Synthesis and optical resolution of a series of inherently chiral calix[4]crowns with cone and partial cone conformations

A series of inherently chiral calix[4]arenes with cone and partial cone conformations and with crown ether moieties of variable size have been readily synthesized. By taking advantage of the carboxy appendage on the lower rim, these were condensed with the chiral auxiliary (S)-BINOL to form diastereomers which, in most cases, could be separated by preparative TLC, or more desirably, by column chromatography on silica gel (diastereomeric excess >99 % based on HPLC analysis). Seven enantiopure antipodes of inherently chiral calix[4]crowns were obtained after hydrolysis. It has been found that both the size of the crown moiety and alkylation of the last phenolic hydroxy group (accompanied with or without a change in the conformation) affect the separation of the diastereomers.     

The Mitsunobu Reaction: Origin,Mechanism, Improvements,and Applications

The Mitsunobu reaction is a widely used and versatile method for the dehydrative oxidation–reduction condensation of an acid/pronucleophile usually with a primary or secondary alcohol that requires the combination of a reducing phosphine reagent together with an oxidizing azo reagent. The utility of this reaction stems from the fact that it is generally highly stereoselective and occurs with inversion of the stereochemical configuration of the alcohol starting material. Furthermore, as carboxylic acids, phenols, imides, sulfonamides, and other compounds can be used as the acid/pronucleophile, this reaction is useful for the preparation of a wide variety of functional groups. This Focus Review of the Mitsunobu reaction summarizes its origins, the current understanding of its mechanism, and recent improvements and applications.     

A Novel Method for Quantification of Circulating DNA in Serum by Capillary Zone Electrophoresis

In this paper, we first presented a novel method for quantification of circulating DNA in human serum based on capillary zone electrophoresis with laser-induced fluorescence detection (CZE-LIF). The serum was digested by proteinase to release free DNA, and then CZE-LIF system was used for the quantification of total circulating DNA. This method was successfully used to quantify the circulating DNA levels in sera from healthy individuals and certain cancer patients.We found the significantly elevated circulating DNA levels in certain prostate cancer patients. Our results demonstrated that CZE-LIF system has good linearity, excellent sensitivity (0.5 ng/mL DNA),satisfactory reproducibility (RSDs in one day and between days were both less than 5%) and reliability, and is well suitable to the quantification of the circulating DNA in human serum or plasma.     

Carbonyldinitrosyltris(fluorosulfato)tungstate(II) and ‐Molybdate(II) Anions: Synthesis,Spectroscopy, and Density Functional Theory Calculations

Carbonyldinitrosyltris(fluorosulfato)tungstate(II) and ‐molybdate‐(II) anions, [fac‐M(CO)(NO)₂(SO₃F)₃]^? (M=W, Mo), which are novel weakly coordinating anions that contain a metal carbonyl/nitrosyl moiety, have been generated in fluorosulfonic acid and completely characterized by multinuclear NMR, IR, and Raman spectroscopy as well as ESI mass spectrometry. ESI MS measurements performed for the first time on a superacidic solution system unambiguously reveal the formation of the monoanionic, mononuclear W and Mo complexes formulated as [M(CO)(NO)₂(SO₃F)₃]^? (M=W, Mo). Multinuclear NMR spectroscopic studies at natural abundance and ¹³C and ¹⁵N enrichment clearly indicate the presence of one CO ligand, two equivalent NO ligands, and two types of nonequivalent SO₃F^? groups in a 2:1 ratio. The IR and Raman spectra reveal that the two equivalent NO ligands have a cis conformation, thus indicating a fac structure. Density functional calculations at the B3LYP level of theory predict that these anions have a singlet ground state (¹A′) with a C_s symmetry along with C–O and N–O vibrational frequencies that are in agreement with the experimental observations. Mulliken population analysis shows that the monovalent negative charge is dispersed on the bulky sphere, the surface of which is covered by all the negatively charged O and F atoms with charge densities much lower than SO₃F^?, suggesting that [fac‐M(CO)(NO)₂(SO₃F)₃]^? (M=W, Mo) are weakly nucleophilic and poorly coordinating anions.     

