Tuesday. At Heathrow, World's Favourite Airline. The seat number 20C was not an allocation it was merely a request. In the view of the Customer Services rep, I and a dozen others had checked in "late" (130 minutes before flight time, in fact, all spent waiting for anarchic WFA check-in procedure), thus we have to sit in Smoking, 12 hours non-stop to Mexico City, in terminal rigor in row 54. Ranks of World Travellers, tightly pressed shoulder to shoulder and knee to buttock, stretch the length of the plane. Reflect that sardines are, at least, head to tail in their tin cans.

Arrive safe but stiff in Mexico City to be met by Juventino Garcia and his research associate, Alma Arevalo. We are collaborators on a European Community research project, between Sheffield University and Universidad Nacional Autonoma de Mexico, concerned with removing sulphur compounds from oil, and we now need to write reports and papers on our first year's work. When fuels containing sulphur are burnt, polluting sulphur dioxide is formed. Mexico is a major oil exporter (as is the United Kingdom), Europe is a major importer, but now reserves of heavier oils containing more sulphur impurities (which lead to more SO2) must be exploited. Our work earlier showed the feasibility of a new chemical route involving platinum for the removal of thiophenes, which are among the most intractable sulphur-containing compounds, by hydrodesulphurization, HDS.

Our job is to extend this and to develop technology towards an eventual commercial realisation.

Wednesday. In the lab at UNAM. Although we have been in daily e-mail contact, we need to review some months' progress since we last got together face to face. We talk to the students. Maira has results relating to the HDS of substituted thiophenes, the worst offenders. But the results raise some very unexpected questions; we must try to find precedents in the literature.

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Thursday. The results are not those expected on the basis of our "chemical intuition". Do we have a new example of shape selectivity, or are we drawing the wrong conclusion because some data are incomplete? We eat lunch: tortilla soup with chunks of fresh avocado, tacos, and steak.

Friday. Juventino gets an e-mail inviting him to lecture on some of our results at the International Platinum Metal Conference in York this July. Now we need to prepare the talk as well as write up two papers as fast as possible; we need grants and must publish.

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Saturday. We adjourn to San Miguel de Allende for Easter and to talk more about our results. Juventino drives us there in record time: the motorway north is empty since it is already well into Semana Santa (Holy Week).

The traffic jams happened last week and even the smog is not quite so bad today. But enough to remind us why we are doing this research.

Many of the signs along the road are familiar in theme if not in words, utilice su cinturon de seguridad ("wear your seat belt"), but the grotesquely twisted grey-green cacti stretching to the horizon on all sides take one unawares. The roadside trees are sparse and spiky but occasionally the scene is enlivened by large bushes of crimson, pink or purple bougainvillaea and by the dramatic violet flowers of the jacaranda trees.

Unexpected too is the convoy of cyclists in gaily striped shirts making a pilgrimage to San Juan de los Largos; every mile or so they have a support vehicle with spare bicycle wheels and a gilded shrine lashed to its roof.

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Sunday. We argue through the results again. The data all seem OK but we will have to convince referees as well, so we plan new urgent experiments; maybe Alma can determine some stability constants for the platinum thiophene complexes?

Monday. We return via the charmingly named Dolores Hidalgo (literally, sorrows of the nobleman), a small dusty town with a delightful square in front of the church where the parish priest, Father Miguel Hidalgo, started the Mexican revolution in 1810. Back in Mexico City: we decide what we are going to try and do over the next few months until we get together again.

Tuesday. Last night in a hotel near the Zocalo: very noisy and kept awake by loud enthusiastic drumming: cannot decide whether it is old Aztec or new heavy metal. On the way to UNAM we pay a brief visit to the Museo Casa de Leon Trotsky in Coyoacan. The house where Trotsky lived still stands, with tracts and pamphlets strewn over the tables, more or less as it was on August 21 1940 when he was assassinated with an ice pick by an agent of Stalin. Trotsky was well aware of his fate and had turned his house into a fortress with high walls and thick steel doors; but to no avail.

Back in the lab we have outstanding coffee: very surprised to see it is Mexican instant. Drive to airport to catch evening flight by WFA back to London; wish the travel grant allowed me to go business class. However prevailing winds make return an hour or so shorter and hence a little less painful than the outward journey; kind stewardess also helps by offering triple gin as anaesthetic.

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PETER MAITLIS Peter Maitlis is research professor of chemistry, University of Sheffield.