Interconversion Process Research Articles

Right- and Left-Handed Helices, What is in between? Interconversion of Helical Structures of Alternating Pyridinedicarboxamide/m-(phenylazo)azobenzene Oligomers.

Some unnatural polymers/oligomers have been designed to adopt a well-defined, compact, three-dimensional folding capability. Azobenzene units are common linkages in these oligomer designs. Two alternating pyridinedicarboxamide/m-(phenylazo)azobenzene oligomers that can fold into both right- and left-handed helices were studied computationally in order to understand their dynamical properties. Helical structures were shown to be the global minima among the many different conformations generated from the Monte Carlo simulations, and extended conformations have higher potential energies than compact ones. To understand the interconversion process between right- and left-handed helices, replica-exchange molecular dynamic (REMD) simulations were performed on both oligomers, and with this method, both right- and left-handed helices were successfully sampled during the simulations. REMD trajectories revealed twisted conformations as intermediate structures in the interconversion pathway between the two helical forms of these azobenzene oligomers. This mechanism was observed in both oligomers in current study and occurred locally in the larger oligomer. This discovery indicates that the interconversion between helical structures with different handedness goes through a compact and partially folded structure instead of globally unfold and extended structure. This is also verified by the nudged elastic band (NEB) calculations. The temperature weighted histogram analysis method (T-WHAM) was applied on the REMD results to generate contour maps of the potential of mean force (PMF). Analysis showed that right- and left-handed helices are equally sampled in these REMD simulations. In large oligomers, both right- and left-handed helices can be adopted by different parts of the molecule simultaneously. The interconversion between two helical forms can occur in the middle of the helical structure and not necessarily at the termini of the oligomer.

Co-Crystals and Salts Obtained from Dinitrogen Bases and 1,2,3,4-Cyclobutane Tetracarboxylic Acid and the Use of the Latter As a Template for Solid-State Photocyclization Reactions

The synthesis, isolation, and characterization of a series of co-crystals and adducts of 1,2,3,4-cyclobutane tetracarboxylic acid (H4CBTC) with the dinitrogen bases 1,2-bis(4-pyridyl)ethane (BPA) and 1,2-bis(4-pyridyl)ethylene (BPE), respectively, are reported. The thermal stability and interconversion process between the dihydrated salt [BPAH2][H2CBTC]·2H2O and its dehydration product and the use of this latter to obtain the neutral co-crystal [BPA]2·[H4CBTC] have been investigated. The products obtained with 1,2-bis(4-pyridyl)ethylene (BPE), namely, the salt [BPEH][H3CBTC] and the co-crystal [BPE]2·[H4CBTC] are prearranged in space so as to be able to react photochemically yielding rctt-tetrakis(4-pyridyl)cyclobutane (TPCB). Recrystallization from ethanol of the photocyclization products yields the channeled structure of the solvated co-crystal [TPCB]·[H4CBTC]·EtOH.

Redox-Modulated Stepwise Photochromism in a Ruthenium Complex with Dual Dithienylethene-Acetylides

Achieving stepwise photochromism in a combined molecule to access all of the possible ring-open/closed isomers is a challenge due to facile energy transfer from ring-open dithienylethene (DTE) to an adjacent ring-closed moiety that prohibits further photocyclization. The preparation, characterization, and photochromic properties of a bis(σ-acetylide) bonded ruthenium(II) complex 2oo and its oxidized form 2oo(+) with two identical DTE-acetylides (L1o) are described. Stepwise and dual photochromic reactions are successfully achieved in both 2oo and 2oo(+), in which the ring-closing absorption band of 2oo(+) shows an obvious blue-shift relative to 2oo. It is demonstrated that stepwise photochromic reactions 2oo→2co→2cc are more facile than 2oo(+)→2co(+)→2cc(+). The lower electronic density at the reactive carbon atoms upon oxidation of Ru(II) to Ru(III) causes photocyclization to have more difficulty proceeding in oxidized species 2oo(+)/2co(+). Upon dual ring-closure, 2cc/2cc(+) exhibits significant electronic interaction between two identical ring-closed DTE units across trans-Ru(dppe)(2) spacer. The interconversion processes among six states are unambiguously demonstrated by NMR, UV-vis-NIR, and IR spectroscopic, and electrochemical and computational studies.

