A strong form of the quantitative isoperimetric inequality

We give a refinement of the quantitative isoperimetric inequality. We prove that the isoperimetric gap controls not only the Fraenkel asymmetry but also the oscillation of the boundary.     

Quantum chemical modeling of chiral catalysis. Part 14. On the coordination of carbonyl compounds to diaza-, oxaza- and dioxaluminolidines of potential use as chiral controllers in organic synthetic chemistry

Conformers of 4-coordinate adducts of carbonyl compounds and diaza-, oxaza- and dioxaluminolidines were investigated by means of ab initio MO methods (RHF). Formaldehyde was used as a model of carbonyl compounds. Relative stabilities of the conformers indicate formation of syn adducts of carbonyl compounds and aluminolidines (C_C=O and aluminolidine ring syn about the Al---O_C=O bond) to be favoured over that of the corresponding anti ones (all syn/anti ratios higher than 99:1, 6–31G//6–31G). The energetic preference for the formation of syn adducts of oxazaaluminolidines was about twice as high as that of diaza- or dioxaluminolidines of which the syn/anti selectivities were found to be practically equal.     

Total synthesis of amaminol A: establishment of the absolute stereochemistry

The first synthetic route to amaminol A with use of an organocatalytic intramolecular Diels-Alder reaction is reported. The absolute stereochemistry is proven with a crystallographic image of a cyclic carbamate of amaminol A.     

Carbohydrates electrocatalytic oxidation using CNT-NiCo-oxide modified electrodes

A new sensor for an amplified electrochemical detection of carbohydrates is proposed, where carbohydrates are oxidized by CNT-NiCo-oxide composite in basic solutions. Cyclic voltammograms of the modified electrode show a stable and well defined redox couple in alkaline media due to the synergy of Ni(II)/Ni(III) system with Co(II)/Co(III). The modified electrode shows excellent electrocatalytic activity towards monosaccharides oxidation at reduced overpotential in alkaline solutions. Six monosaccharides were determined amperometrically at the surface of this modified electrode with high sensitivity over a wide range of concentrations, from 0.02 up to 12.12 mM. Low detection limit of 5 μM for glucose could be obtained.     

Fourier Transform Infrared Spectroscopy of Aliphatic bis(Amidinohydrazones) and Their Deuterated Analogues

The first study on the infrared spectroscopy of the bis(amidinohydrazones) of various glyoxals is reported. The compounds studied include the antileukemic agents glyoxal bis(amidinohydrazone) and methylglyoxal bis(amidinohydrazone) (Mitoguazone) as well as seven mono-and dialkylglyoxal analogues thereof. Free bases as well as doubly protonated species (divalent salts) were investigated. Selectively deuterated analogues were also studied and were synthesized by exchanging nitrogen-bound hydrogen atoms for deuterium atoms. The effects of substituents, protonation and deuteration on the FT-IR spectra of the compounds are discussed.     

Medial tibial pain: a dynamic contrast-enhanced MRI study.

The purpose of this study was to compare the sensitivity of different magnetic resonance imaging (MRI) sequences to depict periosteal edema in patients with medial tibial pain. Additionally, we evaluated the ability of dynamic contrast-enhanced imaging (DCES) to depict possible temporal alterations in muscular perfusion within compartments of the leg. Fifteen patients with medial tibial pain were examined with MRI. T1-, T2-weighted, proton density axial images and dynamic and static phase post-contrast images were compared in ability to depict periosteal edema. STIR was used in seven cases to depict bone marrow edema. Images were analyzed to detect signs of compartment edema. Region-of-interest measurements in compartments were performed during DCES and compared with controls. In detecting periosteal edema, post-contrast T1-weighted images were better than spin echo T2-weighted and proton density images or STIR images, but STIR depicted the bone marrow edema best. DCES best demonstrated the gradually enhancing periostitis. Four subjects with severe periosteal edema had visually detectable pathologic enhancement during DCES in the deep posterior compartment of the leg. Percentage enhancement in the deep posterior compartment of the leg was greater in patients than in controls. The fast enhancement phase in the deep posterior compartment began slightly slower in patients than in controls, but it continued longer. We believe that periosteal edema in bone stress reaction can cause impairment of venous flow in the deep posterior compartment. MRI can depict both these conditions. In patients with medial tibial pain, MR imaging protocol should include axial STIR images (to depict bone pathology) with T1-weighted axial pre and post-contrast images, and dynamic contrast enhanced imaging to show periosteal edema and abnormal contrast enhancement within a compartment.     

Electron impact induced fragmentations of some 2,2-disubstituted 1,3-dithiolanes

Electron impact induced fragmentations of the title compounds were studied by exact mass measurement and metastable ion analysis. Sulphur atoms within the ring effectively stabilize the positive charge. In most cases the loss of the larger substituent, and not the other, methyl group, gives rise to the base peak in the spectrum. Examination of competing metastable transitions shows that generally this is also the lowest activation energy primary process. In general primary ring cleavage reactions are not important unless there is a heteroatom in the substituent that can assist this cleavage.     

Structure of aminoguanidine hemioxalate. Implications for the synthesis of amidinohydrazones

Summary The crystal and molecular structure of aminoguanidine hemioxalate, a salt in which aminoguanidine exists in the monocation form, was determined by single crystal X-ray diffraction. The salt crystallizes in the monoclinic space group P2(1)/n with unit cell dimensions ofa=4.95,b=10.46,c=10.40 Å, =92.57°, andZ=4. The structure contains one oxalate ion for every two CN₄H ₇ ⁺ ions, the latter being practically planar. The structure of the monocation is largely similar to those of aminoguanidine dications except that the monocation is devoid of one of the protons attached to the terminal hydrazine nitrogen. This result is of interest considering the synthesis of amidinohydrazones, indicating that the concentration of the active nucleophile is nearly maximal even when aminoguanidine exists in the monocation form. Therefore, the synthesis of amidinohydrazones should be performed in thepH range in which aminoguanidine exists mainly in the monocation form,i.e. at apH higher than 2. There is, however, no need to elevate thepH to values at which a considerable proportion of aminoguanidine exists as the free base.

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Die Struktur von Aminoguanidinhemioxalat und ihre Bedeutung für die Synthese von Amidinohydrazonen

Zusammenfassung Die Kristallstruktur von Aminoguanidinhemioxalat, einem Salz, in dem Aminoguanidin als Monokation existiert, wurde mit Einkristallröntgenmethoden aufgeklärt. Das Salz kristallisiert in der monoklinen Raumgruppe P2(1)/n mit den Zellparameterna=4.95,b=10.46,c=10.40 Å, =92.57° undZ=4. In der Einheitszelle kommt ein Oxalation auf je zwei flache CN₄H ₇ ⁺ -Ionen. Die Struktur des Monokations ist bekannten Strukturen des Aminoguanidindikations ähnlich, mit der Ausnahme, daß dem Monokation eines der an das äußere Stickstoffatom der Hydrazingruppe gebundenen drei Protonen fehlt. Dieses Ergebnis ist interessant bezüglich der Synthese von Amidinohydrazonen, da es bedeutet, daß die Konzentration des aktiven Nukleophils auch dann beinahe maximal ist, wenn Aminoguanidin in der Monokationform vorliegt. Synthesen von Amidinohydrazonen sollten daher unter solchen Bedingungen ausgeführt werden, unter denen Aminoguanidin hauptsächlich in der Monokationform existiert (pH höher als 2). Es ist jedoch nicht nötig, beipH-Werten zu arbeiten, die so hoch sind, daß ein bedeutender Teil der Verbindung als freie Base vorliegt.