Influence of Dab2 and Pro3 configuration of [Leu]-enkephalins on the interactions with β-cyclodextrin studied by fluorescence spectroscopy, microcalorimetry and 1H NMR spectroscopy

Natural enkephalins and their analogues are very important as potential therapeutic agents (analgetics). Herein we describe the influence of Dab and Pro chirality of cyclic [Leu]enkephalins (X¹-c[Dab²-Pro³-βNal(2)⁴-Leu⁵], where X = Tyr or Phe) on the binding constant with β-cyclodextrin and spatial and mutual orientation of guest and host molecules. The formation of complexes is enthalpy driven for all cyclic [Leu]enkephalins studied as well as for Nal and AcNalNH₂. Moreover, change of Dab residue configuration has a greater influence on changes of the binding constant of cyclic enkephalin with β-CD than change of Pro chirality has. Also, the replacement of Tyr¹ residue by Phe¹ substantially changes the peptide chain conformation. An analysis of 2D NMR spectra reveals that, apart from inclusion complex formed by penetration of cyclodextrin cavity from wider and narrow rims by Nal, Tyr or Phe or Leu residue, a side and/or bottom association complexes are formed.     

Terahertz time-domain spectroscopy of some pentoses

1 Introduction Terahertz time-domain spectroscopy (THz-TDS) is a new spectral technique based on femto-second laser technology developed since the 1980s[1]. Terahertz (THz) waves lie between the infrared and microwave bands in the electromagnetic spectrum covering the frequency range from 100 GHz to 10 THz. Despite great scientific interest, the THz frequency range re- mains one of the least tapped regions of the electro- magnetic spectrum because there are neither conven- ient high-power…     

Negative ion photoelectron spectroscopy of teo−

We have recorded the photoelectron spectrum of Te0⁻ using a hot-cathode discharge ion source and a negative ion photoelectron spectrometer. The adiabatic electron affinity of TeO is determined to be 1.697±0.022 eV. The negative ion parameters determined in this work are: (w_e″(TeO⁻) = 690 ± 80 cm⁻¹, r_e″(TeO⁻) = 1.884 ± 0.028 Å. and D_o     

Raman spectroscopy in the near infrared – a most capable method of vibrational spectroscopy

Raman spectroscopy has enjoyed a dramatic improvement during the last years: The interference by the fluorescence of impurities is virtually eliminated, the sample preparation is considerably easier as for infrared spectroscopy and many applications in routine analytics, quality control and process control in various branches of industry are now possible. It is shown that the up-to-date near-infrared Raman spectrometers now meet most demands for a modern analytical instrument concerning applicability, analytical information and convenience. It can be anticipated that Raman spectroscopy will catch up infrared spectroscopy, the current workhorse of vibrational spectroscopy.     

Study of ε-caprolactone polymerization by NIR spectroscopy

Near-infrared (NIR) spectroscopy is proposed for the in-line quantitative and kinetic study of the polymerization of ε-caprolactone and eventually to facilitate real-time control of the manufacturing process. Spectra were acquired with a fibre-optic probe operating in transflectance mode immersed in the reactor. The NIR data acquired were processed using a multivariate curve resolution alternating least squares (MCR-ALS) algorithm. The proposed method allows calculation of the concentration and spectral profiles of the species involved in the reaction. The key point of this method is the lack of reference concentrations needed to perform the MCR-ALS method. The use of an extended spectral matrix using both process and pure analyte spectra solves the rank deficiency. The concentration profiles obtained were used to calculate a kinetic fitting of the reaction, but the method was improved by applying kinetic constraints (hard modelling). The rate constants of batches at different temperatures and the energy of activation for this reaction were calculated. Whenever possible, the hard modelling combined with the MCR-ALS method improves the fit of the experimental data: the results show good correlation between the NIR and reference data and allow the collection of high-quality kinetic information on the reaction (rate constants and energy of activation).     

Investigation of hydration of α-amino acids by means of absorption millimeter spectroscopy

The hydration indexes for 19 protein -amino acids are measured by means of absorption millimeter spectroscopy (AMS) at 31.42 GHz. The plot of the hydration indexes on the area of surface of aliphatic amino acid molecules accessible for water is a straight line located above the points corresponding to aromatic or polar amino acids. The contribution of nonpolar groups in the hydration index is greater than that of polar groups provided that their accessible surface areas are equal. The contribution to hydration of -OH and-CONH₂ groups in Ser. Gin, and Asn coincides in sign with that of pure hydrophobic hydration but the value of the contribution is significantly smaller. The change in mobility of water molecules, which is the basis of the AMS method, may serve as the physicochemical foundation for the construction of a new hydrophobicity scale for amino acids comparable with the already existing scales.Deceased September 2, 1995.Translated fromIzvestiya Akodemii Nauk. Seriya Khimicheskaya, No. 3, pp. 618–622, March, 1996.     

