Peptide Bonds In Proteins Research Articles

Discovery of an Unexplored Protein Structural Scaffold of Serine Protease from Big Blue Octopus (Octopus cyanea): A New Prospective Lead Molecule.

Serine proteases are a group of enzymes that hydrolyses the peptide bonds in proteins. In mammals, these enzymes help in the regulation of several major physiological functions such as digestion, blood clotting, responses of immune system, reproductive functions and the complement system. Serine proteases obtained from the venom of Octopodidae family is a relatively unexplored area of research. In the present work, we tried to effectively utilize comparative composite molecular modeling technique. Our key aim was to propose the first molecular model structure of unexplored serine protease 5 derived from big blue octopus. The other objective of this study was to analyze the distribution of negatively and positively charged amino acid over molecular modeled structure, distribution of secondary structural elements, hydrophobicity molecular surface analysis and electrostatic potential analysis with the aid of different bioinformatic tools. In the present study, molecular model has been generated with the help of I-TASSER suite. Afterwards the refined structural model was validated with standard methods. For functional annotation of protein molecule we used Protein Information Resource (PIR) database. Serine protease 5 of big blue octopus was analyzed with different bioinformatical algorithms for the distribution of negatively and positively charged amino acid over molecular modeled structure, distribution of secondary structural elements, hydrophobicity molecular surface analysis and electrostatic potential analysis. The functionally critical amino acids and ligand- binding site (LBS) of the proteins (modeled) were determined using the COACH program. The molecular model data in cooperation to other pertinent post model analysis data put forward molecular insight to proteolytic activity of serine protease 5, which helps in the clear understanding of procoagulant and anticoagulant characteristics of this natural lead molecule. Our approach was to investigate the octopus venom protein as a whole or a part of their structure that may result in the development of new lead molecule.

Recognition of protein-linked glycans as a determinant of peptidase activity

The vast majority of proteins are posttranslationally altered, with the addition of covalently linked sugars (glycosylation) being one of the most abundant modifications. However, despite the hydrolysis of protein peptide bonds by peptidases being a process essential to all life on Earth, the fundamental details of how peptidases accommodate posttranslational modifications, including glycosylation, has not been addressed. Through biochemical analyses and X-ray crystallographic structures we show that to hydrolyze their substrates, three structurally related metallopeptidases require the specific recognition of O-linked glycan modifications via carbohydrate-specific subsites immediately adjacent to their peptidase catalytic machinery. The three peptidases showed selectivity for different glycans, revealing protein-specific adaptations to particular glycan modifications, yet always cleaved the peptide bond immediately preceding the glycosylated residue. This insight builds upon the paradigm of how peptidases recognize substrates and provides a molecular understanding of glycoprotein degradation.

Cyclic cis-Locked Phospho-Dipeptides Reduce Entry of AβPP into Amyloidogenic Processing Pathway.

The cis/trans isomerization of X-Pro peptide bonds in proteins in some instances acts as a molecular switch in biological pathways. Our prior work suggests that the cis isomer of the phospho-Thr668-Pro669 motif, located in the cytoplasmic domain of the amyloid-β protein precursor (AβPP), is correlated with an increase in amyloidogenic processing of AβPP and production of amyloid-beta (Aβ), the neurotoxic peptide fragment in Alzheimer's disease (AD). We designed a 100% cis-locked cyclic dipeptide composed of cyclized phospho-Thr-Pro (pCDP) as a mimic for this putative pathological conformation, and three phosphate-blocked derivatives (pCDP-diBzl, pCDP-Bzl, and pCDP-diPOM). Two H4 neuroglioma cell lines were established as AD cell models for use in testing these compounds: H4-AβPP695 for stable overexpression of wild-type AβPP695, and H4-BACE1 for stable overexpression of β-site AβPP cleaving enzyme-1 (BACE1). The level of the secreted AβPP fragment resulting from BACE1 activity, sAβPPβ, served as a key proxy for amyloidogenic processing, since cleavage of AβPP by BACE1 is a requisite first step in Aβ production. Of the compounds tested, pCDP-diBzl decreased sAβPPβ levels in both cell lines, while pCDP-diPOM decreased sAβPPβ levels in only H4-BACE1 cells, all with similar dose-dependences and patterns of proteolytic AβPP fragments. Enzymatic assays showed that none of the pCDP derivatives directly inhibit BACE1 catalytic activity. These results suggest a model in which pCDP-diBzl and pCDP-diPOM act at a common point to inhibit entry of AβPP into the amyloidogenic AβPP processing pathway but through different targets, and provide important insights for the development of novel AD therapeutics.

