Discontinuous pressure effect upon enantiodifferentiating photosensitized isomerization of cyclooctene

A hydrostatic pressure of up to 750 MPa induced discontinuous changes in the enantiomeric excess of the (E)-isomer obtained in the enantio-differentiating photoisomerization of (Z)-cyclooctene and (Z,Z)-cycloocta-1,5-diene, sensitized by chiral benzene-1,2,4,5-tetracarboxylates; indicating a switching of the enantio-differentiation mechanism, which is attributable to dramatic conformational changes of chiral alkoxycarbonyl auxiliaries at a specific pressure.     

Enantiodifferentiating photoisomerization of cyclooctene included and sensitized by aroyl-beta-cyclodextrins: a critical enantioselectivity control by substituents

A series of 6-O-benzoyl-beta-cyclodextrins (CDs) with methyl, methoxy, methoxycarbonyl, and bromo substituent(s) at the ortho-, meta-, and/or para-position(s) were synthesized as chiral sensitizing hosts for the use in supramolecular enantiodifferentiating photoisomerization of (Z)-cyclooctene (1Z) to its chiral (E)-isomer (1E). The complex stability constants (K(S)) of the modified beta-CDs with 1Z in aqueous methanol solutions were highly sensitive to the substituent(s) introduced to the benzoate moiety, and the log K(S) values decreased linearly with slightly different slopes with increasing methanol content. The enantiomeric excess (ee) of 1E obtained upon photosensitization with these hosts was a critical function of the size and position of the substituent, varying from almost zero to 46% ee. This indicates that even an apparently small structural difference between methyl and methoxy can critically affect the enantiodifferentiating photoisomerization of a guest included in the chiral cavity, probably through manipulation of both the orientation of ground-state 1Z and the subsequent rotational relaxation of excited 1Z inside the chiral cavity.     

天然和修饰环糊精的不对称光化学

用修饰的α-,β-,γ-环糊精(CDs)的包结增感作用研究(Z)-环辛烯(1Z)向手性(E)-异构体(1E)的超分子对映差向光异构反应。建立定量圆二色(CD)和差圆二色(DCD)公式, 研究修饰α-,β-,γ-环糊精衍生物与1Z包结反应的构象、化学量和稳定常数。 实验发现结合诱导的CD光谱变化是温度和修饰环糊精浓度的临界函数。同时发现光稳态E/Z随照射时间增长而增加最后达到光稳定状态, 但明显依赖于增感剂结构和溶液中甲醇含量,它与环糊精手性空腔被客体1Z占有率有直接关系。考查含o-,m-,p-羧酸甲酯基团的苯甲酸β-环糊精酯衍生物的光增感和对映差向能力,更好地认识到在CDs空腔内的有效光能转换是怎样发生的。用邻苯二甲酸β-环糊精酯的对映体过剩（ee）从2.9% 增加到24%。有趣的是产物的ee值与取代基常数（Hammett,σ）间没有明显的关系,却与某些苯甲酸β-CD酯的主体占有率有直接关系,即是通过分析在不同甲醇含量的水溶液中被一些β-CD衍生物增感的对映差向光异构反应中的ee,得出被底物1Z占有主体空腔的百分率 。     

Enantiodifferentiating photoisomerization of (Z,Z)-1,3-cyclooctadiene included and sensitized by naphthoyl-curdlan

6-O-(2-naphthoyl)curdlan was newly synthesized as a sensitizing polysaccharide host to examine the chiroptical properties, supramolecular complexation, and photochirogenic behavior with (Z,Z)-1,3-cyclooctadiene (1ZZ). The enantiodifferentiating photoisomerization of 1ZZ included and sensitized by this polysaccharide host gave a highly strained chiral (E,Z)-isomer in up to 8.7% enantiomeric excess (ee) in solution and 11.7% ee in the solid state, which are the highest values ever reported for a supramolecular photochirogenesis of 1EZ.     

