Picosecond time-resolved resonance Raman observation of the iso-CH2Cl-I and iso-CH2I-Cl photoproducts from the "photoisomerization" reactions of CH 2ICl in the solution phase

A preliminary pecosecond Stokes time-resolved resonance Raman investigation was made of the initial formation and subsequent decay of the photoproduct produced following 267 nm excitaiton of CH 2ClI in acetonitrile solution. A coparision was made between density-functional theroy computations for portable photoproduct species and the results from a femtosecond transient absorption study to Raman spectra. This comparision indicated that the iso-CH 2ClI was aminly produced and associated with the 460 nm transient absorption band.published_or_final_versio

Multiple pH Regime Molecular Dynamics Simulation for pK Calculations

Ionisation equilibria in proteins are influenced by conformational flexibility, which can in principle be accounted for by molecular dynamics simulation. One problem in this method is the bias arising from the fixed protonation state during the simulation. Its effect is mostly exhibited when the ionisation behaviour of the titratable groups is extrapolated to pH regions where the predetermined protonation state of the protein may not be statistically relevant, leading to conformational sampling that is not representative of the true state. In this work we consider a simple approach which can essentially reduce this problem. Three molecular dynamics structure sets are generated, each with a different protonation state of the protein molecule expected to be relevant at three pH regions, and pK calculations from the three sets are combined to predict pK over the entire pH range of interest. This multiple pH molecular dynamics approach was tested on the GCN4 leucine zipper, a protein for which a full data set of experimental data is available. The pK values were predicted with a mean deviation from the experimental data of 0.29 pH units, and with a precision of 0.13 pH units, evaluated on the basis of equivalent sites in the dimeric GCN4 leucine zipper

Murine Gammaretrovirus Group G3 Was Not Found in Swedish Patients with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome and Fibromyalgia

BACKGROUND: The recent report of gammaretroviruses of probable murine origin in humans, called xenotropic murine retrovirus related virus (XMRV) and human murine leukemia virus related virus (HMRV), necessitated a bioinformatic search for this virus in genomes of the mouse and other vertebrates, and by PCR in humans. RESULTS: Three major groups of murine endogenous gammaretroviruses were identified. The third group encompassed both exogenous and endogenous Murine Leukemia Viruses (MLVs), and most XMRV/HMRV sequences reported from patients suffering from myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Two sensitive real-time PCRs for this group were developed. The predicted and observed amplification range for these and three published XMRV/HMRV PCRs demonstrated conspicuous differences between some of them, partly explainable by a recombinatorial origin of XMRV. Three reverse transcription real-time PCRs (RTQPCRs), directed against conserved and not overlapping stretches of env, gag and integrase (INT) sequences of XMRV/HMRV were used on human samples. White blood cells from 78 patients suffering from ME/CFS, of which 30 patients also fulfilled the diagnostic criteria for fibromyalgia (ME/CFS/FM) and in 7 patients with fibromyalgia (FM) only, all from the Gothenburg area of Sweden. As controls we analyzed 168 sera from Uppsala blood donors. We controlled for presence and amplifiability of nucleic acid and for mouse DNA contamination. To score as positive, a sample had to react with several of the XMRV/HMRV PCRs. None of the samples gave PCR reactions which fulfilled the positivity criteria. CONCLUSIONS: XMRV/HMRV like proviruses occur in the third murine gammaretrovirus group, characterized here. PCRs developed by us, and others, approximately cover this group, except for the INT RTQPCR, which is rather strictly XMRV specific. Using such PCRs, XMRV/HMRV could not be detected in PBMC and plasma samples from Swedish patients suffering from ME/CFS/FM, and in sera from Swedish blood donors

Picosecond time-resolved resonance Raman study of CH2I-I produced after ultraviolet photolysis of CH2I2 in CH3OH, CH3CN/H2O and CH3OH/H2O solutions

We present picosecond time-resolved resonance Raman spectroscopy experiments investigating the photo-products produced after ultraviolet photolysis of CH2I2 in CH3OH solution and in 50% CH3OH/50% H2O and 50% CH3CN/50% H2O by volume mixed solvents. We observe that isodiiodomethane (CH2I-I) is formed within several picoseconds and has a lifetime that significantly depends on the solvent system (time constant of 3.8 ns in CH3OH, 1.8 ns in 50% CH3CN/50% H2O, and 0.8 ns in 50% CH3OH/50% H2O). Our results indicate that CH2I-I can be formed via geminate recombination in aqueous environments but will have a shorter lifetime than in previous experiments done in several organic solvents. The variations in the lifetime of CH2I-I in the presence of H2O and CH3OH could be due to its chemical reaction with the O-H bond and/or possibly faster cleavage of the weak I-I bond in aqueous solutions. We briefly discuss the potential role of CH2I-I in the release of reactive halogens in aqueous environments.link_to_subscribed_fulltex

