S-propylene Oxide Research Articles

Symmetry Breaking of Atomically Precise Fullerene-like Metal Nanoclusters.

Here we report a neutral fullerene-like core-shell homosilver Ag13@Ag20 nanocluster that is fully protected by an achiral bidentate thiolate ligand (9,12-dimercapto-1,2-closo-carborane, C2B10H10S2H2), which crystallizes in centrosymmetric space group R3̅. Continuous Cu doping in the dodecahedral shell first induced symmetry breaking to generate chiral Ag13@Ag20-nCun (6 ≥ n ≥ 2) containing two acetonitrile ligands in space group P212121, and then produced symmetric all-thiolated Ag13@Ag20-nCun (20 ≥ n ≥ 13) in the higher space group Im3̅. The selectively copper-doped Ag13@Ag20-nCun (6 ≥ n ≥ 2) cluster has its structure reorganized to a lower symmetry that shows chiroptical activity. Moreover, structural distortion of Ag13@Ag20-nCun (6 ≥ n ≥ 2) further expanded in chiral R-/S-propylene oxide, which induced a more prominent core-based CD response. This work revealed a novel mechanism of chirality generation at the atomic level through asymmetric shell-doping of metal nanoclusters, which provides new insight into the origin of chirality in inorganic nanostructures.

Introduction of a Biphenyl Moiety for a Solvent-Responsive Aryl Gold(I) Isocyanide Complex with Mechanical Reactivation.

Luminescent compounds that are sensitive to volatile organic solvents are useful for detection of harmful gases. Although such compounds have been reported, discrimination of various types of volatile organic compounds using one compound remains challenging. We reported a series of gold isocyanide complexes that form various crystalline structures with distinct emission properties, which can be interconverted by mechanical stimulation and solvent addition. Here, we report that introduction of a biphenyl unit into a gold isocyanide scaffold (denoted complex 3) enables discrimination of various volatile organic compounds by forming 11 solvent-containing crystal structures 3/solvent [solvent can be CHCl3, pyridine (Py), CH2Cl2, CH2Br2, dimethylacetamide (DMA), acetaldehyde (AcH), CH3CN, DMF, (S)-propylene oxide (SPO), rac-propylene oxide (racPO), or acetone] with different emission properties (emission maxima of 490-580 nm). Mechanical stimulation of 3/solvent affords amorphous 3ground without solvent inclusion. The resulting 3ground can again detect volatile compounds by forming 3/solvent with concomitant emission color changes. We also afforded a dozen single crystals of 3, which include 11 solvated 3/solvent and one solvent-free 3/none. The molecular arrangements of 3 in 3/solvent and 3/none are all different. Comparison of various crystallographic parameters of 3/solvent and 3/none with their corresponding optical properties indicates that a combination of various structural properties of 3 affects the optical properties of 3. This study reveals that the introduction of a biphenyl moiety could be a useful design to develop versatile indicators for solvents through the formation of multiple luminescent crystal structure.

Polarimetric Detection of Enantioselective Adsorption by Chiral Au Nanoparticles — Effects of Temperature, Wavelength and Size

R- and S-propylene oxide (PO) have been shown to interact enantiospecifically with the chiral surfaces of Au nanoparticles (NPs) modified with D- or L-cysteine (cys). This enantiospecific interaction has been detected using optical polarimetry measurements made on solutions of the D- or L-cys modified Au (cys/Au) NPs during addition of racemic PO. The selective adsorption of one enantiomer of the PO onto the cys/Au NP surfaces results in a net rotation of light during addition of the racemic PO to the solution. In order to optimize the conditions used for making these measurements and to quantify enantiospecific adsorption onto chiral NPs, this work has measured the effect of temperature, wavelength and Au NP size on optical rotation by solutions containing D- or L-cys/Au NPs and racemic PO. Increasing temperature, decreasing wavelength and decreasing NP size result in larger optical rotations.

Quantitation of enantiospecific adsorption on chiral nanoparticles from optical rotation

Au nanoparticles modified with enantiomerically pure d- or l-cysteine have been shown to serve as enantioselective adsorbents of R- and S-propylene oxide. A simple adsorption model and accompanying experimental protocol have been developed to enable optical rotation measurements to be analyzed for quantitative determination of the ratios of the enantiospecific adsorption equilibrium constants of chiral species on the surfaces of chiral nanoparticles, KLS/KDS=KDR/KLR. This analysis is robust in the sense that it obviates the need to measure the absolute surface area of the absorbent nanoparticles, a quantity that is somewhat difficult to obtain accurately. This analysis has been applied to optical rotation data obtained from solutions of R- and S-propylene oxide, in varying concentration ratios, with d- and l-cysteine coated Au nanoparticles, in varying concentration ratios.

