Isomerization Equilibrium Research Articles

Exploring a De Novo Route to Bradyrhizose: Synthesis and Isomeric Equilibrium of Bradyrhizose Diastereomers≠.

A de novo asymmetric strategy for the synthesis of d-bradyrhizose diastereomers from an achiral ketoenolester precursor is described. Key transformations used in the stereodivergent approach include two Noyori asymmetric reductions, an Achmatowicz rearrangement, diastereoselective alkene oxidations, and the first example of a palladium(0)-catalyzed glycosylation of a vinylogous pyranone. The isomeric composition of the bicyclic reducing sugars obtained was analyzed and their behaviour was compared to the natural product, revealing key stereocentres that impact the overall distribution.

Natural anti-neuroinflammatory inhibitors in vitro and in vivo from Aglaia odorata

Fifty compounds including seven undescribed (1, 13, 18–20, 30, 31) and forty-three known (2–12, 14–17, 21–29, 32–50) ones were isolated from the extract of the twigs and leaves of Aglaia odorata with anti-neuroinflammatory activities. Their structures were determined by a combination of spectral analysis and calculated spectra (ECD and NMR). Among them, compounds 13–25 were found to possess tertiary amide bonds, with compounds 16, 17, and 19–21 existing detectable cis/trans mixtures in 1H NMR spectrum measured in CDCl3. Specifically, the analysis of the cis–trans isomerization equilibrium of tertiary amides in compounds 19–24 was conducted using NMR spectroscopy and quantum chemical calculations. Bioactivity evaluation showed that the cyclopenta[b]benzofuran derivatives (2–6, 8, 10, 12) could inhibit nitric oxide production at the nanomolar concentration (IC50 values ranging from 2 to 100 nM) in lipopolysaccharide-induced BV-2 cells, which were 413–20670 times greater than that of the positive drug (minocycline, IC50 = 41.34 μM). The cyclopenta[bc]benzopyran derivatives (13–16), diterpenoids (30–35), lignan (40), and flavonoids (45, 47, 49, 50) also demonstrated significant inhibitory activities with IC50 values ranging from 1.74 to 38.44 μM. Furthermore, the in vivo anti-neuroinflammatory effect of rocaglaol (12) was evaluated via immunofluorescence, qRT-PCR, and western blot assays in the LPS-treated mice model. The results showed that rocaglaol (12) attenuated the activation of microglia and decreased the mRNA expression of iNOS, TNF-α, IL-1β, and IL-6 in the cortex and hippocampus of mice. The mechanistic study suggested that rocaglaol might inhibit the activation of the NF-κB signaling pathway to relieve the neuroinflammatory response.

Bioproduction of Rare d-Allulose from d-Glucose via Borate-Assisted Isomerization.

d-Allulose is a low-calorie functional rare sugar with excellent processing suitability and unique physiological efficacy. d-Allulose is primarily produced from d-fructose through enzymatic epimerization, facing the constraints of a low conversion yield and high production cost. In this study, a double-enzyme cascade system with tetraborate-assisted isomerization was constructed for the efficient production of d-allulose from inexpensive d-glucose. With the introduction of sodium tetraborate (STB), capable of forming complexes with diol-bearing sugars, the conversion yield of d-allulose from d-glucose substantially escalated from the initial 17.37% to 44.97%. Furthermore, d-allulose was found to exhibit the most pronounced binding affinity for STB with an association constant of 1980.51 M-1, notably surpassing that of d-fructose (183.31 M-1) and d-glucose (35.37 M-1). Additionally, the structural analysis of the sugar-STB complexes demonstrated that d-allulose reacted with STB via the cis 2,3-hydroxyl groups in the α-furanose form. Finally, the mechanism underlying STB-assisted isomerization was proposed, emphasizing the preferential formation of an allulose-STB complex that effectively shifts the isomerization equilibrium to the allulose side, thereby resulting in high yield of d-allulose. Such an STB-facilitated isomerization system would also provide a guidance for the cost-effective synthesis of other rare sugars.

