Assembled triphenylamine bis-urea macrocycles: exploring photodriven electron transfer from host to guests.

Absorption of electronic acceptors in the accessible channels of an assembled triphenylamine (TPA) bis-urea macrocycle 1 enabled the study of electron transfer from the walls of the TPA framework to the encapsulated guests. The TPA host is isoskeletal in all host-guest structures analyzed with guests 2,1,3-benzothiadiazole, 2,5-dichlorobenzoquinone and I2 loading in single-crystal-to-single-crystal transformations. Analysis of the crystal structures highlights how the spatial proximity and orientation of the TPA host and the entrapped guests influence their resulting photophysical properties and allow direct comparison of the different donor-acceptor complexes. Diffuse reflectance spectroscopy shows that upon complex formation 1·2,5-dichlorobenzoquinone exhibits a charge transfer (CT) transition. Whereas, the 1·2,1,3-benzothiadiazole complex undergoes a photoinduced electron transfer (PET) upon irradiation with 365 nm LEDs. The CT absorptions were also identified with the aid of time dependent density functional theory (TD-DFT) calculations. Cyclic voltammetry experiments show that 2,1,3-benzothiadiazole undergoes reversible reduction within the host-guest complex. Moreover, the optical band gaps of the host 1·2,5-dichlorobenzoquinone (1.66 eV), and host 1·2,1,3-benzothiadiazole (2.15 eV) complexes are significantly smaller as compared to the free host 1 material (3.19 eV). Overall, understanding this supramolecular electron transfer strategy should pave the way towards designing lower band gap inclusion complexes.

From Incident Light to Persistent and Regenerable Radicals of Urea-Assembled Benzophenone Frameworks: A Structural Investigation.

Herein we probe the effects of crystalline structure and geometry on benzophenone photophysics, self-quenching, and the regenerable formation of persistent triplet radical pairs at room temperature. Radical pairs are not observed in solution but appear via an emergent pathway within the solid-state assembly. Single crystal X-ray diffraction (SC-XRD) of two sets of constitutional isomers, benzophenone bis-urea macrocycles, and methylene urea-tethered dibenzophenones are compared. Upon irradiation with 365 nm light-emitting diodes (LEDs), each forms photogenerated radicals as monitored by electron paramagnetic resonance (EPR). Once generated, the radicals exhibit half-lives from 2 to 60 days before returning to starting material without degradation. Re-exposure to light regenerates the radicals with similar efficiency. Subtle differences in the structure of the crystalline frameworks modulates the maximum concentration of photogenerated radicals, phosphorescence quantum efficiency (φ), and n-type self-quenching as observed using laser flash photolysis (LFP). These studies along with the electronic structure analysis based on the time-dependent density functional theory (TD-DFT) suggest the microenvironment surrounding benzophenone largely dictates the favorability of self-quenching or radical formation and affords insights into structure/function correlations. Advances in understanding how structure determines the excited state pathway solid-state materials undertake will aid in the design of new radical initiators, components of OLEDs, and NMR polarizing agents.

Guest Inclusion Modulates Concentration and Persistence of Photogenerated Radicals in Assembled Triphenylamine Macrocycles.

Substituted triphenylamine (TPA) radical cations show great potential as oxidants and as spin-containing units in polymer magnets. Their properties can be further tuned by supramolecular assembly. Here, we examine how the properties of photogenerated radical cations, intrinsic to TPA macrocycles, are altered upon their self-assembly into one-dimensional columns. These macrocycles consist of two TPAs and two methylene ureas, which drive the assembly into porous organic materials. Advantageously, upon activation the crystals can undergo guest exchange in a single-crystal-to-single-crystal transformation generating a series of isoskeletal host-guest complexes whose properties can be directly compared. Photoinduced electron transfer, initiated using 365 nm light-emitting diodes, affords radicals at room temperature as observed by electron paramagnetic resonance (EPR) spectroscopy. The line shape of the EPR spectra and the quantity of radicals can be modulated by both polarity and heavy atom inclusion of the encapsulated guest. These photogenerated radicals are persistent, with half-lives between 1 and 7 d and display no degradation upon radical decay. Re-irradiation of the samples can restore the radical concentration back to a similar maximum concentration, a feature that is reproducible over several cycles. EPR simulations of a representative spectrum indicate two species, one containing two N hyperfine interactions and an additional broad signal with no resolvable hyperfine interaction. Intriguingly, TPA analogues without bromine substitution also exhibit similar quantities of photogenerated radicals, suggesting that supramolecular strategies can enable more flexibility in stable TPA radical structures. These studies will help guide the development of new photoactive materials.

