Infrared Absorption Bands Research Articles

Nondestructive and quick differentiation between loupe-clean low-alkali natural and hydrothermal synthetic aquamarines: Constraints of infrared spectroscopy

A considerable increase in the price of natural aquamarine has led to the emergence of hydrothermal synthetic aquamarine as a cheap substitute in the market. In this study, comparative analysis was conducted between natural aquamarine obtained from Altay Prefecture in Xinjiang, China, and hydrothermal synthetic aquamarine in the Chinese market to distinguish them with loupe-clean clarity. Nondestructive tests including microscopic observation, X-ray fluorescence spectroscopy, infrared spectroscopy, ultraviolet–visible–near-infrared spectroscopy, and Raman spectroscopy were conducted. The two samples were low-alkali aquamarine, dominated by type Ⅰ H2O, and the infrared spectra showed similar water-related peaks, exhibiting weak absorption bands related to Cl− at 2736 and 2449 cm−1 and CO2 in the crystal channels at 2358 cm−1. Apart from the strong irregular and distinctive growth patterns, infrared absorption bands at 3313 and 4060 cm−1 due to the N–H bond (derived from ammonium halide used in crystal growth) vibrations were found to be present only in hydrothermal synthetic aquamarine. This study reveals implications for identifying hydrothermal synthetic aquamarine when the internal features of loupe-clean aquamarine are not obvious.

Semi-empirical water dimer model of the water vapour self-continuum within the IR absorption bands

Water vapour continuum absorption is an important component of atmospheric radiative transfer codes. It significantly impacts the radiative balance of the atmosphere, but the physical nature of this absorption remains a subject of discussion. Here the H2O self-continuum absorption is considered within the infrared absorption bands (from 50 to 11 200 cm-1) of water vapour exploiting existing measurements. Comparison of this data with the MT_CKD-3.5 continuum model, which is used in many radiative transfer codes, reveals significant quantitative and qualitative differences. New water vapour self-continuum spectra are derived from earlier FTS measurements using HITRAN-2016 in the 5300 and 7200 cm-1 bands. A previously proposed water dimer model is refined and unified based on a broad set of up-to-date experimental data on the H2O continuum. The new model, which is suitable for incorporation into radiative transfer codes, has a much firmer physical basis than existing models. It reproduces the spectral behaviour and magnitude of the in-band water vapour self-continuum for temperatures from 279 to 431 K depending on the band. Importantly, the fitted total equilibrium dimerization constant used in the updated continuum model exceeds independent estimates by a factor of 1.5–3 across the entire temperature and spectral regions studied. Possible causes for this, which are important for understanding the physical origin of the continuum, are discussed. The contribution of water dimer to the continuum is estimated to vary from 40 to 90 % depending on absorption band and temperature.

Accurate determination of alcohol-based diesels using optimal chemical factors

Sustainable environmental policies and energy crises have led to a trend of blending different alcohols into diesel to partly replace the decreasing fossil fuels. To improve the rapidity and accuracy of determining alcohols exist in methanol and ethanol diesel, optimal chemical factors (OCF) feature selection schemes were presented based on different near infrared (NIR) characteristic absorption bands generated by different chemical structure information utilizing support vector machine (SVM). Through comparative analysis with SVM based on entire spectra, Monte Carlo uninformative variable elimination (MC-UVE) spectra and competitive adaptive reweighted sampling (CARS) spectra, the proposed OCF-SVM not only achieved 100 % accuracy, precision, recall and F1-score in classification, but also exhibited the best performance in prediction analysis with the smallest sum of squares due to error (SSE), root mean squared error (RMSE), mean absolute percentage error (MAPE) and the highest R-square. The overall outcomes indicate that the OCF method based on molecular chemical structures can select more pertinent and interpretable spectral features, thereby making the classification and prediction of alcohol-based diesels more exact and credible. Further, the developed OCF strategy together with SVM could supplement existing methods for analysis of alcohol-based diesels and is expected to be recommended for detecting the chemical composition of other fuels.

