CH2 Twisting Research Articles

Ballistic Energy Transport via Long Alkyl Chains: A New Initiation Mechanism.

In an effort to increase the speed and efficiency of ballistic energy transport via oligomeric chains, we performed measurements of the transport in compounds featuring long alkyl chains of up to 37 methylene units. Compounds of the N3-(CH2)n-COOMe type (denoted as aznME) were synthesized with n = 5, 10, 15, 19, 28, 37 and studied using relaxation-assisted two-dimensional infrared spectroscopy. The speed of the ballistic transport, initiated by the N3 tag excitation, increased ca. 3-fold for the longer chains (n = 19-37) compared to the shorter chains, from 14.7 to 48 Å/ps, in line with an earlier prediction (Nawagamuwage et al. 2021, J. Phys. Chem. B, 125, 7546). Modeling, based on solving numerically the Liouville equation, was capable of reproducing the experimental data only if three wavepackets are included, involving CH2 twisting (Tw), wagging (W), and rocking (Ro) chain bands. The approaches for designing molecular systems featuring a higher speed and efficiency of energy transport are discussed.

Study of adipose tissue of Kemerovo piglets: Detection of beige adipocytes

Animals have two types of adipose tissue differing in structure and function: white (WAT) and brown (BAT). Beige adipose tissue (BeAT) is a result of WAT browning, when beige adipocytes appear between white adipocytes in response to exposure to cold, diet or physical activity. BeAT shares morphological and biochemical characteristics with BAT, is thermogenic and dissipates energy in the form of heat, unlike WAT, which is responsible for energy storage. Pigs do not have classic BAT, and modern breeds are sensitive to cold. There is literature information that BeAT has been found in cold-resistant pigs. The aim of the work was to study adipose tissue of piglets of the Kemerovo cold-resistant breed under growing conditions in the cold season and to identify the localization of BeAT. Histological studies have shown two types of adipocytes in subcutaneous fat samples (lateral, backfat and axillary): white, with one large fat droplet, and beige, multilocular. Larger cells were detected in backfat fat (69.36±12.98 µm) compared with lateral (53.25±9.27 µm) and axillary fat (45.94±8.29 µm). Only WAT with a diameter of 35.69±6.96 µm was present in the internal perirenal fat. Raman spectroscopy was used to evaluate the overall fatty acid profile of the tested samples. The main peaks were noted in all samples: 970 cm-1 (=C-H out-of-plane bend), 1266/1272 cm-1 (=C-H symmetrical rock) and 1655 cm-1 (C=C stretching) responsible for unsaturated bonds, and signals at 1297/1301 cm-1 (CH2 twisting), 1430/1460 cm-1 (CH2 symmetrical deformation (scissoring)) and 1735/1746 cm-1 (C=O stretching) corresponding to saturated bonds or ester groups. Internal perirenal fat contained the largest number of saturated fatty acid bonds, subcutaneous axillary fat — the smallest. The average intensity of the peaks was 0.4801010 and 0.639995, respectively. According to the results of gas chromatography, the largest amount of polyunsaturated fatty acids was noted in the subcutaneous fat samples: 20.199 in backfat fat, 21.749 in lateral and 20.436 in axillary fat compared to 18.636 in internal fat. Activation of beige cells in Kemerovo pigs under cold exposure, according to the authors, plays a crucial role in the heat balance, allowing them to tolerate cold without severe shivering. The study of the BeAT formation is of great practical importance for changing energy metabolism and increasing thermogenesis in newborn piglets by genome editing, as well as for improving the quality of pig’s fat.

Electrochemically modulated SERS detection of procaine using FTO electrodes modified with silver-decorated carbon nanosphere

