Truxillines are a group of tropane alkaloids present in coca leaves that are formed by photochemical dimerization of cinnamoylcocaine(s). Proportion of different truxilline forms present in cocaine ...serves as its geographical, manufacture, and storage "fingerprint"; thus, the quantitative determination of truxilline content represents one of the powerful methods of analysis and characterization of cocaine samples. Contrary to the statements repeatedly presented in the literature, namely, that there exist exactly 11 truxillines and that every single truxilline is diastereomer of any other, here we show that, in fact, a total of 15 truxillines exist, which can be divided in two structurally isomeric groups-five mutually diastereomeric truxillates and 10 mutually diastereomeric truxinates.
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•MCR-ALS with EFA is applied in the analysis of lipid bilayers FT-IR spectra.•Phase transition temperatures are obtained from various signatures of lipids.•All lipid signatures give ...equal values of the main phase transition temperatures.•Different lipid parts display slightly different pretransition temperatures.•Possibility for separation of the events related with pretransition is suggested.
Temperature-dependent transmission FT-IR spectroscopy and DSC measurements were conducted on lipid multibilayers constituted from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine. Lipid multibilayers made from 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine, which do not form a ripple phase, were examined as a reference. Spectra were analyzed using multivariate curve resolution technique with alternating least squares and evolving factor analysis (MCR-ALS with EFA) and lipid phase transition temperatures were determined. Polar parts of lipid molecules exert greater response on a ripple phase formation than non-polar ones. However, vibrational signatures of hydrocarbon chains with intramolecular origins display certain qualitative differences that pave the way for future work oriented on uncoupling the events that drive ripple phase formation.
One of the most distinguished quantities that describes lipid main phase transition, i.e. the transition from the gel (Lβ(′)) to the fluid (Lα) phase, is its melting temperature (Tm). Because melting ...is accompanied by a large change in enthalpy the, Lβ(′) → Lα transition can be monitored by various calorimetric, structural and spectroscopic techniques and Tm should be the same regardless of the metric monitored or the technique employed. However, in the case of DPPE multilamellar aggregates there is a small but systematic deviation of Tm values determined by DSC and FTIR spectroscopy. The aim of this paper is to explain this discrepancy by combined UV/Vis spectroscopic and MD computational approach. Multivariate analysis performed on temperature-dependent UV/Vis spectra of DPPE suspensions demonstrated that at 55 ± 1 °C certain phenomenon causes a small but detectable change in suspension turbidity, whereas a dominant change in the latter is registered at 63.2 ± 0.4 °C that coincides with Tm value determined from DSC curve. If this effect should be ignored, the overall data give Tm value the same as FTIR spectra data (61.0 ± 0.4 °C). As the classical MD simulations suggest that about 10° below Tm certain undulations appear at the surface of DPPE bilayers, we concluded that certain discontinuities in curvature fluctuations arise at reported temperature which are to some extent coupled with lipid melting. Ultimately, such events and the associated changes in curvature affect Tm value measured by different techniques.
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•Temperature-dependent UV/Vis spectra of DPPE suspensions were acquired.•Multivariate analyses revealed two sigmoid transitions of DPPE spectral projections.•Low-temperature sigmoid transition originates from DPPE surface undulations.•MD simulations support the existence of surface undulations 10 °C below Tm of DPPE.•The origin of Tm systematic deviation obtained by different techniques is resolved.
We studied and compared in detail an elusive matrix open (m‐state) and cytoplasmic open (c‐state) state of ADP/ATP carrier (AAC) protein embedded in the DOPC bilayer by microsecond molecular dynamics ...(MD) simulations. We analyzed both states with and without cardiolipin (CDL) molecules, with a special emphasis on the recently obtained crystallographic structure of the AAC m‐state. The obtained results show that both states of the protein are stable in the DOPC bilayer and impermeable to water. In comparison with the c‐state of AAC, the m‐state is more dynamic, but at the same time possesses a larger occluded area in the protein cavity. Both states of the protein are less flexible in simulations when CDL molecules are present, which is especially visible for the m‐state. Finally, the analysis of the protein conformational changes during MD simulations shows that protein parts at the protein/lipid boundaries are prone to larger conformational changes in contrast to central region of the protein embedded in the bilayer core, thus further supporting the cycling mechanism suggested for ADP/ATP exchange by AAC.
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•Lipid suspensions are examined with temperature-dependent UV/Vis spectroscopy.•Temperature-dependent turbidity changes are registered.•Multivariate analyses were applied in phase ...transition temperatures determination.•DPPC suspension display pretransition as detectable as the main phase transition.
One of the advantages of investigating lipid phase transitions by thermoanalytical techniques such as DSC is manifested in the proportionality of the signal strength on a DSC curve, attributed to a particular thermotropic event, and its cooperativity degree. Accordingly, the pretransition of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) is less noticeable than its main phase transition; as a matter of fact, when DSC measurements are performed at low heating rate, such low-cooperativity phase transition could go (almost) unnoticed. The aim of this work is to present temperature-dependent UV/Vis spectroscopy, based on a temperature-dependent change in DPPC suspension turbidity, as a technique applicable for determination of lipid phase transition temperatures. Multivariate analyzes of the acquired UV/Vis spectra show that phase transitions of the low-cooperativity degree, such as pretransitions, can be identified with the same certainty as transitions of a high-cooperativity degree.