Reactor development for a one‐step hybrid catalytic conversion of D‐glucose to HMF

AbstractThe design of an “H”‐shaped reactor has been studied to satisfy the possibility of using a triphasic medium to transform d‐glucose into 5‐hydroxymethylfurfural (HMF) by a hybrid catalytic process using an immobilized glucose isomerase, allowing the isomerization of D‐glucose to d‐fructose, and a heterogeneous chemical catalyst to catalyze the dehydration of d‐fructose to HMF. The various parameters influencing the transport of d‐fructose within the reactor were studied, namely the difference in pH between the two aqueous phases, the agitation and the quantity of 3,4‐DCPBA/Aliquat336® used to extract and transport continuously the d‐fructose. The pH discrepancy, which must be between 5.0 and 5.5, turns out to be the real driving force behind the extraction of D‐fructose. The D‐Fru/3,4‐DCPBA molar ratio of 1/0.25 allowed the transport of more than 80 % of the D‐fructose initially present and shows that the same molecule of 3,4‐DCPBA is involved at least twice in the transport of D‐fructose and that the 3,4‐DCPBA/Aliquat336® couple performs a turnover within the organic phase. Finally, a HMF production yield of 30.9 % and an isomerization yield of 79.1 % were obtained, illustrating the shift in the isomerization equilibrium made possible by a D‐fructose extraction yield of 96.8 %.

Molecular platform for photochromic balance based on spiro[indoline-pyranoquinolines

Molecular platforms, capable of exhibiting various well-known properties, allow us to observe under certain structural modifications, due to the combination of these properties, the formation of new effects or phenomena, for example, photochromic balance. The 6-bromo-substituted spiro[indoline-pyranoquinolines] were found to exhibit the properties of photochromic balance, exhibiting both positive and negative T-type photochromism. A detailed study was carried out on the thermodynamics and kinetics of processes, the combination of which forms the effect of photochromic scales: the equilibrium of cyclic and merocyanine isomers of spiropyrans, thermal opening of the pyran ring and thermal recyclisation, and photocolouring and photobleaching of spiropyran solutions. Based on experimental data and quantum chemical modelling, directions for structural tuning have been established for the most pronounced manifestation of the effect of photochromic balances based on spiro[indoline-pyranoquinolines], which include enhancing the electron-withdrawing properties of the substituents in the pyridobenzopyran part of spiropyrans and the introduction of strong electron-donating groups into the indoline fragment.

Effects of Temperature, Axial Ligand, and Photoexcitation on the Structure and Spin-State of Nickel(II) Complexes with Water-Soluble 5,10,15,20-Tetrakis(1-methylpyridinium-4-yl)porphyrin.

Water-soluble metalloporphyrins, depending on the metal center, possess special spectral, coordination, and photochemical features. In nickel(II) porphyrins, the Ni(II) center can occur with low-spin or high-spin electronic configuration. In aqueous solution, the cationic nickel(II) complex (Ni(II)TMPyP4+, where H2TMPyP4+ = 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin), exists in both forms in equilibrium. In this study, an equilibrium system involving the low-spin and high-spin forms of Ni(II)TMPyP4+ was investigated via application of irradiation, temperature change, and various potential axial ligands. Soret band excitation of this aqueous system, in the absence of additional axial ligands, resulted in a shift in the equilibrium toward the low-spin species due to the removal of axial solvent ligands. The kinetics and the thermodynamics of the processes were also studied via determination of the rate and equilibrium constants, as well as the ΔS, ΔH, and ΔG values. Temperature increase had a similar effect. The equilibrium of the spin isomers was also shifted by decreasing the solvent polarity (using n-propanol) as well as by the addition of a stronger coordinating axial ligand (such as ammonia). Since triethanolamine is an efficient electron donor in Ni(II)TMPyP4+-based photocatalytic systems, its interaction with this metalloporphyin was also studied. The results promote the development of efficient photocatalytic systems based on this complex.

Coalescence of AuPd nanoalloys in implicit environments.