Procaine belongs to a class of drugs whose excessive dosage results in cardiac arrest and several allergenic reactions. Therefore, its continuous monitoring is crucial for sustainable health management during treatments. In this study, a reliable electrochemically modulated sensing approach for the quantitative detection of procaine using in-situ surface-enhanced Raman scattering (SERS) was developed. A fluorine-doped tin oxide electrode modified using silver carbon nanosphere (AgCNS-FTO) was designed, electrochemically evaluated, and used as an efficient substrate. The investigation of the electrochemical interaction of procaine molecules towards the modified electrode revealed that upon the optimum electrochemical pre-concentration potential (-0.1 V) and time (400 s), significant enhancements in the intensity of key Raman peaks corresponding to the NH2 bending, C=C stretching, CH2 twisting and C-N stretching modes could be observed. The reported approach enabled a remarkable sensitivity and selectivity towards procaine, resulting in an unprecedented detection limit down to the level of 10-13 M. The reproducibility and stability of the modified FTO electrode were ensured over a duration of one month, and a low RSD of 2.4% was achieved. First-principles calculations proposed the interactive nature between the AgCNS surface and procaine molecules, while the possible protein-ligand binding with the chemokine receptor CXCR4 predicted an anti-inflammatory tendency of procaine with a binding energy of – 5.7 kcal/mol for the pose with the highest affinity. The electrochemically modulated SERS approach developed in the present study shall facilitate the efforts towards the practical quantification of procaine in clinical samples and could be extended to other structural analogues.

Nonlinear optical properties of single crystal of L-OOMHCL incorporation with Glycine Oxalic Acid (GOA) with high chemical stability for optoelectronic applications

In this report, a good nonlinear optical material with high criteria such as optical nonlinearity, chemical and thermal stability for life time system capability. The crystallographic orientation belongs to monoclinic crystal structure with the non-centrosymmetric space group, the prominent peaks were observed as (101), (112) and (300). The calculated lattice parameter values are, a = 6.21 Å, b = 3.67 Å, c = 12.12 Å, α = 90°, β = 103.21°, γ = 90° monoclinic space group of P21/n. A broad and strong peak at 3427 cm−1 was assigned to NH stretch, the OH and CH stretching of the compound were confirmed by the peaks present at 3043 cm−1 and 2934 cm−1. Moreover, the peaks at 1398 cm−1 represent the tartaric acid, another strong peak at 1261 cm−1 was assigned to CH2 twisting. In addition, the DTA curve shows a sharp endothermic peak at 109 °C, which corresponds to the melting point of the compound at this stage the sample lost its 20% of weights due to dehydration. From TGA curve, the L-OOMHCL crystal has good thermal stability up to melting point as there is no major weight loss below that temperature. However, it shows the more weight loss of 95% after the melting point due to the removal of volatile substances. Thus, it confirms the full degradation around 600 °C. The dielectric constant and the dielectric loss of L-OOMHCL crystal were carried out at three different temperatures 313 K, (40 °C) 333 K (60 °C) and 353 K (80 °C) for frequencies varying from 50 Hz to 5 MHz. Finally, we have calculated the refractive index value at the cutoff wavelength 214 nm and the 2.012 which is larger than unity, this results in greater development of polarization in the presence of dc electrical fields, hence leading to greater mobility.

Detection of Saturated Fatty Acids Associated with a Self-Healing Synthetic Biological Membrane Using Fiber-Enhanced Surface Enhanced Raman Scattering.

The Synthetic Biological Membrane (SBM) project at NASA Ames developed a portable, self-repairing wastewater purification system. The self-repair process relies upon secreted fatty acids from a genetically engineered organism. However, solubilized fatty acids are difficult to detect using conventional methods. Surface-enhanced Raman scattering (SERS) was used to successfully detect solubilized fatty acids with the following limits of detection: 10-9, 10-8, 10-9, and 10-6 M for decanoic acid, myristic acid, palmitic acid, and stearic acid, respectively. Additionally, hollow core photonic crystal fiber (HCPCF) was applied as the sampling device together with SERS to develop in situ surveillance of the production of fatty acids. Using SERS + HCPCF yielded an 18-fold enhancement in SERS signal for the CH2 twist peak at 1295 cm-1 as compared to SERS alone. The results will help the SBM project to integrate a self-healing wastewater purification membrane into future water recycling systems.

Detection of Saturated Fatty Acids Associated with a Self-Healing Synthetic Biological Membrane Using Fiber-Enhanced Surface Enhanced Raman Scattering.

