Protein Model Compounds Research Articles

Study on the multiple roles of CaO on nitrogen evolution mechanism of protein inside sewage sludge pyrolysis

The aim of this study was to clarify the multiple influence mechanisms through which Ca influences the emission of NOx precursors (NH3 and HCN) during sewage sludge pyrolysis and to establish a scientific correlation between the mechanisms and temperatures. In this study, the effects of CaO on pyrolysis kinetics and NOx precursor emission temperature of deashed sludge were estimated using Thermogravimetry-mass spectrometry. Based on this, the NH3 and HCN evolution pathways were investigated at these nitrogen emission temperatures by employing sludge protein model compounds in a self-designed all-quartz pyrolysis system. Results showed that the addition of CaO reduced the activation energy of sludge pyrolysis by approximately 0–40 kJ/mol. CaO promoted the retention of nitrogen in char and the conversion of nitrogen into gas phase while hampering its migration to tar. The Ca-fixed nitrogen in char reacted with NH3/HCN to form CaCxNy, such as CaCN2 and CaN2. Notably, results revealed the overwhelming effects of temperature on nitrogen evolution. Specifically, CaO was found to affect only the dominant reaction at the target temperature. At lower temperatures (255–350 °C), CaO promoted the conversion of protein-N to NH3 and inhibited nitrile-N decomposition to HCN in char. In contrast, at comparatively higher temperatures (490–750 °C), CaO inhibited the production of NH3 by promoting the hydrogenation of heterocyclic-N in char and the dimerization of amino acid molecules in tar, while CaO increased HCN release by promoting the dehydrogenation of amine-N in tar and ring opening of heterocyclic-N to form nitrile-N and subsequently HCN. These results would guide NOx control for obtaining energy from nitrogen-rich solid waste for industrial applications and the targeted regulation of NH3 (carbon-free hydrogen-rich fuels) utilization.

Impact of [formula omitted] on the thermophysical and FTIR properties of protein model compounds in aqueous solutions

Ionic liquids (ILs) have gained popularity in recent years due to their wide range of applications in chemical synthesis. They can be used in advancing technologies such as protein solubilization, increased protein activity, biocatalysis replication, and enzyme stability. Because of this, ILs can shed light on the ability of proteins to maintain stability. The present paper outlines the impact of IL on the thermophysical and FTIR properties of specific protein model compounds in aqueous solutions. Thus, densities ρand viscosities ηof some protein model compounds in aqueous solutions of ionic liquid, 1-butyl-3-methylimidazolium chloride, BMImCl, at various temperatures have been carried out at atmospheric pressure. These studies are aimed at gaining new insights into the ability of biomolecules to interact with IL, which is critical for understanding protein behaviour in solutions.Various parameters such as apparent molar volumes (V∅), partial molar volumes (V2O), viscosity B-coefficients, temperature coefficients (dB/dT), transfer parameters, i.e.,ΔtrV2o and ΔtrB, interaction parameters,YAB and YABB, hydration number i.e.nH and Nh, partial molar expansibilities ∂V2O/∂TP, their second-order derivatives ∂2V2O/∂T2P, and isobaric thermal expansion coefficients (αIL) have been calculated from density and viscosity data. In aqueous BMImCl, partial molar expansibilities and temperature coefficients are used to predict the structure maker/breaker behaviour of amino acids. Volume transfer values indicate the dominance of ionic-hydrophilic interactions. Thermodynamic parameters suggest that the formation of the transition state is less favoured in the presence of BMImCl solutions. Also, the effects of the hydrophilic ionic liquid, 1-butyl-3-methylimidazolium chloride,BMImCl on the ion-hydrophilic, hydrophobic-hydrophilic, and hydrophobic-hydrophobic interactions present in ternary systems, as well as the effects of temperature and alkyl chain length, have been discussed. FTIR spectra were measured to analyze the structural changes that occurred in the system. The current work provides some important fundamental experimental data and theoretical support for further exploring the interactions of various amino acids with ILs.

