Perceiving a suitably tuned aqueous solution to unravel water's liquid-liquid critical point (LLCP) has become challenging. In this work, we investigated the structures of light and heavy water in the presence of MgCl2 using excess infrared spectroscopy and density functional theory calculations. The excess spectroscopy enabled us to differentiate the low-density liquid (LDL) water from the other liquid domains of pure water and reveal the new interaction modes between water and the ions. The addition of salt decreases and then increases the population of LDL in aqueous solutions. At the concentrations of 0.4 M in H2O and 0.6 M in D2O, the LDL structures undergo the most significant disruption under ambient conditions in the bulk phase. Furthermore, threshold concentrations of 1 and 1.3 M for light and heavy water, respectively, were found to induce higher LDL populations. The current investigation sheds light on the intriguing liquid-liquid phase transition (LLPT) and the LLCP of water.

The production of citric acid, a vital agricultural commodity utilized across various industries such as food, beverages, pharmaceuticals, agriculture, detergents, and cosmetics, predominantly relies on microbial fermentation, with Aspergillus niger accounting for approximately 90% of global production. In this study, we aimed to optimize the key factors influencing citric acid production, with a focus on strains, fermentation techniques, and carbon sources, particularly sugarcane molasses. A. niger, sourced from the Botany department/Biotechnology laboratories at Govt. College of Science, Lahore, was employed for citric acid production. The process involved inoculum preparation through spore collection from 3 to 5 days of cultured PDA slants. The fermentation medium, comprising cane molasses with a 15% sugar concentration, was meticulously prepared and optimized for various factors, including magnesium sulfate, potassium ferrocyanide, time of addition of potassium ferrocyanide, ammonium oxalate, and calcium chloride. Our optimization results shed light on the significant impact of different factors on citric acid production. For instance, the addition of 0.4 g/L magnesium sulfate led to a maximum yield of 75%, while 2 g/L potassium ferrocyanide, added at 24 h, achieved a yield of 78%. Remarkably, ammonium oxalate, at a concentration of 10 g/L, resulted in a notable 77% yield. Conversely, the addition of calcium chloride exhibited negligible effects on citric acid production, with the control group yielding more at 78%. Our study underscores the potential for optimizing factors to enhance citric acid production by A. niger in submerged fermentation. These findings highlight the pivotal role of magnesium sulfate, potassium ferrocyanide, and ammonium oxalate in augmenting citric acid yields while emphasizing the minimal impact of calcium chloride. Ultimately, these insights contribute to advancing our understanding of microbial citric acid biosynthesis, providing valuable implications for industrial applications and future research endeavors.

Existence and identification of ion pairing in aqueous electrolyte solutions are open questions to unveil the hydration structures of ions in water. In this work, we used a combination of infrared spectroscopy and quantum chemical calculations to investigate the ion pairing and hydrating properties of the aqueous solutions of lithium and sodium iodides by taking water molecules as probes. Spectral information of water molecules staying between the cations and anions in each case, as well as those contacting with the free ions of lithium and sodium, were extracted by using the strategy of equi-molar difference spectra. Peak positions of the solvent-shared ionpair (SIP) water molecules were found to be 3340 cm(-1) and 3580 cm(-1) for LiI and NaI, respectively. With increasing concentration of the salts, the SIPs of NaI appear earlier than the SIPs of LiI, in accordance with the law of matching water affinities. This work opens a window for the identification of ion pairs using FTIR and may shed light on the separation of the precious lithium from sodium and the investigation of the hydration properties of other inorganic salts. (C) 2020 Elsevier B.V. All rights reserved.

The Hofmeister effect of inorganic ions to precipitate proteins has been used to understand the coagulation phenomenon in colloid and protein science. Herein, for the first time, this effect is studied on the hygroscopicity of aerosols using ATR-FTIR spectroscopy. The representative Hofmeister salts (MgSO4, KCl, NH4NO3) and amino acid (glycine) with different amino acid/salt molar ratios (ASRs) are mixed and atomized into micrometer-sized particles. For mixed kosmotrope (MgSO4)/glycine and chaotrope (NH4NO3)/glycine with an ASR of 1:1, both ERHs (efflorescence relative humidities) and DRHs (deliquescence relative humidities) are absent. However, for the mixtures of glycine and neutral salt (KCl), no DRH is observed while 66.2 and 61.4% ERH of glycine is detected for mixtures with ASRs of 1:1 and 1:3, respectively, which is similar to pure glycine. For the mixture of NH4NO3/glycine with an ASR of 1:3, ERH and DRH are found to be 15.4 and 32.2% RH, less than that of pure NH4NO3. Further, interactions between glycine-salt and/or water is also studied in the mixtures during hydration and dehydration. Water-mediated ion-glycine interaction is detected based on the two glycine bands merging into one band. Glycine-SO(4)(2- )interaction is present for glycine/sulfate in all ASRs, while glycine-NO3- interaction is only seen for 1:3 glycine/NH4NO3 mixtures during hydration. This work opens a window to understand the Hofmeister effect on the hygroscopicity of atmospheric aerosols.

