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Snapshots of three consecutive steps in the proteolytic reaction of HIV-1 protease (PR) were obtained in crystal structures at resolutions of 1.2–1.4 Å. Structures of wild-type protease and two mutants (PRV32I and PRI47V) with V32I and I47V substitutions, which are common in drug resistance, reveal the gem-diol tetrahedral intermediate, the separating N- and C-terminal products, and the C-terminal product of an autoproteolytic peptide. These structures represent three stages in the reaction pathway and shed light on the reaction mechanism. The near-atomic-resolution geometric details include a short hydrogen bond between the intermediate and the outer carboxylate oxygen of one catalytic Asp25 that is conserved in all three structures. The two products in the complex with mutant PRI47V have a 2.2 Å separation of the amide and carboxyl carbon of the adjacent ends, suggesting partial cleavage prior to product release. The complex of mutant PRV32I with a single C-terminal product shows density for water molecules in the other half of the binding site, including a partial occupancy water molecule interacting with the product carboxylate end and the carbonyl oxygen of one conformation of Gly27, which suggests a potential role of Gly27 in recycling from the product complex to the ligand-free enzyme. These structural details at near-atomic resolution enhance our understanding of the reaction pathway and will assist in the design of mechanism-based inhibitors as antiviral agents. [ABSTRACT FROM AUTHOR]

Here, we report the mechanisms of chiral transfer at various length scales in the self-assembly of enantiomeric chiral block copolymers (BCPs*). We show the evolution of homochirality from molecular chirality into phase chirality in the self-assembly of the BCPs*. The chirality of the molecule in the BCP* is identified from circular dichroism (CD) spectra, while the handedness of the helical conformation in the BCP* is determined from a split-type Cotton effect in vibrational circular dichroism spectra. Microphase separation of the BCP* is exploited to form a helical (H*) phase, and the handedness of helical nanostructure in the BCP* is directly visualized from transmission electron microscopy tomography. As examined by CD and fluorescence experiments, significant induced CD signals and a bathochromic shift of fluorescence emission for the achiral perylene moiety as a chemical junction of the BCPs* can be found while the concentration of the BCPs* in toluene solution is higher than the critical micelle concentration, suggesting a twisting and shifting mechanism initiating from the microphase-separated interface of the BCPs* leading to formation of the H* phase from self- assembly. [ABSTRACT FROM AUTHOR]

A series of mononuclear gold(I) acetylide complexes with urea moiety, R′3PAuC≡CC6H4-4-NHC(O)NHC6H4-4-R (R′ = cyclohexyl, R = NO2 (2a), CF3 (2b), Cl (2c), H (2d), CH3 (2e), tBu (2f), OCH3 (2g); R′ = phenyl, R = NO2 (3a), OCH3 (3b); R′ = 4-methoxyphenyl, R = H (4a), OCH3 (4b)), have been synthesized and characterized. The crystal structures of Ph3PAuC⁡CC6H4-4-NHC(O)NHC6H4-4-NO2 (3a) and (4-CH3OC6H4)3PAuC≡CC6H4-4-NHC(O)NHC6H5 (4a) have been determined by X-ray diffraction. Complexes 2a-2g, 3b, and 4a-4b show intense luminescence both in the solid state and in degassed THF solution at 298 K. Anion binding properties of complexes 2a-2g, 3a-3b, and 4a-4b have been studied by UV-vis and 1H NMR titration experiments. In general, the log K values of 2a-2g with the same anion in THF depend on the substituent R on the acetylide ligand of 2a-2g: R = NO2 (2a) > CF3 (2b) ⩾ Cl (2c) > H (2d) > CH3 (2e) ≈ tBu (2f) ⩾ OCH3 (2g). Complex 2a with NO2 group shows the dramatic color change toward F- in DMSO, which provides an access of naked eye detection of F-. [ABSTRACT FROM AUTHOR]

We report the design, synthesis, biological evaluation, and the X-ray crystal structure of a novel inhibitor bound to the HIV-1 protease. Various C3-functionalized cyclopentanyltetrahydrofurans (Cp-THF) were designed to interact with the flap Gly48 carbonyl or amide NH in the S2-subsite of the HIV-1 protease. We investigated the potential of those functionalized ligands in combination with hydroxyethylsulfonamide isosteres. Inhibitor 26containing a 3-(R)-hydroxyl group on the Cp-THF core displayed the most potent enzyme inhibitory and antiviral activity. Our studies revealed a preference for the 3-(R)-configuration over the corresponding 3-(S)-derivative. Inhibitor 26exhibited potent activity against a panel of multidrug-resistant HIV-1 variants. A high resolution X-ray structure of 26-bound HIV-1 protease revealed important molecular insight into the ligand-binding site interactions. [ABSTRACT FROM AUTHOR]

