| 1. |
- Bacalum, Mihaela, et al.
(författare)
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A Blue-Light-Emitting BODIPY Probe for Lipid Membranes
- 2016
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 32:14, s. 3495-3505
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Tidskriftsartikel (refereegranskat)abstract
- Here we describe a new BODIPY-based membrane probe (1) that provides an alternative to dialkylcarbocyanine dyes, such as DiI-C,8, that can be excited in the blue spectral region. Compound 1 has unbranched octadecyl chains at the 3,5 -positions and a meso-amino function. In organic solvents, the absorption and emission maxima of 1 are determined mainly by solvent acidity and dipolarity. The fluorescence quantum yield is high and reaches 0.93 in 2-propanol. The fluorescence decays are well fitted with a single -exponential in pure solvents and in small and giant unilamellar vesicles (GUV) with a lifetime of ca. 4 ns. Probe 1 partitions in the same lipid phase as DiI-C-18(5) for lipid mixtures containing sphingomyelin and for binary mixtures of dipalmitoylphosphatidylcholine (DPPC) and dioleoylphosphatidylcholine (DOPC). The lipid phase has no effect on the fluorescence lifetime but influences the fluorescence anisotropy. The translational diffusion coefficients of 1 in GUVs and OLN-93 cells are of the same order as those reported for DiI-C-18. The directions of the absorption and transition dipole moments of 1 are calculated to be parallel. This is reflected in the high steady-state fluorescence anisotropy of 1 in high ordered lipid phases. Molecular dynamic simulations of 1 in a model of the DOPC bilayer indicate that the average angle of the transition moments with respect to membrane normal is ca. 70 degrees, which is comparable with the value reported for al DiI-C-18.
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| 2. |
- Knippenberg, Stefan, et al.
(författare)
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Atomistic Picture of Fluorescent Probes with Hydrocarbon Tails in Lipid Bilayer Membranes : An Investigation of Selective Affinities and Fluorescent Anisotropies in Different Environmental Phases
- 2018
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Ingår i: Langmuir. - : AMER CHEMICAL SOC. - 0743-7463 .- 1520-5827. ; 34:30, s. 9072-9084
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Tidskriftsartikel (refereegranskat)abstract
- By reverting to spectroscopy, changes in the biological environment of a fluorescent probe can be monitored and the presence of various phases of the surrounding lipid bilayer membranes can be detected. However, it is currently not always clear in which phase the probe resides. The well-known orange 1,1'-dioctadecyl-3,3,3',3'-tetramethylindodicarbo-cyanine perchlorate (DiI-C18(5)) fluorophore, for instance, and the new, blue BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) derivative were experimentally seen to target and highlight identical parts of giant unilamellar vesicles of various compositions, comprising mixtures of dipalmitoylphosphatidylcholine (DPPC), dioleoylphosphatidylcholine (DOPC), sphingomyelin (SM), and cholesterol (Chol). However, it was not clear which of the coexisting membrane phases were visualized (Bacalum et al., Langmuir. 2016, 32, 3495). The present study addresses this issue by utilizing large-scale molecular dynamics simulations and the z-constraint method, which allows evaluating Gibbs free-energy profiles. The current calculations give an indication why, at room temperature, both BODIPY and DiI-C18(5) probes prefer the gel (S-o) phase in DOPC/DPPC (2:3 molar ratio) and the liquid-ordered (L-o) phase in DOPC/SM/Chol (1:2:1 molar ratio) mixtures. This study highlights the important differences in orientation and location and therefore in efficiency between the probes when they are used in fluorescence microscopy to screen various lipid bilayer membrane phases. Dependent on the lipid composition, the angle between the transition-state dipole moments of both probes and the normal to the membrane is found to deviate clearly from 90 degrees. It is seen that the DiI-C18(5) probe is located in the headgroup region of the SM/Chol mixture, in close contact with water molecules. A fluorescence anisotropy study also indicates that DiI-C18(5) gives rise to a distinctive behavior in the SM/Chol membrane compared to the other considered membranes. The latter behavior has not been seen for the studied BODIPY probe, which is located deeper in the membrane.
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| 3. |
- Knippenberg, Stefan, et al.
