The structural changes of a bovine casein micelle during temperature change; in situ observation over a wide spatial scale from nano to micrometer.

Bovine milk is the complex colloidal system containing nano to micrometer scale components. Earlier, our research group reported the structural changes in bovine casein micelles in the temperature range of 10-40 °C by in situ small-angle X-ray scattering (SAXS) [H. Takagi, T. Nakano, T. Aoki and M. Tanimoto, Food Chem., 2022, 393, 133389]. In this study, we extend our previous research by investigating the temperature-associated structural alterations in casein micelles over a wide spatial scale using in situ SAXS and ultra-SAXS (USAXS). Furthermore, the temperature dependences of various physical properties of the casein micelles were investigated by analyzing the SAXS intensities. The USAXS results showed that micelles formed 1-dimensional aggregates and that these aggregate structures did not change in the temperature range of 10-40 °C. Changes in electron densities calculated from SAXS intensities showed that the voluminosity reduced and the weight fraction of protein inside the micelles increased during the heating process. The number of water domains in a micelle decreased when the temperature increased from 10 to 40 °C, but did not substantially change in the cooling run at a rate of 1 °C min-1. The number of colloidal calcium phosphate (NCCP) in a micelle can also be calculated from the SAXS intensities; NCCP increases upon heating. This study on the behavior of casein micelles with respect to temperature change in milk over a wide spatial scale showed that the casein micelle structure was sensitive to temperature and can change dramatically with temperature variations.

A SAXS and USAXS study of the influence of pH on the casein micelle structure.

Changes in milk pH significantly influence the behavior and physical properties of casein micelles; however, the effects of these changes on casein micelle structures are still unclear. The aim of this study was to elucidate the effect of changes in pH range from 5.9 to 7.1 on the structure of casein micelles in milk using small-angle X-ray scattering (SAXS) and ultra small-angle X-ray scattering (USAXS). The casein micelles formed one-dimensional aggregates. The micelle radius decreased with decreasing pH, whereas the size of the water domain increased. The distance between colloidal calcium phosphates (CCP) remained unchanged, whereas the CCP radius decreased with decreasing pH. Voluminosity, which was calculated from scattering intensities, increased at increased pH. In conclusion, the micelle structure changed significantly in response to changes in pH. Our findings help to understand the changes in the physical properties of milk at various pH levels in terms of the microscopic structure.

Temperature dependence of the casein micelle structure in the range of 10-40 °C: An in-situ SAXS study.

Milk is used and processed under various environmental temperature, and its physicochemical properties are also strongly affected by temperature. Therefore, it is important to reveal the structure of milk at variable temperatures. In this study, the temperature dependence of the inner structure of bovine casein micelles in the temperature range of 10-40 °C was investigated by in-situ small-angle X-ray scattering (SAXS) method. The micelle size calculated from the SAXS profiles using a micelle model including water domains was almost independent of temperature. The water domain expanded and the distance between the colloidal calcium phosphates (CCP) decreased with increasing temperature. The number of CCPs in a micelle increased, because CCPs were newly formed by the transfer of calcium and inorganic phosphate from serum into the micelle. These structural changes occurred during the cooling process. Therefore, in the temperature range of 10-40 °C, the structure of the casein micelle varied sensitively with the temperature, and these structural changes were thermoreversible in nature.

Random skin biopsy and bone marrow biopsy for diagnosis of intravascular large B cell lymphoma.