The mature HIV-1 protease (PR) bearing the L76V drug resistance mutation (PRL76V) is significantly less stable, with a >7-fold higher dimer dissociation constant (Kd) of 71 ± 24 nM and twice the sensitivity to urea denaturation (UC50 = 0.85 M) relative to those of PR. Differential scanning calorimetry showed decreases in Tm of 12 °C for PRL76V in the absence of inhibitors and 5−7 °C in the presence of inhibitors darunavir (DRV), saquinavir (SQV), and lopinavir (LPV), relative to that of PR. Isothermal titration calorimetry gave a ligand dissociation constant of 0.8 nM for DRV, 160-fold higher than that of PR, consistent with DRV resistance. Crystal structures of PRL76V in complexes with DRV and SQV were determined at resolutions of 1.45−1.46 Å. Compared to the corresponding PR complexes, the mutated Val76 lacks hydrophobic interactions with Asp30, Lys45, Ile47, and Thr74 and exhibits closer interactions with Val32 and Val56. The bound DRV lacks one hydrogen bond with the main chain of Asp30 in PRL76V relative to PR, possibly accounting for the resistance to DRV. SQV shows slightly improved polar interactions with PRL76V compared to those with PR. Although the L76V mutation significantly slows the N-terminal autoprocessing of the precursor TFR-PRL76V to give rise to the mature PRL76V, the coselected M46I mutation counteracts the effect by enhancing this rate but renders the TFR-PRM46I/L76V precursor less responsive to inhibition by 6 μM LPV while preserving inhibition by SQV and DRV. The correlation of lowered stability, higher Kd, and impaired autoprocessing with reduced internal hydrophobic contacts suggests a novel molecular mechanism for drug resistance. [ABSTRACT FROM AUTHOR]

Treatment of [Et4N][Tp*WS3] (1) (Tp* = hydridotris(3,5-dimethylpyrazol-l-yl)borate) with 2 equiv of AgSCN in MeCN afforded a novel neutral compound [(Tp*WS2)2(μ-S2)] (2). Reactions of 2 with excess CuX (X = Cl, Br, I) in MeCN and CH2Cl2 or CHCl3 formed three neutral W/Cu/S dusters [{Tp*W(μ3-S)3Cu3(μ-Cl)}2Cu(μ-Cl)2(μ7-Cl) (MeCN)]2 (3), [{Tp*W(μ3-S)3Cu3}2Br(μ-Br)2(μ4-Br)- (MeCN)] (4), and [{Tp*W(μ3-S)3Cu3}2{Cu2(μ-I)4(μ3-I)2}] (5), respectively. On the other hand, treatment of 2 with CuX (X = Cl, Br) in the presence of Et4NX (X = Cl, Br) produced two anionic W/Cu/S clusters [Et4N][{Tp*W(μ3-S)3Cu3X}2 (μ-X)2(μ4-X)] (6, X = Cl; 7 X = Br). Compounds 2-7 were characterized by elemental analysis, IR., UV-vis, ¹H NMR, electrospray ionization (ESI) mass spectra, and single-crystal X-ray crystallography. The dimeric structure of 2 can be viewed as two [Tp*WS2] fragments in which two W atoms are connected by one S22- dianion. Compounds 3-7 all possess unique halide-bridged double cubanelike frameworks. For 3, two [Tp*W(μ3-S)3Cu3]2+ dications are linked via a μ4-Cl- bridge, two μ-Cl- bridges, and a [Cu(MeCN)(μ-C1)2]+ bridge. For 4, one [Tp*W(μ3-S)3Cu3(MeCN)]2+ dication and one [Tp*W(μ3-S)3Cu3Br]+ cation are linked via a μ4-Br- and two μ-Br bridges. For 5, the two [Tp*W(μ3-S)3Cu3]2+ dications are bridged by a linear [(μ-l)2Cu- (μ3-I)2Cu(μ-I)2]4+ species. For 6 and 7, two [Tp*W(μ3-S)3Cu3X]+ cations are linked by μ4-X- and two μ-X- bridges (x = Cl, Br). In addition, the third-order nonlinear optical (NLO) properties of 2-7 in MeCN/CH2C12 were investigated by using femtosecond degenerate four-wave mixing (DFWM) technique. [ABSTRACT FROM AUTHOR]