Temperature Effect on the Two-Photon Absorption Spectrum of All-trans-β-carotene

In this report, we investigate the influence of temperature on the two-photon absorption (2PA) spectrum of all-trans-β-carotene using the femtosecond white-light-continuum Z-scan technique. We observed that the 2PA cross-section decreases quadratically with the temperature. Such effect was modeled using a three-energy-level diagram within the sum-over-essential states approach, assuming temperature dependencies to the transition dipole moment and refractive index of the solvent. The results show that the transition dipole moments from ground to excited state and between the excited states, which governed the two-photon matrix element, have distinct behaviors with the temperature. The first one presents a quadratic dependence, while the second exhibits a linear dependence. Such effects were attributed mainly to the trans→cis thermal interconversion process, which decreases the effective conjugation length, contributing to diminishing the transition dipole moments and, consequently, the 2PA cross-section.

Determination of barriers to rotation of axially chiral 5‐methyl‐2‐(o‐aryl)imino‐3‐(o‐aryl)thiazolidine‐4‐ones

Thermally interconvertible axially chiral 5-methyl-2-(o-aryl)imino-3-(o-aryl)-thiazolidine-4-ones have been synthesized diastereoselectively, and conformations of the major and minor enantiomeric pairs have been determined by (1)H nuclear magnetic resonance. Chromatographic resolutions of each compound have been performed by enantioselective high-performance liquid chromatography, and the barriers to rotation about the N(3)-C(aryl) bond have been determined by following the thermal interconversion process of the major to minor isomers until equilibrium. The rotational barriers range from 96.2 to 115.2 kJ/mol, depending on the size of ortho substituent on N(3)-aryl ring.

Electrochemical Synthesis and Characterization of Semiconducting Ni(TCNQF4)2(H2O)2 (TCNQF4 = 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane)

AbstractAn electrochemical technique has been used to synthesize Ni(TCNQF4)2(H2O)2 (TCNQF4 = 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane). The method involves the reduction of solid TCNQF4 immobilized on an electrode surface in contact with Ni2+ (aq.)‐containing electrolyte. The electrochemically irreversible, but chemically reversiblesolid–solid TCNQF4/Ni(TCNQF4)2(H2O)2 interconversion process is governed by nucleation and growth kinetics and is represented by the overall reaction: 2TCNQF4 (s, electrode) + Ni2+ (aq.) + 2H2O + 2e [rlhar2] Ni(TCNQF4)2(H2O)2 (s, electrode). Thus, the formation of Ni(TCNQF4)2(H2O)2 involves the one‐electron reduction of TCNQF4 to [TCNQF4]·– coupled with an ingress of Ni2+ (aq.) from the aqueous electrolyte, while the reverse scan represents the oxidation of [TCNQF4]·– to TCNQF4 coupled with the egress of Ni2+ (aq.). Cyclic voltammograms for the TCNQF4/Ni(TCNQF4)2(H2O)2 solid–solid phase transformation are independent of the electrode material and the identity of the Ni2+ (aq.) counteranion but are strongly dependent on the concentration of Ni2+ (aq.) and the scan rate. UV/Vis, infrared, and Raman spectra confirm the presence of [TCNQF4]·– in the newly synthesized material. The composition of Ni(TCNQF4)2(H2O)2 was deduced from thermogravimetric and elemental analyses. Scanning electron microscopic images of Ni(TCNQF4)2(H2O)2 electrocrystallized onto the surface of an indium tin oxide electrode show a thin film morphology. Magnetic and conductivity data demonstrate that the complex behaves as a classical paramagnet and is a typical semiconductor with a band gap close to that of an insulator.

Microcin Amyloid Fibrils A Are Reservoir of Toxic Oligomeric Species

Microcin E492 (Mcc), a low molecular weight bacteriocin produced by Klebsiella pneumoniae RYC492, has been shown to exist in two forms: soluble forms that are believed to be toxic to the bacterial cell by forming pores and non-toxic fibrillar forms that share similar biochemical and biophysical properties with amyloids associated with several human diseases. Here we report that fibrils polymerized in vitro from soluble forms sequester toxic species that can be released upon changing environmental conditions such as pH, ionic strength, and upon dilution. Our results indicate that basic pH (≥8.5), low NaCl concentrations (≤50 mm), and dilution (>10-fold) destabilize Mcc fibrils into more soluble species that are found to be toxic to the target cells. Additionally, we also found a similar conversion of non-toxic fibrils into highly toxic oligomers using Mcc aggregates produced in vivo. Moreover, the soluble protein released from fibrils is able to rapidly polymerize into amyloid fibrils under fibril-forming conditions and to efficiently seed aggregation of monomeric Mcc. Our findings indicate that fibrillar forms of Mcc constitute a reservoir of toxic oligomeric species that is released into the medium upon changing the environmental conditions. These findings may have substantial implications to understand the dynamic process of interconversion between toxic and non-toxic aggregated species implicated in protein misfolding diseases.

