A new totally reflecting X-ray fluorescence spectrometer with detection limits below 10?11 g

Summary A new type of energy dispersive X-ray-fluorescence spectrometer with totally reflecting sample support is presented. At this instrument the incident beam is reflected twice before it is directed towards the sample support. The detection limits in diluted solutions are below 0.1 ppb for about 20 metals. The influence of the matrix is discussed.

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Ein neuartiges totalreflektierendes Röntgenfluorescenz-Spektrometer mit Nachweisgrenzen unter 10^–11 g

Zusammenfassung Ein neuer Typ eines energiedispersiven Röntgenfluorescenzspektrometers mit totalreflektierendem Probenträger wird vorgestellt. Bei diesem Gerät wird der einfallende Strahl zweimal an Quarzspiegeln reflektiert, bevor er auf den Probenträger gelenkt wird. Die Nachweisgrenzen liegen bei günstiger Matrix für 20 Metalle unter 0,1 ppb. Der Einfluß der Matrix wird diskutiert.

     

A simplified polarographic determination of dissolved Cd(II) at the 10?10 M level

Summary To simplify the determination of dissolved Cd(II) in water and sea water-like solutions at the 10^–10–10^–9 M level an automated concentration step was developed consisting of percolating about 21 of sample over a column with an immobilized reagent (ED₃A) and dissolving the trapped cadmium in 0.1 M nitric acid. A concentration factor of 50 or more is easily obtained. Recoveries are about 90%. With anodic stripping differential pulse polarography as a final determination technique overall standard deviations are in the range of 0.1–0.4·10^–10 Mol of Cd.On leave from Lisbon University, Portugal     

Effect of solvent extraction on the atomic-absorption spectrophotometric determination of traces of copper with zinc dibenzyldithiocarbamate

Summary The utility of various organic solvents, such as acetates and ketones, for the CuDBC chelate extraction and subsequent atomic absorption spectrophotometric determination is studied. Methyl propionate was found to be the most sensitive solvent. Data for the different substances are presented.

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Einfluß der Lösungsmittelextraktion auf die AAS-Bestimmung von Kupferspuren mit Zinkdibenzyldithiocarbamat

Zusammenfassung Die Verwendbarkeit verschiedener Lösungsmittel (Acetate und Ketone) für die Extraktion des CuDBC-Komplexes und anschließende atomabsorptions-spektralphotometrische Bestimmung wurde systematisch untersucht. Werte für die verschiedenen Substanzen werden angegeben. Die größte Empfindlichkeit kann mit Methylpropionat erzielt werden.

We wish to thank President Dr. Yawara Yoshitoshi and Prof. Dr. Nobuo Sakurai of Hamamatsu University School of Medicine, for their hospitality and encouragement.     

Thermal expansion of a polydiacetylene single crystal

Summary Fractural length changes l/l of a polydiacetylene (toluene sulfonate) single crystal and its monomer have been measured along the crystallographica-,b-, andc-direction in the temperature range 100 to 400 K. Small steps in the temperature dependence of l/l at 194 K for the polymer and 159 K for the monomer are assumed to be caused by a well known phase transition. From the volume coefficient of thermal expansion the bulk Grüneisenparameter _b has been calculated. Temperature dependence as well as absolute values of _b for the polymer crystal are found to be in accordance with current theories assuming that both inter and intrachain vibrations strongly influence the thermoelastic behaviour of polymer crystals.

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Zusammenfassung Die relative Längenänderung l/l eines Polydiacetylen (Toluolsulfonat) Einkristalls und des zugehörigen Monomerkristalls wurde entlang der kristallographischena-,b-undc-Richtung im Temperaturbereich 100 bis 400 K gemessen. Kleine Stufen im Temperaturverlauf von l/l bei 194 K für den Polymerkristall und bei 159 K für den Monomerkristall werden als Einfluß einer bekannten Phasenumwandlung gedeutet. Aus dem Volumenausdehnungskoeffizienten wurde der Bulk-Grüneisenparameter _b berechnet. Sowohl die Temperaturabhängigkeit als auch absolute Werte von _b für den Polymerkristall befinden sich in Einklang mit theoretischen Modellen, wenn man annimmt, daß sowohl Inter- als auch Intrakettenschwingungen das thermoelastische Verhalten von Polymerkristallen beeinflussen.

     

Synthesis of new cyclolinear permethyloligosilane-siloxanes

α,ω-Bis(heptamethylcyclotetrasiloxanyloxy)oligodimethylsilanes were synthesized for the first time by heterofunctional condensation of hydroxyheptamethylcyclotetrasiloxane with α,ω-dichloropermethyloligosilanes, Cl(Me₂Si) _n Cl (n=2, 4, or 6). The compounds obtained were characterized by spectroscopic methods. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 544–545, March, 1998.     

Conversion of a conventional infrared library into computer-readable form

Summary A conventional infrared spectra collection was converted into computer-readable form. The data format is selected to allow for minimal storage requirements, easy handling, and reconstruction of the source curve.