As volatile organic compounds (VOCs) are a major group of air pollutants, development of materials for efficient adsorption and removal of VOCs is of great significance in both environmental and analytical sciences. Here we report metal-organic frameworks (MOFs) MIL-101 for the effective adsorption of VOCs at atmospheric pressure. A simple device was designed for quartz crystal microbalance (QCM), and six VOCs with various functional groups and polarities, i.e., n-hexane, toluene, methanol, butanone, dichloromethane, and n-butylamine, were chosen as targets to probe the adsorption properties of MIL-101. The developed device allows measurement of the adsorption isotherms and monitoring of the dynamic process for the adsorption of VOCs on MOFs, and also provides a useful tool for characterization of MOFs. The adsorption isotherms of the VOCs on MIL-101 followed the Dubinin-Astakhov equation with the characteristic energy from 5.70 (methanol) to 9.13 kJ mol-1 (n-butylamine), Astakhov exponent from 0.50 (n-butylamine) to 3.03 (n-hexane), and the limiting adsorption capacity from 0.08 (n-hexane) to 12.8 (n-butylamine) mmol g-1. MIL-101 exhibited the strongest affinity to n-butylamine, but the weakest affinity to n-hexane. The determined Astakhov exponents and the isosteric heats of adsorption revealed the energetic heterogeneity of MIL-101. MIL-101 showed the most energetically homogeneous for n-hexane, but the most energetically heterogeneous for n-butylamine. The dynamic process of adsorption monitored by the QCM system demonstrated the distribution of the sorption sites within MIL-101. The metal sites within the MIL-101 were vital in adsorption process. MIL-101 gave much higher affinity and bigger adsorption capacity to VOCs than activated carbon, offering great potential for real applications in the adsorption and removal of VOCs. [ABSTRACT FROM AUTHOR]

Water repellency and ultraviolet (UV) protection are desirable properties for textiles. In this paper, the cotton fabrics were first treated with CeO2sol and then modified with a layer of dodecafluoroheptyl-propyl-trimethoxylsilane (DFTMS). The as-obtained cotton sample was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Fourier transformation infrared spectroscopy (FTIR), water contact angle measurement, and UV−vis spectrophotometry. The modified cotton surface not only exhibited robust superhydrophobicity with a high contact angle of 158° and low roll-off angle of 14° for 5-μL water droplets, but also rendered excellent protection against UV radiation because of incorporation of CeO2particles. [ABSTRACT FROM AUTHOR]

Hypoxia-inducible factor 1 (HIF1) is a heterodimeric basic helix-loop-helix transcription factor that regulates many key genes. δ-Aminolevulinate synthase (ALAS) catalyzes the first and rate-limiting reaction in the heme biosynthetic pathway. In this study, we show that hypoxia-induced expression of erythroid-specific ALAS2 is mediated by HIF1 in erythroid cells. Under hypoxic conditions, significantly increased ALAS2 mRNA and protein levels were detected in K562 cells and erythroid induction cultures of CD34+ hematopoietic stem/progenitor cells. Enforced HIF1α expression increased the level of ALAS2 expression, while HIF1α knockdown by RNA interference decreased the level of ALAS2 expression. In silico analysis revealed three potential hypoxia-response elements (HREs) that are located 611, 621, and 741 bp downstream of the ALAS2 gene. The results from reporter gene and mutation analysis suggested that these elements are necessary for a maximal hypoxic response. Chromatin immunoprecipitation and polymerase chain reaction showed that the HREs could be recognized and bound by HIF1α in vivo. These results demonstrate that the upregulation of ALAS2 during hypoxia is directly mediated by HIF1. We hypothesize that HIF1-mediated ALAS2 upregulation promotes erythropoiesis to satisfy the needs of an organism under hypoxic conditions. This may be accomplished via increased heme levels and an interaction between ALAS2 and erythropoietin. [ABSTRACT FROM AUTHOR]

