二氢卟吩P6醚类衍生物的合成

以蚕沙糊状叶绿素经酸碱降解制得的二氢卟吩P6三甲酯(2)为关键中间体,设计合成了9个二氢卟吩P6醚类衍生物3a～3e和4b～4e,用UV、IR、^1H、NMR、FAB-MS和元素分析确证了它们的结构。     

Synthesis of Zinc Chlorophyll Homo/Hetero‐Dyads and their Folded Conformers with Porphyrin,Chlorin, and Bacteriochlorin π‐Systems

Zinc complex of pyropheophorbide‐b, a derivative of chlorophyll‐b, was covalently dimerized through ethylene glycol diester. The synthetic homo‐dyad was axially ligated with two methanol molecules from the β‐face and both the diastereomerically coordinating methanol species were hydrogen bonded with the keto‐carbonyl groups of the neighboring chlorin in a complex. The resulting folded conformer in a solution was confirmed by visible, ¹H NMR and IR spectra. All the synthetic zinc chlorin homo‐ and hetero‐dyads consisting of pyropheophorbides‐a, b and/or d took the above methanol‐locked and π–π stacked supramolecules in 1% (v/v) methanol and benzene to give redmost (Qy) electronic absorption band(s) at longer wavelengths than those of the corresponding monomeric chlorin composites. The other zinc chlorin and bacteriochlorin homo‐dyads completely formed similar folded conformers in the same solution, while zinc inverse chlorin and porphyrin homo‐dyads partially took such supramolecules. The J‐type aggregation to folded conformers and the redshift values of composite Qy bands were dependent on the electronic and steric factors of porphyrinoid moieties in dyads.     

Complexity in the self-assembly of bifunctional molecules on HOPG: the influence of solvent functionality on self-assembled structures

Self-assembled monolayers of bifunctional molecules HOOC(CH2)nCOOH (n = 20, 18, 16, 14, 12, 10), HOOC(CH2)nCH2OH (n = 13, 14), and HOCH2(CH2)14CH2OH dissolved in octanoic acid were investigated using scanning tunneling microscopy, to understand the self-assembly of bifunctional molecules and the influence of a carboxylic acid solvent on the formation of self-assembled structures on HOPG. In the series of di-acids (HOOC(CH2)nCOOH), only HOOC(CH2)20COOH forms stable coadsorption structures with the solvent octanoic acid. The remaining di-acids form stable single-component monolayers and do not coadsorb with solvent octanoic acid. Coadsorption structures involving mixtures of di-acids were observed. This result suggests that coadsorption with acid solvent or with other di-acids occurs to maximize hydrogen-bond density in the overlayer. A quantitative model based on this concept is proposed. For hetero-bifunctional molecules HOOC(CH2)nCH2OH (n = 13, 14), the coadsorption of HOOC(CH2)14CH2OH and octanoic acid at the molecular level produces a microscopic mesh made of homogeneously arranged openings with a dimension of approximately 12.5 A x approximately 5.0 A x approximately 1.8 A. For the hetero-bifunctional molecule HOOC(CH2)13CH2OH, hydroxyl groups of two adjacent lamellae assemble to form a herringbone geometry, and the two carboxylic acid groups assemble with a straight head-to-head configuration. In addition, a new mixed hydrogen-bonding network of COOH...O-H was observed in another self-assembled structure of this molecule. The bifunctional molecule HOCH2(CH2)14CH2OH exhibits multiple packing patterns on HOPG via different hydrogen-bonding networks. HOCH2(CH2)14CH2OH self-assembles using the H-O...O-H network typical of the n-alcohol herringbone structure, forming an asymmetric adsorbate on HOPG. It also forms domains with another hydrogen-bonding network, in which molecules in adjacent lamellae are parallel to each other. This investigation demonstrates the complexity and diversity of self-assembled structures formed from bifunctional molecules on solid surfaces. It also indicates that a solvent with the same functional group as the solute can significantly impact the formation of the self-assembled structures of these bifunctional molecules.     