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Umwandlung einer konventionellen IR-Bibliothek in computerlesbare Form

Zusammenfassung Eine konventionelle Infrarotspektrensammlung wurde in computerlesbare Form übergeführt. Das gewählte Datenformat erlaubt kompakte Speicherung, leichte Verarbeitung sowie Rekonstruktion der Originalkurve.

On leave from the Chemical Institute Boris Kidric, Ljubljana (Yugoslavia).     

A quality index for spectra library search methods

Summary For an objective judgement of spectra library search methods it is necessary to quantify the success of these methods. Therefore, a procedure for calculating a factor to measure the success of a library search method is described. As an example, the application of the method to low-resolution mass spectra is described.Supported by the Ministry of Science of the Land Northrhine-Westphalia     

Reaction potential map analysis of chemical reactivity—III

Reaction potential maps (RPM) have been introduced as a new tool for the study of molecular reactivity. The equipotential energy maps, which are created on given planes around a molecule, define reaction contours towards specific counter-reagent models and are evaluated by perturbation theory. Since the calculated interaction energy involves electrostatic, polarization, exchange, and charge transfer energies, the RPM's can be used to predict site selectivity in a variety of chemical reactions. We found that the calculated RPM's of the SCN^– anion explained well the experimental observations that it reacts at the S atom with soft electrophiles and at the N atom with hard electrophiles. The difference in reactivity between SCN^– and OCN^– was clearly shown by the RPM's of these anions. The ambident nucleophilic nature of the NO ₂ ^– and the CH₂CHO^– anions was also well represented by their RPM's.     

Temperature dependent crystallographic transformations in chalcedony, SiO2, assessed in mid infrared spectroscopy

Chalcedony consists of hydroxylated 50-100 nanometre measuring α-quartz (SiO(2)) crystallites that lose their surface silanole groups (Si-OH) upon heating between 350°C and 600°C. The loss of the chalcedony's ≈1% of silanole groups allows for the healing of water related defects in the crystallites. We investigated these crystallographic transformations using Fourier Transform mid Infrared Spectroscopy in direct transmission, Attenuated Total Reflection (ATR) and the reflectivity. We found that an absorption band that is specific for chalcedony at 555 cm(-1) disappears gradually upon heating between 350°C and 600°C. The reduction of the band is correlated to the loss of surface silanoles. This result leads to the assignment of the band to free Si-O vibrations in non bridging Si-OH groups that have a lower natural frequency than Si-O vibrations in bridging Si-O-Si. The recognition of a silanole signal in the mid infrared allows for an easy, cheap and rapid recognition of hydroxyl in chalcedony.     

l-Lysine-Based Gelators for the Formation of Oleogels in Four Vegetable Oils

Supramolecular oleogel is a soft material with a three-dimensional structure, formed by the self-assembly of low-molecular-weight gelators in oils; it shows broad application prospects in the food industry, environmental protection, medicine, and other fields. Among all the gelators reported, amino-acid-based compounds have been widely used to form organogels and hydrogels because of their biocompatibility, biodegradation, and non-toxicity. In this study, four N^α, N^ε-diacyl-l-lysine gelators (i.e., N^α, N^ε-dioctanoyl-l-lysine; N^α, N^ε-didecanoyl-l-lysine; N^α, N^ε-dilauroyl-l-lysine; and N^α, N^ε-dimyristoyl-l-lysine) were synthesized and applied to prepare oleogels in four kinds of vegetable oils. Gelation ability is affected not only by the structure of the gelators but also by the composition of the oils. The minimum gel concentration (MGC) increased with the increase in the acyl carbon-chain length of the gelators. The strongest gelation ability was displayed in olive oil for the same gelator. Rheological properties showed that the mechanical strength and thermal stability of the oleogels varied with the carbon-chain length of the gelators and the type of vegetable oil. The microstructure of oleogels is closely related to the carbon-chain length of gelators, regardless of oil type. The highest oil-binding capacity (OBC) was obtained in soybean oil for all four gelators, and N^α, N^ε-dimyristoyl-l-lysine showed the best performance for entrapping oils.     

Molar absorptivity and A 1cm 1% values for proteins at selected wavelengths of the visible and ultraviolet regions. XXIV

The molar absorptivity and A _1cm ^1% values for 154 proteins are reported. The conditions under which these values were obtained and citations to the sources of the data are also provided.     

Molar absorptivity and A 1 cm 1% values for proteins at selected wavelengths of the ultraviolet and visible regions. XXII

The molar absorptivity and A _{1 cm} ^1% values for 150 proteins are reported. The conditions under which these values were obtained and citations to the sources of the data are also provided.     

