Amino Acids In Water Research Articles

Comparative behavioral responses of grass carp (Ctenopharyngodon idella), bighead carp (Hypophthalmichthys nobilis), and silver carp (H. molitrix) to free amino acids in water.

Control and elimination of invasive fishes, like carps (Order Cypriniformes), may be possible by using chemical stimuli to congregate them for removal. To this end, we tested behavioral responses of grass (Ctenopharyngodon idella), bighead (Hypophthalmichthys nobilis), and silver carp (H. molitrix) to L-alanine, L-arginine, L-glutamic acid, and L-aspartic acid. In grass carp, the first three amino acids have been shown to be beneficial for growth, and all four produce a strong olfactory response in this species. This study used pairs of conspecific fish in a video-recorded, sound-insulated, clear acrylic, tube-shaped tank; during trials, an amino acid stimulus was delivered at one end of that tank. Changes in space use, velocity, and acceleration across all amino acids differed significantly among species. Changes in space use by grass carp indicated avoidance of only two amino acids, L-alanine and L-aspartic acid. There was no evidence for attraction to amino acids for grass or silver carp. For bighead carp, change in spatial use on exposure to amino acids indicated attraction across the four amino acids. This attraction was enhanced by lowered velocity. Our results suggested that olfactory sensitivity does not directly translate to behavioral responses. Other sensory cues, for example tactile, visual, and/or taste, may mediate the selective foraging of grass carp. Amino acids may serve as a better olfactory attractant for bighead carp compared to grass or silver carp.

Safety and efficacy of a feed additive consisting of l-arginine produced with Escherichia coliCGMCC 7.401 for all animal species (Eppen Europe SAS).

Following a request from the European Commission, EFSA was asked to deliver a scientific opinion on the safety and efficacy of the feed additive consisting of l-arginine produced by fermentation with a genetically modified strain of Escherichia coli (CGMCC 7.401). The additive is intended to be used in feed and water for drinking for all animal species and categories. The genetic modifications introduced do not raise safety concerns. No viable cells or DNA of the production strain were detected in the final product. The EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) concluded that the additive does not pose any safety concern with regard to the production strain. l-Arginine produced with E. coli CGMCC 7.401 is safe for the target species when supplemented in appropriate amounts to the diet according to the nutritional needs of the target species. The FEEDAP Panel has concerns on the use of amino acids in water for drinking for hygienic reasons, and due to the risk of imbalances when administered simultaneously via feed and water. The use of l-arginine produced with E. coli CGMCC 7.401 in animal nutrition is considered safe for the consumers and for the environment. The endotoxin activity of the additive does not represent a hazard for persons handling the additive. In the absence of data, the FEEDAP Panel cannot conclude on the potential of the additive to be irritant to skin and/or eyes, or to be a dermal or respiratory sensitiser. The additive l-arginine produced with E. coli CGMCC 7.401 is regarded as an efficacious source of the essential amino acid l-arginine for non-ruminant species. For supplemental l-arginine to be as efficacious in ruminants as in non-ruminant species, it requires protection against degradation in the rumen.

Safety and efficacy of a feed additive consisting of l-valine produced with Escherichia coliCGMCC 22721 for all animal species (Eppen Europe SAS).

Following a request from the European Commission, EFSA was asked to deliver a scientific opinion on the safety and efficacy of l-valine produced by fermentation with a genetically modified strain of Escherichia coli (CGMCC 22721) as a nutritional additive for all animal species. The production strain and its DNA were not detected in the final additive. Therefore, the final product does not give raise to any safety concern regarding the genetic modification of the production strain. The EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) concludes that l-valine produced using E. coli CGMCC 22721 is safe for the target species when supplemented in appropriate amounts to the diet according to the nutritional needs of the target species. The FEEDAP Panel has concerns on the use of amino acids in water for drinking for hygienic reasons, and due to the risk of imbalances when administered simultaneously via feed. The use of l-valine produced using E. coli CGMCC 22721 in animal nutrition is considered safe for the consumers and for the environment. The FEEDAP Panel cannot conclude on the potential of l-valine produced using E. coli CGMCC 22721 to irritant to the skin or eyes, a dermal or respiratory sensitiser due to the lack of data. The endotoxin activity of the additive does not represent a hazard for users handling the additive when exposed by inhalation. The additive l-valine produced by fermentation using E. coli CGMCC 22721 is regarded as an efficacious source of the essential amino acid l-valine for non-ruminant nutrition. For the supplemental l-valine to be as efficacious in ruminants as in non-ruminant species, it requires protection against degradation in the rumen.