The optimal design of nanoparticles and nanoalloys arises from the control of their morphology which depends on the synthesis process they undergo. Coalescence is widely accepted as one of the most common synthetic mechanisms, and it occurs both in the liquid and gas phases. Coalescence is when two existing seeds collide and aggregate into a larger object. The resulting aggregate is expected to be far from the equilibrium isomer, i.e. the global minimum of the potential energy surface. While the coalescence of nanoparticles is well studied in a vacuum, sparse computational studies are available for the coalescence in an environment. Using molecular dynamics simulations, we study the coalescence of Au and Pd nanoseeds surrounded by an interacting environment. Comparing the initial stages of the coalescence in a vacuum and the presence of an interacting environment, we show that the formation kinetics strongly depends on the environment and on the size of the nanoalloy. Furthermore, we show that it is possible to tune the resulting nanoalloys' surface chemical composition by changing their surrounding environment.

Influence of the Mesoporosity of Hierarchical ZSM-5 in Toluene Alkylation by Methanol.

Among the different strategies to design highly shape-selective ZSM-5 to obtain para-xylene through toluene alkylation with methanol, the introduction of mesopores to increase reactant and product diffusion has been proposed but barely studied. In this study, we prepared mesoporous ZSM-5 catalysts, named ZSM5-MT(x), from commercial ZSM-5 (Si/Al = 15), using a two-step micelle-templating procedure with octadecyltrimethylammonium bromide as a surfactant in basic medium (x = NaOH/Si). These materials were used as catalysts for the alkylation of toluene by methanol at a low contact time to avoid thermodynamic equilibrium of the xylene isomers. Compared to the parent ZSM-5, the mesoporous ZSM5-MT(x) catalysts did not improve the para-xylene selectivity, revealing that the strategy of increasing diffusion in the catalyst is not a good strategy to follow. However, ZSM5-MT(0.5) showed less deactivation on stream than the parent ZSM-5. Therefore, introducing mesopores to ZSM-5 could be interesting to explore, combined with another strategy of shape selectivity, such as the passivation of the external surface acidity.

Octahedral Zirconium Salan Catalysts for Olefin Polymerization: Substituent and Solvent Effects on Structure and Dynamics.

Group 4 metal-Salan olefin polymerization catalysts typically have relatively low activity, being slowed down by a pre-equilibrium favoring a non-polymerization active resting state identified as a mer-mer isomer (MM); formation of the polymerization active fac-fac species (FF) requires isomerization. We now show that the chemistry is more subtle than previously realized. Salan variations bearing large, flat substituents can achieve very high activity, and we ascribe this to the stabilization of the FF isomer, which becomes lower in energy than MM. Detailed in situ NMR studies of a fast (o-anthracenyl) and a slow (o-tBu) Salan precursors, suitably activated, indicate that preferred isomers in solution are different: the fast catalyst prefers FF while the slow catalyst prefers a highly distorted MM geometry. Crystal structures of the activated o-anthracenyl substituted complex with a moderately (chlorobenzene) and, more importantly, a weakly coordinating solvent (toluene) in the first coordination sphere emphasize that the active FF isomer is preferred, at least for the benzyl species. Site epimerization (SE) barriers for the fast catalyst (ΔS > 0, dissociative) and the slow catalyst (ΔS < 0, associative) in toluene corroborate the solvent role. Diagnostic NMe 13C chemical shift differences allow unambiguous detection of FF or MM geometries for seven activated catalysts in different solvents, highlighting the role of solvent coordination strength and bulkiness of the ortho-substituent on the isomer equilibrium. For the first time, active polymeryl species of Zr-Salan catalysts were speciated. The slow catalyst is effectively trapped in the inactive MM state, as previously suggested. Direct observation of fast catalysts is hampered by their high reactivity, but the product of the first 1-hexene insertion maintains its FF geometry.

