Large Upshift Research Articles

GPU-Accelerated All-Atom Particle-Mesh Ewald Continuous Constant pH Molecular Dynamics in Amber.

Constant pH molecular dynamics (MD) simulations sample protonation states on the fly according to the conformational environment and user specified pH conditions; however, the current accuracy is limited due to the use of implicit-solvent models or a hybrid solvent scheme. Here, we report the first GPU-accelerated implementation, parametrization, and validation of the all-atom continuous constant pH MD (CpHMD) method with particle-mesh Ewald (PME) electrostatics in the Amber22 pmemd.cuda engine. The titration parameters for Asp, Glu, His, Cys, and Lys were derived for the CHARMM c22 and Amber ff14sb and ff19sb force fields. We then evaluated the PME-CpHMD method using the asynchronous pH replica-exchange titration simulations with the c22 force field for six benchmark proteins, including BBL, hen egg white lysozyme (HEWL), staphylococcal nuclease (SNase), thioredoxin, ribonuclease A (RNaseA), and human muscle creatine kinase (HMCK). The root-mean-square deviation from the experimental pKa's of Asp, Glu, His, and Cys is 0.76 pH units, and the Pearson's correlation coefficient for the pKa shifts with respect to model values is 0.80. We demonstrated that a finite-size correction or much enlarged simulation box size can remove a systematic error of the calculated pKa's and improve agreement with experiment. Importantly, the simulations captured the relevant biology in several challenging cases, e.g., the titration order of the catalytic dyad Glu35/Asp52 in HEWL and the coupled residues Asp19/Asp21 in SNase, the large pKa upshift of the deeply buried catalytic Asp26 in thioredoxin, and the large pKa downshift of the deeply buried catalytic Cys283 in HMCK. We anticipate that PME-CpHMD will offer proper pH control to improve the accuracies of MD simulations and enable mechanistic studies of proton-coupled dynamical processes that are ubiquitous in biology but remain poorly understood due to the lack of experimental tools and limitation of current MD simulations.

Naphthalene Diimide-Based Donor-Acceptor-Donor Small Molecules as Metal-Free Organocatalysts for Photocatalytic CO2 Reaction.

The application of organic small molecules as metal-free photocatalysts for light-driven photoreduction of carbon dioxide (CO2) has seldom been explored. This work developed four naphthalene diimide (NDI)-derived donor-acceptor-donor small molecules with different numbers of thiophene units, namely, NDI-2T, NDI-TT, NDI-4T, and NDI-6T, as metal-free photocatalysts to catalyze the reduction of CO2 under irradiation with an air mass 1.5G solar simulator at one-sun intensity. The structure-property relationship was investigated by exploring the effects of the electron-donating ability of the donor units on the optical properties, redox potential, electron-hole distribution, and exciton lifetime. NDI-6T exhibited the most red-shifted absorption, longest exciton lifetime, and strongest electron-hole separation. However, the large upshift in oxidation potential because of the elevated electron-donating ability of the hexathiophene unit significantly reduced the driving force for catalyst regeneration, leading to poor catalytic performance. Alternatively, NDI-4T possessed proper redox potentials, reduced charge-transfer resistance, and excellent photocurrent intensity; therefore, it effectively converted CO2 to a single product of CO in the presence of water as an electron donor without a sacrificial reagent or cocatalyst with a product yield of 168.6 μmol gcat-1 24 h-1, which was considerably higher than those of NDI-TT (111.9 μmol gcat-1 24 h-1), NDI-2T (88.4 μmol gcat-1 24 h-1), and NDI-6T (40.5 μmol gcat-1 24 h-1). This study provides a practical guideline for the molecular design of conjugated organic molecules as promising photocatalysts for CO2 photoreduction.

