- Molecular control over semiconductor surface electronic properties: Dicarboxylic acids on CdTe, CdSe, GaAs, and InP
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We present "design rules" for the selection of molecules to achieve electronic control over semiconductor surfaces, using a simple molecular orbital model. The performance of most electronic devices depends critically on their surface electronic properties, i.e., surface band-bending and surface recombination velocity. For semiconductors, these properties depend on the density and energy distribution of surface states. The model is based on a surface state-molecule, HOMO-LUMO-like interaction between molecule and semiconductor. We test it by using a combination of contact potential difference, surface photovoltage spectroscopy, and time- and intensity-resolved photoluminescence measurements. With these, we characterize the interaction of two types of bifunctional dicarboxylic acids, the frontier orbital energy levels of which can be changed systematically, with air-exposed CdTe, CdSe, InP, and GaAs surfaces. The molecules are chemisorbed as monolayers onto the semiconductors. This model explains the widely varying electronic consequences of such interaction and shows them to be determined by the surface state energy position and the strength of the molecule-surface state coupling. The present findings can thus be used as guidelines for molecule-aided surface engineering of semiconductors.
- Cohen,Kronik,Shanzer,Cahen, David,Liu,Rosenwaks,Lorenz,Ellis
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- A L - dibenzoyl tartaric acid for the preparation of dimethyl
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The invention belongs to the technical field of chemical synthesis method, in particular to a L - dibenzoyl tartaric acid for the preparation of dimethyl, the L - dibenzoyl tartaric acid for the preparation of dimethyl, comprises the following steps: S1, to L - tartaric acid, benzoyl chloride, thionyl chloride as the raw material, Lewis acid as catalyst, toluene as the solvent, through esterification, Anhydrized reaction, purification L - dibenzoyl tartaric acid [...]; S2, will be L - dibenzoyl tartaric acid [...] in pure water in the hydrolysis to obtain L - dibenzoyl tartaric acid hydrate wet product; S3, L - dibenzoyl tartaric acid hydrate the wet product in methanol and catalyst under the action of the esterification reaction, purify to get the L - dibenzoyl tartaric acid dimethyl ester. The invention the raw materials used are cheap and easy to obtain, mild reaction conditions, to recycle the methanol can be used repeatedly, after treatment is convenient, and is suitable for industrial production, it is worth.
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- A L-dibenzoyl tartaric acid synthesis method
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The invention discloses a synthetic method of L-dibenzoyl tartaric acid. The synthetic method comprises the following steps: with L-tartaric acid and benzoyl chloride as raw materials, copper sulfate as a catalyst and toluene as a solvent, carrying out reaction to prepare L-dibenzoyl tartaric anhydride, carrying out hydrolysis with an equal amount of water and toluene to obtain the L-dibenzoyl tartaric acid, wherein the toluene serving as the solvent, as well as the water and the toluene in the hydrolysis step can be repeatedly utilized. With the adoption of the synthetic method, the process is simple, the operation is safe and easy, the process recovery ratio achieves above 95 percent, meanwhile, the cost of the raw materials is low, a part of the raw materials can be recovered and recycled, and a finished product is high in purity and excellent in chiral separation performance.