Thermal Behavior and Infrared Absorbance Bands of Citric Acid

Citric acid is widely used in the Food and Pharmaceutical Industry. Various issues regarding its thermal behavior and infrared spectrum require clarification. Here, we studied citric acid monohydrate (raw, heated, freeze-dried and recrystallized from D2O) via Differential Scanning Calorimetry, Thermogravimetric Analysis, Infrared Spectroscopy, and antioxidant capacity assay. Also, we used ab initio Density Functional Theory calculations for further supporting the interpretations of the experimental results. Citric acid monohydrate exhibits desolvation inability and upon heating does not dehydrate but esterifies. Nor by freeze drying can it be dehydrated. The heated sample is not anhydrous, it exhibits melting inability, and any fluidization occurs simultaneously with decomposition. In other words, the interpretations regarding the two endothermic peaks in the DSC curve of citric acid that have been attributed to water evaporation and melting are not correct. The increase in the molecular weight due to esterification is most likely responsible for the increased antioxidant/chelation capacity of the heated sample. We concluded that what we call citric acid monohydrate and anhydrous do not exist in a pure form (in the solid state) and actually are mixtures of different compositions of citric acid, water and a citric acid oligomer that is produced through esterification. The esterification reaction seems to be able to proceed easily under mild heating or even at room temperature. The presence of the ester oligomer and water affect the infrared spectrum of citric acid monohydrate and anhydrous and is responsible for the existence of multiple peaks in the C=O stretching region, which partially overlaps with the water H-O-H bending vibration. The insights presented in this work could be useful for optimizing the design, performance and quality of food and drug products in which citric acid is used.

On the shape of the simulated infrared spectral density of strongly hydrogen-bonded systems: Mapping and identification of Hadži ABC structure in phosphonic acid dimers in gas phase

Herein, we explore the origin of three-peaked structure, referred to as the Hadži ABC structure, illustrated within the absorption bands in infrared (IR) spectra of strongly H-bonded systems. The exploration is particularly elucidated for two phosphinic acid dimers (R2POOH) in gas phase, namely bis-(iodomethyl)-phosphinic acid dimer (i.e., R = CH2I) at 465 K and dibutyl-phosphinic acid dimer (i.e., R = C4H9O) at 425 K. A direct theoretical illustration of this spectral signature, related predominantly to very strongly hydrogen bonded complexes, is proposed. The spectral density, υSO−H,is determined by the aid of an approach describing the high-frequency O − H stretching modes by harmonic potentials. The intermolecular potential modes (O…O) are assumed to be of anharmonic nature. The approach is founded on the strong anharmonic coupling approximation, which prescribes a linear dependency of the O − H frequency on the O…O stretching coordinate as rationalized by the fundamental model of Maréchal and Witkowski. Both direct relaxation of the O − H vibrational mode and its homolog, indirect one, affecting the O…O stretching mode are taken into consideration. The model also considers Davydov coupling, which describes the mutual interaction that takes place in the centrosymmetric dimer between the two existent hydrogen bonds as well as Fermi resonances, which occur between the bending modes arising in- and out-of-plane of the dimer and the fundamental O − H stretching mode. Interestingly, we illustrate how the (A, B, and C) triplet detected in the IR absorption band of phosphonic acids can be generated and discuss how the ABC structure can be numerically simulated. The approach provides a direct explanation of the emergence of this unusual feature and mainly reveals that the A peak is due to the Davydov coupling mechanism, whereas the BC diad is found to be generated by Fermi resonances. This was elucidated in a distinctly different approach, rationalized by Sheppard and Claydon, affirming that the provenance of the BC diad is exclusively due to Fermi resonances mechanism. Altogether, our results highlight the congregated effects of both Fermi resonance mechanism and Davydov coupling for the formation of the ABC structure. The model paves the way for a deeper understanding of the ABC structure, characteristic of very toxic strongly hydrogen-bonded dimers. This is of capital importance as it allows one to develop a solid understanding of nerve agents, such as phosphonic acids, from theory alone, so as to avoid difficult and dangerous experiments since they are extremely toxic.