Synthetic Zinc and Magnesium Chlorin Aggregates as Models for Supramolecular Antenna Complexes in Chlorosomes of Green Photosynthetic Bacteria

Abstract— A comparison of the spectra of in vitro (3-hydroxymethyl-13¹-oxometallochlorin) and in vivo chlorosomal (bacterio-chlorophyll- c ) aggregates suggests a similar supramolecular structure for the artificial oligomers and the bacte-riochlorophyll- c aggregates in the extramembranous antenna complexes (chlorosomes) of green photosynthetic bacteria. Synthetic zinc and magnesium chlorins have been found to aggregate in 1 % (vol/vol) tetrahydrofuran and hexane solutions and in thin films to form oligomers with the Q_y absorption bands shifted to longer wavelengths by about 1900 (Zn chlorins) and 2100 cm⁻¹ (Mg) relative to the corresponding monomer bands. Visible absorption and circular dichroism spectra of various zinc chlorins establish that a central metal, a 3¹-hydroxy and a 13¹-keto group are functional prerequisites for the aggregation. Vibrational bands measured by IR spectroscopy of solid films reveal two characteristic structural features of the oligomers: (1) a five-coordinated metallochlorin macrocycle with an axial ligand (bands at 1500-1630 cm⁻¹), and (2) a hydrogen bond between the keto oxygen of one chlorin and the hydroxy group of a second chlorin, the oxygen of which is chelated to the metal atom of a third molecule, i.e . C=O…H-O…M (=Zn or Mg).     

IR plus vacuum ultraviolet spectroscopy of neutral and ionic organic acid monomers and clusters: propanoic acid

The vibrational spectrum of molecular propanoic acid, cooled in a supersonic expansion, in the region of 2500 to 7500 cm(-1) is obtained employing infrared plus vacuum ultraviolet nonresonant ionization detected spectroscopy. The fundamental and first overtone of the CH and OH stretch modes of cold propanoic acid molecules can be identified in the spectrum. Propanoic acid neutral and ionic clusters are also studied employing nonresonant ion dip and photodissociation spectroscopic techniques, respectively. For the neutral dimer, a sequence of features observed at ca. 2500-2700 cm(-1) can be assigned as combination bands of low frequency modes with the COH bending overtone; these features characterize the cyclic dimer ring structure. IR spectra of the larger neutral clusters n=3, 4, 5 indicate that they also have cyclic structures in which the OH groups are engaged in the cluster hydrogen bonding network. The CH groups are not involved in this hydrogen bonding structure. Free OH features are observed for the protonated ion clusters (C(2)H(5)COOH)(n)H(+), n=1,...,5, indicating that at least one OH group of these cluster ions is not involved in the cluster hydrogen bonding network. A comparison of the results for four hydrogen bonding neutral and ionic clusters (CH(3)OH, C(2)H(5)OH, CH(3)COOH, and C(2)H(5)COOH) is presented and discussed.     

Synthesis of meso-substituted chlorins via tetrahydrobilene-a intermediates.