Characterisation of purified protease from Bacillus subtilis BS166

Proteases are enzymes that break up the peptide bonds of proteins to release amino acids. Proteases showing better stability at alkaline pH and higher temperatures have potential applications in several industrial processes. The present study was aimed at determining the kinetic properties of the partially purified protease obtained from Bacillus subtilis BS166. Bacillus subtilis BS166 can produce protease above 30 o C and at pH 7.0. The protease was extracted with 0.1 M phosphate buffer of pH 7.0 and precipitated with ammonium sulfate. The activity of the purified protease was higher at pH 9.0 and 40 ο C and showed zero order kinetics for 10 minutes. When the optimum enzyme concentration was 95.52 μg, a straight line was obtained in the Lineweaver-Burk plot graph. Michaelis constant for the purified enzyme was 50.9 μM and Vmax was 2833.4 pmolmin -1 at pH 9.0 and 40 o C.

Proteases and their Inhibitors: From Basic to High Throughput Screening.

Proteases constitute one of the most important groups of industrial enzymes with a worldwide value expected to reach 2.7 billion US dollars by 2019. Proteases represent a group of enzymes that hydrolyze the peptide bonds of proteins, releasing polypeptides or free amino acids. These enzymes are used in cleaning products, production of leathers, textiles, food and dairy products, in the pharmaceutical and diagnostic industries and for water treatment. Another area of interest regarding proteases is the development of drugs that act as protease inhibitors. This review will briefly describe the general methods used in the detection of proteases and the few studies in the development of high throughput screening methods of proteases and protease inhibitors.

Organic solvent tolerant metallo protease of novel isolate Serratia marcescens PPB-26: production and characterization.

Proteases are a class of enzymes that catalyze hydrolysis of peptide bonds of proteins. In this study, 221 proteolytic bacterial isolates were obtained by enrichment culture method from soils of various regions of Himachal Pradesh, India. From these a hyper producer of protease was screened and identified by morphological and physiological testing and by 16S rDNA sequence as Serratia marcescens PPB-26. Statistical optimization of physiochemical parameters enhanced the protease production by 75 %. Protease of S. marcescens PPB-26 was classified as a metalloprotease. It showed optimal activity at 30 °C, pH 7.5 (0.15 M Tris–HCl buffer) and with 0.8 % substrate concentration. It had K m = 0.3 %, V max = 34.5 μmol min−1 mg−1 protein and a half life of 2 days at 30 °C. The enzyme was stable in most metal ions but showed increased activity with Fe2+ and Cu2+ while strong inhibition with Co2+ and Zn2+. Further investigation showed that the enzyme could not only retain its activity in various organic solvents but also showed increased activity with methanol and ethanol. The reported metalloprotease is thus a potential candidate for carrying out industrial peptide synthesis.

How planar are planar peptide bonds?

How planar are planar peptide bonds?