Impact of SnO2 doping on spectroscopic characteristics of the SnO2-Na2O-CoO-B2O3 borate glass matrix

The role of tin oxide (SnO2) on the structure-optical features of borate glasses containing low cobalt oxide impurities was studied. The study was carried out on a glass system [x SnO2 – (80-x) B2O3 – 19.5 Na2O – 0.5 CoO]; x = 0.0, 0.5, 1.0, 2.0 and 3.0 mol%. Glass synthesis was carried out by the melt-quench technique. Structure and optical absorption spectroscopy were carried out to explore the optical transitions of Co cations inside the present glass matrix. The obtained results indicate that, with the further addition of SnO2 content, the molar volume decreased from 31.675 cm3/mol to 29.147 cm3/mol. FTIR studies indicated the basic structural units of trigonal BO3 units and BO4 tetrahedra. Herein also, additional contents of tin oxide increased the nonbridging oxygen contents. The reason behind such increment is attributed to the existence of Sn4+ ions in octahedral coordination acting as network modifiers. Optical absorption spectra indicated the existence of Co ions in both Co2+ and Co3+ oxidation states. Moreover, the existence of significant SnO2 concurred with the significant blue shift in the visible absorption bands and red shift in near infrared absorption bands. The positions absorption bands of Co ions were analyzed in the context of ligand field parameters determinations. The obtained data of the crystal field splitting parameter (10Dqt) showed decreased values from 3451 cm−1 to 3364 cm−1 with more SnO2 addition. While Racah parameter B values were also, attained showing increased values from 967 cm−1 to 985 cm−1 when additional SnO2 is added. Further, the impacted role of SnO2 addition on the structural and optical properties of the present glasses was finally estimated.

Measuring Clear‐Air Vertical Motions From Space

AbstractMeasuring vertical velocity in the atmosphere has long been a challenge due to its small magnitude. Taking advantage of the modulation of free tropospheric relative humidity by vertical motions, we derive analytical relationships that allow us to retrieve vertical motions in clear air from geostationary measurements of brightness temperature in the infrared absorption band of water vapor. The new observations have a resolution of 1 hr and 2 km in time and space, respectively. They capture the variability of mesoscale and large‐scale vertical velocity measured during field campaigns. In the mid‐troposphere, clear‐sky vertical motions are mostly subsiding but highly heterogeneous in space and time. Around organized deep convective systems, strong subsidence (>500 hPa·day−1) is observed within a distance of a few hundred kilometers. In contrast, transient upward motions of up to 100 hPa·day−1 can occur at the mesoscale. Vertical motions in the clear‐sky atmosphere appear to be primarily associated with buoyancy and gravity waves at the mesoscale, and with radiative cooling and equatorial waves at larger spatial scales. This new retrieval reveals a rich range of dynamical features that were previously invisible, thus shedding new light on tropical meteorology.

Extended calculations of nitrogen-induced line broadening coefficients in the [formula omitted] band of ethylene

Computations of room-temperature N2-broadening coefficients are performed for 3546 lines in the ν7 infrared absorption band of ethylene to provide data required for atmospheric studies but missing in spectroscopic databases. The calculations are done in the framework of a semi-classical exact-trajectory approach developed previously (Buldyreva and Nguyen, 2008). The active molecule is rigorously treated as an asymmetric top and the perturber is traditionally considered to be in its ground vibrational state. The data are provided for the P,RP-, P,RQ- and P,RR-subbranches (lines with ΔKa=±1 having observable intensities) for (initial) rotational quantum numbers J up to 22, limited by the available numerical energies for the excited vibrational level. Moreover, potentially detectable lines with ΔKa=±3 are also considered for J≤13, limited by high computational cost. Being validated by comparison with existing experimental results, these data can replace unavailable measurements and will be useful for atmospheric/industrial applications.

Preparation and characterisation of fish skin collagen–chitosan–cinnamon essential oil composite film