First photosensitized enantiodifferentiating isomerization by optically active sensitizer immobilized in zeolite supercages

Enantiodifferentiating photoisomerization of (Z)-cyclooctene sensitized by (R)- or (S)-1-methylheptyl benzoate immobilized in zeolite supercages afforded the respective enantiomer pair, (-)- and (+)-(E)-isomer (1E) in 5% enantiomeric excess, whilst racemic 1E was obtained upon homogeneous-phase photosensitization with the same antipodal sensitizer pair, thus demonstrating for the first time that chirally modified zeolites not only serve as supramolecular photosensitizing media but also enhance the original enantiodifferentiating ability of chiral photosensitizer.     

Pressure control of enantiodifferentiating polar addition of 1,1-diphenylpropene sensitized by chiral naphthalenecarboxylates

Effects of pressure on the enantiodifferentiating methanol addition to 1,1-diphenylpropene (1) sensitized by chiral naphthalenedicarboxylates (3 and 4) were investigated over 0.1-400 MPa. The logarithm of enantiomeric excess (ee) of photoadduct, i.e. 1,1-diphenyl-2-methoxypropane (2), was a linear function of both pressure (P) and temperature (T); further, the product chirality was switched by P in some cases. From the slope of P- ln(k(R)/k(S)) plot, the differential activation volume (Delta DeltaV(double dagger)) was determined for the first time for bimolecular asymmetric photoreactions. The Delta DeltaV(double dagger) values obtained are mostly larger than those obtained for relevant unimolecular photoreactions, and are a critical function of the nature of the chiral auxiliary and solvent, indicating conformation changes of the intervening diastereomeric exciplex or transition state in different solvents. Indeed, fluorescence spectral examinations of the sensitizer and exciplex under high pressure revealed the existence of exciplexes of variable energy and structure, which may rationalize the different Delta DeltaV(double dagger) and product ee obtained. A three-dimensional diagram, correlating the ee with P and T, was constructed from the pressure dependence data at different T, from which we may propose an idea of the multidimensional control of asymmetric reaction by the combined use of the entropy-related environmental factors.     

微径高效液相色谱法分离三唑类手性化合物的对映体

 采用微径高效液相色谱技术在手性纤维素色谱柱上分离了一系列 1 1,2 ,4 三唑类手性化合物。比较了微径液相色谱与传统液相色谱的分离结果 ,研究了化合物的苯环上不同取代基及取代基位置对分离的影响 ,并探讨了分离机理。     

Thermal behaviour under pressure of the thermotropic cubic mesogen 4'- n -alkoxy-3'-nitrobiphenyl-4-carboxylic acids

The thermal behaviour of members of a homologous series which exhibits the optically isotropic cubic phase, the 4'- n -alkoxy-3'-nitrobiphenyl-4-carboxylic acids having alkoxy chains containing 16, 20 and 22 carbon atoms (referred to as ANBC-16, -20 and -22, respectively) was investigated under pressures up to 200-400 MPa by high pressure differential thermal analysis. In the phase diagram of ANBC-16 obtained on heating, a triple point was estimated at 54 ±1 MPa and 205 ±1°C for the SmC, Cub and SmA phases. It was found that the X phase is formed on cooling under all pressures, while appearing on heating at high pressures above about 54 MPa. Thus the X phase appears monotropically between the SmA and Cub phases in the low pressure region and enantiotropically between the SmA and SmC phases under higher pressures. It is strongly suggested that the X phase is a columnar mesophase. For ANBC-20 and -22, the cubic phase tends to be destabilized with increasing pressure. The temperature region of the cubic phase of ANBC-20 becomes narrower with increasing pressure and a triple point for the SmC, Cub and I phases is estimated to be at about 309 MPa. On the other hand, the cubic phase of ANBC-22 is still observed at the highest pressure examined.     