Strain engineering of graphene is a widely researched topic of the decade, one can realize the unique applications of graphene due to the strain affect. Doping in graphene is one of the methods to introduce strain and rare earths (RE) doping in graphene is a challenging task as the size of RE-atoms is much bigger compared to carbon. Herein, neodymium (Nd) is doped in graphene foam (GF) successfully, with the help of double-zone chemical vapor deposition (CVD) at hollow sites (interstitial doping). The doping is confirmed from several characterization tools and magnetotransport properties are detected after word's. An extremely large positive magnetoresistance (PMR similar to 1410% at 5 K under 8 T applied magnetic field) is observed in Nd-doped GF compared to as-grown GF (PMR similar to 250% at 5 K under 8 T applied magnetic field). The PMR afterward starts decreasing upon the fabrication of Nd-composite at high temperature similar to 1400 degrees C. Technologically, topological band structure of graphene upon doping influences the path of charge carriers as a result, a change in fermi-surface occurs, due to which unique applications can be realized. (C) 2021 Elsevier Ltd. All rights reserved.

ATR-FTIR spectroscopy was performed on a series of ZnCl2-ethylene glycol (EG) mixtures with a wide-range of compositions (1 : 1.5-1 : 14 in molar ratios), involving the stable ZnCl2-4EG deep-eutectic solvent (DES) composition, to explore the spectral variations, structural heterogeneity, and hydrogen bonding (H-bonding) properties. To enhance the resolution of the spectra, excess absorption and two-dimensional correlation spectroscopies were employed. In the initial IR spectra, a quasi-isosbestic point was identified, signaling that the major disturbance on EG microstructures by adding ZnCl2 is to form a distinct complex. Further analysis uncovered the main transformation process to be from the EG tetramer to the ZnCl2-4EG complex. It was also found that as the EG content increases, negative charge increasingly transfers to ZnCl2, resulting in the strengthening of the Zn ← O coordination bonds and the weakening and finally dissociation of Zn-Cl bonds. Regarding the ZnCl2-4EG DES, several incomparable specificities were observed. It was found that ZnCl2 destructed the H-bonding network of pure EG to the largest extent, resulting in the highest production of the dimer and trimer of EG. Moreover, in comparison with other compositions, the ZnCl2-4EG DES showed abrupt increases in the negative charge of the salt, the length of the Zn-Cl bond, and the strength of the Zn ← O coordination bond. All these imply the strongest intermolecular interactions and the highest solvation of ZnCl2 in EG at the eutectic composition compared to those of other mixtures, resulting in a super-stable liquid mixture. The work provides physical insights into the structural and interactive properties of deep-eutectic solvents.

Deep-eutectic solvents (DESs) are a new class of green solvents. Here, we report the hydrogen bonding and structural properties of the archetypal DES ethaline, a mixture of choline chloride (ChCl) and ethylene glycol (EG) of a 1:2 molar ratio, and its pseudo-binary mixtures with acetonitrile. The investigations were carried out employing Fourier-transform infrared (FTIR) spectroscopy combined with quantum chemical calculations. Excess and two-dimensional (2D)-correlation spectroscopies were used to identify favorable species in the solutions and to explore the heterogeneity. The results show that the mixing process is the transformation from ethaline and CH3CN dimer to the complexes of ethaline-1CH3CN and ethaline-2CH3CN, together with the increased percentages of the EG dimer, EG trimer, and CH3CN monomer with respect to their total amounts in the mixtures. Theoretical calculations show that, for ChCl, the positive charge is located at the methyl groups and methylenes, rendering their ability to form hydrogen bonds. Adding CH3CN to ethaline can hardly break apart the doubly ionic hydrogen bonds between Ch+ and Cl-. The cosolvent molecules mainly surround the core structure of ethaline, forming noncovalent hydrogen bonds with hydroxyl groups of EG/Ch+ but not Cl-. These in-depth studies on the properties of ethaline and CH3CN/CD3CN mixed solvents may shed light on exploring their applications.