Alkaline protease from a new halotolerant alkaliphilic Bacillus agaradhaerens strain ak-r isolated from egyptian soda lakes

Alkaline proteases are hydrolytic enzymes that cleave peptide bonds in proteins and peptides in alkaline conditions, which occupy a pivotal importance with respect to their industrial applications. This study aimed to isolate new alkaline protease producing alkaliphilic bacteria from Egyptian soda lakes and optimize the fermentation process to enhance the enzyme production. The extensive screening process of the samples collected from Egyptian soda lakes resulted in isolation of a potent alkaline protease producing alkaliphilic strain AK-R. The isolate was identified as Bacillus agaradhaerens strain AK-R based on 16S rRNA gene analysis (99%). Wheat bran and gelatin supported maximum alkaline protease production as carbon and nitrogen sources, respectively. Strain AK-R is halo-tolerant thermo-tolerant alkaliphilic bacterium in nature, as it can grow over a wide range of NaCl concentrations (up to 25%) and up to 55 °C, with maximal growth and enzyme production at 2.5-5%, and pH 11 at 35 °C. Among the tested cations, only Mg 2+ and Ca 2+ ions significantly enhanced the enzyme production by about 1.2, and 1.3 fold compared to control, respectively. Alkaline protease secretion was coherent with the growth pattern, reaching maximal yield after about 32 h (mid stationary phase). In conclusion a new halo-tolerant thermo-tolerant alkaliphilic alkaline protease producing Bacillus agaradhaerens strain AK-R was isolated from Egyptian soda lakes. Optimization of the nutritional and cultivation conditions resulted in increase of enzyme yield by 20 fold. Strain AK-R and its extracellular alkaline protease with salt, pH and temperature, tolerance signify their potential application in laundry and pharmaceuticals industries.

A biotechnology perspective of fungal proteases.

Proteases hydrolyze the peptide bonds of proteins into peptides and amino acids, being found in all living organisms, and are essential for cell growth and differentiation. Proteolytic enzymes have potential application in a wide number of industrial processes such as food, laundry detergent and pharmaceutical. Proteases from microbial sources have dominated applications in industrial sectors. Fungal proteases are used for hydrolyzing protein and other components of soy beans and wheat in soy sauce production. Proteases can be produced in large quantities in a short time by established methods of fermentation. The parameters such as variation in C/N ratio, presence of some sugars, besides several other physical factors are important in the development of fermentation process. Proteases of fungal origin can be produced cost effectively, have an advantage faster production, the ease with which the enzymes can be modified and mycelium can be easily removed by filtration. The production of proteases has been carried out using submerged fermentation, but conditions in solid state fermentation lead to several potential advantages for the production of fungal enzymes. This review focuses on the production of fungal proteases, their distribution, structural-functional aspects, physical and chemical parameters, and the use of these enzymes in industrial applications.

English

Alkaline proteases are used in food industry, leather tanning and processing industry, preparation of pharmaceuticals and also in the fiber industry. An alkaline serine protease producing strain was isolated using soil sample from a natural hot water spring in Sri Lanka. It was identified based on morphological, biochemical and 16s rRNA identifications as Bacillus licheniformis NMS-1. The extacellular protease enzyme was purified by two steps procedure involving ammonium sulfate precipitation followed by DEAE-Sephadex A-25 gel chromatography. The purification gave a 56 fold increase of the specific activity with a yield of 16%. The optimal pH and optimal temperature of the protease were pH 9 and 60°C, respectively. The protease was relatively stable between 20– 80°C. The enzyme was stable within the pH values of 8 – 12. The Km and Vmax values calculated from Lineweaver – Burk plot were 2.7x10-3 mg/ml and 263 mU/mg. Among the protease inhibitors that were tested, PMSF completely inhibited the enzyme activity indicating that the protease is a serine protease. The enzyme retained more than 50% of its activity after 60 min incubation at 60°C. The major protease types used commercially are heat stable alkaline proteases. Alkaline serine proteases are enzymes that cleave peptide bonds in protein in which serine serves as the nucleophilic amino acid at the enzyme active site. Properties of this protease have shown it’s suitability for industrial applications such as detergent industry. Key words: Alkaline protease, purification, characterization, Bacillus licheniformis NMS-1, thermophilic, serine protease.