(författare)
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Benchmarking Post-Hartree-Fock Methods To Describe the Nonlinear Optical Properties of Polymethines : An Investigation of the Accuracy of Algebraic Diagrammatic Construction (ADC) Approaches
- 2016
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society. - 1549-9618 .- 1549-9626. ; 12:11, s. 5465-5476
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Tidskriftsartikel (refereegranskat)abstract
- Third-order nonlinear optical (NLO) properties of polymethine dyes have been widely studied for applications such as all-optical switching. However, the limited accuracy of the current computational methodologies has prevented a comprehensive understanding of the nature of the lowest excited states and their influence on the molecular optical and NLO properties. Here, attention is paid to the lowest excited-state energies and their energetic ratio, as these characteristics impact the figure-of-merit for all-optical switching. For a series of model polymethines, we compare several algebraic diagrammatic construction (ADC) schemes for the polarization propagator with approximate second-order coupled cluster (CC2) theory, the widely used INDO/MRDCI approach and the symmetry adapted cluster configuration interaction (SAC-CI) algorithm incorporating singles and doubles linked excitation operators (SAC-CI SD-R). We focus in particular on the ground-to-excited state transition dipole moments and the corresponding state dipole moments, since these quantities are found to be of utmost importance for an effective description of the third-order polarizability gamma and two-photon absorption spectra. A sum-overstates expression has been used, which is, found to quickly converge. While ADC(3/2) has been found to be the most appropriate method to calculate these properties, CC2 performs poorly.
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| 4. |
- Knippenberg, Stefan, et al.
(författare)
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Push/Pull Effect as Driving Force for Different Optical Responses of Azobenzene in a Biological Environment
- 2020
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 124:15, s. 8310-8322
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Tidskriftsartikel (refereegranskat)abstract
- The specific relationship between the alkyl tail lengths of four azobenzene probes embedded in DOPC liquid disorder membrane and their (non) linear optical (NLO) properties have been considered in the current study. Using extensive molecular dynamics calculations, the push/pull effect of the alkyl tails on the position and orientation of the probes in the model membrane are discussed. The simulations indicate that with increasing tail lengths the cis isomers are pushed closer to the membrane surface, while the trans ones are rather pulled toward the membrane center. Throughout hybrid quantum mechanics/molecular mechanics calculations, the linear and nonlinear optical properties of these compounds have been investigated. The pushing effect of the tails for cis azobenzene is translated in strong responses in the (non) linear I optical spectroscopies, while the opposite is seen for the trans isomers. The cis isomer can be seen as the active state of the azobenzene compound for membrane recognition. The current work highlights the correlation between the tails of photosensitive membrane probes and their NLO properties, and focuses on unexpected behaviors of azobenzene derivatives in biological environments which can be exploited in distinguishing between soft and stiff cellular compartments that are of utmost importance for ion carrier transport.
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| 5. |
- Knippenberg, Stefan, et al.
(författare)
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Strong Electronic Coupling Dominates the Absorption and Fluorescence Spectra of Covalently Bound BisBODIPYs
- 2015
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 119:8, s. 1323-1331
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Tidskriftsartikel (refereegranskat)abstract
- The absorption spectrum of a representative BisBODIPY molecule is investigated using high-level quantum chemical methodology; the results are compared with experimental data. The S1 and S2 excited states are examined in detail to illuminate and to understand the electronic coupling between them. With the help of model systems in which the distance between the BODIPY monomers is increased or in which the dihedral angle between the subunits is changed, the electronic coupling is quantified, and its influence on energetics and oscillator strengths is highlighted. For the explanation of the experimental spectrum, orbital interaction effects are found to be important. Because of the large experimental Stokes shift of BisBODIPY, the nature of the emissive state is investigated and found to remain C2 symmetric as the ground state, and no localization of the excitation on one BODIPY subunit occurs. The excitonic coupling is in BisBODIPY still larger than the geometry relaxation energy, which explains the absence of a pseudo-Jahn-Teller effect.
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| 6. |
- Osella, Silvio, et al.
(författare)
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Combining (Non)linear Optical and Fluorescence Analysis of DiD To Enhance Lipid Phase Recognition
- 2018
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Ingår i: Journal of Chemical Theory and Computation. - : AMER CHEMICAL SOC. - 1549-9618 .- 1549-9626. ; 14:10, s. 5350-5359
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Tidskriftsartikel (refereegranskat)abstract
- The widespread interest in phase recognition of lipid membranes has led to the use of different optical techniques to enable differentiation of healthy and not fully functional cells. In this work, we show how the combination of different (non)linear optical methods such as one-photon absorption (OPA), two-photon absorption (TPA), and second harmonic generation (SHG) as well as the study of the fluorescence decay time leads to an enhanced screening of membrane phases using a fluorescent 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine (DiD) probe. In the current study we consider the pure liquid disordered phases of DOPC (dioleoyl-sn-glycero-3-phosphocholine, room temperature) and DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, 323 K), the solid gel phase of DPPC (298 K), and the liquid ordered phase of a 2:1 binary mixture of sphingomyelin and cholesterol. By means of extensive hybrid quantum mechanics molecular mechanics calculations and based upon the (non)linear absorption of the embedded probes, it is found that DiD can be used to identify the lipid bilayer phase. The joint TPA and SHG as well as fluorescence analyses qualifies DiD as a versatile probe for phase recognition. In particular, the SHG data obtained by means of hyper-Rayleigh scattering and by electric field induced second harmonic generation reveal differences in polarization of the probe in the different environments. The TPA results finally confirm the particular location of the probe in between the polar headgroup region of the 2:1 SM:Chol mixture in the liquid ordered phase.
