Study of hydration of sarcosine, formation of its zwitterion and their different oligomers in aqueous media: a Raman spectroscopic and theoretical study

A DFT study of the effect of hydrostatic pressure on the structure and electronic properties of sarcosine crystal

CONTEXT

We perform density functional theory calculations to study the dependence of the structural and electronic properties of the amino acid sarcosine crystal structure on hydrostatic pressure application. The results are analyzed and compared with the available experimental data. Our findings indicate that the crystal structure and properties of sarcosine calculated using the Grimme dispersion-corrected PBE functional (PBE-D3) best agree with the available experimental results under hydrostatic pressure of up to 3.7 GPa. Critical structural rearrangements, such as unit cell compression, head-to-tail compression, and molecular rotations, are investigated and elucidated in the context of experimental findings. Band gap energy tuning and density of state shifts indicative of band dispersion are presented concerning the structural changes arising from the elevated pressure. The calculated properties indicate that sarcosine holds great promise for application in electronic devices that involve pressure-induced structural changes.

METHODS

Three widely used generalized gradient approximation functionals-PBE, PBEsol, and revPBE-are employed with Grimme's D3 dispersion correction. The non-local van der Waals density functional vdW-DF is also evaluated. The calculations are performed using the projector-augmented wave method in the Quantum Espresso software suite. The geometry optimization results are visualized using VMD. The Multiwfn and NCIPlot programs are used for wavefunction and intermolecular interaction analyses.

Silica Nanospheres Coated Silver Islands as an Effective Opto-Plasmonic SERS Active Platform for Rapid and Sensitive Detection of Prostate Cancer Biomarkers

The in vitro diagnostics of cancer are not represented well yet, but the need for early-stage detection is undeniable. In recent decades, surface-enhanced Raman spectroscopy (SERS) has emerged as an efficient, adaptable, and unique technique for the detection of cancer molecules in their early stages. Herein, we demonstrate an opto-plasmonic hybrid structure for sensitive detection of the prostate cancer biomarker sarcosine using silica nanospheres coated silver nano-islands as a facile and efficient SERS active substrate. The SERS active platform has been developed via thin (5-15 nm) deposition of silver islands using a simple and cost-effective Radio Frequency (RF) sputtering technique followed by the synthesis and decoration of silica nanospheres (~500 nm) synthesized via Stober's method. It is anticipated that the coupling of Whispering Gallery Modes and photonic nano-jets in SiO2 nanospheres induce Localized Surface Plasmon Resonance (LSPR) in Ag nano-islands, which is responsible for the SERS enhancement. The as-fabricated SERS active platform shows a linear response in the physiological range (10 nM to 100 μM) and an extremely low limit of detection (LOD) of 1.76 nM with a correlation coefficient of 0.98 and enhancement factor ~2 × 107. The findings suggest that our fabricated SERS platform could be potentially used for the rapid detection of bio-chemical traces with high sensitivity.

Glucose-induced self-assembly and phase separation in hydrophilic triblock copolymers and the governing mechanism

Poly(ethylene oxide, EO)-poly(propylene oxide, PO)-poly(ethylene oxide, EO)-based triblock copolymers (BCPs) with 80% hydrophilicity stay molecularly dissolved as Gaussian chains at ambient temperature, even at fairly high concentrations (>5 %w/v). This study presents the plausible micellization behaviour of such very-hydrophilic Pluronics® - F38, F68, F88, F98, and F108 - incited upon the addition of glucose at low concentrations and temperatures. The outcomes obtained from phase behaviour and scattering studies are described. At temperatures near to ambient temperature, these BCPs form micelles with a central core made of a PO block, surrounded by a corona of highly hydrated EO chains. The phase transitions in these hydrophilic Pluronics® in the presence of glucose are demonstrated via the dehydration of the copolymer coil, leading to a decrease in the I₁/I₃ ratio, as determined using fluorescence spectroscopy. The temperature-dependent cloud point (CP) showed a marked decrease with an increase in the PO molecular weight and also in the presence of glucose. The change in solution relative viscosity (η_rel) caused by glucose is due to the enhanced dehydration of the EO block of the BCP amphiphile. Dynamic light scattering (DLS) and small-angle neutron scattering (SANS) investigations suggested that the dimensions of the hydrophobic core increase during the dehydration of the EO-PO blocks upon a temperature increase or after adding varying concentrations of glucose, thereby resulting in a micellar shape transition. It has been observed that added glucose influences the phase behaviour of BCPs in an analogous way to the influence of temperature. Also, plausible interactions between the EO-PO blocks and glucose were suggested based on the evaluated optimized descriptors obtained from a computational simulation approach. In addition, the core-shell blended micelles obtained using these BCPs are successfully utilized for drug (curcumin, Cur) solubilization based on the observed peak intensities from UV-visible spectroscopy. The loading of Cur into glucose-containing and glucose-free hydrophilic Pluronic® micelles shows how the radius of the micellar core (R_c) increases in the presence of glucose, thereby indicating Cur solubility enhancement for the Pluronic® micelles. Various kinetics models were employed, demonstrating a drug release profile that enables this approach to be used as an ideal platform for drug delivery.