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Paragraph 0099-0102
(2017/03/21)
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- New chiral zwitterionic phosphorus heterocycles: Synthesis, structure, properties and application as chiral solvating agents
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A family of new chiral zwitterionic phosphorus-containing heterocycles (zPHC) have been derived from methylene-bridged bis(imidazolines). These structures were unambiguously determined, including single-crystal XRD analysis for two compounds. The stability, acid/base and electronic properties of these dipolar phosphorus heterocycles were subsequently investigated. zPHCs can be successfully employed as a new class of chiral solvating agents for the enantiodifferentiation of chiral carboxylic and sulfonic acids by NMR spectroscopy. The stoichiometry and binding constants for the donor-acceptor complexes formed were established by NMR titration methods. A convenient synthetic approach to a new class of chiral zwitterionic phosphorus-containing heterocycles starting from methylene-bridged bis(imidazolines) was designed and executed. Stability and properties of the synthesized compounds were investigated. The applicability of the designed compounds as chiral solvating agents for the determination of the enantiomeric excesses of chiral acids was demonstrated. Copyright
- Sheshenev, Andrey E.,Boltukhina, Ekaterina V.,Grishina, Anastasiya A.,Cisa?ova, Ivana,Lyapkalo, Ilya M.,Hii, King Kuok
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p. 8136 - 8143
(2013/07/27)
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- COMPOSITIONS AND METHODS FOR CYCLOFRUCTANS AS SEPARATION AGENTS
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The present invention relates to derivatized cyclofructan compounds, compositions comprising derivatized cyclofructan compounds, and methods of using compositions comprising derivatized cyclofructan compounds for chromatographic separations of chemical species, including enantiomers. Said compositions may comprise a solid support and/or polymers comprising derivatized cyclofructan compounds.
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Page/Page column 45-49; 51
(2010/12/31)
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- Tartaric acid and its acyl derivatives. Part 5. Direct synthesis of monoacyltartaric acids and novel mono(benzoyl)tartaric anhydride: Unusual findings in tartaric acid acylation
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Practical acylation of unprotected tartaric acid 1 by acyl chlorides to the corresponding monoacyltartaric acids 2 has been shown. Several unusual cases in the acylation of 1 are observed; it has been found that two routes of acylation are possible. In the benzoylation of 1, in addition to the expected products, the formation of a previously undescribed monobenzoyltartaric anhydride 7a is reported. An unusual DME cleavage during the course of acylation was also observed. ARKAT USA, Inc.
- Bernas, Urszula,Hajmowicz, Halina,Madura, Izabela D.,Majcher, Monika,Synoradzki, Ludwik,Zawada, Krzysztof
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scheme or table
p. 1 - 12
(2010/12/24)
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- Development of new HPLC chiral stationary phases based on native and derivatized cyclofructans
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An unusual class of chiral selectors, cyclofructans, is introduced for the first time as bonded chiral stationary phases. Compared to native cyclofructans (CFs), which have rather limited capabilities as chiral selectors, aliphatic-and aromatic-functionalized CF6s possess unique and very different enantiomeric selectivities. Indeed, they are shown to separate a very broad range of racemic compounds. In particular, aliphatic-derivatized CF6s with a low substitution degree baseline separate all tested chiral primary amines. It appears that partial derivatization on the CF6 molecule disrupts the molecular internal hydrogen bonding, thereby making the core of the molecule more accessible. In contrast, highly aromaticfunctionalized CF6 stationary phases lose most of the enantioselective capabilities toward primary amines, however they gain broad selectivity for most other types of analytes. This class of stationary phases also demonstrates high "loadability" and therefore has great potential for preparative separations. The variations in enantiomeric selectivity often can be correlated with distinct structural features of the selector. The separations occur predominantly in the presence of organic solvents.
- Sun, Ping,Wang, Chunlei,Breitbach, Zachary S.,Zhang, Ying,Armstrong, Daniel W.
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experimental part
p. 10215 - 10226
(2010/05/01)
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- Method to separate stereoisomers
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A method to resolve the stereoisomers of an optically active compound comprising an amine moiety. The method provides a mixture comprising two stereoisomers of a compound comprising a amine moiety. The method supplies l-fenchyloxyacetic acid, treats the mixture of stereoisomers with that l-fenchyloxyacetic acid, and collects one of those two stereoisomers having greater than a 99 percent enantiomeric excess.
