Simultaneous determination of three diarylheptanoids and an alpha-tetralone derivative in the green walnut husks (Juglans regia L.) by high-performance liquid chromatography with photodiode array detector

By optimizing extraction, separation and analytical conditions, a reliable and accurate high-performance liquid chromatographic (HPLC) method coupled with photodiode array detector (DAD) at room temperature is developed for simultaneous determination of three diarylheptanoids (juglanin A, juglanin B, rhoiptelol) and an alpha-tetralone derivative (regiolone) in methanol extracts from the green walnut husks (Juglans regia L.) The sample pretreatment process involved the reflux extraction using methanol as the extract with a ratio of liquor to sample of 15 mL/g. The separation was achieved on a SinoChrom ODS-AP C(18) column with gradient elution using acetonitrile and 2% (v/v) acetic acid in water. The intra-day and inter-day precision (RSD%) for the analytes ranged from 1.08 to 1.51 and 0.60 to 1.13, respectively. The average recoveries obtained were from 88.4% to 96.2% for the analytes with RSDs below 3.13%. The correlation coefficients of the calibration curve exceeded 0.999. The detection limits were 0.51, 0.25, 0.32 and 0.35 ng at a signal-to-noise ratio of 3, respectively. Quantitative analyses of the samples from different grown sites and in obtained different months showed that the contents of the analytes varied significantly. The method was then successfully applied for the detection and isolation of a new diarylheptanoid derivative in the green walnut husks (J. regia L.). The structure of the new compound was elucidated by various spectroscopic methods including 2D NMR techniques (COSY, HMQC, HMBC), HR-ESI-MS and X-ray single-crystal diffraction analysis.     

Determination of a novel diarylheptanoid (Juglanin B) from green walnut husks (Juglans regia L.) in rat plasma by high‐performance liquid chromatography

A simple and reliable analytical method based on high‐performance liquid chromatography (HPLC) coupled with a diode array detector (DAD) was developed for the determination of a novel diarylheptanoid (Juglanin B) from green walnut husks (Juglans regia L.) in rat plasma using rhoiptelol as an internal standard. Chromatographic separation was carried out on a Sinochrom ODS‐AP C₁₈ column (250 × 4.6 μm i.d., 5 mm) with acetonitrile–10 mM postassium dihydrogen phosphate (pH = 3; 55:45, v/v) as mobile phase, and the detection wavelength was set at 214 nm. The plasma samples were prepared using methanol as protein precipitator. The extraction recovery of Juglanin B ranged from 70.26 to 78.59%, and the calibration curve had a good linearity in the range 0.08–50 μg/mL (r² = 0.9932). The RSDs of intra‐ and inter‐day precision ranged from 1.19 to 4.92% and 4.35 to 4.54%, respectively. The HPLC‐DAD method described is a simple, rapid and reliable method for the determination of Juglanin B level and for use in studies involving pharmacokinetics. Copyright © 2009 John Wiley & Sons, Ltd.     

New Cyclic Diarylheptanoids from Platycarya strobilacea

Five new cyclic diarylheptanoids (platycary A–E, compounds 1–5) and three previously identified analogues (i.e., phttyearynol (compound 6), myricatomentogenin (compound 7), and juglanin D (compound 8)) were isolated from the stem bark of Platycarya strobilacea. The structures of these compounds were determined using NMR, HRESIMS, and electronic circular dichroism (ECD) data. The cytotoxicity of compounds 1–5 and their ability to inhibit nitric oxide (NO) production, as well as protect against the corticosterone-induced apoptosis of Pheochromocytoma (PC12) cells, were evaluated in vitro using the appropriate bioassays. Compounds 1 and 2 significantly inhibited the corticosterone-induced apoptosis of PC12 cells at a concentration of 20 μΜ.     