Stability, Electronic Properties, and Structural Isomerism in Small Copper Clusters

ABSTRACTWe present extensive pseudopotential density functional theory calculations dedicated to analyze the stability, electronic properties, and structural isomerism in Cu6 clusters. We consider structures of different symmetries and charge states. Our total energy calculations reveal a strong competition between two- and three-dimensional atomic arrays, the later being mostly energetically preferred for the anionic structures. The bond lengths and electronic spectra strongly depend on the local atomic environment, a result that is expected to strongly influence the catalytic activity of our clusters. Using the nudged elastic band method we analyze the interconversion processes between different Cu6 isomers. Complex atomic relaxations are obtained when we study the transition between different cluster structures; however relatively small energy barriers of approximately 0.3 eV accompany the atomic displacements. Interestingly, we obtain that by considering positively charged Cu6+ systems we reduce further the energy barriers opposing the interconversion process. The previous results could imply that, under a range of experimental conditions, it should be possible to observe different Cu6cluster structures in varying proportions.

Theoretical study of the conformational energy hypersurface of cyclotrisarcosyl

Abstract The multidimensional Conformational Potential Energy Hypersurface (PEHS) of cyclotrisarcosyl was comprehensively investigated at the DFT (B3LYP/6-31G(d), B3LYP/6-31G(d,p) and B3LYP/6-311++G(d,p)), levels of theory. The equilibrium structures, their relative stability, and the Transition State (TS) structures involved in the conformational interconversion pathways were analyzed. Aug-cc-pVTZ//B3LYP/6-311++G(d,p) and MP2/6-31G(d)//B3LYP/6-311++G(d,p) single point calculations predict a symmetric cis-cis-cis crown conformation as the energetically preferred form for this compound, which is in agreement with the experimental data. The conformational interconversion between the global minimum and the twist form requires 20.88 kcal mol-1 at the MP2/6-31G(d)//B3LYP/6-311++G(d,p) level of theory. Our results allow us to form a concise idea about the internal intricacies of the PEHSs of this cyclic tripeptide, describing the conformations as well as the conformational interconversion processes in this hypersurface. In addition, a comparative analysis between the conformational behaviors of cyclotrisarcosyl with that previously reported for cyclotriglycine was carried out

Multistep conformational interconversion mechanism of cyclododecane. A simple and fast analysis using potential energy curves

AbstractAn ab initio and Density Functional Theory (DFT) study of the conformational properties of cyclododecane was carried out. The energetically preferred equilibrium structures, their relative stability, and some of the transition state (TS) structures involved in the conformational interconversion pathways were analyzed from RHF/6‐31G(d), B3LYP/6‐31G(d,p) and B3LYP/6311++G(d,p) calculations. Aug‐cc‐pVDZ//B3LYP/6311++G(d,p) single point calculations predict that the multistep conformational interconversion mechanism requires 11.07 kcal/mol, which is in agreement with the available experimental data. These results allow us to form a concise idea about the internal intricacies of the preferred forms of cyclododecane, describing the conformations as well as the conformational interconversion processes in the conformational potential energy hypersurface. Our results indicated that performing an exhaustive analysis of the potential energy curves connecting the most representative conformations is a valid alternate tool to determine the principal conformational interconversion paths for cyclododecane. This methodology represents a satisfactory first approximation for the conformational analysis of medium‐ and large‐size flexible cyclic compounds. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012

Synthesis and Conformation of Chiral Biheteroaryls

Bridging 2,3 and 2',3' positions in 2,2'-dihydroxy-1,1'-binaphthyl and 2,2'-diamino-1,1'-binaphthyl, respectively, resulted in formation of chiral O- and N-bis-tricyclic compounds accessible in 4 steps from known 3,3'-diiodo precursors. In both cases, 2-fold ring closing metathesis of tetraallyl intermediates proceeded regioselectively to give tetrahydrobinaphtho[2,3-b]oxepine and -azepine, respectively. In case of the N-mesyl-N-allyl precursor, three, at room temperature separable, rotamers were isolated and characterized by NMR spectroscopy and X-ray structure determination. Their interconversion (process I) was followed by NMR, yielding rate constants and thermodynamic parameters. The rotamers with either C(1) or C(2) symmetry were stereospecifically cyclized to conformatively moderately stable bis-sulfonamides. Also in this case, the kinetics of their interconversion (process II) was investigated and from two of them the crystal structure was determined. Processes I and II were investigated by a DFT method, M06-2X, to gain insight into electronic and steric peculiarities responsible for the remarkable conformative stabilities. Transition state geometries and energies were calculated and compared with empirical data.