The structure-based design, synthesis, and biological evaluationof a series of nonpeptidic macrocyclic HIV protease inhibitors aredescribed. The inhibitors are designed to effectively fill in thehydrophobic pocket in the S1′−S2′ subsites andretain all major hydrogen bonding interactions with the protein backbonesimilar to darunavir (1)or inhibitor 2.The ring size, the effect of methyl substitution, and unsaturationwithin the macrocyclic ring structure were assessed. In general, cyclicinhibitors were significantly more potent than their acyclic homologues,saturated rings were less active than their unsaturated analoguesand a preference for 10- and 13-membered macrocylic rings was revealed.The addition of methyl substituents resulted in a reduction of potency.Both inhibitors 14band 14cexhibited markedenzyme inhibitory and antiviral activity, and they exerted potentactivity against multidrug-resistant HIV-1 variants. Protein−ligandX-ray structures of inhibitors 2and 14cprovided critical molecular insights into the ligand-binding siteinteractions. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) have received great attention due to their fascinating structures and intriguing potential applications in various fields. Herein, we report the first example of the utilization of MOFs for solid-phase microextraction (SPME). MOF-199 with unique pores and open metal sites (Lewis acid sites) was employed as the coating for SPME fiber to extract volatile and harmful benzene homologues. The SPME fiber was fabricated by in situ hydrothermal growth of thin MOF-199 films on etched stainless steel wire. The MOF-199-coated fiber not only offered large enhancement factors from 19613 (benzene) to 110860 (p-xylene), but also exhibited wide linearity with 3 orders of magnitude for the tested benzene homologues. The limits of detection for the benzene homologues were 8.3-23.3 ng L-1. The relative standard deviation (RSD) for six replicate extractions using one SPME fiber ranged from 2.0% to 7.7%. The fiber-to-fiber reproducibility for three parallel prepared fibers was 3.5%-9.4% (RSD). Indoor air samples were analyzed for the benzene homologues using the SPME with the MOF-199-coated fiber in combination with gas chromatography-flame ionization detection. The recoveries for the spiked benzene homologues in the collected indoor air samples were in the range of 87%-106%. The high affinity of the MOF-199-coated fiber to benzene homologues resulted from the combined effects of the large surface area and the unique porous structure of the MOF-199, the π-π interactions of the aromatic rings of the analytes with the framework 1,3,5-benzenetricarboxylic acid molecules, and the π-complexation of the electron-rich analytes to the Lewis acid sites in the pores of MOF-199. [ABSTRACT FROM AUTHOR]

Fibrils of the intrinsically disordered protein α-synuclein are hallmarks of Parkinson's disease. The fluorescent dye thioflavin T is often used to characterize fibrillation, but this assay may not provide quantitative information about structure and mechanism. To gain such information, we incorporated the 19F-labeled amino acid, 3-fluorotyrosine, into recombinant human α-synuclein at its endogenous tyrosine residues. Tyrosine 39 is in the positively charged N-terminal region of this 140-residue protein. The other three tyrosines, 125, 133, and 136, are near the C-terminus. 19F nuclear magnetic resonance spectroscopy was used to study several properties of labeled α-synuclein, including its conformation, conformational changes induced by urea, spermine, and sodium dodecyl sulfate (SDS), its interaction with SDS micelles, and the kinetics of fibril formation. The results show that the tyrosines are in disordered regions but that there is some structure near position 39 that is disrupted by urea. SDS binding alters the conformation near position 39, but the C-terminal tyrosines are disordered under all conditions. The NMR data also indicate that SDS-micelle-bound α-synuclein and the free protein exchange on the 10 ms time scale. Studies of fibrillation show the utility of 19F-labeled NMR. The data indicate that fibrillation is not accompanied by the formation of large quantities of low molecular weight intermediates. Although dye binding and 9F NMR data show that 1 mM SDS and 1 mM spermine accelerate aggregation compared to buffer alone, only the NMR data indicate that the species formed in SDS are smaller than those formed in buffer or buffer plus spermine. We conclude that 19F NMR spectroscopy is useful for obtaining residue-level, quantitative information about the structure, binding, and aggregation of α-synuclein. [ABSTRACT FROM AUTHOR]

Almost everything we know about protein biophysics comes from studies on purified proteins in dilute solution. Most proteins, however, operate inside cells where the concentration of macromolecules can be >300 mg/mL. Although reductionism-based approaches have served protein science well for more than a century, biochemists now have the tools to study proteins under these more physiologically relevant conditions. We review a part of this burgeoning postreductionist landscape by focusing on high-resolution protein nuclear magnetic resonance (NMR) spectroscopy, the only method that provides atomic-level information over an entire protein under the crowded conditions found in cells. [ABSTRACT FROM AUTHOR]