The Synthetic Biological Membrane (SBM) project at NASA Ames developed a portable, self-repairing wastewater purification system. The self-repair process relies upon secreted fatty acids from a genetically engineered organism. However, solubilized fatty acids are difficult to detect using conventional methods. Surface-enhanced Raman scattering (SERS) was used to successfully detect solubilized fatty acids with the following limits of detection: 10-9 M, 10-8 M, 10-9 M, and 10-6 M for decanoic acid, myristic acid, palmitic acid, and stearic acid, respectively. Additionally, hollow core photonic crystal fiber (HCPCF) was applied as the sampling device together with SERS to develop in situ surveillance of the production of fatty acids. Using SERS + HCPCF yielded an 18 fold enhancement in SERS signal for the CH2 twist peak at 1295 cm-1 as compared to SERS alone. The results will help the SBM project to integrate a self-healing wastewater purification membrane into future water recycling systems.

Gradient Temperature Raman Spectroscopy of Fatty Acids with One to Six Double Bonds Identifies Specific Carbons and Provides Systematic Three Dimensional Structures

Specialized pro-resolving mediators provide promising targets for new drugs and natural products. Much work has been accomplished on the structure/ function of the lipoxygenase and cyclooxygenase enzymes but not on the substrates. A better visualization of three-dimensional lipid structures will allow increased refinement of the interactions that produce the pro-resolving mediators, and lead to improvements in synthetic pathways. We present systematic analysis of oleic (18:1n-9), linoleic (18:2n-6), alpha-linolenic (18:3n-3), arachidonic (20:4n-6), docosapentaenoic (22:5n-3), and docosahexaenoic (22:6n-3) acids. Continuous gradient temperature Raman spectroscopy (GTRS) applies the temperature gradients utilized in differential scanning calorimetry to Raman spectroscopy. GTRS can identify and differentiate specific carbon chain sites, finally allowing Raman analysis to explain why the long-chain polyunsaturated fatty acids (LC-PUFA) exhibit such extreme functional differences despite minimal changes in chemical structure. Detailed vibrational analysis of the important frequency ranges 1450 - 1200 cm-1 (includes CH2 bending and twisting) and 1750 - 1425 cm-1 (includes C=C stretching and C-C stretching plus H-C in-plane rocking) shows for the first time that each molecule has its own characteristic set of modes with only some redundancy/commonality. The number and frequency of modes correlates with three-dimensional molecular structure, not the degree of unsaturation. The high degree of specificity of lipoxygenase and cyclooxygenase enzymes should be reconsidered in light of the fact that individual sites on the polyunsaturated fatty acid chain are nonequivalent, and each LC-PUFA molecule has an individual, specific three dimensional structure incorporating torsion.

Investigation of the Molecular Mechanisms of Melting and Crystallization of Isotactic Polypropylene by in Situ Raman Spectroscopy

In situ Raman spectroscopy has been used to reveal the molecular behavior of isotactic polypropylene during melting and crystallization. The 400 cm–1 band assigned to C–C–C bending shows a blue-shift during heating, suggesting an increase in conformational disorder, whereas the 1330 cm–1 band assigned to CH2 twisting shows a red-shift owing to an increase in the interchain distance. We suggest that interchain expansion proceeds even in the melt state, while the chain conformation becomes sufficiently disordered at the melting point. During the cooling process, the peak shifts at given temperatures are essentially the same as those during heating, except for the supercooled region where the peak shifts show obvious hystereses. By extrapolating the linear correlation between the peak shift of the 400 cm–1 band and the characteristic length along the chain axis, the critical stem size for crystallization is estimated to be ∼2.4 nm.

Continuous gradient temperature Raman spectroscopy of N-6DPA and DHA from −100 to 20 °C