As a well-known Criegee intermediate (CI) scavenger, SO2 can react with CIs in the gas phase to form sulphuric acid, which can be further converted to sulfate aerosols, which make an important contribution to haze formation. Despite the potential importance, the interaction of SO2 with the CIs produced by heterogeneous oxidation of unsaturated fatty acids remains largely unclear. In this work, the heterogeneous reactions of oleic acid (OA) thin films with O-3 and O-3/SO2 mixture gases are studied under four different relative humidities (RHs): 5%, 30%, 60% and 80%, using microscopic Fourier transform infrared (micro-FTIR) spectrometer combined with a gas-flow system. A detailed comparison on formation rates of ester and intensity ratios of 1742 cm(-1) band (envelope C=O of ester) to 1712 cm(-1) band (feature C=O of carboxyl) between the two reaction systems shows that the addition of SO2 inhibits the conversion of carboxyl to ester at any RH. As the SO2 concentration increases, the formation rates and final relative amount of ester decrease. Based on these data, it can be concluded that SO2 consumes part condensed-phase CIs produced by ozonolysis of OA, resulting in a significant inhibition in ester formation. The present results provide an important atmospheric implication on the reaction between SO2 and condensed-phase CIs, which may be a missing sulfate production pathway in the atmosphere.

Bisulfate anion has vast applications in industrial and environmental chemistry. Its dissociation to sulfate anion has been studied computationally and by size-selected clusters. In this study, Micro-Raman spectroscopy is applied at different relative humidity (RH)% on small droplets of aqueous solutions of NaHSO4, NH4HSO4, and H2SO4 to explore the dissociation of HSO4- experimentally in bulk and supersaturated state. Our cumulative experimental results support the conclusion obtained from gas-phase cluster study that HSO4- starts dissociating at very low number of water molecules (H2O similar to 1). However, dissociation of HSO4- is found dependent on the cation attached with this weak acid. The magnitude of dissociation is found as NH4HSO4 approximate to H2SO4 > NaHSO4. In addition, studying the hydration process of HSO4- in the presence of three different cations enabled us to observe various species in three systems. Theoretical values obtained from extended aerosol inorganic model supports the experimental results.

Deep-eutectic solvents (DESs) are regarded as alternative green solvents to ionic liquids. In this work we report the structural properties and hydrogen bonding (H-bonding) interactions of an aqueous DES system. The used DES, ethaline (ETH), is composed of choline chloride and ethylene glycol (EG) in 1 : 2 molar ratio. The investigations were carried out by FTIR spectroscopy combined with quantum chemical calculations. Excess spectroscopy and two-dimensional correlation spectroscopy (2D-COS) were used to explore the data in detail. The results showed that, upon mixing, ETH transforms to EG dimers and trimers and D2O clusters transform to various ETH-D2O complexes. Theoretical calculations show that water molecules insert between the anion and cation of ETH, break the strong doubly ionic Cl- horizontal ellipsis H-OCh+ H-bond, share charges of the ions and form H-bond with them, thus modulate the interaction properties of ETH. This study deepens our molecular-level understanding of the system and would shed light on its applications.

The Front Cover illustrates the different patterns of excess spectra (multi-/two-state) in the binary systems containing C6F5I/C6F5Br and the acetate-based ionic liquid. They show different interaction modes and provide information on the existing species in the systems, helping to understand the solubility property of halogenated drug molecules in ionic liquids. More information can be found in the Article by J. Xu et al. on page 1030 in Issue 9, 2018 (DOI: 10.1002/cphc.201701302).