Intravascular lymphoma (IVL) is a rare type of extranodal lymphoma in which the lymphoma cells proliferate exclusively in the lumina of small vessels. The diagnosis of IVL requires histological confirmation. Although random skin biopsy from healthy-appearing skin in patients with suspected IVL appeared to be useful, the sensitivity of this method for the diagnosis of IVL remains unknown. We performed a random skin biopsy from 12 consecutive cases of IVL diagnosed at our institution over the past 4 years and evaluate its relevance of clinical and laboratory characteristics, presence or absence of skin lesions, and bone marrow involvement. All 12 patients were diagnosed antemortem by either random skin biopsy or bone marrow biopsy and treated with rituximab-containing chemotherapy. Random skin biopsy was performed in all 12 patients, and the results were positive in ten patients (83.3%). Erythematous skin lesions were seen in 3 of 12 patients, but biopsy was positive for lymphoma lesion in two patients. Bone marrow invasion was seen in 11 of the 12 patients (91.6%) by bone marrow smear and/or flow cytometric analysis, but was detected in only half of the patients by trephine biopsy. We concluded that random skin biopsy from normal-appearing skin is highly sensitive in the diagnosis of IVL comparable to bone marrow trephine biopsy. It should be performed irrespective of the presence or absence of skin lesions in patients who were suspicious of IVL.

Evaluation of the performance of osmotic dehydration sheets on freshness parameters in cold-stored beef biceps femoris muscle.

This study aimed to evaluate the effects of osmotic dehydration sheet (ODS) packaging on the quality parameters of beef biceps femoris muscle samples stored at 4°C for 0, 1, 3 and 7 days. Quality indices such as Hunter color values (L(∗), a(∗) and b(∗), the percentage of metmyoglobin (Met-Mb%), K value (freshness index), and the contents of adenosine triphosphate (ATP)-related compounds (ARCs), thiobarbituric acid reactive substances (TBA-RS) and volatile basic nitrogen (VBN) were measured. ODS gave lower a(∗) and b(∗) values and lower Met-Mb% compared with control samples wrapped in polyvinylidene chloride film (PVDCF) (P<0.01), but had no effect on L(∗) (P<0.01). As a result, with higher levels of osmotic dehydration produced by the ODS, the percentage of weight loss and the total contents of ARCs and inosine monophosphate of the samples also increased (P<0.05). The K values of ODS samples were also significantly lower than PVDCF-wrapped samples (P<0.05). Low performance ODS wrapping reduced the TBA-RS values below those found with PVDCF and high performance ODS processing (P<0.01). Moreover, the use of ODS had no effect on VBN values. Thus, although the bright red of beef samples changed to a dark purple color and the weights of samples decreased, the ODS approach has potential as a tool for decreasing the deterioration of other quality indices such as Met-Mb%, TBA-RS, ARCs, K values and the VBN content of cold-stored beef.

Transition of ovalbumin to thermostable structure entails conformational changes involving the reactive center loop.

Ovalbumin is a serpin without inhibitory activity against proteases. During embryonic development, ovalbumin in the native (N) form undergoes changes and takes a heat-stable form, which was previously named HS-ovalbumin. It has been known that N-ovalbumin is artificially converted to another thermostable form called S-ovalbumin by heating at an alkaline pH. Here, we characterized further the three ovalbumin forms, N, HS, and S. The epitope of the monoclonal antibody 2B3/2H11, which recognizes N- and HS-ovalbumin but not S-ovalbumin, was found to reside in the region Glu-Val-Val-Gly-Ala-Ser-Glu-Ala-Gly-Val-Asp-Ala-Ala-Ser-Val-Ser-Glu-Glu-Phe-Arg, which corresponds to 340-359 of amino acid residues and is contained in the reactive center loop (RCL). Removal of RCL by elastase or subtilisin mitigated binding of the antibody. Dephosphorylation experiments indicated that the phosphorylated Ser-344 residue located on RCL is crucial for the epitope recognition. We suggest that the shift to the heat-stable form of ovalbumin accompanies a movement of RCL.

Triclosan-lysozyme complex as novel antimicrobial macromolecule: a new potential of lysozyme as phenolic drug-targeting molecule.