One of the great unanswered questions with respect to biological science in general is the absolute necessity of docosahexaenoic acid (DHA, 22:6n-3) in fast signal processing tissues. N-6 docosapentaenoic acid (n-6DPA, 22:5n-6), with just one less double bond, group, is fairly abundant in terrestrial food chains yet cannot substitute for DHA. Gradient temperature Raman spectroscopy (GTRS) applies the temperature gradients utilized in differential scanning calorimetry (DSC) to Raman spectroscopy, providing a straightforward technique to identify molecular rearrangements that occur near and at phase transitions. Herein we apply GTRS and DSC to n-6DPA and DHA from −100 to 20°C. 20Mb three-dimensional data arrays with 0.2°C increments and first/second derivatives allowed complete assignment of solid, liquid and transition state vibrational modes, including low intensity/frequency vibrations that cannot be readily analyzed with conventional Raman. N-6DPA and DHA show significant spectral changes with premelting (−33 and −60°C, respectively) and melting (−27 and −44°C, respectively). The CH2(HCCH)CH2 moieties are not identical in the second half of the DHA and DPA structures. DPA has bending (1450cm−1) over almost the entire temperature range. In contrast, DHA contains major CH2 twisting (1265cm−1) with no noticeable CH2 bending, consistent with a flat helical structure with a small pitch. Further modeling of neuronal membrane phospholipids must take into account torsion present in the DHA structure, which essential in determining whether the lipid chain is configured more parallel or perpendicular to the hydrophilic head group.

Ballistic Energy Transport in Oligomers.

The development of nanocomposite materials with desired heat management properties, including nanowires, layered semiconductor structures, and self-assembled monolayer (SAM) junctions, attracts broad interest. Such materials often involve polymeric/oligomeric components and can feature high or low thermal conductivity, depending on their design. For example, in SAM junctions made of alkane chains sandwiched between metal layers, the thermal conductivity can be very low, whereas the fibers of ordered polyethylene chains feature high thermal conductivity, exceeding that of many pure metals. The thermal conductivity of nanostructured materials is determined by the energy transport between and within each component of the material, which all need to be understood for optimizing the properties. For example, in the SAM junctions, the energy transport across the metal-chain interface as well as the transport through the chains both determine the overall heat conductivity, however, to separate these contributions is difficult. Recently developed relaxation-assisted two-dimensional infrared (RA 2DIR) spectroscopy is capable of studying energy transport in individual molecules in the time domain. The transport in a molecule is initiated by exciting an IR-active group (a tag); the method records the influence of the excess energy on another mode in the molecule (a reporter). The energy transport time can be measured for different reporters, and the transport speed through the molecule is evaluated. Various molecules were interrogated by RA 2DIR: in molecules without repeating units (disordered), the transport mechanism was expected and found to be diffusive. The transport via an oligomer backbone can potentially be ballistic, as the chain offers delocalized vibrational states. Indeed, the transport regime via three tested types of oligomers, alkanes, polyethyleneglycols, and perfluoroalkanes was found to be ballistic, whereas the transport within the end groups was diffusive. Interestingly, the transport speeds via these chains were different. Moreover, the transport speed was found to be dependent on the vibrational mode initiating the transport. For the difference in the transport speeds to be explained, the chain bands involved in the wavepacket formation were analyzed, and specific optical bands of the chain were identified as the energy transporters. For example, the transport initiated in alkanes by the stretching mode of the azido end group (2100 cm(-1)) occurs predominantly via the CH2 twisting and wagging chain bands, but the transport initiated by the C=O stretching modes of the carboxylic acid or succinimide ester end groups occurs via C-C stretching and CH2 rocking bands of the alkane chain. Direct formation of the wavepacket within the CH2 twisting and wagging chain bands occurs when the transport is initiated by the N═N stretching mode (1270 cm-1) of the azido end-group. The transport via optical chain bands in oligomers involves rather large vibrational quanta (700-1400 cm(-1)), resulting in efficient energy delivery to substantial distances. Achieved quantitative description of various energy transport steps in oligomers, including the specific contributions of different chain bands, can result in a better understanding of the transport steps in nanocomposite materials, including SAM junctions, and lead towards designing systems for molecular electronics with a controllable energy transport speed.

Band-selective ballistic energy transport in alkane oligomers: toward controlling the transport speed.