Flavonoids and biological activities of Jussiaea repens

A new acylated avicularin, namely avicularin 2'-(4'-O-n-pentanoyl)-gallate (1) along with 12 metabolites have been isolated from the ethyl acetate extract of the aerial parts of Jussiaea repens L. (Onagraceae). Their structures were established as trifolin 2'-O-gallate (2), quercetrin (3), guaijaverin (4), reynoutrin (5), juglanin (6), avicularin (7), hyperin (8), trifolin (9), hyperin 2'-O-gallate (10), rutin (11), kaempferol (12) and quercetin (13) on the basis of their chromatographic properties, chemical and spectroscopic evidences. The investigated ethyl acetate extract was found to be non-toxic (LD(50) up to the maximum soluble dose 4 g kg(-1) body wt.) and had significant antioxidant, hepatoprotective, anti-inflammatory and antidiabetic activities. Also some of the isolated flavonoids showed cytotoxic activity against Ehrlich ascitis carcinoma cells.     

An integrated approach of homogenization-ultrasound-assisted extraction followed by high-speed countercurrent chromatography for rapidly preparative separation naphthoquinones and diarylheptanes from Juglands mandshurica Maxim. exocarp

This research investigated the effectiveness of an integrated method for the extraction and separation of naphthoquinones and diarylheptanes from exocarp of Juglands mandshurica Maxim. (namely, green walnut husks). The target compounds were obtained by ultra-turrax homogenization (UTH) coupled with ultrasound-assisted extraction (UAE) technology followed by high-speed countercurrent chromatography (HSCCC). The UTH-UAE extraction method achieved higher efficiency with 2.49- and 2.36-fold to those by UAE, and 1.39- and 1.34-fold to those by UTH in a short time. HSCCC was adopted for further separation and purification; six target compounds, namely, regiolone (RE), juglone (JU), myricatomento-genin (MG), galleon (GA), 2-oxatrycyclo[13.2.2.13,7]eicosa-3,5,7(20),15,17,18-hexaen-10-16-diol (OE), and juglanin A (JA), were separated with more than 95.37% purities and more than 84.71% final recovery rates, respectively. In this study, the integrated strategy of extraction and separation could get high purity compounds quickly, which would provide time and solvent saved method for the natural products separation from plants.     

An O-acylated flavonoid glycoside from the needles ofPicea koraiensis

Summary 1. The needles of the Koyama spruce have yielded a new acylated flavonoid glycoside for which the structure of 3,4,5,7-tetrahydroxyflavone 3-O--L-(2-O-p-coumaroylarabinofuranoside) has been established.2. The structure of juglanin (kaempferol 3--L-arabinoside) has been refined as kaempferol 3-O--L-arabinofuranoside.Irkutsk Institute of Organic Chemistry, Siberian Branch of the Academy of Sciences of the USSR. All-Union Scientific-Research Institute of Medicinal Plants, Moscow. I. M. Sechenov I Moscow Medical Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 200–204, March–April, 1978.     

LC Method for Analysis of Three Flavonols in Rat Plasma and Urine after Oral Administration of Polygonum aviculare Extract

A high-performance liquid chromatographic method has been developed for the simultaneous analysis of the flavonols myricitrin (1), avicularin (2), and juglanin (3) in rat plasma and urine after oral administration of the total flavonoids from Polygonum aviculare. Samples were prepared by solid-phase extraction then separated on a C₁₈ reversed-phase column by use of a mobile-phase gradient prepared from methanol and aqueous formic acid solution. The flow rate was 1 mL min⁻¹. Detection was performed at 254 nm. The calibration range was 11–1,100 μg mL⁻¹ for both 2 and 3 in plasma; in urine the calibration ranges for 1, 2, and 3 were 32–1,600, 11–1,100, and 22–1,100 μg mL⁻¹, respectively. Intra-day and inter-day RSD were less than 4.33 and 3.62% for 2 and 3, respectively, in plasma, and no more than 4.03 and 2.22% for all the analytes in urine. The analytical sensitivity and selectivity of the assay enabled successful application to pharmacokinetic studies of flavonols 1–3 in rats.

