@article {1733, title = {Phase-sensitive sum-frequency vibrational spectroscopy and its application to studies of interfacial alkyl chains.}, journal = {Journal of the American Chemical Society}, volume = {129}, year = {2007}, month = {2007 Aug 22}, pages = {10056-7}, abstract = {

The first general phase-sensitive sum-frequency vibrational spectroscopy (SFVS) was described, which recovers the phase information lost in conventional SFVS measurements. Using a self-assembled monolayer, we demonstrated that this novel technique measures the absolute orientation of surface molecular moieties and is very powerful in resolving spectral features.

}, issn = {0002-7863}, doi = {10.1021/ja071989t}, author = {Ji, Na and Ostroverkhov, Victor and Chen, Chao-Yuan and Shen, Yuen-Ron} } @article {1736, title = {A novel spectroscopic probe for molecular chirality.}, journal = {Chirality}, volume = {18}, year = {2006}, month = {2006 Feb}, pages = {146-58}, abstract = {

Recent advances in developing sum frequency generation (SFG) as a novel spectroscopic probe for molecular chirality are reviewed. The basic principle underlying the technique is briefly described, in comparison with circular dichroism (CD). The significantly better sensitivity of the technique than CD is pointed out, and the reason is discussed. Bi-naphthol (BN) and amino acids are used as representatives for two different types of chiral molecules; the measured chirality in their electronic transitions can be understood by two different molecular models, respectively, that are extensions of models developed earlier for CD. Optically active or chiral SFG from vibrational transitions are weaker, but with the help of electronic-vibrational double resonance, the vibrational spectrum of a monolayer of BN has been obtained. Generally, optically active SFG is sufficiently sensitive to be employed to probe in-situ chirality of chiral monolayers and thin films.

}, keywords = {Algorithms, Chemistry, Molecular Conformation, Physical, Physicochemical Phenomena, Stereoisomerism}, issn = {0899-0042}, doi = {10.1002/chir.20238}, author = {Ji, Na and Shen, Yuen-Ron} } @article {1735, title = {Three-dimensional chiral imaging by sum-frequency generation.}, journal = {Journal of the American Chemical Society}, volume = {128}, year = {2006}, month = {2006 Mar 22}, pages = {3482-3}, abstract = {

A sum-frequency generation (SFG) microscope that is sensitive toward molecular chirality was demonstrated for the first time. Optically active images of chiral 1,1{\textquoteright}-bi-2-naphthol solutions were obtained with submicron spatial resolution. Three-dimensional sectioning capability of our microscope was also demonstrated. This optically active SFG microscopy can potentially become a powerful imaging technique for biological samples.

}, keywords = {Computer-Assisted, Fluorescence, Image Processing, Microscopy, Naphthols, Stereoisomerism}, issn = {0002-7863}, doi = {10.1021/ja057775y}, author = {Ji, Na and Zhang, Kai and Yang, Haw and Shen, Yuen-Ron} } @article {2729, title = {Toward chiral sum-frequency spectroscopy.}, journal = {Journal of the American Chemical Society}, volume = {128}, year = {2006}, month = {2006 Jul 12}, pages = {8845-8}, abstract = {

Chiral sum-frequency (SF) spectroscopy that measures both the real and the imaginary components of the SF spectral response was demonstrated for the first time. It was based on interference of the SF signal with a dispersionless SF reference. Solutions of 1,1{\textquoteright}-bi-2-naphthol (BN) were used as model systems, and their chiral SF spectra over the first exciton-split transitions were obtained. Chiral spectra are useful for determination of absolute configuration and conformation of chiral molecules.

