Characterization and quantification of secondary metabolite profiles in leaves of red and white clover species by NIR and ATR-IR spectroscopy

Different varieties of two clover species (Trifolium pratense L. and Trifolium repens L.), cultivated in 2008 and 2009 were analysed by near-infrared (NIR) and mid-infrared (MIR) spectroscopy for establishing a fast and reliable quantification protocol for isoflavones and phenolic acids. Based on HPLC–UV/MS reference data, good results were obtained by PLS regression for the prediction of total isoflavone (R² = 0.90) as well as for glycitin content (R² = 0.88). Because of the lower concentration of formononetin and phenolic acids, their prediction quality was generally slightly lower (R² = 0.73 and R² = 0.64, respectively) compared to those of the isoflavones. The applicability of ‘leave one out’ cross validation for such a large data set is proven by comparison to an averaged randomized test-set validation leading to similar results. Additionally, the large sample set (n = 624) was screened by hierarchical cluster analysis allowing a fast evaluation of influences resulting from different cultivation parameters on the isoflavone and phenolic acid content. Climatic changes (cultivation year, date of harvest) seem to have the most impact on the metabolic profile as indicated by higher variability in the referring spectra when both cultivation years were simultaneously regarded. This work offers a new vibrational spectroscopic approach for the qualitative and quantitative determination of isoflavone and phenolic acid profiles, directly performed in the plant material without any laborious sample preparation and time-consuming chromatography. Once validated by HPLC reference, MIR and NIR spectroscopy can be used for the reliable prediction of secondary metabolites in clover as well as for fast screening and pre-evaluation of the diversity of a large sample set, aiming to reduce analytical costs, chemical waste and expenditure of time.     

Near-infrared spectroscopy as an effective tool for monitoring the conformation of alkylammonium surfactants in montmorillonite interlayers

Application of near-infrared (NIR) spectroscopy to probing the arrangement of trimethylalkylammonium cations in montmorillonite interlayers has been demonstrated. Detailed analysis of the mid-IR (MIR) and NIR spectra of montmorillonite from Jelšový Potok (JP, Slovakia) saturated with surfactants with varying alkyl chain length (even numbers of carbon atoms from C6 to C18) was performed to show the advantages of the NIR region in characterizing surfactant conformations. The position of the ν_as(CH₂), (∼2930–2920 cm⁻¹), ν_s(CH₂) (∼2860–2850 cm⁻¹), 2ν_as(CH₂) (∼5810–5785 cm⁻¹), (ν + δ)_as(CH₂) (∼4340–4330 cm⁻¹) and (ν + δ)_s(CH₂) (∼4270–4250 cm⁻¹) signals was used as an indicator of the gauche/trans conformer ratio. For all bands, a shift toward lower wavenumber on increasing the alkyl chain length from 6 to 18 carbons suggests a transition from disordered liquid-like to more ordered solid-like structures of the surfactants. The magnitude of the shift was significantly higher for 2ν_as(CH₂) (28 cm⁻¹) than for ν_as(CH₂) (8 cm⁻¹) or ν_s(CH₂) (10 cm⁻¹), showing the NIR region to be a useful tool for examining this issue. Comparison of the IR spectra of crystalline alkylammonium salts and the corresponding organo-montmorillonites demonstrated a confining effect of montmorillonite layers on surfactant ordering. For each alkyl chain length the CH₂ bands of the organo-montmorillonites appeared at higher wavenumbers than for the unconfined surfactant, thus indicating a higher disorder of the alkyl chains. The wavenumber difference between corresponding samples was always higher in the NIR than in the MIR region. All these findings show NIR spectroscopy to be useful for conformational studies.     