Supramolecular photochirogenesis. 2. Enantiodifferentiating photoisomerization of cyclooctene included and sensitized by 6-O-modified cyclodextrins

Supramolecular enantiodifferentiating photoisomerization of (Z)-cyclooctene (1Z) to the chiral (E)-isomer (1E) via inclusion and sensitization by modified alpha-, beta-, and/or gamma-cyclodextrin derivatives, possessing benzoate (2a, 3a, 4a), isomeric phthalates (3b-d), and tethered benzamide (3e) chromophores, has been investigated in aqueous methanol solutions at varying temperatures. The photostationary-state 1E/1Z ratios obtained upon sensitization with 2-4 in 1:1 water-methanol reached 0.4-0.8, which are higher than the value of ca. 0.25 reported for sensitizations by conventional alkyl benzoates in hydrocarbon solvents, although the ratio was reduced to 0.2-0.4 in water or methanol. The sensitizations of 1Z by alpha- and gamma-cyclodextrin benzoates (2a, 4a) with size-mismatched cavities gave 1E of poor enantiomeric excesses (ee's) smaller than 3 and 5%, respectively. In contrast, beta-cyclodextrin derivatives (3a-e) afforded much higher ee's of up to 24%, depending on the solvent composition. Thus, the modification of cyclodextrin with a sensitizing group successfully enhanced the product through the excited-state supramolecular interaction within the cavity. Interestingly, the product ee's obtained with benzoate 3a and methyl phthalate 3b are not a simple function of either temperature or solvent, but are nicely correlated with the host occupancy or the percentage of occupied host. This means that the entropy factor plays an insignificant role in this supramolecular photochirogenesis system, which is in sharp contrast to the decisive role of entropy in the conventional (nonsupramolecular) counterpart performed in homogeneous solutions, where an inversion of product chirality by temperature variation is reported to occur.     

Volume of supercooled water under pressure and the liquid-liquid critical point

The volume of water (H(2)O) was obtained at about 200-275 K and 40-400 MPa by using emulsified water. The plot of volume against temperature showed slightly concave-downward curvature at pressures higher than ≈200 MPa. This is compatible with the liquid-liquid critical-point hypothesis, but hardly with the singularity-free scenario. When the critical point is assumed to exist at ≈50 MPa and ≈223 K, the experimental volume and the derived compressibility are qualitatively described by the modified Fuentevilla-Anisimov scaling equation.     

Stereoselective E/Z photoisomerization of oxazolidinone functionalized enecarbamates: direct and triplet sensitized irradiation

Oxazolidinone-functionalized enecarbamates undergo diastereoselective E/Z photoisomerization upon direct and triplet sensitized irradiations with chiral/achiral sensitizers, showing that the enhanced product diastereoselectivity depends on the solvent and temperature.     

Pressure dependence of peroxynitrite reactions. Support for a radical mechanism

Activation volumes (delta V++) have been determined for several reactions of peroxynitrite using the stopped-flow technique. Spontaneous decomposition of ONOOH to NO3- in 0.15 M phosphate, pH 4.5, gave delta V++ = 6.0 +/- 0.7 and 14 +/- 1.0 cm3 mol-1 in the presence of 53 microM and 5 mM nitrite ion, respectively. One-electron oxidations of Mo(CN)8(4-) and Fe(CN)6(4-), which are first order in peroxynitrite and zero order in metal complex, gave delta V++ = 10 +/- 1 and 11 +/- 1 cm3 mol-1, respectively, at pH 7.2. The limiting yields of oxidized metal complex were found to decrease from 61 to 30% of the initially added peroxynitrite for Mo(CN)8(3-) and from 78 to 47% for Fe(CN)6(3-) when the pressure was increased from 0.1 to 140 MPa. The bimolecular reaction between CO2 and ONOO- was determined by monitoring the oxidation of Fe(CN)6(4-) by peroxynitrite in bicarbonate-containing 0.15 M phosphate, pH 7.2, for which delta V++ = -22 +/- 4 cm3 mol-1. The Fe(CN)6(3-) yield decreased by approximately 20% upon increasing the pressure from atmospheric to 80 MPa. Oxidation of Ni(cyclam)2+ by peroxynitrite, which is first order in each reactant, was characterized by delta V++ = -7.1 +/- 2 cm3 mol-1, and the thermal activation parameters delta H++ = 4.2 +/- 0.1 kcal mol-1 and delta S++ = -24 +/- 1 cal mol-1 K-1 in 0.15 M phosphate, pH 7.2. These results are discussed within the context of the radical cage hypothesis for peroxynitrite reactivity.     