Transport behaviour and FT-IR study of some protein model compounds + 1-butyl-3-methylimidazolium bromide mixtures at different temperatures

Low volatility, low flammability, thermal stability, and biocompatibility contributed to ILs' popularity as eco-friendly media. Therefore, ILs can provide some insights regarding the ability of proteins towards stability. The objective of these studies was to gain new insights into the ability of biomolecules to interact with one another, which is essential for comprehending the behaviour of proteins in solution. Several other properties, including viscosity B-coefficients, temperature coefficient (dB/dT), activation free energy of viscous flow per mole of solvent (Δμ1o#) and solute (Δμ2o#), thermodynamic activation parameter, ΔG2o1→1′, viscometric pair (ηAB) and triplet (ηABB) interaction coefficients along with activation free energy of enthalpy (ΔH2o#) and entropy (ΔS2o#) were obtained by the use of appropriate models. Solvation number (Sn) and hydration number (Nh) were also calculated along with group conributions. Fourier transform infrared spectroscopy (FTIR) has been recorded to perceive interactions among these ternary systems. The current study contributes to understanding the structure and molecular interactions between ILs, amino acids/proteins, and industrial processes.

How Glutamate Promotes Liquid-liquid Phase Separation and DNA Binding Cooperativity of E. coli SSB Protein

E. coli single-stranded-DNA binding protein (EcSSB) displays nearest-neighbor (NN) and non-nearest-neighbor (NNN)) cooperativity in binding ssDNA during genome maintenance. NNN cooperativity requires the intrinsically-disordered linkers (IDL) of the C-terminal tails. Potassium glutamate (KGlu), the primary E. coli salt, promotes NNN-cooperativity, while KCl inhibits it. We find that KGlu promotes compaction of a single polymeric SSB-coated ssDNA beyond what occurs in KCl, indicating a link of compaction to NNN-cooperativity. EcSSB also undergoes liquid–liquid phase separation (LLPS), inhibited by ssDNA binding. We find that LLPS, like NNN-cooperativity, is promoted by increasing [KGlu] in the physiological range, while increasing [KCl] and/or deletion of the IDL eliminate LLPS, indicating similar interactions in both processes. From quantitative determinations of interactions of KGlu and KCl with protein model compounds, we deduce that the opposing effects of KGlu and KCl on SSB LLPS and cooperativity arise from their opposite interactions with amide groups. KGlu interacts unfavorably with the backbone (especially Gly) and side chain amide groups of the IDL, promoting amide-amide interactions in LLPS and NNN-cooperativity. By contrast, KCl interacts favorably with these amide groups and therefore inhibits LLPS and NNN-cooperativity. These results highlight the importance of salt interactions in regulating the propensity of proteins to undergo LLPS.

REGULARITIES OF CHANGES IN THERMODYNAMIC PARAMETERS INDUCED BY THE COMPLEXES FORMATION OF URACIL WITH SOME AROMATIC AMINO ACIDS IN A BUFFER SOLUTION AT PH 7.4

The increasing interest in the physicochemical studies of nucleic acid bases and their derivatives is due mainly to their biological and pharmaceutical importance. Despite increasing data on the interaction of DNA with proteins, the molecular mechanism of recognition of particles in the resulting DNA-protein complexes is not well understood yet. The investigation of the nature and the forces that stabilize nucleic acid structures and their complexes with other molecules is not only of fundamental significance but may also find practical applications. In this paper, we discussed the interaction of model compounds of nucleic acids and proteins using the example of complexes of uracil with aromatic amino acids: L-histidine, L-tryptophan, and L-phenylalanine in aqueous buffer solutions with physiological value of pH to be 7.4. The available literature data on the thermochemical, volume, and heat capacity properties of these systems were used. It should be noted that a change in the acidity of the medium induces a shift in the equilibrium of ionic forms, tautomers, and this leads to a variation in the reactivity of the reagents. The obtained characteristics of the complex formation process differ markedly from the results obtained for an aqueous solution without the use of buffer. A generalization of data on the change in thermodynamic parameters (equilibrium constants, Gibbs energy, enthalpy, entropy, apparent molar volume, and apparent molar heat capacity) under the formation of uracil complexes with above aromatic amino acids depending on their physicochemical properties is given. The dependence of the thermodynamic parameters of the formation of complexes on the acid-base properties of amino acids as a characteristic of the electron density on the carboxylate group has been established. Changes in the standard apparent molar heat capacity and in the standard apparent molar volume of uracil under the addition of amino acids correlate with the hydrophobicity of the added amino acids.