A novel anti-infection strategy to alleviate antibiotic-resistance problem and non-specific toxicity associated with chemotherapy is explored in this study. It is based on utilizing a bacteriolytic enzyme (lysozyme) as a carrier to allow specific targeting of a potential phenolic antimicrobial drug (triclosan) to microbial cells. Lysozyme (LZ) was complexed, via electrostatic and hydrophobic condensation at alkaline pH, to various degrees with triclosan (TCS), a negatively charged phenolic antimicrobial that inhibits bacterial fatty acid synthesis. Fluorescence and absorbance spectra analysis revealed non-covalent association of TCS with the aromatic residues at the interior of LZ molecule. The conjugation greatly promoted the lytic activity of LZ as the degree of TCS derivatization increased. The complexation with LZ turned TCS into completely soluble in aqueous solution. TCS-LZ complexes showed significantly enhanced bactericidal activity against several strains of Gram-positive and Gram-negative bacteria compared to the activity of TCS or LZ alone when tested at the same molar basis. Strikingly, TCS-LZ complex, but not LZ or TCS alone, exhibited unique specificity to scavenge superoxide radicals, generated by the natural xanthine/xanthine oxidase coupling system, without affecting the catalytic function of oxidase. This finding is the first to describe that the membrane disrupting function of lysozyme can be utilized to specifically target antimicrobial drug(s) to pathogen cells and heralding a fascinating opportunity for the potential candidacy of TCS-LZ as novel antimicrobial strategy for human therapy.

Ovotransferrin is a redox-dependent autoprocessing protein incorporating four consensus self-cleaving motifs flanking the two kringles.

Embryos of avian eggs and mammals are highly sensitive to oxidative stress and hence maintaining a steady reducing environment during the embryonic development is known to confer protection. Although information is completely lacking, proteins of avian egg albumin which have been suggested to play various biological functions, are the major targets for such reducing state during embryogenesis. In this study, we found that ovotransferrin (OTf), the second major protein in egg albumin, undergoes autocleavage at distinct sites upon reduction with thiol-reducing agent or thioredoxin-reducing system. Mass spectral and microsequencing analysis indicated that OTf is able to cleave itself through the unique chemical reactivity of four tripeptides motifs, HTT (residues 209-211), HST (residues 542-544) and two CHT (residues 115-117 and 454-456). Intriguingly, these self-cleavage sites were uniquely located upstream and downstream of the two disulfide kringle domains (residues 115-211 and 454-544) of OTf. These reduction-scissile sequences, His/Cys-X-Thr, are evolutionary conserved self-cleavage motifs found in several autoprocessing proteins including hedgehog proteins. Interestingly, reduction of other two members of transferrin family induced autocleavage patterns, similar to that of OTf, in bovine lactoferrin (bLf) while human lactoferrin (hLf) showed much less self-cleaving activity. This finding is the first to describe that transferrins are a new subset in the class of proteins able to carry out autoprocessing, providing insight into this unusual biochemical process that appears to be a molecular switch involved in triggering a yet unidentified function(s) of OTf as well as bLf.

Glycation and phosphorylation of beta-lactoglobulin by dry-heating: effect on protein structure and some properties.

Beta-lactoglobulin (beta-Lg) was glycated with maltopentaose and subsequently phosphorylated by dry-heating in the presence of pyrophosphate to investigate the structural and functional properties of phosphorylated beta-Lg. The circular dichroism spectra showed that the change of the secondary structure in the beta-Lg molecule by glycation and subsequent phosphorylation was small. The differential scanning calorimetry thermograms of beta-Lg showed that the denaturation temperature of the most stable domain was only slightly affected, whereas the retinol-binding activity of beta-Lg was somewhat reduced by glycation and subsequent phosphorylation. These results indicated that the conformational changes of the beta-Lg molecule by glycation and subsequent phosphorylation were mild. The anti-beta-Lg antibody response was somewhat reduced by glycation, but significant changes were not observed by phosphorylation. Although the stability of beta-Lg against heat-induced insolubility was improved by glycation alone, it was further enhanced by phosphorylation. The calcium phosphate solubilizing ability of beta-Lg was enhanced by phosphorylation following glycation.