Dark-habituation increases the dark-background-contingent upshift of gaze in macaque monkeys

What is the effect of prior experience on sensorimotor behavior? We studied the following intriguing behavior: monkeys fixating a small target direct their gaze above the target if the background is dark. Fixating a target once on a bright background, then on a dark background, yields 2 gaze directions, typically one above the other; hence the name, ‘dark-background-contingent upshift of gaze', which is abbreviated as ‘upshift’. Is the upshift only an attempt to avoid using the fovea in the dark? If it is, we might expect to also observe a downshift and a sideshift. We studied gaze direction in a large group of 10 rhesus monkeys from Tübingen, to which we added published data from 4 cynomolgus monkeys from Rehovot. The upshift was ubiquitous, and there was no systematic sideshift. What is the function of the upshift? Is it related to vision in the dark? Here, we concentrate on the effect of the monkeys’ previous training. Seven of the 14 monkeys were accustomed to working in the dark (‘dark-habituated’), while the other 7 had worked in bright ambient light (‘bright-habituated’). The main result of this study is that the dark-habituated monkeys had a much larger upshift: the mean upshift was 2.2° in the dark-habituated monkeys, versus 0.5° in the bright-habituated. Thus, the upshift depends on habituation; the size of the upshift reflects months-long cumulative experience. These findings suggest that the function of the upshift is indeed related to seeing in the dark.

Varying electronic coupling at graphene–copper interfaces probed with Raman spectroscopy

As the synthesis of graphene on copper became one of the primary preparation methods for both fundamental research and industrial application, Raman spectra of graphene/Cu systems need to be quantitatively understood regarding how their interactions affect the electronic structure of graphene. Using multi-wavelength Raman spectroscopy, we investigated three types of graphene bound on Cu: graphene grown on Cu foils and Cu film/SiO2, and Cu-evaporated exfoliated graphene. 2D peak frequencies of the first two samples were ~17 cm−1 higher than expected for 1.96 eV excitation even when the effect of strain was considered. More notably, the upshift in 2D decreased with increasing excitation energy. Based on control experiments using Cu-evaporated graphene, we revealed that the spectral anomaly was induced by environment-dependent nonlinear dispersion in the electronic bands of graphene and determined the degree of the electronic modification. We also showed that the large upshifts of G and 2D peaks originating from differential thermal expansion of Cu could be significantly reduced by backing Cu films with dielectric substrates of insignificant thermal expansion. The quantitative analysis of electronic coupling between graphene and Cu presented in this study will be highly useful in characterizing as-grown graphene and possibly in other forms.

Does the water-oxidizing Mn4CaO5 cluster regulate the redox potential of the primary quinone electron acceptor QA in photosystem II? A study by Fourier transform infrared spectroelectrochemistry

Redox titration using fluorescence measurements of photosystem II (PSII) has long shown that impairment of the water-oxidizing Mn4CaO5 cluster upshifts the redox potential (Em) of the primary quinone electron acceptor QA by more than 100 mV, which has been proposed as a photoprotection mechanism of PSII. However, the molecular mechanism of this long-distance interaction between the Mn4CaO5 cluster and QA in PSII remains unresolved. In this study, we reinvestigated the effect of depletion of the Mn4CaO5 cluster on Em(QA−/QA) using Fourier transform infrared (FTIR) spectroelectrochemistry, which can directly monitor the redox state of QA at an intended potential. Light-induced FTIR difference measurements at a series of electrode potentials for intact and Mn-depleted PSII preparations from spinach and Thermosynechococcus elongatus showed that depletion of the Mn4CaO5 cluster hardly affected the Em(QA−/QA) values. In contrast, fluorescence spectroelectrochemical measurement using the same PSII sample, electrochemical cell, and redox mediators reproduced a large upshift of apparent Em upon Mn depletion, whereas a smaller shift was observed when weaker visible light was used for fluorescence excitation. Thus, the possibility was suggested that the measuring light for fluorescence disturbed the titration curve in Mn-depleted PSII, in contrast to no interference of infrared light with the PSII reactions in FTIR measurements. From these results, it was concluded that the Mn4CaO5 cluster does not directly regulate Em(QA−/QA) to control the redox reactions on the electron acceptor side of PSII.

On the Propagation of a Circularly Polarized Electromagnetic Wave Through a Temporal Interface Between Air and a Magneto Plasma

It is shown that a right-hand/left-hand circularly polarized wave propagating along the magnetic field is converted to three waves by a suddenly created plasma. The right-hand circularly polarized wave is converted to two forward (R-mode and slow R-mode of the magnetoplasma) and one backward (L-mode) propagating waves; and in the left-hand circular polarization case, the wave is converted to one forward (L-mode) and two backward (R-mode and slow R-mode) propagating waves. As the background magnetic field approaches zero, the slow R-mode converts to a wiggler magnetic field, which is found in the unmagnetized case. Conservation of wave energy and power flux in the mode conversion is verified. Using the Abraham expression as the relationship between the momentum and energy of a photon in a dielectric medium, conservation of momentum in the mode conversion is also demonstrated. When a strong magnetic field is embedded in the background, a suddenly created low-density plasma can achieve a large frequency upshift on a right-hand circularly polarized wave.

