Thickness, Morphology and Structure of Sol-Gel Hybrid Films: II—The Role of the Solvent

The influence of the solvent on the thickness, morphology and structure of silica-polytetrahydrofuran hybrid films, prepared by spin coating, has been analysed. The inorganic precursor, tetraethylorthosilicate, was hydrolysed under acid catalysis, the hydrolysis molar ratio being 4. Polymers of average molecular weight (M _n) 650 and 2900 were incorporated in the initial colloidal solutions, in a low concentration (organic/inorganic molar ratio 0.01). Two solvents were compared: ethanol, protic, and tetrahydrofuran, aprotic and a little less polar. The thickness and surface texture parameters of the films were determined by profilometry, their morphology characterized by SEM and their structure studied by FTIR. It is shown that the solvent has no effect on the molecular structure of the films, but strongly influences the surface texture and the morphology of both pure silica and hybrid films. The solutions prepared in tetrahydrofuran present shorter gelation times (t _G) and allow the deposition of good quality films almost up to the gelation point (to a reduced time, t/t _G, of 0.9). The films are thinner than those prepared from corresponding ethanolic solutions at the same reduced ageing times. For pure silica films, tetrahydrofuran is the best choice, since it reduces the fractured region on the edge of the substrate. For hybrid films, this effect is achieved by the polymer and tetrahydrofuran is responsible for a higher arithmetical mean roughness. Therefore, ethanol becomes the preferable solvent.     

New approach to nonracemic 1-alkylamino-3-aryloxypropan-2-ols belonging to β-blockers via cyclic sulfites

Nonracemic -blockers, viz., (S)-propranolol and (S)-timolol, were prepared from (S)-glycidol in three steps consisting in the reaction with SOCl₂ followed by the reaction of the resulting (4S)-4-chloromethyl-2-oxo-1,3,2-dioxathiolanes with the corresponding phenol and the final cleavage of (4R)-aryloxymethyl sulfites under the action of amines in DMF.     

The solid-state structure of (+)-(i)-menthyl 2-formamido-4, 4,4-trifluorobutanoate and the hydrogenation of the 2-butenoate precursor

Hydrogenation ofZ-(–)-(1R, 3R, 4S)-menthyl 2-formamido-4,4,4-trifluoro-2-butenoate catalyzed by Pd/C was performed at atmospheric pressure to yield a mixture of (2R, 1R, 3R, 4S)- and (2S, 1R, 3R, 4S)-menthyl 2-formamido-4,4,4-trifluorobutanoate diastereomers in a 5545 ratio, respectively. Repeated fractional crystallization from ethyl acetate and vapor diffusion of petroleum ether afforded (+)–(2S, 1R, 3R, 4S)-menthyl 2-formamido-4,4,4-trifluorobutanoate as clear colorless, crystalline prisms which were subjected to single-crystal X-ray diffraction analysis. The crystals belong to the orthorhombic system P2₁2₁2₁, and at 213 K:a=5.054(1),b= 10.000(2),c=32.707(1) Å,V=1652.9(4) ų,Z=4,R(F)=0.040, andR _w (F)=0.037. The finding of the (2S)-configuration for the formamido-acid portion of the (+)-ester enabled the configurational assignment of the asymmetric hydrogenation products ofZ-methyl 2-formamido-4, 4,4-trifluoro-2-butenoate catalyzed by chiral diphosphine/rhodium(I) complexes.     

Stereoselectivity and Chiral Recognition in the Electron-Transfer Reaction between Spinach Ferredoxin and Optically Active Cobalt(III) Complexes

The kinetics of the electron transfer between reduced spinach [2Fe-2S]-ferredoxin and the optically active complexes [Co((R,R)- or (S,S)-alamp)py]⁺ ( I ), [Co((R,R)- or (S,S)-promp)H₂O]⁺ ( IIa ), and [Co((R,R)- or (S,S)-promp)py]⁺ ( IIb ) have been investigated. The reactions are stereoselective, and for I and IIa , the Stereoselectivity strongly depends on temperature due to large differences in the activation enthalpy between enantiomeric reagents. Isokinetic behaviour is observed between enantiomers, the ΔΔH values being largely compensated by the ΔΔS values. The compensation behaviour is explained by the combination of stereochemical interactions and desolvation processes on formation of the precursor complex or the transition state.     