     

LC Method for Analysis of Three Flavonols in Rat Plasma and Urine after Oral Administration of Polygonum aviculare Extract

A high-performance liquid chromatographic method has been developed for the simultaneous analysis of the flavonols myricitrin (1), avicularin (2), and juglanin (3) in rat plasma and urine after oral administration of the total flavonoids from Polygonum aviculare. Samples were prepared by solid-phase extraction then separated on a C₁₈ reversed-phase column by use of a mobile-phase gradient prepared from methanol and aqueous formic acid solution. The flow rate was 1 mL min^?1. Detection was performed at 254 nm. The calibration range was 11–1,100 μg mL^?1 for both 2 and 3 in plasma; in urine the calibration ranges for 1, 2, and 3 were 32–1,600, 11–1,100, and 22–1,100 μg mL^?1, respectively. Intra-day and inter-day RSD were less than 4.33 and 3.62% for 2 and 3, respectively, in plasma, and no more than 4.03 and 2.22% for all the analytes in urine. The analytical sensitivity and selectivity of the assay enabled successful application to pharmacokinetic studies of flavonols 1–3 in rats.     

Film growth precursor development for metal nitrides. Synthesis, structure, and volatility of molybdenum(VI) and tungsten(VI) complexes containing bis(imido)metal fragments and various nitrogen donor ligands

The molybdenum and tungsten complexes W2(NtBu)4(pz)4(pzH).(C6H14)0.5 (pz = pyrazolate), M(NtBu)2(Me2pz)2(Me2pzH)2 (Me2pz = 3,5-dimethylpyrazolate), M(NtBu)2(tBu2pz)2 (tBu2pz = 3,5-di-tert-butylpyrazolate), M2(NtBu)4(Me2pz)2Cl2, W(NtBu)2(C2N3(iPr)2)2py2, M(NtBu)2-(CN4CF3)2py2, and W(NtBu)2(PhNNNPh)2 were prepared by various synthetic routes from the starting materials Mo(NtBu)2Cl2, W(NtBu)2(NHtBu)2, and W(NtBu)2Cl2py2. These new complexes were characterized by spectral and analytical methods and by X-ray crystal structure determinations. The volatilities and thermal stabilities were evaluated to determine the potential of the new complexes for use in thin film growth of metal nitride films. Mo(NtBu)2(tBu2pz)2 and W(NtBu)2(tBu2pz)2 were found to have the optimum combination of volatility and thermal stability for application in atomic layer deposition thin film growth procedures.     

N,N'-ethylenebis(pyridoxylideneiminato) and N,N'-ethylenebis(pyridoxylaminato): synthesis, characterization, potentiometric, spectroscopic, and DFT studies of their vanadium(IV) and vanadium(V) complexes