Essential oil of Salvia aucheri mesatlantica as a green inhibitor for the corrosion of steel in 0.5 M H2SO4

Essential oil of aerial parts of Salvia aucheri Boiss. var. mesatlantica was obtained by hydrodistillation and analyzed by GC and GC/MS. The oil was predominated by camphor (49.59%). The inhibitory effect of this essential oil was estimated on the corrosion of steel in 0.5 M H₂SO₄ using electrochemical polarization and weight loss measurements. The corrosion rate of steel is decreased in the presence of natural oil. The inhibition efficiency was found to increase with oil content to attain 86.12% at 2 g/L. Polarization curves revealed that the oil of S. aucheri mesatlantica acts as mixed type inhibitor with a strong predominance of anodic character. The temperature effect on the corrosion behavior of steel in 0.5 M H₂SO₄ without and with the inhibitor at 2 g/L was studied in the temperature range from 303 to 343 K, the associated activation energy have been determined. The adsorption of oil on the steel surface was found to obey Langmuir’s adsorption isotherm.     

Direct electron transfer-type four-way bioelectrocatalysis of CO2/formate and NAD+/NADH redox couples by tungsten-containing formate dehydrogenase adsorbed on gold nanoparticle-embedded mesoporous carbon electrodes modified with 4-mercaptopyridine

Tungsten-containing formate dehydrogenase from Methylobacterium extorquens AM1 (FoDH1) catalyzes formate oxidation with NAD⁺. FoDH1 shows little direct communication with carbon electrodes, including mesoporous Ketjen Black-modified glassy carbon electrode (KB/GCE); however, it shows well-defined direct electron transfer (DET)-type bioelectrocatalysis of carbon dioxide reduction, formate oxidation, NAD⁺ reduction, and NADH oxidation on gold nanoparticle (AuNP)-embedded KB/GCE treated with 4-mercaptopyridine. Microscopic measurements reveal that the AuNPs (d = 5 nm) embedded on the KB surface are uniformly dispersed. Electrochemical data indicate that the pyridine moiety on the AuNPs plays important roles in facilitating the interfacial electron transfer kinetics and increasing the probability of productive orientation of FoDH1. The formal potential of the electrochemical communication site, which is most probably an ion‑sulfur cluster, is evaluated as − 0.591 ± 0.005 V vs. Ag | AgCl | sat. KCl from Nernst analysis of the steady-state catalytic waves.     

Bioelectrocatalytic formate oxidation and carbon dioxide reduction at high current density and low overpotential with tungsten-containing formate dehydrogenase and mediators

We show a great possibility of mediated enzymatic bioelectrocatalysis in the formate oxidation and the carbon dioxide (CO₂) reduction at high current densities and low overpotentials. Tungsten-containing formate dehydrogenase (FoDH1) from Methylobacterium extorquens AM1 was used as a catalyst and immobilized on a Ketjen Black-modified electrode. For the formate oxidation, a high limiting current density (j_lim) of ca. 24 mA cm^− 2 was realized with a half wave potential (E_1/2) of only 0.12 V more positive than the formal potential of the formate/CO₂ couple (E°′_CO2) at 30 °C in the presence of methyl viologen (MV^2 +) as a mediator, and j_lim reached ca. 145 mA cm^− 2 at 60 °C. Even when a viologen-functionalized polymer was co-immobilized with FoDH1 on the porous electrode, j_lim of ca. 30 mA cm^− 2 was attained at 60 °C with E_1/2 = E°′_CO2 + 0.13 V. On the other hand, the CO₂ reduction was also realized with j_lim ≈ 15 mA cm^− 2 and E_1/2 = E°′_CO2 − 0.04 V at pH 6.6 and 60 °C in the presence of MV^2 +.     

Behaviour of Li+ and Cu2+ in heated montmorillonite: Evidence from far-, mid-, and near-IR regions