Selective host-guest chemistry, self-assembly and conformational preferences of m-xylene macrocycles probed by ion-mobility spectrometry mass spectrometry.

We demonstrated ion-mobility spectrometry mass spectrometry (IMS-MS) as a powerful tool for interrogating and preserving selective chemistry including non-covalent and host-guest complexes of m-xylene macrocycles formed in solution. The technique readily revealed the unique favorability of a thiourea-containing macrocycle MXT to Zn2+ to form a dimer complex with the cation in an off-axis sandwich structure having the Zn-S bonds in a tetrahedral coordination environment. Replacing thiourea with urea generates MXU which formed high-order oligomerization with weak binding interactions to neutral DMSO guests detected at every oligomer size. The self-assembly pathway observed for this macrocycle is consistent with the crystalline assembly. Further transformation of urea into squaramide produces MXS, a rare receptor for probing sulfate in solution. Tight complexes were observed for both monomeric and dimeric of MXS in which HSO4- bound stronger than SO42- to the host. The position of HSO4- at the binding cavity is a 180° inversion of the reported crystallographic SO42-. The MXS dimer formed a prism-like shape with HSO4- exhibiting strong contacts with the 8 amine protons of two MXS macrocycles. By eliminating intermolecular interferences, we detected the low energy structures of MXS with collisional cross section (CCS) matching cis-trans and cis-cis squaramides-amines, both were not observed in crystallization trials. The experiments collectively unravel multiple facets of macrocycle chemistry including conformational flexibility, self-assembly and ligand binding; all in one analysis. Our findings illustrate an inexpensive and widely applicable approach to investigate weak but important interactions that define the shape and binding of macrocycles.

Enhancing the Stability of Photogenerated Benzophenone Triplet Radical Pairs through Supramolecular Assembly.

Supramolecular assembly of urea-tethered benzophenone molecules results in the formation of remarkably persistent triplet radical pairs upon UV irradiation at room temperature, whereas no radicals were observed in solution. The factors that lead to emergent organic radicals are correlated with the microenvironment around the benzophenone carbonyl, types of proximal hydrogens, and the rigid supramolecular network. The absorption spectra of the linear analogues were rationalized using time-dependent density functional theory calculations on the crystal structure and in dimethyl sulfoxide, employing an implicit solvation model to describe structural and electronic solvent effects. Inspection of the natural transition orbitals for the more important excitation bands of the absorption spectra indicates that crystallization of the benzophenone-containing molecules should present a stark contrast in photophysical properties versus that in solution, which was indeed reflected by their quantum efficiencies upon solid-state assembly. Persistent organic radicals have prospective applications ranging from organic light-emitting diode technology to NMR polarizing agents.

[Surgical treatment of a complex adolescent carpal fracture : A rare injury to the growing skeleton]. / Versorgung einer komplexen jugendlichen Handwurzelfraktur : Eine seltene Verletzung am wachsenden Skelett.

We report the case of a 15-year-old boy with combined fractures of the scaphoid, capitate, and hamate that represents a rare variation of the well-known Fenton's syndrome. Fixation was performed for the unstable fractures of the scaphoid and capitate with the use of cannulated Herbert screws and K­wires respectively. K­wires were removed after 6 months, with subsequent physiotherapy. After 6 months, CT confirmed complete consolidation of the two surgically treated carpal fractures and the conservatively treated fracture of the hamate. Regarding function, the patient is able to incorporate the hand into his school-related activities and has a good range of motion, with strong closure of the fist.