Intramolecular transport of vibrational energy in two series of oligomers featuring alkane chains of various length was studied by relaxation-assisted two-dimensional infrared spectroscopy. The transport was initiated by exciting various end-group modes (tags) such as different modes of the azido (ν(N≡N) and ν(N═N)), carboxylic acid (ν(C═O)), and succinimide ester (νas(C═O)) with short mid-IR laser pulses. It is shown that the transport via alkane chains is ballistic and the transport speed is dependent on the type of the tag mode that initiates the transport. The transport speed of 8.0 Å/ps was observed when initiated by either ν(C═O) or νas(C═O). When initiated by ν(N≡N) and ν(N═N), the transport speed of 14.4 ± 2 and 11 ± 4 Å/ps was observed. Analysis of the vibrational relaxation channels of different tags, combined with the results for the group velocity evaluation, permits identification of the chain bands predominantly contributing to the transport for different cases of the transport initiation. For the transport initiated by ν(N≡N) the CH2 twisting and wagging chain bands were identified as the major energy transport channels. For the transport initiated by ν(C═O), the C-C stretching and CH2 rocking chain bands served as major energy transporters. The transport initiated by ν(N═N) results in direct formation of the wave packet within the CH2 twisting and wagging chain bands. These developments can aid in designing molecular systems featuring faster and more controllable energy transport in molecules.

Vibrational behavior of Gelucire 50/13 by Raman and IR spectroscopies: A focus on the 1800–1000 cm−1 spectral range according to temperature and degree of hydration

The present paper reports on physical and thermal properties of polyoxyethylene glycol glycerides (Gelucire 50/13) used as sustained release matrix forming agent in pharmaceutical applications. Gelucire 50/13 was essentially studied by Raman and IR spectroscopies according to the temperature and the degree of hydration. The hydration behavior of this amphiphilic excipient has been investigated with increasing water contents to study the behavior during dissolution. In the spectral range 1800–1000cm−1, Raman and IR spectroscopies of Gelucire 50/13 were performed to characterize the contribution of its each components at room temperature, with emphasis placed on the evolution of the CH2 wagging and twisting, ν(CC) and ν(CO) vibrational modes regions (1400–1000cm−1), along with analysis of the IR and Raman-active δ(CH2) deformation region (1500–1400cm−1).In comparison with temperature and degree of hydration, in the spectral range 1800–1000cm−1, the vibrational changes were directly correlated with conformational changes of the Gelucire structure. Overall, IR and Raman spectroscopy clearly demonstrated that the different functional groups studied could be characterized independently, allowing for the understanding of their role in Gelucire structure.

Abstract P4-01-20: Explore the differences and relationships between normal, ADH tissues and DCIS, IDC in breast by shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS)

Abstract Background: The mechanism that ADH changes to DCIS and even IDC is still not clear now. Raman spectroscopy is a powerful, non-invasive analytical tool which can provide detailed and meaningful information about biochemical composition of tissues at molecular level. Our aim was to find the differences and relationships between normal, ADH tissues and DCIS, IDC in breast based on their various biochemical characteristics by Raman spectroscopy. Methods: The frozen sections were collected from 39 patients (all female; ages 27-74) who underwent surgical resection or mammotome biopsy at the Department of Breast Surgery, the First Hospital of Jilin University. After operation the samples were immediately frozen at -20∼-25°C and two contiguous sections (6 μm thickness) were cut from a sample by freezing microtome. One was stained with haematoxylin and eosin for routine histopathological analysis; the other was detected by Microscopic confocal Raman spectrometer (HORIBA JY Lab800, 633nm) with its mirror image (the H&E section). After the spectra we needed had been obtained, the Au@SiO2 shell-isolated nanoparticles (SHINs) were added to the surface of frozen sections immediately and then the spectra with SHINs were collected. Results: A total of 475 Raman spectra and 470 SHINERS spectra were obtained from 9 normal breast tissues, 7 ADH, 8 DCIS, and 15 IDC breast tissues. The Raman signals were significantly enhanced by SHINs. The main spectral features of normal tissues at around 1301, 1442, 1654, and 1743 cm−1 are attributed to lipids. Meanwhile, no strong protein peaks emerged. The peaks of ADH, DCIS and IDC tissues located at 1004, 1033, 1610 and 1658 cm−1 from vibrational modes of proteins shows more stronger. 830, 880, 970, 1090 and 1157cm−1, representing DNA feature peaks, hold the same rules. Table 1: Peak assignments of the Raman spectra of Breast tissues (wavenumbers in cm-1)NBADHDCISIDCMajor Assignments 880878880O-P-O stretch, DNA1003100410041003phenylalanine1092109210911090O-P-O stretch, DNA1301,14421302,14421303,14431303,1442CH2 twist and CH2 deformation, lipids 15261527C = C stretch of carotene 165816581658Amide I, α-helix1743174717451747C = O stretch, lipids These show that diseased tissues contained more proteins and nucleic acids. The spectra of DCIS and IDC tissues contained 1527 cm−1, stemming from C = C stretching of carotene. The spectral features between ADH, DCIS and IDC tissues are described as followings: firstly, the concentrations of proteins, nucleic acids and carotene increased gradually but lipids content reduced from ADH to IDC. Secondly, ADH and DCIS tissues have extraordinary strong band of amide I, but in IDC tissues the peak almost cannot observed. Additionally, DCIS tissues have the red shifted and broad peak of CH2, which explains acyl backbone of lipids and proteins has fractured. Conclusion: The changes including content and molecular structure of lipids, carotene, proteins and nucleic acids accompany with deterioration, indicating the Raman spectroscopy can be used to explore the differences and relationships between normal, ADH tissues and DCIS, IDC in breast. Simultaneously, it might be used to discover the mechanism that ADH convert to DCIS. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-01-20.