Salicylaldehyde based oxazolidines as catalysts for the asymmetric addition of diethylzinc to aldehydes

A series of oxazolidines have been prepared by condensation of N‐isopropyl norephedrine with a variety of salicylaldehyde derivatives. Despite the stereochemical relationship of (1R,2S)‐norephedrine with (1R,2S)‐ephedrine, the resultant oxazolidines 12‐14 were determined to have a stronger stereochemical relationship with (1S,2S)‐pseudoephedrine based oxazolidines. The resultant oxazolidines were used as catalytic ligands in the addition of diethylzinc to several aldehydes. It was determined that the oxazolidine derivative 12 gave the highest yield and a moderate enantioselectivity.     

Synthesis of Enantiomerically Pure 2-Isoxacephems

Summary. (R,6R,7R)-7-(1-Acetoxyethyl)-3-methyl-2-isoxacephem-4-carboxylic acid and its enantiomer have been prepared. The ring systems were formed from the corresponding enantiomerically pure N-unsubstituted -lactams. The reduction of methyl [(R,2S,3R)-3-(1-acetoxyethyl)-1-(4-methoxyphenyl)-4-oxoazetidine-2-carboxylate] has been solved via a hemi-acetal. The structure and the configuration of a new stereogenic center in this intermediate was predicted by using 2D NMR technique and unambiguously proven by x-ray.     

Synthesis of Enantiomerically Pure 2-Isoxacephems

(R,6R,7R)-7-(1-Acetoxyethyl)-3-methyl-2-isoxacephem-4-carboxylic acid and its enantiomer have been prepared. The ring systems were formed from the corresponding enantiomerically pure N-unsubstituted -lactams. The reduction of methyl [(R,2S,3R)-3-(1-acetoxyethyl)-1-(4-methoxyphenyl)-4-oxoazetidine-2-carboxylate] has been solved via a hemi-acetal. The structure and the configuration of a new stereogenic center in this intermediate was predicted by using 2D NMR technique and unambiguously proven by x-ray.     

Multifractal analysis of drop‐casted copper (II) tetrasulfophthalocyanine film surfaces on the indium tin oxide substrates

This paper applies multifractal spectrum theory to characterize the structural complexity of 3D surface roughness of copper (II) tetrasulfophthalocyanine (CuTsPc) films on the indium tin oxide (ITO) substrate, obtained with atomic force microscopy (AFM) analysis. CuTsPc films were prepared by drop cast method on ITO substrate. CuTsPc films surface roughness was studied by AFM in tapping‐mode?, in air, on square areas of 2500 µm². A novel approach, on the basis of computational algorithms for analysis of 3D roughness surface applied for AFM data, was presented. Results revealed that the 3D surface roughness of CuTsPc films prepared by drop cast method on ITO substrate can be described using the multifractal geometry. The generalized dimensions D_q and the multifractal spectrum f(α) provided quantitative values that characterize the local scale properties of CuTsPc films surface geometry at nanometer scale. Data provide valuable information to describe the spatial arrangement of 3D surface roughness of CuTsPc films on ITO substrate, which was not taken into account by classical surface statistical parameters. Copyright © 2014 John Wiley & Sons, Ltd.     

Asymmetric anionic polymerization of maleimides bearing bulky substituents

Asymmetric anionic homopolymerizations of N‐substituted maleimide (RMI) bearing bulky substituents [R = benzyl, diphenylmethyl (DPhMI), 9‐fluorenyl (9‐FlMI), triphenylmethyl, (diphenylmethyloxycarbonyl)methyl, (9‐fluorenyloxycarbonyl)methyl] were carried out with complexes of organometal compounds (alkyllithium, diethylzinc) with six chiral ligands to obtain optically active polymers. The chiroptical properties of the polymers were affected strongly by the substituents on nitrogen in the maleimide ring, the organometal and chiral ligands. Poly(DPhMI) initiated by an n‐butyllithium/(−)‐sparteine (Sp) complex showed a positive specific rotation ([α] +60.3°). Poly(9‐FlMI) prepared with a florenyllithium/Sp complex exhibited the highest specific rotation (+65.7°). The specific rotations of the poly(RMI) obtained were attributed to different contents between the stereogenic centers (S,S) and (R,R) based on threo‐diisotactic structures of the main chain. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 310–320, 2000     

Crystal structures of heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin complexes with (R)- and (S)-Flurbiprofen