Pressure and temperature-controlled enantiodifferentiating [4+4] photocyclodimerization of 2-anthracenecarboxylate mediated by secondary face- and skeleton-modified gamma-cyclodextrins

A series of secondary-face-substituted and skeleton-modified gamma-cyclodextrins (gamma-CDs) were prepared as chiral hosts for enantiodifferentiating [4+4] photocyclodimerization reactions of 2-anthracenecarboxylic acid (AC). These gamma-CD derivatives form stable ternary complexes with ACs, with altroside-bearing gamma-CDs undergoing induced-fit conformational changes upon complexation, and the photocyclodimerization of AC was, thus, dramatically accelerated. The enantiomeric excess (ee) of anti-head-to-head cyclodimer 3 was greatly enhanced in general with altroside-bearing gamma-CDs 7-9. Although mono-altro-gamma-CD 9 and 3A-azido-3A-deoxy-altro-gamma-CD 7 gave 2 in ee's smaller than those obtained with native gamma-CD, 3A-amino-3A-deoxy-altro-gamma-CD 8 yielded 2 in much higher ee's, which is likely to be ascribed to the combined effects of the less-symmetric cavity and the electrostatic interactions. The influence of temperature and high pressure on the supramolecular photochirogenic reaction has been investigated in depth. An ee as high as 71% was obtained for cyclodimer 2 in the photocyclodimerization of AC mediated by 8 at 210 MPa and -21.5 degrees C.     

聚合物内压测定及对应状态模型

实验测定了PEG(M~n=200),PEG(M~n=300),PEG(M~n=400),PDMS(M~w=15000)和PDMS(M~w=20000)在20-90℃温度范围的热压力系数和密度,它们的热压力系数和内压几乎与分子量无关。据此还建立了一个聚合物内压的对应状态模型,它只含一个可调参数,能满意地适用于各种聚合物。     

Phase behaviour of the thermotropic cubic mesogen 1,2-bis-(4- n -octyloxybenzoyl)hydrazine under pressure

The phase transition behaviour of an optically isotropic, thermotropic cubic mesogen 1,2-bis-(4- n -octyloxybenzoyl)hydrazine, BABH(8), was investigated under pressures up to 200 MPa using a high pressure differential thermal analyser, wide-angle X-ray diffraction and a polarizing optical microscope equipped with a high pressure optical cell. The phase transition sequence, low temperature crystal (Cr 2 )-high temperature crystal (Cr 1 ) - cubic (Cub)-smectic C (SmC)-isotropic liquid (I) observed at atmospheric pressure, is seen in the low pressure region below about 30 MPa. The cubic phase disappears at high pressures above 30-40 MPa, in conjunction with the disappearance of the Cr 1 phase. The transition sequence changes to Cr 2 -SmC-I in the high pressure region. Since only the Cub-SmC transition line among all the phase boundaries has a negative slope (d T /d P ) in the temperature-pressure phase diagram, the temperature range for the cubic phase decreases rapidly with increasing pressure. As a result, a triple point was estimated approximately as 31.6 ±2.0 MPa, 147.0 ±1.0°C for the SmC, Cub and Cr 1 phases, indicating the upper limit of pressure for the observation of the cubic phase. Reversible changes in structure and optical texture between the Cub and SmC phases were observed from a spot-like X-ray pattern and dark field for the cubic phase to the Debye-Sherrer pattern and sand-like texture for the SmC phase both in isobaric and isothermal experiments.     

Enantiodifferentiating photoaddition of alcohols to 1,1-diphenylpropene in supercritical carbon dioxide: sudden jump of optical yield at the critical density

In the enantiodifferentiating photoaddition of ROH (R = Me, Et, i-Pr) to 1,1-diphenylpropene sensitized by fructosyl 1,4-naphthalenedicarboxylate in supercritical carbon dioxide, the enantiomeric excess of photoadduct increased with increasing bulkiness of the alcohol at all pressures used, with an accompanying sudden jump at the critical density, for which the enhanced clustering of alcohol, particularly in the subcritical pressure region, was revealed to be responsible from the fluorescence spectral examinations.     

