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The non-crossing requirement in non-concatenated ring polymers creates topological constraints, which impose important restrictions on the phase space of the system. For ring polymers interpenetration is costly entropically and compact structures evolve for high molecular weights - ring polymers are assumed to become mass fractals confining rings into territories. Other than the dynamics of linear or branched chains that predominantly takes place via the chain ends, rings do not feature ends and their dynamics is considered to be self-similar and thus fundamentally different to those of chains displaying ends. The present state of the art model for the description of the internal relaxations in dense ring systems was developed by Rubinstein et al. /1/. This self-consistent Fractal Loopy Globule (FLG) model is based on the conjecture that the overlap criterion /2,3/ in the packing model for entanglements also governs the rule for overlapping loops in polymer rings. The constant overlap of loops is conjectured to occur in a self-similar way over a wide range of length scales from the elementary loop size Ne up to ring size R. The dynamics of such rings in a melt is governed by topological constraints that dilute with progressing time, because with time loops of increasing sizes are relaxed and cease to be obstacles.Recently, combining results of SANS /4/ with PFG- NMR and NSE the unique topology driven self-similar internal ring dynamics predicted by the FLG model could be verified experimentally /5/: We find the center of mass diffusion taking place in three dynamic regimes from short to long times: (i) a strongly sub-diffusive regime, where the center-of-mass mean square displacement scales as t^\alpha (0.4 ≤ \alpha ≤ 0.6) , until it reaches roughly the value R_g^2; (ii) a second regime with a t^0.75 scaling that (iii) at roughly 2.5 R_g^2 crosses over to Fickian diffusion. While the second anomalous diffusion regime has been found in simulations and was predicted by theory, we attribute the first one to the effect of cooperative dynamics resulting from the correlation hole potential. The internal dynamics at scales below the elementary loop size is well described by ring Rouse motion. At larger scales the dynamics is self-similar and follows very well the predictions of the scaling models with preference for the FLG model.ReferencesReferences:1. T. Ge, S. Panyukov, and M. Rubinstein, Macromolecules 49, 708–722 (2016)2. T. A. Kavassalis and J. Noolandi, Macromolecules 22, 2709–2720 (1989)3. L. J. Fetters, D. J. Lohse, D. Richter, T. A. Witten, and A. Zirkel, Macromolecules (1994)4. M. Kruteva, J. Allgaier, M. Monkenbusch, L. Porcar, and D. Richter, ACS Macro Letters , 507–511 (2020)5. M. Kruteva,M. Monkenbusch, J. Allgaier, O. Holderer, S. Pasini, I. Hofmann and D. Richter, Phys. Rev. Lett. (2020)

Here we present an approach to measure dynamic membrane properties of phospholipid membranes close to an interface. As an example we show results of the membrane dynamics of a phospholipid membrane multilayer-stack on a solid substrate (silicon). On this sample we were able to measure local interaction and friction parameters using Grazing Incidence Neutron Spin Echo Spectroscopy (GINSES), where an evanescent neutron wave probes the fluctuations close to a rigid interface. With this method it is possible to access length scales in the nano to micrometer region as well as energies in the μeV range. Using a new neutron resonator structure we achieved the required intensity gain for this experiment. During our investigations we found an excitation mode of the phospholipid membrane that has not been reported previously and only became visible using the new methodology. We speculate that the energy transported by that undulation can also serve to distribute energy over a larger area of the membrane, stabilizing it. This new methodology has the capability to probe the viscoelastic effects of biological membranes, becoming a new tool for tribology on the nanoscale and has allowed the observation of the hitherto invisible property of phospholipid membranes using neutrons.

With the advent of new instruments (e. g. Imagine at HFIR, MANDI at SNS and BIODIFF at FRMII) and well established instruments (iBIX at JPARC and LADI at ILL) neutron protein crystallography has seen a resurrection from the past pioneering work by Schoenborn. New sample environment options at the instruments and a growing user community have greatly enhanced the outcome of the existing neutron diffractometers. Measurements at 100 K in a nitrogen gas stream (cryostream) are now routinely possible at most neutron diffractometers. Efforts to increase the flux at the sample position and to reduce the background at the detector enable to measure smaller and smaller protein crystals. Yet, measuring crystals with volumes below 0.1 mm3 is still a big challenge and usually works only in exceptional cases. The main scientific questions addressed are: Hydrogen bonding to ligands/substrates, protonation states of amino acids in intermediate states of the catalytic process and determining the correct structure of metallo-proteins which are subjected to reduction due to the radiation damage caused by x-rays. But also the water shell on the outer surface of the protein can be studied, whereby water molecules of different flexibility can be observed.As an example for a neutron diffractometer, the instrument BIODIFF is introduced: It is a joint project of the Jülich Centre for Neutron Science (JCNS) and the FRM II. BIODIFF is designed as a monochromatic instrument with a narrow wavelength spread of less than 3 %. To cover a large solid angle the main detector of BIODIFF consists of a neutron imaging plate in a cylindrical geometry with online read-out capability. An optical CCD-camera pointing at the sample position is used to quickly align the sample (or a Cadmium replica of it) with respect to the neutron beam. The main advantage of BIODIFF is the possibility to adapt the wavelength to the size of the unit cell of the sample crystal while operating with a clean monochromatic beam that keeps the background level low.In this contribution, a review of most recent application examples of neutron protein crystallography is given. New developments are discussed which may lead to a widening of the application scope of this method. Especially the need for large protein (typically > 0.5 mm3 in volume) crystals is addressed.