Hepatakis(2,3,6-tri-O-methyl)--cyclodextrin (TM--CDx) forms crystalline complexes with (R)-Flubiprofen (R-FP), C₆₃H₁₁₂O₃₅C₁₅H₁₃O₂F·H₂O, and (S)-Flurbiprofen (S-FP), C₆₃H₁₁₂O₃₅C₁₅H₁₃O₂F. The crystal structures were determined by X-ray analysis. Crystals of both compounds are orthorhombic and the space group isP2₁2₁2₁ with cell dimensions:a=15.092(2),b=21.714(3), andc=28.269(4) Å for theR-FP complex, anda=15.271(2),b=21.451(3) andc=27.895(3) Å for theS-FP complex. The macrocyclic ring of TM--CDx is markedly distorted because of the inability to form intramolecular hydrogen bonds and the steric hindrance involving methyl groups. In both complexes, the phenyl group is inserted into the host cavity from the O(2), O(3) side, which is wider than the O(6) side. The biphenyl moiety ofR-FP is fixed in theR-configuration within the host cavity. The phenyl group ofS-FP is disordered, andR-andS-configurations are statistically distributed with equal probability. TM--CDx molecules are stacked along theb axis to form a column structure. The TM--CDx molecule is laterally shifted with respect to the column axis, and a half of the guest molecule protrudes outside from the crevis of the column. The carboxyl group ofR-FP forms a hydrogen bond with water located outside the host cavity, while the carboxyl group ofS-FP is hydrogen-bonded to an oxygen atom of an adjacent TM--CDx. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82064 (24 pages).     

Amorphous silicon carbonitride thin‐film coatings produced by remote nitrogen microwave plasma chemical vapour deposition using organosilicon precursor

Amorphous silicon carbonitride (a‐SiCN) films were produced by remote nitrogen plasma chemical vapour deposition (RP‐CVD) from bis(dimethylamino)methylsilane precursor. The effect of substrate temperature (T _S) on the kinetics of RP‐CVD, chemical structure, surface morphology and some properties of the resulting films is reported. The T _S dependence of film growth rate implies that RP‐CVD is an adsorption‐controlled process. Fourier transform infrared spectroscopic examination revealed that an increase in T _S from 30 to 400°C involves the elimination of organic moieties from the film and the formation of Si─C and Si─N network structure. The films were characterized in terms of their surface roughness and basic physical and optical properties, such as density and refractive index, respectively. Reasonably good relationships between the structural parameters represented by relative integrated intensity of infrared absorption bands from the Si─C and Si─N bonds (controlled by T _S) and the film properties are determined. Due to their small surface roughness, high density and high refractive index, the a‐SiCN films produced at T _S ≥ 350°C would seem to be useful protective coatings for metals and optical devices.     

Diamines Having a C2 Symmetry. Synthesis and Application as Ligands in the Hydrogenation of Prochiral Substrates over Rhodium Complexes

Chiral diamines having a C ₂ symmetry, (4S,5S)-2,2-dimethyl-4,5-bis(aminomethyl)-1,3-dioxolane and (5S,5'S)-2,2,2',2'-tetramethyl-3,3'-diphenyl-5,5'-bioxazolidine, were synthesized on the basis of (+)-(2R,3R)-tartaric acid. Their structure was proved by X-ray analysis. The products were used as ligands in rhodium catalyst for enantioselective hydrogenation of -acetamidocinnamic and itaconic acids.     

Surface chiroselective assembly of enantiopure crystalline porous films containing bichiral building blocks

The development of chiral crystalline porous materials (CPMs) containing multiple chiral building blocks plays an important role in chiral chemistry and applications but is a challenging task. Herein, we report the first example of bichiral building block based enantiopure CPM films containing metal–organic cages (MOCs) and metal complexes. The functionalized substrate was immersed subsequently into homochiral metal complex (R)- or (S)-Mn(DCH)₃ (DCH = 1,2-diaminocyclohexane) and racemic Ti₄L₆ cage (L = embonate) solutions by a layer-by-layer growth method. During the assembly process, the substrate surface coordinated with (R)- or (S)-Mn(DCH)₃ can, respectively, layer-by-layer chiroselectively connect Δ- or Λ-Ti₄L₆ cages to form homochiral (R, Δ)- or (S, Λ)-CPM films with a preferred [111] growth orientation, tunable thickness and homogeneous surface. The resulting enantiopure CPM films show strong chirality, photoluminescence, and circularly polarized luminescence (CPL) properties as well as good enantioselective adsorption toward enantiomers of 2-butanol and methyl-lactate. The present in situ surface chiroselective strategy opens a new route to assemble homochiral CPM films containing multiple chiral building blocks for chiral applications.