Chlorin building blocks incorporating a geminal dimethyl group in the reduced ring and synthetic handles in specific patterns at the perimeter of the macrocycle are expected to have utility in biomimetic and materials chemistry. A prior route employed condensation of a dihydrodipyrrin (Western half) and a bromodipyrromethane-monocarbinol (Eastern half), followed by oxidative cyclization of the putative dihydrobilene-a to form the meso-substituted zinc chlorin in yields of approximately 10%. The limited stability of the dihydrodipyrrin precluded study of the chlorin-forming process. We now have refined this methodology. A tetrahydrodipyrrin Western half (2,3,4,5-tetrahydro-1,3,3-trimethyldipyrrin) has been synthesized and found to be quite stable. The condensation of the Western half and an Eastern half (100 mM each) proceeded smoothly in CH(3)CN containing 100 mM TFA at room temperature for 30 min. The resulting linear tetrapyrrole, a 2,3,4,5-tetrahydrobilene-a, also is quite stable, enabling study of the conversion to chlorin. Refined conditions for the oxidative cyclization were found to include the following: the tetrahydrobilene-a (10 mM), AgTf (3-5 molar equiv), Zn(OAc)(2) (15 molar equiv), and 2,2,6,6-tetramethylpiperidine (15 molar equiv) in CH(3)CN at reflux exposed to air for 4-6 h, affording the zinc chlorin. The chlorin-forming process could be implemented in either a two-flask process or a one-flask process. The two-flask process was applied to form six zinc chlorins bearing substituents such as pentafluorophenyl, 3,5-di-tert-butylphenyl, TMS-ethyl benzoate, iodophenyl, or ethynylphenyl (deprotection of the TMS-ethynyl group occurred during the oxidative cyclization process). The stepwise yields (isolated) for the condensation and oxidative cyclization processes forming the tetrahydrobilene and zinc chlorin were 32-72% and 27-62%, respectively, giving overall yields of zinc chlorin from the Eastern and Western halves of 12-45%. Taken together, the refinements introduced enable 100-mg quantities of chlorin building blocks to be prepared in a facile and rational manner.     

Chlorin e6-liposome interaction. Investigation by the methods of fluorescence spectroscopy and inductive resonance energy transfer

On the basis of spectral fluorescence and polarization measurements and results obtained on the luminescence quenching of the membrane fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH) by incorporated chlorin e6 (chl e6) molecules, it is shown that the interaction of the water-soluble pigment with smaller unilamellar lipid vesicles occurs by a mechanism of partition between the aqueous and lipid phases (partition coefficient Kp = 6.7 x 10(3) and provides rigid fixing of chl e6 monomers at the boundary between the polar and non-polar parts of the lipid membrane. In terms of inductive resonance electronic excitation energy transfer between DPH and chl e6 (R0 = 36.2 A), we have analysed data on DPH fluorescence quenching under different conditions of chl e6 localization in the lipid bilayer and have concluded that the incorporation of the pigment molecules into the vesicles from the aqueous phase occurs mainly into the external monolayer.     

一个锰(Ⅲ)Schiff碱配合物[Mn(napn)(CH_3OH)_2]ClO_4的合成与晶体结构

合成了一个新配合物[Mn(napn)(CH3OH)2]ClO4 (C26H26 Cl N2O8Mn,Mr = 584.88,H2napn = 双a-萘酚醛缩乙二胺),并测定了其晶体结构。晶体属于三斜晶系,空间群P ,a = 7.813(1),b = 13.025(2),c = 14.089(2) ? = 64.89(3), = 83.98(3), = 78.11(3)海琕 = 1270.16 ?,Z = 2, Dc = 1.529 g/cm3, F(000) = 604, R = 0.0837, wR = 0.1636。锰(Ⅲ)离子的配位构型为拉长的八面体。Schiff碱配体napn2-中的N2O2在赤道平面与锰(Ⅲ)形成四配位,2个CH3OH中的O原子分别在赤道平面两侧轴向位置与锰(Ⅲ)配位。由于Jahn-Teller效应,轴向上的MnO平均键长为2.52 拧A硗猓О写嬖诜肿幽诤头肿蛹淝饧?     

光促进温和条件下烯烃与二氧化碳的羰基化反应

羰基化反应是有机合成化学中常用的方法之一,但常规的羰基化反应大多要求高温(150～200℃)、高压(10～20 M Pa)或使用贵金属催化剂(如钌、铑、铱等),并且C₁源多用一氧化碳^[1].开发和利用CO₂这一丰富的C₁资源,并最大限度地降低其排放量具有挑战意义.但CO₂活化比较困难,在通常条件下难以转化成其它化学品^[2].在光促进下的羰基化反应可克服上述困难,使反应在温和条件及非贵金属催化下完成,同时可用CO₂代替CO作为C₁源,因此这是一个对环境友好的工艺^[3].本文报道烯烃在光促进常温常压和非贵金属钴配合物催化下与二氧化碳的羰基化反应,同时通过¹³CO₂和¹³CH₃OH同位素实验,对反应产物的结构进行了分析.     