Ovotransferrin possesses SOD-like superoxide anion scavenging activity that is promoted by copper and manganese binding.

The embryo of oviparous species is confronted by a highly oxidative stress generating as it grows and must rely on effective antioxidant system for protection. Proteins of avian egg albumin have been suggested to play the major redox-modulatory role during embryo development. Recently, we found that ovotransferrin (OTf) undergoes distinct thiol-linked self-cleavage in a redox-dependent process. In this study, we explore that OTf is SOD mimic protein with a potent superoxide anion (O(2)(-)) scavenging activity. The O(2)(-) scavenging activity was investigated using the natural xanthine/xanthine oxidase (X/XOD) coupling system. OTf exhibited O(2)(-) scavenging activity in a dose-dependent manner and showed remarkably higher scavenging activity than the known antioxidants, ascorbate or serum albumin. The isolated half-molecules of OTf exhibited higher scavenging activity than the intact molecule, whereas the N-lobe showed much greater activity. OTf dramatically quenched the O(2)(-) flux but had no effect on the urate production in the X/XOD system, indicating its unique specificity to scavenge O(2)(-) but not oxidase inhibition. Strikingly, metal-bound OTf exhibited greater O(2)(-) dismutation capacity than the apo-protein, ranging from moderate (Zn(2+)-OTf and Fe(2+)-OTf) to high (Mn(2+)-OTf and Cu(2+)-OTf) activity with the Cu(2+)-OTf being the most potent scavenger. In a highly sensitive fluorogenic assay, the metal-bound OTf exhibited significant increase in the rate of H(2)O(2) production in the X/XOD reaction than the apo-OTf, providing evidence that Zn(2+)-, Mn(2+)- and Cu(2+)-OTf possess SOD mimic activity. This finding is the first to describe that OTf is an O(2)(-) scavenging molecule, providing insight into its novel SOD-like biological function, and heralding a fascinating opportunity for its potential candidacy as antioxidant drug.

Immunomodulatory effects of phosphorylated dextrin in mouse spleen cell cultures.

Corn dextrin preparations with average degradation degrees of 16.7 and 167, or average molecular masses of 2,700 and 27,000, were covalently introduced with 4.5 and 11.2 to 35.4 mol of phosphoric acid, respectively, per mole by dry-heating at 110 to 140 degrees C for 24 h with sodium phosphate, and their effects on cell proliferation and production of immunoglobulin A (IgA) were investigated in C3H/HeN mouse spleen cell cultures. All the phosphorylated dextrin had mitogenic effects and stimulated proliferative responses induced by lipopolysaccharide (LPS) and concanavalin A (ConA). The phosphorylated dextrin with an average degradation degree of 16.7 was divided into 3 fractions, which had 3.6, 4.0 and 6.5 mol of phosphoric acid per mole when the molecular mass of each dextrin was postulated to be 2,700. LPS-induced proliferation was greatest with the preparation having 3.6 mol of phosphoric acid per mole of dextrin, whereas ConA-induced proliferation was strongest with 6.5 mol of phosphoric acid. On the other hand, the divided dextrin enhanced production of IgA by approximately 1.2-, 2.0- and 2.2-fold in accordance with the increasing amount of phosphoric acid. These results indicate that phosphorylated dextrin stimulates humoral immune responses in mouse spleen cell cultures.

Processing of lysozyme at distinct loops by pepsin: a novel action for generating multiple antimicrobial peptide motifs in the newborn stomach.