Unravelling the reaction mechanism of matrix metalloproteinase 3 using QM/MM calculations

The matrix metalloproteinase family (MMP) constitutes a family of zinc (Zn) proteases that catalyze the breaking of peptide bonds in proteins. These enzymes are very promising drug targets, since they are involved in remodeling and degradation of the extracellular matrix, which is a key process required for cancer metastasis, and thus, their reaction mechanism has been an area of intensive research. Early proposal based on acid base catalyzed hydrolysis, suggested that a conserved zinc bound water molecule acted as the nucleophile attacking the peptide bond carbon, after being activated by essential glutamate. The possibility of a direct nucleophilic attack by the enzyme, performed by the glutamate was also suggested. These are the key yet unsolved issues about MMP reaction mechanism.In the present work, we used hybrid quantum/classical calculations to analyze the structure and energetics of different possible hydrolysis reaction paths. The results support a water mediated mechanism, where both the nucleophile water molecule and the carbonyl oxygen of the scissile peptide bond are coordinated to zinc in the reactive configuration, while the essential glutamate acts as the base accepting the proton from the nucleophilic water. Formation of the carbon–oxygen bond and breaking of carbon–nitrogen bond were found to be concerted events, with a computed barrier of 14.8kcal/mol. Substrate polarization was found to be important for the observed reaction mechanism, and a substantial change in the metal coordination environment was observed, particularly, regarding the zinc–histidine coordination.

PEPTIDASES SECRETADAS POR FUNGOS TERMOFILICOS: uma revisão sistemática

Peptidases are enzymes which act on peptide bonds of proteins and peptides, releasing peptides and/or amino acids. These enzymes are commercialized worldwide and cover about 60% of the enzyme market, because of their wide application in different industrial sect ors. Desirable characteristics of peptidases for in dustrial application are: thermostability, stability at a pH range, organic s olvents among others. The search for thermostable e nzymes contributes to the increase of studies involving th ermophilic fungi, since these microorganisms have t hermophilic ability (have the ability to grow at high temperatu res) as the main physiological characteristic, they are easy to grow, compared to bacteria, and secrete enzymes. Processe s to obtain enzymes do not need refined equipments, what makes product manufacture cheaper. This review was based on a survey made on studies made in the past ten ye ars with thermophilic fungi and their peptidases as well as their potential application.

MOFzyme: Intrinsic protease-like activity of Cu-MOF.

The construction of efficient enzyme mimetics for the hydrolysis of peptide bonds in proteins is challenging due to the high stability of peptide bonds and the importance of proteases in biology and industry. Metal-organic frameworks (MOFs) consisting of infinite crystalline lattices with metal clusters and organic linkers may provide opportunities for protease mimic which has remained unknown. Herein, we report that Cu2(C9H3O6)4/3 MOF (which is well known as HKUST-1 and denoted as Cu-MOF here), possesses an intrinsic enzyme mimicking activity similar to that found in natural trypsin to bovine serum albumin (BSA) and casein. The Michaelis constant (Km) of Cu-MOF is about 26,000-fold smaller than that of free trypsin indicating a much higher affinity of BSA for Cu-MOF surface. Cu-MOF also exhibited significantly higher catalytic efficiency than homogeneous artificial metalloprotease Cu(II) complexes and could be reused for ten times without losing in its activity. Moreover, Cu-MOF was successfully used to simulate trypsinization in cell culture since it dissociated cells in culture even without EDTA.