Demetalation kinetics of chlorophyll derivatives possessing different substituents at the 7-position under acidic conditions

Conversion of the formyl group at the 7-position in chlorophyll (Chl) b to the methyl group via the hydroxymethyl group is biologically important in Chl b degradation. To clarify the effects of the 7-substituents on demetalation properties of chlorophyllous pigments in the early process of Chl b degradation, we report demetalation kinetics of the zinc Chl derivative possessing a 7-hydroxymethyl group, which is a good model compound of the intermediate molecule in the early process of Chl b degradation, under acidic conditions, and compare its properties with those of zinc Chl derivatives possessing a methyl and a formyl group, which are model compounds of Chls a and b, respectively. Demetalation rate constants of 7-hydroxymethyl zinc chlorin were much larger than those of 7-formyl zinc chlorin, but were slightly smaller than those of 7-methyl zinc chlorin. The activation energy for demetalation reaction of 7-formyl zinc chlorin was larger than those of other derivatives. Demetalation rate constants of 7-deformyl-7-hydroxymethyl Chl b were also larger than those of Chl b, and were similar to those of Chl a. These indicate that the 7-hydroxymethyl group in the chlorin macrocycle has a smaller effect on demetalation compared with the 7-formyl group.     

Influence of the boron atom on the solvatochromic properties of 4-nitroaniline-functionalized boronate esters

Para-nitroaniline derivatives with peripheral 1,2- and 1,3-diol functionalities [O(2)N-C(6)H(4)-NR(1)-CH(2)CH(OH)CH(2)OH; O(2)N-C(6)H(4)-NR(1)-CH(CH(2)OH)(2); R(1) = -H, -CH(3)] covalently bonded to the amino group are esterified with various para-substituted phenylboronic acids [R(2)-C(6)H(4)-B(OH)(2); R(2) = -OCH(3), -CH(3), -H, -Br, -CHO, -NO(2), -B(OH)(2)], and the solvatochromic properties of these esters are investigated in 33 solvents of different polarity. To interpret the solvent effects, the established linear solvation energy (LSE) multiparameter equations of Kamlet-Taft and the improved Catalán scales are used. Although the boron atom is separated by two or three sp(3)-hybridized carbon atoms from the actual chromophore, solvation effects have a significant positive solvatochromic effect on the nitroaniline unit (R(1) = -CH(3)) as result of the solvent acting as a donor at the boron atom. The influence of the substituent R(2) on the coefficient b of the LSE relationship according to Kamlet-Taft and Catalán, which reflects the quantitative influence of the hydrogen-bonding acceptor or the electron-pair donor capacity of the solvent on the position of the UV-vis absorption maximum, can be determined via a linear Hammett relationship [b = f(σ(p))]. The interpretation of the effects is based on the electronic influence of the solvated boronic acid ester unit on the 4-nitroaniline group, predominantly through inductive interactions.     

Simple minimum principle to derive a quantum-mechanical/molecular-mechanical method

We propose a minimum principle to derive a QM/MM (quantum-mechanical/molecular-mechanical) method from the first principle. We approximate the Hamiltonian of a spectator substituent as the structure-dependent effective Hamiltonian in a least-squares sense. This effective Hamiltonian is expanded with the orthogonal operator set called the normal-ordered product. We determine the structure-dependent energy that corresponds to the classical MM energy and the extra one-electron potential that takes account of the interface effects. This QM/MM method is free from the double-counting problem and the artificial truncation of the localized molecular orbitals. As a numerical example we determine the one-electron effective Hamiltonian of the methyl group. This effective Hamiltonian is applied to the ethane and CH(3)CH(2)X molecules (X=CH(3), NH(2), OH, F, COOH, NH(3) (+), OH(2) (+), and COO(-)). It reproduced the relative energies, potential energy curves, and the Mulliken populations of the all-electron calculations fairly well.     