Pr@C82 Metallofullerene: Calculated Isomeric Populations

Relative equilibrium populations of the five lowest-energy isolated-pentagon-rule (IPR) isomeric structures of Pr@C82 under high-temperature fullerene synthesis conditions were calculated with the Gibbs energy terms based on molecular characteristics derived using density functional theory (DFT) treatments (B3LYP/6-31+G*∼SDD energetics and B3LYP/6-31G*∼SDD entropy). Two leading isomers were identified, major Pr@C2v;9-C82 and minor Pr@Cs;6-C82. The calculated isomeric relative equilibrium populations agreed with observations.

3-Methoxythiophene-Based Indophenine Reaction Generating an Isomeric Dynamic Equilibrium System.

A 3-methoxythiophene-based indophenine reaction with N-(2-hexyldecyl)isatin in the presence of concentrated sulfuric acid produces an indophenine cis-trans isomeric dynamic equilibrium system, which is dominated by the (Z,E,Z) configuration with a trace of the (Z,Z,Z) configuration.

Photoisomerization of linear merocyanines in salt solutions

AbstractThe trans‐cis isomerization in the excited state of linear merocyanine L‐Mero4 and phenyl substituted linear merocyanine P‐L‐Mero4 in salt solution and in ionic liquid was investigated using frequency upconversion measurements. Strontium chloride and cesium iodide were added to solvent dimethyl sulfoxide (DMSO) and dimethylformamide (DMF) to vary the ionic strength. The time‐resolved fluorescence curves of merocyanines displayed multiple exponential decay behavior. The second temporal component with time constant τ2 ≈ 2.8 (11) ps of L‐Mero4 (P‐L‐Mero4) in DMSO was assigned to the duration to reach the isomerization equilibrium between the trans and the twisted conformers. The τ2 increased at higher salt concentrations and was explained by the attachment of salt ions on the polar excited merocyanines decelerating the isomerization rate. The rotational correlation time constants obtained from the anisotropy decay of fluorescence were 360 and 240 ps in neat DMSO for L‐Mero4 and P‐L‐Mero4, respectively, and they increased to 790 and 450 ps in the most concentrated SrCl2. Using Perrin relation, we estimated the increase in the rotating volume at [SrCl2] = 536 mM, revealing ≈15 SrCl2 molecules surrounding L‐Mero4 and 7 SrCl2 on P‐L‐Mero4. The experimental data indicated that the ion–molecule interaction was stronger with SrCl2 and on L‐Mero4 than on P‐L‐Mero4.

Double‐Bond Isomerization of Rapeseed Oil Methyl Esters in a Continuous Flow Reactor Efficiently Catalyzed by H‐Mordenite

AbstractUnsaturated fatty acids are attractive alternatives to fossil‐based materials as a source of hydrocarbons, but potential applications are limited by the preset chain length of 16–20 carbon atoms. However, if the double bond can be randomly moved along the chain, subsequent bond‐breaking operations such as ethenolysis or oxidative cleavage will give rise to products with chain lengths ranging from 2 to 18 carbon atoms. A process for the double bond isomerization of rapeseed oil methyl esters in a flow‐through reactor using zeolites as the catalyst is herein disclosed. Using H‐mordenite as the catalyst at a flow of 0.125 mL min−1 at 290 °C, near equilibrium isomerization is reached with up to 49% recovery of linear monomeric products after 5 h and up to 44% after 48 h. The main side products are oligomers (3%–15%) and skeletal isomerization products (10%–23%).Practical applications: With a suitable follow‐up modification addressing the double bond (metathesis, ozonolysis, oxidative cleavage), the product mixtures of double‐bond positional isomers can be used in the production of short‐chain base chemicals. In repetitive combination with metathesis catalysis, biofuels with customized chain length distributions can be generated.