Spectroscopy of hydrothermal reactions, 19: pH and salt dependence of decarboxylation of α‐alanine at 280–330°C in an FT‐IR spectroscopy flow reactor

The spontaneous decarboxylation of 0.5 m aqueous α‐alanine solutions as a function of pH (1–9 at 320°C, where neutrality is approximately 6) was determined with a flow reactor at 280–330°C and 275 bar by FT‐IR spectroscopy. The kinetics for the cationic and anionic forms have not been previously reported. The rate constants for the cationic form [CH₃(NH₃⁺)CHCO₂H], the anionic form [CH₃(NH₂)CHCO₂^?], and the zwitterion form [CH₃(NH₃⁺)CHCO₂^?] were obtained and followed the first‐order rate law. The rate of decarboxylation of the zwitterion is three times greater than that of the cationic and anionic forms in the temperature and pH ranges of study. The corresponding Arrhenius parameters were determined and compared with previously reported data. The addition of KCl (1 and 2 m) at the natural pH of α‐alanine resulted in a reduction of the decarboxylation rate, suggesting that the transition state is less polar than the zwitterion and/or that the activity of the zwitterion has been reduced. The α‐alanine solution is therefore somewhat more robust in solutions of high ionic strength, such as seawater, than it is in pure water. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 271–277, 2002     

Optimization of the abnormal Beckmann rearrangement: application to steroid 17-oximes

A novel and practical procedure was developed for the abnormal Beckmann rearrangement of steroid 17-oximes. Treatment of the 17-oximes with TFA/CH(OMe)(3) in boiling THF for 2 h gives the corresponding 13,17-seco alkene nitrile products in unprecedented high yields (70-92%). Since the alkene nitriles can be subsequently converted into 18-norsteroids, this general method provides a highly efficient route to these biologically important compounds and, by extension, to other structurally related natural products.     

Folded chain crystals as micro-phases

Summary A thermodynamic treatment of homo-polymer systems out of linear chains with folded chain crystals is developed outgoing from appropriate models for single component systems. An expansion of thermodynamics to multi-micro-phase systems the structure of which is partially or totaly frozen is indispensable. General properties of melt crystallized homopolymers with folded chain crystals can be recognized indeed when the thermodynamic formalisms developed are applied.

---

Zusammenfassung Das Schmelzen in polymeren Einteilchensystemen mit Faltungskristallen einheitlicher Dicke kann thermodynamisch als Umwandlung 1. Ordnung in einer Richtung behandelt werden, wenn die Faltungslänge bis zur Umwandlungstemperatur konstant bleibt (Faltungslänge als innerer Zusatzparameter). Eine wesentliche begriffliche Erweiterung ist für eine phänomenologische Beschreibung mit den Mitteln der Thermodynamik unumgänglich, wenn eine Faltungskristallit-Dickenverteilung existiert, weil dann prinzipiell nur noch partielle Koexistenz bestimmter Fraktionen metastabiler autonomer Mikrophasen mit der Schmelze möglich ist. Partielles Aufschmelzen und Rektistallisation können so dann auch in Betracht genommen werden. Die entwickelten Konzeptionen bewähren sich in der Anwendung auf bekannte Experimente.