Tetra-2,3-pyrazinoporphyrazines with externally appended pyridine rings. 1. Tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine: a new macrocycle with remarkable electron-deficient properties

A new pyrazinoporphyrazine macrocycle carrying externally appended pyridine rings, tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine (hydrated), [Py(8)TPyzPzH(2)].2H(2)O, was prepared in high yield by direct cyclotetramerization of the precursor, 2,3-dicyano-5,6-di(2-pyridyl)-1,4-pyrazine, [(CN)(2)Py(2)Pyz], in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The single-crystal X-ray structure of [(CN)(2)Py(2)Pyz] shows a noncoplanar positioning of the pyrazine and pyridine rings in the two slightly different independent molecular units present in the crystal. UV-vis spectra of [Py(8)TPyzPzH(2)] were measured in two nondonor solvents (CHCl(3), CH(2)Cl(2)), a slightly basic solvent (pyridine), and an acidic solvent (CH(3)COOH). In all cases, the spectral changes are consistent with the occurrence of molecular aggregation and colloidal dispersions which break up with time to give clear solutions containing exclusively the monomeric form of the macrocycle, either neutral [Py(8)TPyzPzH(2)] (in CHCl(3), CH(2)Cl(2), and CH(3)COOH) or dianionic [Py(8)TPyzPz](2)(-) (in pyridine). A spectrally monitored titration of [Py(8)TPyzPzH(2)] in CH(2)Cl(2) with TBA(OH) shows the loss of two protons from the macrocyclic core and quantitative conversion of [Py(8)TPyzPzH(2)] to [Py(8)TPyzPz](2)(-). Cyclic voltammetry and thin-layer spectroelectrochemical measurements show that [Py(8)TPyzPzH(2)] is present in CH(2)Cl(2) while [Py(8)TPyzPz](2)(-) is present in pyridine, but both forms of the compound exhibit identical electrochemical behavior, consistent with a conversion of the dianion to the neutral porphyrazine in pyridine prior to electroreduction via four reversible one-electron transfer steps. No oxidations of the macrocycle are observed in either solvent containing 0.1 M tetrabuthylammonium perchlorate (TBAP). A comparison of the electrochemical behavior for [Py(8)TPyzPzH(2)] with what is reported for related phthalocyanine and porphyrazine analogues highlights the remarkable electron-accepting properties of the presently investigated free-base macrocycle.     

Mixed substituted porphyrins: structural and electrochemical redox properties

To examine the influence of mixed substituents on the structural, electrochemical redox behavior of porphyrins, two new classes of beta-pyrrole mixed substituted free-base tetraphenylporphyrins H2(TPP(Ph)4X4) (X = CH3, H, Br, Cl, CN) and H2(TPP(CH3)4X4) (X = H, Ph, Br, CN) and their metal (M = Ni(II), Cu(II), and Zn(II)) complexes have been synthesized effectively using the modified Suzuki cross-coupling reactions. Optical absorption spectra of these porphyrins showed significant red-shift with the variation of X in H2(TPPR4X4), and they induce a 20-30 nm shift in the B band and a 25-100 nm shift in the longest wavelength band [Q(x)(0,0)] relative to the corresponding H2TPPR4 (R = CH3, Ph) derivatives. Crystal structure of a highly sterically crowded Cu(TPP(Ph)4(CH3)4).2CHCl3 complex shows a combination of ruffling and saddling of the porphyrin core while the Zn(TPP(Ph)4Br4(CH3OH)).CH3OH structure exhibits predominantly saddling of the macrocycle. Further, the six-coordinated Ni(TPP(Ph)4(CN)4(Py)2).2(Py) structure shows nearly planar geometry of the porphyrin ring with the expansion of the core. Electrochemical redox behavior of the MTPPR4X4 compounds exhibit dramatic cathodic shift in first ring oxidation potentials (300-500 mV) while the reduction potentials are marginally cathodic in contrast to their corresponding MTPPX4 (X = Br, CN) derivatives. The redox potentials were analyzed using Hammett plots, and the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap decreases with an increase in the Hammett parameter of the substituents. Electronic absorption spectral bands of H2TPPR4X4 are unique that their energy lies intermediate to their corresponding data for the H2(TPPX8) (X = CH3, Ph, Br, Cl) derivatives. The dramatic variation in redox potentials and large red-shift in the absorption bands in mixed substituted porphyrins have been explained on the basis of the nonplanarity of the macrocycle and substituent effects.     