Elucidation of the nature of noncovalent interactions between ionic liquids (ILs) and halogenated molecules is of particular importance for both fundamental research and drug development. Herein, the noncovalent interactions between 1-butyl-3-methyl-imidazolium acetate and three halobenzenes C6 F5 X (X=I, Br, H) were investigated. The iodine derivative shows the strongest interaction with the IL, followed by C6 F5 Br and C6 F5 H. As indicated by the positive/negative peaks and "multi/two-state" phenomena in the excess IR spectra, combined with DFT calculations, various interaction modes were differentiated. Three complexes, namely anion-C6 F5 I, anion-2 C6 F5 I, and ion-pair-C6 F5 I in the IL-C6 F5 I system were identified, whereas only ion-pair-C6 F5 Br/C6 F5 H complexes, together with self-associates, were found in the other two systems. A possible reason for the behavior of the IL-C6 F5 I system could be that the iodine-based halogen-bonding interactions in the system are strong enough to break interactions between the IL cations and anions. This might make C6 F5 I a good co-solvent to regulate the properties of acetate-based ILs.

The density-functional theory (OFT) calculations using B3LYP functional were performed to inspect the mechanism of the reductive elimination of ethane from a cobalt (III) dimethyl complex, (PMe3)(3)Co (CH3)(2)I Three different pathways, i.e., radical mechanism (path A), concerted C-C bond formation (path B) and alpha-hydride elimination (path C) were studied for the reductive elimination reaction. A PMe3 ligand of the hexa-coordinated cobalt complex dissociates to form penta-coordinated complex. The penta-coordinated complex undergoes reductive elimination reaction. The calculated Gibbs free energy for the formation of methyl radical is 27.6 kcal/mol. Path B involving concerted C-C bond formation shows the activation energy barrier of 12.8 kcal/mol for the reductive elimination reaction. The calculated activation energy barrier for alpha-hydride elimination mechanism is 53.1 kcal/mol. Path B shows the lowest activation energy barrier of 12.8 kcal/mol, however, this value is much lower than the experimentally determined activation energy (25.0 kcal/mol). With MN12SX functional, the activation energy value improves to 20.8 kcal/mol which is close to the experimental value. (C) 2018 Elsevier B.V. All rights reserved.

Task-specific ionic liquids (ILs) are those with functional groups introduced in the cations or anions of ILs to bring about specific properties for various tasks. In this work, the hydrogen bonding interactions between a hydroxyl functionalized IL 1-(2-hydroxylethyl)-3-methylimidazolium tetrafluoroborate ([C2OHMIM][BF4]) and acetonitrile were investigated in detail by infrared spectroscopy, excess spectroscopy, two-dimensional correlation spectroscopy, combined with hydrogen nuclear magnetic resonance and density functional theory calculations (DFT). The hydroxyl group rather than C2H is found to be the main interaction site in the cation. And the ν(OH) is more sensitive than v(C−Hs) to the environment, which has been taken as an intrinsic probe to reflect the structural change of IL. Examining the region of ν(OH), by combining excess spectroscopy and DFT calculation, a number of species were identified in the mixtures. Other than the hydrogen bond between a cation and an anion, the hydroxyl group allows the formation of a hydrogen bond between two like-charged cations. The OH⋯O hydrogen bonding interactions in the hydroxyl-mediated cation-cation complexes are cooperative, while OH⋯F and C2H⋯F hydrogen bonding interactions in cation-anion complexes are anti-cooperative. These in-depth studies on the properties of the ionic liquid-acetonitrile mixtures may shed light on exploring their applications as mixed solvents and understanding the nature of doubly ionic hydrogen bonds.

Cooperative behaviors of the hydrogen bonding networks in proteins have been discovered for a long time. The structural origin of this cooperativity, however, is still under debate. Here we report a new investigation combining excess infrared spectroscopy and density functional theory calculation on peptide analogs, represented by N -methylformamide (NMF) and N -methylacetamide (NMA). Interestingly, addition of the strong hydrogen bond acceptor, dimethyl sulfoxide, to the pure analogs caused opposite effects, namely red- and blue-shift of the N−H stretching infrared absorption in NMF and NMA, respectively. The contradiction can be reconciled by the marked lowering of the energy levels of the self-associates between NMA molecules due to a cooperative effect of the hydrogen bonds. On the contrary, NMF molecules cannot form long-chain cooperative hydrogen bonds because they tend to form dimers. Even more interestingly, we found excellent linear relationships between changes on bond orders of N−H/N−C/C = O and the hydrogen bond energy gains upon the formation of hydrogen bonding multimers in NMA, suggesting strongly that the cooperativity originates from resonance-assisted hydrogen bonds. Our findings provide insights on the structures of proteins and may also shed lights on the rational design of novel molecular recognition systems.

