Comparison of the mass spectra of 6-thiotheophyllines and 6-sulfinytheophyllines

Under electron impact, 6-thiotheophyllines eliminate various fragments from the pyrimidine moiety. In a retro Diels-Alder reaction, they lose the fragment X?C?NCH₃ from positions 1 and 2 of the pyrimidine ring. In 6-sulfinyltheophyllines, the sulfinyl group is the main target for fragmentation; it can lose either oxygen or sulfur, and the abundance of [M—16]⁺ and [M—32]⁺ is much higher than the abundance of the molecular ion. Elimination of the sulfur atom of the 6-sulfinyl substituent, with retention of its oxygen, may be explained by intermediate formation of a ring. All further fragmentations of the 6-sulfinyl derivatives proceed by a primary loss of oxygen or sulfur, followed by elimination of fragments from the pyrimidine moiety, similar to the primary processes, observed in the mass spectra of the 6-thiotheophyllines.     

Epidermal lignin deposition in quinoa cotyledons in response to UV-B radiations

UV-B radiation (280-320 nm) is harmful to living organisms and has detrimental effects on plant growth, development and physiology. In this work we examined some mechanisms involved in plant responses to UV-B radiation. Seedlings of quinoa (Chenopodium quinoa Willd.) were exposed to variable numbers of UV-B radiation doses, and the effect on cotyledons was studied. We analyzed (1) cotyledons anatomy and chloroplasts ultrastructure; (2) peroxidase activity involved in the lignification processes; and (3) content of photosynthetic pigments, phenolic compounds and carbohydrates. Exposure to two UV-B doses induced an increase in the wall thickness of epidermal cells, which was associated with lignin deposition and higher activity of the peroxidase. The chloroplast ultrastructure showed an appearance typical of plants under shade conditions, likely in response to reduced light penetration into the mesophyll cells due to the screening effect of epidermal lignin deposition. Exposure to UV-B radiation also led to (1) enhancement in the level of phenolics, which may serve a protective function; (2) strong increase in the fructose content, a fact that might be related to higher requirement of erythrose-4P as a substrate for the synthesis of lignin and phenolics; and (3) reduction in the chlorophyll concentration, evidencing alteration in the photosynthetic system. We propose that the observed lignin deposition in epidermal tissues of quinoa is a resistance mechanism against UV-B radiation, which allows growing of this species in Andean highlands.     

An evaluation of some simple sulfonic acids as nonaqueous titrants

The simple aliphatic and aromatic sulfonic acids show evidence of possibilities as new titrants in a glacial acetic acid medium. Excellent precision is obtained in potentiometric titrations with both ethane- and methane sulfonic acids with a standard deviation of 0.2%. Benzenemonosulfonic and naphthalenesulfonic acids both give an average precision of 0.4%. In visual titrations with with crystal violet indicator, the color changes at the end-point are very sharp. The chief advantage of these acids as titrants lies in the fact that they dissolve readily in glacial acetic acid and can be titrated to give reproducible results with the glass-calomel electrode system. None of the sulfonic acids tested was as strong a titrant as perchloric acid, but, unlike perchloric acid, they did not form precipitates or gels in the titration with potassium acid phthalate.     

On the analytic solutions of the monoenergetic neutron transport equation for slab geometry

The classical initial value problem for the monoenergetic neutron transport equation in slab geometry is solved, using the power series method. A general formula for analytic solutions of this equation is presented. It is shown that a polynomial solution exists only forc=1 and is linear inx and . Other analytic solutions are given in a closed form. The Taylor series expansion method is compared with the spherical harmonic approach.

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Zusammenfassung Das klassische Eigenwertproblem für die monoenergetische Neutronentransportgleichung in ebener Geometrie wird mit Hilfe der Taylorreihe gelöst und eine allgemeine Formel für analytische Lösungen dieser Gleichung angegeben. Es wird gezeigt, dass die Polynomiallösung nur fürc=1 exisitiert und linear ist in undx. Obwohl die analytischen Lösungen nur beschränkt praktische Anwendung haben zeigt sich, dass die abgebrochene Taylorreihe für praktische Probleme verwendbar ist. Rechnungen mit der abgebrochenen Taylorreihe wirden mitP _N -Rechnungen verglichen.

     

Initial members of the family of molecular mid-valent high-nuclearity iron nitrides: [Fe4N2X10]4- and [Fe10N8X12]5- (X = Cl-, Br-)

Current theoretical and experimental evidence points toward X = N as the identity of the interstitial atom in the [MoFe7S9X] core of the iron-molybdenum cofactor cluster of nitrogenase. This atom functions with mu6 bridging multiplicity to six iron atoms and, if it is nitrogen as nitride, raises a question as to the existence of a family of molecular iron nitrides of higher nuclearity than known dinuclear Fe(III,IV) species with linear [Fe-N-Fe]5+,4+ bridges. This matter has been initially examined by variation of reactant stoichiometry in the self-assembly systems [FeX4]1-/(Me3Sn)3N (X = Cl-, Br-) in acetonitrile. A 2:1 mol ratio affords [Fe4N2Cl10]4- (1), isolated as the Et4N+ salt (72%). This cluster has idealized C2h symmetry with a planar antiferromagnetically coupled [Fe(III)4(mu3-N)2]6+ core containing an Fe2N2 rhombus to which are attached two FeCl3 units. DFT calculations have been performed to determine the dominant magnetic exchange pathway. An 11:8 mol ratio leads to [Fe10N8Cl12]5- (3) as the Et4N+ salt (37%). The cluster possesses idealized D2h symmetry and is built of 15 edge- and vertex-shared rhomboids involving two mu3-N and six mu4-N bridging atoms, and incorporates two of the core units of 1. Four FeN2Cl2 and four FeN3Cl sites are tetrahedral and two FeN5 sites are trigonal pyramidal. The cluster is mixed-valence (9Fe(III) + Fe(IV)); a discrete Fe(IV) site was not detected by crystallography or M?ssbauer spectroscopy. The corresponding clusters [Fe4N2Br10]4- and [Fe10N8Br12]5- are isostructural with 1 and 3, respectively. Future research is directed toward defining the scope of the family of molecular iron nitrides.     