Molecular platform based on a spiroindolinonaphthopyran of the diphenyloxazole series for the creation of polychromogenic molecular systems

A spiroindolinonaphthopyran of the diphenyloxazole series along with photochromism possesses a number of chromogenic properties such as solvatochromism, ionochromism, solid state phasochromism and fluorescence. The nature of these effects is associated both with the possibility of the spiropyran existence under its two forms (cyclic and merocyanine) and with the peculiarities of the molecular structure, in particular, with the presence of a diphenyloxazole fragment. Photochromic properties of the spiroindolinonaphthopyran do not exhibit a drastic dependence on the nature of solvents, including those that are capable of specific intermolecular hydrogen bond interactions. In addition, good resistance to photodegradation in the mode of photochromic balance opens up possibilities for designing polychromogenic molecular systems based on them. The positive solvatochromism of the first type, which is noticeably manifested in the case of merocyanine isomers, allowed establishing the weak polarity of their ground state. Solvatochromism of the second type demonstrates a significant spectral contrast (up to 227 nm) due to the existence of an equilibrium of cyclic and merocyanine isomers. The intensity of the effect increases upon passing from toluene to DMSO due to the shift of the equilibrium towards the merocyanine isomers. The presence of a chelate center formed by the merocyanine oxygen atom and the nitrogen atom of the diphenyloxazole fragment allows observing ionochromic transformations of the spiropyran molecule associated with the formation of coloured complex compounds upon its interaction with Co, Cu, Ni, Zn, Cd, Mn ions. It has been established that solutions of Zn, Cd, and Mn complexes exhibit the negative photochromism properties. The change in the solid state of spirpyran is accompanied by a change in the ability to undergo photochromic transformations. Under standard conditions the spiropyran exhibits photochromic properties in the crystalline state, but not in the amorphous one. The combination of chromogenic properties makes it possible to implement fluorescent molecular switches, bipolar absorption switches, photodynamic chemosensors, and solid-state phase transitions control the chromogenic properties based on spiropyrans of diphenyloxazole series. The possibility of structural modification leading to an enhancement of some properties and/or a weakening of other ones makes it possible to consider a spiroindolinonaphthopyran of a diphenyloxazole series as a molecular platform for creating polychromogenic molecular systems with desired properties.

Recycling preparation of high-purity tagatose from galactose using one-pot boronate affinity adsorbent-based adsorption-Assisted isomerization and simultaneous purification

D-tagatose, one of the most valuable low-calorie rare sugars, is in huge market demand in the current food and medicine industries due to its excellent physiological functions. The production and recovery of high-purity tagatose from galactose isomerization presents two major challenges due to the exist thermodynamically limitation and their high structural similarity. Interestingly, the prepared macroporous polymeric boronate-affinity adsorbent (PBA-adsorbent) exhibited superior binding affinity towards tagatose than galactose. In a 1:1 galactose-to-tagatose binary solution, the PBA-adsorbent presented a much higher adsorption capacity towards tagatose (QTag = 53.94 mg/g) than galactose (QGal = 7.06 mg/g) and therefore enabled an excellent purification efficiency. Herein, a novel strategy for combining the PBA-adsorbent-based adsorption-assisted galactose-to-tagatose isomerization and simultaneous purification of tagatose, where the isomerization of galactose and the recovery of tagatose occur concurrently in the same PBA-adsorbent loaded column system, is presented. Through in situ selective capture of the newly formed tagatose, while leaving behind the galactose, the applied strategy enables an improved galactose-to-tagatose isomerization equilibrium with the yield of tagatose reaching up to 52.92%. Simultaneously, the adsorbed tagatose can be recovered efficiently via a two-stage sequential desorption process, which improves the tagatose purity to ∼ 85% with a promising recovery ratio of 87.42%. Remarkably, both the prepared PBA-adsorbent and the applied strategy exhibited excellent operational stability. Through pH-controlled desorption, the loaded PBA-adsorbent and the column system can be easily regenerated, well proving their good durability and recyclability in sustainable industrial applications. Furthermore, a possible mechanism involving the effect of boron-to-sugar ratio, the variation of boron intrinsic chemical states, and pH-responsive selective adsorption and sequential desorption was proposed to help understand how the applied PBA-adsorbent based strategy facilitates the highly efficient galactose-to-tagatose isomerization.

Design and Study of a Photo-Switchable Polymeric System in the Presence of ZnS Nanoparticles under the Influence of UV Light Irradiation.