Molecular interactions of a representative pyrrolidinium-based ionic liquid 1-butyl-1-methyl-pyrrolidinium bis(triflorosulfonyl)- imide ([BMPyrr][TFSI]) with dimethyl sulfoxide (DMSO) and acetonitrile (AN) have been analyzed in this work. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and density functional theory (DFT) calculations are used in the investigation, while excess infrared spectra and two-dimensional correlation spectroscopy are used to explore the data in detail. It has been found that the molecular solvents can interact with TFSI- (mainly with S=O and weakly with S–N–S group). AN interacts feebly with BMPyrr+ as compared with the strong interaction of DMSO. The strength of the interactions depends on the electron donating ability of the solvent. Upon mixing, hydrogen bonds regarding C−Hs in cation and S–N–S in anion are weakened, while that regarding S=O in anion is strengthened. Among the C−Hs which are connected directly with the N of the cation, C1−H is the main interaction site for both DMSO and AN. This means that C1−H is the most acidic hydrogen in pyrrolidinium cation.

Three strains ofBacillus licheniformis were isolated and screened for α-amylase production by solid-state fermentation. Of these, IS-2 gave relatively higher enzyme production (32±2.3 U/[g·min]) and was selected for improvement after treatment withN-methylN-nitroN-nitroso guanidine (NG) or nitrous acid (NA) to enhance its hydrolytic potential. Among the mutant variants, NA-14 gave higher enzyme production (98±1.6 U/[g·min]), and hence, was selected for kinetic and thermal characterization. M1 as a moistening agent (pH 7.0, optimized) supported 2.65-fold improved amylolytic activity by the derepressed mutant 72 h after inoculation. The values of product yield coefficient (Y p/x=1833.3 U/g) and specific rate constant (q p=25.46 U/[g·h]) with starch were severalfold improved over those from other carbon sources and the other cultures. The purified enzyme from NA-14 was most active at 40°C; however, the activity remained almost constant up to 44°C. The NA-induced random mutagenesis substantially improved the enthalpy (ΔH D=94.5±11 kJ/mol) and entropy of activation (ΔS=−284±22 J/[mol·K]) for α-amylase activity and substrate binding for starch hydrolysis. The results of this study (117.8±5.5 U/[g·min]) revealed a concomitant improvement in the endogenous metabolism of the mutant culture for α-amylase production.

The present study was concerned with the selection of suitable surfactant for the production of alpha amylase by Bacillus subtilis GCBM-25 in 250 ml shake flask containing 50 ml of fermentation medium. Different surfactants (laundry soap, detergent powder, sulphonic acid, acyle benzene sulphonic acid, liquid soap, Tween 80, sodium silicate, bath soap, sodium tripolyphosphate, sodium lauryl ether sulphate or sodium lauryl sulphate) @ 2.0 % (w/v) were tested for enzyme production. Of all the surfactants, laundry soap gave better production of alpha amylase (605 U/ml/min) 44 h after inoculation (4.0 % inoculum size). The production of enzyme was found to be optimum (857 U/ml/min) when Millon soap @ 3.2 % (w/v) was added to the medium. The thermostability of the enzyme was decreased from 70 to 50 o C as the surfactant was added to the fermentation medium.

The present study deals with the effect of calcium, magnesium and zinc ions on the activity of alpha amylase produced by Bacillus licheniformis GCBCM-25. The enzyme activity was increased when calcium chloride (CaCl2) at 8.0 mm level was added into the enzyme broth in comparison to that of control. With the addition of magnesium chloride (MgCl2) or zinc chloride (ZnCl2), enzyme activity became very low.

The present study is concerned with the selection of new medium for the production of alpha amylase by Bacillus licheniformis. Different agricultural by-products such as wheat bran, sunflower meal, cotton seed meal, soybean meal, rice husk or rice bran were tested for the production of alpha amylase. Among different agricultural by-products evaluated, wheat bran was found to be the best basal and standardized medium for optimal production of alpha amylase. The production was increased 2-folds when soluble starch was replaced with pearl millet starch at 1% level and nutrient broth concentrations was reduced from 1% level to 0.5%. The newly selected fermentation medium containing (% w/v) wheat bran 1.25, nutrient broth 0.5, pearl millet starch 1.0, lactose 0.5, NaCl 0.5, CaCl2 0.2 in 100 ml of phosphate buffer. The kinetic values of Y(p/x), Y(p/s), and Q(p) indicated that the production of enzyme was greater in newly selected medium than the conventional more expensive medium.