From Simple Probe to Smart Composites: Water-Soluble Pincer Complex With Multi-Stimuli-Responsive Luminescent Behaviors.

Water-soluble smart materials with multi-stimuli-responsiveness and ultra-long room-temperature phosphorescence (RTP) have garnered broad attention. Herein, a water-soluble terpyridine zinc complex (MeO-Tpy-Zn-OAc), featuring a simple donor-π-acceptor (D-π-A) structure is presented, which responds to a variety of stimuli, including changes in solvents, pH, temperature, and the addition of amino acids. Notably, MeO-Tpy-Zn-OAc functions as a fluorescence probe, capable of visually and selectively discriminating aspartate or histidine among other common amino acids in water. Additionally, when incorporated into polyvinyl alcohol (PVA) to form the composite MeO-Tpy-Zn-OAc@PVA, the material exhibits reversible writing, photochromism, and a prolonged RTP with a 14 s afterglow. These unique properties enable the composite to be utilized in potential applications such as secure data encryption and inkless printing.

Homochiral Tetraphenylethene-Based Metal-Organic Frameworks with Circularly Polarized Luminescence for Enantioselective Recognition.

A pair of water-stable and highly porous homochiral fluorescent silver-organic framework enantiomers, namely, R-Ag-BPA-TPyPE (R-1) and S-Ag-BPA-TPyPE (S-1), had been prepared as enantioselective fluorescence sensors. Combining homochiral 1,1'-binaphthyl-2,2'-diyl hydrogen phosphate (BPA) with an AIE-based ligand tetrakis[4-(pyridin-4-yl)phenyl]ethene (TPyPE) in complexes R-1 and S-1 made them possess favorable circularly polarized luminescence (CPL) properties, and their CPL spectra were almost mirror images of each other. The luminescence dissymmetry factors (glum) are ±2.2 × 10-3 for R-1 and S-1, and the absolute fluorescence quantum yields (ΦFs) are 32.0% for R-1 and S-1, respectively. Complex R-1 could enantioselectively recognize two enantiomers of amino acids in water or DMF with high Stern-Volmer constants of 236-573 M-1 and enantioselectivity ratios of 1.40-1.78.

Molecular two-point recognition of fructosyl valine and fructosyl glycyl histidine in water by fluorescent Zn(II)-terpyridine complexes bearing boronic acids.