Zeeman-tuned rotational level-crossing spectroscopy in a diatomic free radical.

Rotational levels of molecular free radicals can be tuned to degeneracy by using laboratory-scale magnetic fields. Because of their intrinsically narrow width, these level crossings of opposite-parity states have been proposed for use in the study of parity-violating interactions and other applications. We experimentally study a typical manifestation of this system using BaF138. Using a Stark-mixing method for detection, we demonstrate level-crossing signals with spectral width as small as 6 kHz. We use our data to verify the predicted line shapes, transition dipole moments, and Stark shifts and to precisely determine molecular magnetic g factors. Our results constitute an initial proof of concept for use of this system to study nuclear spin-dependent parity-violating effects.

[Use of patient radiation shielding in diagnostic and interventional radiology]. / Einsatz von Patienten-Strahlenschutzmitteln in der diagnostischen und interventionellen Radiologie.

The use of patient contact shielding provides an opportunity to reduce patient radiation exposure. Recently, the use has been the subject of controversy. The Radiation Protection Committee has published a recommendation on the use of patient radiation shields by considering the recent findings on dose savings but also the risks of incorrect use. In this article, a specification for the more frequently used types of X­ray examination is given, which describes whether and which radiation contact shielding should be used. This is accompanied by a rationale for the use or non-use of patient radiation protection agents. Problems and possible errors are explained, as well as how to deal with special situations such as pregnant women and children.

[Radiation protection during fluoroscopic interventions]. / Strahlenschutz bei fluoroskopischen Interventionen.

Facts and figures about the frequencies of fluoroscopically guided interventions (FGI), typical patient exposures and occupational exposures are listed. Limits of radiation exposure do not exist for patients but only for occupationally exposed medical personnel. Measures for radiation protection of patients and personnel are explained. Nearly all technical radiation protection measures for patients also protect the personnel. To reduce the exposure of medical personnel, radiation protection equipment should be attached to the X­ray modality and personal radiation protection equipment should be worn. The diagnostic reference values and the obligation to report incidents, including the reporting criteria, are explained. The radiation protection of patients and personnel for FGI in Germany is well regulated by diagnostic reference values, reporting criteria, prescribed or recommended protective measures, personal dosimetry and the obligation to involve medical physics experts.

Evaluating the Effects of Metal Adduction and Charge Isomerism on Ion-Mobility Measurements using m-Xylene Macrocycles as Models.

Gas-phase ion-mobility spectrometry provides a unique platform to study the effect of mobile charge(s) or charge location on collisional cross section and ion separation. Here, we evaluate the effects of cation/anion adduction in a series of xylene and pyridyl macrocycles that contain ureas and thioureas. We explore how zinc binding led to unexpected deprotonation of the thiourea macrocyclic host in positive polarity ionization and subsequently how charge isomerism due to cation (zinc metal) and anion (chloride counterion) adduction or proton competition among acceptors can affect the measured collisional cross sections in helium and nitrogen buffer gases. Our approach uses synthetic chemistry to design macrocycle targets and a combination of ion-mobility spectrometry mass spectrometry experiments and quantum mechanics calculations to characterize their structural properties. We demonstrate that charge isomerism significantly improves ion-mobility resolution and allows for determination of the metal binding mechanism in metal-inclusion macrocyclic complexes. Additionally, charge isomers can be populated in molecules where individual protons are shared between acceptors. In these cases, interactions via drift gas collisions magnify the conformational differences. Finally, for the macrocyclic systems we report here, charge isomers are observed in both helium and nitrogen drift gases with similar resolution. The separation factor does not simply increase with increasing drift gas polarizability. Our study sheds light on important properties of charge isomerism and offers strategies to take advantage of this phenomenon in analytical separations.

Single-crystal-to-single-crystal guest exchange in columnar assembled brominated triphenylamine bis-urea macrocycles.