Revealing the interactions of water with cryoprotectant and protein by near–infrared spectroscopy

Taking formamide (FA) as a model compound of protein, the water structure in the ternary mixtures of dimethyl sulfoxide (DMSO)–water–FA was studied by near–infrared (NIR) spectroscopy. The interaction of DMSO and water, and the effect of FA on the interaction, were analyzed with the help of chemometric methods. Continuous wavelet transform (CWT) was used to enhance the resolution of the spectra. A peak at 6437 cm−1 depicting the interaction of DMSO and water through hydrogen bonding (SO…HO) was observed in the transformed spectra. When FA exists in the mixture, the intensity of the peak decreases with the increase of formamide content, showing that FA may replace the water to form the hydrogen bond of SO and HN. In addition, temperature–dependent NIR spectroscopy was used to analyze the effect of the three components on the spectral variation with temperature. Analyzing the spectral data by alternating trilinear decomposition (ATLD) and multiple linear regression, two varying spectral features were obtained that are related to water and DMSO, but no spectral feature was found that significantly varies with the content of FA. The result implies that DMSO is still the key component to prevent the water from icing, although FA may reduce slightly the anti–freezing effect.

Hydrothermal Reduction of NaHCO3 into Formate with Protein-Based Biomass over Pd/γ-Al2O3 Nanocatalysts

CO2/HCO3– reduction with a renewable reductant has a promising potential for tackling the CO2 problem, but achieving high efficiency is still a challenge. Herein, protein-based biomass as the renewable reductant is found to achieve efficient NaHCO3 reduction under hydrothermal conditions. With the Pd/γ-Al2O3 nanocatalyst, the efficiency of NaHCO3 reduction reached 49.0% with l-alanine (the model compound of protein) as the reductant, which was attributed to the superior hydrogen activation property of Pd and the enhanced adsorption of NaHCO3 on the Pd/γ-Al2O3 surface. Furthermore, the mechanism study revealed that the reductive −NH2 group in protein fulfilled NaHCO3 reduction, which was moderately oxidized to N2 (not NO2– or NO3–) as the ultimate product, indicating additional merits of amending the natural nitrogen cycle and eliminating the burden of disposing toxic nitrite/nitrate. The universality of the proposed strategy was also examined with the direct use of protein and protein-based biomass of microalgae as the reductant. With efficient NaHCO3 reduction being achieved, this strategy of NaHCO3 reduction by protein-based biomass could provide a novel and sustainable approach to CO2 conversion and also a potential method of amending the anthropogenic-imbalanced nitrogen cycle.

Mustards-Derived Terpyridine-Platinum Complexes as Anticancer Agents: DNA Alkylation vs Coordination.

The development of bifunctional platinum complexes with the ability to interact with DNA via different binding modes is of interest in anticancer metallodrug research. Therefore, we report platinum(II) terpyridine complexes to target DNA by coordination and/or through a tethered alkylating moiety. The platinum complexes were evaluated for their in vitro antiproliferative properties against the human cancer cell lines HCT116 (colorectal), SW480 (colon), NCI-H460 (non-small cell lung), and SiHa (cervix) and generally exhibited potent antiproliferative activity although lower than their respective terpyridine ligands. 1H NMR spectroscopy and/or ESI-MS studies on the aqueous stability and reactivity with various small biomolecules, acting as protein and DNA model compounds, were used to establish potential modes of action for these complexes. These investigations indicated rapid binding of complex PtL3 to the biomolecules through coordination to the Pt center, while PtL4 in addition alkylated 9-ethylguanine. PtL3 was investigated for its reactivity to the model protein hen egg white lysozyme (HEWL) by protein crystallography which allowed identification of the Nδ1 atom of His15 as the binding site.