Energetics of C-F, C-Cl, C-Br, and C-I bonds in 2-haloethanols. enthalpies of formation of XCH(2)CH(2)OH (X = F, Cl, Br, I) compounds and of the 2-hydroxyethyl radical

The energetics of the C-F, C-Cl, C-Br, and C-I bonds in 2-haloethanols was investigated by using a combination of experimental and theoretical methods. The standard molar enthalpies of formation of 2-chloro-, 2-bromo-, and 2-iodoethanol, at 298.15 K, were determined as Delta(f)H(degree)m(CH2CH2OH, l) = -315.5 +/- 0.7 kJ.mol-1, Delta(f)H(degree)mBrCH2CH2OH, l) = -275.8 +/- 0.6 kJ.mol-1, Delta(f)H(degree)m(ICH2CH2OH, l) = -207.3 +/- 0.7 kJ.mol-1, by rotating-bomb combustion calorimetry. The corresponding standard molar enthalpies of vaporization, Delta(vap)H(degree)m(ClCH2CH2OH) = 48.32 +/- 0.37 kJ.mol-1, Delta(vap)H(degree)m(BrCH2CH2OH) = 54.08 +/- 0.40 kJ.mol-1, and Delta(vap)H(degree)m(ICH2CH2OH) = 57.03 +/- 0.20 kJ.mol-1 were also obtained by Calvet-drop microcalorimetry. The condensed phase and vaporization enthalpy data lead to Delta(f)H(degree)m(ClCH2CH2OH, g) = -267.2 +/- 0.8 kJ.mol-1, Delta(f)H(degree)m(BrCH2CH2OH, g) = -221.7 +/- 0.7 kJ.mol-1, and Delta(f)H(degree)m(ICH2CH2OH, g) = -150.3 +/- 0.7 kJ.mol-1. These values, together with the enthalpy of selected isodesmic and isogyric gas-phase reactions predicted by density functional theory (B3LYP/cc-pVTZ) and CBS-QB3 calculations were used to derive the enthalpies of formation of gaseous 2-fluoroethanol, Delta(f)H(degree)m(FCH2CH2OH, g) = -423.6 +/- 5.0 kJ.mol-1, and of the 2-hydroxyethyl radical, Delta(f)H(degree)m(CH2CH2OH, g) = -28.7 +/- 8.0 kJ.mol-1. The obtained thermochemical data led to the following carbon-halogen bond dissociation enthalpies: DHo(X-CH2CH2OH) = 474.4 +/- 9.4 kJ.mol-1 (X = F), 359.9 +/- 8.0 kJ.mol-1 (X = Cl), 305.0 +/- 8.0 kJ.mol-1 (X = Br), 228.7 +/- 8.1 kJ.mol-1 (X = I). These values were compared with the corresponding C-X bond dissociation enthalpies in XCH2COOH, XCH3, XC2H5, XCH=CH2, and XC6H5. In view of this comparison the computational methods mentioned above were also used to obtain Delta(f)H(degree)m-594.0 +/- 5.0 kJ.mol-1 from which DHo(F-CH2COOH) = 435.4 +/- 5.4 kJ.mol-1. The order DHo(C-F) > DHo(C-Cl) > DHo(C-Br) > DHo(C-I) is observed for the haloalcohols and all other RX compounds. It is finally concluded that the major qualitative trends exhibited by the C-X bond dissociation enthalpies for the series of compounds studied in this work can be predicted by Pauling's electrostatic-covalent model.     