Selective recognition of fructosyl amino acids in water by arylboronic acid-based receptors is a central field of modern supramolecular chemistry that impacts biological and medicinal chemistry. Fructosyl valine (FV) and fructosyl glycyl histidine (FGH) occur as N-terminal moieties of human glycated hemoglobin; therefore, the molecular design of biomimetic receptors is an attractive, but very challenging goal. Herein, we report three novel cationic Zn-terpyridine complexes bearing a fluorescent N-quinolinium nucleus covalently linked to three different isomers of strongly acidified phenylboronic acids (ortho-, 2Zn; meta-, 3Zn and para-, 4Zn) for the optical recognition of FV, FGH and comparative analytes (D-fructose, Gly, Val and His) in pure water at physiological pH. The complexes were designed to act as fluorescent receptors using a cooperative action of boric acid and a metal chelate. Complex 3Zn was found to display the most acidic -B(OH)2 group (pKa = 6.98) and exceptionally tight affinity for FV (K = 1.43 × 105 M-1) with a strong quenching analytical response in the micromolar concentration range. The addition of fructose and the other amino acids only induced moderate optical changes. On the basis of several spectroscopic tools (1H, 11B NMR, UV-Vis, and fluorescence titrations), ESI mass spectrometry, X-ray crystal structure, and DFT calculations, the interaction mode between 3Zn and FV is proposed in a 1 : 1 model through a cooperative two-point recognition involving a sp3 boronate-diol esterification with simultaneous coordination bonding of the carboxylate group of Val to the Zn atom. Fluorescence quenching is attributed to a static complexation photoinduced electron transfer mechanism as evidenced by lifetime experiments. The addition of FGH to 3Zn notably enhanced its emission intensity with micromolar affinity, but with a lower apparent binding constant than that observed for FV. FGH interacts with 3Zn through boronate-diol complexation and coordination of the imidazole ring of His. DFT-optimized structures of complexes 3Zn-FV and 3Zn-FGH show a picture of binding which shows that the Zn-complex has a suitable (B⋯Zn) distance to the two-point recognition with these analytes. Molecular recognition of fructosyl amino acids by transition-metal-based receptors has not been explored until now.

Exploration of interactions between L-aspartic acid and saccharides in aqueous medium at T = (293.15–313.15) K: Physicochemical and spectroscopic approach

In this study, we report the density, viscosity, taste behavior and UV– Vis spectrophotometry results of L-Aspartic acid (Asp) in aqueous solutions of L-arabinose and D-xylose over an integral composition regime (2.0 wt%, 2.5 wt%, and 3.0 wt%) at atmospheric pressure (P = 101 kPa) and at temperature ranges of (293.15, 298.15, 303.15, 308.15, and 313.15) K. The various densimetric and rheological parameters such as apparent molar volume (Vϕ), apparent molar volume at infinite dilution (Vϕ0), apparent molar isobaric expansion at infinite dilution (Eϕ0), Hepler’s constant (∂2VΦ0/∂T2)P, relative viscosity (ηr), viscosity coefficients (BJandAF), Gibbs free energy of activation of viscous flow of solvent and solute (Δμ1#,0andΔμ2#,0respectively), and corresponding change in enthalpy ΔH2#,0, entropy ΔS2#,0, apparent molar volume of transfer at infinite dilution (Vɸ,tr0) viscosity B-coefficients of transfer (BJ,tr), interaction coefficients (using the McMillan-Mayer theory), dB/dT and solvation number (Sn) have been calculated using the experimentally collected physical characteristic data (density and viscosity). Variation of these parameters with concentration and temperature were analyzed in the light of ion-ion, ion–dipole and ion-hydrophilic interactions between solute (L-Aspartic acid)-cosolute (L-arabinose and D-xylose) in aqueous medium. An effort has also been made to compare the taste behaviours of the amino acid in water and in an aqueous solution of saccharides, as the taste behaviour is separated into four basic taste qualities in distinct ranges. To access different common intermolecular interactions in the systems under consideration, the cosphere overlap model has also been used. A detailed evaluation of the results from the thermodynamic and physicochemical parameters shows that Asp acts as a structure builder when L-arabinose/D-xylose is present. The preservation of effective ionic interactions in the studied systems was further confirmed by UV spectral analysis.

VLE determination and microscopic properties of amino acid aqueous solutions

The vapor–liquid equilibrium (VLE) data of amino acids holds immense importance in chemical engineering. The VLE data of L-Alanine + H2O, DL-Valine + H2O and DL-Methionine + H2O were measured experimentally. The feasibility of VLE data is studied by using NRTL-Xu model, and the parameters of these systems were given. Furthermore, the Fourier Transform Infrared (FTIR) spectroscopy technique was used to study the microscopic properties of the amino acid solutions. Finally, the total mean interaction energy of water in the systems was studied by COSMOthermX. The results show that the vapor pressure increases with increasing temperature in the system, the vapor pressure of the higher solubility system is lower than the low solubility system and the pure solvent. From the FTIR results, it can be seen that the greater the solubility of amino acids in water, the stronger the hydrogen bond interaction with water. Meanwhile, the results of COSMOthermX show that the total mean interaction energy in the systems is least affected by the concentration. The structure–activity relationship between macroscopic properties (VLE) and microscopic interactions (hydrogen bonds) was established.