The Schiff base N,N'-ethylenebis(pyridoxylideneiminato) (H(2)pyr(2)en, 1) was synthesized by reaction of pyridoxal with ethylenediamine; reduction of H(2)pyr(2)en with NaBH(4) yielded the reduced Schiff base N,N'-ethylenebis(pyridoxylaminato) (H(2)Rpyr(2)en, 2); their crystal structures were determined by X-ray diffraction. The totally protonated forms of 1 and 2 correspond to H(6)L(4+), and all protonation constants were determined by pH-potentiometric and (1)H NMR titrations. Several vanadium(IV) and vanadium(V) complexes of these and other related ligands were prepared and characterized in solution and in the solid state. The X-ray crystal structure of [V(V)O(2)(HRpyr(2)en)] shows the metal in a distorted octahedral geometry, with the ligand coordinated through the N-amine and O-phenolato moieties, with one of the pyridine-N atoms protonated. Crystals of [(V(V)O(2))(2)(pyren)(2)].2 H(2)O were obtained from solutions containing H(2)pyr(2)en and oxovanadium(IV), where Hpyren is the "half" Schiff base of pyridoxal and ethylenediamine. The complexation of V(IV)O(2+) and V(V)O(2) (+) with H(2)pyr(2)en, H(2)Rpyr(2)en and pyridoxamine in aqueous solution were studied by pH-potentiometry, UV/Vis absorption spectrophotometry, as well as by EPR spectroscopy for the V(IV)O systems and (1)H and (51)V NMR spectroscopy for the V(V)O(2) systems. Very significant differences in the metal-binding abilities of the ligands were found. Both 1 and 2 act as tetradentate ligands. H(2)Rpyr(2)en is stable to hydrolysis and several isomers form in solution, namely cis-trans type complexes with V(IV)O, and alpha-cis- and beta-cis-type complexes with V(V)O(2). The pyridinium-N atoms of the pyridoxal rings do not take part in the coordination but are involved in acid-base reactions that affect the number, type, and relative amount of the isomers of the V(IV)O-H(2)Rpyr(2)en and V(V)O(2)-H(2)Rpyr(2)en complexes present in solution. DFT calculations were carried out and support the formation and identification of the isomers detected by EPR or NMR spectroscopy, and the strong equatorial and axial binding of the O-phenolato in V(IV)O and V(V)O(2) complexes. Moreover, the DFT calculations done for the [V(IV)O(H(2)Rpyr(2)en)] system indicate that for almost all complexes the presence of a sixth equatorial or axial H(2)O ligand leads to much more stable compounds.     

Stereoselective reactions of acyclic allylic phosphates with organocopper reagents

A series of acyclic allylic alcohols of general structure R(1)CH==CHCH(OH)R(2) were resolved by Sharpless kinetic resolution. The hydroxyl groups of these enantiomerically enriched alcohols were derivatized to diethyl phosphates, and the derivatives were reacted with organocopper reagents. Cleanest substitution reactions were observed with reagents R(3)(2)CuCNLi(2). With R(1) = Me and R(3) = n-Bu, the size of R(2) affected both the regioselectivity and stereoselectivity of the displacement. Larger R(2) groups gave higher regio- and stereoselectivities: with R(2) = 3-pentyl, >98% S(N)2' regioselectivity and >98% anti stereoselectivity were observed. Bn(2)CuCNLi(2) gave stereoselectivities comparable to those observed with n-Bu(2)CuCNLi(2) but t-Bu(2)CuCNLi(2) exhibited much lower diastereofacial preference.     

二元羧酸二(二茂镱)的合成

本文报道了五个新的二元羧酸二(二茂镱)的合成:(COO)_2Yb_2(C_5H_5)_4(1),CH_2(COO)_2Yb_2(C_5H_5)_4(2),(CH_2COO)_2Yb_2(C_5H_5)_4(3),o-C_6H_4(COO)_2Yb_2(C_5H_5)_4(4),p-C_6H_4(COO)_2Yb_2(C_5H_5)_4(5),并考察了它们对空气的稳定性。     

A new route to achiral and chiral 1,2-bis(phosphino)ethanes, 1-arsino-2-phosphinoethanes, and 1,3-bis(phosphino)propanes and the molecular structure and catalytic activity of some rhodium(I) complexes derived thereof