Neutron protein crystallography is a technique which can readily report on the hydrogen atom positions in proteins. This is in some cases valuable information on drug target proteins and their hydrogen bonding with substrates and inhibitors. Other main scientific questions addressed are: protonation states of amino acids in intermediate states of the catalytic process and determining the correct structure of metallo-proteins which are subjected to reduction due to the radiation damage caused by x-rays. As an example for a neutron diffractometer, the instrument BIODIFF is introduced: It is a joint project of the Jülich Centre for Neutron Science (JCNS) and the FRM II. BIODIFF is designed as a monochromatic instrument with a narrow wavelength spread of less than 3 %. To cover a large solid angle the main detector of BIODIFF consists of a neutron imaging plate in a cylindrical geometry with online read-out capability. The main advantage of BIODIFF is the possibility to adapt the wavelength to the size of the unit cell of the sample crystal while operating with a clean monochromatic beam that keeps the background level low.In this contribution, a review of most recent application examples of neutron protein crystallography for drug development is given. Especially the need for large protein crystals (typically > 0.5 mm3 in volume) is addressed.

The research reactor Heinz Maier-Leibnitz (FRM II) is a modern high flux neutron source which feeds at the present 27 state of the art instruments. The newly build neutron single crystal diffractometer BIODIFF is especially designed to collect data from crystals with large unit cells. The main field of application is the structure analysis of proteins, especially the determination of hydrogen atom positions. BIODIFF is a joint project of the Forschungszentrum Jülich (FZJ/JCNS) and the Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II). Typical scientific questions addressed are the determination of protonation states of amino acid side chains and the characterization of the hydrogen bonding network between the protein and an inhibitor or substrate. BIODIFF is designed as a monochromatic instrument. By using a highly orientated pyrolytic graphite monochromator (PG002) the diffractometer is able to operate in the wavelength range of 2.4 Å to about 5.6 Å. Contaminations of higher order wavelengths are removed by a neutron velocity selector. To cover a large solid angle and thus to minimize the data collection time the main detector of BIODIFF consists of a neutron imaging plate system in a cylindrical geometry. A Li/ZnS scintillator CCD camera is available for additional detection abilities. The main advantage of BIODIFF is the possibility to adapt the wavelength to the size of the unit cell of the sample crystal while operating with a clean monochromatic beam that keeps the background level low. BIODFF is equipped with a standard Oxford Cryosystem “Cryostream 700+” which allows measurements in the temperature regime from 90K up to 500K.

The neutron single crystal diffractometer BIODIFF at the research reactor Heinz Maier-Leibnitz (FRM II) is especially designed to collect data from crystals with large unit cells. The main field of application is the structural analysis of proteins, especially the determination of hydrogen atom positions. BIODIFF is a joint project of the Jülich Centre for Neutron Science (JCNS) and the FRM II. Typical scientific questions addressed are the determination of protonation states of amino acid side chains and the characterization of the hydrogen bonding network between the protein active centre and an inhibitor or substrate. BIODIFF (see scheme below) is designed as a monochromatic instrument with a narrow wavelength spread of less than 3 %. By using a highly orientated pyrolytic graphite monochromator (PG002) the diffractometer is able to change its central wavelength in the range between 2.4 Å and 5.6 Å. Contaminations of higher order wavelengths are removed by a neutron velocity selector. To cover a large solid angle the main detector of BIODIFF consists of a neutron imaging plate in a cylindrical geometry with online read-out capability. With a radius of 200 mm and a height of 450 mm it covers a solid angle of approximately 2π with a spatial resolution of up to 125 µm. A fast Li/ZnS scintillator CCD camera is available for additional detection abilities. An optical CCD-camera pointing at the sample position is used to quickly align the sample with respect to the neutron beam. The main advantage of BIODIFF is the possibility to adapt the wavelength to the size of the unit cell of the sample crystal while operating with a clean monochromatic beam that keeps the background level low. BIODFF is equipped with a standard Oxford Cryosystem “Cryostream 700+” which allows measurements in the temperature range from 90 K up to 500 K (see picture below). A standard closed cycle cryostat is also available for measurements down to 4 K in vacuum. This may be used for the determination of magnetic unit cells of inorganic crystals in zero magnetic field. Recent applications of BIODIFF also include clay powder diffraction and diffraction from lipid membranes in a controlled humidity environment.

The research reactor Heinz Maier-Leibnitz (FRM II) is a modern high flux neutron source which feeds some 30 state of the art neutron beam instruments. Currently 24 are operational, others in commissioning or under construction. The newly built neutron single crystal diffractometer BIODIFF is especially designed to collect data from crystals with large unit cells. The main field of application is the structural analysis of proteins, especially the determination of hydrogen atom positions. BIODIFF is a joint project of the Jülich Centre for Neutron Science (JCNS) and the FRM II. Typical scientific questions addressed are the determination of protonation states of amino acid side chains (see e. g. [1,2]) and the characterization of the hydrogen bonding network between the protein active centre and an inhibitor or substrate. BIODIFF is designed as a monochromatic instrument. By using a highly orientated pyrolytic graphite monochromator (PG002) the diffractometer is able to operate in the wavelength range of 2.4 Å to about 5.6 Å. Contaminations of higher order wavelengths are removed by a neutron velocity selector. To cover a large solid angle the main detector of BIODIFF consists of a neutron imaging plate in a cylindrical geometry with online read-out capability. A fast Li/ZnS scintillator CCD camera is available for additional detection abilities. An optical CCD-camera pointing at the sample position is used to quickly align the crystal with respect to the neutron beam. The main advantage of BIODIFF is the possibility to adapt the wavelength to the size of the unit cell of the sample crystal while operating with a clean monochromatic beam that keeps the background level low. BIODIFF is equipped with a standard Oxford Cryosystem “Cryostream 700+” which allows measurements in the temperature regime from 90K up to 500K (see Figure underneath).