C-type lysozyme (cLZ) is an antimicrobial enzyme that plays a major defense role in many human secretions. Recently, we have identified a helix-loop-helix antimicrobial peptide fragment of cLZ. This finding suggests that processing by coexisting proteases might be a relevant physiological process for generating peptides that contribute to the in vivo mucosal defense role of cLZ. In this study, we found that pepsin, under condition relevant to the newborn stomach (pH 4.0), generated various peptides from cLZ with potent bactericidal activity against several strains of Gram-negative and Gram-positive bacteria. Microsequencing and mass spectral analysis revealed that pepsin cleavage occurred at conserved loops within the alpha-domain of cLZ. We found that the bactericidal domain, which was isolated by gel filtration and reversed-phase HPLC, contains two cationic alpha-helical peptides generated from a helix-loop-helix domain (residues 1-38 of cLZ) by nicking at leucine17. A third peptide consisting of an alpha-helix (residues 18-38) and a two-stranded beta-sheet (residues 39-56) structure was also identified. These peptides share structural motifs commonly found in different innate immune defenses. Functional cellular studies with outer membrane-, cytoplasmic membrane vitality- and redox-specific fluorescence dyes revealed that the lethal effect of the isolated antimicrobial peptides is due to membrane permeabilization and inhibition of redox-driven bacterial respiration. The results provide the first demonstration that pepsin can fine-tune the antimicrobial potency of cLZ by generating multiple antimicrobial peptide motifs, delineating a new molecular switch of cLZ in the mucosal defense systems. Finally, this finding offers a new strategy for the design of antibiotic peptide drugs with potential use in the treatment of infectious diseases.

Thermostabilized ovalbumin that occurs naturally during development accumulates in embryonic tissues.

We have reported that ovalbumin accumulates without digestion in various tissues during embryonic development of the chicken. There are different types of ovalbumin with respect to thermal stability and one of them, which was named "HS-ovalbumin" in the present study, was found to have a T(m) value of 83 degrees C and to be present dominantly in albumen, egg yolk, amniotic fluid, and serum of fertilized eggs. HS-ovalbumin, arising physiologically from its native form (N-ovalbumin), is reminiscent of the previously described intermediate form appearing during the production processes of the so-called S-ovalbumin, which disappeared shortly in fertilized eggs. We showed that HS-ovalbumin is distinguishable from S-ovalbumin by a monoclonal antibody and also from N-ovalbumin by the stability to heating. At the late stages of development, ovalbumin of amniotic fluid seems to be swallowed through pharynx, carried in the intestine through stomach, and absorbed in the blood. Analyses by monoclonal antibody and heat treatment indicated that the HS-form occupies the largest fraction of ovalbumin that accumulates in the embryonic tissues. The current findings suggest that HS-ovalbumin is crucial for embryogenesis.

[Prevention of osteoporosis by foods and dietary supplements. Bioavailability of milk micellar calcium phosphate].

Micellar calcium phosphate (MCP), which is a main form in milk, cross-links caseins through their phosphate groups. MCP was separated as the complex with casein phosphopeptide (CPP). Whey calcium, which is separated in a different form from that in bovine milk and used as a calcium ingredient in recent food industry, has superior calcium bioavailability to other calcium ingredients. Growing female rats were fed either MCP-CPP complex or whey calcium as the sole source of calcium for 6 weeks, and the calcium bioavailability was estimated from apparent calcium absorption rate and the bone strength of the femur. The calcium bioavailability of the MCP-CPP complex was significantly higher than that of whey calcium. The higher calcium bioavailability of MCP-CPP complex is due to in part to its solubility in the small intestine.

Phosphorylation of ovalbumin by dry-heating in the presence of pyrophosphate: effect on protein structure and some properties.