SummaryThe composite film with collagen as the main component has been widely used due to its characteristics of non‐toxicity, environmental protection and health. Fish skin, a by‐product of fish, is an excellent source of collagen. Thus, collagen was extracted from an under‐utilised species, Atlantic cod (Gadus morhua) skin, and the composite film of fish skin collagen–chitosan–cinnamon essential oil was prepared by casting. The effects of the ratio of collagen to chitosan (2:8, 4:6, 5:5, 6:4, 8:2) and the concentration of essential oil (0%, 0.1%, 0.2%, 0.3%, and 0.4% (v/v)) on the composite film were studied. The structures of the composite films were analysed using scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FTIR), and X‐ray diffractometry (XRD). The collagen content of Atlantic cod skin is approximately 50.12%, which is significantly higher than that found in basa fish and Nile tilapia (P < 0.05). The content of hydroxyproline was 4.51%. Analyses of tensile strength, elongation at break, water vapor permeability, and water solubility showed Co4Ch6 (Co:Ch = 4:6) had the optimal comprehensive performance, and Co4Ch6–0.2 (Co4Ch6 with 0.2% CEO) had high water resistance in the high‐humidity environment. As the CEO concentration rose, the composite films' infrared absorption bands were enhanced in amplitude, and the XRD peaks were gradually intensified, indicating the internal crystallinity and, thereby, the opacity of the composite films were improved. The bacteriostasis zones Co4Ch6–0.4 against Escherichia coli and Staphylococcus aureus were 2.02 cm and 1.73 cm, respectively. The DPPH radical scavenging rate of Co4Ch6 rose with the increase in CEO concentration, and the DPPH radical scavenging rate of C04Ch6–0.4 was up to 48.56%. Thus, the composite films prepared from fish skin collagen, chitosan, and cinnamon essential oils have outstanding mechanical properties, barrier ability, and antimicrobial activity and are promising for application in food packaging and storage. In addition, the composite films showed a potential antioxidation ability, which might be used as green bioactive films to preserve nutraceutical products.

Infrared Spectroscopy of SARS-CoV-2 Viral Protein: from Receptor Binding Domain to Spike Protein.

Spike (S) glycoprotein is the largest structural protein of SARS-CoV-2 virus and the main one involved in anchoring of the host receptor ACE2 through the receptor binding domain (RBD). S protein secondary structure is of great interest for shedding light on various aspects, from functionality to pathogenesis, finally to spectral fingerprint for the design of optical biosensors. In this paper, the secondary structure of SARS-CoV-2 S protein and its constituting components, namely RBD, S1 and S2 regions, are investigated at serological pH by measuring their amide I infrared absorption bands through Attenuated Total Reflection Infrared (ATR-IR) spectroscopy. Experimental data in combination with MultiFOLD predictions, Define Secondary Structure of Proteins (DSSP) web server and Gravy value calculations, provide a comprehensive understanding of RBD, S1, S2, and S proteins in terms of their secondary structure content, conformational order, and interaction with the solvent.

Investigation of spectral bands and sensor parameters for methane emission detection imaging spectrometer

Recently, interest has increased in developing remote sensing (RS) sensor systems with a high spatial and spectral resolution for quantifying methane (CH4) emissions from point sources. Evaluating sensor parameters can lead to a better understanding of technological advancements in CH4 emission estimation. This study addresses several important topics, including the robust algorithm for point source CH4 emission detection, selecting optimum CH4 absorption bands and their sensitivity analysis, and evaluating sensor parameters such as spatial and spectral resolution and signal-to-noise ratio (SNR). Since the matched filter algorithm efficiently detects point source emissions with palpable accuracy, it has been used here for the Airborne Visible InfraRed Imaging Spectrometer – Next Generation (AVIRIS-NG) sensor data acquired over the USA. The optimum band selection for CH4 detection was determined using a normalized sensitivity method to investigate the effects of aerosol, water vapor (WV), and surface albedo variations. The impact of these parameters on the CH4 absorption bands in the short-wave infrared (SWIR) range has been analyzed using MODerate resolution atmospheric TRANsmission (MODTRAN) radiative transfer (RT) model simulations. Using AVIRIS-NG data as a testbed, various methods have been used to reconstruct original data and generate data sets with different sensor specifications. The effects of the sensor parameters, such as spatial and spectral resolution and SNR, on the detection accuracy were analyzed. The results show the significance of SNR over the spatial and spectral resolution for better emission detection. It indicates the reasonable selection of sensor parameters that can help to create an optimal sensor system that will ultimately support the development of an imaging spectrometer suitable for CH4 emission estimation.