Golden seaweed tides from beach inundations as a valuable sustainable fuel resource: Fast pyrolysis characteristics, product distribution and pathway study on Sargassum horneri based on model compounds

This study investigates the pyrolysis characteristics and product distribution in the individual pyrolysis of Sargassum horneri (S. horneri) golden seaweed tide components (cellulose, protein and polysaccharide model compounds) and how the primary components lead to the observed product selectivity to explore their application as feedstocks for bio-oil production. The thermogravimetric analysis (DTG) curve of S. horneri was fitted by single pyrolysis curves of cellulose, protein and polysaccharide, which verified the feasibility of the selected model compounds. A higher heating rate significantly enhances the devolatilization performance of S. horneri and its main pseudocomponents. The fast pyrolysis of protein involves random cleavage of the main chain to form diketopiperazines (DKPs), and the side group will undergo cross-linking, cyclization, dehydroaromatization and other reactions to form amide/amines/nitriles, esters, hydrocarbons and N-heterocyclic compounds in particular. The fast pyrolysis of cellulose involves dehydration and 1,4-glycosidic bond-cleavage reactions as well as further rearrangement of intramolecular structures to form the intermediate product levoglucosan, secondary decomposition of levoglucosan to form aldehydes and ketones and rearrangement of intramolecular structures to form furan and its derivatives. The fast pyrolysis of polysaccharide involves depolymerization, dehydration, decarboxylation, decarbonylation and scission and condensation reactions to form lower molecular weight products, such as furfural, carbon dioxide, ketoesters and hydrocarbons. The results also indicate that the three main model compounds of S. horneri each exert a different influence on the product distribution under high-temperature pyrolysis.

Understanding catalytic mechanisms of HZSM-5 in hydrothermal liquefaction of algae through model components: Glucose and glutamic acid

Hydrothermal liquefaction (HTL) of algae has attracted great interest as a thermal conversion for biofuels. In an effort to understand the catalytic mechanism by which algae undergoes HTL in the presence of HZSM-5, the different roles of the major components (carbohydrates and proteins) were investigated. Glucose and glutamic acid were selected as model compounds of carbohydrates and proteins, respectively. Glucose, glutamic acid, and their binary mixtures were processed under hydrothermal conditions in the presence of HZSM-5 over a temperature range of 220–330 °C. The products were analyzed using a combination of elemental analysis (EA), thermal gravimetric analysis (TGA), gas chromatography mass spectrometry (GC-MS), and Fourier transform infrared (FT-IR) spectroscopy to characterize the physicochemical properties. The effects of HZSM-5 on the yield and quality of bio-oil were investigated. Results indicated that the addition of HZSM-5 did not significantly affect the bio-oil yield of glutamic acid but increased the bio-oil yields from glucose and their binary mixtures. The hydrogen-to-carbon (H/C) ratio and the higher heating values (HHVs) of the bio-oils were all greatly increased in the presence of HZSM-5. The addition of HZSM-5 reduced the contents of undesirable oxygenated compounds, nitrogenous compounds, and increased the hydrocarbon content. Maillard reactions between glucose and glutamic acid were also strengthened by HZSM-5.

Investigation of the reaction between a soy-based protein model compound and formaldehyde

To guide the preparation of soy protein-based adhesives, the reaction between protein and formaldehyde as a possible cross-linker was studied in this paper under different pHs. To simplify the investigations, dipeptide N-(2)-l-alanyl-l-glutamine (AG) was used as a model compound for protein. Based on the analysis of the results of ESI-MS and 13C-NMR of the reaction products between AG and formaldehyde prepared under different pHs, it was found that the pH has strong effects on these reactions. Under strong acid conditions, such as pH 1–3, the methylolation reaction mainly occurred at the aliphatic amino groups of AG. However, it was very difficult for the resulted methylolated AG to be further condensed. Under weak acid conditions, such as pH 5, both the methylolation reaction between amido groups and formaldehyde and the further condensation reaction were possible. However, the condensation reaction was still rather weak under these conditions. At alkaline conditions, the methylolation reaction occurred between all of the three types of amino groups of AG and formaldehyde with both methylene bonds and methylene–ether bonds present in the system. Methylene bonds were mainly from the reaction between AG methylols and amido groups and aliphatic amino groups of AG. Ether bridges were formed between two methylolated AG mainly from amido groups.