Self-assembly of brominated triphenylamine bis-urea macrocycles affords robust porous materials. Urea hydrogen bonds organize these building blocks into 1-dimensional columns, which pack via halogen-aryl interactions. The crystals are stable when emptied, present two distinct absorption sites for Xe with restricted Xe diffusion, and exhibit single-crystal-to-single-crystal guest exchange.

UV-irradiation of self-assembled triphenylamines affords persistent and regenerable radicals.

UV-irradiation of assembled urea-tethered triphenylamine dimers results in the formation of persistent radicals, whereas radicals generated in solution are reactive and quickly degrade. In the solid-state, high quantities of radicals (approximately 1 in 150 molecules) are formed with a half-life of one week with no significant change in the single crystal X-ray diffraction. Remarkably, after decay, re-irradiation of the solid sample regenerates the radicals to their original concentration. The photophysics upon radical generation are also altered. Both the absorption and emission are significantly quenched without external oxidation likely due to the delocalization of the radicals within the crystals. The factors that influence radical stability and generation are correlated to the rigid supramolecular framework formed by the urea tether of the triphenylamine dimer. Electrochemical evidence demonstrates that these compounds can be oxidized in solution at 1.0 V vs. SCE to generate radical cations, whose EPR spectra were compared with spectra of the solid-state photogenerated radicals. Additionally, these compounds display changes in emission due to solvent effects from fluorescence to phosphorescence. Understanding how solid-state assembly alters the photophysical properties of triphenylamines could lead to further applications of these compounds for magnetic and conductive materials.

A biomechanical comparison of Bosworth and poly-L lactic acid bioabsorbable screws for treatment of acromioclavicular separations.

PURPOSE: The purpose of this study was to determine the failure load of intact coracoclavicular ligaments and the pullout strength of a poly-L lactic acid screw (PLLA, Linvatec, Largo, FL) compared with a titanium screw (Bosworth, Stryker Howmedica Osteonics, Allendale, NJ) in the repair of fifth-degree acromioclavicular separations. TYPE OF STUDY: Biomechanical cadaveric study. METHODS: The ultimate tensile strength of coracoclavicular ligaments was determined using a servohydraulic testing machine (MTS, Eden Prairie, MN) by creating grade V acromioclavicular separations. Titanium Bosworth screws and Linvatec PLLA screws were placed across the reduced coracoclavicular joint and through the base of the coracoid process of right and left matched cadaveric shoulder specimens, respectively. The axial pullout strength was determined by MTS uniaxial tensile testing along the screw axis to determine the ultimate fixation failure load at a rate of 1 mm/second. RESULTS: Intact coracoclavicular ligaments required an axial load of 340.15 +/- 100.77 N to fail. The bioabsorbable PLLA screw provided fixation strength that was significantly less than the Bosworth screw fixation strength: 272.01 +/- 63.26 and 367.01 +/- 111.54 N, respectively (P < .05, paired t test). CONCLUSIONS: The titanium Bosworth screw restored strength to the acromioclavicular joint equivalent to the intact coracoclavicular ligament; however, the bioabsorbable PLLA screw fixation was significantly weaker than the intact ligaments and the Bosworth repair. CLINICAL RELEVANCE: Titanium Bosworth screws supply more strength of fixation in grade V acromioclavicular separations than the PLLA screw tested in this study.

Palliative radiotherapy in recurrent head-and-neck tumors by a percutaneous superfractionated treatment schedule.

PURPOSE: A frequent problem in treatment of patients with head-and-neck tumors is recurrence in pre-irradiated areas, thus limiting dose for another full-course radiotherapy. We present our experience with a percutaneous superfractionated short-term radiotherapy regimen that may be useful for palliative irradiation. METHODS AND MATERIALS: Twenty-three patients with head-and-neck tumor recurrence after radiotherapy or extensive tumor growth have been treated by a superfractionated regimen. At each of two subsequent days, eight fractions of 1 Gy were applied with an interfraction interval of 1 h, resulting in a total dose of 16 Gy. Time between the last fraction of the first day and the first fraction of the second day was 17 h. RESULTS: In 16 of 23 patients (70%), our irradiation schedule could achieve a palliative effect such as tumor necrosis or reduction of swelling or pain. Seven patients showed erythema (WHO I) at the end of the second day. Neither mucositis nor late effects of treatment were observed. CONCLUSIONS: Our superfractionated schedule is feasible without severe acute side reactions and can achieve a palliative effect in advanced or recurrent head-and-neck cancer.