Enantiospecific Desorption of R- and S-Propylene Oxide from d- or l-Lysine Modified Cu(100) Surfaces

The enantiospecific desorption kinetics of R- and S-propylene oxide (PO) from a Cu(100) surface modified by enantiomerically pure D- or L-lysine have been studied using temperature programmed desorption. These experiments have used R- or S-PO as the chiral probe for study of enantiospecific adsorption on Cu(100) surfaces modified with D- or L-lysine. This chiral probe/modifier/Cu system manifests a significant diastereomeric effect in the R- and S-PO peak desorption temperatures and, hence, true enantiospecific behavior. The enantiospecificity in the PO desorption kinetics is observed only over a narrow range of lysine modifier coverage with a maximum at a lysine coverage leaving an empty site density of θ(O) ≈ 0.25. The observation of enantiospecific behavior in the PO/lysine/Cu(100) system is in contrast with the failed results of prior attempts to observe enantiospecific desorption from chirally modified Cu surfaces. The potential for hydrogen-bonding interactions between the chiral probe and chiral modifier, which can depend on the coverage and configuration of the adsorbed modifier, may play a crucial role in enantiospecific adsorption on lysine modified Cu surfaces.

Enantioselective Reactions on a Au/Pd(111) Surface Alloy with Coadsorbed Chiral 2-Butanol and Propylene Oxide

The coadsorption of R- and S-propylene oxide with R-2-butanol was studied on a dilute Au/Pd(111) alloy containing ∼8% gold using temperature-programmed desorption and reflection absorption infrared spectroscopy. Alloy formation strongly affects the surface chemistry of these molecules as compared to clean Pd(111). A portion of the propylene oxide decomposes to form CO and ethylidyne species on the alloy, while on clean Pd(111), it adsorbs reversibly. 2-Butanol reacts to form a 2-butoxide species on the alloy that either rehydrogenates to form 2-butanol or undergoes a β-hydride elimination reaction to yield 2-butanone. Coadsorption of R-2-butanol with either R- or S-propylene oxide led to a larger 2-butanone yield in the presence of S-propylene oxide with an enantiomeric excess (ee) of ∼14%. This led to an enantioselective depletion of the 2-butoxide species such that the subsequent 2-butanol formation is highly enantioselective, with 100% ee.

Enantioselective Chemisorption of Propylene Oxide on a 2-Butanol Modified Pd(111) Surface: The Role of Hydrogen-Bonding Interactions

The enantioselective chemisorption of R- and S-propylene oxide has been measured either on clean Pd(111) that has been exposed to S-2-butanol at various temperatures to vary the proportion of 2-butanol and 2-butoxide species or by adsorbing S-2-butanol on oxygen-covered Pd(111) to form exclusively 2-butoxide. The results reveal that enantioselective chemisorption is only found when 2-butanol is present on the surface. This is ascribed to enantiospecific hydrogen-bonding interactions between 2-butanol and propylene oxide. Measurements of the variation in enantiospecificity with 2-butanol exposure suggest that propylene oxide can interact either with a single adsorbed 2-butanol molecule or, at higher coverages, with two adsorbed 2-butanol species to form enantioselective sites.

Coupled cluster calculations of the optical rotation of S-propylene oxide in gas phase and solution

We present ab initio calculations of the optical rotation of S-propylene oxide in both gas phase and solution using the coupled cluster methodology combined with a dielectric continuum description of the solvent. The coupled cluster calculations are performed using the CCS, CC2, CCSD and CC3 methods. None of the presented gas phase results are in accord with the experimental sign of the optical rotation at 355 nm. Thereby, the experimental sign change between the gas phase and the cyclohexane solution optical rotation at 355 nm is not reproduced theoretically. The vibrational effects are considered to be significant and may be of crucial importance in order to bring accordance between the calculated and the experimentally established sign of the gas phase optical rotation at 355 nm.