EKSTRAKSI DAN KARAKTERISASI PARSIAL EKSTRAK KASAR ENZIM KATEPSIN DARI IKAN PATIN

Decomposition of protein by enzymatic process will lead to changes in odor, texture, and appearance of fish. The enzymes that play a role in the enzymatic process is primarily proteolytic enzymes. Cathepsin is one of the proteolytic enzymes found in animal tissue that hydrolyzes peptide bonds of proteins. This study aims to extract the cathepsin, characterize the crude extract derived from catfish. The stages of this research consist of the extraction and characterization of the cathepsin from catfish. Result of the extraction was crude extract of cathepsin with activity of 0.278 U/mL. The enzyme had optimum temperature of 50°C, pH 6 and substrate concentration of 2%. The activity of the cathepsin was inhibited by metal ions of Fe 3+ , Cu 2+ , Ca 2+ , but increased by metal ions of Mg 2+ .

Viral proteases: important targets of peptidemimetic compounds.

Proteases catalyze the hydrolysis of peptide bonds of proteins and peptides to produce smaller peptides and free amino acids. These enzymes are involved in physiologic processes such as blood coagulation and cellular death, and are related to life cycle of several viruses, such as hepatitis C, dengue, and AIDS. These features make most of proteases very important therapeutic targets for new pharmaceutical compounds. The development of peptidemimetics with improved pharmacokinetic properties is driving extensive research in the field of viral protease inhibitors. The present paper aims to highlight the design and synthesis of peptidemimetics that are able to inhibit viral proteases related to hepatitis C, dengue, and AIDS.

Sweet taste of cell death: role of carbohydrate recognition systems

T he number of cellular and molecular markers of apoptosis described in cytoplasm, nucleus and mitochondria, is increasing yearly. Howe ver, up to recent time, plasma membrane (PM) markers stayed to be less studied [1], and only phosphatidylserine (PS) externalization has been well characterized in that compartment, and already proposed for application in biolo gy studies and medical diagnostics [2]. It should be stressed that PM markers of apoptosis possess some important advantages compared to all other markers of this phenomenon, since they are better accessible to extra-cellular interactions without disturbing cell integrity. Since PM markers of apoptotic cells can be recognized by the phagocytic and neighboring epithelial cells, they are very important for efficient elimination of apoptotic cells from tissues and organs. Cell death was shown to be accompanied by time-dependent sequence of intracellular events, starting with a trigger signal and ending with a complete removal of dying cells by their neighbors and macrophages. It is discussed since when one can consider the cell “dead” or “apoptotic”. The organism senses the dying cells by a change of their surface markers and by a release of particular intercellular molecules [3] also related to changes in plasma membrane. Thus, the PM-derived apoptosis markers seem to be the most “physiological” measure of whether the cell is alive, dying, or already dead (necrotic). Recently, glycoproteins (GPs) integrated in the PM of apoptotic cells, were addressed by the investigators searching for novel cell surface markers of apoptosis. The carbohydrate moiety of plasma membrane GPs, unlike the DNA or proteins, does not need a specific matrix for its synthesis. Besides, unlike 3′→5′ phospodiester bonds in DNA, or peptide bonds in proteins, two carbohydrate molecules can be joined together by eleven different bond combinations providing a huge number of possible oligosaccharides and much higher information potential that is perfectly described by H.-J. Gabius [4]. Carbohydrate binding proteins, the lectins, have demonstrated to be a powerful tool for recognizing different carbohydrate moieties. They were discovered over 100 years ago, and hundreds of lectins with various carbohydrate specificity and different functions were described in plants and animals [5, 6]. A principal function of lectin-carbohydrate interaction is well expressed at the immune response [7, 8], including autoimmunity [9], and cell elimination from the organism [10]. It was hypothesized [11], that such interaction could be an evolutionary ancestor of the antibody-antigen interaction.

Research applications of proteolytic enzymes in molecular biology.