Bichiral building block based enantiopure CPM films containing metal–organic cages (MOCs) and metal complexes are chiroselectively assembled on the substrate surface by a layer-by-layer method.     

Chiral recognition in molecular and macromolecular pairs of (S)‐ and (R)‐1‐cyano‐2‐methylpropyl‐4′‐ {[4‐(8‐vinyloxyoctyloxy)benzoyl]oxy}biphenyl‐4‐ carboxylate enantiomers

(S)‐1‐Cyano‐2‐methylpropyl‐4′‐{[4‐(8‐vinyloxyoctyloxy)benzoyl]oxy}biphenyl‐ 4‐carboxylate [ (S)‐11 ] and (R)‐1‐cyano‐2‐methylpropyl‐4′‐{[4‐(8‐vinyloxyoctyloxy)benzoyl]oxy}biphenyl‐4‐carboxylate [( R)‐11 ] enantiomers, both greater than 99% enantiomeric excess, and their corresponding homopolymers, poly[ (S)‐11 ] and poly[ (R)‐11 ], with well‐defined molecular weights and narrow molecular weight distributions were synthesized and characterized. The mesomorphic behaviors of (S)‐11 and poly[ (S)‐11 ] are identical to those of (R)‐11 and poly[ (R)‐11 ], respectively. Both (S)‐11 and (R)‐11 exhibit enantiotropic S_A, S, and S_X (unidentified smectic) phases. The corresponding homopolymers exhibit S_A and S phases. The homopolymers with a degree of polymerization (DP) less than 6 also show a crystalline phase, whereas those with a DP greater than 10 exhibit a second S_X phase. Phase diagrams were investigated for four different pairs of enantiomers, (S)‐11 /( R)‐11 , (S)‐11 /poly[ (R)‐11 ], and poly[ (S)‐11 ]/poly[ (R)‐11 ], with similar and dissimilar molecular weights. In all cases, the structural units derived from the enantiomeric components are miscible and, therefore, isomorphic in the S_A and S phases over the entire range of enantiomeric composition. Chiral molecular recognition was observed in the S_A and S_X phases of the monomers but not in the S_A phase of the polymers. In addition, a very unusual chiral molecular recognition effect was detected in the S phase of the monomers below their crystallization temperature and in the S phase of the polymers below their glass‐transition temperature. In the S phase of the monomers above the melting temperature and of the polymers above the glass‐transition temperature, nonideal solution behavior was observed. However, in the S_A phase the monomer–polymer and polymer–polymer mixtures behave as an ideal solution. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3631–3655, 2000     

C–HPt(II) interaction-controlled self-assembly and photophysics of chiral bis(pyrrol-2-ylmethyleneamino)cyclohexane platinum(II) complexes

Reaction of (R,R)-(−)- and (S,S)-(+)-1,2-bis(pyrrol-2-ylmethyleneamino)cyclohexane with K₂PtCl₄ afforded chiral, neutral platinum(II) Schiff base complexes of (R,R)-PtL and (S,S)-PtL with high yields. The rare C–HPt(II) intermolecular interaction was found to show considerable strength and directionality for controlling M and P helical supramolecular architectures of (R,R)-PtL and (S,S)-PtL, respectively, in crystal lattices. More importantly, the open square-planar geometry of platinum(II) complexes allows axial C–HPt(II) interaction, resulting in the ³(ππ^*) excited state with some mixing of the Pt(II) metal character observed both in concentrated solutions and in the solid state at room temperature.     