Effects of red mud on emission control of NOx precursors during sludge pyrolysis: A protein model compound study

The nitrogen-containing gases pyrolyzed from sewage sludge can be converted into NOx compounds, which would cause severe environmental pollution. This study developed a new strategy to reduce the emission of NOx precursors such as ammonia (NH3) and hydrogen cyanide (HCN) using red mud. The highest reduction efficiencies (15.10% for NH3 and 24.72% for HCN) were achieved at 900 °C while compared with those pyrolyzed from raw sludge without the addition of red mud. The transformation and distribution of nitrogenous compounds in three-phase pyrolysates were studied at 400–800 °C for pyrolysis process of a model soybean protein compound. The nitrogenous compounds, i.e., amine-N, heterocyclic-N, and nitrile-N, were identified as the three main intermediates related with the production of NOx precursors. Ferric oxide (Fe2O3) and calcium oxide (CaO) presented in red mud were identified as the driving force which facilitated nitrogen stabilization in char (e.g., at 800 °C, 21.63% increase of char-N after addition of Fe2O3, and 41.54% increase of char-N after addition of CaO). These metal oxides possibly reacted with protein-N to form FexN and CaCxNy, inhibited the secondary cracking of amine-N compounds in tar (e.g., at 800 °C, 2.33% increase of amine-N after addition of Fe2O3, and 0.38% increase of amine-N after addition of CaO), and reduced the production of nitrile-N (e.g., at 800 °C, 30.41% reduction of nitrile-N after addition of Fe2O3, and 27.40% reduction of nitrile-N after addition of CaO) and heterocyclic-N compounds (e.g., at 800 °C, 21.60% reduction of heterocyclic-N after addition of Fe2O3, and 13.98% reduction of heterocyclic-N after addition of CaO). Hence, the emission of NH3 and HCN in gas phase can be controlled. Moreover, Fe2O3 showed better capability in controlling the emission of NOx precursors than CaO (higher reduction of NH3-N and higher reduction of HCN-N). These results indicate that red mud is an efficient catalyst to reduce emission of NOx precursors through controlling intermediates at 400–800 °C.

Elucidation of reaction pathways of nitrogenous species by hydrothermal liquefaction process of model compounds

The reaction pathway of nitrogen containing compounds under hydrothermal liquefaction (HTL) conditions was investigated by using amino acids as protein model compounds. The effect of organic acids and alkaline catalysts was also investigated by determining the structure and the partition of nitrogen containing species between the resulting solid, aqueous and bio-oil phases.Representative results showed that operating in a water-acetic acid (95/5% v/v) binary solvent system resulted in a dramatic improvement in carbon recovery in the oil phase due to the transformation of water soluble hydrophilic products into oil soluble derivatives by acylation of the amino moiety.The conclusions of this study provide a useful tool to improve the HTL process applied to nitrogen rich biomass, such as the organic fraction of urban waste, sewage sludge, and aquatic biomass (microalgae).

Non-uniform distribution of adsorptive fouling along hollow fiber membrane: Characterization and quantification

Abstract Non-uniform distribution of local flux along the hollow fiber (HF) membrane length poses a high risk of partially overloaded flux to exacerbate membrane fouling. In-depth analysis of its effect on fouling is critical to the design of membrane geometry (e.g. fiber length, inner and outer diameters). This study focused on HF membrane adsorptive fouling by soluble organic substances under the influence of local flux distribution. The non-uniform distribution of adsorbed foulant was experimentally observed via fluorescence and contact angle measurements. An HF-Thomas model was then developed to describe the dynamic adsorption process (free/adsorbed concentration as a function of time), by incorporating Langmuir and Linear adsorption kinetics into the hydrodynamics of the HF membrane lumen. The model fitting was found to be effective in determining the HF membrane adsorption parameters (equilibrium and rate constants) of typical polysaccharide, protein, and humic acid model compounds. Extended simulation was conducted using the HF-Thomas model to explore the impacts of local flux distribution on foulant mass transfer and adsorptive fouling distribution under different scenarios of membrane geometry. The non-uniformity of flux and adsorption was found to be markedly amplified by a comprehensive dimensionless factor, λl (which derives from fiber length, inner and outer diameters, and intrinsic filtration resistance). Therefore, λl may qualify as a critical parameter for HF membrane design. According to the results of this study, λl

