the particle size reduction, which correlate with the results of magnetic measurements on magnetite nanoparticles. Saturation magnetization of the oxidized particles was found to be 20% lower than that for Fe3O4 with the same particle size, but their r1 relaxivities were similar. Since oxidation of magnetite is spontaneous under ambient conditions, it was important to learn that the oxidation product has no disadvantages as compared to its precursor, and therefore it may be a better imaging agent due to its chemical stability. Please click Additional Files below to see the full abstract

Photoinduced Electron Transfer In Naphthalimide-pyridine Systems: Effect Of Proton Transfer On Charge Recombination Efficiencies

We studied the effect of proton-coupled electron transfer on lifetimes of the charge-separated radicals produced upon light irradiation of the thiomethyl-naphthalimide donor SMe-NI-H in the presence of nitro-cyano-pyridine acceptor (NO(2)-CN-PYR). The dynamics of electron and proton transfer were studied using femtosecond pump-probe spectroscopy in the UV/vis range. We find that the photoinduced electron transfer between excited SMe-NI-H and NO(2)-CN-PYR occurs with a rate of 1.1 x 10(9) s(-1) to produce radical ions SMe-NI-H(center dot+) and NO(2)-CN-PYR(center dot-). These initially produced radical ions in a solvent cage do not undergo a proton transfer, possibly due to unfavorable geometry between N-H proton of the naphthalimide and aromatic N-atom of the pyridine. Some of the radical ions in the solvent cage recombine with a rate of 2.3 x 10(10) s(-1), while some escape the solvent cage and recombine at a lower rate (k = 4.27 x 10(8) s(-1)). The radical ions that escape the solvent cage undergo proton transfer to produce neutral radicals SMe-NI(center dot) and NO(2)-CN-PYR-H(center dot). Because neutral radicals are not attracted to each other by electrostatic interactions, their recombination is slower that the recombination of the radical ions formed in model compounds that can undergo only electron transfer (SMe-NI-Me and NO(2)-CN-PYR, k = 1.2 x 10(9) s(-1)). The results of our study demonstrate that proton-coupled electron transfer can be used as an efficient method to achieve long-lived charge separation in light-driven processes

Electronic Properties Of 4-substituted Naphthalimides

This paper describes a study of excited-state properties of naphthalmide (NI) and four 4-substituted derivatives: 4-chloronaphthalimide (Cl-NI), 4-methylthionaphthalmide (MeS-NI), 4-nitronaphthalimide (O(2)N-NI), and 4-(N,N-dimethylaminonaphthalimide (Me(2)N-NI). Steady-state absorption and fluorescence spectra were collected in solvents of varying polarity to determine the excited-state character of NI derivatives. Furthermore. the excited-state dynamics were studied Using femtosecond transient absorption spectroscopy. The experimental findings were compared to calculated data obtained using time-dependent density functional (TD-DFT) methods. We found that light absorption by all NI derivatives leads to the production of the second excited state (S(2)), which was found to have a n,pi* character. Within similar to 40 ps, the S(2) state undergoes internal conversion to produce the S(1) state. The S(1) state is relatively long-lived (similar to 4 ns) and has charge-transfer character in NI derivatives with electron-withdrawing and electron-donating groups (MeS-NI, O(2)N-Ni, and Me(2)N-NI). In the case of NI and Cl-NI, the S(1) state has a pi,pi* character and undergoes intersystem crossing to produce the T(1) state within 400 ps