Photoelectron spectroscopy and electronic structures of β-diketonate complexes of rare-earth elements

The electronic structures of lanthanide tris(β-diketonate) complexes and their adducts, being of interest as luminophores, were studied by UV photoelectron spectroscopy of vapors and X-ray photoelectron spectroscopy. The spectral regularities identified by the density functional theory revealed the influence of the substitution of the Me groups in the ligands by Bu^t, CF₃, and neutral ligand in the adducts on the electronic structure of the complexing agent from Pr to Lu.     

Fluorescence spectroscopy of fulvic acids’ interaction with surfactants

Fluorescence spectra of two fulvic acid (FA) samples, FA0 from underground water and FA1 from forest soil, were recorded in various surfactant solutions. Alkyltrimethylammonium ions with different alkyl chain lengths induced a decrease in the fluorescence intensity for both FAs at concentrations below the critical micelle concentration (cmc) and an enhancement above the cmc. The intensity minimum thus obtained at the cmc was deeper for surfactants with longer alkyl chains. This effect was attributable to the formation of insoluble FA–surfactant complexes below the cmc and to the solubilization of the complex into micelles above the cmc. Dodecylpyridinium chloride caused a monotonic decrease in the FA fluorescence even far above the cmc. This was attributable to the quenching of FA fluorescence by the positioning of the pyridinium head group near the FA fluorophore. Anionic and nonionic surfactants showed little to no effect on the FA fluorescence.     

M?ssbauer spectroscopy and structural analysis of solids

Mössbauer spectroscopy is reviewed as a method of analysis of hyperfine interactions in the solid state. It is sensitive both to the atomic scale and to phase structures. It utilizes the interactions between the hyperfine fields and nuclei in solids measured by a nuclear technique. The importance of various Mössbauer isotopes is discussed, the ⁵⁷Fe being still the most important. Principles of the qualitative determination of the structure sites and/or phase attachment are explained on the basis of the measurement of hyperfine structure parameters (i.e. the isomer (chemical) shift, the quadrupole and magnetic splittings). The role of the hyperfine field distribution determination is stressed, especially the magnetic hyperfine induction distribution in magnetically ordered solids. Conditions are explained for the feasibility of quantitative estimations of site occupancy and phase abundance. With respect to the predominant role of the magnetic hyperfine structure predestinating Mössbauer spectroscopy to be considered simultaneously as a special magnetic measuring technique, examples are chosen from the field of new magnetic materials. For the substituted hexagonal (M-type) ferrites (aimed, e.g., for the perpendicular magnetic recording), Mössbauer determination of the cation site occupancy is discussed. Structural changes in ion implanted Fe-B-based amorphous alloys detected by the hyperfine field distribution are shown. For the magnetically extremely soft FeCuNbSiB alloys, produced by the controlled crystallization of an amorphous ribbon, the estimation of their rather complicated phase composition by the Mössbauer phase analysis is demonstrated.Common enterprise of the Department of Low Temperature Physics with the Institute of Physics and Institute of Inorganic Chemistry, Czech Academy of Sciences, Prague     

Infrared laser spectroscopy of the fundamental band of a 3π CO

Many rotational components of the fundamental band of metastable a ³Π CO have been measured in absorption using diode laser spectroscopy with concentration modulation detection. Line positions are in good agreement with predictions from optically derived parameters. Resolved or partially resolved splittings arising from lambda-doubling appear for the three Ω components. Splittings in the Ω = 1 and 2 spectra agree satisfactorily with molecular beam (rf) and microwave results while those in the Ω = 0 fundamental deviate by several linewidths (up to 0.015 cm-⁻¹) from calculated values.     

Rapid determination of enantiomeric excess of α-chiral cyclohexanones using circular dichroism spectroscopy

Ketone handedness was discriminated using circular dichroism (CD) spectroscopy by monitoring the metal-to-ligand charge transfer (MLCT) bands of complexes between [Cu(I)((S)-1)(CH(3)CN)(2)]PF(6) and derivatized α-chiral cyclohexanones (4). This method was able to quantify the enantiomeric excess of unknown samples using a calibration curve, giving an absolute error of ±7%. The analysis was fast, allowing potential application of this assay in high-throughput screening (HTS).     

Rapid determination of enantiomeric excess of α-chiral aldehydes using circular dichroism spectroscopy

A method for enantiodiscrimination of α-chiral aldehydes is reported. The method utilizes circular dichroism (CD) spectroscopy and a sensing ensemble composed of 2-(1-methylhydrazinyl) pyridine (1) and Fe(II)(TfO)₂. Aldehydes react rapidly with hydrazine (1) to form chiral imines, which form complexes with Fe(II). By monitoring the CD bands above 320 nm, one can determine the enantiomeric excess (ee) values of α-chiral aldehydes with an average absolute error of ±5%. The analysis was fast, and thus can have potential applications in high-throughput screening (HTS) of catalytic asymmetric induction.     