The three-dimensionally ordered macroporous (3DOM) ZrO2: Er3+, Yb3+ materials were successfully synthesized by the sol–gel method combined with a polystyrene latex sphere templating technique, and their morphologies, surface physicochemical properties, and upconversion photoluminescence (UC-PL) properties were studied. The results indicate that the materials exhibited both porosity and strong UC-PL under the excitation of a 978 nm diode laser. In comparison with the nonporous samples, the relative intensity of the red (4F9/2-4I15/2) to the green (4S3/2/2H11/2-4I15/2) emission decreased visibly because of the decreased nonradiative relaxation in the 3DOM materials. It was also observed that the relative intensity of the green emission to the red emission increased significantly with the increasing excitation power. An indirect three-photon populating process occurred for the green emission as the excitation power and Yb3+ concentration was high enough. [ABSTRACT FROM AUTHOR]

We report the design, synthesis, and biological evaluation of a series of novel HIV-1 protease inhibitors. The inhibitors incorporate stereochemically defined flexible cyclic ethers/polyethers as high affinity P2-ligands. Inhibitors containing small ring 1,3-dioxacycloalkanes have shown potent enzyme inhibitory and antiviral activity. Inhibitors 3dand 3hare the most active inhibitors. Inhibitor 3dmaintains excellent potency against a variety of multi-PI-resistant clinical strains. Our structure−activity studies indicate that the ring size, stereochemistry, and position of oxygens are important for the observed activity. Optically active synthesis of 1,3-dioxepan-5-ol along with the syntheses of various cyclic ether and polyether ligands have been described. A protein−ligand X-ray crystal structure of 3d-bound HIV-1 protease was determined. The structure revealed that the P2-ligand makes extensive interactions including hydrogen bonding with the protease backbone in the S2-site. In addition, the P2-ligand in 3dforms a unique water-mediated interaction with the NH of Gly-48. [ABSTRACT FROM AUTHOR]

The goal of this study was to develop a new type of core−shell micelles based on biocompatible and biodegradable amphiphilic copolymers, named PCL-CS, using chondroitin sulfate (CS) as a hydrophilic segment and poly(ϵ-caprolactone) (PCL) as a hydrophobic segment. The copolymers, prepared from the various compositions between CS and PCL, were characterized by Fourier transform infrared spectrometer, proton nuclear magnetic resonance spectrometer, and differential scanning calorimeter. The PCL-CS copolymers could be assembled into micelles using a simple emulsion. With the fluorescent probe technique, the critical micelle concentrations were obtained in the range of 1.26 × 10 −3−8.86 × 10 −3mg/mL. The spherical images of micelles were visualized in the presence of polyvinyl alcohol (PVA) with the use of the transmission electron microscope. The particle sizes of micelles were all smaller than 300 nm, neither aggregate nor change in hydrodynamic sizes after 15 days staying in solutions containing salts or PVA by dynamic light scattering. The intracellular uptake of KB cells incubated with PCL-CS micelles was evidenced by confocal laser scanning microscope upon loading fluorescein isothiocyanate labeled bovine serum albumin as a probe. [ABSTRACT FROM AUTHOR]

Diphenylphosphinic acid (DPPA) was synthesized and characterized by infrared spectroscopy (IR), nuclear magnetic resonance ( 1H NMR), mass spectroscopy (MS), and elemental analysis. The melting point and the enthalpy of fusion of DPPA were measured by a differential scanning calorimeter (DSC), and the thermal stability of DPPA was measured by thermogravimetric analysis (TGA). The solubility data of DPPA in nine solvents were measured and correlated with an empirical equation. The estimated uncertainty of all the solubility values based on error analysis and repeated observations was within 2.0 %. [ABSTRACT FROM AUTHOR]