Upshift of the d Band Center toward the Fermi Level for Promoting Silver Ion Release, Bacteria Inactivation, and Wound Healing of Alloy Silver Nanoparticles.

Silver (Ag)-based nanoparticles (NPs) with a high potential of Ag+ release have been known to be capable of promoting bacteria inactivation and the wound healing process; however, keeping a steady flux of high levels of Ag+ in Ag-based NPs is still challenging. Herein, a novel strategy in terms of altering the intrinsic electronic structure of Ag NPs was attempted to facilitate Ag oxidation and boost the Ag+ flux, as results of improved antibacterial and wound healing performance of Ag NPs. Gold (Au), platinum (Pt), and palladium (Pd) were doped into Ag NPs to tune their d band centers to upshift toward the Fermi level, and the formed Pd-Ag alloy NPs showed the largest shift, followed by Pt-Ag and Au-Ag NPs, as determined by density function theory calculation and ultraviolet photoemission spectroscopy measurement. Further X-ray photoelectron spectroscopy analysis indicates that a larger upshift could induce less electron filling in the antibonding orbital and a higher Ag oxidation level, leading to the more remarkable Ag+ release as determined by inductively coupled plasma optical emission spectrometry. All these alloy Ag NPs could more efficiently inhibit bacterial growth and accelerate the wound healing process than pure Ag NPs, and their antibacterial activity and wound healing performance were progressively proportional to the upshift values of the d band center. Taken together, tuning the d band center to upshift toward the Fermi level becomes a feasible strategy for designing therapeutic Ag-based NPs with a promising antibacterial and wound healing performance.

Abstract 3909: Interactions of glioma cells with chlorotoxin: an ATR-FTIR spectroscopy study

Abstract Chlorotoxin is a scorpion-derived peptide that preferentially binds to tumor cells of neuroectodermal origin, like glioma, but not to normal non-transformed cells. We have previously reported the development of a targeted nanodelivery system using chlorotoxin. Chlorotoxin has been studied as an imaging and targeting agent for drug and radioisotope delivery, but the mechanism of interaction of chlorotoxin with cancer cells has not been well understood and it needs to be further evaluated in order to optimize its use as a targeting compound for cancer cells. In this study, we used U87 human glioma cell line to evaluate the binding kinetics of chlorotoxin by Attenuated Total Reflection Fourier Transform Infra-Red (ATR-FTIR) spectroscopy. As a sensitive and label free technique, ATR-FTIR is a powerful diagnostic tool for the comparison of cancer cells with normal cells. First, we characterized the signature spectra of chlorotoxin and U87 cells by assigning and evaluating the infrared absorption bands and their second derivatives. Next, we studied the spectral differences between U87 cells incubated with and without chlorotoxin for incremental time periods ranging from 15 minutes to 24 hours. We also examined the metabolic changes in U87 cells induced with chlorotoxin at different incubation time points by measuring the ratios of integrated areas corresponding to different chemical conformations of proteins, lipids, carbohydrates, and nucleic acids. Our results revealed spectral changes in U87 cells at different stages of incubation with chlorotoxin. The most notable change occurred after 30 minutes of incubation, where the band assigned to CH3 bending of lipid membranes shifted from 1456 cm-1 to 1450 cm-1. Consequently, a new shoulder appeared at wavenumber of 1466 cm-1 assigned to CH2 bending of lipid membranes for U87 cells treated with chlorotoxin. These changes indicate a direct interaction due to the presence of a molecular binding site between chlorotoxin and the lipids of the cell membrane. Another significant alternation occurred after 1 hour of incubation of U87 cells with chlorotoxin in the spectral region assigned for nucleic acids. This interaction included a large upshift of the band at 1036 cm-1 to 1051 cm-1 assigned to C-O stretching vibrations of ribose ring in RNA due to the hydrogen bonding with chlorotoxin. These findings suggest at least two different interactions of chlorotoxin with U87 human glioma cells that can be further explored for improving chlorotoxin containing drug delivery systems. We are currently using the ATR-FTIR method to conduct control experiments by measuring possible interactions of chlorotoxin with normal human astrocytes. Citation Format: Rana Falahat, Marzenna Wiranowska, Ryan Toomey, Norma Alcantar. Interactions of glioma cells with chlorotoxin: an ATR-FTIR spectroscopy study. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3909.

