Global bifurcation of fixed points and the Poincaré translation operator on manifolds

Let M be a differentiable manifold and [0, )×MM be a C¹ map satisfying the condition (0, p)=p for all pM. Among other results, we prove that when the degree (also called Hopf index or Euler characteristic) of the tangent vector field wMTM, given by w(p)=(/)(0, p), is well defined and nonzero, then the set (of nontrivial pairs) admits a connected subset whose closure is not compact and meets the slice {0}×M of [0, )×M. This extends known results regarding the existence of harmonic solutions of periodic ordinary differential equations on manifolds.     

CZE separation of strawberry anthocyanins with acidic buffer and comparison with HPLC

Anthocyanins, the major colourants of strawberries, are polar pigments that are positively charged at low pH. Herein, we have assessed a new analytical method for the separation of anthocyanins using CZE. Acidic buffer solutions (pH <2) were employed in order to maintain pigments in the cation flavylium form and achieve high molar absorptivity at 510 nm. These spectral properties enabled us to identify strawberry anthocyanins in a preliminary stage by detection in the visible range, although the method was optimised at 280 nm to obtain the best S/N. The effects of buffer composition highlighted the necessity of adding an organic modifier to the running buffer to obtain a suitable separation. The electrophoretic method permitted the separation of the three main anthocyanins of strawberry extracts, namely pelargonidin 3-glucoside (Pg-glu), pelargonidin 3-rutinoside and cyanidin 3-glucoside. The electrophoretic results, expressed as retention time and separation efficiency of the major anthocyanin (Pg-glu), were compared to those achieved in HPLC, the analytical technique traditionally used for the investigation of anthocyanins in vegetable matrix. The content of Pg-glu in strawberries (cv. Camarosa), calculated with HPCE and HPLC methods, resulted respectively in 11.41 mg/L and 11.37 mg/L.     

A label-free method based on MALDI-TOF mass spectrometry for the absolute quantitation of troponin T in mouse cardiac tissue

A label-free absolute quantitation method based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been developed. This methodology was applied to mouse heart in order to quantify cardiac troponin T (cTnT), which is considered to be a sensitive marker of heart damage. The cTnT was extracted, isolated by reversed-phase high-performance liquid chromatography, digested, and analyzed by MALDI-TOF MS. The MS-based quantitation was performed using matrix-matched calibration curves (due to a matrix effect) of two synthetic peptides, one cTnT-specific peptide and one internal standard peptide, respectively. Recoveries at three spiking levels ranged from 87–96%, with relative standard deviations of below 10%. The method detection limit and the method quantitation limit, expressed as the amount of cTnT for the amount of total sarcomeric protein extract, were 0.03 mg g⁻¹ and 0.15 mg g⁻¹, respectively. This method appears to be accurate and generally suitable for improving absolute protein quantitation.     

Detection of bacterial quorum sensing <Emphasis Type="Italic">N</Emphasis>-acyl homoserine lactones in clinical samples

Bacteria communicate among themselves using certain chemical signaling molecules. These signaling molecules generally are N-acyl homoserine lactones (AHLs) in Gram-negative bacteria and oligopeptides in Gram-positive bacteria. In addition, both Gram-positive and Gram-negative bacteria produce a family of signaling molecules known as autoinducer-2 that they employ for their communications. Bacteria coordinate their behavior by releasing and responding to the chemical signaling molecules present in proportion to their population density. This phenomenon is known as quorum sensing. The role of bacteria in the pathogenesis of several diseases, including gastrointestinal (GI) disorders, is well established. Moreover, rather recently bacterial quorum sensing has been implicated in the onset of bacterial pathogenicity. Thus, we hypothesized that the signaling molecules involved in bacterial communication may serve as potential biomarkers for the diagnosis and management of several bacteria-related diseases. For that, we previously developed a method based on genetically engineered whole-cell sensing systems for the rapid, sensitive, cost-effective and quantitative detection of AHLs in biological samples, such as saliva and stool, from both healthy and diseased individuals with GI disorders. Although various analytical methods, based on physical-chemical techniques and bacterial whole-cell biosensors, have been developed for the detection of AHLs in the supernatants of bacterial cultures, only a few of them have been applied to AHL monitoring in real samples. In this paper, we report work performed in our laboratory and review that from others that describes the detection of AHLs in biological, clinical samples, and report some of our recent experimental results.     

