The photodissociation of CO from HbCO at ambient temperature is studied by means of a femtosecond IR technique. The bleaching of the FeCO absorption and the appearance of a new IR absorption near that of free CO are both observed at 300 fs after optical excitation. The bleach does not recover on the time scale of a few picoseconds but does recover by ;7--4% within 1 ns, which suggests that a barrier to recombination is formed within a few picoseconds. The CO spectrum does not change significantly between 300 fs and 1 ns, suggesting that the CO quickly finds some locations in the heme pocket that are not more than a few angstroms from the iron. The de-ligated CO appears in its ground vibrational level. There is evidence that 85 ± 10% of this CO remains in the heme pocket at 1 ns; it probably resides there for 50 ns. The flow of excess vibrational energy from the heme to the solvent was directly observed in the IR experiments. The heme cools within 1-2 ps while thermal disruption of the surrounding solvent structure requires ""30 ps.Ultrafast spectroscopic methods have contributed much to understanding the photophysics and structural dynamics that occur after the photodissociation of oxy-and carboxyhemoglobin (1-3). The motion of the iron out of the heme plane has been discussed in some detail already, and evidence from optical spectroscopy (3) and Raman scattering (4, 5) suggests that the heme is partially or fully domed within 350 fs and perhaps as rapidly as 50 fs. This time frame for motion of the iron and its associated proximal histidine is also found in theoretical simulations of the heme relaxation (6). On the other hand, very little is yet known about the properties of the ligand generated by photolysis in ambient temperature solution.In the normal operation of hemoglobin, 02 diffuses into the protein from the solvent and bonds to the iron. Questions regarding ligand diffusion into and escape from the heme pocket as well as binding within the protein therefore have central importance to the function of hemoglobin. The hemoglobin structure, as determined from x-ray analysis (7), has no channel large enough to facilitate passage of a ligand between the solvent and heme. Hence, diffusion to the heme requires significant globin motions (7-9). Although transient optical methods are sensitive, the electronic spectrum of hemes cannot respond to changes in the location of a relatively inert diatomic molecule within the protein. Thus, experiments that can observe the ligand directly and monitor any changes in its structure or environment are expected to extend significantly our understanding of hemoprotein function. Such measurements on free CO would enable us to address some new issues for hemoglobin under ambient aqueous conditions. For example, additional information could be obtained on the rate of generation of CO and on the pathways of photodissociation (10, 11), the efficiency of subnanosecond geminate recombination of CO to iron could be brought into relation with results from nanosecond (12) and m...

The trans-cis isomerization rates for stiff-diphenylbutadiene (S-DPB) in n-alkane solvents were measured using single photon counting methods and the rotational reorientation times 'T R for S-DPB and trans stilbene were obtained by picosecond polarization spectroscopy. In neither case did 'TR vs viscosity show Stokes-Einstein-Debye (SED) behavior. The values of 'T R were used to calculate the angular velocity correlation frequencies /3 using the Hubbard relation. The variation of isomerization rate with /3 was found to be predicted well by the Kramers equation when barrier frequencies of 154 cm-I for stilbene and 16 cm-I for S-DPB were used. This Kramers-Hubbard fit finesses questions regarding the validity of the one dimensional Kramers model and focuses attention on the SED equation. The dynamical relationship between the torsional friction, important in isomerization, and rotational friction, which determines the overall angular motion of the molecules, is discussed. a) This research was supported by grants from NSF (CHE83-03916) and NIH (GM-12592): and in part by the NSF/MRL program under Grant No. DMR8S19059.

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Background Radiomics approaches based on multiparametric MRI (mp‐MRI) have shown high accuracy in prostate cancer (PCa) management. However, there is a need to apply radiomics to the preoperative prediction of extracapsular extension (ECE). Purpose To develop and validate a radiomics signature to preoperatively predict the probability of ECE for patients with PCa, compared with the radiologists' interpretations. Study Type Retrospective. Population In total, 210 patients with pathology‐confirmed ECE status (101 positive, 109 negative) were enrolled. Field Strength/Sequence T2‐weighted imaging (T2WI), diffusion‐weighted imaging, and dynamic contrast‐enhanced imaging were performed on two 3.0T MR scanners. Assessment A radiomics signature was constructed to predict the probability of ECE prior to radical prostatectomy (RP). In all, 17 stable radiomics features of 1619 extracted features based on T2WI were selected. The same images were also evaluated by three radiologists. The predictive performance of the radiomics signature was validated and compared with radiologists' interpretations. Statistical Tests A radiomics signature was developed by a least absolute shrinkage and selection operator (LASSO) regression algorithm. Samples enrolled were randomly divided into two groups (143 for training and 67 for validation). Discrimination, calibration, and clinical usefulness were validated by analysis of the receiver operating characteristic (ROC) curve, calibration curve, and the decision curve, respectively. The predictive performance was then compared with visual assessments of three radiologists. Results The radiomics signature yielded an AUC of 0.902 and 0.883 in the training and validation cohort, respectively, and outperformed the visual assessment (AUC: 0.600–0.697) in the validation cohort. Pairwise comparisons demonstrated that the radiomics signature was more sensitive than the radiologists (75.00% vs. 46.88%–50.00%, all P < 0.05), but obtained comparable specificities (91.43% vs. (88.57%–94.29%); P ranged from 0.64–1.00). Data Conclusion A radiomics signature was developed and validated that outperformed the radiologists' visual assessments in predicting ECE status. Level of Evidence: 4 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2019;50:1914–1925.