Recent progress in the field of photosensitive materials has prompted a need to develop efficient methods to synthesize materials with basic intermolecular architectural designs and novel properties. Accordingly, in this work we design and study a photoactive polymer as a photo-switchable polymeric system in the presence and absence of ZnS nanoparticles (average size < 10 nm) at 5 wt.%. The influence of UV light irradiation on its properties were also studied. The photoactive block copolymer was obtained from styrene (S) and methyl methacrylate (MMA) as monomers and 1-(2-hydroxyethyl)-3,3-dimethylindoline-6-nitrobenzopyran (SP) was grafted to the block copolymer backbone as a photochromic agent. Furthermore, the incorporation of ZnS (NPs) as photo-optical switch component into the system enhances the purple colored photo-emission, with the open form of the spiropyran derivative (merocyanine, MC). The ZnS stabilize the isomeric equilibrium in the MC interconversion of the photochromic agent. The photo-switchable properties of the PS-b-PMMA-SP in the presence of ZnS (NPs) were examined using UV-VIS spectroscopy, Photoluminescence (PL) spectroscopy, optical fluorescence and scanning electronic microscopy (SEM-EDX.). The observed changes in the absorbance, fluorescence and morphology of the system were associated to the reversible interconversion of the two states of the photochromic agent which regulates the radiative deactivation of the luminescent ZnS NPs component. After UV irradiation the photoactive polymer becomes purple in color. Therefore, these basic studies can lead to the development of innovative functional and nanostructured materials with photosensitive character as photosensitive molecular switches.

On the conformational equilibria between isobutyl halide (CH3)2CH–CH2X (X=Cl, Br and I) rotational isomers: A combined ultrasonic relaxation spectroscopic and computational study

In this study, ultrasonic relaxation spectroscopy and molecular orbital calculations have been used to investigate the rotational-isomeric equilibria in isobutyl halide (CH3)2CH–CH2X (X = Cl, Br and I) liquids as a function of frequency and temperature under isobaric conditions. The sound absorption in the a/f2 representation appeared to deviate from straight line with frequency in the MHz region revealing a single Debye-type relaxation process, which is attributed to thermal relaxation of a rotational isomeric equilibrium for all isobutyl halide systems. From the temperature dependence of the relaxation parameters, the associated thermodynamic parameters and the respective volume changes were estimated for each liquid and discussed in view of the outcome of density functional theory electronic structure calculations. The activation enthalpy was found to be strongly dependent on the ionic radius of the halide. Furthermore, the lower energy state of all isobutyl halide systems is two-fold degenerate. The experimental results indicate that a shear viscosity relaxation is questionable in the frequency region covered in this work. The observed-to-classical absorption ratio α/αcl and the volume-to-shear viscosity ratio nV/ns have been evaluated and used as a measure to monitor the strength of the intermolecular bonding. The values and the strong temperature dependence of these ratios are typical of a relaxation process associated to rotational isomers equilibrium. The results have been discussed in the context of inter- and intra-molecular interactions.

Thermoswitching of Helical Inversion of Dynamic Polyphenylacetylenes through cis-trans Isomerization of Amide Pendants

The cis-trans isomerization of amides plays a vital role in all kinds of structural changes and biological activities, involving protein folding, protein misfolding, and even protein molecular recognition. However, the helical inversion of synthetic macromolecules arising from the cis-trans isomerization of tertiary amides, as a good mimic of natural protein, has been rarely researched. Herein, we synthesized meta-disubstituted polyphenylacetylenes (PPAs) with different N-substituted tertiary amides as one of the pendants, poly{(−)-3-methoxycarbonyl-5-[N-methyl-N-(S)-(1-phenylethyl)carbamoyl]phenylacetylene}(sP-NMe) and poly{(−)-3-methoxycarbonyl-5-[N-propyl -N-(S)-(1-phenylethyl)carbamoyl]phenylacetylene} (sP-NPr). The cis-trans isomerization of amides was investigated by a combinational analysis of 1H/13C nuclear magnetic resonance (NMR), heteronuclear multiple quantum coherence (HMQC), variable-temperature NMR, Raman spectroscopy, ultraviolet–visible (UV–vis) spectroscopy, electronic circular dichroism (ECD), vibrational circular dichroism (VCD), and computer calculations. The substituted amide of sP-NMe favors the trans isomer at low temperatures, and the polyene main chain takes the right-handed helical conformation. When increasing the temperature, the ratio of the cis isomer in sP-NMe increases, which causes helical inversion. The screw sense of the polymer backbone of sP-NMe can be thermoreversibly switched upon tuning the cis-trans isomerization equilibrium of the tertiary amide pendant. In comparison, sP-NPr has the left-handed conformation with the majority of the cis isomer owing to the bulky propyl group, and cis-trans isomerization cannot induce helical inversion upon thermal treatment. The results reveal that helical inversion caused by the cis-trans isomerization of amide groups is highly dependent on the size of N-alkyl substituents.