A series of unsymmetrical 1,2-bis(phosphino)ethanes R(2)PCH(2)CH(2)PR'(2) and 1-arsino-2-phosphinoethanes R(2)AsCH(2)CH(2)PR'(2) mainly with bulky substituents R and R' were prepared from the cyclic sulfate by stepwise cleavage of the carbon-oxygen bonds by LiPR(2) and LiPR'(2) or LiAsR(2) and LiPR'(2), respectively. Analogously, racemic mixtures of R(2)PCH(2)CH(Me)PPh(2)(R =iPr, Cy ) as well as the enantiomers (R)-, (R)- and (R)-tBu(2)PCH(2)CH(Me)PPh(2)(R)- were obtained from the corresponding unsymmetrical cyclic sulfates and (S)-. On a similar route, the racemates of the 1,3-bis(phosphino)propanes R(2)PCH(2)CH(2)CH(Me)PPh(2)(R =iPr, tBu ), optically pure (R)- and (S,S)-iPr(2)PCH(Me)CH(2)CH(Me)PPh(2)(S,S)- were prepared. The reaction of [[RhCl([small eta](4)-C(8)H(12))](2)] with chelating ligands L-L, where L-L is R(2)PCH(2)P(men)(2)(R =iPr, Ph; men =(1S,2R,5S)-menthyl), Cy(2)AsCH(2)P(men)(2), or (R)-, (R)-, (R)-, (R)- and (S,S)-, in the presence of AgPF(6), gave the complexes [Rh(eta(4)-C(8)H(12))(L-L)]PF(6) which were used as pre-catalysts in the hydrogenation of the methyl ester of alpha-acetamidocinnamic acid (ACM). Depending on L-L, the solvent, the temperature and the pressure of H(2), optical yields of up to 69% ee were achieved. For two of the rhodium complexes, and, the molecular structures were determined by X-ray crystallography.     

Coupling of CpCr(CO)3 and heterocyclic dithiadiazolyl radicals. synthetic, x-ray diffraction, dynamic NMR, EPR, CV, and DFT studies

The reaction of the 1,2,3,5-dithiadiazolyls (4-R-C(6)H(4)CN(2)S(2))(2) (R = Me, 2a; Cl, 2b; OMe, 2c; and CF3, 2d) and (3-NC-5-tBu-C(6)H(3)CN(2)S(2))(2) (2e) with [CpCr(CO)(3)](2) (Cp = eta(5)-C(5)H(5)) (1) at ambient temperature respectively yielded the complexes CpCr(CO)(2)(eta(2)-S(2)N(2)CC(6)H(4)R) (R = 4-Me, 3a; 4-Cl, 3b; 4-OMe, 3c; and 4-CF(3), 3d) and CpCr(CO)(2)(eta(2)-S(2)N(2)CC(6)H(3)-3-(CN)-5-(tBu)) (3e) in 35-72% yields. The complexes 3c and 3d were also synthesized via a salt metathesis method from the reaction of NaCpCr(CO)(3) (1B) and the 1,2,3,5-dithiadiazolium chlorides 4-R-C(60H(4)CN(2)S(2)Cl (R = OMe, 8c; CF(3), 8d) with much lower yields of 6 and 20%, respectively. The complexes were characterized spectroscopically and also by single-crystal X-ray diffraction analysis. Cyclic voltammetry experiments were conducted on 3a-e, EPR spectra were obtained of one-electron-reduced forms of 3a-e, and variable temperature 1H NMR studies were carried out on complex 3d. Hybrid DFT calculations were performed on the model system [CpCr(CO)(2)S(2)N(2)CH] and comparisons are made with the reported CpCr(CO)(2)(pi-allyl) complexes.     

α-氨基酸乙酯卤根合铂(II)的合成和构型研究

Sixteen new halogenoethylaminoacidato Pt(II) complexes were synthesized and characterized, of which eightiodo complexes (PtA2I2) (A = DL-a-AlaOEt, L-a-alaOEt, DL-a-PheOEt, L-a-PheOEt, DI-A-AspOEt, L-a-AspOEt, DL-a-SerOEt and L-a-Lys OEt), four chloro compounds (PtA2Cl2)(A = DL-a-PheOEt, DL-a-AspOEt, L-a-Asp OEt) and (DL-a-PheHOEt)2(PtCl4) were obtained by reaction of K2 (PtX4)(X = I^-, Cl^-) with the corresponding ethylaminoacidates in water. The other chlorethylaminoacidato Pt(II) complexes (PtA2Cl2) (A = DL-a-AlaOEt, L-a-AlaOEt, L-a-PheOEt, DL-a-Ser OEt) were synthesized in acetone by exchange reaction of the corresponding iodo complexes with AgCl in order to avoid hydrolysis of the ethyl aminoacidates. Molar conductivity determination showed that all the Pt(II) complexes obtained were neutral molecules with the exception of (DL-a-PheHOEt)2(PtCl4) which existed as an anion. As shown by diole moment determination and modified thiourea reaction, iodo complexes 1-7 and some of the chloro complexes (PtA2Cl2) (A = DL-a-alaOEt, D-a-AlaOEt, DL-a-SerOEt) were of cis-configuration and the other chloro complexes were of trans-configuration.     