On the Simple Complexity of Carbon Monoxide on Oxide Surfaces: Facet-Specific Donation and Backdonation Effects Revealed on TiO2 Anatase Nanoparticles.

Atomic-scale relationships between the structure of TiO2 surfaces and the physicochemical properties of surface sites, functional for titania-based applications, can be obtained from IR spectroscopy by using carbon monoxide (CO) as a molecular probe. In the literature, it is reported that strongly unsaturated cationic Ti sites (Lewis acid), which are important for reactivity, should cause a large upshift of the CO stretching frequency. By using IR spectroscopy of CO on TiO2 nanomaterials and theoretical analyses, here this model is challenged. It is shown that the stretching frequency of adsorbed CO results from a facet-dependent and synergic CO-surface donation (upshift) - surface-CO backdonation (downshift) mechanism. These results imply that the interaction of adsorbed molecules with the Ti centers is tuned by the surface oxygen atoms of the first coordination sphere, which play an active role as indirect electron density donors (Lewis base).

Redox potential of the terminal quinone electron acceptor QB in photosystem II reveals the mechanism of electron transfer regulation

Photosystem II (PSII) extracts electrons from water at a Mn4CaO5 cluster using light energy and then transfers them to two plastoquinones, the primary quinone electron acceptor QA and the secondary quinone electron acceptor QB. This forward electron transfer is an essential process in light energy conversion. Meanwhile, backward electron transfer is also significant in photoprotection of PSII proteins. Modulation of the redox potential (Em) gap of QA and QB mainly regulates the forward and backward electron transfers in PSII. However, the full scheme of electron transfer regulation remains unresolved due to the unknown Em value of QB. Here, for the first time (to our knowledge), the Em value of QB reduction was measured directly using spectroelectrochemistry in combination with light-induced Fourier transform infrared difference spectroscopy. The Em(QB (-)/QB) was determined to be approximately +90 mV and was virtually unaffected by depletion of the Mn4CaO5 cluster. This insensitivity of Em(QB (-)/QB), in combination with the known large upshift of Em(QA (-)/QA), explains the mechanism of PSII photoprotection with an impaired Mn4CaO5 cluster, in which a large decrease in the Em gap between QA and QB promotes rapid charge recombination via QA (-).

Relaxation mechanism of β-carotene from S2 (1Bu(+)) state to S1 (2Ag(-)) state: femtosecond time-resolved near-IR absorption and stimulated resonance Raman studies in 900-1550 nm region.

Carotenoids have two major low-lying excited states, the second lowest (S2 (1Bu(+))) and the lowest (S1 (2Ag(-))) excited singlet states, both of which are suggested to be involved in the energy transfer processes in light-harvesting complexes. Studying vibrational dynamics of S2 carotenoids requires ultrafast time-resolved near-IR Raman spectroscopy, although it has much less sensitivity than visible Raman spectroscopy. In this study, the relaxation mechanism of β-carotene from the S2 state to the S1 state is investigated by femtosecond time-resolved multiplex near-IR absorption and stimulated Raman spectroscopy. The energy gap between the S2 and S1 states is estimated to be 6780 cm(-1) from near-IR transient absorption spectra. The near-IR stimulated Raman spectrum of S2 β-carotene show three bands at 1580, 1240, and 1050 cm(-1). When excess energy of 4000 cm(-1) is added, the S1 C═C stretch band shows a large upshift with a time constant of 0.2 ps. The fast upshift is explained by a model that excess energy generated by internal conversion from the S2 state to the S1 state is selectively accepted by one of the vibronic levels of the S1 state and is redistributed among all the vibrational modes.