Techno-Economic Assessment of Mixed-Furan Production from Diverse Biomass Hydrolysates

We present techno-economic analyses of high-yield production of furans [5-hydroxymethylfurfural (HMF) and furfural] from mixed-sugar hydrolysates via a novel hybrid enzyme-chemo-catalytic process. In this process, glucose and xylose in biomass hydrolysates are first isomerized to corresponding ketoses (i.e., fructose and xylulose) using immobilized glucose–xylose isomerase. This enzymatic step is closely integrated with selective extraction of the keto-sugars into a water–immiscible octanol phase containing aryl boronic acids that have a selective affinity for keto-sugars. As a result, isomerization and extraction occur simultaneously and drive the isomerization equilibrium toward the formation of the ketose isomers—a process termed simultaneous isomerization and reactive extraction (SIRE). Then, the keto-sugars in the octanol phase are back-extracted into an acidic ionic liquid (IL) that is uniquely suited for sugar dehydration reactions—a process step termed back extraction (BE). Thereafter, the ketose-rich sugar mixture undergoes dehydration to furans in the IL, which is part of a biphasic reaction medium with tetrahydrofuran (THF) that facilitates extraction and stabilization of the furans as they are formed. Finally, the furans are recovered from THF. Overall, the SIRE–BE–dehydration process provides a pathway for high-yield conversion of lignocellulosic mixed-sugar hydrolysates to HMF and furfural. We performed the chemical process design for a furan production facility operating at a feed rate of 1000 MT/day of biomass hydrolysate sugars (dry basis) via the SIRE–BE–dehydration pathway. The process design corresponded closely with experiments and included integration of novel and energy-efficient product and chemical recovery methods. We estimated the minimum furan selling price (MFSP) to be $1.42/kg—a promising price point for industrially important chemical products. Sensitivity analyses identified feedstock sugar cost and overall furan yield as the dominant contributors to the selling price, and modest improvements of 10% in both parameters could reduce the MFSP to $1.23/kg, a price which is competitive for fuel and polymer precursor applications.

Hydrophilic meso-substituted cyanine dyes in solution and in complexes with serum albumins: spectral properties and molecular docking study

The absorption and fluorescence spectral properties of three meso-substituted hydrophilic thiacarbocyanine dyes were studied in solutions and in noncovalent complexes with human and bovine serum albumins (HSA and BSA, respectively). The presence of alkyl substituents at the meso-position of the polymethine chain of the dyes determines the occurrence of a cis–trans equilibrium. Dyes form aggregates in aqueous media; the effect of electrolyte (NaCl) on aggregation has been studied. The interaction of the dyes with albumins leads to the decomposition of the aggregates and is accompanied by a shift in the isomeric equilibrium. Complexation with HSA leads to accumulation of dye monomers in the trans-form. However, in the case of BSA the cis-to-trans isomeric shift is incomplete. Using the fluorescence data, the effective binding constants of the trans-isomers with albumins (Ka) and the detection limits of albumin molecules (LD and LQ) were determined. The data obtained are indicative of high selectivity of some dyes to HSA compared to BSA. The results of molecular docking experiments correspond to the data obtained from the spectra. The influence of the dyes on intrinsic fluorescence of HSA and BSA was also studied, and fluorescence quenching, static in nature, was detected.