Ovalbumin (OVA) was phosphorylated by dry-heating in the presence of pyrophosphate at pH 4.0 and 85 degrees C for 1 and 5 days, and the physicochemical and structural properties of phosphorylated OVA were investigated. The phosphorus content of OVA increased to 1.01% by phosphorylation, and the electrophoretic mobility of PP-OVA also increased. Although the solubility of dry-heated OVA decreased, the decrease was slightly depressed by phosphorylation. The circular dichroism spectra showed that the change of the secondary structure in the OVA molecule, as measured by alpha-helix content, was mild by phosphorylation. The exchange reaction between the sulfhydryl and disulfide groups was enhanced and the surface hydrophobicity of OVA increased by phosphorylation. The tryptophan fluorescence intensity of OVA decreased by phosphorylation, suggesting that the conformational change occurred in the OVA molecule by phosphorylation. Although the differential scanning calorimetry thermograms of OVA showed a lowering of the denaturation temperature from 78.3 to 70.1 degrees C by phosphorylation, the stability of OVA against heat-induced insolubility at pH 7.0 was improved. The results indicated molten (partially unfolded) conformations of OVA formed by dry-heating in the presence of pyrophosphate.

Strategies for new antimicrobial proteins and peptides: lysozyme and aprotinin as model molecules.

The increasing development of bacterial resistance to traditional antibiotics has reached alarming levels, thus necessitating the strong need to develop new antimicrobial agents. These new antimicrobials should possess both novel modes of action as well as different cellular targets compared with the existing antibiotics. Lysozyme, muramidase, and aprotinin, a protease inhibitor, both exhibit antimicrobial activities against different microorganisms, were chosen as model proteins to develop more potent bactericidal agents with broader antimicrobial specificity. The antibacterial specificity of lysozyme is basically directed against certain Gram-positive bacteria and to a lesser extent against Gram-negative ones, thus its potential use as antimicrobial agent in food and drug systems is hampered. Several strategies were attempted to convert lysozyme to be active in killing Gram-negative bacteria which would be an important contribution for modern biotechnology and medicine. Three strategies were adopted in which membrane-binding hydrophobic domains were introduced to the catalytic function of lysozyme, to enable it to damage the bacterial membrane functions. These successful strategies were based on either equipping the enzyme with a hydrophobic carrier to enable it to penetrate and disrupt the bacterial membrane, or coupling lysozyme with a safe phenolic aldehyde having lethal activity toward bacterial membrane. In a different approach, proteolytically tailored lysozyme and aprotinin have been designed on the basis of modifying the derived peptides to confer the most favorable bactericidal potency and cellular specificity. The results obtained from these strategies show that proteins can be tailored and modelled to achieve particular functions. These approaches introduced, for the first time, a new conceptual utilization of lysozyme and aprotinin, and thus heralded a great opportunity for potential use in drug systems as new antimicrobial agent.

Phosphorylation of egg white proteins by dry-heating in the presence of phosphate.

Food proteins were phosphorylated by heating in a dry state in the presence of phosphate. When casein, whey protein isolate (WPI), and egg white proteins (EWP), which were lyophilized from their solutions in a phosphate buffer, were dry-heated at various temperatures and pH levels for 1-5 days, EWP was more highly phosphorylated than casein and WPI. Phosphorylation of EWP was promoted with a decrease of pH from 7.0 to 3.0 when the incubation temperature was raised from 55 to 100 degrees C. The phosphorus content of EWP increased from 0.08 to 0.64% by dry-heating at pH 3.0 and 85 degrees C for 5 days in the presence of phosphate. The electrophoretic mobility of EWP increased with an increase in the phosphorylation level. The heat-induced polymerization of EWP by dry-heating was not affected by the presence of phosphate. Although the solubility of EWP decreased by dry-heating at pH 3.0-5.5, the phosphorylation depressed the insolubilization at low pH. The phosphate bonds in phosphorylated EWP (P-EWP) were stable at pH 2.0-10.0 and were more acid-labile and base-stable than phosphoesters of egg riboflavin-binding protein (RfBP). (31)P NMR spectral data suggested that besides phosphoesters, phosphodiester and polyphosphate bonds were introduced in P-EWP. Heat stability of EWP was improved, and calcium phosphate-solubilizing ability of EWP was enhanced by phosphorylation.