Proteolytic enzymes (also termed peptidases, proteases and proteinases) are capable of hydrolyzing peptide bonds in proteins. They can be found in all living organisms, from viruses to animals and humans. Proteolytic enzymes have great medical and pharmaceutical importance due to their key role in biological processes and in the life-cycle of many pathogens. Proteases are extensively applied enzymes in several sectors of industry and biotechnology, furthermore, numerous research applications require their use, including production of Klenow fragments, peptide synthesis, digestion of unwanted proteins during nucleic acid purification, cell culturing and tissue dissociation, preparation of recombinant antibody fragments for research, diagnostics and therapy, exploration of the structure-function relationships by structural studies, removal of affinity tags from fusion proteins in recombinant protein techniques, peptide sequencing and proteolytic digestion of proteins in proteomics. The aim of this paper is to review the molecular biological aspects of proteolytic enzymes and summarize their applications in the life sciences.

Exploring chemical reaction mechanisms through harmonic Fourier beads path optimization

Here, we apply the harmonic Fourier beads (HFB) path optimization method to study chemical reactions involving covalent bond breaking and forming on quantum mechanical (QM) and hybrid QM∕molecular mechanical (QM∕MM) potential energy surfaces. To improve efficiency of the path optimization on such computationally demanding potentials, we combined HFB with conjugate gradient (CG) optimization. The combined CG-HFB method was used to study two biologically relevant reactions, namely, L- to D-alanine amino acid inversion and alcohol acylation by amides. The optimized paths revealed several unexpected reaction steps in the gas phase. For example, on the B3LYP∕6-31G(d,p) potential, we found that alanine inversion proceeded via previously unknown intermediates, 2-iminopropane-1,1-diol and 3-amino-3-methyloxiran-2-ol. The CG-HFB method accurately located transition states, aiding in the interpretation of complex reaction mechanisms. Thus, on the B3LYP∕6-31G(d,p) potential, the gas phase activation barriers for the inversion and acylation reactions were 50.5 and 39.9 kcal∕mol, respectively. These barriers determine the spontaneous loss of amino acid chirality and cleavage of peptide bonds in proteins. We conclude that the combined CG-HFB method further advances QM and QM∕MM studies of reaction mechanisms.

N‐Terminal Labeling of Peptides by Trypsin‐Catalyzed Ligation for Quantitative Proteomics