Evaluation of Accuracy of Electrochemical Isoflavonoid Index for the Determination of Total Isoflavones in Soy Samples

The accuracy of a novel electroanalytical route to determine total isoflavones using a secondary standard from Drug Master File (SW/1211/03) as metrological reference with well‐known traceability and its applicability using representative soy samples is demonstrated. Calibration protocols were used i) for choosing a suitable isoflavone standard to determine the total isoflavone content, ii) to evaluate matrix effects and, iii) to evaluate the overall reliability and performance of the method in analytical operations, extraction and analysis. The inherent electroactivity of both, aglycones and glycoside structures and the similar analytical sensitivity exhibited by the prominent soy isoflavones was relevant to determine the total amount with reliability in terms of accuracy (E<10%) and precision (RSDs<7%) in soy samples. In consequence, the introduction of the term isoflavonoid index as the total amount of isoflavones obtained when they are amperometrically monitorized at +1.0 V as a particular case of the electrochemical index concept is proposed.     

EFFECT OF PHOTIC STIMULATION ON THE HUMAN MENSTRUAL CYCLE

To test the hypothesis that artificial light can be used to regularize the human menstrual cycle, 16 women with histories of menstrual irregularity and/or abnormally long cycles were studied. It was assumed that a 29-day cycle is the "normal" length. Thus, light exposure was begun on the evening of day 14, with the expectation that ovulation would be triggered by day 15 and menstruation on day 30. The light regimen was continued for 2-3 nights more. Temperature graphs indicated all subjects were ovulating. 41 control and 41 matching experimental cycle lengths were obtained. The experimental cycle lengths were less variable than the control lengths and showed a sharp peak at 29 days. In the 11 subjects exposed to light for more than 1 cycle, 9 showed a decrease in the range of cycle length (3.3% level of significance difference between control and experimental groups in terms of cycle length). It is concluded that these data provide evidence that photic stimulation can regularize menstrual cycle length and thus influence the time of ovulation, thereby facilitating use of the rhythm method of birth control. Further studies involving larger samples and more sophisticated measurements of ovulation in relation to photic stimulation are recommended.     

Transformation of schiff bases derived from alpha‐naphthaldehyde. Synthesis,spectral data and biological activity of new‐3‐aryl‐2‐(α‐naphtyl)‐4‐thiazolidinones and N‐aryl‐N‐[1‐(α‐naphthyl)but‐3‐enyl]amines

New N‐aryl substituted 2‐(α‐naphthyl)‐4‐thiazolidinones were prepared by the cyclocondensation of α‐mercaptoacetic acid and corresponding N‐(α‐naphthyliden)anilines. The same starting materials were utilized to obtain a new series of N‐aryl‐N‐[1‐(α‐naphthyl)but‐3‐enyl]amines, which was synthesized through an addition of the Grignard reagent (allylmagnesium bromide) to the double bond C?N of the aldimines. The antichagasic and trichomonacidal in vitro activity, as well as, the antifungal and cytotoxic properties of some of these compounds were evaluated.     

Preparation of de novo globular proteins based on proline dendrimers

A synthetic method for the preparation of protein-like globular dendrimers derived from a combination of proline, glycine and imidazolidin ring as branching unit is described. The methodology allows the synthesis of novel peptide dendrimers up to fourth generation. Dendrimers were synthesized by a convergent solid-phase peptide synthesis approach. The conformational properties of branched polyproline peptides and proline dendrimers were studied by CD experiments. CD data suggest conformational plasticity of branched peptides for PPI and PPII, and a stable well-defined secondary structure of proline dendrimers for PPII.     

Analysis of T-2 and HT-2 toxins in cereal grains by immunoaffinity clean-up and liquid chromatography with fluorescence detection

A sensitive, precise and accurate method has been developed for the simultaneous determination of T-2 and HT-2 toxins in cereal grains at ppb levels using high-performance liquid chromatography (HPLC) with fluorescence detection and 1-antroylnitrile (1-AN) as labeling reagent after immunoaffinity clean-up. Cereal samples were extracted with methanol/water (90:10, v/v), and the extracts were cleaned-up through commercially available immunoaffinity columns containing monoclonal anti-T-2 antibodies (T-2 test HPLC, Vicam). T-2 and HT-2 toxins were quantified by reversed-phase HPLC with fluorometric detection (excitation wavelength 381 nm, emission wavelength 470 nm) after derivatization with 1-AN. The monoclonal antibody showed 100% cross-reactivity with both T-2 and HT-2 toxin, and the immunoaffinity column clean-up was effective up to 1.4 microg of both toxins. The method was successfully applied to the analysis of T-2 and HT-2 toxins in wheat, maize and barley. Recoveries from spiked samples with toxin levels from 25 to 500 microg/kg ranged from 70% to 100%, with relative standard deviation generally lower than 8%. The limit of detection of the method was 5 microg/kg for T-2 toxin and 3 microg/kg for HT-2 toxin, based on a signal-to-noise ratio 3:1. HT-2 toxin was detected in ten naturally contaminated wheat samples out of 14 samples analyzed, with toxin levels ranging from 10 to 71 microg/kg; three of them contained also T-2 toxin up to 12 microg/kg.