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•Multivariate analysis is applied on FT-IR spectra of aqueous solutions of salts.•Water signatures are reconstructed using low- and high temperature component.•Hysteresis between two ...components reveals water hydrogen bond network fluctuations.•Fluctuations in water hydrogen bond network are ion-invariant.
Aqueous solutions of salts composed from monovalent ions are explored using temperature-dependent FT-IR spectroscopy in transmission. Water combination band, being extremely sensitive to the network of hydrogen bonds due to the contribution of water librations (ρLH2O), is analyzed in uni- and multivariate fashion. Univariate analysis of the combination band maximum (νmax) reveals that perturbation of water hydrogen bond network by ions is primary driven by electrostatic interactions between water and ions. Using multivariate curve resolution with alternating least squares and evolving factor analysis this band is separated into two components that represent low- and high-density water. The observed asymmetry in their behavior is interpreted in terms of fluctuations of a hydrogen bond network of two water components. The significance of the found phenomenon is unambiguously confirmed by performing analogous analysis in the spectral range that contains partial signature of water linear bending (δHOH) and is free from ρLH2O, in which the asymmetry is absent. Additionally, we show that this phenomenon, namely ion-invariant behavior of water fluctuations, persists even in the regime of high ionic strengths. Although ions indeed participate in shaping of water hydrogen bond network, this straightforward approach shows that its temperature-dependent fluctuations are ion-independent.
•MCE and MCI show affinity to clustering in PBS buffer solution.•MCE and MCI shift the phase transition temperature of DMPC.•MCE and MCI change the bilayer thickness.•Flavonol clusters is highly ...relevant to drug delivery.
We here report on flavonols (myricetin (MCE) and its glycoside myricitrin (MCI)) – 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) membrane interactions focusing on the effects of flavonol clustering on the membrane thermotropic and nanomechanical properties.
Atomic force microscopy (AFM), force spectroscopy (FS) and differential scanning calorimetry (DSC) together with molecular dynamics (MD) simulations provided a consistent picture of flavonol - DMPC membrane interactions. DMPC membrane as a supported lipid bilayer preserved its integrity even at higher flavonol molar fraction x. When present at x = 0.1 – 0.3, MCE and MCI both slightly improve DMPC bilayer fluidity which is evidenced by the decrease in the main phase transition temperature Tm. MCE is found within the interior of the bilayer, while MCI incorporates in the head group-water interface region. AFM and FS confirmed clusters as protrusions with an average height of 0.012 μm and average diameters of 0.60 and 0.24 μm for MCE and MCI clusters, respectively. The average membrane thickness in DMPC fluid phase decreases for 7% at xMCE = 0.30, while only 4% at xMCI = 0.27.
The induced membrane changes are dependent on the chemical and physical properties of inserted flavonols. The hypothesis regarding the tendency of flavonol to clustering in membranes by increasing flavonol molar fraction has been confirmed.
The effects of solvent and temperature on the complexation of adamantyl mannoside with β‐cyclodextrin and 6‐O‐monotosyl‐6‐deoxy‐β‐cyclodextrin were explored experimentally and by means of molecular ...dynamics simulations. Efficient binding was observed only in hydrogen‐bonded solvents, which indicated solvophobically driven complexation. The stability of the inclusion complex was considerably higher in aqueous media. A pronounced temperature dependence of ΔrH○ and ΔrS○, resulting in perfect enthalpy–entropy compensation, was observed in water. The complexation thermodynamics was in line with classical rationale for the hydrophobic effect at lower temperatures and the nonclassical explanation at higher temperatures. This finding linked cyclodextrin complexation thermodynamics with insights regarding the effect of temperature on the hydration water structure. The complexation enthalpies and entropies were weakly dependent on temperature in organic media. The signs of ΔrH○ and ΔrS○ were in accordance with the nonclassical hydrophobic (solvophobic) effect. The structures of the optimized product corresponded to those deduced spectroscopically, and the calculated and experimentally obtained values of ΔrG○ were in very good agreement. This investigation clearly demonstrated that solvophobically driven formation of cyclodextrin complexes could be anticipated in structured solvents in general. However, unlike in water, adamantane and the host cavity behaved solely as structure breakers in the organic media explored so far.
Favorable guest conditions: The effects of solvent and temperature on the complexation of adamantyl mannoside with β‐cyclodextrin and 6‐O‐monotosyl‐6‐deoxy‐β‐cyclodextrin are explored experimentally and by means of molecular dynamics simulations. Efficient binding is observed only in hydrogen‐bonded solvents, which indicates solvophobically driven complexation.
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•Standard partial molar volumes of aqueous guanidinium chloride.•Microscopic view in guanidinium hydration at high temperatures and pressures.•Hydrophilic response in guanidinium ...plane to increased temperatures, pressures.•Hydrophobic response of guanidinium faces to increased temperatures, pressures.
The effect of increasing temperature and pressure is studied for aqueous guanidinium chloride (GdmCl) at infinite dilutions. Experimentally determined partial molar volumes are combined with classical molecular dynamics simulations of GdmCl and the detailed analysis of the hydration structure is presented. We find that Gdm+ ion behaves differently than Cl– ion in terms of overall hydration structure, where Gdm+ has an anisotropic hydration shell compared to an isotropically hydrated Cl– ion. The difference in the hydration structure between the ions is also visible in the corresponding Kirkwood-Buff integrals and in temperature and pressure effects on single ion standard molar volumes. The detailed analysis shows a unique behavior of Gdm+ hydration structure which at the same time displays both hydrophilic and hydrophobic response to increase in temperature and pressure.