Novel cluster anions Li2F-and Li6F-with alkalide character have been studied in the present paper. In contrast to a typical neutral alkalide, Li2F-contains a F-anion instead of the neutral ligand and forms an alkalide anion F-LiLi-. In addition to a F-anion ligand, Li6F-contains a Li3superalkali cation instead of the alkali metal cation and a Li3-superalkali anion instead of the alkali metal anion, and this alkalide anion can be denoted by F-Li3Li3-, which is supported by NBO charge results. The results indicate that the F-anion can polarize not only the Li atom but also the Li3superalkali to form alkalide anions with excess electrons. For Li2F-, two linear structures (1and 3states) are obtained. For Li6F-, the structure of the 1A1state is a trigonal antiprism capped by the F-anion with C3vsymmetry, while the structure of the 7A‘ state is a slightly distorted trigonal antiprism with Cssymmetry. Due to the excess electrons on the alkali metal and superalkali anions (Li-and Li3-), the alkalide anions Li2F-and Li6F-have large first hyperpolarizabilities (01.116 × 104−1.764 × 105au). For the spin multiplicity effect on electric properties, in these two alkalide anions, the values of the static electric properties, especially the first hyperpolarizabilities, of the high spin states are larger than the corresponding values of the low spin states. For the substitution effect of superalkali atoms, in the two singlet states, as the Li3superalkalis substitute the Li atoms, the value of the mean of polarizability increases, while the values of dipole moment and the first hyperpolarizability decrease. [ABSTRACT FROM AUTHOR]

A new sensing mechanism based on CN isomerization, which shows a very significant fluorescence enhancement to the metal cations in a simple and efficient way, is demonstrated. A coumarin derivative (L) containing a CN group was designed as an example for illustration. The free ligand Lis almost nonfluorescent due to the isomerization of CN double bond in the excited state. However, the solution of ligand shows about a 200-fold increase of fluorescence quantum yield (about 30%) upon addition of Zn(ClO4)2. [ABSTRACT FROM AUTHOR]

We present the synthesis and characterization of a fused-ring compound, dithieno[2,3-d:2',3'-d']thieno[3,2-b:4,5-b']dithiophene (pentathienoacene, PTA). In contrast to pentacene, PTA has a larger band gap than most semiconductors used in organic field-effect transistors (OFETs) and therefore is expected to be stable in air. The large π-conjugated and planar molecular structure of PTA would also form higher molecular orders that are conductive for carrier transport. X-ray diffraction and atomic force microscopy experiments on its films show that the molecules stack in layers with their long axis upright from the surface. X-ray photoelectron spectroscopy suggests that there are no chemical bonds at the PTA/Au interlace. OFETs based on the PTA have been constructed, and their performances as p-type semiconductors are also presented. A high mobility of 0.045 cm²/V s and an on/off ratio of 10³ for a PTA OFET have been achieved, demonstrating the potential of PTA for application in future organic electronics. [ABSTRACT FROM AUTHOR]

Saccharomyces cerevisiae Dmc1, a meiosis-specific homologue of RecA, catalyzes homologous pairing and strand exchange during meiotic DNA recombination. The purified budding yeast Dmc1 (ScDmc1) protein exhibits much weaker recombinase activity in vitro as compared to that of the Escherichia coli RecA protein. Using atomic force microscopy (AFM) with carbon nanotube tips, we found ScDmc1 forms rings with an external diameter of 18 nm and a central cavity of 4 nm. In the presence of single- stranded DNA (ssDNA), the majority of the ScDmc1 protein (90%) bound DNA as protein rings; only a small faction (10%) was able to form filamentous structure. In contrast, nearly all RecA proteins form fine helical nucleoprotein filaments with ssDNA under identical conditions. RecA-mediated recombinase activity is initiated through the nucleation of RecA onto ssDNA to form helical nucleoprotein filaments. Our results support the notion that ScDmc1 becomes catalytically active only when it forms a helical nucleoprotein filament with ssDNA. [ABSTRACT FROM AUTHOR]

Characterizes nonanuclear lanthanide(III)-copper(II) complexes of macrocyclic oxamide. Application of an elemental analysis and electronic spectra; Determination of the crystal structures of the complexes; Evaluation of the magnetic properties of the complexes.

Chiral quaternary ammonium salts derived from cinchonidine have been applied to catalyze the stereoselective iodolactonizations of trans-5-aryl-4-pentenoic acids leading to a mixture of two regioselectively iodolactonized products with fair to excellent yield (37-98%) and moderate enantioselectivity (exo = 42.0% ee, endo = 31.0% ee) under mild conditions. This work is the first example of asymmetric iodolactonization reaction in the presence of less than a stoichiometric amount of chiral reagent. [ABSTRACT FROM AUTHOR]