Space- and time-resolved observation of extreme laser frequency upshifting during ultrafast-ionization

A 65-fs, 800-nm, 2-TW laser pulse propagating through a nitrogen gas jet has been experimentally studied by 90° Thomson scattering. Time-integrated spectra of scattered light show unprecedented broadening towards the blue which exceeds 300 nm. Images of the scattering region provide for the first time a space- and time-resolved description of the process leading quite regularly to such a large upshift. The mean shifting rate was as high as δλ/δt ≈ 3 Å/fs, never observed before. Interferometry shows that it occurs after partial laser defocusing. Numerical simulations prove that such an upshift is consistent with a laser-gas late interaction, when laser intensity has decreased well below relativistic values (a0 ≪ 1) and ionization process involves most of the laser pulse. This kind of interaction makes spectral tuning of ultrashort intense laser pulses possible in a large spectral range.

Raman Spectroscopy of Ripple Formation in Suspended Graphene

Using Raman spectroscopy, we measure the optical phonon energies of suspended graphene before, during, and after thermal cycling between 300 and 700 K. After cycling, we observe large upshifts ( approximately 25 cm(-1)) of the G band frequency in the graphene on the substrate region due to compression induced by the thermal contraction of the underlying substrate, while the G band in the suspended region remains unchanged. From these large upshifts, we estimate the compression in the substrate region to be approximately 0.4%. The large mismatch in compression between the substrate and suspended regions causes a rippling of the suspended graphene, which compensates for the change in lattice constant due to the compression. The amplitude (A) and wavelength (lambda) of the ripples, as measured by atomic force microscopy, correspond to an effective change in length Deltal/l that is consistent with the compression values determined from the Raman data.

Cross-phase modulation between lasers in a tunnel ionizing gas

The phase modulation of a low power long pulse probe laser beam in a rapidly tunnel ionizing gas (helium) under a relativistic short pulse laser is investigated. The relativistic pulse creates a fast increasing plasma density at its front, far ahead of the intensity peak. The probe pulse sees these changes as modulation in its phase and undergoes large frequency upshift. The spectral content of the blueshifted potion of the probe pulse is large when its intensity peak commoves with the ionization front. There are two ionization front created by first and second ionizations, and the separation between the two increases as laser propagates through the gas. The rate of density variation by first and second ionizations, however, is fairly the same and varies little as the spot size of the laser beam increases up to three times its initial value. The ionization front velocity, as well as the upshift in probe pulse frequency, is bigger for sharper laser pulse.

Chromophore Structure of Cyanobacterial Phytochrome Cph1 in the Pr State: Reconciling Structural and Spectroscopic Data by QM/MM Calculations

A quantum mechanics (QM)/molecular mechanics (MM) hybrid method was applied to the Pr state of the cyanobacterial phytochrome Cph1 to calculate the Raman spectra of the bound PCB cofactor. Two QM/MM models were derived from the atomic coordinates of the crystal structure. The models differed in the protonation site of His260 in the chromophore-binding pocket such that either the δ-nitrogen (M-HSD) or the ɛ-nitrogen (M-HSE) carried a hydrogen. The optimized structures of the two models display small differences specifically in the orientation of His260 with respect to the PCB cofactor and the hydrogen bond network at the cofactor-binding site. For both models, the calculated Raman spectra of the cofactor reveal a good overall agreement with the experimental resonance Raman (RR) spectra obtained from Cph1 in the crystalline state and in solution, including Cph1 adducts with isotopically labeled PCB. However, a distinctly better reproduction of important details in the experimental spectra is provided by the M-HSD model, which therefore may represent an improved structure of the cofactor site. Thus, QM/MM calculations of chromoproteins may allow for refining crystal structure models in the chromophore-binding pocket guided by the comparison with experimental RR spectra. Analysis of the calculated and experimental spectra also allowed us to identify and assign the modes that sensitively respond to chromophore-protein interactions. The most pronounced effect was noted for the stretching mode of the methine bridge A-B adjacent to the covalent attachment site of PCB. Due a distinct narrowing of the A-B methine bridge bond angle, this mode undergoes a large frequency upshift as compared with the spectrum obtained by QM calculations for the chromophore in vacuo. This protein-induced distortion of the PCB geometry is the main origin of a previous erroneous interpretation of the RR spectra based on QM calculations of the isolated cofactor.

The possible way to evaluate the purity of double-walled carbon nanotubes over single wall carbon nanotubes by chemical doping

Here, we carried out Raman study on chemically doped single wall carbon nanotube (SWNT)/double-walled carbon nanotube (DWNT) mixed bucky-papers. Their highly different Raman responses (e.g., a large upshift of tangential mode of SWNT and no large changes in the frequencies of tangential mode assigned to the outer tubes of the DWNT) upon doping with the sulfuric acid could be used as a qualitative indicator of the purity of the DWNT samples with the concentration of its SWNTs contents.