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| 7. |
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| 8. |
- Osella, Silvio, et al.
(författare)
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Conformational Changes as Driving Force for Phase Recognition : The Case of Laurdan
- 2019
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Ingår i: Langmuir. - : AMER CHEMICAL SOC. - 0743-7463 .- 1520-5827. ; 35:35, s. 11471-11481
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Tidskriftsartikel (refereegranskat)abstract
- The development of a universal probe to assess the phase of a lipid membrane is one of the most ambitious goals for fluorescence spectroscopy. The ability of a well-known molecule as Laurdan to reach this aim is here exploited as the behavior of the probe is fully characterized in a dipalmitoyl-phosphatidylcholine (DPPC) solid gel (So) phase by means of molecular dynamics simulations. Laurdan can take two conformations, depending on whether the carbonyl oxygen points toward the beta-position of the naphthalene core (Conf-I) or to the alpha-position (Conf-II). We observe that Conf-I has an elongated form in this environment, whereas Conf-II takes an L-shape. Interestingly, our theoretical calculations show that these two conformations behave in an opposite way from what is reported in the literature for a DPPC membrane in a liquid disordered (Ld) phase, where Conf-I assumes an L-shape and Conf-II is elongated. Moreover, our results show that in DPPC (So) no intermixing between the conformations is present, whereas it has been seen in a fluid environment such as DOPC (Ld). Through a careful analysis of angle distributions and by means of the rotational autocorrelation function, we predict that the two conformers of Laurdan behave differently in different membrane environments.
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| 9. |
- Osella, Silvio, et al.
(författare)
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Environmental effects on the charge transfer properties of Graphene quantum dot based interfaces
- 2019
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Ingår i: International Journal of Quantum Chemistry. - : Wiley. - 0020-7608 .- 1097-461X. ; 119:10
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Tidskriftsartikel (refereegranskat)abstract
- Graphene quantum dots (GQD) are interesting materials due to the confined sizes which allow to exploit their optoelectronic properties, especially when they interface with organic molecules through physisorption. In particular, when interfaces are formed, charge transfer (CT) processes can occur, in which electrons can flow either from the GQD to the absorbed molecule, or vice versa. These processes are accessible by modeling and computational analysis. Yet, the presence of different environments can strongly affect the outcome of such simulations which, in turn, can lead to wrong results if not taken into account. In this multiscale study, we assess the sensibility of the computational approach and compute the CT, calculated at interfaces composed by GQD and amino-acene derivatives. The hole transfer is strongly affected by dynamic disorder and the nature of the environment, and imposes stringent descriptions of the modeled systems to ensure enhanced accuracy of the transfer of charges.
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| 10. |
- Osella, S., et al.
(författare)
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Exhibiting environment sensitive optical properties through multiscale modelling : A study of photoactivatable probes
- 2022
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Ingår i: Journal of Photochemistry and Photobiology A. - : Elsevier BV. - 1010-6030 .- 1873-2666. ; 425
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Tidskriftsartikel (refereegranskat)abstract
- To assess a tumor biomarker like the cyclooxygenase-2 enzyme (COX-2), non-invasive imaging techniques are powerful tools. The (non-) linear optical properties of activatable fluorescent probes which are selectively bound to the biomarker can therefore be exploited. The here presented molecular modelling results based on multi-scale modelling techniques highlight the importance of the conformational versatility and of changes in the electronic interactions of such probes when they are embedded in water or in the COX-2 homodimer enzyme. The ANQIMC-6 probe, which combines the binding domain/scaffold of indomethacin (IMC) on COX-2 with the optical properties of acenaphtho[1,2-b]quinoxaline (ANQ), is found to be folded in the solvent and unfolded in the enzyme. A concerted movement of the probe and the protein is seen, while the rotational autocorrelation function exhibits also the intrinsic properties of the probe. Hybrid Quantum Mechanics/Molecular Mechanics (QM/MM) calculations are used to simulate the one-photon and two-photon absorption spectra along with the first hyperpolarizability. The transition has a local character in vacuum, but changes to a charge transfer one in the presence of the microenvironment of the enzyme. This is also visible through a change of the shape of the absorption spectrum, while at the same time the simulated signals of second harmonic generation experiments are strongly enhanced. The results of this work prove that an environment sensitive probe with an anchoring group and an optical active part can be constructed for use in absorption spectroscopy, without the need to revert to fluorescence experiments.
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