The cysteine radical cation: structures and fragmentation pathways

A theoretical study on the structures, relative energies, isomerization reactions and fragmentation pathways of the cysteine radical cation, [NH(2)CH(CH(2)SH)COOH].+, is reported. Hybrid density functional theory (B3LYP) has been used in conjunction with the 6-311++G(d,p) basis set. The isomer at the global minimum, Captodative-1, has the structure NH(2)C.(CH(2)SH)C(OH)(2)+; the stability of this ion is attributed to the captodative effect in which the NH(2) functions as a powerful pi-electron donor and C(OH)(2)+ as a powerful pi-electron acceptor. Ion Distonic-S-1, H(3)N(+)CH(CH(2)S.)COOH, in which the radical is formally situated on the S atom, is higher in enthalpy (DeltaH degrees (0)) than Captodative-1 by 6.1 kcal mol(-1), but is lower in enthalpy than another isomer Distonic-C-1, H(3)N(+)C.(CH(2)SH)COOH, by 8.2 kcal mol(-1). Isomerization of the canonical radical cation of cysteine, [H(2)NCH(CH(2)SH)COOH].+, (Canonical-1), to Captodative-1 has an enthalpy of activation of 25.8 kcal mol(-1), while the barrier against isomerization of Canonical-1 to Distonic-S-1 is only 9.6 kcal mol(-1). Two additional transient tautomers, one with the radical located at C(alpha) and the charge on SH(2), and the other a carboxy radical with the charge on NH(3), are reported. Plausible fragmentation pathways (losses of small molecules, CO(2), CH(2)S, H(2)S and NH(3), and neutral radicals COOH. , HSCH(2). and NH(2).) from Canonical-1 are examined.     

Infrared photodissociation spectroscopy of Al(+)(CH(3)OH)(n) (n = 1-4)

Infrared photodissociation spectra of Al(+)(CH(3)OH)(n) (n = 1-4) and Al(+)(CH(3)OH)(n)-Ar (n = 1-3) were measured in the OH stretching region, 3000-3800 cm(-1). For n = 1 and 2, sharp absorption bands were observed in the free OH stretching region, all of which were well reproduced by the spectra calculated for the solvated-type geometry with no hydrogen bond. For n = 3 and 4, there were broad vibrational bands in the energy region of hydrogen-bonded OH stretching vibrations, 3000-3500 cm(-1). Energies of possible isomers for the Al(+)(CH(3)OH)(3),4 ions with hydrogen bonds were calculated in order to assign these bands. It was found that the third and fourth methanol molecules form hydrogen bonds with methanol molecules in the first solvation shell, rather than a direct bonding with the Al(+) ion. For the Al(+)(CH(3)OH)(n) clusters with n = 1-4, we obtained no evidence of the insertion reaction, which occurs in Al(+)(H(2)O)(n). One possible explanation of the difference between these two systems is that the potential energy barriers between the solvated and inserted isomers in the Al(+)(CH(3)OH)(n) system is too high to form the inserted-type isomers.     

Infrared and Raman bands of phytantriol as markers of hydrogen bonding and interchain interaction