Aryl Crown Ethers Based on d‐Glucose Scaffold – Highly Selective Receptors of Amino Acid Ester Hydrochlorides

AbstractAmino acids are important biomolecules with a broad scope of applications in chemical and biological sciences. Their functions and properties depend on their absolute configuration. Therefore, methods for chiral recognition and separation of amino acids are highly sought after. For the purposes of diagnostic and medicinal applications chiral recognition of amino acids in water is particularly relevant. However synthetic receptors for enantioselective binding of amino acids in aqueous media are rare. Recently we reported a d‐glucose‐based crown ether for chiral recognition of amino acid esters in water. We achieved enantioselectivities towards amino acids with hydrophobic sidechains which were among the highest ever reported for a small molecule receptor. The binding affinities were however moderate. Herein we disclose analogs of that receptor, containing aryl functionalities in the crown ether fragment. The new receptors show considerably improved binding affinities for amino acid ester hydrochlorides in water, while retaining high enantio‐ or chemoselectivities.

Phase separation in amino acid mixtures is governed by composition

Macromolecular phase separation has recently come to immense prominence as it is central to the formation of membraneless organelles, leading to a new paradigm of cellular organization. This type of phase transition, often termed liquid-liquid phase separation (LLPS), is mediated by molecular interactions between biomolecules, including nucleic acids and both ordered and disordered proteins. In the latter case, the separation between protein-dense and -dilute phases is often interpreted using models adapted from polymer theory. Specifically, the “stickers and spacers” model proposes that the formation of condensate-spanning networks in protein solutions originates from the interplay between two classes of residues and that the main determinants for phase separation are multivalency and sequence patterning. The duality of roles of stickers (aromatics like Phe and Tyr) and spacers (Gly and polar residues) may apply more broadly in protein-like mixtures, and the presence of these two types of components alone may suffice for LLPS to take place. In order to explore this hypothesis, we use atomistic molecular dynamics simulations of capped amino acid residues as a minimal model system. We study the behavior of pure amino acids in water for three types of residues corresponding to the spacer and sticker categories and of their multicomponent mixtures. In agreement with previous observations, we find that the spacer-type amino acids fail to phase separate on their own, while the sticker is prone to aggregation. However, ternary amino acid mixtures involving both types of amino acids phase separate into two phases that retain intermediate degrees of compaction and greater fluidity than sticker-only condensates. Our results suggest that LLPS is an emergent property of amino acid mixtures determined by composition.

Salt effects on the solubility of aromatic and dicarboxylic amino acids in water

The salt effect on the solubility of the amino acids l-aspartic acid, l-glutamic acid, l-tryptophan, and l-tyrosine, seldomly found in the literature, was studied at 298.2 K, in aqueous solutions of KCl and (NH4)2SO4, for salt concentrations up to 2.0 mol·kg−1. In this concentration range, both salts are salting-in agents for glutamic acid and aspartic acid, with a stronger effect induced by (NH4)2SO4. Regarding the two aromatic amino acids, a slight increase in the solubility was obtained at low salt concentrations, followed by a stronger salting-out effect, more pronounced by (NH4)2SO4 than by KCl. The relative solubility data obtained in this work were compared to literature data for other amino acids in the same electrolyte solutions to establish a relative solubility ranking connected to their structure.Finally, the solubility data were modeled using the electrolyte Perturbed-Chain Statistical Association Theory (ePC-SAFT). The modeling requires parameters for the amino acids and ions as well as melting properties of the amino acids. All these parameters and properties were obtained from previous works. To quantitatively describe the solubility of amino acids upon salt addition, binary interaction parameters (kij) between any amino acid and anions were determined, while between any amino acid and the cations were fixed to kij = 0.08. The kij parameters between amino acid and the inorganic anions show very similar values for amino acids of the same chemical class (e.g. kij between anion and amino acid with apolar side chains), which may be used to systematically reduce the number of adjustable parameters in future work.