Dynamic 1H NMR study around the carbon–carbon single bond and partial carbon–carbon double bond in the two particular phosphorus ylides and in an enaminoester

Herein, a series of separate dynamic (1)H NMR effects are reported at different temperatures within a particular enaminoester involving a phenanthridine. These effects are attributed to restricted rotation around the two single bonds such as carbon-carbon (H(a)-C-<arrow curve left)>C-H(b)) and nitrogen-carbon (NC<arrow curve left)>COOCH(3)). Activation energies (E(a)) for these interconversion processes in their rotational isomers are equal to 20 and 20 ± 1 kJ mol(-1), respectively. In addition, three dynamic (1)H NMR effects are investigated at different temperatures for a particular phosphorus ylide involving a 2-indolinone around the carbon-carbon single bond (H-C-<arrow curve left)>C-PPh(3)) within the two Z- and E-rotational isomers and partial carbon-carbon double bond (OCH(3)-C=<arrow curve right)>C-PPh(3)). Activation energies (E(a)) for these interconversion processes in rotational isomers are equal to 53, 63 and 73 ± 1 kJ mol(-1) , respectively. This behavior was also observed for other phosphorus ylide containing 2-mercaptobenzoxazole around the carbon-carbon single bond and partial carbon-carbon double bond with their relevant activation energies containing 13, 10 and 75 ± 1 kJ mol(-1), respectively.

Conformation and Self-Assembly of the Transmembrane Peptide Gramicidin A: Insights from ion Mobility Spectrometry and Molecular Dynamics

Gramicidin A which is composed of alternating L- and D-amino acids is a naturally occurring pentadecapeptide from Bacillus brevis known to form monovalent metal ion channels in lipid membranes. The active form is a noncovalently bound dimer. The conformation and self-assembly behavior of gramicidin A highly depends on the solution environment. In this presentation, we report the use of electrospray-ion mobility-mass spectrometry to study the conformation of alkali metals adducts of gramicidin A monomer, as well as the monomerization and conformer interconversion equilibrium of gramicidin A dimer as a function of the solvent. The conformation of gramicidin A monomer vary significantly upon binding different metal adducts. Enhanced sampling molecular dynamics simulations are performed on alkali metals adducts to provide thermodynamics information of different conformers and gain insights of the interaction of different metal ions with the monomer. The kinetics of the monomerization and conformer interconversion processes of dimer in various alcohol solutions (Ethanol, 1-Propanol and, Isobutanol) are monitored by using the ion mobility profile of the monomer and the dimer. The rate constants and the temperature dependence of the rate constants of the monomer compare well with literature values which were obtained by using fluorescence. Furthermore, we found that the water content in the alcohol solution greatly influences the self-assembly process significantly. The role of water in catalyzing the conformer interconversion is being investigated further. Ion mobility spectrometry (IMS) combined with molecular dynamics simulations is a merging technique for conformational analysis of gas-phase low-lying energy level structures of biomolecules. In this study, we will demonstrate that this gas phase technique can also be of utility in studying a solution phase structural dynamics problem.

Role of four-membered rings in C32fullerene stability and mechanisms of generalized Stone-Wales transformation: a density functional theory investigation

