A simple approach for determination of the phase transition temperature using infrared temperature-induced isosbestic points

The isosbestic point in the Raman spectra of the hydration shell

Isosbestic point is often observed in a series of spectra, but their interpretation is still controversial, such as whether the continuum model can produce an isosbestic point. In order to answer this question, the Raman spectra of hydration shell with continuous distribution structure in different ionic aqueous solutions were separated by Raman ratio spectra, and an isosbestic point was successfully observed. Our experimental results show that the continuum model can indeed produce the isosbestic point. In order to deepen the understanding of the isosbestic point, we calculate the first moment of the Raman spectra and conduct molecular dynamics (MD) simulations. Both experimental and theoretical findings indicate that elevated temperatures lead to increased disorder among water molecules within the hydration shell.

Crystal structure and spectroscopic determination of the phase transitions in methylammonium- and formamidinium bismuth iodide perovskites

Understanding of the structural properties of hybrid organic-inorganic perovskites (HOIPs) and their behavior is crucial for their use as photovoltaics and for the design and assembly of solar cells. As part of this work, a detailed study was conducted to further understand bismuth iodide perovskites, with a specific focus on the phase transitions of methylammonium and formamidinium analogs. A detailed analysis of the temperature-dependent IR spectra was also performed in order to analyze the structural changes that occur. The presence of five phases in the methylammonium bismuth iodide (MABiI) and four phases in formamidinium bismuth iodide (FABiI) were determined. An additional confirmation of the reported results was obtained from the differential scanning calorimetry. The ambiguities concerning the crystal structure of FABiI were resolved based on the results by X-ray powder diffraction (XRPD).

Surface-enhanced Raman sensor with molecularly imprinted nanoparticles as highly sensitive recognition material for cancer marker amino acids

Surface-enhanced Raman scattering (SERS) is a powerful technique primarily due to its high sensitivity and signal-enhancing properties, which enable the identification of unique vibrational fingerprints. These fingerprints can be used for the diagnosis and monitoring of diseases such as cancer. It is crucial to selectively identify cancer biomarkers for early diagnosis. A correlation has been established between the reduction in the concentration of specific amino acids and the stage of the disease, particularly tryptophan (TPP) and tyrosine (TRS) in individuals diagnosed with prostate cancer. In this work, we present a strategy to analyze TPP and TRS amino acids using molecularly imprinted polymer nanoparticles (nanoMIPs), which selectively detect target molecules in a SERS sensor. NanoMIPs are synthesized using the solid-phase molecular imprinting method with TPP and TRS as templates. These are then immobilized on a SERS substrate with gold nanoparticles to measure samples prepared from tryptophan and tyrosine in phosphate-buffered saline. The detection and quantification limits of the designed sensor are 7.13 μM and 23.75 μM for TPP, and 22.11 μM and 73.72 μM for TRS, respectively. Our study lays the groundwork for future investigations utilizing nanoMIPs in SERS assessments of TPP and TRS as potential biomarkers for prostate cancer detection.

Site specifically probing the unfolding process of human telomere i-motif DNA using vibrationally enhanced alkynyl stretch

The microscopic unfolding process of a cytosine-rich DNA forming i-motif by hemi-protonated base pairs is related to gene regulation. However, the detailed thermal unfolding mechanism and the protonation/deprotonation status of site-specific cytosine in DNA in a physiological environment are still obscure. To address this issue, a vibration-enhanced CC probe tagged on 5'E terminal cytosine of human telomere i-motif DNA was examined using linear and nonlinear infrared (IR) spectroscopies and quantum-chemistry calculations. The CC probe extended into the major groove of the i-motif was found using nonlinear IR results only to introduce a minor steric effect on both steady-state structure and local structure dynamics; however, its IR absorption profile effectively reports the cleavage of the hemi-protonated base pair of C1-C13 upon the unfolding with C1 remaining protonated. The temperature mid-point (Tm) of the local transition reported using the CC tag was slightly lower than the Tm of global transition, and the enthalpy of the former exceeds 60% of the global transition. It is shown that the base-pair unraveling is noncooperative, with outer base pairs breaking first and being likely the rate limiting step. Our results offered an in-depth understanding of the macroscopic unfolding characteristics of the i-motif DNA and provided a nonlinear IR approach to monitoring the local structural transition and dynamics of DNA and its complexes.

Temperature dependent phase transitions and their relation to isosbestic point formation. Case study of C(NH2)3PbI3

Besides the vast research regarding the hybrid organic-inorganic perovskite (HOIP) materials used in the solar cell production, their properties are still not fully uncovered. In this paper, detailed investigation on the phase transitions in guanidinium lead iodide (GAPbI₃) using vibrational spectroscopy techniques (IR and Raman) are presented. In addition to the well-known three phases of GAPbI₃ (denoted as I, II and III) another one existing in the temperature range from 48 °C to 160 °C is characterized. The thorough inspection of the vibrational spectra revealed some interesting changes occurring in the low temperature region (from -90 to -62 °C) that suggest presence of a new phase. Finally, a redefinition of the phase nomenclature according to the recommendations given by the IUCr is proposed.