Improvement of functional properties of egg white protein through phosphorylation by dry-heating in the presence of pyrophosphate.

Egg white protein (EWP) was phosphorylated by dry-heating in the presence of pyrophosphate at pH 3.0-7.0 and 85 degrees C for 1 and 5 days, and the functional properties of the phosphorylated EWP (PP-EWP) were investigated. The phosphorylation was accelerated with a decrease of pH from 7.0 to 3.0 and for heating times from 1 to 5 days. The phosphorus content of EWP increased approximately 1.05% by dry-heating at pH 4.0 and 85 degrees C for 5 days in the presence of pyrophosphate, which was higher than that of casein. The electrophoretic mobility of EWP increased with an increase in the phosphorylation level. The surface hydrophobicity of EWP increased by phosphorylation. The heat stability, emulsifying properties, and digestibility of EWP were improved by phosphorylation. The calcium phosphate-solubilizing ability of EWP was enhanced by phosphorylation. A firmer and transparent heat-induced gel of PP-EWP was obtained, and the water-holding capacity of heat-induced PP-EWP gel was higher that that of the control. These results suggest that phosphorylation by dry-heating in the presence of pyrophosphate is a useful method for improving the functional properties of EWP.

A novel type of milk calcium has higher calcium bioavailability compared with the hydroxyapatite type of milk calcium.

We prepared a novel type of milk calcium from milk whey, and evaluated its calcium bioavailability as compared with conventional industrial milk calcium obtained from milk whey, which has been reported to be an excellent calcium source. An X-ray diffraction analysis showed that the chemical form of conventional industrial milk calcium from milk whey through the neutralization and precipitation method (NP-MCa) is hydroxyapatite type, and that of a novel type of milk calcium obtained using the ultrafiltration method (UF-MCa) is different from hydroxyapatite. Growing rats were fed either NP-MCa or UF-MCa as the source of calcium for 33 d. The calcium absorption rate in the UF-MCa diet group was significantly higher than that in the NP-MCa diet group. The calcium content of the femur in the UF-MCa diet group was significantly higher than that in the NP-MCa diet group. The breaking force of the excised femur in the UF-MCa diet group was also significantly higher than that in the NP-MCa diet group. The serum calcium level, alkaline phosphatase activity and calcitonin level were not significantly different between the experimental groups, but the PTH level of the serum in the UF-MCa diet group was significantly lower than that in the NP-MCa diet group. These results indicate that the calcium bioavailability of the novel type of milk calcium (UF-MCa) is higher than that of the hydroxyapatite type of milk calcium (NP-MCa).

Liquid chromatographic determination of microcystins in water samples following pre-column excimer fluorescence derivatization with 4-(1-pyrene)butanoic acid hydrazide.

A method to measure the concentrations of microcystins (MCs) in water samples has been developed by incorporating pre-column fluorescence derivatization and liquid chromatography (LC). A solid-phase extraction for pretreatment was used to extract the MCs in water samples. The MCs were derivatized with excimer-forming 4-(1-pyrene)butanoic acid hydrazide (PBH). The MCs could then be detected by fluorescence after separation with a pentafluorophenyl (PFP)-modified superficially porous (core shell) particle LC column. The derivatization reactions of MCs with PBH proceeded easily in the presence of 4,6-dimethoxy-1,3,5-triazin-2-yl-4-methylmorpholinium (DMT-MM) as a condensation reagent, and the resulting derivatives could be easily separated on the PFP column. The derivatives were selectively detected at excimer fluorescence wavelengths (440-540 nm). The instrument detection limit and the instrument quantification limit of the MCs standards were 0.4-1.2 µg L(-1) and 1.4-3.9 µg L(-1), respectively. The method was validated at 0.1 and 1.0 µg L(-1) levels in tap and pond water samples, and the recovery of MCs was between 67 and 101% with a relative standard deviation of 11%. The proposed method can be used to quantify trace amounts of MCs in water samples.