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Page/Page column 3
(2010/02/13)
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- PROCESSES FOR THE RECOVERY OF OPTICALLY ACTIVE DIACYLTARTATIC ACIDS
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When a salt of an amine and an optically active diacyltartaric acid, or a diastereomer salt of an optically active amine and an optically active diacyltartaric acid, obtained by optically resolving a racemic amine using the optically active diacyltartaric acid, is salt-exchanged with an acid aqueous solution, the optically active diacyltartaric acid is added in the acid aqueous solution beforehand. Furthermore, a raw material containing a racemic amine and an optically active diacyltartaric acid is optically resolved, and the diastereomer salt of the optically active amine and the optically active diacyltartaric acid respectively of one isomer type, is separated. The obtained diastereomer salt is dissociated using an acid aqueous solution containing the optically active diacyltartaric acid, for recovering the optically active diacyltartaric acid, and the obtained' optically active diacyltartaric acid is recycled into an optical resolution step as a raw material of the optical resolution step.
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Page/Page column 9-10
(2008/06/13)
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- Process for the continuous production of basic cyclic optically active alpha - amino acids
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PCT No. PCT/EP96/04073 Sec. 371 Date Mar. 24, 1998 Sec. 102(e) Date Mar. 24, 1998 PCT Filed Sep. 18, 1996 PCT Pub. No. WO97/12881 PCT Pub. Date Apr. 10, 1997The invention pertains to a process for the continuous production of basic cyclic optically active alpha -amino acids of general formula (I) by continuous racemate splitting via diastereomeric salt pairs with re-racemisation of the residual amino acid or amino acid derivative in the mother liquid with the aid of an optically active acid.
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- Heteroaromatic diphosphines as chiral ligands
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Chiral diphosphines constituted by an aromatic pentatomic biheterocyclic system, suitable to act as chiral ligands, complexes between said diphosophines and transition metals, and their utilization as chiral catalysts in sterocontrolled reactions, such as diastereo- and enantioselective reduction reactions. Process for the preparation of said chiral diphosophines and process for the preparation of said complexes and for their utilization as chiral catalysts in sterocontrolled reactions.
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- New access to enantiopure O,O'-dibenzoyltartaric acid: Resolution of the mixed calcium methoxyacetate by preferential crystallization
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A convenient resolution of racemic O,O'-dibenzoyltartaric acid by preferential crystallization of its mixed calcium salt formed with methoxyacetic acid is described. The separation of the partially prepared salt 2 followed by a subsequent recrystallization results in a simple and effective resolution of the title compound during which pure enantiomers of 1 can be obtained even on a large scale. The crystal structure of the conglomerate forming complex 2 is also reported.
- Elekes, Ferenc,Kovari, Zoltan,Mravik, Andras,Boecskei, Zsolt,Fogassy, Elemer
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p. 2895 - 2900
(2007/10/03)
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- Simple resolution of O,O'-dibenzoyltartaric acid by preferential crystallization of its calcium salt-methoxyethanol complex
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The enantiomers of the title compound can be obtained in a simple two-step crystallization procedure starting from the racemate. The compound 2 of the calcium O,O'-dibenzoyl-tartrate formed with two molecules of 2-methoxyethanol exists as a conglomerate, making a simple enantioseparation possible.
- Mravik, Andras,Lepp, Zsolt,Fogassy, Elemer
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p. 2387 - 2390
(2007/10/03)
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- Diastereomer salts of phenylalanine and N-acyl derivatives thereof and process for the separation of optically active phenylalanine and N-acyl derivatives thereof
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The present invention relates to the separation of optically active phenylalanine and N-acyl derivatives thereof and novel diastereomer salts of the said compounds. According to the invention a racemic compound of the formula STR1 is reacted with an optically active resolving agent of the formula STR2 in a polar solvent and/or a mixture of solvents comprising at least one apolar solvent and optionally an achiral acid or base, thereafter (a) when using the D-isomer of the resolving agent of the formula II, the crystalline diastereomer salt formed with the L-isomer of the compound of the formula I is separated, or (b) when using the L-isomer of the resolving agent of the formula II, the crystalline diastereomer salt formed with the D-isomer of the compound of the formula I is separated, and the enantiomers of the compound of the formula I from the diastereomer salt or the mother liquor are liberated by the aid of an achiral acid or base and the optically active product is separated in crystalline form.
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