Intraoperative radiotherapy for pre-irradiated head and neck cancer.

BACKGROUND AND PURPOSE: Radiotherapy of recurrent head and neck tumours is limited in dose due to pre-treatment up to normal tissue tolerance doses. Surgery alone is limited by the problems related to pre-surgery, post-radiation fibrosis, and infiltration of tumours into nerves and vessels too closely to be completely removed. Our aim was to evaluate the possible role of intraoperative radiotherapy (IORT) in such tumours treated with palliative intent. METHODS: In the last 10 years, we performed 113 intraoperative irradiations in a total of 84 pre-irradiated patients with head and neck cancer. The patient data were evaluated with regard to palliative effect, complications of treatment, recurrence and survival after IORT. RESULTS: Palliation of symptoms, as assessed by clinical evaluation, was achieved in 88% of symptomatic patients, often just by removal of large exophytic or exulcerating tumours, with IORT preventing their immediate recurrence after surgery. The complication rate did not exceed that expected after surgery alone. The median survival after IORT was 6.8 months, with a median time to local tumour recurrence or progression of 3.7 months. CONCLUSION: Intraoperative irradiation can be used as a palliative treatment option in pre-treated head and neck tumours with satisfactory results. With large and infiltrating tumours, however, recurrences or tumour progression occur close to the IORT portals, thus rendering this method unsuitable for achieving long-term control in such extended tumours.

Mode of breast cancer detection: a study from the German part of the Maas-Rhine-EUREGIO.

Cancer screening programmes differ throughout the European Union with regard to their content as well as their acceptance by the population. In Germany, mammography is not yet part of the recommended screening programme, although its routine use is recommended by several national and international institutions. We were interested in the present methods of breast cancer detection and the correlation to tumour stage, histology and prognosis. Patients with breast cancer, presenting in our department between January 1990 and December 1994 (1,050 cases), were asked whether the suspicious finding was first detected by themselves, their physician, or in routine mammography. Seventy-two per cent of tumours were detected by patients themselves, 12% by the physician at routine cancer screening or for other reasons, and 16% were found in mammography performed without clinical suspicion of cancer. Tumours found by physicians or by mammography were treated much sooner than those first recognized by the patient and, thus, were of lower T and N stages. Surgery could more often be breast-conserving in these cases. Of the T2 stages, as far as can be determined after the short follow-up, patients with tumours detected by screening showed a better survival rate. In spite of the introduction of cancer screening programmes most breast carcinomas are still detected by patients themselves. Therapy is often started after a great delay, so that the tumours are found to be at more advanced stages and show a worse prognosis than those detected by clinical examination or mammography.

[Computer tomography for TNM based radiation planning of urological tumours (author's transl]. / Unterstützung einer am TNM-System orientierten Bestrahlungsplanung urologischer Tumoren durch die Computertomographie.

From the extensive statistics concerning treatment results of urological tumours which are available from central tumour registers, a first draft of a treatment plan has been worked out, which is based on tumour spread. Since the extent of tumour invasion is documented by the TNM system of the UICC, one is justified in speaking of TNM orientated treatment planning. For planning it is necessary to consider not only tumour type and depth of infiltration of local tissues, but also the lymph node anatomy, whether the nodes are involved or not. Computer tomography assist significantly in the performance of such TNM orientated treatment planning, particularly in determining the extent of the volume to be irradiated, It must be stressed that computer tomography does not replace the use of simulators, but that it is a valuable addition. In our view, computer tomography has also an undoubted value in treatment planning of urological tumours where palliation only is the aim. It provides the possibility of checking the effect of the chosen treatment by a non-invasive diagnostic method.