Origin invariant calculation of optical rotation without recourse to London orbitals

We propose an inherently origin invariant formulation of specific optical rotation obtained from the conventional velocity gauge expression by subtracting the static limit from the electric dipole–magnetic dipole polarizability: 〈〈 p → , L → 〉〉 ω→〈〈 p → , L → 〉〉 ω−〈〈 p → , L → 〉〉 0 . London (gauge including) atomic orbitals are therefore not needed to ensure origin invariance and, consequently, this modified velocity gauge formulation may be employed in conjunction with variational and non-variational quantum chemical methods alike. Sample calculations on S-propylene oxide and 3,4-methylenedioxymethamphetamine using self-consistent field and coupled cluster wave functions underline this point and show that the basis set convergence of the modified velocity gauge formulation is similar to the conventional length gauge and London expressions.

Enantiospecific desorption of R- and S-propylene oxide from a chiral Cu(643) surface.

Enantiospecific desorption of R- and S-propylene oxide from a chiral Cu(643) surface.

Synthesis and solution properties of lanthanum(III), europium(III), and lutetium(III) THP complexes and an x-ray diffraction study of a crystal containing four stereoisomers of a europium(III) THP complex (THP = 1,4,7,10-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane). Methyl groups impart rigidity to S,S,S,S-THP macrocyclic complexes

The macrocycle 1,4,7,10-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane (THP) prepared from racemic propylene oxide and cyclen (1,4,7,10-tetraazacyclododecane) consists of a mixture of stereoisomers that arise from the chiral {alpha}-carbons of the hydroxypropyl groups. {sup 13}C NMR studies suggest that five different diastereomers are formed. Lanthanum(III), europium(III), and lutetium(III) THP complexes are synthesized from the mixture of THP stereoisomers. Europium(III) THP complexes containing R,R,R,S and S,S,S,R configurations at the {alpha}-carbons of the hydroxypropyl groups cocrystallize from solution. The complex [Eu(THP)(H{sub 2}O)]{sub 2}(CF{sub 3}SO{sub 3}){sub 6}{center_dot}2EtOH{center_dot}H{sub 2}O crystallizes in the centrosymetric monoclinic space group P2{sub 1}/c (No. 14). Four stereoisomers (two enantiomeric pairs) of the complex appear in the crystal. Each asymmetric unit consists of two different diastereomers of the europium(III) cation, six triflate anions, two ethanol molecules, and one water molecule of solvation. The structure was solved and refined to R = 5.54% and R{sub w} = 5.72% for those 3351 reflections with {vert_bar}F{sub o}{vert_bar} > 6{sigma}{vert_bar}F{sub o}{vert_bar}. In addition, synthesis of the THP stereoisomer with all hydroxypropyl groups containing the S-configuration (S-THP) is accomplished by use of S-propylene oxide. The synthesis of lanthanum(III), europium(III), and lutetium(III) complexes of S-THP is reported; {sup 1}H and {sup 13}C NMR spectra of the lanthanum and lutetium complexes indicatemore » that only one diastereomer is present in solution.« less

Asymmetric synthesis of 2,4-disubstituted butyrolactones using the iron chiral auxiliary [(η 5-C 5H 5)Fe(CO)(PPh 3)

Treatment of the lithium enolate derived from homochiral S-[(n 5η-C 5H 5)Fe(CO)(PPh 3)COCH 2CH 3] with homochiral R- or S-propylene oxide or R-styrene oxide in the presence of diethylaluminium chloride followed by oxidative decomplexation generated cis-2S,4R-dimethyl butyrolactone, trans-2S,4S-dimethyl butyrolactone and cis-2S,4S-2-methyl-4-phenyl butyrolactone respectively. An X-ray crystal structure of the latter compound established unambiguously the relative and absolute configurations. Treatment of the lithium enolate from homochiral R-[(ηn 5-C 5H 5)Fe(CO)(PPh 3)COCH 2CH 3]with R-styrene oxide in the presence of diethylaluminium chloride followed by oxidative decomplexation generated trans-2R,4S-2-methyl-4-phenyl butyrolactone. In the presence of diethylaluminium chloride the enolate from S-[(η 5-C 5H 5)Fe(CO)(PPh 3)COCH 2CH 3] with racemic styrene oxide exhibited chiral discrimination in favour of the R-epoxide to the extent of 100:1