Hydrogen bonding and interchain interactions in phytantriol, 3,7,11,15-tetramethyl-1,2,3-hexadecanetriol, have been studied by Fourier transform infrared (FT-IR) and Raman spectroscopies. Assignments of the bands were performed based on the OH/OD isotopic substitution, molecular modeling, and measurements of polarized Raman spectra. Marker bands were evaluated from the temperature-dependent spectral changes. It is shown that Raman spectroscopy provides sensitive markers, namely I(delta(CH2))/I(deltas(CH3)), tau(CH)2, I(nus(CH3)(FR))/I(nus(CH2)), and nus(CH2) for probing the interactions between the hydrocarbon chains. Hydrogen bonding interaction might be studied through the difference Raman spectroscopy by the analysis of polarized band at 811 cm-1. Relationship is found between the frequencies of IR bands at 883-873 and 1097-1086 cm-1, associated with the vibrations localized at the primary COH site, and the frequencies of OH stretching mode, making these bands specific markers in the analysis of hydrogen bonding. Evaluated marker bands may be of utility to probe the interchain and hydrogen bonding interaction of phytantriol with guest molecules in the practically important aqueous liquid-crystalline phases of this lipid.     

Synthesis and electronic properties of regioisomerically pure oxochlorins

We describe a two-step conversion of C-alkylated zinc chlorins to zinc oxochlorins wherein the keto group is located in the reduced ring (17-position) of the macrocycle. The transformation proceeds by hydroxylation upon exposure to alumina followed by dehydrogenation with DDQ. The reactions are compatible with ethyne, iodo, ester, trimethylsilyl, and pentafluorophenyl groups. A route to a spirohexyl-substituted chlorin/oxochlorin has also been developed. Representative chlorins and oxochlorins were characterized by static and time-resolved absorption spectroscopy and fluorescence spectroscopy, resonance Raman spectroscopy, and electrochemistry. The fluorescence quantum yields of the zinc oxochlorins (Phi(f) = 0.030-0.047) or free base (Fb) oxochlorins (Phi(f) = 0.13-0.16) are comparable to those of zinc tetraphenylporphyrin (ZnTPP) or free base tetraphenylporphyrin (FbTPP), respectively. The excited-state lifetimes of the zinc oxochlorins (tau = 0.5-0.7 ns) are on average 4-fold lower than that of ZnTPP, and the lifetimes of the Fb oxochlorins (tau = 7.4-8.9 ns) are approximately 40% shorter than that of FbTPP. Time-resolved absorption spectroscopy of a zinc oxochlorin indicates the yield of intersystem crossing is >70%. Resonance Raman spectroscopy of copper oxochlorins show strong resonance enhancement of the keto group upon Soret excitation but not with Q(y)()-band excitation, which is attributed to the location of the keto group in the reduced ring (rather than in the isocyclic ring as occurs in chlorophylls). The one-electron oxidation potential of the zinc oxochlorins is shifted to more positive potentials by approximately 240 mV compared with that of the zinc chlorin. Collectively, the fluorescence yields, excited-state lifetimes, oxidation potentials, and various spectral characteristics of the chlorin and oxochlorin building blocks provide the foundation for studies of photochemical processes in larger architectures based on these chromophores.     

Internal rotation in propionic acid: near-infrared-induced isomerization in solid argon

The conformational system of propionic acid (CH3CH2COOH) is studied in solid argon. It is predicted by the ab initio calculations that this molecule has four stable conformers. These four structures are denoted Tt, Tg+/-, Ct, and Cg+/-, and they differ by the arrangement around the C-O and Calpha-C bonds. The ground-state Tt conformer is the only form present at 8 K after deposition of an argon matrix containing propionic acid. For the CH3CH2COOH and CH3CH2COOD isotopologues, narrow-band excitation of the first hydroxyl stretching overtone of the conformational ground state promotes the Calpha-C and C-O internal rotations producing the Tg+/- and Ct conformers, respectively. A subsequent vibrational excitation of the produced Tg+/- form induces its conversion to the Cg+/- conformer by rotation around the C-O bond. In the dark, all of the produced conformers decay to the conformational ground state at different rates. The decay kinetics and its temperature dependence allow the identification of the conformers by IR absorption spectroscopy, which is supported by ab initio calculations of their vibrational spectra. For the CH3CH2COOD isotopologue, the excitation of molecules isolated in different matrix sites results in site-dependent photoisomerization rates for the Calpha-C and C-O internal rotations, which also confirm the identification of the photoproducts.