Preparation of both enantiomers of β-(3,4-dihydroxybenzyl)-β-alanine, higher homologues of Dopa

β²-(3,4-Dihydroxybenzyl)-β-alanine [β²-Homo-Dopa, 1] is a novel β-amino acid homologue of Dopa, the most successful therapeutic agent in the treatment of Parkinson's disease. Enantioenriched (R)-1 and (S)-1 were obtained via the diastereoselective alkylation of enantiopure pyrimidinone (R)- and (S)-3, chiral derivatives of β-alanine, with veratryl iodide. The major diastereomeric products (2S,5R)-4 and (2R,5S)-4 were hydrolyzed with 57% HBr, and the desired β-amino acids were purified by silica gel chromatography. Alternatively, enantioenriched (R)- and (S)-1 were prepared by means of the highly diastereoselective alkylation (3,4-dimethoxybenzyl iodide) of open-chain β-aminopropionic acid derivatives (R,R,S)-8 and (S,S,R)-8 containing the chiral auxiliary α-phenylethylamine. Finally, nearly enantiopure (R)- and (S)-1 were obtained by resolution of racemic N-benzyloxycarbonyl-2-(3,4-dibenzyloxybenzyl)-3-aminopropionic acid, rac-12, with (R)- or (S)-α-phenylethylamine, followed by catalytic hydrogenolysis.     

Polyhydroxylated pyrrolizidines. Part 8. Enantiospecific synthesis of looking-glass analogues of hyacinthacine A5 from DADP

(1R,2S,3S,5R,7aR)-1,2-Dihydroxy-3-hydroxymethyl-5-methylpyrrolizidine[(−)-3-epihyacinthacine A₅, 1a] and (1S,2R,3R,5S 7aS)-1,2-dihydroxy-3-hydroxymethylpyrrolizidine[(+)-3-epihyacinthacine A₅, 1b] have been synthesized either by Wittig's or Horner-Wadsworth-Emmond's (HWE's) methodology using aldehydes 4 and 9, both prepared from (2S,3S,4R,5R)-3,4-dibenzyloxy-2′-O-tert-butyldiphenylsilyl-2,5-bis(hydroxymethyl)pyrrolidine (2, partially protected DADP), and the appropriate ylides, followed by cyclization through an internal reductive amination process of the resulting α,β-unsaturated ketones 5 and 10, respectively, and total deprotection.     

Asymmetrical synthesis of organometallic analogs of natural compounds. 8. Reactions of pentafluorobenzaldehyde with the Ni(II) complex of a schiff base of glycine and (S)-2-[N-(benzylprolyl)amino]benzophenone

Reaction of pentafluorobenzaldehyde with a Ni(II) complex of a Schiff base formed from glycine and (S)-2-[N-(benzylprolyl)amino]benzophenone yields, depending on the reaction conditions, the hitherto unknown, diastereo-and enantiomerically pure amino acids 2R,3S--(4-methoxytetrafluorophenyl)serine, 2S,3R--(4-methoxytetrafluorophenyl)serine, 2S,3S--(pentafluorophenyl)serine, and 2S,3R--(pentafluorophenyl)serine.A. N. Nesmeyanov Institute of Organometallic Compounds, Russian Academy of Sciences, 117813 Moscow. Institute of Bioorganic Chemistry and Petroleum Chemistry, Ukrainian Academy of Sciences, 252028 Kiev. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 687–693, March, 1992.     

Absolute configuration of side chains of polyhydroxylated steroidal compounds from the starfish <Emphasis Type="Italic">Henricia derjugini</Emphasis>

The absolute configurations of the side chains of polyhydroxylated steroids from the starfish Henricia derjugini were determined by Moshers method using ¹H NMR spectra of R-(+)- and S-(–)--methoxy--(trifluoromethyl)phenylacetates of these compounds. The chiral centers have the (24S) configuration in a steroidal hexaol and henricioside H₁, the (24R,25S) configuration in henricioside H₂, and the (24R, 25R) configuration in henricioside H₃.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2530–2533, November, 2004.     

2,5,6,7,8-Pentasubstituted (S)- and (R)-[2-chroman-2-yl]ethanols as intermediates for the synthesis of α-tocopherol and its chiral analogs

In the presence of lipase from the yeast Candida cylindracea, partial acetylation of (±)-2-[6-benzyloxy-2,5,7,8-tetramethylchroman-2-yl]ethanol with vinyl acetate gives S-(+)-acetate whose alkaline hydrolysis affords (S)-(–)-alcohol. Repeated enzymatic acetylation of the residual alcohol up to 39% conversion afforded the R-enantiomer. The enantiomeric alcohols were oxidized to (S)- or (R)-aldehydes having the same sign of []_D as the original alcohols. These alcohols were converted into S-(+)- and R-(–)-enantiomers of the antioxidant MDL-73404, a hydrophilic analog of -tocopherol.