Labeling tryptic peptides with stable isotopes is one of the most important methods for quantitative proteomics, and many ingenious chemical labeling strategies have been developed. Incorporation of one isotopically labeled tag onto a peptide terminus represents an ideal labeling approach, as it would simplify the interpretation of mass spectra. Moreover, the absence of labels on the side chains would facilitate the quantification of post-translational modifications (PTMs). However, to date all the reported chemical labeling strategies, including dimethyl labeling, iTRAQ (isobaric tags for absolute and relative quantification), and ICAT (isotope-coded affinity tags), result in the modification of side chains. One promising method to achieve the incorporation of a single tag is enzymatic labeling. Proteolytic O labeling can specifically label tryptic peptide termini without modification of side chains, but the small change in mass and O/O back-exchange, i.e. the exchange of O with O after the labeling process hinder its wide application in quantitative proteomics. Herein, we report a novel enzymatic labeling approach, in which trypsin is used as a ligase to specifically incorporate amino acids labeled with stable isotopes onto the N termini of peptides for quantitative analysis. Trypsin is a serine protease that specifically hydrolyzes peptide bonds in proteins after arginine and lysine residues. However, trypsin also catalyses peptide synthesis in organic solvents. Therefore, it is possible to covalently link isotopically labeled amino acids to tryptic peptides by using trypsin as a ligase. In this study, arginine, the prototype substrate for trypsin, was used as an acyl moiety donor. The primary amine group of arginine was protected with a benzoyl group (Bz) to prevent the formation of dipeptides or oligopeptides, and the carboxy group was esterified with ethanol to activate the acyl donor (see the Supporting Information, Figure S1). The final product, Na-benzoyl-l-arginine ethyl ester (Bz–R–OEt), was used as a substrate for the trypsin-catalyzed ligation. The quantitative proteomics workflow based on the trypsincatalyzed N-terminal labeling is shown in Figure 1a. Trypsin was first used as a protease to digest proteins in an aqueous solution (1m urea/50 mm Tris-HCl, pH 8.0). Then, the generated tryptic peptides were lyophilized and transferred to an ethanol solution containing 4% aqueous buffer (0.1m TrisHCl, pH 8.0). Next, trypsin immobilized on magnetic nanoparticles (IM-trypsin) and Bz–R–OEt were added to the ethanol solution for the N-terminal labeling of peptides with Bz–R based on a kinetically controlled mechanism (see the Supporting Information). Finally, quantification of the proteins was achieved by the differential labeling of two samples by using Bz–R–OEt (light label) and Bz–(C6)R–OEt (bearing six C atoms; heavy label), the incorporation of which are indicated by mass shifts of 260 and 266 Da, respectively. We first validated the protease and ligase activities of trypsin by using the synthetic peptide VGKANEELAGVVAEVQK (Figure 1b; m/z= 1740.86), which contains one trypsin cleavage site. In aqueous solution, treatment with IMtrypsin generated a shorter peptide ANEELAGVVAEVQK (Figure 1b, m/z= 1456.82). Treatment of the obtained peptide with an ethanol solution containing Bz–R–OEt and IMtrypsin gave an N-terminus labeled peptide Bz–RANEELAGVVAEVQK (Figure 1b, m/z= 1716.9). Similar results were also obtained for three other synthetic peptides that contained one trypsin cleavage site (Supporting Information, Figure S2). These examples clearly illustrate that trypsin functions as a protease in an aqueous solution whereas it acts as an N-terminus ligase in an ethanol solution. Thus, these results imply that this enzymatic labeling approach can be used to label peptides generated by trypsin digestion of a proteome sample. In this study, free trypsin was used for the digestion of proteins, as is conventional in proteomics analysis, whereas IM-trypsin (trypsin from the same source) was used for ligation because it is more tolerant to organic solvents and it is readily removed using magnetism. We tested whether the labeling of side-chain primary amino groups would also be facilitated by trypsin ligase. A synthetic peptide VIFIEHAKRKG, containing two sidechain amino groups and one terminal primary amino group, was labeled by trypsin. The Arg tag was incorporated only onto the terminal primary amino group and not onto the sidechain amino groups (see the Supporting Information, Figure S3a). These results are markedly different from those of other amine labeling approaches. For example, for labeling [*] Y. Pan, Prof. Dr. M. Ye, Dr. L. Zhao, K. Cheng, M. Dong, C. Song, H. Qin, Dr. F. Wang, Prof. Dr. H. Zou CAS Key Lab of Separation Sciences for Analytical Chemistry National Chromatographic R&A Center, Dalian Institute of Chemical Physics, Chinese Academy of Sciences Dalian 116023 (China) E-mail: mingliang@dicp.ac.cn hanfazou@dicp.ac.cn

Emergent Paramagnetism in D- and L-Alanine Crystals: Spin-Orbital Separation in Quasi-One-Dimensional N<sup>+</sup>H…O<sup>?</sup> Bonds

We investigated the field-dependent magnetic properties of chiral alanine crystals, especially associated with the electronic orbital motions. Based on the chirality of the zwitterionic model ( + NH3- C(CH3)H-CO2 - ) and the helicity of the lattice structure of peptide bond in proteins, when an external field of +5 T was applied parallel to the preferred axis c(z) of the N + H…O - hydrogen bond in D-alanine, the electron spin-flip manifested emergent paramagnetism at 297.6 K. Because the spin magnetic dipole moment of hydrogen in L-alanine was originally aligned antiparallel to the field, the electron spins flipped firstly perpendicular to the field then manifested paramagnetism at 303.9 K. The magnetic field of 5 T split a degenerate energy level in the paramagnetic state of chiral alanine. Furthermore, the spin-orbital separation of the quasi-one dimensional N + H…O - hydrogen bond in the crystal lattice provided evidence for the hallmark of one-dimensional physics.