Ab initio calculations on magnetic and optical characteristics of pure ZnO and Mn(II)-doped ZnO monolayers with and without neutral charged vacancies defects

At high Curie temperatures, diluted magnetic semiconductors exhibit induced ferromagnetism and spin-dependent interactions, making them useful in magneto-electronic devices. In spite of the fact that ferromagnetism and optical emission dynamics are characterized by intricate microstructural and compositional features, the origins of these phenomena are not yet completely understood. Here, we used first principles calculations to study how vacancy defects affect the electrical, optical, and magnetic properties of pure ZnO and Mn@ZnO monolayers. In the pristine monolayer, the Zn vacancy produces magnetism with a total magnetic moment of 2 μB, but the oxygen vacancy does not. The magnetic semiconducting characteristic of the Mn substitution at the Zn site is shown by a total magnetization of 5 μB. The magnetic ground state of the ZnO monolayer doped with Mn is significantly influenced by the presence of native defects. More specifically, Zn vacancies are essential for stabilizing the FM states due to the bound magnetic polarons (BMPs) formation, but O vacancies have no influence on the magnetic ground state of the Mn(II)@ZnO monolayer. Based on the optical study, we discovered that Zn and O vacancies in the ZnO ML produce optical absorption peaks at 1.92 eV and 2.90 eV, respectively. The substitution of Mn(II) at Zn site not only increases the band gap of the ZnO monolayer but also produces d-d transition bands at lower energy side of fundamental energy gap peak. The Zn vacancies in the Mn(II)@ZnO ML produce an infrared absorption band around 1.13 eV, which could be due to the formation of the BMP, and enhance the optical absorption efficiency. The ZnO ML’s energy gap and Mn ion’s d-d transition bands exhibit a blueshift in AFM systems and a redshift in the FM systems. In far configuration, the Mn(II)@ZnO monolayer show no shift in the fundamental bandgap and intra-band transition of the Mn(II) spins due to the Mn(II) ion’s paramagnetic nature.

Synthesis, Structural Characterization, and Infrared Analysis of Double Perovskites Pr2NiMnO6, Gd2NiMnO6, and Er2NiMnO6 Functional Nano-Ceramics.

We synthesized Pr2NiMnO6, Gd2NiMnO6, and Er2NiMnO6 double perovskites in a nano-ceramic form by a sol-gel method. By means of room-temperature X-ray powder diffraction measurements, we determined the crystal structure of the three compounds, which is monoclinic, corresponding to a double perovskite structure, described by space group P21/n structure. From the determined structures, the bulk moduli were estimated to be 173-179 GPa. The average size particle of nanoparticles was determined from X-ray diffraction by the Langford method plot and by the Scherrer formula. The morphology and homogeneity of nanoparticles were analyzed by scanning electron microscopy. We found that they form compact agglomerations of approximately 200 nm in diameter. Fourier transform infrared spectroscopy measurements were performed, determining the absorption spectrum. The assignment of the measured infrared absorption bands is discussed.

Polymer amide as a source of the cosmic 6.2 μm emission and absorption

ABSTRACT Cosmic infrared emission and absorption spectra often carry a well-defined and invariant 6.2 $\mu \rm m$ band that has been proposed to emanate from very small dust grains that may carry polyaromatic hydrocarbons. Hemoglycin, a well-defined polymer of glycine that also contains iron, has been found in meteorites of the primordial CV3 class and therefore originated in the solar protoplanetary disc. Here, we suggest that the polymer hemoglycin should also be considered as a source of the cosmic 6.2 $\mu{\rm m}$ emission and absorption. In quantum calculations, the principal amide I infrared absorption band of hemoglycin is centred, before splitting, at 6.0 $\mu\rm m$. Multiple hemoglycin polymers interact to split amide I into the strong (a-) band in the region of 6.2 $\mu\rm m$ and the much weaker (a+) band in the region of 5.8 $\mu\rm m$. Experimentally, these two components are seen in extracts of the Sutter’s Mill meteorite and in stromatolite ooid. The two 11-mer glycine antiparallel chains of hemoglycin have an exact structural analogue in antiparallel poly-l-lysine beta sheet crystals which in the laboratory have an (a-) absorption peak at 6.21 $\mu\rm m$. This wavelength coincidence, the demonstrated propensity of hemoglycin 4.9 nm rods to form accreting lattice structures, and its proven existence in the solar protoplanetary disc suggest that the cosmic 6.2 $\mu\rm m$ emission and absorption could be from small grains that are hemoglycin lattices or shell-like vesicles carrying internal organic molecules of various types. Calculated hemoglycin ultraviolet absorptions associated with iron in the molecule match the observed ultraviolet extinction feature at nominal 2175 Å.

