Theoretical Aspects of Molecular Recognition

Molecular recognition is a key process in non-covalent interactions, which determines, among others, host-guest complexation, drug action and protein-protein interaction. A simple and attractive formulation is the lock-and-key analogy defining the host as a lock accommodating the guest as a key. We stress three major aspects of molecular recognition, determining both complementarity between host and guest and similarity within a group of guest molecules. These aspects are: steric, i.e. maximization of close contacts, electrostatic, i.e. maximization of electrostatic attraction between host and guest, as well as hydrophobic, i.e. avoiding hydrophobic hydration, which can be reached by the maximization of apolar contacts between interacting molecules. Some examples are presented from our laboratory: the complexes of acylaminoacyl peptidase with small peptides, the effect of heparin binding on inhibitory potency of C1- inhibitor as well as small-molecule ligand binding to prolyl oligopeptidase and calmodulin

Non-Commercial Homestay;an exploration of encounters and experiences of guests visiting the UK.

This paper explores the experiences of tourists travelling within the UK using hosts through the web based non commercial homestay organisations. The author, as a host explores the guests’ expectations, experiences and views on hospitality within this unique but growing form of accommodation. In order to ascertain the benefits to the guest, within non commercial homestay it is necessary to review the concept of value for the guest, explore the different forms or dimensions of hospitality, and ascertain levels of reciprocity within the host guest relationship. The paper shows that reciprocity within this hospitality context is asymmetrical and that the sacrifice made by the guest is to the benefit of the host be it non financial

PROTECT: container process isolation using system call interception

Virtualization is the underpinning technology enabling cloud computing service provisioning, and container-based virtualization provides an efficient sharing of the underlying host kernel libraries amongst multiple guests. While there has been research on protecting the host against compromise by malicious guests, research on protecting the guests against a compromised host is limited. In this paper, we present an access control solution which prevents the host from gaining access into the guest containers and their data. Using system call interception together with the built-in AppArmor mandatory access control (MAC) approach the solution protects guest containers from a malicious host attempting to compromise the integrity of data stored therein. Evaluation of results have shown that it can effectively prevent hostile access from host to guest containers while ensuring minimal performance overhead

Supramolecular assembly of cucurbit[6]uril and N-butyl-4-pyrrolidinopyridine

The nature of the supramolecular host-guest complex involving 4-pyrrolidinopyridine (BuPC4) and cucurbit[6]uril (Q[6]) has been investigated by NMR and UV spectroscopy, MALDI-TOF mass spectrometry, X-ray crystallography and isothermal titration calorimetry (ITC). The results revealed that the alkyl chain of the guest BuPC4 is located inside the cavity of the Q[6] host, whereas the other section of the BuPC4 guest remains outside of the portal

Recognition-mediated hydrogel swelling controlled by interaction with a negative thermoresponsive LCST polymer

Most polymeric thermoresponsive hydrogels contract upon heating beyond the lower critical solution temperature (LCST) of the polymers used. Herein, we report a supramolecular hydrogel system that shows the opposite temperature dependence. When the non-thermosesponsive hydrogel NaphtGel, containing dialkoxynaphthalene guest molecules, becomes complexed with the tetra cationic macrocyclic host CBPQT4+, swelling occurred as a result of host–guest complex formation leading to charge repulsion between the host units, as well as an osmotic contribution of chloride counter-ions embedded in the network. The immersion of NaphtGel in a solution of poly(N-isopropylacrylamide) with tetrathiafulvalene (TTF) end groups complexed with CBPQT4+ induced positive thermoresponsive behaviour. The LCST-induced dethreading of the polymer-based pseudorotaxane upon heating led to transfer of the CBPQT4+ host and a concomitant swelling of NaphtGel. Subsequent cooling led to reformation of the TTF-based host–guest complexes in solution and contraction of the hydrogel

Zeolite-dye micro lasers

We present a new class of micro lasers based on nanoporous molecular sieve host-guest systems. Organic dye guest molecules of 1-Ethyl-4-(4-(p-Dimethylaminophenyl)-1,3-butadienyl)-pyridinium Perchlorat were inserted into the 0.73-nm-wide channel pores of a zeolite AlPO$_4$-5 host. The zeolitic micro crystal compounds where hydrothermally synthesized according to a particular host-guest chemical process. The dye molecules are found not only to be aligned along the host channel axis, but to be oriented as well. Single mode laser emission at 687 nm was obtained from a whispering gallery mode oscillating in a 8-$\mu$m-diameter monolithic micro resonator, in which the field is confined by total internal reflection at the natural hexagonal boundaries inside the zeolitic microcrystals.Comment: Accepted for publication in Phys. Rev. Let

Fast Diffusion of Long Guest Rods in a Lamellar Phase of Short Host Particles

We investigate the dynamic behavior of long guest rod-like particles immersed in liquid crystalline phases formed by shorter host rods, tracking both guest and host particles by fluorescence microscopy. Counter-intuitively, we evidence that long rods diffuse faster than short rods forming the one-dimensional ordered smectic-A phase. This results from the larger and non-commensurate size of the guest particles as compared to the wavelength of the energy landscape set by the lamellar stack of liquid slabs. The long guest particles are also shown to be still mobile in the crystalline smectic-B phase, as they generate their own voids in the adjacent layers.Comment: 5 pages, 4 figures, Accepted in Phys. Rev. Let

Guest Workers in the Underground Economy

Guest-worker programs have been providing rapidly growing economies with millions of temporary foreign workers over the last couple of decades. With the duration of stay strictly limited by program rules in most of the host countries and wages paid to guest workers often set at sub-market levels, many of the migrants choose to overstay and seek employment in the underground economy. This paper develops a general-equilibrium model that relates the flow of guest workers transiting to the underground economy to the rules of the program, enforcement measures of the host country and market conditions facing migrants at home and abroad