Proton binding to proteins: pK(a) calculations with explicit and implicit solvent models.

Ionizable residues play important roles in protein structure and activity, and proton binding is a valuable reporter of electrostatic interactions in these systems. We use molecular dynamics free energy simulations (MDFE) to compute proton pKa shifts, relative to a model compound in solution, for three aspartate side chains in two proteins. Simulations with explicit solvent and with an implicit, dielectric continuum solvent are reported. The implicit solvent simulations use the generalized Born (GB) model, which provides an approximate, analytical solution to Poisson's equation. With explicit solvent, the direction of the pKa shifts is correct in all three cases with one force field (AMBER) and in two out of three cases with another (CHARMM). For two aspartates, the dielectric response to ionization is found to be linear, even though the separate protein and solvent responses can be nonlinear. For thioredoxin Asp26, nonlinearity arises from the presence of two substates that correspond to the two possible orientations of the protonated carboxylate. For this side chain, which is partly buried and has a large pKa upshift, very long simulations are needed to correctly sample several slow degrees of freedom that reorganize in response to the ionization. Thus, nearby Lys57 rotates to form a salt bridge and becomes buried, while three waters intercalate along the opposite edge of Asp26. Such strong and anisotropic reorganization is very difficult to predict with Poisson-Boltzmann methods that only consider electrostatic interactions and employ a single protein structure. In contrast, MDFE with a GB dielectric continuum solvent, used for the first time for pKa calculations, can describe protein reorganization accurately and gives encouraging agreement with experiment and with the explicit solvent simulations.

Learning to recognize speech that is spectrally reduced and frequency upshifted

The current study explored to what extent training could ameliorate the deleterious effect of large frequency upshifts in spectrally reduced speech. During each training session, subjects attempted recognition of IEEE sentences spoken by a single talker once and received feedback for their responses. Training sentences were processed to simulate an 8-channel CIS cochlear implant processor with a ‘‘6 mm frequency upshift’’ [Fu and Shannon, J. Acoust. Soc. Am. 105, 1889 (1999)]. Three test sessions were administered to all subjects to assess recognition of sentences (IEEE and HINT), consonants (/aCa/), and vowels (in /hVd/ and /bVt/ contexts) pre-, post-, as well as at the mid-point of training. Four processing conditions (i.e., unprocessed, 8-channel-unshifted, 8-channel-upshifted, and 8-channel-upshifted-and-compressed) were tested for each type of materials. Preliminary data suggest that performance improved for most subjects during training, but there were substantial individual differences in learning rates and asymptotic performance levels. Vowels were more difficult to recognize and showed smaller training-related gains when compared to consonants and sentences. The rank ordering of recognition performance was consistent among the four processing conditions (unshifted best; upshifted-and-compressed intermediate; upshifted worst) for all measures. Data comparing the efficacy of an alternative training method will also be presented.

TEMPERATURE DEPENDENCE OF RAMAN SCATTERING IN K3Ba3C60

Raman spectra at different temperatures are reported for K3Ba3C60.A systematic change of the Raman spectra with temperature is observed.The development of the linewidth and intensity for all modes with temperature is in sharp contrast to the case for pure C60.An anomalously large up-shift of 9 cm-1 between 20 K and room temperature for the pinch Ag(2) mode suggests the existence of hybridization between the C60 molecules and the intercalants.The relative intensity of the doublet of Ag(1) systemtically changes with decreasing temperature.

Temperature dependence of Raman scattering in K3Ba3C60

Raman spectra at different temperatures are reported for K3Ba3C60. A systematic change of the Raman spectra with temperature is observed. The development of the linewidth and intensity for all modes with decreasing temperature is in sharp contrast to the case for pure C60. For the two lowest-frequency Hg modes, the appearance of the low-frequency components and an increase in their intensity are observed as temperature decreases. This could be related to an internal strain between the doped part of the crystal and the undoped part of the crystal, and the Jahn-Teller effect. An anomalously large upshift of 9 cm-1 between 20 K and room temperature for the pinch Ag(2) mode suggests the existence of hybridization between the C60 molecules and the intercalants. The doublet of Ag(1) at low temperature could arise from the splitting of the crystal field.