Infrared spectroscopy in the far (FIR), mid (MIR), and near (NIR) regions was used to study the structural changes of a thermally treated clay mineral montmorillonite saturated with Li⁺ or Cu²⁺ cations (Li-JP and Cu-JP samples). Cation exchange capacity (CEC) values decreased by 89 and 64% in Li- and Cu-samples, respectively, heated at 300 °C. The IR spectra confirm that the charge of exchangeable cations significantly affect their final position after fixation upon heating. No absorption bands related to the vibrations of interlayer cations were observed in the FIR spectra of unheated or heated samples; however, different modification of the complex vibrational mode involving motion of octahedral aluminium relative to the tetrahedral sheet was observed near 197 cm⁻¹. The vibrations of OH groups in both MIR (ν_OH, 3630–3670 cm⁻¹) and NIR (2ν_OH, 7070–7170 cm⁻¹) regions proved that the Li⁺ migrated into the octahedral vacancies, thus creating local trioctahedral domains, such as AlMgLiOH. Though Cu²⁺ has similar ionic radius as Li⁺, no spectral features indicating its presence in the octahedral positions have been found even in the sample heated at 300 °C. Fixed Cu(II) is supposed to be located deep in the ditrigonal cavities of the tetrahedral sheets of Cu-JP. The NIR spectra of heated Cu-JP samples show new components near 7045 and 5170 cm⁻¹. These modes are believed to correspond to overtone bands associated with hydrated Cu²⁺ ions tightly bound in close proximity to the ditrigonal cavities of the basal surface (O_basalCu²⁺H₂O). The NIR spectra confirm that in Cu-JP heated at 200 °C, then saturated with Li⁺ and Cu²⁺ and heated again at 300 °C small Li⁺ ions migrate into the vacant octahedral sites even though Cu(II) have been trapped in the hexagonal cavities of the tetrahedral sheets in the course of previous heat treatment.     

Partial least squares-near infrared determination of pesticides in commercial formulations

A solvent free, fast and environmentally friendly near infrared-based methodology (NIR) was developed for pesticide determination in commercially available formulations. This methodology was based on the direct measurement of the diffuse reflectance spectra of solid samples and a multivariate calibration model (partial least squares, PLS) to determine the active principle concentration in commercial formulations. The PLS calibration set was built on using the spiked samples by mixing different amounts of pesticide standards and powdered samples. Buprofezin, Diuron and Daminozide were used as test analytes. Concentration of Buprofezin in the samples was calculated employing a 4-factors PLS calibration using the spectral information in the range between 2231–2430 and 1657–1784 nm. For Diuron determination a 1-factor PLS calibration model using the spectral range 1110–2497 nm, after a linear removed correction. Daminozide determination was carried out employing a 4-factors PLS model using the spectral information in the ranges 1644–1772 and 2014–2607 nm without baseline correction. The root mean square errors of prediction (RMSEP) found were 1.1, 1.7 and 0.7% (w/w) for Buprofezin, Diuron and Daminozide determination, respectively. The developed PLS-NIR procedure allows the determination of 120 samples/h, does not require any sample pre-treatment and avoids waste generation.     

Near-infrared spectroscopy: A powerful tool in studies of acid-treated clay minerals

The benefit of near-infrared (NIR) spectroscopy in studies of acid-treated clay minerals is demonstrated. The effects of mineral type, composition and content of non-swelling interlayers on the dissolution rate are investigated. Detailed analysis of the NIR region is performed by comparing the first overtone (2ν_OH) and combination (ν + δ)_OH bands with the fundamental stretching (ν) and bending (ν) vibrations. Spectra of acid-treated samples show a gradual decrease in the intensities of the structural OH overtone (near 7100 cm^?1) and combination (4600–4300 cm^?1) bands reflecting a fewer number of octahedral atoms. The appearance of the 2ν_SiOH vibration for terminal (isolated) SiOH groups near 7315 cm^?1 indicates the formation of a protonated silica phase. The band near 7130 cm^?1 remaining in the spectra of acid-treated samples is assigned to 2ν_HOSiOH of geminal silanol groups. Thus the creation of geminal silanols, previously detected by ²⁹Si MAS-NMR spectroscopy in acid-treated hectorite, is confirmed also by NIR spectroscopy. The assignment of the 4555 cm^?1 band to the (ν + δ)_SiOH combination enabled calculation of the wavenumber for the SiO–H bending vibration (～810 cm^?1) that is not observable in the mid-IR region due to overlapping with the Si–O band of amorphous silica (～800 cm^?1). The NIR spectra confirm that trioctahedral hectorite is much more susceptible to dissolution in HCl than dioctahedral nontronite. The dissolution rate of kaolinite present in the Badin clay as an admixture is lower than that of the main mineral nontronite. The accessibility of the interlayers for protons significantly influences the stability of clay minerals in HCl. Mixed-layered mineral illite/smectite with only 30% of swelling interlayers dissolves more slowly than smectite of similar chemical composition containing mainly swelling interlayers.     