}, keywords = {Molecular Conformation, Naphthols, Sensitivity and Specificity, Solutions, Spectrum Analysis}, issn = {0002-7863}, doi = {10.1021/ja060888c}, author = {Ji, Na and Ostroverkhov, Victor and Belkin, Mikhail and Shiu, Ying-Jen and Shen, Yuen-Ron} } @article {1737, title = {A dynamic coupling model for sum frequency chiral response from liquids composed of molecules with a chiral side chain and an achiral chromophore.}, journal = {Journal of the American Chemical Society}, volume = {127}, year = {2005}, month = {2005 Sep 21}, pages = {12933-42}, abstract = {

A theoretical formulation for optically active sum frequency generation (OA-SFG) from isotropic chiral solutions was proposed for molecules with a chiral side chain and an intrinsically achiral chromophore. Adapting an electron correlation model first proposed by H{\"o}hn and Weigang for linear optical activity, we presented a dynamic coupling model for OA-SFG near the electronic resonance of the achiral chromophore. As a demonstration, we used this model to explain the observed OA-SFG spectra of a series of amino acids near the electronic resonance of the intrinsically achiral carboxyl group. Our model shows that the nonlinear chiroptical response comes about by the through-space correlative electronic interactions between the chiral side chain and the achiral chromophore, and its magnitude is determined by the position and orientation of the bonds that make up the chiral side chain. Using the bond polarizability values in the literature and the conformations of amino acids obtained from calculation, we were able to reproduce the relative OA-SFG strength from a series of amino acids.

}, keywords = {Amino Acids, Chemical, Infrared, Models, Spectrophotometry, Thermodynamics}, issn = {0002-7863}, doi = {10.1021/ja052715d}, author = {Ji, Na and Shen, Yuen-Ron} } @article {1738, title = {Optically active sum frequency generation from molecules with a chiral center: amino acids as model systems.}, journal = {Journal of the American Chemical Society}, volume = {126}, year = {2004}, month = {2004 Nov 24}, pages = {15008-9}, abstract = {

With amino acids as model systems, optically active sum frequency generation (OA-SFG) was used to probe the chirality of molecules with a chiral center and an intrinsically achiral chromophore in isotropic solution for the first time. Like that of circular dichroism (CD), the OA-SFG{\textquoteright}s near electronic resonance originates from the extrachromophoric chiral perturbation on the carboxyl chromophore. The difference in the relative strengths of OA-SFG and CD among different amino acids can be explained by the difference in the details of perturbations.

}, keywords = {Amino Acids, Chemical, Circular Dichroism, Models, Optics and Photonics, Stereoisomerism}, issn = {0002-7863}, doi = {10.1021/ja045708i}, author = {Ji, Na and Shen, Yuen-Ron} } @article {1739, title = {Sum frequency vibrational spectroscopy of leucine molecules adsorbed at air-water interface.}, journal = {The Journal of Chemical Physics}, volume = {120}, year = {2004}, month = {2004 Apr 15}, pages = {7107-12}, abstract = {

Sum frequency vibrational spectroscopy was used to study adsorption of leucine molecules at air-water interface from solutions with different concentrations and pH values. The surface density and the orientation of the isopropyl head group of the adsorbed leucine molecules could be deduced from the measurements. It was found that the orientation depends on the surface density, but only weakly on bulk pH value at the saturated surface density. The vibrational spectra of the interfacial water molecules appeared to be strongly affected by the charge state of the adsorbed leucine molecules. Enhancement and inversion of polar orientation of interfacial water molecules by surface charges or field controllable by the bulk pH value were observed.

}, keywords = {Adsorption, Air, Chemistry, Hydrogen-Ion Concentration, Leucine, Physical, Spectrophotometry, Spectrum Analysis, Surface Properties, Water}, issn = {0021-9606}, doi = {10.1063/1.1669375}, author = {Ji, Na and Shen, Yuen-Ron} } @article {1740, title = {Surface vibrational spectroscopy on shear-aligned poly(tetrafluoroethylene) films.}, journal = {Journal of the American Chemical Society}, volume = {125}, year = {2003}, month = {2003 Nov 26}, pages = {14218-9}, abstract = {

Sum-frequency vibrational spectroscopy was used to obtain the first surface vibrational spectra of shear-deposited highly oriented poly(tetrafluoroethylene) (PTFE, Teflon) thin films. The surface PTFE chains appeared to lie along the shearing direction. Vibrational modes observed at 1142 and 1204 cm-1 were found to have the E1 symmetry, in support of some earlier analysis in the long-lasting controversy over the assignment of these modes.

}, issn = {0002-7863}, doi = {10.1021/ja037964l}, author = {Ji, Na and Ostroverkhov, Victor and Lagugn{\'e}-Labarthet, Fran\c cois and Shen, Yuen-Ron} }