Density functional theory (DFT) methods have been applied to study C(32) fullerenes built from four-, five-, and six-membered rings. The relative energies of pure C(32) fullerenes have been evaluated to locate three most stable structures, 32:D(4d) with two squares, 1:D(3) without square and 5:C(s) with one square. Structural analysis reveals that there is a rearrangement pathway between the lowest energy classical isomer 1:D(3) and the lowest energy non-classical isomer 32:D(4d), and 5:C(s) behaves just as an intermediate between them. The kinetic processes of generalized Stone-Wales transformation (GSWT) with four-membered rings have been explored and two distinct reaction mechanisms are determined by all the transition states and intrinsic reaction coordinates with PBE1PBE/6-31G(d) approach for the first time. One mechanism is the concerted reaction with a rotating dimer closed to the cage surface and another is the stepwise reaction with a carbene-like sp(3) structure, whereas the latter is sorted into two paths based on four-membered ring vanishing before or after the formation of the carbene-like structure. It is indicated that there is no absolute preference for any mechanism, which depends on the adaptability of different reactants on the diverse mechanisms. Furthermore, it's found that the interconversion process with the participation of squares is more reactive than the rearrangement between C(60)_I(h) and C(60)_C(2v), implying some potential importance of non-classical small fullerenes in the fullerene isomerization.

Reversible organogels triggered by dynamic K+ binding and release

In this study, a new lipophilic guanosine derivative was synthesized as an organogelator. The self-aggregation behavior of this organogelator was investigated by NMR, XRD and AFM. In solution, the lipophilic guanosine derivative can form a stable ribbon-like structure through NH(1)-N(7) and NH(2)-O(6) hydrogen bonds. However, gelation would occur in some aprotic solvents after the concentration reached a definite value. More interesting, the ribbon-like structure was able to change to G-quartets in the presence of K(+), which led to the transformation from a gel to a sol. Upon the addition of the cryptand [2.2.2], which can efficiently complex with K(+), G-quartets reverted to the original ribbon-like structure and the gel recovered. Subsequently, upon the addition of acids, K(+) was released from the cryptate with the transformation of gel-to-sol simultaneously. Finally, upon the addition of bases which deprotonated [H(+) ⊂ 2.2.2], the liberated cryptand [2.2.2] recaptured K(+) and the gel was regenerated again. This process of interconversion between G-ribbon 1(n) and octamer 1(8)·K(+) was well monitored by circular dichroism spectra.

Separation of triphenyl atropisomers of a pharmaceutical compound on a novel mixed mode stationary phase: A case study involving dynamic chromatography, dynamic NMR and molecular modeling

Analysis of atropisomers is of considerable interest in the pharmaceutical industry. For complex chiral molecules with several chiral centers hindered axial rotation can lead to formation of interconverting diastereomers that should be separable on achiral stationary phases. However, achieving the actual separation may be difficult as the on-column separation speed must match or be faster then the rate of isomer interconversion. Often, this requirement can be satisfied by using low-temperature conditions and by improving selectivity via use of chiral stationary phases. In the current study, we present an alternative approach utilizing an Obelisc R column, a novel mixed mode stationary phase that provided acceptable separation of triphenyl atropisomers inside a conventional HPLC temperature range. The separation was investigated under various chromatographic conditions. The interconversion chromatograms exhibited classic peak–plateau-peak behavior indicating the simultaneous atropisomer separation and interconversion. The elution profiles were integrated in order to deconvolute the peak areas of the “pure” (non-exchanged) and interconverted species; these data were used to obtain kinetic information. Analysis of retention data rendered thermodynamic information on the mechanism of retention and selectivity. Chromatographic kinetic data were complemented with variable-temperature NMR and molecular modeling studies, which provided additional support and insights into the energetics of the interconversion process.

Structure and Dynamics of [3.3]Paracyclophane As Studied by Nuclear Magnetic Resonance and Density Functional Theory Calculations

Strained cyclophanes with small (-CH(2)-)(n) bridges connecting two benzene rings are interesting objects of basic research, mostly because of the nonplanarity of the rings and of interference of π-electrons of the latter. For title [3.3]paracyclophane, in solutions occurring in two interconverting cis and trans conformers, the published nuclear magnetic resonance (NMR) data are incomplete and involve its partially deuterated isotopomers. In this paper, variable-temperature NMR studies of its perprotio isotopomer combined with DFT quantum chemical calculations provide a complete characterization of the solution structure, NMR parameters, and interconversion of the cis and trans isomers of the title compound. Using advanced methods of spectral analysis, total quantitative interpretation of its proton NMR spectra in both the static and dynamic regimes is conducted. In particular, not only the geminal but also all of the vicinal J(HH) values for the bridge protons are determined, and for the first time, complete Arrhenius data for the interconversion process are reported. The experimental proton and carbon chemical shifts and the (n)J(HH), (1)J(CH), and (1)J(CC) coupling constants are satisfactorily reproduced theoretically by the values obtained from the density functional theory calculations.