Effect of gamma irradiation on cell lysis and polyhydroxyalkanoate produced by Bacillus flexus

Bacillus flexus cultivated on sucrose and sucrose with plant oil such as castor oil produced polyhydroxybutyrate (PHB), a homopolymer of polyhydroxyalkanoate (PHA) and PHA copolymer (containing hydroxybutyrate and hexanoate), respectively. Gamma irradiation of these cells (5–40 kGy) resulted in cell damage and aided in the isolation of 45% and 54% PHA on biomass weight, correspondingly. Molecular weight of PHB increased from 1.5×10⁵ to 1.9×10⁵ after irradiation (10 kGy), with marginal increase of tensile strength from 18 to 20 MPa. At the same irradiation dosage, PHA copolymer showed higher molecular weight increase from 1.7×10⁵ to 2.3×10 ⁵ and tensile strength from 20 to 35 MPa. GC, GC–MS, FTIR and ¹H NMR were used for the characterization of PHA. Gamma irradiation seems to be a novel technique, to induce cross-linking and molecular weight increase of PHA copolymer and aid in easy extractability of intracellular PHA, simultaneously.     

Synthesis,growth, and characterization of a new NLO material 3-(2,3-dimethoxyphenyl)-1-(pyridin-2-yl)prop-2-en-1-one

3-(2,3-Dimethoxyphenyl)-1-(pyridin-2-yl)prop-2-en-1-one (DMPP) a potential second harmonic generating (SHG) has been synthesized and grown as a single crystal by the slow evaporation technique at ambient temperature. The structure determination of the grown crystal was done by single crystal X-ray diffraction study. DMPP crystallizes with orthorhombic system with cell parameters a = 20.3106(8) Å, b = 4.9574(2) Å, c = 13.4863(5) Å, α = 90°, β = 90°, γ = 90° and space group Pca2₁. The crystals were characterized by FT-IR, thermal analysis, UV–vis–NIR spectroscopy and SHG measurements. Various functional groups present in DMPP were ascertained by FTIR analysis. DMPP is thermally stable up to 80 °C and optically transparent in the visible region. The crystal exhibits SHG efficiency comparable to that of KDP.     

Sub-critical water extraction of bitumen from Huadian oil shale lumps

Three sizes of Huadian oil shale lumps from 1 cm to 10 cm were extracted by sub-critical water at 350 °C and 16 MPa for 2–70 h. The oil shale lumps were fractured alone the shale texture in sub-critical water that greatly improved the extraction efficiency of bitumen from the large- and middle-sized sample. The extract yields of bitumen from different sized samples were similar when the extraction time is longer than 20 h and stabilized at about 18 wt.% (ad) after 50 h duration. With the increase of extraction time, asphaltene and preasphaltene extracts were gradually decomposed to maltene. The gas chromatography–mass spectrometry (GC–MS) analysis of the extracts showed that n-alkanes, n-alk-1-enes, isoprenoids, n-alk-2-ones and n-alkanoic acids were the major components. In contrast, aromatic extracts were rare and most of them were remained in the shale residue. The pyrolysis gas chromatography–mass spectrometry (Py-GC–MS) analysis of the spent shale showed that the final undecomposed organics in kerogen were some macromolecular linear hydrocarbon, n-alk-2-ones and n-alkanoic acids fragments. The comparison of the classical pyrolyzate and the sub-critical water extracts showed that the water extracts contained more long-chain alkanes than anhydrous pyrolysis and the alkene extracts could transform to alkanes in sub-critical water. Moreover, the n-alkanoic acids could be decomposed to short-chain compounds through the cleavage of carbon carbon bonds.     