Use of flours from traditional pan and salt‐bed‐roasted Kodo grains in the production of breakfast cereal: Spatial, morphological, techno‐functional, structural, and rheological analyses

AbstractKodo millet, possesses the goodness of iron and low glycemic index, notably, its starch has inadequate application owing to retrogradation and low amylose content. Dry‐roasting seems worthy as an inexpensive pretreatment process to preserve desirable textural characteristics of whole cereal grains with peculiarity of moisture levels below 20% for a very short time. The aim of this work was to analyze indepth studies to explain morphological, techno‐functional, structural, and rheological transformation of Kodo starch components generated during roasting of conditioned whole kernels at 15% and 20% initial moisture content (IM). The micrographs displayed a honeycomb‐like structure in all roasted flours. The X‐ray diffraction intensity decreased and showed partial rupture to A‐type orthorhombic crystals of Kodo starch after roasting, while lamellar growth across the multilayer matrix was also generated (23° and 37.35°). The fusion of the starch granules with endosperm's macromolecules observed plausible techno‐functional, and rheological properties, emphasized as non‐nutritional properties substantially improved sensory attributes of food as an additive. Roasted flour at higher IM thus made it easier to integrate into instant ready‐to‐eat breakfast cereals of improved amylose content (23.69%–29.31%) with lowered water activity (.4671–.5170) of varied skin strength (196.17–1894.41 g), elasticity (4.03–10.21 mm), and cell size (164.03–1059.10 μm) detected from puncture‐test force measurement. The infrared absorbance band illustrated loss of peak at 1047 cm−1 and endosperm's expansion (195.34%–309.30%) lowered kernel hardness (42.3–17.78 N) indicated structural loss upon roasting, may significantly reduce milling cost, and provide a commercially pretreated readied kernel or flour for industrial applications.Practical applicationsKodo millet, of the Poaceae family thrives well in abiotic stress and scanty rainfall exhibit meager application owing to low amylose content. Applying preprocessing traditional roasting techniques upon moistened kernel, get popped cereal. Milling of such cereal retards subcellular loss, indicating increased amylose, water, and oil absorption with avid aroma. This is critical in the preparation of cost‐effective dietary formulations for children and geriatrics, thus making it easier for integration into ready‐to‐eat wholesome breakfast cereals.

Infrared spectroscopy of the α-hydroxyethyl radical isolated in cryogenic solid media.

The α-hydroxyethyl radical (CH3·CHOH, 2A) is a key intermediate in ethanol biochemistry, combustion, atmospheric chemistry, radiation chemistry, and astrochemistry. Experimental data on the vibrational spectrum of this radical are crucially important for reliable detection and understanding of the chemical dynamics of this species. This study represents the first detailed experimental report on the infrared absorption bands of the α-hydroxyethyl radical complemented by abinitio computations. The radical was generated in solid para-H2 and Xe matrices via the reactions of hydrogen atoms with matrix-isolated ethanol molecules and radiolysis of isolated ethanol molecules with x rays. The absorption bands with maxima at 3654.6, 3052.1, 1425.7, 1247.9, 1195.6 (1177.4), and 1048.4cm-1, observed in para-H2 matrices appearing upon the H· atom reaction, were attributed to the OHstr, α-CHstr, CCstr, COstr + CCObend, COstr, and CCstr + CCObend vibrational modes of the CH3·CHOH radical, respectively. The absorption bands with the positions slightly red-shifted from those observed in para-H2 were detected in both the irradiated and post-irradiation annealed Xe matrices containing C2H5OH. The results of the experiments with the isotopically substituted ethanol molecules (CH3CD2OH and CD3CD2OH) and the quantum-chemical computations at the UCCSD(T)/L2a_3 level support the assignment. The photolysis with ultraviolet light (240-300nm) results in the decay of the α-hydroxyethyl radical, yielding acetaldehyde and its isomer, vinyl alcohol. A comparison of the experimental and theoretical results suggests that the radical adopts the thermodynamically more stable anti-conformation in both matrices.

Absorption spectra of the purple nonsulfur bacteria light-harvesting complex: A DFT study of the B800 part

We’ve studied the B800 part of Rhodoblastus acidophilus light-harvesting complex (LH2) by several quantum chemical techniques based on the density functional theory (DFT) and determined the specific method and a minimal reliable model suitable for further studies of the LH2. In addition to bacteriochlorophyll a molecules, the minimal model includes two α and one β chain amino acids. Within the model, we are able to reproduce the contribution of the B800 ring of nine bacteriochlorophyll a molecules to the near infrared Qy absorption band. We also discuss the use of hybrid DFT calculations for precise energy and optical estimations and DFT-based tight binding (DFTB) method for the large-scale calculations. Crucial importance of Hartree-Fock exchange interaction for the correct description of B800 peak position was shown.

