Use of multivariate statistical techniques to optimize the separation of isoflavones by liquid chromatography

The aim of this paper is to optimize and validate a high performance liquid chromatography (HPLC) method for separation and quantification of five isoflavones. A statistical central composite design was used to separate all peaks. These multivariate procedures were efficient in determining the optimal separation condition using resolution, capacity factor, asymmetry and number of theoretical plates.      

Electrochemical characterization of Prussian blue type nickel hexacyanoferrate redox mediator for potential application as charge relay in dye-sensitized solar cells

A polynuclear electronically/ionically (redox) conducting mixed-valent inorganic material such as nickel(II) hexacyanoferrate(II,III), NiHCF, was considered for potential application as a redox mediator (charge relay) in dye-sensitized solar cell (DSSC). The NiHCF redox reactions were found fast and reversible not only when the system was studied as thin film exposed to an aqueous supporting electrolyte but also as bulk material (pasted powder) in solid state, i.e., in the absence of contact with external liquid electrolyte phase. Usefulness of NiHCF material was diagnosed using conventional electroanalytical approaches, solid-state voltammetric methodology, as well as the dynamic electrochemical impedance spectroscopy technique that permitted monitoring of impedance spectra under potentiodynamic conditions. The material was utilized in a mixed-valent state, i.e., as a mixture of K₄Ni^II[Fe^II(CN)₆] and K₃Ni^II[Fe^III(CN)₆] in which iron(II) and iron(III) sites were at the 1:1 ratio. Under such conditions, dynamics of electron-hopping between mixed-valent iron sites was maximized. Our DSSC utilized cis–dithiocyanoatobis(4,4′-dicarboxylic acid-2,2′-bipyridine) ruthenium(II) dye (N3) adsorbed onto TiO₂ semiconductor and NiHCF as redox mediator. Although performance of our DSSC was not optimized in terms of the NiHCF film thickness and morphology, as well as lower photocurrents in comparison to those characteristic of the iodine/iodide based DSSC were obtained, our system yielded readily fairly high open-circuit photovoltages on the level of 800 mV. An important issue was that the formal potential of NiHCF was more positive relative to the potential of the iodide/triiodide couple while being still more negative than that equivalent to the ground state of the N3 dye. Thus, NiHCF mediator was able to regenerate the dye.

     

Kinetic studies on pH controlled partial dechelation of the trans-imidazole-[Cr(His)2]+ cation

Partial dechelation of one tridentate N,N??,O-histidine in trans-imidazole-[Cr(His)₂]⁺ (where N and N?? are amine and imidazole nitrogen atoms, respectively, and O is carboxylate oxygen) has been studied. The aquation process is both acid and base catalyzed and the product with didentate His is converted back into the substrate at pH 4?C7. Kinetics of the chelate ring opening were studied spectrophotometrically within the 0.01?C1.0?M HClO₄ and 0.1?C1.0?M NaOH ranges under first-order conditions. The following dependences of k _obs on [H⁺] and [OH^?] were determined: $$ \left( {k_{\text{obs}} } \right)_{\text{H}} = a + b\left[ {{\text{H}}^{ + } } \right] + c/\left[ {{\text{H}}^{ + } } \right] $$ $$ \left( {k_{\text{obs}} } \right)_{\text{OH}} = a^{\prime } + b^{\prime } \left[ {{\text{OH}}^{ - } } \right]. $$ Mechanisms of the chelate ring opening in acidic and alkaline media are proposed, and activation parameters for the process in acidic solution have been determined. Additionally, kinetic studies were performed on the second dechelation stage in acidic media, which is ca. 15 times slower than the first one.     

Convergence of dip-pen nanolithography and acoustic biosensors towards a rapid-analysis multi-sample microsystem

The present work demonstrates for the first time patterning of a ready-to-use biosensor with several different biomolecules using Dip-Pen Nanolithography (DPN) for the development of a procedure towards more rapid and efficient multi-sample detection. The biosensor platform used is based on a Surface Acoustic Wave (SAW) device integrated with a parallel-channel microfluidic module, termed as "microfluidics-on-SAW" ("μF-on-SAW"), for reproducible multi-sample analysis. Lipids with different functionalized head groups were patterned at distinct, microfluidic-formed rectangular domains with sharp edges all located on the same sensor surface; pattern quality was verified using a fluorescent microscope. The functionality of the head groups, the efficiency of the patterning method, and the suitability of DPN for the surface modification of the acoustic device were subsequently examined through acoustic experiments. The μF-on-SAW configuration was used to detect specific binding between the pre-patterned functionalized lipids with their corresponding biomolecules. The achievement of an improved sensitivity (5-fold compared to previous acoustic configurations) and reduced preparation time by at least 2 h clearly indicates the suitability of DPN as a direct patterning method for ready-to-use acoustic sensor devices like the μF-on-SAW towards integrated, rapid-analysis, multi-sample biosensing microsystem development.     