Determination of vinyl orientation of mouse neuroglobin by 2D nuclear Overhauser spectroscopy

1H NMR has been used to determine the 2-,4-vinyl orientation of heme active site from oxidized mouse neuroglobin (mNgb).The NOEs between 3-methyl and Hα, Hβ of 2-vinyl, together with the NOEs between 5-methyl and Hα, Hβ of 4-vinyl, allowed the unambiguous determination of trans and cis orientations for the 2- and 4-vinyl groups in the mNgb, respectively.     

Illuminating the flesh of bone identification – An application of near infrared spectroscopy

Near infrared (NIR) reflectance spectroscopy coupled with chemometric analysis was evaluated as a non-destructive tool to discriminate skull bone samples from different animal species. In total 70 skull bones from animals of three classes (mammalians, avian and reptiles) were scanned in the wavelength range between 950 to 1650 nm. Principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were used to analyse the NIR spectra of the skull samples. Correct classification rates of 96% and 81% were obtained for the classification of skull bone samples according to avian and mammalian classes, respectively. Overall, a 91% correct classification rate was obtained for the classification of skull samples according to the class (mammalian and avian). This study demonstrates the potential of NIR spectroscopy coupled with chemometric as data processing, as a means of a rapid, non-destructive classification technique for skull bone samples.     

Determination of debye temperatures of supported ion particles by m?ssbauer spectroscopy

The Debye temperatures of alumina- and titania-supported iron particles were determined using Mössbauer spectroscopy between 5 and 280 K. The Debye temperatures were obtained from a nonlinear optimization algorithm using the temperature dependence of the second order Doppler shift (SOD) and the resonant absorption area (RAA). To test its reliability, the same method was used to determine of an -iron-foil and pyrophoric iron.     

Friction force spectroscopy of β- and κ-casein monolayers

Friction force spectroscopy (FFS) has been applied to study the tribological properties of β- and κ-casein layers on hydrophobic substrates in aqueous solutions. Nanometer-sized imaging tips were employed. This allowed exerting and determining the high pressures needed to remove the layers and registering the topographic evolution during this process. Both β- and κ-casein layers showed similar and not particularly high initial frictional responses (friction coefficient of ～1 when measured with a silicon nitride tip). The pressures needed to remove the layers were of the same order of magnitude for both proteins, ～10(8) Pa, but slightly higher for those composed of β-casein. The technique has also shown to be useful in studying the two-dimensional lateral diffusion of the proteins and the wear on the layers they form.     

Determination of configurational–isomeric composition of synthetic isoprene rubbers using NMR spectroscopy

Production pieces of synthetic isoprene rubbers are studied using the nuclear magnetic resonance spectroscopy method. The measurements are performed by ¹Н and ¹³С NMR spectroscopy with variation of the conditions of sample preparation and taking and processing of spectra, which allows improving the accuracy of quantitative analysis of the content of monomer units characterized by different configurations.     

Comparison of high-performance liquid chromatography — Mass spectroscopy and capillary electrophoresis— mass spectroscopy for the analysis of phenolic compounds in diethyl ether extracts of red wines

Summary Reversed-phase high-performance liquid chromatography-mass spectroscopy (HPLC-MS) and capillary electrophoresis-mass spectroscopy (CE-MS) have been compared for the analysis of phenolic compounds in diethyl ether extracts of red wines. MS was performed in the electrospray negative-ionization mode. Despite the much higher separation efficiency of CE compared with LC, LC-MS furnishes far superior information for elucidation of the structure of the constituents. LC-MS enabled the identification of twenty-four compounds whereas only thirteen were characterized by CE-MS.     

Determination of α-amylase activity using Fourier transform infrared spectroscopy

A new method for the determination of -amylase activity in aqueous solutions and human serum with FTIR-spectroscopy is proposed. The chemical reaction catalyzed by the enzyme under study can be followed directly when applying FTIR-spectroscopic detection also in the case, where no colored or electrochemical active species are generated or consumed during the course of the reaction of -amylase with simple starch. Therefore the determination of the -amylase activity could successfully be performed by recording two FTIR-spectra, one immediately after mixing the sample and a substrate (starch-) solution and the other after a 20 min reaction time. From these two FTIR-spectra a difference spectrum was calculated hereby eliminating an unspecific absorption of the matrix. The intensities of the resulting difference spectra corresponded to the extent of the reaction which took place during the investigated time interval and hence could be related to the activity of the enzyme in the sample. The developed method is linear from 80 to 1400 U/l (r.s.d.=5% for 700 U/l) in aqueous solutions and was also successfully applied to the determination of -amylase activity in human serum where a linear working range from 100 to 800 U/l (r.s.d.=11% for 150 U/l) was achieved.