Safety and efficacy of a feed additive consisting of l-methionine produced by the combined activities of Corynebacterium glutamicum KCCM 80245 and Escherichia coli KCCM 80246 for all animal species (CJ Europe GmbH).

Following a request from the European Commission, the FEEDAP Panel was asked to deliver a scientific opinion on the safety and efficacy of l‐methionine ≥ 98.5% or ≥ 90% produced by the combined activities of Corynebacterium glutamicum KCCM 80245 and Escherichia coli KCCM 80246) as nutritional additive for all animal species. The two production strains are genetically modified. l‐Methionine is intended to be used in feed or water for drinking for all animal species. Neither viable cells nor recombinant DNA of the production strains were detected in the final products. The additive does not pose any safety concern associated with the genetic modification of the production strains. The use of both products of l‐methionine produced by C. glutamicum KCCM 80245 and E. coli KCCM 80246 in supplementing feed to compensate for l‐methionine deficiency in feedingstuffs is safe for the target species. The FEEDAP Panel has concerns about the use of amino acids in water for drinking for hygienic reasons, and due to the risk of imbalances when administered simultaneously via feed. The use of both products of l‐methionine produced by C. glutamicum KCCM 80245 and E. coli KCCM 80246 in animal nutrition is considered safe for the consumers and for the environment. The additive, in either product, is not an irritant to skin/eyes and not a dermal sensitiser and shows no toxicity by inhalation. Considering the respiratory exposure to endotoxins, l‐methionine ≥ 90% is a risk for the user. Both products of the additive produced by C. glutamicum KCCM 80245 and E. coli KCCM 80246 are considered as an efficacious source of the essential amino acid l‐methionine for non‐ruminant animal species. For the supplemental l‐methionine to be as efficacious in ruminants as in non‐ruminant species, it would require protection against degradation in the rumen.

Safety and efficacy of a feed additive consisting of l-valine produced by Escherichia coli CCTCC M2020321 for all animal species (Kempex Holland BV).

Following a request from the European Commission, EFSA was asked to deliver a scientific opinion on the safety and efficacy of l‐valine as a nutritional additive for all animal species. The production strain and its DNA were not detected in the final additive. Therefore, the final product does not give raise to any safety concern with regard to the genetic modification of the production strain. The EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) concludes that l‐valine produced using Escherichia coli CCTCC M2020321 is safe when supplemented in appropriate amounts to the diet according to the nutritional needs of the target species. The FEEDAP Panel has concerns on the use of amino acids in water for drinking for hygienic reasons, and due to the risk of imbalances when administered simultaneously via feed. The use of l‐valine produced using E. coli CCTCC M2020321 in animal nutrition is considered safe for the consumers and for the environment. The FEEDAP Panel cannot conclude on the potential of l‐valine produced using E. coli CCTCC M2020321 to be toxic by inhalation, irritant to the skin or eyes, or a dermal sensitiser due to the lack of data. The endotoxin activity of the additive does not represent a hazard for users handling the additive when exposed by inhalation. The additive l‐valine produced by fermentation using E. coli CCTCC M2020321 is regarded as an efficacious source of the essential amino acid l‐valine for non‐ruminant nutrition. For the supplemental l‐valine to be as efficacious in ruminants as in non‐ruminant species, it requires protection against degradation in the rumen.

Learning the Hydrophobic, Hydrophilic, and Aromatic Character of Amino Acids from Thermal Relaxation and Interfacial Thermal Conductance.