High pressure Raman investigation on trans-urocanic acid

Trans-urocanic acid (t-UCA) is an important epidermal UV protector predominantly found in human skin. Exposure of UV radiation triggers photoisomerization of t-UCA into its other conformer, cis-urocanic acid (cis-UCA), which has been shown to be a mediator of UV-induced immune-suppression leading to skin cancer. In this report, we present the investigation of molecular changes of t-UCA under high pressures by in-situ high pressure Raman spectroscopy. The study indicates onset of ring opening polymerization of t-UCA at pressure above 1.4 GPa. At pressures beyond 5 GPa, a well discernible characteristic vibrational mode (CC stretch) accompanied by several other spectral features such as δ CO₂^- and δ NH modes of cis-UCA point towards the isomerization of residual t-UCA monomers into cis-UCA. The content of cis-UCA gradually increased with increase in pressure. On release to ambient conditions, the spectrum of the quenched sample showed Raman modes of polymer and cis-UCA indicating that the changes are irreversible.

Influence of Humectants on the Thermotropic Behaviour and Nanostructure of Fully Hydrated Lecithin Bilayers

Humectants are used widely in topical formulations as they provide cosmetic and health benefits to skin. Of particular interest to our laboratories is the interaction of humectants in phospholipid based topical skin care formulations. This study probed the effects of three exemplary humectants on a fully hydrated lecithin system (DPPC) by use of X-ray scattering and differential scanning calorimetry. While the three humectants affected the nanostructure of 1, 2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC, bilayers in a similar manner; leading to an increased membrane order, differences in the effect on the thermal behaviour of DPPC suggest that betaine and sarcosine interacted via a different mechanism compared to acetic monoethanolamide, AMEA. At concentrations above 0.4M, betaine and sarcosine stabilised the gel phase by depletion of the interfacial water via the preferential exclusion mechanism. At the same time, a slight increase in the rigidity of the membrane was observed with an increase in the membrane thickness. Overall, the addition of betaine or sarcosine resulted in an increase in the pre- and main transition temperatures of DPPC. AMEA, on the other hand, decreases both transition temperatures and although the interlamellar water layer was also decreased, there was evidence from the altered lipid chain packing, that AMEA molecules are present also at the bilayer interface, at least at high concentrations. Above the melting point in the fluid lamellar phase, none of the humectants induced significant structural changes, neither concerning the bilayer stacking order nor its overall membrane fluidity.

Metal-coded hydrogel magnetic molecularly imprinted polymer for preconcentration and cleanup of sarcosine: Determination in urine; coupled to on-column capillary electrophoresis

In this study, sarcosine metal-coded hydrogel magnetic molecularly imprinted polymer (Hydro-MeC-MMIP) has been fabricated and coupled to on-column derivatization capillary electrophoresis (CE). As a metal-coding approach, sarcosine-Cu²⁺-ligand (Sar-Cu²⁺-L) chelate complex was introduced as a template to overcome the problems associated with the fabrication of MMIP for a small molecule having limited functional groups such as sarcosine. To our best knowledge, it is the first time that methacrylamide (MA) coated Fe₃O₄ (Fe₃O₄@MA) with abounded reactive double-bound on the surface has been used as a magnetic core in the one-pot synthesis of MMIPs. As prepared, Hydro-MeC-MMIP was characterized by different microscopic, spectroscopic, and thermal gravimetric methods. Hydro-MeC-MMIP was used to extract and preconcentrate sarcosine in the urine sample with no treatment and dilution. Sarcosine was quantified by on-column derivatization capillary electrophoresis equipped with a photodiode array detector. A mixture of thirteen amino acids was separated with a total run time of 12 min. Three structural analogs, including alanine, sarcosine, and glycine, were significantly resolved. Under optimal experimental conditions, the method's detection and quantification limits were 9.93 and 33.10 ng mL^-1, respectively. The linear range of 50-2000 ng mL^-1 and 96% recovery, along with the relative standard deviation of 6.07% (n = 6) for the target amino acid, were obtained. This method provides a simple, low-cost, fast, and efficient tool for extracting and quantifying sarcosine in the urine. The present method can address inconsistency in evaluating sarcosine as a candidate biomarker for prostate cancer with a simple CE/UV; no need for a sophisticated detection system such as a mass spectrometer.

Surface enhanced Raman scattering based reaction monitoring of in vitro decyclization of creatinine → creatine

Raman signatures of decyclization of creatinine to creatine appear after 120 min at pH 8, 60 min at pH 10 and 30 min at pH 12. Signature of reversibility at later stages of the reaction.

Temperature dependent Raman and DFT study of creatine

Temperature dependent Raman spectra of creatine powder have been recorded in the temperature range 420-100K at regular intervals and different clusters of creatine have been optimized using density functional theory (DFT) in order to determine the effect of temperature on the hydrogen bonded network in the crystal structure of creatine. Vibrational assignments of all the 48 normal modes of the zwitterionic form of creatine have been done in terms of potential energy distribution obtained from DFT calculations. Precise analysis gives information about thermal motion and intermolecular interactions with respect to temperature in the crystal lattice. Formation of higher hydrogen bonded aggregates on cooling can be visualized from the spectra through clear signature of phase transition between 200K and 180K.