Novel poly (neutral red) nanowires as a sensitive electrochemical biosensing platform for hydrogen peroxide determination

Poly (neutral red) nanowires (PNRNWs) have been synthesized for the first time by the method of cyclic voltammetric electrodeposition using porous anodic aluminum oxide (AAO) template and were examined by scanning electron microscopy (SEM) and transmission electron microscope (TEM). Moreover, horseradish peroxidase (HRP) was encapsulated in situ in PNRNWs (denoted as PNRNWs–HRP) by electrochemical copolymerization for potential biosensor applications. The PNRNWs showed excellent efficiency of electron transfer between the HRP and the glassy carbon (GC) electrode for the reduction of H₂O₂ and the PNRNWs–HRP modified GC electrode showed to be excellent amperometric sensors for H₂O₂ at −0.1 V with a linear response range of 1 μM to 8 mM with a correlation coefficient of 0.996. The detection limit (S/N = 3) and the response time were determined to be 1 μM and <5 s and the high sensitivity is up to 318 μA mM⁻¹ cm⁻².     

Chemical composition,antibacterial and antioxidant activities of essential oils from leaves of three Melaleuca species of Pakistani flora

This study presents essential oil composition of three Melaleuca species namely, Melaleuca bracteata F. Muell, Melaleuca fulgens R. Br. subsp. steedmanii and Melaleuca leucadendron (L.) L. collected from different regions of Pakistan. The chemical composition of essential oils was analyzed by GC-FID and GC–MS. Eugenol methyl ether was identified as a principal component in M. bracteata (82.3%), M. fulgens (87.8%) and M. leucadendron (95.4%) oils. In vitro antibacterial studies were done by agar well diffusion and microdilution method and the tested essential oils exhibited bacteriostatic and bactericidal effects against the tested foodborne pathogens at 4–8 µg/ml. Time kill assay showed significant bactericidal effect of oils for four weeks. The antioxidant potential was assessed by free radical scavenging activity and reducing power assay. The oils showed strong antioxidant activity with approximately 89.0–89.5% inhibition of 2,2-diphenyl-1-picrylhydrazyl radical and ferric reducing power in the range of 1.94 ± 0.007–2.04 ± 0.04% at 100 µg/ml.     

Characterization of slow pyrolysis oil obtained from linseed (Linum usitatissimum L.)

This study presents the characterization of pyrolysis oil obtained from linseed (Linum usitatissimum L.) produced by slow pyrolysis in the maximum yield. The pyrolysis oil was analyzed to determine its elemental composition and calorific value. The chemical composition of the pyrolysis oil and fractions were investigated using chromatographic and spectroscopic techniques (¹H NMR, IR, and GC). The chemical class composition of the oil was determined by liquid column chromatographic fractionation. The oil was separated into pentane soluble and insoluble fractions by using pentane. The column was eluted successively with n-pentane, toluene and methanol to yield aliphatic, aromatic and polar fractions, respectively. The results of the adsorption chromatography of the oil showed that the pyrolysis oil consists of 88 wt% n-pentane soluble. The aliphatic, aromatic and polar fractions of oils obtained in slow pyrolysis are 30, 34, 36 wt%, respectively. The aliphatic and aromatic subtraction make up ∼64 wt% in slow pyrolysis oil. This seems to be more appropriate for the production of hydrocarbons and chemicals.     

Vibrational analysis of liquid n-butylmethylether

The complex refractive index spectrum in the NIR and MIR range of liquid n-butylmethylether (NBME) was determined. Thin film recording technique was required to obtain quantitative transmission spectra in the MIR range. The experimental part was supported by a conformer population analysis and anharmonic vibrational analysis based on the B2PLYP/N07D method. The resulting population of 11 NBME conformers was analyzed and their calculated anharmonic vibrational spectra and calculated abundances (at 298 K) were used to obtain the resultant spectrum of n-butylmethylether. The band assignment procedure was based on the calculated potential energy distributions.     