Bioenergy from Food Wastes: Thermal Decomposition of Carbohydrates, Lipids, and Proteins

Abstract. Food wastes differ in composition based on their sources and hence are difficult to use in gasification and pyrolysis technologies. The objectives of this study were to investigate the thermal devolatilization kinetics and pyrolysis products of three representative food components: lipids, carbohydrates, and protein. Devolatilization of carbohydrates and proteins occurred up to 600°C with a total weight loss of 90%. In particular, dextrose, sucrose, histidine, and phenylalanine exhibited a combined two-reaction decomposition scheme, whereas starch and valine exhibited a single-reaction scheme. Sucrose had a higher activation energy than dextrose as more energy was needed to cleave glyosidic linkages. Valine had the lowest activation energy (70.2 kJ mol-1) of all the protein model compounds due to its simple structure. However, the lipids primarily vaporized below 400°C and did not decompose. Pyrolysis products of carbohydrates were largely composed of furan and sugar-based compounds, whereas those of proteins varied depending on the type of protein. Because lipids mainly vaporized, only slight conversion (<1%) into different lipid types and hydrocarbons was observed. Keywords: Carbohydrate, Devolatilization, Food waste, Lipid, Protein, Py-GC/MS, Pyrolysis, Reaction kinetics, TGA.

The Reaction between Furfuryl Alcohol and Model Compound of Protein.

To guide the preparation of protein-based adhesive, especially the soy-based adhesive, the reaction between a simple dipeptide N-(2)-l-alanyl-l-glutamine (AG), being used as a model compound of protein, and its cross-linker furfuryl alcohol were studied in this paper. The products that were prepared with furfuryl alcohol and AG under different pHs were analyzed by ESI-MS, 13C NMR, and FT-IR. It was found that the medium environment had great effects on the competition of the co-condensation reaction between furfuryl alcohol and AG and self-condensation reaction of furfuryl alcohol molecules in the mixing system with furfuryl alcohol and AG. Under alkaline conditions, both co- and self-condensation were not obviously detected. Only when the value of pH was higher than 11, were a few co-condensation reaction products gotten. The reaction occurred mainly between furfuryl alcohol and the primary amido groups of AG. Under acid conditions, both co- and self-condensation were observed. The more acid the preparation conditions were, the easier to be observed the self-condensation of furfuryl alcohol molecules would be than the co-condensation between furfuryl alcohol and AG. When the value of pH was higher than 5, both co- and self-condensation were not outstanding. In this study, under pH 3, the co- and self-condensation found equilibrium. There was a great possibility for the primary amido and aliphatic amino groups of AG molecules to react with furfuryl alcohol molecules. No reaction was detected between the secondary amido groups of AG and furfuryl alcohol.

Study of interactions between metal ions and protein model compounds by energy decomposition analyses and the AMOEBA force field.

The interactions between metal ions and proteins are ubiquitous in biology. The selective binding of metal ions has a variety of regulatory functions. Therefore, there is a need to understand the mechanism of protein-ion binding. The interactions involving metal ions are complicated in nature, where short-range charge-penetration, charge transfer, polarization, and many-body effects all contribute significantly, and a quantitative description of all these interactions is lacking. In addition, it is unclear how well current polarizable force fields can capture these energy terms and whether these polarization models are good enough to describe the many-body effects. In this work, two energy decomposition methods, absolutely localized molecular orbitals and symmetry-adapted perturbation theory, were utilized to study the interactions between Mg2+/Ca2+ and model compounds for amino acids. Comparison of individual interaction components revealed that while there are significant charge-penetration and charge-transfer effects in Ca complexes, these effects can be captured by the van der Waals (vdW) term in the AMOEBA force field. The electrostatic interaction in Mg complexes is well described by AMOEBA since the charge penetration is small, but the distance-dependent polarization energy is problematic. Many-body effects were shown to be important for protein-ion binding. In the absence of many-body effects, highly charged binding pockets will be over-stabilized, and the pockets will always favor Mg and thus lose selectivity. Therefore, many-body effects must be incorporated in the force field in order to predict the structure and energetics of metalloproteins. Also, the many-body effects of charge transfer in Ca complexes were found to be non-negligible. The absorption of charge-transfer energy into the additive vdW term was a main source of error for the AMOEBA many-body interaction energies.

