Tim May

Comparing and correlating solubility parameters governing the self-assembly of molecular gels using 1,3:2,4-dibenzylidene sorbitol as the gelator.

Solvent properties play a central role in mediating the aggregation and self-assembly of molecular gelators and their growth into fibers. Numerous attempts have been made to correlate the solubility parameters of solvents and gelation abilities of molecular gelators, but a comprehensive comparison of the most important parameters has yet to appear. Here, the degree to which partition coefficients (log P), Henry’s law constants (HLC), dipole moments, static relative permittivities (εr), solvatochromic ET(30) parameters, Kamlet–Taft parameters (β, α, and π), Catalan’s solvatochromic parameters (SPP, SB, and SA), Hildebrand solubility parameters (δi), and Hansen solubility parameters (δp, δd, δh) and the associated Hansen distance (Rij) of 62 solvents (covering a wide range of properties) can be correlated with the self-assembly and gelation of 1,3:2,4-dibenzylidene sorbitol (DBS) gelation, a classic molecular gelator, is assessed systematically. The approach presented describes the basis for each of the parameters and how it can be applied. As such, it is an instructional blueprint for how to assess the appropriate type of solvent parameter for use with other molecular gelators as well as with molecules forming other types of self-assembled materials. The results also reveal several important insights into the factors favoring the gelation of solvents by DBS. The ability of a solvent to accept or donate a hydrogen bond is much more important than solvent polarity in determining whether mixtures with DBS become solutions, clear gels, or opaque gels. Thermodynamically derived parameters could not be correlated to the physical properties of the molecular gels unless they were dissected into their individual HSPs. The DBS solvent phases tend to cluster in regions of Hansen space and are highly influenced by the hydrogen-bonding HSP, δh. It is also found that the fate of this molecular gelator, unlike that of polymers, is influenced not only by the magnitude of the distance between the HSPs for DBS and the HSPs of the solvent, Rij, but also by the directionality of Rij: if the solvent has a larger hydrogen-bonding HSP (indicating stronger H-bonding) than that of the DBS, then clear gels are formed; opaque gels form when the solvent has a lower δh than does DBS.

Multicomponent Hollow Tubules Formed Using Phytosterol and γ-Oryzanol-Based Compounds: An Understanding of Their Molecular Embrace

The formation kinetics of self-assembling tubules composed of phytosterol:gamma-oryzanol mixtures were investigated at the Canadian Light Source on the mid-IR beamline using synchrotron radiation and Fourier transform infrared spectroscopy (FT-IR). The Avrami model was fitted to the changing hydrogen bonding density occurring at 3450 cm(-1). The nucleation process was found to be highly dependent on the molecular structure of the phytosterol. The nucleation event for cholesterol:gamma-oryzanol was determined to be sporadic whereas 5alpha-cholestan-3beta-ol:gamma-oryzanol and beta-sitosterol:gamma-oryzanol underwent instantaneous nucleation. One-dimensional growth occurred for each phytosterol:gamma-oryzanol mixture and involved the evolution of highly specific intermolecular hydrogen bonds. More detailed studies on the cholesterol:gamma-oryzanol system indicated that the nucleation activation energy, determined from multiple rate constants, obtained using the Avrami model, was at a minimum when the two compounds were at a 1:1 weight ratio. This resulted in drastic differences to the microscopic structures and affected the macroscopic properties such as turbidity. The formation of the phytosterol:gamma-oryzanol complex was due to intermolecular hydrogen bonding, which was in agreement with the infrared spectroscopic evidence.

Step-scan IR spectroelectrochemistry with ultramicroelectrodes: nonsurface enhanced detection of near femtomole quantities using synchrotron radiation.

The result of interfacing step-scan spectroelectrochemistry with an IR microscope and synchrotron infrared (SIR) radiation is provided here. An external reflectance cell containing a 25 μm gold ultramicroelectrode is employed to achieve an electrochemical time constant less than one microsecond. The use of a prototypical electrochemical system, i.e., the mass-transport controlled reduction of ferricyanide, allows for a proof of principle evaluation of the viability of SIR for step-scan spectroelectrochemistry. An analysis of the importance of accounting for synchrotron source variation over the prolonged duration of a step-scan experiment is provided. Modeling of the material flux in the restricted diffusion space afforded by the external reflectance cell allows the quantitative IR results to be compared to theoretical predictions. The results indicate that only at very short times does linear diffusion within the cavity dominate the electrode response and the majority of the transient signal operates under conditions of quasi-hemispherical diffusion. The analytical information provided by the IR signal is found to be considerably less than that derived from the current response due the latters pronounced edge effects. The results provide a detection limit of 36 fmol for step-scan SIR measurements of ferrocyanide. Implications for future IR spectroelectrochemical studies in the microsecond domain are discussed.

Synchrotron Infrared Radiation for Electrochemical External Reflection Spectroscopy: A Case Study Using Ferrocyanide

Synchrotron infrared radiation has been successfully coupled through an infrared (IR) microscope to a thin-cavity external reflectance cell to study the diffusion controlled redox of a ferrocyanide solution. Excellent signal-to-noise ratios were achieved even at aperture settings close to the diffraction limit. Comparisons of noise levels as a function of aperture size demonstrate that this can be attributed to the high brilliance of synchrotron radiation relative to a conventional thermal source. Time resolved spectroscopic studies of diffusion controlled redox behavior have been measured and compared to purely electrochemical responses of the thin-cavity cell. Marked differences between the two measurements have been explained by analyzing diffusion in both the axial (linear) and radial dimensions. Whereas both terms contribute to the measured current and charge, only species that originate in the volume element above the electrode and diffuse in the direction perpendicular to the electrode surface are interrogated by IR radiation. Implications for the use of ultramicroelectrodes and synchrotron IR (SIR) to study electrochemical processes in the submillisecond time domain are discussed.