---

Notation g ^c (y);g ^m (Y) molar Gibbs-free energy of a chain of a lengthy within an extended chain crystal and the melt rsp - g _o ^c ;g _o ^m molar free enthalpy of the unit in the crystal lattice and the melt rsp - g(y,y, f) molar Gibbs-function of an ideally folded chain crystal with the fold heighty _f - gco(y, y _ef,y _f) molar free enthalpy of the crystal corey _co - g ₀ ^ex ((y_ef) excess free enthalpy of the longitudinal layers of folded chain crystals - g ^f(y_ef,g _o ^ex ) molar free enthalpy of the longitudinal layers of the folded chain crystals - g ^tot molar free enthalpy of a chain of the lengthy within a folded chain crystal with longitudinal layers - h _o ^1c ,h _o ^m molar enthalpy of the chain unit within the crystal lattice and the melt rsp - h =h _o ^m -h _o ^c molar heat of fusion of the unit - C _p=C _p ^m -C _p ^c difference of the molar specific heat of a unit within the melt and within the chain crystal - h ^D molar defect enthalpy of local defects within the crystal lattice - h ^D molar defect enthalpy of the unit - s _o ^c ,s _o ^m molar entropy of the chain unit within the crystal lattice and the melt rsp - s _c ^m conformational entropy of a chain in the melt - s _gk conformational entropy of a chain of lengthy within a super-lattice as indicated in figure 5, - s molar entropy of fusion of the melt - s _n ^c nematic configurational entropy - T absolute temperature - T _M melting temperature of extended chain crystals of infinite size - T _M(y) melting temperature of extended chain crystals containing only chains of the lengthy - T _M (y, y _f) melting temperatureof folded chain crystals of the thicknessy _f composed of chains of the lengthy - T _M(y _f) melting temperature of folded chain crystals of the thicknessy _fy - _eh excess free enthalpy of the chain ends occupying crystallographic places - _ef excess free enthalpy of a single fold loop - z coordination number of the lattice - 7 Euler's constant - R Boltzmann's constant - y number of chain units - y _f height of lamelliform folded chain crystals - f=(y/y _f - 1) number of fold loops of a chain of a lengthy when being built into a folded chain crystal of the thicknessy _f - y _co thickness of the crystal core of the simplified twophase model - y _et average thickness of the surface layers of folded chain crystals - N _c number of crystallized units of a chain of the lengthy - x _c molar number of crystallized units of a chain of the lengthy - x _nc molar number of noncrystallized units - excess free enthalpy parameter - (y _f) thickness distribution of the fold heightsy _f With 15 figures and 2 tables     

Über 1-Alkyl-bzw. 1-Aryl-dihydro-6-methyl-2(1H)-pyrimidinthione

The title compounds7 are formed in a general reaction by heating β-isothiocyanoketones3 with primary amines in inert solvents, or by thermal elimination of water from tetrahydro-6-hydroxy-6-methyl-2(1H)-pyrimidinethiones5, also in inert solvents. The 1-alkyl compounds can also be prepared under similar conditions from α,β-unsaturated ketones by reaction with alkylammonium rhodanides. The NMR-spectra show that the 1-substituted dihydro-6-methyl-2(1H)-pyrimidinethiones are in tautomeric equilibrium with the tetrahydro-6-methylene-2(1H)-pyrimidinethiones13. The reactivity of 1-alkyl and 1-aryldihydro-6-methyl-2(1H)-pyrimidinethiones is similar to that of dihydro-4,4,6-trimethyl-2(1H)-pyrimidinethione7 j, although their ring stability is certainly less.     

Beiträge zur Chemie des Sulfamids, 1. Mitt.: Zur Konstitution des Disilber-sulfamids

According to spectroscopic (IR, broadline proton NMR) and chemical (alkylation) investigations of disilver sulphamide the following molecular structure is assumed: $$\begin{gathered} O \hfill \\ || \hfill \\ H_2 N\_\_S\_\_NAg| \hfill \\ OAg \hfill \\ \end{gathered}$$ From the IR and NMR data deduction concerning the nature of the chemical bonds in this compound is possible. The instability of the still unknown mono-and trisilver sulphamide is discussed with regard to the structure of disilver sulphamide.     

Synthesis, crystal structure and magnetic property of the novel dinuclear nickel(II) complex with 4-(p-methoxyphenyl)-3,5-bis(pyridine-2-yl)-1,2,4-triazole

A novel dinuclear nickel(II) complex, [Ni₂(MOBPT)₂Cl₂(H₂O)₂]Cl₂ · 7H₂O (MOBPT = 4-(p-methoxyphenyl) −3,5-bis(pyridine-2-yl)-1,2,4-triazole), has been synthesized and characterized by elemental analysis, IR and single crystal X-ray diffraction methods. The crystal structure determination shows that the dinuclear Ni₂N₈ unit is almost planer in which each Ni^II ion is coordinated by four nitrogen atoms from MOBPT equatorially and a water molecule and a chloride ion axially in a distorted octahedral geometry. Magnetic measurements reveal a relatively weak antiferromagnetic exchange in the complex.