Anion‐ and Spacer‐Directed Host–Guest Complexes of Bipyridine with Pyrogallol[4]arene

New oval‐shaped capsular and bilayer‐type hydrogen‐bonded arrangements of C‐propyl‐ol‐pyrogallol[4]arene (PgC3‐OH) with bipyridine‐type spacer complexes are reported here. These complexes are engineered by virtue of derivatization of C‐alkyl tails of pyrogallol[4]arene and the use of divergent spacer ligands. Complexes of PgC3‐OH, PgC3‐OH with bpy (4,4′‐bipyridine) and PgC3‐OH with bpa (1,2‐bis(4‐pyridyl)acetylene) have bilayer type arrangements; however, the use of hydrogen chloride causes protonation of bpy molecule, which is then entrapped flat within an offset oval‐shaped dimeric hydrogen‐bonded PgC3‐OH nanocapsule. The presence of chloride anion in the crystal lattice controls the geometry of the resultant nanoassembly.     

Natural (−)‐Vasicine as a Novel Source of Optically Pure 1‐Benzylpyrrolidin‐3‐ol

A facile and scalable methodology for the preparation of optically active (3S)‐1‐benzylpyrrolidin‐3‐ol ( 3 ), an important drug precursor, is reported. Starting from the naturally occurring alkaloid (?)‐vasicine ( 1 ), a major alkaloid of the plant Adhatoda vasica, 3 was obtained in 84% overall yield (Scheme 3).     

Synthesis of nanocrystalline material by sputtering and laser ablation at low temperatures

Physical vapor deposition techniques such as sputtering and laser ablation – which are very commonly used in thin film technology – appear to hold much promise for the synthesis of nanocrystalline thin films as well as loosely aggregated nanoparticles. We present a systematic study of the process parameters that facilitate the growth of nanocrystalline metals and oxides. The systems studied include TiO₂, ZnO, γ-Al₂O₃, Cu₂O, Ag and Cu. The mean particle size and crystallographic orientation are influenced mainly by the sputtering power, the substrate temperature and the nature, pressure and flow rate of the sputtering gas. In general, nanocrystalline thin films were formed at or close to 300 K, while loosely adhering nanoparticles were deposited at lower temperatures. Received: 31 October 2000 / Accepted: 9 January 2001 / Published online: 26 April 2001     

Studies on Enethiol-Thione Equilibrium of Some 1,5-Disubstituted 2,4-Dithiobiurets

Eaethiol contents of 1, 5-diphenyl 2, 4-dithiobiuret (DP); 1, 5-di-p-tolyl 2, 4-dithiobiuret (DPT); 1-phenyl 5-p-tolyl 2, 4-dithiobiuret (PPT); 1-phenyl 5-o-tolyl 2, 4-dithiobivret (POT); and 1-methyl 5-p-tolyl 2, 4-dithiobiuret (MPT) have been studied by alkali titration method in methanol and by spectrophotometric method in different solvents of varying polarities, ranging from pyridine (Z, 64.0) to methanol (Z, 83.6). Free energy of tautomerisation has been calculated. The effect of substituents on the phenyl group on enethiol contents have been studied. It has been observed that temperature has no effect on enethiol-thione equilibrium.     

Effect of Solvents on the Spectra of Some N′-2-(Substituted Pyridyl)-N-Substituted-Thioureas

Some N′-2-(substituted pyridyl)-N-substituted thiourea (in all 12-substituted pyridyl thioureas) have been examined in ultraviolet region in a series of solvents covering a broad polarity range i. e. from benzene (Z, 54.0) to ethylene glycol (Z, 85.1). Transition energies and oscillator strengths have been calculated and transition energy (E_T) has been plotted against Z-values, a new-empirical measurement of solvent polarity. A linear relationship was observed between the transition energy and Z-value for pyridyl μ→μ* and thiocarbonyl μ→μ* transitions. The effect of substituent present in pyridyl group on λ_max of a compound in the same solvent has been studied. Solvent sensitivites of these ligands have also been calculated.     

The heteroscedastic method: Multivariate implementation

Summary Over the past decade, procedures have been developed which allow one (in the univariate case) to make inferences about means even in the presence of unknown and unequal variances. A general method (called The Heteroscedastic Method) allowing this in all statistical problems simultaneously was formulated in 1979 and allowed specifically for the multivariate case (e.g., MANOVA and other multivariate inferences). While in the univariate case The Heteroscedastic Method is readily implemented, in the multivariate case practical implementation was not heretofore possible since a certain problem in construction of matrices required by the method had not been solved. In this paper we solve that problem and give a computer algorithm allowing for use of the solution in The Heteroscedastic Method.     

Urea derivatives of piperazine doped with pyrazole-4-carboxylic acids: Synthesis and antimicrobial evaluation

A series of novel N-cycloalkyl/aryl-4-(1,3-diphenyl-1H-pyrazole-4-carbonyl)piperazine-1-carboxamides 9a-g has been synthesized for biological interest by simple base catalyzed reaction of various N-cycloalkyl/aryl isocyanates with (1,3-diphenyl-1H-pyrazol-4-yl)(piperazin-1-yl)methanone hydrochloride 8 . The compound 8 was synthesized in excellent yield by the reaction of 1,3-diphenyl-1H-pyrazole-4-carbonyl chloride with boc-piperazine followed by deprotection of boc group with dioxane-HCl. All the novel intermediates and urea derivatives have been screened for antimicrobial activity. The compound 9a was found an excellent compound to be active against all Gram (−ve) and Gram (+ve) bacterial strains E. coli, Y. enterocolitica, B. cereus, and S. aureus. It also showed comparable antifungal activity against C. albicans with MIC 78.1 μg/ml as compared to reference standard miconazole.     

Tandem acetalation-acetylation of sugars and related derivatives with enolacetates under solvent-free conditions

Molecular iodine catalyzes acetalation and acetylation of reducing sugars and sugar glycosides with stoichiometric amounts of enol acetates under solvent-free conditions, thereby facilitating the synthesis of various types of orthogonally protected sugar derivatives in short time and good yields. The outcome of the reaction can be controlled by variation in temperature. Thus at lower temperature, it is possible to obtain the acetonide acetate as a single product whereas peracetate is the major product at higher temperature.     

Exploring the ellipsoidal and core-shell geometries of copper-seamed C-alkylpyrogallol[4]arene nanocapsules in solution

Small-angle neutron scattering (SANS) studies were used to probe the stability and geometry of copper-seamed C-alkylpyrogallol[4]arene (PgC(n)Cu; n = 11, 13, 17) hexamers in solution. Novel structural features are observed at chain lengths greater than 10 in both solid and solution phase. Scattering data for the PgC(11)Cu and PgC(13)Cu in chloroform fitted as core-shell spheres with a total spherical radius of about 22.7 and 22.9 ? respectively. On the other hand, the scattering curve for the PgC(17)Cu hexamer at both 1% and 5% mass fractions in o-xylene did not fit as a discrete sphere but rather as a uniform ellipsoid. The geometric dimensions of the ellipsoid radii are 24 ? along the minor axis and 115 ? along the major axis. It is expected that an individual hexamer with heptadecyl chains would exhibit a uniform radius of ca. 24 ?. However, an approximate ratio of 1:5 between radii lengths for the minor axis and major axis is consistent with interpenetration of the heptadceyl chains of adjacent hexamers to form a single ellipsoidal assembly.