Lithuanian Journal of Physics

Title

2026-04-30T17:02:05+03:00

2026-04-30T17:04:03+03:00

Non-Arrhenius behaviour of NMR self-diffusion of the neat room temperature ionic liquid 1-butyl-3-methyl imidazolium tetra- fluoroborate [bmim][BF4].

2026-05-12T08:43:24+03:00

Room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]) was investigated using ¹H, ¹⁹F, ¹¹B and ¹⁰B DOSY NMR spectroscopy in a temperature range of 288–338 K. The dynamics of the [BF₄] anion and [bmim] cation have been found to be similar, indicating that both constituents behave as a rigid unit in the studied temperature range. The diffusion coefficients varied from 6.9 ∙ 10^–11 m² s^–1 at the highest temperature to 6.1 ∙ 10^–12 m² s_–1 at the lowest temperature. The dynamics of the diffusion coefficient was found not obeying the Arrhenius law and therefore was analyzed using the Vogel–Fulcher–Tammann (VFT) equation for the diffusivity. The glass transition temperature was found to be in a range of 172–181 K, which coincides with the values obtained using other techniques and found in the literature; the parameter B which is related to activation energy was found equal to 828–1115 K.

Infrared spectroscopic determination of dry infectious and normal cerebrospinal fluids

2026-05-12T08:43:10+03:00

erebrospinal fluid (CSF) reflects the pathological processes in neural tissues, therefore, by analyzing it, pathologies can be detected. In our study, we applied infrared (IR) spectroscopy for the analysis of dried infectious and normal CSF films of 30 patients. The presence of glucose, bicarbonates, amino acids and lactate was established from the attenuated total reflectance (ATR) IR spectra. The differences between infectious and normal CSF samples are related to lactate and amino acids and allow one to distinguish these two sample groups. The applied method allows one to analyze a small sample amount that is an advantage compared to the routine clinical evaluation of the CSF where significantly larger amounts of the fluid are required.

Complex of TPPS4 and L-ascorbic acid: Protonation of the porphyrin centre

2026-05-12T08:42:56+03:00

The L-ascorbic acid and TPPS₄ complex in water is treated as a close contact associate (intermolecular distance <0.2 nm). The paper presents the modelling of the structures and electronic excitations of two types of complexes using quantum-chemical methods. In both complexes, L-ascorbic acid acts as a reducing agent. In the second complex [L-ascorbic acid + TPPS₄ + L-ascorbic acid], intermolecular charge transfer occurs. Protonation of the TPPS₄ centre can be realized by connecting two L-ascorbic acid molecules as proton sources. The presence of L-ascorbic acid in the solvent enables an efficient protonation of the primary structure: TPPS₄ → H₂TPPS₄.

Influence of Fe2+ on lipid orientation in the cell membrane bilayer: Quantum chemical modelling

2026-05-12T08:42:44+03:00

To understand the dynamics of hole formation and the progression of hole closure in the membrane layer at the molecular level, the structures of phospholipids and iron-ion associates were modelled using quantum-mechanical methods. It has been found that metal ion fixation to the lipid chain is insignificant in forming lipid conformational movement. Similarly, metal ion fixation in the case of the –N(CH₃)₃ head in the lipid head group is not formed. The iron ion binds two lipid molecules in the orthophosphoric region, forming an energetically stable bridge between orthophosphoric fragments. As a result of this process, the lipid aliphatic chains change their conformation: a curved chain forms around the metal ion centre from a straight structure. A typical molecular charge redistribution during excitation was determined and described. It is stated that, due to the energetically favourable position of the Fe²⁺ ion, one lipid serves as a charge donor and the other as a charge acceptor.

EPR of X-ray-irradiated [(CH3)2NH2][Zn(HCOO)3] hybrid perovskite

2026-05-12T08:42:31+03:00

Incorporating paramagnetic metal ions into hybrid materials is a standard practice to enable electron paramagnetic resonance (EPR) studies of phase transitions and dynamics. Yet, the inclusion of foreign ions in the lattice can significantly distort the local structure, resulting in the inaccurate understanding of the material properties. Less invasive paramagnetic defects can be formed by high energy irradiation. Here, we report a continuous-wave (CW) EPR study of X-ray-irradiated [(CH₃)₂NH₂][Zn(HCOO)₃] hybrid perovskite, which possesses a structural phase transition at ~160 K. The CW EPR spectrum reveals a rhombic g-tensor with no clearly resolved hyperfine splittings. Assisted by the DFT calculations, we assign the spectrum to a radical species on the formate linker. The temperature dependence of the measured gzz component reveals a broad anomaly in a broad temperature range close to the phase transition point, which we relate to the change in the dynamics of a formate linker.

A computational QM/MD 17O NMR study of tautomeric equilibrium of mycotoxin citrinin in dichloromethane solution

2026-05-12T08:45:32+03:00

The tautomeric equilibrium of citrinin in dichloromethane was investigated using classical molecular dynamics and linear-response QM/MM calculations of ¹⁷O NMR shielding constants. MD simulations showed that solvent distribution around the para- and ortho-quinone methide tautomers is essentially uniform, as expected for an isotropic non-hydrogen-bonding solvent of medium polarity. The tautomeric ratio between the p- and o-citrinin forms was optimized to best match experimental and computed relative ¹⁷O NMR spectra. The resulting tautomeric ratio of p-to-o-citrinin of 7:4 closely reproduces the experimental value of 4:3, confirming the near-thermodynamic equivalence of the two tautomers, with a slight preference for the para form. A thermodynamic-cycle-based quantum-chemical estimate yielded virtually the same qualitative conclusion. Attempts to include the endiol tautomer of citrinin showed it to be unstable in a dielectric-continuum solvent model; thus, the endiol tautomer is not expected to form in dichloromethane and does not contribute to the observed NMR spectra.

Structural and dielectric properties of trans-stilbene–TPD-type molecular composites

2026-05-12T08:45:19+03:00

The crystallization behaviour and dielectric response of trans‑stilbene embedded in a small‑molecule hole‑transport matrix were examined as a function of composition. In contrast to polymeric hosts, the crystallizing tritolyl‑triarylamine-based material – structurally related to TPD – enables a direct analysis of mutual crystallization effects between the two molecular solids. Composite films containing 5–80% trans-stilbene were prepared by drop casting and characterized using X-ray diffraction, optical microscopy, and dosed charging measurements. XRD and microscopy reveal concentration-dependent phase coexistence and morphological evolution, while dielectric measurements show a pronounced nonmonotonic dependence on the composition, with an enhanced effective permittivity at intermediate concentrations (20–40%). The results highlight the interplay between molecular crystallization and interfacial polarization as a key mechanism governing and enhancing the electrostatic properties of stilbene-tolylamine intermolecular composites.