Electronic Properties Of N(5)-ethyl Flavinium Ion

We investigated the electronic properties of N(5)-ethyl flavinium perchlorate (Et-Fl(+)) and compared them to those of its parent compound, 3-methyllumiflavin (Fl). Absorption and fluorescence spectra of Fl and Et-Fl(+) exhibit similar spectral features, but the absorption energy of Et-Fl(+) is substantially lower than that of Fl. We calculated the absorption signatures of Fl and Et-Fl(+) using time-dependent density functional theory (TD-DFT) methods and found that the main absorption bands of Fl and Et-Fl(+) are (pi,pi*) transitions for the S(1) and S(3) excited states. Furthermore, calculations predict that the S(2) state has (n,pi*) character. Using cyclic voltammetry and a simplistic consideration of the orbital energies, we compared the HOMO/LUMO energies of Fl and Et-Fl(+). We found that both HOMO and LUMO orbitals of Et-Fl(+) are stabilized relative to those in Fl, although the stabilization of the LUMO level was more pronounced. Visible and mid-IR pump-probe experiments demonstrate that Et-Fl(+) exhibits a shorter excited-state lifetime (590 ps) relative to that of Fl (several nanoseconds), possibly due to faster thermal deactivation in Et-Fl(+), as dictated by the energy gap law. Furthermore, we observed a fast (23-30 ps) S(2) -\u3e S(0) internal conversion in transient absorption spectra of both Fl and Et-Fl(+) in experiments that utilized pump excitations with higher energy

Study of Marine Natural Products as Anti-SARS-CoV-2 Agents Using Molecular Modeling

Corresponding author (BioMolecular Sciences): Priyanka Samanta, [email protected]://egrove.olemiss.edu/pharm_annual_posters_2022/1018/thumbnail.jp

Proton-Coupled Electron Transfer for Long-Lived Charge Separation and Photocatalytic Water Splitting

The current dissertation covers a fundamental chemical process of proton coupled electron transfer (PCET) which involves simultaneous transfer of both proton and electron in the chemical system. Ultrafast spectroscopy is a valuable tool that provides insight into the process of PCET. Femtosecond and nanosecond transient absorption (TA) experiments, as well as time-resolved infrared (TRIR) spectroscopy, are widely used to monitor electron and proton transfer processes as they allow one to investigate of both the electron and the proton transfer processes. To perform high quality experiments on the subpicosecond/subnanosecond timescale we designed new data acquisition software. The variety of controls allows the user to monitor different acquisition parameters. The graphs display the transient spectrum at current delay position, decay at the certain wavelength, and overall dynamics of the processes which occurs after excitation by colored map. Several subprograms were designed to tune the white light continuum and overlap between the pump and the probe beam. Using this software and equipment we investigated photophysical properties of 4-substituted naphthalimides (NI). The compounds chosen for the study can be split into two groups: NI and chloronaphthalimide (ClNI) which have high oxidation potentials, weak fluorescence and upon excitation form nonpolar ππ* excited state, and other three NI which forms long-lived ICT states and have lower oxidation potentials and higher fluorescence quantum yields. After detailed investigation only 4-methylthionaphthalimide (MeSNI) was chosen as a model compound for PCET study. The appropriate pyridine (NO2CNpy) was chosen since it can be considered as strong acceptor and can undergo reversible 1e- reduction with formation of the strong absorbing radical-anion. Due to weak basic properties it does not form the salt with NI derivatives; however it still can undergo formation of hydrogen-bonded complex. Using NMR titration the binding constant was calculated. Since it is very small the 100% complexation can never be achieved which makes analysis of the excited state dynamics complicated. The visible pump-probe experiment with MeSNI, MeSNIMe, NO2CNpy, and py combined with spectroelectrochemical studies confirmed the photoinduced electron transfer and proton coupled electron transfer for MeSNI. To investigate flavionum salt derivatives that serve as compound for photocatalytic water splitting we synthesized N(5)-ethyl flavonium perchlorate, N(5)-ethyl flavonium pseudobase, N(5)-isopropyl flavinium perchlorate, N(5)-isopropyl flavonium pseudobase and their methoxy derivatives. We used two synthetic approaches publised previously. The first which involves reduction with lithium aluminum hydride reduces number of steps and provides better yields while the second one which based on monoalkylation of the aniline derivatives allows introduction of variety of substituents. MeLF and EtFl+ from the steady-state absorption and emission spectroscopy experiments demonstrate the similar features since they have similar electronic structures according to the calculations. The long wavelength absorption for the N(5)-ethyl flavonium perchlorate is explained by stabilization of LUMO level. This is more pronounced in case of isopropyl group. From transient spectroscopy experiments EtFl+ demonstrates a shorter excited state lifetime compared to that of MeLF, due to faster thermal deactivation in EtFl+ dictated by the energy gap law. The hydroxy and methoxy forms have different photophysical properties compared to the salt and methyllumiflavin since the conjugation is decreased. This leads to the hypsochromic shift of absorption and emission maxima, decreased lifetime, and low fluorescence quantum yield. From visible pump-probe experiment no significant differenc..