In this study, the thermal relaxation of the 20 naturally occurring amino acids in water and in the protein lysozyme is investigated using transient nonequilibrium molecular dynamics simulations. By modeling the thermal relaxation process, the relaxation times of the amino acids in water occurs over a time scale covering 2-5 ps. For the hydrophobic amino acids, the relaxation time is controlled by the size of the hydrocarbon side chain, while for hydrophilic amino acids, the number of hydrogen bonds does not significantly affect the time scales of the heat dissipation. Our results show that the interfacial thermal conductance at the amino acid-water interface is in the range of 40-80 MW m-2 K-1. Hydrophobic and aromatic amino acids tend to have a lower interfacial thermal conductance. Notably, we show that amino acids can be correlated with their thermal relaxation times and molar masses, into simply connected phases with the same hydrophilicity, hydrophobicity, and aromaticity. The thermal relaxation slows down by a factor of up to five in the protein relative to that in water. In the case of the hydrophobic amino acids in the protein lysozyme, the slow down in the thermal relaxation relative to that in water appears to be controlled primarily by the size of the side chain.

Entropy Effects in Intermolecular Associations of Crown-Ethers and Cyclodextrins with Amino Acids in Aqueous and in Non-Aqueous Media.

The analysis of the ratios of entropy and enthalpy characteristics and their contributions to the change in the Gibbs energy of intermolecular interactions of crown ethers and cyclodextrins with amino acids is carried out. Two different types of macrocycles were chosen for examination: crown ethers with a hydrophilic interior and cyclodextrins with a hydrophobic inner cavity and a hydrophilic exterior. The thermodynamics of complex formation of crown ethers and cyclodextrins with amino acids in water and aqueous-organic solvents of variable composition was examined. The contributions of the entropy solvation of complexes of 18-crown-6 with glycine, alanine, phenylalanine to the change in the entropy of complexation in water-ethanol and water-dimethyl sulfoxide solvents was calculated and analyzed. It was found that the ratios of the entropy and enthalpy solvation of the reagents for these systems have similar trends when moving from water to aqueous-organic mixtures. The relationship between the thermodynamic characteristics and structural features of the complexation processes between cyclodextrins and amino acids has been established. The thermodynamic enthalpy–entropy compensation effect was revealed, and its features for complexation of cyclodextrins and 18-crown-6 were considered. It was concluded that, based on the thermodynamic parameters of molecular complexation, one could judge the mode of the formation of complexes, the main driving forces of the interactions, and the degree of desolvation.

Removal performance and mechanism of typical amino acids in water by the peroxymonosulfate/Fe3O4 nanoparticles

Abstract Dissolved organic nitrogen (DON) as precursors of nitrogenous disinfection byproducts (N-DBPs) has become a serious issue for drinking water treatment. Here, Fe3O4/peroxymonosulfate (PMS) system was used to examine the amino acid removal and formation of N-DBPs in the system and the corresponding mechanisms. Results showed a remarked variation in removal efficiency of three typical amino acids, i.e., glutamate (78%), histidine (53%) and phenylalanine (27%) in Fe3O4/PMS system at optimum conditions (0.1 g/L Fe3O4, 1.5 mM PMS, 1 h). Notably, Fe3O4/PMS treatment led to dichloroacetonitrile (DCAN) formation caused by the chlorination of glutamate, phenylalanine and histidine being reduced by 53.3%, 9.7% and 41.9%, respectively. The degradation and subsequent N-DBPs formation in the Fe3O4/PMS system mainly depended on the types and properties of the amino acids. The formation of dichloroacetamide (DCAcAm) exhibited different trends, which may be due to the different R group structure of the three amino acids and the special aromaticity of the imidazole ring in the histidine side chain that facilitates its quick electrophilic substitution and ring-opening reaction. This study highlights that the Fe3O4/PMS system is a promising strategy to remove DON and efficiently eliminate N-DBPs formation in the drinking water treatment process depending on the amino acid type.