Interface for time-resolved electrochemical infrared microspectroscopy using synchrotron infrared radiation

A description of a coupled electrochemical and spectrometer interface using synchrotron infrared radiation is provided. The interface described allows for the precise and accurate timing needed for time-resolved IR spectroscopic studies of electrochemical systems. The overall interface uses a series of transistor-transistor logic trigger signals generated from the commercial FTIR spectrometer to regulate the recording of control, electrochemical, and IR signals with reproducible and adjustable timing. The instrument has been tested using a thin-layer electrochemical cell with synchrotron light focused through microscope optics. The time-resolved response of the benzoquinone/dihydroxybenzoquinone redox couple is illustrated as an example of the instruments capability.

Infrared Beamlines at the Canadian Light Source

The Canadian Light Source (CLS) is commissioning two infrared beamlines. The Mid infrared beamline 01B1‐1 will span from 2.5 to 25 micron wavelengths (4,000 cm−1 to 400 cm−1), and will supply diffraction‐limited spatial resolution to infrared microscopy. The Far infrared beamline 02B1‐1 will span from 2.5 to 1000 micron wavelengths (4,000 cm−1 to 10 cm−1), and will deliver ultrahigh spectral resolution (<0.001 cm−1) for gas‐phase spectroscopic studies of stable and unstable molecules. The optics and features of each beamline and current status of the facility commissioning are presented.

A far-infrared beamline for ultrahigh vacuum surface vibrational spectroscopy at Aladdin

A far-infrared beamline has been implemented on port 031 of the Aladdin Storage Ring. Port 031 has been designed to capture the edge radiation produced by the fringe field of a bending magnet rather than normal bending magnet radiation. Calculations indicate that in cases where the aperture is limited edge radiation provides higher flux than bending magnets, particularly at the longer wavelengths. The far-infrared (IR) beamline shares this port with a mid-IR microscope beamline and uses the same optics to collect and collimate the light. To install the far-IR beamline, a special mirror was designed to deflect light to the purged bench and microscopes or to move out of the light path and allow the light to continue to the far-IR beamline. The vacuum bench employs a Thermo Nicolet interferometer with a solid substrate beamsplitter modified for use under rough vacuum. The light from the interferometer is focused through CsI windows on a sample in an ultrahigh vacuum chamber. The specular reflected light from the sample is collected by an elliptical mirror and focused onto a bolometer detector. The details of the beamline will be discussed as well as the first experimental results.

SPECTRAL ASSIGNMENTS AND ANALYSIS OF THE GROUND STATE OF NITROMETHANE IN HIGH-RESOLUTION FTIR SYNCHROTRON SPECTRA

The Fourier Transform infrared spectra of CH3NO2, have been recorded, in the 400-950 cm−1spectral region, at a resolution of 0.00096 cm−1, using the Far-Infrared Beamline at Canadian Light Source. The observed spectra contain four fundamental vibrations: the NO2 in-plane rock (475.2 cm−1), the NO2 out-of-plane rock (604.9 cm−1), the NO2 symmetric bend (657.1 cm−1), and the CN-stretch (917.2 cm−1). For the lowest torsional state of CN-stretch and NO2 in-plane rock, transitions involving quantum numbers, m′′ = 0; J ′′ ≤ 50 and Ka ′′ ≤ 10, have been assigned with the aid of an automated ground state combination difference program together with a traditional Loomis Wood approachb. Ground state combination differences derived from more than 2100 infrared transitions have been fit with the six-fold torsionrotation program developed by Ilyushin et.alc. Additional sextic and octic centrifugal distortion parameters are derived for the ground vibrational state.

Observation of Multi‐bunch Interference with Coherent Synchrotron Radiation

The observation of Multi‐bunch interference with coherent synchrotron radiation at the Canadian Light Source is discussed along with the possibility that some of the spectral features are driven by the radiation impedance of the vacuum chamber.

WIRMS 2009: Fifth International Workshop on Infrared Microscopy and Spectroscopy with Accelerator-based Sources

Striking growth in the field and spectacular new science were the hallmarks of WIRMS 2009, the Fifth International Workshop on Infrared Microscopy and Spectroscopy with Accelerator Based Sources, which was held September 13–17, 2009, at The Banff Center in beautiful Banff, Alberta, Canada, surrounded by the majestic Rocky Mountains. This was the first time that WIRMS was held in Canada, following successful workshops at Porquerolles (France, 2001), Lake Tahoe (USA, 2003), Rathen (Germany, 2005), and Awaji (Japan, 2007). WIRMS 2009 was chaired by Brant Billinghurst, Tim May, and Luca Quaroni, and was made possible by generous sponsorship from the Canadian Light Source, CanmetENERGY, Bruker, Varian, the Canadian Institute for Synchrotron Radiation, Advanced Design Consulting USA Inc., Blue Sky Spectroscopy, and IUPAC. The 60 participants, from 20 light sources located all over the world, enjoyed four days of scientific talks, discussions, and posters surrounded by some of the continents most stunning scenery as well as unseasonably beautiful weather.