Experimental and theoretical investigation of the apomorphine Raman spectrum

AbstractApomorphine (aporphine‐10,11‐diol, CA Registry Number 58004) is a non‐narcotic derivative of morphine discovered in 1869 by Mattheisen1 and it is a well‐known potent short‐acting dopamine agonist at D1 and D2 dopamine receptors, typically used in the treatment of patients with advanced Parkinson's disease (PD). To identify the unknown vibrational spectrum of this compound, apomorphine bare salt and its commercial drug formulation (Apofin) were examined by means of Raman spectroscopy. In the Raman spectrum of apomorphine (both bare salt and commercial drug), two strong characteristic signals were found, which were assigned with the help of first‐principles calculations: the band at 1589 cm−1 (assigned to the stretching mode of the B aromatic ring coupled with CH in‐plane bending) and the band at 1302 cm−1 (assigned to O‐H in‐plane bending and CH2 twisting and wagging vibrations). Copyright © 2009 John Wiley & Sons, Ltd.

In Situ IRRAS Studies of NH Stretching Bands and Molecular Structures of the Monolayers of Amphiphiles Containing Amide and Amine Units at the Air−Water Interface

The monolayers of the amphiphiles containing amide and amine units at the air-water interface on water surface have been studied using infrared reflection absorption spectroscopy (IRRAS). Sharp NH stretching bands are observed in the monolayers of N-octadecanoyl-l-alanine (ALA) (at pH 3.0) and N-octadecyloxalamide (OXA), while no NH stretching band is clearly detected in the monolayers of octadecan-1-amine (OA) and N-hexadecylethane-1,2-diamine (EDA) (at pH 9.3). It is considered that the presence and absence of the NH stretching bands are related to properties of amides and amines, roles of N-H bonds in hydrogen bond donor/acceptor, and orientation of transition moment directions of NH stretching vibrations. The intermolecular hydrogen-bonding interactions between the adjacent amides of ALA and OXA induce the parallel packing of the CCC planes of corresponding alkyl chains, while the chains are uniaxially oriented in the monolayers of OA and EDA. In the presence of CuCl2 in the subphase, Cu2+ ions coordinate to the headgroups of OA and EDA in the monolayers; moreover a new peak at 1220 cm(-1) is observed for the EDA monolayer and assigned to the CH2 twisting and wagging modes relevant to the ethylenediamine headgroups. The presence of the peak is related to the dehydration of the headgroups induced by the twisted tetrahedral coordination, and the coordinated headgroups undergo an orientation change with surface pressure.

Study of Disorder in Different Phases of Tetratriacontane and a Binary Alkane Mixture, Using Vibrational Spectroscopy

Raman spectroscopy has been used to investigate the monoclinic crystal --> rotator --> melt phase transitions in n-C(34)H(70), for both real-time heating and cooling runs. Changes in band intensity and frequency in the CH2 bending, CH2 twisting, skeletal C-C stretching, and CH3 rocking regions revealed both transitions, particularly when using band components related to gauche bonds. In the room temperature infrared spectrum, the CH2 rocking-twisting and CH2 wagging progressions were observed and indexed for n-C(34)H(70) and a 2:1 (w/w) mixture of C(34)H(70) and C(36)D(74). This led to best estimates for the all-trans crystal core in both cases of 33 to 34 carbon atoms, indicating that the core corresponds to almost the whole of the C(34)H(70) molecule.

