Responsa for Bava Metzia 130:13

Q. What laws govern those transactions which fall in the category of asmakta?
A. Such transactions are valid if accompanied by a kinyan and concluded before an authoritative court. However, some asmakta transactions are valid even when not accompanied by a kinyan and not concluded before an authoritative court. Thus the Talmud rules that if a person lends money to another against a field, and the debtor says that in case he does not repay the debt within three years title to the field shall have vested in the creditor from now on, the transaction is valid (B.M. 65b, 66b). An earnest deposited in connection with a marriage engagement becomes forfeited upon the breaking of the engagement, even though the original transaction was not made before an authoritative court and was not accompanied by a kinyan. A mere promise to pay a fine to charity, as when a person promises to give a certain amount to charity in case he plays cards, is also binding. Regarding this law I wrote at length in a Responsum, which you will find in the possession of our friend R. Isaac of Straubing, and is too long to be repeated here. A decision by a court of arbitration is not binding unless the acceptance of the judges by the litigants was accompanied by a kinyan. Search further in the sources and you will learn the details of these laws.
SOURCES: B. p. 291, no. 364.

Q. One quarter of a house belongs to A, and the other three quarters to B. A, needing money, negotiated a loan from a Gentile, who was willing to put up a mortgage of fifteen marks on A's part of the house on the following conditions: 1) That A pay the Gentile one mark per annum in perpetuity; 2) that in case A fails to pay the one mark per annum, the mortgaged part of the house is to belong to the Gentile; 3) that in case the house burns down, the ground shall be mortgaged to the Gentile on the same condition; and 4) that in case A wants to sell his part of the house, the Gentile is to have the privilege of buying it at twelve (?) marks less than the offer of the highest bidder. Before concluding this transaction, A informed B of his intentions and of the Gentile's terms, and offered to borrow the amount from B on the same terms. B vigorously protested against A's mortgaging part of the house to a Gentile who might cause B trouble; but, at the same time, he refused to lend fifteen marks to A on the ground that it would be considered a taxable loan, and that the one mark per annum would be considered usury from a fellow Jew.
A. If A sells his part of the house to B on condition that it be rented to A in perpetuity at one mark per annum, the sale will be legal and B will be permitted to collect the one mark per annum. If, however, B refuses to buy A's part on such terms, A may mortgage it to a Gentile.
SOURCES: Pr. 970.

Q. R(achel), a widow, entered into the following agreement with B and his wife L(eah): 1) B and his wife undertook to provide food for R and her servant-girl until her death; 2) R, on the other hand, was to give to B and L her late husband's chain valued at fifteen marks; 3) B and his wife were to come to live in R's house (R owned a half interest in a house) and were to pay the interest to the mortgagee of R's house who was a Gentile; 4) in case B or his wife survived R the fifteen marks would be forfeited; and 5) in case both, B and his wife, died before R, she was to receive from their estate fifteen marks minus one-quarter mark for every year from the time of signing the contract. R delivered the chain to B and L. Subsequently B died and L moved to a place where there was no minyan. R demands from L her board and the interest due on the mortgaged house. L claims that she cannot afford to live in one place and provide food for R and her servant in another place. R refuses to leave her city, her daughter, her relatives, and the place where she can pray with a minyan. Can R compel L to provide food for her in R's city; and is not the contract void since in case L died before R and the latter reclaimed her money, the food L provided her with would constitute illegal interest?
A. L cannot force R to come to live with her, and R can not force L to support her while L is away, for neither of them would have entered into the original agreement had they forseen such eventualities. Moreover, the contract is void since there is a possibility that the food R receives from L would constitute illegal interest on R's money. L, therefore, should deduct from the fifteen marks, the amount she expended on R's food, and return the rest to R.
Q. R drew an instrument in which she stated that from then on and after her death, her (real) estate should belong to her brother, to certain people and to charity, on condition that she retain the right to sell any part of it if hard pressed for funds with which to feed and clothe herself. R, now, desires to sell part of her property claiming that she needs the money for her sustenance. The charity-trustee refuses to grant her permission to do so, claiming that R is not hard pressed for funds since she receives her food from L and since she has sufficient clothes.
A. If it is known that R is not in dire need of money for her sustenance, she may not sell any part of her property. But if this is not a known fact, R may promise under oath that she will not sell any part of her property unless she will need the money for her sustenance. She will be permitted, then, to sell such part of her property the proceeds of which will suffice for her sustenace for a period of six months. That money should be deposited with a trustee who would pay her a monthly allowance.
SOURCES: Pr. 1006.