Solubility of α-amino acids in water under high pressure: glycine, -alanine, -valine, -leucine, and -isoleucine

The solubility of glycine, -alanine, -valine, -leucine, and -isoleucine in water was measured at 298.15 K and pressures up to 400 MPa. The standard deviation of the logarithm of the solubility is 0.001–0.003, equal to or better than the accuracy of atmospheric pressure measurement in the literature (0.001–0.05). A variety of solubility phenomena were observed. The solubility of glycine decreased with increasing pressure, whereas that of -alanine increased. The -valine and -isoleucine have a solubility maximum at around 100 MPa, and -leucine seems to exhibit a solid-phase phase transition at around 200 MPa. Pressure coefficient of the solubilities at 0.10 MPa is compared with that thermodynamically estimated in reference to aqueous density measurements of glycine and -alanine at 298.15 K and 0.10 MPa, supporting a reliability of our high-pressure measurements.     

Phase behaviour of the discotic mesogen 5,10,15,20-tetrakis (4-n-dodecylphenyl)porphyrin under pressure

The phase behaviour of the discotic mesogen 5,10,15,20-tetrakis(4-n -dodecylphenyl)porphyrin (C12TPP) was investigated under hydrostatic pressures up to 300MPa by high pressure DTA and wide angle X-ray diffraction methods. The typical enantiotropic phase transitions of C12TPP, low- to high-temperature crystal (Cr2-Cr1), Cr1-discotic lamellar phase (DL), and DL-isotropic liquid (I) are observed at pressures up to 10MPa. Application of hydrostatic pressure to the sample generates a pressure-induced crystal polymorph (Cr3) between the Cr2 and Cr1 phases, and the phase transitions Cr2-Cr3-Cr1-DL-I occur reversibly in the pressure region between 10 and 180MPa. On heating at higher pressures above 180MPa, the fourth crystal polymorph (Cr4) is formed between the Cr2 and Cr3 phases at lower temperatures, and at the same time the fifth crystal polymorph (Cr5) appears abruptly between the Cr1 and DL phases at high temperatures. The Cr2-Cr4-Cr3-C1-(Cr5)-DL-I transition processes were observed at 180 200MPa. Further increasing the pressure above 270MPa induces entirely different thermal behaviour: only two peaks for the pressure-induced transition between the sixth and fifth polymorphs (Cr6-Cr5) and the Cr5-I transitions are detected at low and high temperatures on heating, while both the DTA and WAXD experiments on cooling show the formation of the DL phase as a monotropic phase between the I and Cr5 phases, indicating the I DL Cr5 Cr6 process. The thermal behaviour was ambiguous and complex in the pressure region between 200 and 260MPa because the peaks for the intermediate crystal transitions were too small to detect with confidence. The two different sequences of the Cr2-Cr4-Cr3-Cr1-DL-I and Cr6-Cr5-(DL)-I processes seems to occur competitively. The T vs. P phase diagram of a sample cooled at 300MPa was studied to determine the triple point of the DL phase and to investigate the phase stability of the pressure-induced crystal polymorphs. The Cr6-Cr5-I transition process was observed on heating at 200 and 300MPa, while the Cr6-Cr5-DL-I process was detected at lower pressures below 100MPa. Since the Cr5-DL transition temperature changes linearly with a slope dT/dP 40 degrees C/100 MPa, while the DL-I transition temperature changes slightly (dT/dP 5.5 degrees C/100MPa), the DL phase forms a triangle in the T vs. P diagram. The triple point of the DL phase was found to be 240.8MPa and 168.8 C. The Cr6 polymorph reorganized to the stable Cr2 form under atmospheric pressure on annealing at room temperature overnight.     