Thermoanalytical and microscopical investigation of the microstructure of emulsions containing polymeric emulsifier

Polymeric emulsifiers provide exceptional stability to oil-in-water, water-in-oil or multiple emulsions by their steric stabilization. Pemulens as polymeric emulsifiers are able to stabilize o/w type emulsions because their short lipophilic part integrates into the oil droplets while their long hydrophilic part forms a micro gel around the droplet. In our present study the microstructure and integration of the polymeric emulsifier at the water-oil interface was investigated with thermogravimetric and microscopical methods. It was established that depending on the amount of both of the polymeric emulsifier and added coemulsifier the microstructure of the system changes.     

Electrostatic interactions between a protein and oppositely charged micelles

Micellar solutions made of a fully fluorinated surfactant, LiPFN, form water-soluble complexes with lysozyme in a wide concentration range. Such complexes are stabilized by electrostatic and, very presumably, double-layer interactions. The mixtures were investigated by combining electrophoretic mobility, DLS, and dielectric relaxation methods. The former gives information on the surface charge density of protein-micelle complexes and indicates that the resulting adducts retain a negative charge (i.e., charge neutralization is incomplete). The double-layer thickness of proteins, micelles, and protein-micelle complexes is also connected to the dielectric relaxation frequency. Changes in particle size (inferred by DLS), charge density, and double-layer thickness are closely interrelated to each other. A model was developed to quantify such properties.     

Lipase-catalyzed preparation of corticosteroid 17α-esters endowed with antiandrogenic activity

Several 17α-monoesters of cortexolone and its Δ⁹-derivative are endowed with antiandrogenic activity. Their synthesis can be accomplished by means of a lipase-catalyzed chemoselective alcoholysis of the corresponding 17α,21-diesters.     

Headspace sampling of the volatile fraction of vegetable matrices

The evolution of vapour phase sampling of the volatile fraction of vegetable matrices, or of products directly related to them, over the period 1996-2007 is reviewed. High concentration capacity headspace (HCC-HS) and dynamic headspace (D-HS) techniques, that is headspace sampling approaches where the analytes in the vapour phase are concentrated into a sorbent, an adsorbent or a solvent, are considered. Advantages, disadvantages and applications to the vegetable field of several successful techniques based on these approaches are critically presented, including in-tube sorptive extraction (INCAT, HS-SPDE), headspace sorptive extraction (HSSE), solid-phase aroma concentrate extraction (SPACE), large surface area HCC-HS sampling (MESI, MME, HS-STE), headspace liquid-phase microextraction (HS-LPME) and dynamic headspace samplings (D-HS). The developments necessary to overcome some of the limits of the above approaches and techniques are also discussed in view of their application to new fields.     

Determination of aflatoxins in hazelnuts by various sample preparation methods and liquid chromatography-tandem mass spectrometry

A sensitive and reliable liquid chromatography-tandem mass spectrometric with electrospray ionization method for determining aflatoxins in hazelnuts has been developed. Three different extraction techniques, such as homogenization, ultrasonic extraction, and matrix solid phase dispersion have been tested and compared in terms of recovery, matrix effect, accuracy and precision. Ultrasound extraction was the most performing sample preparation method. Absolute recoveries for analytes and I.S. ranged from 93 to 101%. Accuracy and precision were calculated using matrix matched calibration, and ranged 91-102% and 2-11%, respectively. CC alpha and CC beta for aflatoxin B1 (EU limit=2 microg/kg) were 2.15 and 2.33 microg/kg, respectively. A ruggedness test performed on three other matrices demonstrated that sonication time was critical and a matrix matched calibration must be constructed for every sort of matrix.     

Glucose-based surfactants with hydrogenated, fluorinated, or hemifluorinated tails: synthesis and comparative physical-chemical characterization

(Hemi)fluorinated hydrophobic chains have been found to minimize the denaturating propensity of surfactants toward membrane proteins. The work reported herein deals with the synthesis of a new series of non-ionic glucose-based surfactants endowed with a hybrid hemifluorocarbon chain. The convergent synthesis is based on a one-pot reduction/alkylation of hemifluorinated thioacetate and glucosylated trishydroxymethyl acrylamidomethane using NaBH4 in methanol. This "mild" alkylation was studied in order to improve yields and to pass up the use of an excess of commercially unavailable hemifluorinated thiols. The physical-chemical properties in aqueous solution of this novel series were studied by surface tension measurement and dynamic light scattering (DLS), as well as their behavior upon reverse-phase chromatography, and were compared with those of their hydrogenated and perfluorinated analogues. The atypical effect of the additional ethyl tip to the fluorinated chain was demonstrated by higher critical micellar concentration values and abnormal hydrophobicities measured by reverse-phase chromatography. Moreover, according to Israelachvili's concept, DLS studies showed that surfactants bearing bulkier polar head self-assemble into small and well-defined aggregates, suggesting the formation of spherical micelles rather than the cylindrical ones usually observed with classical fluorinated surfactants.