Acidities of platinum(II) mu-hydroxo complexes bearing diphosphine ligands

The pK(a) values in DMSO of the monoprotic complexes [(L(2)Pt)(2)(mu-OH)(mu-NMePh)](2+) (4) (L(2) = Ph(2)PCH(2)CH(2)PPh(2) (dppe), Ph(2)PCMe(2)PPh(2) (dppip)) are 11.9 +/- 0.1 (L(2) = dppe) and 13.5 +/- 0.2 (L(2) = dppip) as determined by (31)P NMR equilibrium titration with bases of known pK(a). Complexes 4 were prepared by treatment of [L(2)Pt(mu-OH)](2)(2+) (1) with N-methylaniline. The oxo complexes [(L(2)Pt)(2)(mu-O)(mu-NMePh)](+), formed in the equilibrium titration reactions, were independently synthesized in THF by deprotonation of [(L(2)Pt)(2)(mu-OH)(mu-NMePh)](2+) with NaN(SiMe(3))(2) and characterized as NaBF(4) adducts. Similar experiments with diprotic [L(2)Pt(mu-OH)](2)(2+) (L(2) = dppe, Ph(2)PCH(2)CH(2)CH(2)PPh(2) (dppp)) were complicated by exchange processes and were less conclusive, giving pK(a1) < 18 and pK(a2) > 18 in DMSO.     

Galactose oxidase models: tuning the properties of CuII-phenoxyl radicals

Four tripodal ligands with an N(3)O coordination sphere were synthesized: (2-hydroxy-3-tert-butyl-5-nitrobenzyl)bis(2-pyridylmethyl)amine (LNO(2)H), (2-hydroxy-3-tert-butyl-5- fluorobenzyl)bis(2-pyridylmethyl)amine (LFH), (2-hydroxy-3,5-di-tert-butylbenzyl)bis(2-pyridylmethyl)amine (LtBuH) and (2-hydroxy-3-tert-butyl-5-methoxybenzyl)bis(2-pyridylmethyl)amine (LOMeH). Their square-pyramidal copper(II) complexes, in which the phenol subunit occupies an axial position, were prepared and characterized by X-ray crystallography and UV/Vis and EPR spectroscopy. The phenolate moieties of the copper(II) complexes of LtBuH and LOMeH were electrochemically oxidized to phenoxyl radicals. These complexes are EPR-active (S=1), highly stable (k(decay)=0.008 min(-1) for [Cu(II)(LOMe(.))(CH(3)CN)](2+)) and stoichiometrically oxidise benzyl alcohol. Two additional tripodal ligands providing an N(2)O(2) coordination sphere were also studied: (2-pyridylmethyl)(2-hydroxy-3-tert-butyl-5-methoxybenzyl)(2-hydroxy-3-tert-butyl-5-nitrobenzyl)amine (L'OMeNO(2)H(2)) and (2-pyridylmethyl)bis(2-hydroxy-3-tert-butyl-5- methoxy)benzylamine (L'OMe(2)H(2)). Their copper(II) complexes were isolated as dimers ([Cu(2II)(L'OMe(2))(2)], [Cu(2II)(L'OMeNO(2))(2)]) that are converted to monomers on addition of pyridine. The complexes were investigated by X-ray crystallography and UV/Vis and EPR spectroscopy. Their one-electron electrochemical oxidation leads to copper(II)-phenoxyl systems that are less stable than those of the N(3)O complexes. The N(2)O(2) complexes are more reactive than the N(3)O analogues: they aerobically oxidize benzyl alcohol to benzaldehyde at a higher rate, as well as ethanol to acetaldehyde (40-80 turnovers).     