Phase behaviour of the discotic mesogen 5,10,15,20-tetrakis (4-n-dodecylphenyl)porphyrin under pressure

The phase behaviour of the discotic mesogen 5,10,15,20-tetrakis(4-n -dodecylphenyl)porphyrin (C12TPP) was investigated under hydrostatic pressures up to 300MPa by high pressure DTA and wide angle X-ray diffraction methods. The typical enantiotropic phase transitions of C12TPP, low- to high-temperature crystal (Cr2-Cr1), Cr1-discotic lamellar phase (DL), and DL-isotropic liquid (I) are observed at pressures up to 10MPa. Application of hydrostatic pressure to the sample generates a pressure-induced crystal polymorph (Cr3) between the Cr2 and Cr1 phases, and the phase transitions Cr2-Cr3-Cr1-DL-I occur reversibly in the pressure region between 10 and 180MPa. On heating at higher pressures above 180MPa, the fourth crystal polymorph (Cr4) is formed between the Cr2 and Cr3 phases at lower temperatures, and at the same time the fifth crystal polymorph (Cr5) appears abruptly between the Cr1 and DL phases at high temperatures. The Cr2-Cr4-Cr3-C1-(Cr5)-DL-I transition processes were observed at 180 200MPa. Further increasing the pressure above 270MPa induces entirely different thermal behaviour: only two peaks for the pressure-induced transition between the sixth and fifth polymorphs (Cr6-Cr5) and the Cr5-I transitions are detected at low and high temperatures on heating, while both the DTA and WAXD experiments on cooling show the formation of the DL phase as a monotropic phase between the I and Cr5 phases, indicating the I DL Cr5 Cr6 process. The thermal behaviour was ambiguous and complex in the pressure region between 200 and 260MPa because the peaks for the intermediate crystal transitions were too small to detect with confidence. The two different sequences of the Cr2-Cr4-Cr3-Cr1-DL-I and Cr6-Cr5-(DL)-I processes seems to occur competitively. The T vs. P phase diagram of a sample cooled at 300MPa was studied to determine the triple point of the DL phase and to investigate the phase stability of the pressure-induced crystal polymorphs. The Cr6-Cr5-I transition process was observed on heating at 200 and 300MPa, while the Cr6-Cr5-DL-I process was detected at lower pressures below 100MPa. Since the Cr5-DL transition temperature changes linearly with a slope dT/dP 40 degrees C/100 MPa, while the DL-I transition temperature changes slightly (dT/dP 5.5 degrees C/100MPa), the DL phase forms a triangle in the T vs. P diagram. The triple point of the DL phase was found to be 240.8MPa and 168.8 C. The Cr6 polymorph reorganized to the stable Cr2 form under atmospheric pressure on annealing at room temperature overnight.     

The speed of sound and derived thermodynamic properties of pure water at temperatures between (253 and 473) K and at pressures up to 400 MPa

The speed of sound in high-purity water has been measured in the temperature range (253 to 473) K at pressures up to 400 MPa. The experimental technique used was based on a double-path pulse-echo method with a single 5-MHz ultrasound transducer placed between two unequally spaced reflectors. The cell was calibrated in water at T = 298.15 K and p = 1 MPa against the speed of sound given by the 1995 equation-of-state formulation of the International Association for the Properties of Water and Steam (IAPWS-95) which, for that state point, has an uncertainty of 0.005%. Corrections for the effects of temperature and pressure on the path length difference are considered in detail. The estimated expanded relative uncertainty of the speed of sound determined in this work is shown to be between 0.03% and 0.04% at a confidence level of 95%. The density and isobaric specific heat capacity of water have been obtained in the temperature range (253.15 to 473.15) K at pressure up to 400 MPa by thermodynamic integration of the sound-speed data subject to initial values computed from IAPWS-95 on the isobar at p = 0.1 MPa. The speed of sound, density, and isobaric specific heat capacity were compared with IAPWS-95 with corresponding absolute relative deviations within 0.3%, 0.03%, and 1%, respectively at T ≥ 273.15 K and p ≤ 400 MPa; larger deviations, especially for heat capacity, were found at lower temperatures. The results imply that the uncertainties of properties computed from IAPWS-95 may be significantly reduced over the major part of the region investigated in this work.