Measurement of benzene concentration in urban air using passive sampling

The concentration of benzene in urban air in the Tri-City area of Poland (Gdańsk–Sopot–Gdynia, and Tczew) was assessed using diffusive passive samplers (Radiello). Samples were collected during a four-year monitoring campaign (2007–2010) at selected monitoring stations managed by the Agency of Regional Air Quality Monitoring in the Gdańsk Metropolitan Area (ARMAAG) Foundation. The performance of the passive samplers was investigated in a field study that measured the benzene concentration in urban air. The results obtained by the Radiello samplers were compared with the results obtained using an on-line monitor (Chrompack CP 7001). Statistical analysis of the results obtained by the two different techniques (passive and on-line) was performed by a linear regression method (Student’s t-test). The influence of temperature fluctuations on the uptake rate behavior of the passive samplers was also investigated.     

Spectroscopic and Structural Study of a New Conducting Pyrazolium Salt

The increase in conductivity with temperature in 1H-pyrazol-2-ium 2,6-dicarboxybenzoate monohydrate was analyzed, and the influence of the mobility of the water was discussed in this study. The electric properties of the salt were studied using the impedance spectroscopy method. WB97XD/6-311++G(d,p) calculations were performed, and the quantum theory of atoms in molecules (QTAiM) approach and the Hirshfeld surface method were applied to analyze the hydrogen bond interaction. It was found that temperature influences the spectroscopic properties of pyrazolium salt, particularly the carbonyl and hydroxyl frequencies. The influence of water molecules, connected by three-center hydrogen bonds with co-planar tetrameters, on the formation of structural defects is also discussed in this report.     

Effectiveness of Volatile Natural Deep Eutectic Solvents (VNADESs) for the Green Extraction of Chelidonium majus Isoquinoline Alkaloids

The Chelidonium majus plant is rich in biologically active isoquinoline alkaloids. These alkaline polar compounds are isolated from raw materials with the use of acidified water or methanol; next, after alkalisation of the extract, they are extracted using chloroform or dichloromethane. This procedure requires the use of toxic solvents. The present study assessed the possibility of using volatile natural deep eutectic solvents (VNADESs) for the efficient and environmentally friendly extraction of Chelidonium alkaloids. The roots and herb of the plant were subjected three times to extraction with various menthol, thymol, and camphor mixtures and with water and methanol (acidified and nonacidified). It has been shown that alkaloids can be efficiently isolated using menthol–camphor and menthol–thymol mixtures. In comparison with the extraction with acidified methanol, the use of appropriate VNADESs formulations yielded higher amounts of protopine (by 16%), chelidonine (35%), berberine (76%), chelerythrine (12%), and coptisine (180%). Sanguinarine extraction efficiency was at the same level. Additionally, the values of the contact angles of the raw materials treated with the tested solvents were assessed, and higher wetting dynamics were observed in the case of VNADESs when compared with water. These results suggest that VNADESs can be used for the efficient and environmentally friendly extraction of Chelidonium alkaloids.     

Parallel imaging of coagulation pathway proteases activated protein C,thrombin, and factor Xa in human plasma

Activated protein C (APC), thrombin, and factor (f) Xa are vitamin K-dependent serine proteases that are key factors in blood coagulation. Moreover, they play important roles in inflammation, apoptosis, fibrosis, angiogenesis, and viral infections. Abnormal activity of these coagulation factors has been related to multiple conditions, such as bleeding and thrombosis, Alzheimer''s disease, sepsis, multiple sclerosis, and COVID-19. The individual activities of APC, thrombin, and fXa in coagulation and in various diseases are difficult to establish since these proteases are related and have similar substrate preferences. Therefore, the development of selective chemical tools that enable imaging and discrimination between coagulation factors in biological samples may provide better insight into their roles in various conditions and potentially aid in the establishment of novel diagnostic tests. In our study, we used a large collection of unnatural amino acids, and this enabled us to extensively explore the binding pockets of the enzymes'' active sites. Based on the specificity profiles obtained, we designed highly selective substrates, inhibitors, and fluorescent activity-based probes (ABPs) that were used for fast, direct, and simultaneous detection of APC, thrombin, and fXa in human plasma.

Using a collection of natural and unnatural amino acids, we synthesized a set of fluorescent activity-based probes for the fast, direct, and simultaneous detection of coagulation factors in human plasma.