Polaron-exciton model of resonance energy transfer

It is shown that F?rster's expression for the electronic energy transfer rate can be recast in a form predicted for exciton motion that interacts strongly with molecular vibrations. Using a simple model based on the Kennard-Stepanov theory, F?rster's expression for the spectral overlap is shown to be of a thermally activated form, as obtained previously by multiphonon theory. In contrast, the high-frequency internal vibrations contribute a factor which results from tunneling through a potential barrier between potential curves in the configuration coordinate diagram. We thus show that resonance energy transfer is equivalent to phonon-assisted hopping of a trapped excitonic polaron.     

Separation of steroid compounds by overloaded preparative chromatography with precipitation in the fluid phase

In order to gain a commercially acceptable yield compared to the adsorption capacity of the column, a rather large amount of sample is separated with preparative chromatography. During the competitive adsorption of the sample-components, the species adsorbing better can force the rest out of the adsorbent phase. As a consequence, the concentrations of the later components may increase in the fluid phase to a level that those species start to precipitate. A mathematical model which takes the precipitation and dissolution into consideration is presented in this paper. Data calculated by this model are compared to that we obtained by using a previous mathematical model as well as the experimental results gained by a laboratory scale separation of steroid compounds on an organic polymer adsorbent. The equilibrium adsorption-desorption and equilibrium precipitation-dissolution is the first approximation of the complicated process mentioned above. In our next publication we are to extend the model with kinetic terms belonging to adsorption-desorption and precipitation-dissolution process respectively.     

Enumeration of wurtzite derivatives and related dipolar tetrahedral structures

Pólya's theorem and related results are used to count and classify by space group all possible wurtzite derivatives with small unit cells having composition ABX₂, AB₂X₃, AB₃X₄, or ABC₂X₄. The same arguments are applied to the dipolar tetrahedral structures, which resemble wurtzite but have a different pattern of occupancy of the tetrahedral voids in the hcp anion framework. Covalent molecular orbital and electrostatic calculations are used to study the two real and eight hypothetical structures for Li₃PO₄. Both predict shared edges to be destabilizing, in keeping with Pauling's rules.     

Beitrag zur photometrischen Bestimmung von Penicillin mit p-Dimethylaminobenzaldehyd

Zusammenfassung Es wird eine photometrische Methode zur quantitativen Bestimmung von Penicillin mit p-Dimethylaminobenzaldehyd beschrieben. Die Farbreaktion ist auf eines der Spaltprodukte zurückzuführen, die sich bei der saueren Hydrolyse des Penicillins bilden. Die hydrolytische Spaltung wird am besten durch 1 stündiges Erwärmen im siedenden Wasserbad mit 6 n Schwefelsäure durchgeführt. Für den Konzentrationsbereich bis zu etwa 0,08 mg Penicillin/ml Lösung hat das Beersche Gesetz seine volle Gültigkeit. 0,01 mg Penicillin/ml kann noch quantitativ erfaßt werden.     

Triterpenoids from Abies species

From an acid fraction of an ethereal extract of Siberian fir needles two new stereoisomeric acids, the molecules of which have a modified lanostane carbon skeleton, have been isolated in the form of methyl esters. The structures of the molecules of these substances have been established by the use of¹³C and¹H NMR,¹H-¹H and¹³C-¹H two-dimensional NMR spectra, circular dichroism, and chemical transformations as (24Z)- and (24E)-8(14 13)-abeo-17,13-friedo-lanosta-8,14(30),24-triene-3,23-dion-26-oic acids.Institute of Organic Chemistry, Siberian Branch, Academy of Sciences of the USSR, Novosibirsk. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 511–517, July–August, 1991.     

Analysis of terbutaline in human plasma by high-performance liquid chromatography with electrochemical detection using a micro-electrochemical flow cell.

A high-performance liquid chromatographic method is described for the determination of terbutaline in human plasma in the range 1-35 ng/ml. Detection was achieved using a carbon fibre micro-electrochemical detector and a column-switching system. The microelectrode cell has advantages over conventional glassy carbon electrode-based detection systems in that it is easy to prepare, flexible in its operation and suffers less trouble from problems such as air bubbles and leaks. Furthermore, it has a better detection limit for terbutaline (0.8 ng/ml) to that obtained using a conventional glassy carbon electrode flow detector (2 ng/ml). Sample clean-up was by on-line solid-phase extraction with column switching, providing a method which was sensitive and reproducible, where the mean overall coefficient of variation was 5.60% and drug recovery in excess of 86% at the concentration levels studied.     

A high-performance liquid chromatographic assay of the electro-oxidation of purines : Uric Acid and the Nucleotide Drug Tubercidin-5′-Monophosphate

A high-performance liquid chromatographic assay is described for establishing the completeness of electro-oxidation of a purine nucleotide drug tubercidin-5′-monophosphate (TMP) and the sequence of product formation. The assay shows that TMP was completely oxidized after ca. 2 h of electrolysis and that the product distribution continued to change after this time. The same assay was also used to show the sequence of product formation in the electro-oxidation of uric acid. Both separations were isocratic, with a 0.02 M potassium dihydrogenphosphate (pH 4.6–5.1) mobile phase.     

Investigations in the fie ld of substituted furanurona ldehydes steric directivity of the nitromethane condensation

Summary 1. The condensation of the anomeric methyl 2,3-di-O-benzyl-D-xylofuranosiduronaldehydes with nitromethane has been studied.2. It has been shown that the position of the substituent at the glycosidic center has an influence on the steric directivity of this reaction.3. The structure of the 6-nitro-6-deoxyhexofuranosides synthesized has been confirmed by their conversion into known derivatives of methyl D-glucofuranosides.Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 8–12, January–February, 1972.     

Reactions of dithiocarbamic acids derived from alkaloids, morpholine, and piperidine with acrylic acid and its derivatices

-(Thiocarbamoylthio)propionic acids derived from alkaloids, morpholine, and piperidine and their esters, amides, and nitriles were prepared by reactions of the corresponding dithiocarbamic acids with acrylic acid and its derivatives. Some of the compounds were tested for insecticidal activity.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 8, 2004, pp. 1336–1339.Original Russian Text Copyright © 2004 by Zhivotova, Gazaliev, Ibraev, Fazylov, Kasenov.     

Regioselective hydroborations of methylvinylchlorosilanes

The regioselectivity of the hydroboration of the methylchlorovinylsilanes, Cl_nMe_3?nSiCHCH₂ (n= 0 ? 3), has been investigated using BH₃←THF, 9-BBN, disiamyl- and dicyclohexylborane. Methylation of the adducts with methylmagnesium bromide is complicated by formation of tetraalkylboronates. Alkaline hydrogen peroxide oxidation of the boronates gives reasonable yields of the corresponding α- and β-trimethylsilylethanols forn= 0 and 1. Forn= 2 and 3, conversion of the adducts to the corresponding α- and β- deuteroethylsilanes by treatment with excess sodium methoxide in methanol-0-d provides a more effective means of derivatization. Addition of the alkenes,n= 2 or 3, to excess BH₃←THF givesca. 90% of the α-boro-organo-chlorosilanes. For all of the alkenes, the dialkylboranes giveca. 80% of the β-boron adducts.