Insight into resolution enhancement in generalized two-dimensional correlation spectroscopy

Generalized two-dimensional correlation spectroscopy (2D-COS) can be used to enhance spectral resolution in order to help differentiate highly overlapped spectral bands. Despite the numerous extensive 2D-COS investigations, the origin of the 2D spectral resolution enhancement mechanism(s) is not completely understood. In the work here, we studied the 2D-COS of simulated spectra in order to develop new insights into the dependence of 2D-COS spectral features on the overlapping band separations, their intensities and bandwidths, and their band intensity change rates. We found that the features in the 2D-COS maps that are derived from overlapping bands were determined by the spectral normalized half-intensities and the total intensity changes of the correlated bands. We identified the conditions required to resolve overlapping bands. In particular, 2D-COS peak resolution requires that the normalized half-intensities of a correlating band have amplitudes between the maxima and minima of the normalized half-intensities of the overlapping bands. © 2013 Society for Applied Spectroscopy

Disulfide Bridges Remain Intact while Native Insulin Converts into Amyloid Fibrils

Amyloid fibrils are β-sheet-rich protein aggregates commonly found in the organs and tissues of patients with various amyloid-associated diseases. Understanding the structural organization of amyloid fibrils can be beneficial for the search of drugs to successfully treat diseases associated with protein misfolding. The structure of insulin fibrils was characterized by deep ultraviolet resonance Raman (DUVRR) and Nuclear Magnetic Resonance (NMR) spectroscopy combined with hydrogen-deuterium exchange. The compositions of the fibril core and unordered parts were determined at single amino acid residue resolution. All three disulfide bonds of native insulin remained intact during the aggregation process, withstanding scrambling. Three out of four tyrosine residues were packed into the fibril core, and another aromatic amino acid, phenylalanine, was located in the unordered parts of insulin fibrils. In addition, using all-atom MD simulations, the disulfide bonds were confirmed to remain intact in the insulin dimer, which mimics the fibrillar form of insulin

Photoresponsive azobenzene photonic crystals

We demonstrate azobenzene photochemically driven diffraction switching of a photonic crystal consisting of a crystalline colloidal array (CCA) polymerized within a hydrogel matrix. A novel azobenzene derivative that has a large ground-state activation barrier between the cis and trans forms in water is used. The system is actuated by excitation with UV light (wavelength of 365 nm), which photoisomerizes the azobenzene trans state to the cis ground state. The increased dipole moment of the cis state increases the free energy of mixing, causing a hydrogel swelling, which red-shifts the embedded CCA diffraction. Excitation with visible light photoisomerizes the cis state to the trans state, which resets the diffraction. This material acts as a memory storage material. Information is recorded and erased by exciting the photonic crystal in the UV or visible spectral region. The written information is read out completely and nondestructively by the wavelength of the Bragg diffraction (in this case, in the red)

UVRR spectroscopic studies of valinomycin complex formation in different solvents

PMID = 1555641

UV resonance Raman study of the spatial dependence of α-helix unfolding

We used ultraviolet resonance Raman (UVRR) spectra to examine the spatial dependence and the thermodynamics of α-helix melting of an isotopically labeled α-helical, 21-residue, mainly alanine peptide. The peptide was synthesized with six natural abundance amino acids at the center and mainly perdeuterated residues elsewhere. Cα deuteration of a peptide bond decouples Cα-H bending from N-H bending, which significantly shifts the random coil conformation amide III band; this shift clearly resolves it from the amide III band of the nondeuterated peptide bonds. Analysis of the isotopically spectrally resolved amide III bands from the external and central peptide amide bonds show that the six central amide bonds have a higher α-helix melting temperature (∼32°C) than that of the exterior amide bonds (∼5°C)

Photochemically Controlled Photonic Crystals

We have developed photochemically controlled photonic crystals that may be useful in novel recordable and erasable memories and/or display devices. These materials can operate in the UV, visible, or near-IR spectral regions. Information is recorded and erased by exciting the photonic crystal with ∼360 nm UV light or ∼480 nm visible light. The information recorded is read out by measuring the photonic crystal diffraction wavelength. The active element of the device is an azobenzene-functionalized hydrogel, which contains an embedded crystalline colloidal array. UV excitation forms cis-azobenzene while visible excitation forms trans-azobenzene. The more favorable free energy of mixing of cis-azobenzene causes the hydrogel to swell and to red-shift the photonic crystal diffraction. We also observe fast nanosecond, microsecond, and millisecond transient dynamics associated with fast heating lattice constant changes, refractive index changes, and thermal relaxations

Femtosecond time-resolved UV-visible absorption spectroscopy of trans-azobenzene: dependence on excitation wavelength

Femtosecond time-resolved UV-visible absorption spectroscopy has been used to study the photochemistry of trans-azobenzene in n-hexane. Excitation to the S<SUB>1</SUB>(nπ*) state results in transient absorption bands at ca. 400 nm (strong) and 550 nm (weaker) which decay with a lifetime 2.5± 0.2 ps on excitation at 503 nm, close to the S<SUB>1</SUB> origin, and with an additional fast component of ca. 0.6 ps on excitation at 390 or 420 nm, both well above the S<SUB>1</SUB> origin. Excitation to the S<SUB>2</SUB>(ππ*) state results in transient absorption at 400 nm which decays with a dominant component of ca. 0.9 ps and a weaker component of ca. 15 ps; this 400 nm band itself is observed to rise synchronously as a transient band at 475 nm decays with a lifetime of &lt;200 fs. These results are discussed in terms of the dual mechanism proposed for azobenzene photoisomerization