Vibrational linestrengths for the ground and first excited electronic states of HeH<Subscript>2</Subscript><Superscript>+</Superscript>

Together with recent improved potential-energy surface calculations for the ground (X) and first excited (Ã) electronic states of HeH₂ ⁺, the electric dipole moment surfaces for each state and the transition dipole moments connecting the two states were evaluated for the entire range of the energy calculations. Using these functions the linestrengths of all dipole-allowed transitions between the bound vibrational levels within each of the two states (XX) and (ÃÃ) as well as between them (ÃX) are evaluated here. These data are believed to be useful both in the experimental search for the yet unobserved molecular spectra of HeH₂ ⁺ and in evaluating theoretical rates for the radiative association or photodissociation processes involving the two lowest electronic states of the ion.Contribution to the Björn Roos Honorary Issue     

A Direct Carbon-13 and Nitrogen-15 NMR Study of Samarium(III)–Isothiocyanate Complexation in Aqueous Solvent Mixtures

Multinuclear magnetic resonance studies of trivalent lanthanide inner-shell ion-pairing with nitrate and isothiocyanate are continuing. For NCS^– solutions in water–acetone–Freon mixtures at low temperature, generally –100 to –125°C, ligand exchange is slow enough to permit the observation of ¹³C and ¹⁵N NMR signals for coordinated and free anions. For samariuni(III) solutions, four coordinated NCS^–signals, displaced about +35 ppm and +250 ppm from free anion, are observed in the ¹³C and ¹⁵N NMR spectra, respectively. The ¹³C and ¹⁵N NMR data are complementary, showing a signal area concentration dependence and measured coordination numbers consistent with the formation of Sm(NCS)²⁺ through Sm(NCS) ₄ ¹ . The coordination numbers reach a maximum of about three moles of NCS^– per mole of Sm(III) with both nuclides, a result confirmed by spectral appearance showing the dominance of Sm(NCS)₃ at the highest concentration studied. An analysis of the chemical shifts indicates that binding occurs at the nitrogen atom of NCS^–. In water–methanol, due to the higher dielectric constant of such mixtures, coordination was less extensive. A competitive binding study with Ci^– by ³⁵Ci NMR demonstrated conclusively the superior coordinating ability of NCS^–.     

Antioxidant Extracts of Nettle (Urtica dioica) Leaves: Evaluation of Extraction Techniques and Solvents

Nettle (Urtica dioica) is a great source of bioactive compounds. The objective of this study was to evaluate the extraction techniques (ultrasound, without stirring, and stirring), solvents (methanol, water, and ethanol), and extraction times (1–4 h) to maximize antioxidant capacity of the Urtica dioica extracts. In the case of total phenolic content (TPC) and ABTS^•+ (2,2-azino-bis(3-etilbenzotiazolin)-6-sulfonic acid) free radical scavenging values, ultrasound extraction was the most efficient method, while the best results of DPPH^• (1,1-diphenyl-2-picrylhydrazyl) assay in nettle extracts (91.08%) were obtained using stirring extraction, water as solvent, and 3 h of extraction time. Based on the obtained mathematical models, the optimization revealed that the best extraction conditions were ultrasound treatment with water as solvent and an extraction time of 3.15 h, obtaining values of 21.9 mg eq gallic acid/g dried nettle for TPC, 71.8% for %ABTS^•+ and 86.6% for %DPPH^•. This work proves that aqueous extract of nettle leaves through the ultrasound technique is an important source of natural antioxidants and can be considered a potential alternative to synthetic antioxidants.     

The Chemical Constituents from Fruits of Catalpa bignonioides Walt. and Their α-Glucosidase Inhibitory Activity and Insulin Secretion Effect

Catalpa pod has been used in traditional medicine for the treatment of diabetes mellitus in South America. Studies on the constituents of Catalpa species have shown that it is rich in iridoids. In the present study, three previously undescribed compounds (2–4), including two secoiridoid derivatives along with twelve known compounds, were isolated from the fruits of Catalpa bignonioides Walt. In addition, fully assigned ¹³C-NMR of 5,6-dihydroxy-7,4’-dimethoxyflavone-6-O-sophoroside (1) is reported for the first time in the present study. The structures of compounds were determined on the basis of extensive spectroscopic methods, including UV, IR, 1D, and 2D NMR, mass spectroscopy, and CD spectroscopic data. All the isolated compounds were evaluated for α-glucosidase inhibitory activity. Among the tested compounds, compounds 2, 3, and 9 exhibited significant inhibitory activity against α-glucosidase enzyme assay. Meanwhile, the effect of compounds 2, 3, and 9 on glucose-stimulated insulin secretion (GSIS) was measured using pancreatic β-cells. Compounds 2, 3, and 9 exhibited non-cytotoxicity-stimulated insulin secretion in INS-1 cells. The expression levels of proteins associated with β-cell function and insulin secretion such as phosphorylation of total insulin receptor substrate-2 (IRS-2), phosphatidylinositol 3-kinase (PI3K), Akt, activated pancreatic duodenal homeobox-1 (PDX-1), and peroxisome proliferator-activated receptor-γ (PPAR-γ) were increased in INS-1 cells after treatment with compounds 2, 3, and 9. The findings of the present study could provide a scientific warrant for their application as a potential antidiabetic agent.     

A new phytoecdysteroid

A new phytoecdysteroid,viz, 2-deoxy-3-epi-4β, 20-dihydroxycedysone ((20R,22R)-3α,4β 14α,20,22,25-hexahydroxy-5β-cholest-7-en-6-one), named coronatasteronc, was isolated fromSerratula coronata and identified by NMR spectroscopy. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1954–1955, November, 2000.