Studies on molecular interactions of l-histidine/l-serine in aqueous diphenhydramine hydrochloride solutions at various temperatures: Volumetric, ultrasonic and viscometric approach

Thermophysical properties for varying concentrations of essential (L-histidine) and non-essential (L-serine) amino acids in water and (0.05–0.15) mol kg−1 mixed aqueous diphenhydramine hydrochloride solvent system has been deliberated at different temperatures ranging (293.15−318.15) K and ambient pressure (101.3 kPa). The experimentally obtained data has been utilized to compute different volumetric, compressibility and rheological parameters such as apparent molar volume (Vϕ), partial molar volume (V0ф), partial molar expansibility (E0ϕ), apparent molar isentropic compression (Kϕ,s), partial molar isentropic compression (K0ϕ,s), hydration number (nH), transfer parameters, viscosity coefficients etc. The structure breaking ability of the solute molecules has been comprehended using Hepler′s constant (temperature derivative of partial molar expansibility at constant pressure) and dB/dT (temperature derivative of viscosity B-coefficient) values. Further, by using the co-sphere overlap model various sorts of solute-drug interactions prevailing in the systems have been discussed.

On the Accuracy of QM/MM Models: A Systematic Study of Intramolecular Proton Transfer Reactions of Amino Acids in Water.

This work presents a systematic assessment of QM/QM' and QM/MM models with respect to direct QM calculations for the tautomerization (neutral to zwitterion) reactions of amino acids (glycine, alanine, valine, aspartate, and neutral and protonated histidine) solvated in a 160 water cluster. The effect of varying QM region size and choice of embedding potentials, including fixed-charge and polarizable molecular mechanics force fields (TIP3P and EFP) and various semiempirical QM methods (PM7, GFN2-xTB, DFTBA, DFTB3, HF-3c, and PBEh-3c), on the accuracy of the models was examined. A surprising finding was that molecular mechanics force fields outperformed many of the semiempirical methods. Generally, the errors in the QM/QM' and QM/MM models converge slowly with respect to the QM region size, requiring 50 or more waters to be included in the QM region before the error in the model falls below 1 kcal mol-1 of its pure QM result. Different QM region selection schemes were also compared, and it was found that selection based on Natural Population Analysis (NPA) atomic charges significantly reduced the error in the QM/QM' and QM/MM models particularly if a low-quality embedding potential was used. It is envisaged that these results will be useful for the development of future hybrid QM models.

Chiral Amplification of Phosphoramidates of Amines and Amino Acids in Water

AbstractThe origin of biomolecular homochirality continues to be one of the most fascinating aspects of prebiotic chemistry. Various amplification strategies for chiral compounds to enhance a small chiral preference have been reported, but none of these involves phosphorylation, one of nature's essential chemical reactions. Here we present a simple and robust concept of phosphorylation‐based chiral amplification of amines and amino acids in water. By exploiting the difference in solubility of a racemic phosphoramidate and its enantiopure form, we achieved enantioenrichment in solution. Starting with near racemic, phenylethylamine‐based phosphoramidates, ee's of up to 95 % are reached in a single amplification step. Particularly noteworthy is the enantioenrichment of phosphorylated amino acids and their derivatives, which might point to a potential role of phosphorus en‐route to prebiotic homochirality.

Chiral Amplification of Phosphoramidates of Amines and Amino Acids in Water.

The origin of biomolecular homochirality continues to be one of the most fascinating aspects of prebiotic chemistry. Various amplification strategies for chiral compounds to enhance a small chiral preference have been reported, but none of these involves phosphorylation, one of nature's essential chemical reactions. Here we present a simple and robust concept of phosphorylation‐based chiral amplification of amines and amino acids in water. By exploiting the difference in solubility of a racemic phosphoramidate and its enantiopure form, we achieved enantioenrichment in solution. Starting with near racemic, phenylethylamine‐based phosphoramidates, ee's of up to 95 % are reached in a single amplification step. Particularly noteworthy is the enantioenrichment of phosphorylated amino acids and their derivatives, which might point to a potential role of phosphorus en‐route to prebiotic homochirality.