1,1-二(2-苯并咪唑基)-2-苯基乙烯衍生物荧光受体的合成与阳离子识别

合成了3种新型1,1-二(2-苯并咪唑基)-2-苯基乙烯衍生物——1,1-二(2-苯并咪唑基)-2(4-氰基苯基)乙烯(1)、1,1-二(2-苯并咪唑基)-2(4-甲氧羰基苯基)乙烯(2)和1,1-二(2-苯并咪唑基)-4-苯基-1,3-丁二烯(3),通过核磁共振氢谱和碳谱(1H、13C NMR)、质谱(MS)对它们进行了结构表征。用紫外可见吸收光谱(UV-V is)和荧光发射光谱测定了该阳离子受体与不同金属离子(Zn2 、Cd2 、Hg2 和Cu2 )的络合选择性。结果表明:该荧光受体对Zn2 、Cd2 、Hg2 和Cu2 均具有较高的选择性和荧光响应。     

Robust chiral zirconium alkoxide initiators for the room-temperature stereoselective ring-opening polymerisation of rac-lactide

Chiral Schiff bases (1H to 4H) and a series of their Group 4 metal alkoxide complexes [(R-1)2Ti(O(i)Pr)2, (R-2)2Ti(O(i)Pr)2, (R-1)(2)Zr(O(i)Pr)2, (R-2)2Zr(O(i)Pr)2, (R-3)2Zr(O(i)Pr)2, (R-4)2Zr(O(i)Pr)2, (S-1)2Zr(O(i)Pr)2 and (rac-1)2Zr(O(i)Pr)2] have been prepared and characterised by 1H, and 13C NMR spectroscopy. In solution, both Lambda and Delta isomers were observed, suggesting a low degree of chiral induction from the ligand. One ligand (R-4H) and three complexes [Delta-(R,R-2)2Ti(O(i)Pr)2, Lambda-(R,R-1)2Zr(O(i)Pr)2 and Delta-(R,R-3)2Zr(O(i)Pr)2] have also been characterised by single crystal X-ray diffraction. All complexes were found to have a pseudo-octahedral alpha-cis geometry. The complexes were tested as initiators for the ring-opening polymerisation of rac-lactide in solution and in the melt. The titanium complexes are inactive in solution and afford atactic polylactide in the melt. Zr(iv) complexes afford heterotactically enriched polylactide both in toluene solution (at 20 degrees C and 80 degrees C) and in the melt. Polymerisations were generally found to be well-controlled, giving predictable molecular weights and low molecular weight distributions. Ligand variation (substituents and/or chirality) has little effect on either the activity or selectivity of initiators. Zirconium initiators were found to be unusually robust as they were able to maintain well-controlled polymerisation following addition of water to reactions in solution and when using unpurified monomer for reactions in the melt.     

Infrared spectra of CO2-H2 complexes

Infrared spectra of weakly bound CO(2)-H(2) complexes have been studied in the region of the CO(2) v(3) asymmetric stretch, using a tunable diode laser probe and a pulsed supersonic jet expansion. For CO(2)-paraH(2), results were obtained for three isotopic species, (12)C(16)O(2), (13)C(16)O(2), and (12)C(18)O(2). These spectra were analyzed using an asymmetric rotor Hamiltonian, with results that resembled those obtained previously for OCS- and N(2)O-paraH(2), except that half the rotational levels were missing due to the symmetry of CO(2) and the spin statistics of the (16)O or (18)O nuclei. However, for CO(2)-orthoH(2), more complicated spectra were observed which could not be assigned, in contrast with OCS- and N(2)O-H(2) where the paraH(2) and orthoH(2) spectra were similar, though distinct. The CO(2)-paraH(2) complex has a T-shaped structure with and intermolecular distance of about 3.5 Angstroms, and the CO(2) v(3) vibration exhibits a small redshift (-0.20 cm(-1)) in the complex.