Aminolysis reaction of calix[4]arene esters and crystal structures and conformational behaviors of calix[4]arene amides

We first make use of aminolysis of calix[4]arene esters to synthesize calix[4]arene amides. When the two ethyl esters of the calix[4]arene esters are aminolysized, the 1, 3-amide derivative is formed selectively. The crystal structures of the calix-[4] arene with two butyl amide (3b) and four butyl amide moieties (4b) were determined. The intermolecular hydrogen bonds make 4b form two-dimensional net work insolid state. The 1H NMR spectra prove mat 3b is of a pinched cone conformation, while 4b and tetraheptylamide-calix[4]arene (6b) take fast interconversion between two C2r isomers in solution and appear an apparent cone conformation at room temperature. As decreasing temperature, the interconversion rate decreases gradually and, finally, the interconversion process is frozen at Tc = −10°C, which makes both conformations of 4b and 6b the pinched cone structures. The hydrogen bond improves the interconversion barrier, and the large different values of the potential barrier between 6b and 4b (or 6b) may be of forming different hydrogen bonds.

LIX ®63 stability in the presence of Versatic 10 under proposed commercial extract and strip conditions, part III: Effect of manganese and cobalt loading on oxime stability at 30 °C

The combination of LIX ®63 with the carboxylic acid Versatic 10 exhibits synergistic properties, enabling direct separation of Co and Zn from Mn, Mg and Ca, a process of interest to the proposed El Boleo copper/cobalt project. Previous work on the chemical stability of this system had revealed the potential for rapid degradation of LIX ®63 oxime (‘oxime’) at high temperature (40, 50 °C) when extracting cobalt and zinc from El Boleo solutions. The present study under extract conditions at 30 °C found increased manganese loading, achieved by increasing operating pH from 4.5 to 6.0, facilitated increased rates of oxime degradation and ‘irreversible’ loading of cobalt. This cobalt was able to be reductively stripped using zinc metal, yielding anti oxime and ‘keto-oxime’. Operation at pH 4.5 resulted in low manganese loading (about 0.2 g/L) and a calculated oxime half life of 67 weeks. Increasing the pH to 6.0 resulted in manganese loading of 2.5 g/L and a decrease in oxime half life to 24 weeks. Operation at pH 6.0 in the absence of manganese gave an oxime half life of 66 weeks. Zinc loading, cobalt loading and changes in pH between 4.5 and 6.0 (excluding the resulting impact on manganese loading) did not appear to have any adverse effect on oxime stability. At a given pH (5.0), ‘irreversible’ Co loading increased with increasing Co concentration in the aqueous solution. This did not have any noticeable effect on oxime half life. The metal:oxime:carboxylic acid stoichiometries of the Zn, Mn and Co synergist complexes were determined by continuous variation and maximum loading studies to be 1:3:2 for all three metals although 1:2:2 remained a possibility for manganese. Inter-conversion of syn oxime to anti oxime was observed to occur via two different mechanisms under the conditions used: a rapid process facilitated by manganese complexation; and a slower, temperature-based isomer re-equilibration process which occurred in the absence of manganese. This inter-conversion process, which resulted in increased manganese and zinc loading occurring relative to fresh organic (cobalt already being fully loaded), also opens up the possibility of decreasing the amount of LIX ®63 required in the El Boleo process.

Reversible, Solvent-Induced Chirality Switch in Atrane Structure: Control of the Unidirectional Motion of the Molecular Propeller

Here we demonstrate that atrane-hemicryptophane molecular cages exhibit a reversible change in chirality uniquely controlled by the solvent, thus establishing the feasibility of a new mode of stimulation for atrane-based molecular switches. The oxidovanadium(V) complexes of hemicryptophane molecules exist as diastereomeric mixtures because of the P or M handedness of the cyclotriveratrylene unit and the chiral ether groups with the S configuration. The Δ/Λ propeller-like arrangement of the atrane moiety introduces a new local dissymmetry because of the conformationally restricted helical structure. (1)H NMR experiments provided significant data for the Δ ⇆ Λ interconversion process, where the solvent profoundly influences the chirality sense of the propeller motion, making control of the chirality by the choice of solvent possible. The reversible chirality inversion process is induced by alternating changes of solvent from CDCl(3) to C(6)D(6). The ratio of the rates of the clockwise and anticlockwise tilting motions of the atrane structure shows that the solvent directs the rotational motion of the vanatrane moiety, so the propeller sense of the motion can be considered as unidirectional.