Ultrafast Relaxation Dynamics of Photoexcited Heme Model Compounds: Observation of Multiple Electronic Spin States and Vibrational Cooling.

Hemin is a unique model compound of heme proteins carrying out variable biological functions. Here, the excited state relaxation dynamics of heme model compounds in the ferric form are systematically investigated by changing the axial ligand (Cl/Br), the peripheral substituent (vinyl/ethyl-meso), and the solvent (methanol/DMSO) using femtosecond pump-probe spectroscopy upon excitation at 380 nm. The relaxation time constants of these model compounds are obtained by global analysis. Excited state deactivation pathway of the model compounds comprising the decay of the porphyrin excited state (S*) to ligand to metal charge transfer state (LMCT, τ1), back electron transfer from metal to ligand (MLCT, τ2), and relaxation to the ground state through different electronic spin states of iron (τ3 and τ4) are proposed along with the vibrational cooling processes. This is based on the excited state absorption spectral evolution, similarities between the transient absorption spectra of the ferric form and steady state absorption spectra of the low-spin ferrous form, and the data analysis. The observation of an increase of all the relaxation time constants in DMSO compared to the methanol reflects the stabilization of intermediate states involved in the electronic relaxation. The transient absorption spectra of met-myoglobin are also measured for comparison. Thus, the transient absorption spectra of these model compounds reveal the involvement of multiple iron spin states in the electronic relaxation dynamics, which could be an alternative pathway to the ground state beside the vibrational cooling processes and associated with the inherent features of the heme b type.

Gasification Characteristics of Aminobutyric Acid and Serine as Model Compounds of Proteins under Supercritical Water Conditions

The gasification characteristics of aminobutyric acid and serine were determined under supercritical water conditions using a tubular flow reactor. A 1.0 wt% aqueous solution of these two amino acids was gasified at temperatures ranging from 400 to 650 °C and a pressure of 25 MPa with residence time of 86-222 s. The products were identified and quantified by gas chromatography, and the total organic carbon in the aqueous phase was also determined. The gasification characteristics were compared with those of glycine and alanine. The carbon gasification efficiency increased with higher reaction temperature. The gasification rate followed first order kinetics and was explained well by the Arrhenius equation. The gasification rate of aminobutyric acid was similar to that of glycine and alanine but the gasification rate of serine is faster. The oxygen in the hydroxyl group of serine is highly electronegative, so serine is more reactive than glycine and alanine.

Chemically sulfated natural galactomannans with specific antiviral and anticoagulant activities

Naturally occurring galactomannans were sulfated to give sulfated galactomannans with degrees of substitution of 0.7–1.4 per sugar unit and molecular weights of M¯n=0.6×104–2.4×104. Sulfated galactomannans were found to have specific biological activities in vitro such as anticoagulant, anti-HIV and anti-Dengue virus activities. The biological activities were compared with those of standard dextran and curdlan sulfates, which are polysaccharides with potent antiviral activity and low cytotoxicity. It was found that sulfated galactomannans had moderate to high anticoagulant activity, 13.4–36.6unit/mg, compared to that of dextran and curdlan sulfates, 22.7 and 10.0unit/mg, and high anti-HIV and anti-Dengue virus activities, 0.04–0.8μg/mL and 0.2–1.1μg/mL, compared to those curdlan sulfates, 0.1μg/mL, respectively. The cytotoxicity on MT-4 and LCC-MK2 cells was low. Surface plasmon resonance (SPR) of sulfated galactomannans revealed strong interaction with poly-l-lysine as a model compound of virus proteins, and suggested that the specific biological activities might originate in the electrostatic interaction of negatively charged sulfate groups of sulfated galactomannans and positively charged amino groups of surface proteins of viruses. These results suggest that sulfated galactomannans effectively prevented the infection of cells by viruses and the degree of substitution and molecular weights played important roles in the biological activities.