Direct observation of a hydrogen-bonded charge-transfer state of 4-dimethylaminobenzonitrile in methanol by time-resolved IR spectroscopy

Anomalies in the fluorescence spectra of dual fluorescence molecules explained? A comparison of the time-resolved I R absorption of the C≡N band of photoexcited 4-dimethylaminobenzonitrile in MeCN and MeOH provides the first direct observation of the formation of a hydrogen-bonded intramolecular charge-transfer (ICT) state in MeOH and its coexistence with a "free" ICT state (see picture). The so-called dual fluorescence will be triple, not dual.link_to_subscribed_fulltex

Solvent effects on the charge transfer excited states of 4-dimethylaminobenzonitrile (DMABN) and 4-dimethylamino-3, 5-dimethylbenzonitrile (TMABN) studied by time-resolved infrared spectroscopy: a direct observation of hydrogen bonding interactions

Time-resolved infrared absorption spectra of the C≡N bands of photoexcited TMABN and DMABN have been measured in non-polar hexane, polar aprotic THF and polar protic butanol with high temporal and spectral resolution (<0.5 ps and 5 cm -1, respectively). In butanol, the intramolecular charge transfer (ICT) state C≡N infrared absorption bands of DMABN and TMABN both develop from an initial singlet into a doublet, demonstrating the co-existence of two charge transfer excited states, one of which is hydrogen-bonded and the other similar to the state formed in aprotic solvents. The ICT C≡N absorption band of TMABN is already strong at the earliest measurement time of 2 ps in THF, hexane, and butanol, indicating prompt population of ICT by a barrierless process, as expected from the pre-twisted structure of this molecule. There are little or no subsequent fast kinetics in hexane and THF but the signal observed in butanol continues to grow substantially at later times, prior to decay, indicating population transfer from a second state excited at 267 nm. No CN absorption band attributable to this state is observed, consistent with it being similar to the LE state of DMABN. The kinetics of the later stages of the hydrogen-bonding of both DMABN and TMABN in butanol takes place on timescales consistent with known values for dipolar solvation relaxation and result in a ratio of the hydrogen-bonded to non-bonded species of ∼3:1 at equilibrium for both molecules. The contrast between the prompt population of the charge transfer state of TMABN in all three solvents and charge transfer rates in DMABN limited to 13 ps -1 in THF and 9 ps -1 in butanol is fully consistent with the TICT description for the ICT state structure. © The Royal Society of Chemistry and Owner Societies.link_to_subscribed_fulltex

Time-resolved spectroscopy study of the triplet state of 4-diethylaminobenzonitrile (DEABN)

The nonradiative deactivation processes of intramolecular charge transfer (ICT) and intersystem crossing (ISC) and their dependence on solvent polarity for DEABN have been studied using transient absorption (TA) spectroscopy. The TA spectra have been taken in non-polar hexane and polar acetonitrile solvents within the 400-630 nm spectral region at time delays of 2 ps to 6 ns. The results are complemented by nanosecond time-resolved resonance Raman (TR 3) spectra of the triplet state of DEABN over the 700 to 2300 cm -1 frequency range. There is no significant difference between the Raman spectra recorded in hexane, acetonitrile and methanol solvents and this implies the triplet state has only one form. Comparison of DEABN triplet Raman spectrum with ab initio DFT geometry and vibrational analysis of DEABN ground state and triplet state TR 3 spectra of the closely related compound dimethylaminobenzonitrile (DMABN) indicates the DEABN triplet state is planar or near planar in structure with noticeable biradical character.link_to_subscribed_fulltex

Direct observation of a hydrogen-bonded charge-transfer state of 4-dimethylaminobenzonitrile in methanol by time-resolved IR spectroscopy

Anomalies in the fluorescence spectra of dual fluorescence molecules explained? A comparison of the time-resolved I R absorption of the C≡N band of photoexcited 4-dimethylaminobenzonitrile in MeCN and MeOH provides the first direct observation of the formation of a hydrogen-bonded intramolecular charge-transfer (ICT) state in MeOH and its coexistence with a "free" ICT state (see picture). The so-called dual fluorescence will be triple, not dual.link_to_subscribed_fulltex