Measurement and correlation of the (p, ρ, T) relation of liquid n-heptane,n-nonane, 2,4-dichlorotoluene,and bromobenzene in the temperature range from (233.15 to 473.15) K at pressures up to 30 MPa for use as density reference liquids

Comprehensive (p, ρ, T) measurements on n-heptane, n-nonane, 2,4-dichlorotoluene, and bromobenzene were carried out in the homogeneous liquid phase for temperatures from (233.15 to 473.15) K at pressures up to 30 MPa. The measurements were performed by using an accurate single-sinker densimeter based on the Archimedes’ buoyancy principle. The total uncertainty of the measurements in density was estimated to be 0.02% (level of confidence 95%), except for densities at T ? 413.15 K, where the uncertainty was estimated to be 0.03%. Based on the experimental results, accurate correlation equations for the density of the four liquids have been established. Comparisons with previous results of other experimentalists and with values calculated from current equations of state are presented. The purpose of this work was to provide accurate correlation equations for the densities of the four selected liquids so that these liquids can be used as density reference liquids for the calibration of densimeters and, in particular, for the calibration of vibrating-tube densimeters.     

Volatile components,antioxidant and antimicrobial activity of Citrus acida var. sour lime peel oil

Essential oil of Citrus acida Roxb. var. sour lime was analyzed by GC–MS. Out of 59 components 18 were identified from their fragmentation pattern. Among the identified constituents, o-cymene (16.62%) was found as a major component followed by α-cedrene (10.57%), decadienal (8.043%), bisabolene (5.066%) and β-humelene (4.135%). Citronellyl acetate (2.371%), linalool acetate (2.371%), carvone (1.806%), decanone (1.474%), isopulegol acetate (1.296%), farnesol (1.254%), 4′-methoxyacetophenone (1.207%), and Δ-carene (1.070%) were found in minor quantities whereas α-terpineole (0.607%), dihydroxylinalool acetate (0.650%), cis-nerone (0.574%), caryophyllene oxide (0.433%), and 2,2-dimethyl-3,4-octadienal (0.375%) were found in minute amounts.The antimicrobial activity of the essential oil of C. acida was determined by disc diffusion method, against different bacteria (Bacillus subtilis, Bacillus cereus, Staphylococcus aureus, Escherichia coli, Enterobacter aerogenes, Salmonella typhymurium) and fungi (Aspergillus ficuum, Aspergillus niger, Aspergillus fumigatus, Aspergillus flavis, Fusarium saloni, Fusarium oxysporum, Pencillium digitatum, Candida utilis). Maximum zone of inhibition was resulted against B. subtilis (22 mm) followed by C. utilis (20 mm) and B. cereus (19.8 mm), whereas the minimum zone of inhibition was shown by P. digitatum (10 mm). The inhibition zones, measured after 48 h and 96 h, showed that it is active against all tested bacteria and fungi. The results of antioxidant activity of essential oil of C. acida var. sour lime showed that it was able to reduce the stable radical DPPH to yellow-colored DPPH-H reaching 91.7% of DPPH scavenging effect comparative to ascorbic acid being a strong antioxidant reagent.     

High-precision micro-combustion calorimetry of anthracene

A high-precision micro-combustion calorimeter was developed. Details of the calorimeter are described. The energy equivalent of the calorimeter and the standard deviation of the mean were determined to be (67.8330  ±  0.0024)J · K ^− 1after calibration with thermochemical standard benzoic acid (five experiments). The standard enthalpy of combustion of anthracene was determined to be  − (7065.0  ±  1.1)kJmol ^− 1.     

Thermodynamic properties of some cyclohexyl esters in the condensed state

The heat capacities and the enthalpies of phase transitions of cyclohexyl esters (formate, acetate, butyrate, and valerate) in the condensed state between T =  (5 and 320) K were measured in a vacuum adiabatic calorimeter. It was found that all liquid compounds were supercooled by cooling them fromT =  300 K at a rate of (0.02 to 0.03)K · s ^− 1and formed glasses. Crystalline phases were obtained for all esters and the residual entropies of glasses at T →  0 were evaluated. The glass transition temperatures and the heat capacity jumps accompanying the glass transitions, as well as the thermodynamic parameters of fusion of crystalline phases, were determined for all the esters. The molar thermodynamic functions of the investigated compounds in the crystalline, liquid, supercooled liquid, and glassy states were obtained. The regular changes of some thermodynamic properties in the series of cyclohexyl esters are discussed.