Fabrication and characterization of tamarind seed gum based novel hydrogel for the targeted delivery of omeprazole magnesium

The tamarind seed gum based novel hydrogel was fabricated by varying concentration of polymer, monomer and crosslinker for the targeted delivery of omeprazole magnesium at stomach pH of 1.5. The free radical graft copolymerization of 2-acrylamido-2-methyl propane sulfonic acid with tamarind seed gum backbone resulted in hydrogel. The formation of sulfonic acid pendant groups in hydrogel was observed by the existence of an infrared absorption band at 1152 cm−1 for SO group. The conversion to semicrystalline nature on incorporation of drug evidenced by powder X-ray diffraction studies with peaks at 2θ = 20.4° 31.5° and 52.2°. The scanning electron microscopy images showed bigger voids which narrowed down for drug loaded matrix, supported by the presence of a peak for magnesium in the energy dispersive X-ray spectroscopy. The greatest swelling was observed at pH 7 with second-order rate constant 1.5371 (g/g)/min and drug release was found to be 97.85 ± 1 % over 1200 min at pH 1.5. The drug release transport was found combination of diffusion and erosion of polymer chain to be super case II diffusion and Hill equation model was good fit. The hydrogel drug conjugate found to be non-toxic at tested concentrations (17 mg/50 mg) on in-vivo testing in Drosophila model.

Stability of monomeric indigo in the electronic ground state: An experimental matrix isolation infrared and theoretical study

Monomers of indigo were investigated using experimental (matrix-isolation) and theoretical methods. For the first time, the infrared spectrum of indigo molecules isolated in low-temperature Ar matrices was recorded and subjected to a detailed theoretical analysis. An excellent agreement between the experimental spectrum of indigo monomers and the spectrum theoretically predicted for the highly-symmetric (C2h) most stable dioxo form of the compound allowed a very reliable assignment of the observed infrared absorption bands. Matrix-isolated monomers of indigo were exposed to UV–vis radiation of different wavelengths. The conducted experiments demonstrated that molecules of indigo do not undergo any structural changes, even under irradiation with short-wavelength UV (λ > 200 nm) light. Theoretical calculations concerning the stability of photoproducts that could be potentially generated from indigo were conducted. The calculations carried out for the species generated by hydrogen-atom transfer from N1′ to O atom attached to the opposite ring revealed that both the oxo-hydroxy and dihydroxy tautomers of indigo should be unstable in the ground electronic state. The calculations carried out for the C2H tautomer (which may be generated by a hydrogen atom shift from N1′ to C2 of the opposite ring) led to optimization of the structure that is potentially stable, but very much distorted from planarity.

Infrared Spectral Signatures of Nucleobases in Interstellar Ices I: Purines.

The purine nucleobases adenine and guanine are complex organic molecules that are essential for life. Despite their ubiquitous presence on Earth, purines have yet to be detected in observations of astronomical environments. This work therefore proposes to study the infrared spectra of purines linked to terrestrial biochemical processes under conditions analogous to those found in the interstellar medium. The infrared spectra of adenine and guanine, both in neat form and embedded within an ice made of H2O:NH3:CH4:CO:CH3OH (10:1:1:1:1), were analysed with the aim of determining which bands attributable to adenine and/or guanine can be observed in the infrared spectrum of an astrophysical ice analogue rich in other volatile species known to be abundant in dense molecular clouds. The spectrum of adenine and guanine mixed together was also analysed. This study has identified three purine nucleobase infrared absorption bands that do not overlap with bands attributable to the volatiles that are ubiquitous in the dense interstellar medium. Therefore, these three bands, which are located at 1255, 940, and 878 cm-1, are proposed as an infrared spectral signature for adenine, guanine, or a mixture of these molecules in astrophysical ices. All three bands have integrated molar absorptivity values (ψ) greater than 4 km mol-1, meaning that they should be readily observable in astronomical targets. Therefore, if these three bands were to be observed together in the same target, then it is possible to propose the presence of a purine molecule (i.e., adenine or guanine) there.