Spectroscopic interrogations of isostructural metalloporphyrin-based metal-organic frameworks with strongly and weakly coordinating guest molecules

<p>Two isostructural metal-organic frameworks based on cobalt(II) and nickel(II) metalloporphyrin linkers, Co-PCN222 and Ni-PCN222, are investigated using resonance Raman and X-ray absorption spectroscopy. The spectroscopic consequences of framework formation and host–guest interaction with weakly and strongly coordinating guest molecules (acetone and pyridine) are assessed. Structure sensitive vibrational modes of the resonance Raman spectra provide insights on the electronic and structural changes of the porphyrin linkers upon framework formation. XANES and EXAFS measurements reveal axial binding behavior of the metalloporphyrin units in Co-PCN222, but almost no axial interaction with guest molecules at the Ni porphyrin sites in Ni-PCN222.</p

Spectroscopic Evidence for Room Temperature Interaction of Molecular Oxygen with Cobalt Porphyrin Linker Sites within a Metal–Organic Framework

Metalloporphyrin-based metal–organic frameworks offer a promising platform for developing solid-state porous materials with accessible, coordinatively unsaturated metal sites. Probing small-molecule interactions at the metalloporphyrin sites within these materials on a molecular level under ambient conditions is crucial for both understanding and ultimately harnessing this functionality for potential catalytic purposes. Co-PCN-222, a metal–organic framework based on cobalt­(II) porphyrin linkers. is investigated using in situ UV–vis diffuse-reflectance and X-ray absorption spectroscopy. Spectroscopic evidence for the axial interaction of diatomic oxygen with the framework’s open metalloporphyrin sites at room temperature is presented and discussed

Spectroscopic Evidence of Pore Geometry Effect on Axial Coordination of Guest Molecules in Metalloporphyrin-Based Metal Organic Frameworks

A systematic comparison of host–guest interactions in two iron porphyrin-based metal–organic frameworks (MOFs), FeCl-PCN222 and FeCl-PCN224, with drastically different pore sizes and geometries is reported in this fundamental spectroscopy study. Guest molecules (acetone, imidazole, and piperidine) of different sizes, axial binding strengths, and reactivity with the iron porphyrin centers are employed to demonstrate the range of possible interactions that occur at the porphyrin sites inside the pores of the MOF. Binding patterns of these guest species under the constraints of the pore geometries in the two frameworks are established using multiple spectroscopy methods, including UV–vis diffuse reflectance, Raman, X-ray absorption, and X-ray emission spectroscopy. Line shape analysis applied to the latter method provides quantitative information on axial ligation through its spin state sensitivity. The observed coordination behaviors derived from the spectroscopic analyses of the two MOF systems are compared to those predicted using space-filling models and relevant iron porphyrin molecular analogues. While the space-filling models show the ideal axial coordination behavior associated with these systems, the spectroscopic results provide powerful insight into the actual binding interactions that occur in practice. Evidence for potential side reactions occurring within the pores that may be responsible for the observed deviation from model coordination behavior in one of the MOF/guest molecule combinations is presented and discussed in the context of literature precedent