FT-IR Study of the Morphological Interactions in PHB/PAZO Blends and their Dependence on Solvent Variation

In this article, we demonstrate the vital role the solvent plays in influencing the resultant blend morphology in semi-crystalline PHB/PAZO blends. We will establish the relationship between the blend's FT-IR profiles and the morphology. We will also investigate the possible formation of a PHB/PAZO complex, previously reported. PHB/PAZO blends were prepared in chloroform, acetone and toluene, chosen because of the similarity of their solubility parameter to that of amorphous PHB. The FT-IR spectral bands in PHB responsible for changes in morphology were observed in the 950-1350 cm−1 region. These bands denote the amorphous band at 1185 cm−1, the asymmetric C-O-C vibrations, the CH2 wag and twist at 1231 cm−1 and a crystal vibration at 1279 cm−1. A series of less prominent bands sensitive to the crystalline and amorphous regions were also observed. We deduced that penetration of PHB's crystalline shell by the solvent does occur and is crucial to complex formation and to blend miscibility.

Two-photon vibronic spectroscopy of allene at 7.0–10.5 eV: experiment and theory

2 + 1 resonance-enhanced multiphoton ionization (REMPI) spectra of allene at 7.0–10.5 eV have been observed. The excited vibronic symmetry has been determined from polarization-ratio measurements. Based on the vibronic energies and peak intensities calculated using ab initio MO and time-dependent density functional theory, the very congested REMPI spectra have been assigned as due to π* ← π, 3p ← π, 4s ← π, 4p ← π, and 4d ← π transitions. Vibrational progressions related to the CH2 twisting (ν4 ∼770 cm−1) have been observed for several excited electronic states. Calculated Franck–Condon factors also confirm that CH2 twisting is the most active mode in the vibronic spectra of allene. In this study, theoretical calculations of two-photon intensities and polarization ratios have been made through the ab initio computed one-photon transition dipole moments to various electronic states as intermediates. As a starting point to interpret the complicated vibronic spectrum of allene, the theoretical approach, without vibronic couplings, has been applied to predict the peak positions, spectral intensities, and polarization ratios of Rydberg states, and qualitatively shows a considerable agreement with experimental observations.

Revisiting the stationary points on the potential energy surface of tetramethylene at the MR-AQCC level using analytic gradients

The stationary points on the potential energy surface (PES) of tetramethylene have been investigated using highly correlated multireference methods and extended basis sets. Full geometry optimization using analytic gradients as well as systematic scans of the PES employing different basis sets show that all minima and most of the saddle points found at the lower computational level (mostly CASSCF) cease to exist. Finally, only the G2 (gauche cyclization with conrotatory double CH2 twist) and the CT (cis–trans isomerization) saddle points have been confirmed. Activation and reaction enthalpies have been computed and are within 1–2 kcal/mol in agreement with experimental results.

Raman Mapping Study of Compatibilized and Uncompatibilized Polymer Blends of Nylon 12 and Polyethylene

Raman mapping images have been obtained for compatibilized and uncompatibilized polymer blends in films of Nylon 12 and high density polyethylene (HDPE) (blend ratios were 20/80, 50/50, and 80/20). A total of 400 Raman spectra were measured for each sample with areas of 100 μm2and in step sizes of 0.5 μm (for 20 × 20 probe spots). To develop the Raman mapping images, the intensity ratio of two bands, a band at 1635 cm−1due to Nylon 12 (amide I mode) and that at 1296 cm−1arising from both HDPE and Nylon 12 (CH2twisting) is used. The Raman mapping images of the uncompatibilized polymer blends show a clear “sea-island” structure while those of the compatibilized polymer blends exhibit a compatibilized structure. The Raman mapping images enable simultaneous exploration of the morphology and molecular structure of the blends. We have also developed a Raman mapping image that represents the variation of crystallinity in the uncompatibilized film.